Gastrointestinal nematode challenge induces some conserved gene expression changes in the gut mucosa of genetically resistant sheep

Reducing fecal egg count through selective breeding alters dorper lamb response to Haemonchus contortus in an artificial challenge trial

Infection by gastrointestinal nematodes (GIN), particularly Haemonchus contortus, can be detrimental to sheep health and performance. Genetic susceptibility to GIN varies between breeds, with those lacking high levels of natural resistance often requiring frequent anthelmintic treatment when facing parasitic challenge. Genetic technology can serve as a tool to decrease GIN susceptibility via selection for sheep with reduced fecal egg count (FEC) estimated breeding values (EBVs). However, the physiological changes that result from implementation of this strategy are not well described. Additionally, there is a need for comparison of animals from recent selective breeding against breeds with inherent GIN resistance. In this study we administered a challenge of H. contortus to Dorper x White Dorper (DWD; n = 92) lambs that have been genetically selected for either low (DWD-) or high (DWD+) FEC EBVs and Barbados Blackbelly x Mouflon (BBM; n = 19) lambs from a genetically resistant breed backgrounds. Lamb FEC, packed-cell volume (PCV) and serum IgG were measured at intermittent levels over 5 weeks. At day 21 and day 35, the selectively bred DWD- had a lower mean FEC compared to DWD+, but were higher than BBM. Reductions in both PCV and serum IgG from initial day 0 levels were observed in DWD lambs, but not in BBM. Furthermore, from a subset of lambs (n = 24) harvested at day 21, DWD- only tended (p = 0.056) to have lower mean worm counts than DWD+, with BBM having the lowest mean worm count. Differentially expressed genes (DEGs) identified via RNA-sequencing of abomasal tissue at day 21 indicate a more pronounced Th2 immune response and more rapid worm expulsion occurred in iBBM than iDWD- and iDWD+ lambs. However, gene expression in DWD- suggests an association between reduced FEC EBV and gastric acid secretion and the ability to limit worm fecundity. Ultimately, selection of Dorper sheep for low FEC EBV can reduce susceptibility to GIN, but it will likely require multiple generations with this trait as a breeding priority before presenting a similar resistance level to Caribbean breeds.

Genomic Regions Associated with Resistance to Gastrointestinal Nematode Parasites in Sheep-A Review

Gastrointestinal nematodes (GINs) can be a major constraint and global challenge to the sheep industry. These nematodes infect the small intestine and abomasum of grazing sheep, causing symptoms such as weight loss, diarrhea, hypoproteinemia, and anemia, which can lead to death. The use of anthelmintics to treat infected animals has led to GIN resistance, and excessive use of these drugs has resulted in residue traced in food and the environment. Resistance to GINs can be measured using multiple traits, including fecal egg count (FEC), Faffa Malan Chart scores, hematocrit, packed cell volume, eosinophilia, immunoglobulin (Ig), and dagginess scores. Genetic variation among animals exists, and understanding these differences can help identify genomic regions associated with resistance to GINs in sheep. Genes playing important roles in the immune system were identified in several studies in this review, such as the CFI and MUC15 genes. Results from several studies showed overlapping quantitative trait loci (QTLs) associated with multiple traits measuring resistance to GINs, mainly FEC. The discovery of genomic regions, positional candidate genes, and QTLs associated with resistance to GINs can help increase and accelerate genetic gains in sheep breeding programs and reveal the genetic basis and biological mechanisms underlying this trait.

Analysis of the stability of the reference genes GAPDH, SDHA and RPL-19 in sheep from a semi-arid region infected by gastrointestinal nematodes

Analyzing the stability of reference genes already described as universal is an important methodology to lead gene expression analysis because different studies have shown that the expression of universal reference genes may vary between experimental treatments. In this sense, the glyceraldehyde 3-phosphate dehydrogenase (GAPDH), Succinate dehydrogenase complex subunit A (SDHA) and Ribosomal Protein L-19 (RPL-19) reference genes (already described in other studies with sheep from different regions, breeds and infectious agents or in organisms evolutionarily close to sheep) were investigated in the abomasum, small and large intestines of resistant and susceptible crossbred sheep groups to gastrointestinal nematode infections in the Semi-arid region in Northeast of Brazil. The animals were naturally infected to determine the resistance or susceptibility status by counting eggs per gram (EPG) of feces from the gastrointestinal tract after 33 weeks of observations of infection evolution. Relative gene expression was performed by RT-qPCR methodology using Sybr green and relative gene expression stability was tested by different software programs such as REST, BestKeeper, geNorm and Normfinder. Our results showed the susceptible animals had increase in egg counts per gram of feces than resistant animals (p < 0.001), and both groups showed a mixed infection by nematodes of the genus Haemonchus, Trichostrongylus, Oesophagostomum and Trichuris. Furthermore, we show the importance of analyzing different genes in different software programs and the importance to choose ideal reference genes. In this sense, GAPDH was the most stable gene in the abomasum, whereas SDHA was the most stable in the small and large intestines. In addition, we discuss about variables which can interfere in relative expression such as breed, species, climate and tissue. However, utilizing other reference genes already described in other studies with the same and different variables should be performed.

Enhanced mucosal response in sheep harbouring βA beta-globin against haemonchosis

Association between ovine β-globin polymorphisms and resistance against haemonchosis was described and related to the mechanism of high oxygen affinity βA ➔ βC switch during anaemia, but there are no studies regarding the involved local host responses. Phenotypic parameters and local responses were evaluated in sheep from two β-globin haplotypes naturally infected with Haemonchus contortus. Morada Nova lambs were monitored at 63, 84 and 105 days of age for faecal egg counts and packed cell volume (PCV) under natural infection with H. contortus. At 210 days of age, lambs of Hb-AA and Hb-BB β-globin haplotypes were euthanised, and the fundic region of abomasum was sampled for evaluation of microscopic lesions and relative expression of genes related to immune, mucin and lectin activities. Lambs harbouring the βA allele presented an improved resistance/resilience against clinical haemonchosis, showing higher PCV during infection. Hb-AA animals presented increased eosinophilia in the abomasum compared to Hb-BB animals, accompanied by higher Th2 profile, mucin and lectin activity transcripts, while the inflammatory response was increased in Hb-BB animals. This is the first report to demonstrate an enhanced local response in the primary site of H. contortus infection related to βA allele of β-globin haplotype.

Interaction networks and pathway analysis of genetic resistance to gastrointestinal nematodes in sheep

Gastrointestinal nematode (GINs) infections are one of the causative agents of health and economic issues in sheep production systems worldwide. Considerable genetic variations in resistance or susceptibility in different sheep breeds are documented, but published results are conflicting. Recent advances obtained by high-throughput technologies such as commercial SNP chips, whole-genome sequencing, or whole transcriptome profiling provide new insights into breeding for host resistance or nematode control at the genetic levels. This study aimed to identify potential biomarkers associated with the resistance to ovine GINs through a network analysis approach. Comprehensive gene and protein interaction networks were reconstructed for candidate genes involved in the most related immune pathways associated with resistance to ovine GINs using data mining from literature. Generally, 30 genes including CD53, CHIA, RELN, HRH1, EPS15, LRP8, ATP2B1, IL4, IL5, IL13, IL2RA, IL23R, TNFα, IFNγ, TBX21, SH3RF1, HERC2, PTPN1, BIN1, HERC5, C3AR1, NOS2, STAT5B, STAT4, CCL1, CCL8, VIL1, CXCR1, CXCR2, and CXCR4 located on chromosomes 1, 2, 3, 4, 5, 6, 11, 13, 19, and 20 have been found as containing effective regions with the most related pathways to nematode infections. The results obtained by network analysis showed two functional modules, belonging to the interleukins family (IL4, IL5, IL13, IL23R, and IL2RA) and chemokine receptors or ligands family (CXCR1, CXCR2, CXCR4, CCL1, and CCL8). Interleukins are a group of cytokines that are expressed by white blood cells with a major role in the immune system. Chemokines are also a family of chemoattractant cytokines which play a vital role in cell migration that influence the immune system by a process known as chemotaxis. The results provide useful information for the functional annotation of candidate genes related to parasite resistance and add new information towards a consensus on quantitative trait loci (QTLs) related to the incidence of nematode infections.

Genome-Wide Association Study of Parasite Resistance to Gastrointestinal Nematodes in Corriedale Sheep

Selection of genetically resistant animals is one alternative to reduce the negative impact of gastrointestinal nematodes (GIN) on sheep production. The aim of this study was to identify genomic regions associated with GIN resistance in Corriedale sheep by single-step genome-wide association studies (ssGWAS) using 170, 507 and 50K single nucleotide polymorphisms (SNPs). Analysis included 19,547 lambs with faecal egg counts (FEC) records, a pedigree file of 40,056 animals and 454, 711 and 383 genotypes from 170, 507 and 50K SNPs, respectively. Genomic estimated breeding values (GEBV) were obtained with single-step genomic BLUP methodology (ssGBLUP), using a univariate animal model, which included contemporary group, type of birth and age of dam as class fixed effects and age at FEC recording as covariate. The SNP effects as wells as p-values were estimated with POSTGSF90 program. Significance level was defined by a chromosome-wise False Discovery Rate of 5%. Significant genomic regions were identified in chromosomes 1, 3, 12 and 19 with the 170 SNP set, in chromosomes 7, 12 and 24 using the 507 SNP chip and only in chromosome 7 with the 50K SNP chip. Candidate genes located in these regions, using Oar_v4.0 as reference genome, were TIMP3, TLR5, LEPR and TLR9 (170 SNPs), SYNDIG1L and MGRN1 (507 SNP chip) and INO80, TLN2, TSHR and EIF2AK4 (50K SNP chip). These results validate genomic regions associated with FEC previously identified in Corriedale and other breeds and report new candidate regions for further investigation.

Contribution of the Immune Response in the Ileum to the Development of Diarrhoea caused by Helminth Infection: Studies with the Sheep Model

Gastrointestinal helminths are a global health issue, for humans as well as domestic animals. Most studies focus on the tissues that are infected with the parasite, but here we studied the ileum, a tissue that is rarely infected by helminths. We tested whether inflammation in the ileum contributes to the development and severity of diarrhoea, by comparing sheep that are susceptible (n = 4) or resistant (n = 4) to the disease. We analyzed the ileum transcriptome using RNASeq sequencing approach and various bioinformatics tools including FastQC, STAR, featureCounts, DESeq2, DAVID, clusterProfiler, Cytoscape (ClusterONE) and EnrichR. We identified 243 differentially expressed genes (DEGs), of which 118 were up-regulated and 125 were down-regulated DEGs in the diarrhoea-susceptible animals compared to the diarrhoea-resistant animals. The resulting DEGs were functionally enriched for biological processes, pathways and gene set enrichment analysis. The up-regulated DEGs suggested that an inflammatory immune response was coupled with genes involved in 'Th2 immune response' and 'anti-inflammatory response'. The down-regulated DEGs were related to ion transport, muscle contraction and pathways preventing inflammation. We conclude that i) susceptibility to helminth-induced diarrhoea involves an inflammatory response at a non-infectious site; ii) down-regulation of pathways preventing inflammation can contribute to the severity of diarrhoea; and iii) genes involved in anti-inflammatory responses can reduce the inflammation and diarrhoea.

Investigating the development of diarrhoea through gene expression analysis in sheep genetically resistant to gastrointestinal helminth infection

Gastrointestinal helminths infect livestock causing health problems including severe diarrhoea. To explore the underlying biological mechanisms relating to development and control of diarrhoea, we compared 4 sheep that were susceptible to development of diarrhoea with 4 sheep that were diarrhoea-resistant. Transcriptomes in the tissues where the parasites were located were analyzed using RNASeq. By considering low-diarrhoea sheep as control, we identified 114 genes that were down-regulated and 552 genes that were up-regulated genes in the high-diarrhoea phenotype. Functional analysis of DEGs and PPI sub-network analysis showed that down-regulated genes in the high-diarrhoea phenotype were linked to biological processes and pathways that include suppression of ‘antigen processing and presentation’, ‘immune response’, and a list of biological functional terms related to ‘suppression in immune tolerance’. On the other hand, up-regulated genes in the high-diarrhoea phenotype probably contribute to repair processes associated with tissue damage, including ‘extracellular matrix organization’, ‘collagen fibril organization’, ‘tissue morphogenesis’, ‘circulatory system development’, ‘morphogenesis of an epithelium’, and ‘focal adhesion’. The genes with important roles in the responses to helminth infection could be targeted in breeding programs to prevent diarrhoea.

Differential responses of abomasal transcriptome to Haemonchus contortus infection between Haemonchus-selected and Trichostrongylus-selected merino sheep

Haemonchus contortus is the most prevalent and pathogenic gastrointestinal nematode infecting sheep and goats. The two CSIRO sheep resource flocks, the Haemonchus-selected flock (HSF) and Trichostrongylus-selected flock (TSF) were developed for research on host resistance or susceptibility to gastrointestinal nematode infection. A recent study focused on the gene expression differences between resistant and susceptible sheep within each flock, with lymphatic and gastrointestinal tissues. To identify features in the host transcriptome and understand the molecular differences underlying host resistance to H. contortus between flocks with different selective breeding and genetic backgrounds, we compared the abomasal transcriptomic responses of the resistant or susceptible animals between HSF and TSF flocks. A total of 11 and 903 differentially expressed genes were identified in the innate infection treatment in HSF and TSF flocks between resistant and susceptible sheep respectively, while 52 and 485 genes were identified to be differentially expressed in the acquired infection treatment, respectively. Among them, 294 genes had significantly different gene expression levels between HSF and TSF flock animals within the susceptible sheep by both the innate and acquired infections. Moreover, similar expression patterns of the 294 genes were observed, with 273 genes more highly expressed in HSF and 21 more highly expressed in the TSF within the abomasal transcriptome of the susceptible animals. Gene ontology enrichment of the differentially expressed genes identified in this study predicted the likely differing function between the two flock's susceptible lines in response to H. contortus infection. Nineteen pathways were significantly enriched in both the innate and adaptive immune responses in susceptible animals, which indicated that these pathways likely contribute to the host resistance development to H. contortus infection in susceptible sheep. Biological networks built for the set of genes differentially abundant in susceptible animals identified hub genes of PRKG1, PRKACB, PRKACA, and ITGB1 for the innate immune response, and CALM2, MYL1, COL1A1, ITGB1 and ITGB3 for the adaptive immune response, respectively. Our results offered a quantitative snapshot of host transcriptomic changes induced by H. contortus infection between flocks with different selective breeding and genetic backgrounds and provided novel insights into molecular mechanisms of host resistance.

Trickle infection with Heligmosomoides polygyrus results in decreased worm burdens but increased intestinal inflammation and scarring

Introduction

Intestinal roundworms cause chronic debilitating disease in animals, including humans. Traditional experimental models of these types of infection use a large single-dose infection. However, in natural settings, hosts are exposed to parasites on a regular basis and when mice are exposed to frequent, smaller doses of Heligmosomoides polygyrus, the parasites are cleared more quickly. Whether this more effective host response has any negative consequences for the host is not known.

Results

Using a trickle model of infection, we found that worm clearance was associated with known resistance-related host responses: increased granuloma and tuft cell numbers, increased levels of granuloma IgG and decreased intestinal transit time, as well as higher serum IgE levels. However, we found that the improved worm clearance was also associated with an inflammatory phenotype in and around the granuloma, increased smooth muscle hypertrophy/hyperplasia, and elevated levels of Adamts gene expression.

Discussion

To our knowledge, we are the first to identify the involvement of this protein family of matrix metalloproteinases (MMPs) in host responses to helminth infections. Our results highlight the delicate balance between parasite clearance and host tissue damage, which both contribute to host pathology. When continually exposed to parasitic worms, improved clearance comes at a cost.

From innate to adaptive immunity: Abomasal transcriptomic responses of merino sheep to Haemonchus contortus infection

Although many important mediators and critical pathways are found to be involved in host immune responses to Haemonchus contortus infection, the initial responses to infection in the naïve and in the previously exposed state have not been compared at the transcriptional level. To further understand the development of adaptive immunity to H. contortus infection, we compared the early abomasal gene expression patterns between a primary and a tertiary challenge for four lines of sheep to discover differentially expressed genes (DEGs). The sheep were from the resistant (R) and susceptible (S) lines of two flocks of sheep selected for divergent responses to gastro-intestinal parasites (HSF and TSF). The flocks have separate origins and were initiated using two different strains of Merino sheep. One of the DEGs, mast cell proteinase 1, had significantly lower expression in tertiary compared to primary infections for all four lines of sheep. This gene was not identified in previous studies where resistant and susceptible sheep samples were compared within infection time points. Comparing the differentially expressed genes (DEGs) for the two R lines reveals that responses differed very little between the primary and tertiary challenges for HSFR and only two genes were identified, in contrast to the TSFR where there were 134 genes identified including the two identified using the HSFR animals. Similarly, comparing the primary and tertiary challenges for HSFS identified 15 DEGs, whilst for TSFS there were 128 DEGs identified. It is surprising that so few genes respond similarly between the two challenge regimes across the four lines of sheep, and suggests significant differences in immune mechanisms between the two flocks (across the lines) and also between the lines within flocks. Our results offer a quantitative snapshot comparing the transcriptome in the ovine abomasum between primary and tertiary infections with H. contortus in both genetically resistant and susceptible sheep.

Between-population differences in constitutive and infection-induced gene expression in threespine stickleback

Vertebrate immunity is a complex system consisting of a mix of constitutive and inducible defences. Furthermore, host immunity is subject to selective pressure from a range of parasites and pathogens which can produce variation in these defences across populations. As populations evolve immune responses to parasites, they may adapt via a combination of (1) constitutive differences, (2) shared inducible responses, or (3) divergent inducible responses. Here, we leverage a powerful natural host‐parasite model system (Gasterosteus aculeatus and Schistochephalus solidus) to tease apart the relative contributions of these three types of adaptations to among‐population divergence in response to parasites. Gene expression analyses revealed limited evidence of significant divergence in constitutive expression of immune defence, and strong signatures of conserved inducible responses to the parasite. Furthermore, our results highlight a handful of immune‐related genes which show divergent inducible responses which may contribute disproportionately to functional differences in infection success or failure. In addition to investigating variation in evolutionary adaptation to parasite selection, we also leverage this unique data set to improve understanding of cellular mechanisms underlying a putative resistance phenotype (fibrosis). Combined, our results provide a case study in evolutionary immunology showing that a very small number of genes may contribute to genotype differences in infection response.

Identification of Regulatory Functions of LncRNAs Associated With T. circumcincta Infection in Adult Sheep

Several recent studies have demonstrated the role of long non-coding RNAs (lncRNAs) in regulating the defense mechanism against parasite infections, but no studies are available that investigated their relevance for immune response to nematode infection in sheep. Thus, the aim of the current study was to (i) detect putative lncRNAs that are expressed in the abomasal lymph node of adult sheep after an experimental infection with the gastrointestinal nematode (GIN) Teladorsagia circumcincta and (ii) to elucidate their potential functional role associated with the differential host immune response. We hypothesized that putative lncRNAs differentially expressed (DE) between samples from animals that differ in resistance to infection may play a significant regulatory role in response to nematode infection in adult sheep. To obtain further support for our hypothesis, we performed co-expression and functional gene enrichment analyses with the differentially expressed lncRNAs (DE lncRNAs). In a conservative approach, we included for this predictive analysis only those lncRNAs that are confirmed and supported by documentation of expression in gastrointestinal tissues in the current sheep gene atlas. We identified 9,105 putative lncRNA transcripts corresponding to 7,124 gene loci. Of these, 457 were differentially expressed lncRNA loci (DELs) with 683 lncRNA transcripts. Based on a gene co-expression analysis via weighted gene co-expression network analysis, 12 gene network modules (GNMs) were found significantly correlated with at least one of 10 selected target DE lncRNAs. Based on the principle of “guilt-by-association,” the DE genes from each of the three most significantly correlated GNMs were subjected to a gene enrichment analysis. The significant pathways associated with DE lncRNAs included ERK5 Signaling, SAPK/JNK Signaling, RhoGDI Signaling, EIF2 Signaling, Regulation of eIF4 and p70S6K Signaling and Oxidative Phosphorylation pathways. They belong to signaling pathway categories like Cellular Growth, Proliferation and Development, Cellular Stress and Injury, Intracellular and Second Messenger Signaling and Apoptosis. Overall, this lncRNA study conducted in adult sheep after GIN infection provided first insights into the potential functional role of lncRNAs in the differential host response to nematode infection.

Physiological, Immunological and Genetic Factors in the Resistance and Susceptibility to Gastrointestinal Nematodes of Sheep in the Peripartum Period: A Review

Parasitic diseases of sheep involving gastrointestinal nematodes (GIN) are one of the main problems that affect fl ock productivity, especially during the peripartum period. Around lambing, the ewes are immunosuppressed and the nematode faecal egg count (FEC) increases at four weeks before lambing, reaching a peak between the fourth and sixth week postpartum and subsequently decreasing towards weaning. Prolactin has been credited with a suppressive effect on immune system, along with other hormones that intervene in metabolism, such as leptin, which has an important role in the activation of other hormones. Cortisol has also been included; this is stimulated by any stressful event and inhibits the proliferation of T-cells and alters the function of immunoglobulins. Another related hormone is pepsinogen, which is considered a marker of the integrity of the abomasum mucosa, as well as the albumin concentration that increases in the presence of a GIN infection. The humoral and cellular immune response, as well as inflammatory reactions, are the main mechanisms of action against GIN. Lymphocytes direct the effector mechanisms in a Th2 cell response, including interleukins (IL-4, IL-5, IL-9, IL-10) and transforming growth factor beta (TGF-β) together with immunoglobulins (IgA, IgG, IgM and IgE), which prevent the invasion of pathogens. Eosinophils with a cytotoxic effect are indicators of a parasitic infection, with importance in the immune protection of infected individuals. The genetic selection of resistant individuals measured by FEC is dependent on the heritability (h²), which is moderately inheritable and highly repeatable. Effects that influence the resistance or susceptibility of sheep to GIN infections in the peripartum period are determined by the interaction of various factors, such as genotype or breed, nutrition, age, type of birth, season and production system, etc., which are studied in this review.

Nematode-induced pathological lesions and alterations of mucin pattern identified in abomasa of wild ruminants

Pathological lesions as well as mucin alterations in abomasa infected by nematodes have been thoroughly studied in livestock, but such data from wild ruminants are limited or completely lacking. Pathological data for Ashworthius sidemi, an invasive nematode are particularly rare. We necropsied the abomasa of 21 wild ruminants belonging to five cervid species and detected mixed nematode infections, dominated by A. sidemi. Samples from both gross lesions and mucous membranes without macroscopically apparent pathological alterations were subjected to standard histological procedures and histochemical staining. Histological examination found chronic abomasitis, manifested by edema, and hyperemia. Various degrees of lymphoplasmacytic infiltration were observed in all samples. Initial fibrosis (8/20, 40%) was detected in samples from both gross lesions and areas without macroscopically visible changes. Tissue from hemorrhagic lesions was superficially eroded. Generalized loss of surface polysaccharides was apparent in all samples. Only residual periodic acid-Schiff and Alcian blue (pH2.5) positivity was detected in the upper abomasal pits and in mucosal neck. This study found that nematode infections, mostly by A. sidemi, caused chronic inflammation and negatively affected abomasal mucin formation in wild ruminants.

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Histological examination of tissue samples identified nematode-induced abomasitis.

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Loss of superficial polysaccharides was apparent in all tissue samples.

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Mainly acidic residual mucins were detected in abomasal pits and mucosal neck zone.

Single nucleotide polymorphisms from candidate genes associated with nematode resistance and resilience in Corriedale and Pampinta sheep in Argentina

Selective breeding of genetically resistant animals is considered a promising strategy to face the problem of nematode resistance to anthelmintics and mitigate concerns about the presence of chemical residues in animal food products and the environment. Gastrointestinal nematode resistance is a complex, multifactorial trait related to host immunity. However, the mechanisms underlying host resistance and response to infection remain to be fully elucidated. In this context, the objective of this study was to provide insight into the chromosomal regions determining nematode resistance and resilience in Corriedale and resistance in Pampinta sheep breeds. A total of 170 single nucleotide polymorphisms (SNP) from 76 candidate genes for immune response were studied in 624 Corriedale and 304 Pampinta animals. Lambs underwent artificial or natural challenges with infective larvae mainly from Haemonchus contortus. Fecal egg counts, estimated breeding values for fecal egg counts, and rate of packed cell volume change and FAMACHA© score change over the challenge were used, when available, as indicators of host parasite resistance or resilience. Phenotype-genotype association studies were conducted and significance values obtained were adjusted for multiple testing errors. Eight SNPs, located on OARs 3, 6, 12, and 20, reached significance in Corriedale sheep under artificial challenge. Those SNP represent allelic variants from the MHC-Ovine Lymphocyte Antigen-DRA, two C-type lectin domain families, the Interleukin 2 receptor β, the Toll-like receptor 10, the Mannan binding lectin serine peptidase 2, and the NLR family, CARD domain containing 4 genes. On Pampinta lambs under natural challenge, we found three significant SNPs, located in the TIMP metallopeptidase inhibitor 3, the FBJ murine osteosarcoma viral oncogene homolog, and the Interleukin 20 receptor alpha genes, on OARs 3, 7, and 8, respectively. The results obtained herein confirm genomic regions previously reported as associated with nematode resistance in other sheep breeds, reinforcing their role in host response to parasites. These findings contribute to gain knowledge on parasite resistance and resilience in Corriedale sheep and report for the first time SNPs associated with resistance to gastrointestinal parasite infections in Pampinta breed.

Local and systemic immune mediators of Morada Nova lambs with divergent Haemonchus contortus resistance phenotypes

AIMS

Local and systemic immune mediators of Morada Nova lambs with divergent Haemonchus contortus resistance phenotypes were evaluated.

METHODS AND RESULTS

Lambs were ranked through faecal egg counts (FEC) after two parasitic challenges with 4,000 H.contortus L₃ . After the second challenge, the lambs underwent a third artificial infection and were euthanized 7 days later. Immune-related genes were quantified locally in abomasal mucosa and lymph nodes (CD4, IFNγ, IL4, IL5, IL13, IL2RA and MS4A2) and systemically in the whole blood (IL4 and IL13). Anti-H. contortus IgG and IgA antibodies and eosinophils and mast cells counts were also investigated. Resistant animals presented higher systemic IgG and IgA titres, both negatively correlated with FEC. Susceptible animals had higher blood levels of IL4 transcripts. At the local level, resistant lambs had higher eosinophils counts and superior MS4A2 levels in abomasal fundic mucosa, besides higher IgA levels in abomasal mucus, while susceptible lamb had superior IL4 expression in abomasal lymph nodes.

CONCLUSION

These data indicate that resistant lambs had an immune response mediated by antibody-mediated cytotoxicity. Also, the systemic humoral profile, particularly IgA isotype, seems to be a good resistance marker for Morada Nova sheep, as we found differences between groups even when FEC did not differ.

The potential for vaccines against scour worms of small ruminants

This review addresses the research landscape regarding vaccines against scour worms, particularly Trichostrongylus spp. and Teladorsagia circumcincta. The inability of past research to deliver scour-worm vaccines with reliable and reproducible efficacy has been due in part to gaps in knowledge concerning: (i) host-parasite interactions leading to development of type-2 immunity, (ii) definition of an optimal suite of parasite antigens, and (iii) rational formulation and administration to induce protective immunity against gastrointestinal nematodes (GIN) at the site of infestation. Recent 'omics' developments enable more systematic analyses. GIN genomes are reaching completion, facilitating "reverse vaccinology" approaches that have been used successfully for the Rhipicephalus australis vaccine for cattle tick, while methods for gene silencing and editing in GIN enable identification and validation of potential vaccine antigens. We envisage that any efficacious scour worm vaccine(s) would be adopted similarly to "Barbervax™" within integrated parasite management schemes. Vaccines would therefore effectively parallel the use of resistant animals, and reduce the frequency of drenching and pasture contamination. These aspects of integration, efficacy and operation require updated models and validation in the field. The conclusion of this review outlines an approach to facilitate an integrated research program.

RNA-Sequencing of ovine PBMC after exposure to Haemonchus contortus larval antigen

Mechanisms of immune activation in effector cells during Haemonchus contortus infection in sheep are currently unknown. Microarray experiments have been performed on tissues of H contortus infected sheep of varying parasite resistance during early and late points of infection, but not in immune effector cells. The purpose of this study was to compare early gene activation in peripheral blood mononuclear cells (PBMC) from primed parasite susceptible (Suffolk) and resistant (St. Croix) sheep in response to H contortus larval antigen (HcLA). Peripheral blood mononuclear cells were cultured for 6 hours with HcLA, and RNA-sequencing was performed. St. Croix PBMC upregulated 499 unique genes in response to HcLA while Suffolk PBMC upregulated 130 unique genes and 25 genes were shared between the two breeds. St. Croix PBMC had increased expression of genes associated with immune function, signal transduction, response to stress and others. In addition, while mechanisms of innate recognition of H contortus are unknown, multiple pattern recognition receptors were found to be upregulated in St. Croix PBMC cultured with HcLA and none were found to be upregulated in Suffolk PBMC. These patterns of immune gene activation may contribute to St. Croix's rapid response and ability to resist H contortus infection.

Four single nucleotide polymorphisms (SNPs) are associated with resistance and resilience to Haemonchus contortus in Brazilian Morada Nova sheep

Gastrointestinal nematodes are a major constraint in sheep production. Breeding for resistance has proven to be an effective and feasible approach to address this problem. The use and investigation of genetic markers for resistance traits could accelerate genetic progress and lead to a better understanding of underlying molecular mechanisms. Thus, the aim of this study was to evaluate if five single nucleotide polymorphisms SNPs OAR2_14765360, OAR6_81718546, OAR11_62887032, OAR12_69606944 and OAR15_59871543 are associated with resistance and resilience traits in a flock of the Morada Nova sheep breed. Lambs were submitted to two consecutive parasite challenges by oral infection with 4000 infective larvae L₃) of Haemonchus contortus. Fecal egg counts (FEC), packed cell volume (PVC) and body weight were measured every one or two weeks for 42 days in each trial. DNA samples from 287 lambs, 131 ewes and 4 rams were amplified by ARMS-PCR or PCR-RFLP and genotypes were determined. Analysis of variance (ANOVA) was used for association analyses between genotypes and phenotypes. In case of significant association, the allele substitution effect was calculated based on a linear model. OAR2_14765360 and OAR12_69606944 were associated with FEC, and OAR12_69606944 also had significant effects on PCV and weight gain, showing favourable associations of the CC genotype with all evaluated traits. Both OAR6_81718546 and OAR11_62887032 were associated with weight gain, and OAR6_81718546 had an additional effect on PCV. OAR15_59871543 was not polymorphic in the population. OAR6_81718546 and OAR12_69606944 presented significant allele substitution effects of -1.06 ± 0.52 kg for the T allele on final body weight and 0.74 ± 0.32 for the C allele in PCV of the same sampling date, respectively. This is the first report of SNPs associated with gastrointestinal nematode resistance in this sheep breed. Our findings support the existence of quantitatice trait loci (QTL) for resistance and resilience in linkage disequilibrium with the polymorphic SNPs and suggest their future use for explorations of these traits in Morada Nova sheep.

Association study reveals Th17, Treg, and Th2 loci related to resistance to Haemonchus contortus in Florida Native sheep1

The aim of this study was to identify for the first time single nucleotide polymorphisms (SNPs) associated with Haemonchus contortus resistance in Florida Native sheep, using a targeted sequencing approach. One hundred and fifty-three lambs were evaluated in this study. At the start of the trial, phenotypic records for fecal egg count (FEC), FAMACHA score, body condition score (BCS), and weight were recorded and deworming of sheep with levamisole (18 mg/kg of body weight) was performed. Ten days post-deworming (baseline) and 28 d post-baseline, a full hematogram of each sheep was obtained and FEC, FAMACHA score, BCS, and weight were assessed. Average daily gain was calculated at the end of the trial. Out of 153 animals, 100 sheep were selected for genotyping using a targeted sequencing approach. Targeted sequencing panel included 100 candidate genes for immune response against H. contortus. SNPs were discarded if call rate <95% and minor allele frequency ≤0.05. A mixed model was used to analyze the response variables and included the identity by state matrix to control for population structure. A contemporary group (age, group, and sex) was included as fixed effect. Bonferroni correction was used to control for multiple testing. Eighteen SNPs on chromosomes 1, 2, 3, 4, 6, 7, 11, 15, 18, 20, 24, and 26 were significant for different traits. Our results suggest that loci related to Th17, Treg, and Th2 responses play an important role in the expression of resistant phenotypes. Several genes including ITGA4, MUC15, TLR3, PCDH7, CFI, CXCL10, TNF, CCL26, STAT3, GPX2, IL2RB, and STAT6 were identified as potential markers for resistance to natural H. contortus exposure. This is the first study that evaluates potential genetic markers for H. contortus resistance in Florida Native sheep.

Identification of potential functional variants underlying ovine resistance to gastrointestinal nematode infection by using RNA-Seq

In dairy sheep flocks from Mediterranean countries, replacement and adult ewes are the animals most affected by gastrointestinal nematode (GIN) infections. In this study, we have exploited the information derived from an RNA-Seq experiment with the aim of identifying potential causal mutations related to GIN resistance in sheep. Considering the RNA-Seq samples from 12 ewes previously classified as six resistant and six susceptible animals to experimental infection by Teladorsagia circumcincta, we performed a variant calling analysis pipeline using two different types of software, gatk version 3.7 and Samtools version 1.4. The variants commonly identified by the two packages (high-quality variants) within two types of target regions - (i) QTL regions previously reported in sheep for parasite resistance based on SNP-chip or sequencing technology studies and (ii) functional candidate genes selected from gene expression studies related to GIN resistance in sheep - were further characterised to identify mutations with a potential functional impact. Among the genes harbouring these potential functional variants (930 and 553 respectively for the two types of regions), we identified 111 immune-related genes in the QTL regions and 132 immune-related genes from the initially selected candidate genes. For these immune-related genes harbouring potential functional variants, the enrichment analyses performed highlighted significant GO terms related to apoptosis, adhesion and inflammatory response, in relation to the QTL related variants, and significant disease-related terms such as inflammation, adhesion and necrosis, in relation to the initial candidate gene list. Overall, the study provides a valuable list of potential causal mutations that could be considered as candidate causal mutations in relation to GIN resistance in sheep. Future studies should assess the role of these suggested mutations with the aim of identifying genetic markers that could be directly implemented in sheep breeding programmes considering not only production traits, but also functional traits such as resistance to GIN infections.

Innate Immune Responses Associated with Resistance against Haemonchus contortus in Morada Nova Sheep

The immune response against Haemonchus contortus infections is primarily associated with the Th2 profile. However, the exact mechanisms associated with increased sheep resistance against this parasite remains poorly elucidated. The present study is aimed at evaluating mediators from the innate immune response in lambs of the Morada Nova Brazilian breed with contrasting H. contortus resistance phenotypes. Briefly, 287 lambs were characterized through fecal egg counts (FEC) and packed cell volume (PCV) after two independent experimental parasitic challenges with 4,000 H. contortus L₃. 20 extreme resistance phenotypes (10 most resistant and 10 most susceptible) were selected, subjected to a third artificial infection with 4,000 L₃, and euthanized 7 days later. Tissue samples were collected from abomasal fundic and pyloric mucosa and abomasal lymph nodes. Blood samples were collected at days 0 and 7 of the third parasitic challenge. RNA was extracted from tissue and blood samples for relative quantification of innate immune-related genes by RT-qPCR. For the abomasal fundic mucosa, increased TNFα and IL1β expression levels (P < 0.05) were found in the susceptible animals, while resistant animals had IL33 superiorly expressed (P < 0.05). Higher levels (P < 0.05) of TLR2 and CFI were found in the abomasal pyloric mucosa of resistant animals. TNFα was at higher levels (P < 0.05) in the blood of susceptible lambs, at day 0 of the third artificial infection. The exacerbated proinflammatory response observed in susceptible animals, at both local and systemic levels, may be a consequence of high H. contortus parasitism. This hypothesis is corroborated by the higher blood levels of TNFα before the onset of infection, which probably remained elevated from the previous parasitic challenges. On the other hand, resistant lambs had an enhanced response mediated by TLR recognition and complement activation. Nevertheless, this is the first study to directly associate sheep parasitic resistance with IL33, an innate trigger of the Th2-polarized response.

Signatures of selection for resistance to Haemonchus contortus in sheep and goats

Background

Gastrointestinal nematode infection (GNI) is the most important disease affecting the small ruminant industry in U.S. The environmental conditions in the southern United States are ideal for the survival of the most pathogenic gastrointestinal nematode, Haemonchus contortus. Host genetic variation for resistance to H. contortus allows selective breeding for increased resistance of animals. This selection process increases the prevalence of particular alleles in sheep and goats and creates unique genetic patterns in the genome of these species. The aim of this study was to identify loci with divergent allelic frequencies in a candidate gene panel of 100 genes using two different approaches (frequentist and Bayesian) to estimate Fst outliers in three different breeds of sheep and goats exposed to H. contortus.

Results

Our results for sheep populations showed SNPs under selection in C3AR1, CSF3, SOCS2, NOS2, STAT5B, TGFB2 and IL2RA genes using frequentist and Bayesian approaches. For goats, SNPs in CD1D, ITGA9, IL12A, IL13RA1, CD86 and TGFB2 genes were under selection. Common signatures of selection in both species were observed in NOS2, TGFB2 and TLR4 genes. Directional selection was present in all SNPs evaluated in the present study.

Conclusions

A total of 13 SNPs within 7 genes of our candidate gene panel related to H. contortus exposure were identified under selection in sheep populations. For goats, 11 SNPs within 7 genes were identified under selection. Results from this study support the hypothesis that resistance to H. contortus is likely to be controlled by many loci. Shared signatures of selection related to mechanisms of immune protection against H. contortus infection in sheep and goats could be useful targets in breeding programs aimed to produce resistant animals with low FEC.

Gene expression profiles of the small intestine of village chickens from an Ascaridia galli infested environment

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The transcriptome of chickens from parasite infested environment was sequenced.

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Different genes were reported between A. galli infected and non-infected chickens.

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Upregulated immune and inflammatory response genes are associated with fighting parasites.

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T cell receptor signalling and arachidonic acid metabolism pathways were impacted.

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Different segments of the intestines differed in gene expression and associated pathways.

Nematodes of the genus Ascaridia are known to infect many species of birds and result in fatal diseases. A. galli damages the intestinal mucosa of chickens leading to blood loss, secondary infection and occasionally the obstruction of small intestines due to high worm burden. This study investigated the gene expression profiles in chickens from two different provinces of South Africa naturally exposed to A. galli infestations and tested either positive or negative for the parasite. The study further investigated gene expression profiles of the A. galli infected duodenum, jejunum and ileum tissues of the small intestines. The A. galli positive intestines displayed hypertrophy of the intestinal villi with accumulation of inflammatory cells and necrosis of the crypts of Lieberkühn glands, lesions that were absent in the uninfected intestines. Total RNA isolated from small intestines of infected and non-infected intestines was sequenced using Illumina HiSeq technology to generate up to 23,856,130 reads. Between any two-way comparisons of the intestines, 277 and 190 transcripts were significantly expressed in Limpopo and KwaZulu-Natal (KZN) chickens, respectively. Gene ontology analysis of the differentially expressed genes (DEGs) revealed an enrichment of genes reported to function in the immune response, defense response, inflammatory response and cell signalling genes. T cell receptor signalling pathways and arachidonic acid metabolism pathways were among the most significantly impacted pathways. Overall, the study provided insights into adaptative mechanisms for chickens extensively raised in parasite infected environments.

Transcriptome analysis unraveled potential mechanisms of resistance to Haemonchus contortus infection in Merino sheep populations bred for parasite resistance

Haemonchus contortus is one of the most pathogenic gastrointestinal nematodes in small ruminants. To understand molecular mechanisms underlying host resistance to this parasite, we used RNA-sequencing technology to compare the transcriptomic response of the abomasal tissue, the site of the host-parasite interaction, of Merino sheep bred to be either genetically resistant or susceptible to H. contortus infection. Two different selection flocks, the Haemonchus selection flock (HSF) and the Trichostrongylus selection flock (TSF), and each contains a resistant and susceptible line, were studied. The TSF flock was seemingly more responsive to both primary and repeated infections than HSF. A total of 127 and 726 genes displayed a significant difference in abundance between resistant and susceptible animals in response to a primary infection in HSF and TSF, respectively. Among them, 38 genes were significantly affected by infection in both flocks. Gene ontology (GO) enrichment of the differentially expressed genes identified in this study predicted the likely involvement of extracellular exosomes in the immune response to H. contortus infection. While the resistant lines in HSF and TSF relied on different mechanisms for the development of host resistance, adhesion and diapedesis of both agranulocytes and granulocytes, coagulation and complement cascades, and multiple pathways related to tissue repair likely played critical roles in the process. Our results offered a quantitative snapshot of changes in the host transcriptome induced by H. contortus infection and provided novel insights into molecular mechanisms of host resistance.

Exploring the mechanisms of resistance to Teladorsagia circumcincta infection in sheep through transcriptome analysis of abomasal mucosa and abomasal lymph nodes

The present study exploited the RNA-seq technology to analyze the transcriptome of target tissues affected by the Teladorsagia circumcincta infection in two groups of adult ewes showing different statuses against gastrointestinal nematode (GIN) infection with the aim of identifying genes linked to GIN infection resistance in sheep. For this, based on the accumulated faecal egg count of 18 adult Churra ewes subjected to a first experimental infection with T. circumcincta, six ewes were classified as resistant and six others as susceptible to the infection. These 12 animals were dewormed and infected again. After humanitarian sacrifice of these 12 animals at day 7 post-infection, RNA samples were obtained from abomasal mucosa and lymph node tissues and RNA-Seq datasets were generated using an Illumina HiSeq 2000 sequencer. The distribution of the genes based on their expression level were very similar among the two different tissues and conditions. The differential expression analysis performed with two software (DESeq and EdgeR) only identified common differentially expressed genes (DEGs), a total of 106, in the lymph node samples which were considered as GIN-activated. The enrichment analysis performed for these GIN-activated genes identified some pathways related to cytokine-mediated immune response and the PPARG signaling pathway as well as disease terms related to inflammation and gastro-intestinal diseases as enriched. A systematic comparison with the results of previous studies confirmed the involvement of genes such as ITLN2, CLAC1 and galectins, in the immune mechanism activated against T. circumcincta in resistant sheep.

Trehalose-6-phosphate phosphatase as a broad-spectrum therapeutic target against eukaryotic and prokaryotic pathogens

As opposed to organism-based drug screening approaches, protein-based strategies have the distinct advantage of providing insights into the molecular mechanisms of chemical effectors and thus afford a precise targeting. Capitalising on the increasing number of genome and transcriptome datasets, novel targets in pathogens for therapeutic intervention can be identified in a more rational manner when compared with conventional organism-based methodologies. Trehalose-6-phosphate phosphatases (TPPs) are structurally and functionally conserved enzymes of the trehalose biosynthesis pathway which play a critical role for pathogen survival, in particular, in parasites. The absence of these enzymes and trehalose biosynthesis from mammalian hosts has recently given rise to increasing interest in TPPs as novel therapeutic targets for drugs and vaccines. Here, we summarise some key aspects of the current state of research towards novel therapeutics targeting, in particular, nematode TPPs.

Abomasal dysfunction and cellular and mucin changes during infection of sheep with larval or adult Teladorsagia circumcincta

This is the first integrated study of the effects on gastric secretion, inflammation and fundic mucins after infection with L3 T. circumcincta and in the very early period following transplantation of adult worms. At 3 months-of-age, 20 Coopworth lambs were infected intraruminally with 35,000 L3; infected animals were killed on Days 5, 10, 15, 20 and 30 post-infection and 6 controls on either Day 0 or 30 post-infection. Another 15 Romney cross lambs received 10,000 adult worms at 4-5 months-of-age though surgically-implanted abomasal cannulae and were killed after 6, 12, 24 and 72 hours; uninfected controls were also killed at 72 hours. Blood was collected at regular intervals from all animals for measurement of serum gastrin and pepsinogen and abomasal fluid for pH measurement from cannulated sheep. Tissues collected at necropsy were fixed in Bouin's fluid for light microscopy, immunocytochemistry and mucin staining and in Karnovsky's fluid for electron microscopy. Nodules around glands containing developing larvae were seen on Day 5 p.i., but generalised effects on secretion occurred only after parasite emergence and within hours after transplantation of adult worms. After L3 infection, there were maximum worm burdens on Days 10-15 post-infection, together with peak tissue eosinophilia, inhibition of gastric acid secretion, hypergastrinaemia, hyperpepsinogenaemia, loss of parietal cells, enlarged gastric pits containing less mucin and increased numbers of mucous neck cells. After adult transplantation, serum pepsinogen was significantly increased after 9 hours and serum gastrin after 18 hours. Parallel changes in host tissues and the numbers of parasites in the abomasal lumen suggest that luminal parasites, but not those in the tissues, are key drivers of the pathophysiology and inflammatory response in animals exposed to parasites for the first time. These results are consistent with initiation of the host response by parasite chemicals diffusing across the surface epithelium, possibly aided by components of ES products which increased permeability. Parietal cells appear to be a key target, resulting in secondary increases in serum gastrin, pit elongation, loss of surface mucins and inhibition of chief cell maturation. Inflammation occurs in parallel, and could either cause the pathology or exacerbate the direct effects of ES products.

Quantification and expression studies of IL-13 gene in response to experimental infection with Haemonchus contortus in Garole and Sahabadi sheep

To evaluate the role of IL-13 gene in Garole/Sahabadi sheep against resistant/susceptibility to Haemonchus contortus five Garole sheep (Group I) with consistently showing low egg per gram of faeces (EPG) (≤150) and another five Garole sheep (Group II) with high EPG (≥500) were selected and fed orally with active H. contortus third stage (L₃) larvae at the dose rate of 500 larvae/kg body weight. Five Sahabadi sheep (Gr-III) known susceptible to H. contortus were also challenged with the same dose as the previous groups. Blood was collected from each group on day 0, 7 and 14days post infection (dpi). The serum level of IL-13 cytokine was evaluated by ELISA at different days of post infection. The ovine IL-13 was partially isolated and the RNAm level of IL-13 expression was studied by real-time PCR at different days post infection. In the resistant Garole sheep (Gr-I) the concentration of IL-13 cytokine increased significantly (P≤0.05) 14days PI compared to susceptible Garole (Gr-II)/Sahabadi (Group-III). In similar way the relative expression of IL-13 in group I (Gr-I) was found more than seven fold higher than Gr-II and Gr-III on 14 dpi. The Th₂ type immune response to H. contortus characterized by higher serum level of IL-13 cytokine and IL-13 gene expression indicated that IL-13 gene plays a vital role for the reduced establishment and/or survival of established H. contortus in resistant Garole sheep.

Transcriptional immune response in mesenteric lymph nodes in pigs with different levels of resistance to Ascaris suum

A single nucleotide polymorphism on chromosome 4 (SNP TXNIP) has been reported to be associated with roundworm (Ascaris suum) burden in pigs. The objective of the present study was to analyse the immune response to A. suum mounted by pigs with genotype AA (n = 24) and AB (n = 23) at the TXNIP locus. The pigs were repeatedly infected with A. suum from eight weeks of age until necropsy eight weeks later. An uninfected control group (AA; n = 5 and AB; n = 5) was also included. At post mortem, we collected mesenteric lymph nodes and measured the expression of 28 selected immune-related genes. Recordings of worm burdens confirmed our previous results that pigs of the AA genotype were more resistant to infection than AB pigs. We estimated the genotype difference in relative expression levels in infected and uninfected animals. No significant change in expression levels between the two genotypes due to infection was observed for any of the genes, although IL-13 approached significance (P = 0.08; Punadjusted = 0.003). Furthermore, statistical analysis testing for the effect of infection separately in each genotype showed significant up-regulation of IL-13 (P<0.05) and CCL17 (P<0.05) following A. suum infection in the 'resistant' AA genotype and not in the 'susceptible' AB genotype. Pigs of genotype AB had higher expression of the high-affinity IgG receptor (FCGR1A) than AA pigs in both infected and non-infected animals (P = 1.85*10-11).

The host immune response to gastrointestinal nematode infection in sheep

Gastrointestinal nematode infection represents a major threat to the health, welfare and productivity of sheep populations worldwide. Infected lambs have a reduced ability to absorb nutrients from the gastrointestinal tract, resulting in morbidity and occasional mortality. The current chemo‐dominant approach to nematode control is considered unsustainable due to the increasing incidence of anthelmintic resistance. In addition, there is growing consumer demand for food products from animals not subjected to chemical treatment. Future mechanisms of nematode control must rely on alternative, sustainable strategies such as vaccination or selective breeding of resistant animals. Such strategies take advantage of the host's natural immune response to nematodes. The ability to resist gastrointestinal nematode infection is considered to be dependent on the development of a protective acquired immune response, although the precise immune mechanisms involved in initiating this process remain to be fully elucidated. In this study, current knowledge on the innate and acquired host immune response to gastrointestinal nematode infection in sheep and the development of immunity is reviewed.

Breeding for resistance to gastrointestinal nematodes - the potential in low-input/output small ruminant production systems

The control of gastrointestinal nematodes (GIN) is mainly based on the use of drugs, grazing management, use of copper oxide wire particles and bioactive forages. Resistance to anthelmintic drugs in small ruminants is documented worldwide. Host genetic resistance to parasites, has been increasingly used as a complementary control strategy, along with the conventional intervention methods mentioned above. Genetic diversity in resistance to GIN has been well studied in experimental and commercial flocks in temperate climates and more developed economies. However, there are very few report outputs from the more extensive low-input/output smallholder systems in developing and emerging countries. Furthermore, results on quantitative trait loci (QTL) associated with nematode resistance from various studies have not always been consistent, mainly due to the different nematodes studied, different host breeds, ages, climates, natural infections versus artificial challenges, infection level at sampling periods, among others. The increasing use of genetic markers (Single Nucleotide Polymorphisms, SNPs) in GWAS or the use of whole genome sequence data and a plethora of analytic methods offer the potential to identify loci or regions associated nematode resistance. Genomic selection as a genome-wide level method overcomes the need to identify candidate genes. Benefits in genomic selection are now being realised in dairy cattle and sheep under commercial settings in the more advanced countries. However, despite the commercial benefits of using these tools, there are practical problems associated with incorporating the use of marker-assisted selection or genomic selection in low-input/output smallholder farming systems breeding schemes. Unlike anthelmintic resistance, there is no empirical evidence suggesting that nematodes will evolve rapidly in response to resistant hosts. The strategy of nematode control has evolved to a more practical manipulation of host-parasite equilibrium in grazing systems by implementation of various strategies, in which improvement of genetic resistance of small ruminant should be included. Therefore, selection for resistant hosts can be considered as one of the sustainable control strategy, although it will be most effective when used to complement other control strategies such as grazing management and improving efficiency of anthelmintics currently.

Histochemical study of the effects on abomasal mucins of Haemonchus contortus or Teladorsagia circumcincta infection in lambs

Previously, chemical analysis of gastric fundic mucin showed that infection of sheep with Haemonchus contortus or Teladorsagia circumcincta changed the proportions of monosaccharides and decreased terminal mucin fucosylation and sialylation. To identify the effects of these parasites on the two mucin-secreting cell lineages, fundic and antral tissues were collected for histochemistry from 69 lambs aged from 3-4 to 9-10 months-of-age which had received a single infection of either H. contortus or T. circumcincta and euthanased at Day 21 or 28 post- infection respectively. All fundic tissues were stained separately with: (1) with Periodic Acid Schiff (PAS) for all mucins; (2) Alcian Blue (AB) pH 2.5 for acidic mucins (sialylated and sulphated); (3) AB pH 1 for sulphated mucins and (4) High Iron Diamine (HID) for sulphated mucins. Antral and fundic tissues from 24 lambs were also stained for acidic and neutral mucins or with specific lectins for α-1-linked fucose and for α-2,3- and α-2,6-linked sialic acids. Only mucin sulphation appeared to differ visually in uninfected lambs over this age range: there was weak staining with HID in tissues from lambs 3-6 months-of-age, but was generally more intense in those over 7 months-of-age. Sulphomucins were not apparent in surface mucous cells (SMC) or generally in the upper pits. Sialylomucins were located predominantly in the pits and glands, with small amounts of sialylated mucins in SMC and on the luminal surface, mainly in younger animals up to 6 months-of-age and less in the older animals. Parasitism markedly reduced the predominantly neutral surface mucin5AC of the SMC and pit cells, despite pit elongation in both antrum and fundus, whereas the acidic Muc6 secreted by mucus neck cells (MNC) increased along with MNC hyperplasia. Sulphated mucins were present mainly from the mid-pits downward and heavy staining was more common in older animals. In these sheep, the markedly reduced neutral mucin in the SMC and pit cells in both antrum and fundus contrasts with reported hypersecretion of mucus in the intestine, which is believed to aid in parasite expulsion. It has been proposed that intestinal goblet cell hypersecretion occurs only in resistant animals, therefore reduced mucins in the abomasum may be indicative of susceptibility to abomasal parasites.

Genomic Regions Associated with Sheep Resistance to Gastrointestinal Nematodes

Genetic markers for sheep resistance to gastrointestinal parasites have long been sought by the livestock industry as a way to select more resistant individuals and to help farmers reduce parasite transmission by identifying and removing high egg shedders from the flock. Polymorphisms related to the major histocompatibility complex and interferon (IFN)-γ genes have been the most frequently reported markers associated with infection. Recently, a new picture is emerging from genome-wide studies, showing that not only immune mechanisms are important determinants of host resistance but that gastrointestinal mucus production and hemostasis pathways may also play a role.

Immunity to Haemonchus contortus and Vaccine Development

Sheep are capable of developing protective immunity to Haemonchus contortus through repeated exposure to this parasite, although this immune protection is the result of a complex interaction among age, gender, physiological status, pregnancy, lactation, nutrition and innate and adaptive immunity in the host animal. There are multiple effectors of the protective immune response, which differ depending on the developmental stage of the parasite being targeted, and our understanding of the effector mechanisms has developed considerably in the 2000s. The rational design of vaccines based on 'natural' or 'exposed' antigens depends on an understanding of this exposure-induced immunity. However, the most effective current vaccines rely on protection via the induction of high circulating antibody levels to 'hidden' gut antigens of H. contortus. The success of this latter strategy has resulted in the launch of a vaccine, which is based on extracts of the parasite's gut, to aid in the control of Haemonchus in Australia. The development of recombinant subunit vaccines based on the components of the successful native vaccine has not yet been achieved and most of the recent successes with recombinant subunit vaccines have focussed on antigens unrelated to the gut antigens. The future integration of an understanding of the immunobiology of this parasite with advances in antigen identification, expression (or synthesis) and presentation is likely to be pivotal to the further development of these recombinant subunit vaccines. Recent progress in each of the components underpinning this integrated approach is summarized in this review.

Genome-wide scan of gastrointestinal nematode resistance in closed Angus population selected for minimized influence of MHC

Genetic markers associated with parasite indicator traits are ideal targets for study of marker assisted selection aimed at controlling infections that reduce herd use of anthelminthics. For this study, we collected gastrointestinal (GI) nematode fecal egg count (FEC) data from post-weaning animals of an Angus resource population challenged to a 26 week natural exposure on pasture. In all, data from 487 animals was collected over a 16 year period between 1992 and 2007, most of which were selected for a specific DRB1 allele to reduce the influence of potential allelic variant effects of the MHC locus. A genome-wide association study (GWAS) based on BovineSNP50 genotypes revealed six genomic regions located on bovine Chromosomes 3, 5, 8, 15 and 27; which were significantly associated (-log₁₀ p=4.3) with Box-Cox transformed mean FEC (BC-MFEC). DAVID analysis of the genes within the significant genomic regions suggested a correlation between our results and annotation for genes involved in inflammatory response to infection. Furthermore, ROH and selection signature analyses provided strong evidence that the genomic regions associated BC-MFEC have not been affected by local autozygosity or recent experimental selection. These findings provide useful information for parasite resistance prediction for young grazing cattle and suggest new candidate gene targets for development of disease-modifying therapies or future studies of host response to GI parasite infection.

Cloning and tissue distribution of novel splice variants of the ovine ghrelin gene

Background

The ghrelin axis is involved in the regulation of metabolism, energy balance, and the immune, cardiovascular and reproductive systems. The manipulation of this axis has potential for improving economically valuable traits in production animals, and polymorphisms in the ghrelin (GHRL) and ghrelin receptor (GHSR) genes have been associated with growth and carcass traits. Here we investigate the structure and expression of the ghrelin gene (GHRL) in sheep, Ovis aries.

Results

We identify two ghrelin mRNA isoforms, which we have designated Δex2 preproghrelin and Δex2,3 preproghrelin. Expression of Δex2,3 preproghrelin is likely to be restricted to ruminants, and would encode truncated ghrelin and a novel C-terminal peptide. Both Δex2 preproghrelin and canonical preproghrelin mRNA isoforms were expressed in a range of tissues. Expression of the Δex2,3 preproghrelin isoform, however, was restricted to white blood cells (WBC; where the wild-type preproghrelin isoform is not co-expressed), and gastrointestinal tissues. Expression of Δex2 preproghrelin and Δex2,3 preproghrelin mRNA was elevated in white blood cells in response to parasitic worm (helminth) infection in genetically susceptible sheep, but not in resistant sheep.

Conclusions

The restricted expression of the novel preproghrelin variants and their distinct WBC expression pattern during parasite infection may indicate a novel link between the ghrelin axis and metabolic and immune function in ruminants.

Functional investigation of a QTL affecting resistance to Haemonchus contortus in sheep

This study reports a functional characterization of a limited segment (QTL) of sheep chromosome 12 associated with resistance to the abomasal nematode Haemonchus contortus. The first objective was to validate the identified QTL through the comparison of genetically susceptible (N) and resistant (R) sheep produced from Martinik × Romane back-cross sheep. The R and N genotype groups were then experimentally infected with 10 000 H. contortus larvae and measured for FEC (every three days from 18 to 30 days post-challenge), haematocrit, worm burden and fertility. Significant differences in FEC and haematocrit drop were found between R and N sheep. In addition, the female worms recovered from R sheep were less fecund. The second step of the characterization was to investigate functional mechanisms associated with the QTL, thanks to a gene expression analysis performed on the abomasal mucosa and the abomasal lymph node. The gene expression level of a candidate gene lying within the QTL region (PAPP-A2) was measured. In addition, putative interactions between the chromosome segment under study and the top ten differentially expressed genes between resistant MBB and susceptible RMN sheep highlighted in a previous microarray experiment were investigated. We found an induction of Th-2 related cytokine genes expression in the abomasal mucosa of R sheep. Down-regulation of the PAPP-A2 gene expression was observed between naïve and challenged sheep although no differential expression was recorded between challenged R and N sheep. The genotyping of this limited region should contribute to the ability to predict the intrinsic resistance level of sheep.

A genome-wide survey reveals a deletion polymorphism associated with resistance to gastrointestinal nematodes in Angus cattle

Gastrointestinal (GI) nematode infections are a worldwide threat to human health and animal production. In this study, we performed a genome-wide association study between copy number variations (CNVs) and resistance to GI nematodes in an Angus cattle population. Using a linear regression analysis, we identified one deletion CNV which reaches genome-wide significance after Bonferroni correction. With multiple mapped human olfactory receptor genes but no annotated bovine genes in the region, this significantly associated CNV displays high population frequencies (58.26 %) with a length of 104.8 kb on chr7. We further investigated the linkage disequilibrium (LD) relationships between this CNV and its nearby single nucleotide polymorphisms (SNPs) and genes. The underlining haplotype blocks contain immune-related genes such as ZNF496 and NLRP3. As this CNV co-segregates with linked SNPs and associated genes, we suspect that it could contribute to the detected variations in gene expression and thus differences in host parasite resistance.

Review: Genetics of helminth resistance in sheep

Karrow, N. A., Goliboski, K., Stonos, N., Schenkel, F. and Peregrine, A. 2014. Review: Genetics of helminth resistance in sheep. Can. J. Anim. Sci. 94: 1–9. Gastrointestinal helminth parasites are an important source of economic loss to sheep producers. A rapid increase in anthelmintic resistance has occurred around the globe; therefore, the industry is exploring alternative strategies such as genetic selection to control losses attributed to helminth infection. Since helminths have co-evolved with sheep for millions of years, natural selection for enhanced helminth resistance has occurred within certain breeds from various parts of the world. These breeds of sheep are being used to better understand the genetic aspects of helminth resistance. If the genetic variants that contribute to this phenotype can be identified, it may be possible to use selection strategies to introduce resistance alleles into other breeds or to increase their frequency within breeds. This review will provide an up-to-date overview of the pathology of helminth disease, the immune response to helminth infection, and the search for genes that confer helminth resistance.

Response of resistant and susceptible Brazilian Somalis crossbreed sheep naturally infected by Haemonchus contortus

This study was carried out to evaluate the performance of Brazilian Somalis sheep to natural infections by gastrointestinal nematodes. During 98 days, 75 weaned sheep, initially 3-4 months old, were kept on the same pasture and evaluated. Fecal and blood samples were collected for parasitological and hematological exams. After this period, the eight most resistant and the eight most susceptible animals were selected based on their individual averages of nematode fecal egg counts and were slaughtered for worm burden determination and nematodes identification. Abomasum and abomasum lymph nodes were also recovered for gene expression analysis. The animals selected as resistant had lower fecal egg counts during experimental period and smaller worm burdens than the susceptible ones (P < 0.05). The genus Haemonchus, followed by Trischostrongylus and Oesophagostomum, were identified in composite cultures. Haemonchus contortus was the specie identified in the abomasum. Packed cell volume and total plasma protein means were higher in the resistant group (27.2% and 6.1 g/dL) than in the susceptible one (22.5% and 5.3 g/dL), respectively. Regarding cytokine gene expression, IL-4 (P < 0.05) was up-regulated in the abomasum of resistant animals and TNF-α (P < 0.03) and IFN-γ (P < 0.03) in susceptible ones. In abomasum lymph nodes, IL-4 (P < 0.04) and IL-13 (P < 0.05) were up-regulated in the resistant animals and IFN-γ in the susceptible one (P < 0.01). This work provides further evidence that, within a given animal breed, individuals have different responses when infected by gastrointestinal nematodes. Resistant animals who responded more quickly and efficiently to these infections activated a TH2-type response.

Exploring the abomasal lymph node transcriptome for genes associated with resistance to the sheep nematode Teladorsagia circumcincta

This study exploited Blackface lambs that varied in their resistance to the abomasal nematode parasite, Teladorsagia circumcincta. Infection of these lambs over 3 months identified susceptible (high adult worm count, high faecal egg count and low IgA antibody) and resistant animals that had excluded all parasites. Previous work had shown that susceptibility and resistance is dependent on the differential immune response to the parasite, which occurs within the abomasal (gastric) lymph node (ALN) that drains the site of infection. The Affymetrix ovine gene array was used to interrogate the transcriptome of the ALN to identify genes and physiological pathways associated with resistance. We used a bovine RT-qPCR array of 84 genes to validate the gene array, and also report digital gene expression analysis on the same tissues, reanalysed using the Oar v3.1 sheep genome assembly. These analyses identified Humoral Immune Response, Protein Synthesis, Inflammatory Response and Hematological System Development and Function as the two top-ranked networks associated with resistance. Central genes within these networks were IL4, IL5, IL13RA2 and in particular IL13, which confirmed that differential activation of Th2 polarized responses is critical to the resistance phenotype. Furthermore, in resistant sheep there was up-regulation of genes linked to control and suppression of inflammation. The identity of differentially-expressed chemokines and receptors in the resistant and susceptible sheep also begins to explain the cellular nature of the host response to infection. This work will greatly help in the identification of candidate genes as potential selectable markers of genetic resistance.

Intranasal immunization of lambs with serine/threonine phosphatase 2A against gastrointestinal nematodes

Seven 3-month-old, female, helminth-free lambs were immunized intranasally with three doses (1 mg total) of a recombinant part of the catalytic region of the serine/threonine phosphatase 2A (PP2Ar) (group 1 [G1]). In addition, four lambs were used as an adjuvant control group (G2), four as unimmunized, infected controls (G3), and four as unimmunized, uninfected controls (G4). Fifteen days after the last immunization, lambs from G1, G2, and G3 were challenged with 10,000 larval stage 3 (L3) organisms in a plurispecific nematode infection composed of ca. 40% Trichostrongylus colubriformis, 40% Haemonchus contortus, and 20% Teladorsagia circumcincta. All the lambs were clinically monitored throughout the experiment. Parasitological (fecal egg output and immunological response), biopathological (packed-cell volume and leukocyte and eosinophil counts), and zootechnical (live-weight gain) analyses were conducted. On day 105 of the experiment, all the animals were slaughtered and the adult worm population in their abomasa examined. Intranasal administration of PP2Ar with bacterial walls as an adjuvant elicited a strong immune response in the immunized lambs, as evidenced by their humoral immune response. Immunized animals and animals receiving the adjuvant shed significantly (P < 0.001) fewer numbers of parasites' eggs in their feces. The immunization significantly reduced the helminth burden in the abomasa by the end of the experiment (>68%), protection being provided against both Haemonchus and Teladorsagia. Live-weight gain in the immunized lambs was similar to that in the uninfected controls versus the infected or adjuvanted animal groups. Our results suggest that heterologous immunization of ruminants by intranasal administration may be efficacious in the struggle to control gastrointestinal helminths in these livestock.

The immunology and genetics of resistance of sheep to Teladorsagia circumcincta

Teladorsagia circumcincta is one of the most economically important gastrointestinal nematode parasites of sheep in cool temperate regions, to which sheep show genetically-varying resistance to infection. This is a very common parasite and viable sheep production requires the extensive use of anthelmintic drugs. However, the emergence of drug-resistant parasites has stimulated the search for alternative control strategies to curb production losses. Lambs become infected soon after weaning and begin to control parasite burden within 8-10 weeks of continual infection. This control is an acquired characteristic mediated by the development of parasite-specific antibodies. This paper describes the immunology associated with resistance and susceptibility, focussing on differential T cell activation that regulates the production of specific effector mechanisms. It continues by summarizing the methods used to identify genes that could be exploited as molecular markers of selection for resistance. In particular it focusses on the link between understanding the molecular immunology of infection and the identification of candidate genes for selection.