Identification of single nucleotide polymorphisms in the bovine solute carrier family 11 member 1 (SLC11A1) gene and their association with infection by Mycobacterium avium subspecies paratuberculosis

Advances in understanding the genetic architecture of antibody response to paratuberculosis in sheep by heritability estimate and LDLA mapping analyses and investigation of candidate regions using sequence-based data

BACKGROUND

Paratuberculosis is a contagious and incurable disease that is caused by Mycobacterium avium subsp. paratuberculosis (MAP) with significant negative effects on animal welfare and farm profitability. Based on a large naturally infected flock over 12 years, we analyzed repeated enzyme-linked immunosorbent assay tests (ELISA), OvineSNP50 BeadChip genotypes and whole-genome sequences imputed from 56 influential animals. The main goals were to estimate the genetic parameters of proxy traits for resistance to MAP, identify genomic regions associated with the host's immune response against MAP and search for candidate genes and causative mutations through association and functional annotation analyses of polymorphisms identified by sequencing.

RESULTS

Two variables were derived from ELISA tests. The first, a binary variable, assessed the infection status of each animal over the entire productive life, while the second considered the level of antibody recorded over time. Very similar results were obtained for both variables. Heritability estimates of about 0.20 were found and a significant region capturing 18% and 13% of the genetic variance was detected on ovine chromosome 20 by linkage disequilibrium and linkage analysis on OvineSNP50 positions. Functional annotation and association analyses on the imputed sequence polymorphisms that were identified in this region were carried out. No significant variants showed a functional effect on the genes that mapped to this region, most of which belong to the major histocompatibility complex class II (MHC II). However, the conditional analysis led to the identification of two significant polymorphisms that can explain the genetic variance associated with the investigated genomic region.

CONCLUSIONS

Our results confirm the involvement of the host's genetics in susceptibility to MAP in sheep and suggest that selective breeding may be an option to limit the infection. The estimated heritability is moderate with a relevant portion being due to a highly significant region on ovine chromosome 20. The results of the combined use of sequence-based data and functional analyses suggest several genes belonging to the MHC II as the most likely candidates, although no mutations in their coding regions showed a significant association. Nevertheless, information from genotypes of two highly significant polymorphisms in the region can enhance the efficiency of selective breeding programs.

Sarcoidosis, Mycobacterium paratuberculosis and Noncaseating Granulomas: Who Moved My Cheese

Clinical and histological similarities between sarcoidosis and tuberculosis have driven repeated investigations looking for a mycobacterial cause of sarcoidosis. Over 50 years ago, "anonymous mycobacteria" were suggested to have a role in the etiology of sarcoidosis. Both tuberculosis and sarcoidosis have a predilection for lung involvement, though each can be found in any area of the body. A key histopathologic feature of both sarcoidosis and tuberculosis is the granuloma-while the tuberculous caseating granuloma has an area of caseous necrosis with a cheesy consistency; the non-caseating granuloma of sarcoidosis does not have this feature. This article reviews and reiterates the complicity of the infectious agent, Mycobacterium avium subsp. paratuberculosis (MAP) as a cause of sarcoidosis. MAP is involved in a parallel story as the putative cause of Crohn's disease, another disease featuring noncaseating granulomas. MAP is a zoonotic agent infecting ruminant animals and is found in dairy products and in environmental contamination of water and air. Despite increasing evidence tying MAP to several human diseases, there is a continued resistance to embracing its pleiotropic roles. "Who Moved My Cheese" is a simple yet powerful book that explores the ways in which individuals react to change. Extending the metaphor, the "non-cheesy" granuloma of sarcoidosis actually contains the difficult-to-detect "cheese", MAP; MAP did not move, it was there all along.

Effect of selected single nucleotide polymorphisms in SLC11A1, ANKRA2, IFNG and PGLYRP1 genes on host susceptibility to Mycobacterium avium subspecies paratuberculosis infection in Indian cattle

Paratuberculosis (PTB) is a chronic infectious enteritis of ruminants, caused by Mycobacterium avium subspecies paratuberculosis (MAP) that brings huge economic loss to the dairy farmers. The study was conducted to explore the association of selected SNPs in IFNG, SLC11A1, ANKRA2 and PGLYRP1 genes with resistance to PTB disease in Indian cattle population. A case-control resource population was established based on the results of diagnostic tests used for detection of MAP infection status viz. ELISA, Johnin PPD test, faecal microscopy and IS900 blood PCR. The PCR-RFLP method was used for genotyping of SNPs. SNPs rs109453173 in SLC11A1, rs110853455 in IFNG and rs41933863 in ANKRA2 genes were significantly (P<0.05) associated with resistance to MAP infection. For SNP rs109453173, GG genotype and G allele was found to be associated with resistance against MAP infection than CC and CG genotypes and C allele, respectively. For SNP rs110853455, AG genotype was found to be associated with susceptibility to MAP infection than AA and GG genotype. For SNP rs41933863, the AG genotype provided three and six times more resistance against MAP infection than GG and AA genotype. The results of this study are suggestive of SNPs rs109453173, rs110853455 and rs41933863 as potential markers for screening MAP resistant cattle and a breeding programme favouring GG genotype and G allele for rs109453173, AG genotype for rs41933863 and against AG genotype for rs110853455 might confer resistance against MAP infection in Indian cattle. However, investigation of these SNPs in an independent and larger population will warrant the strength of association for resistance against MAP infection in cattle.

Johne's Disease in Dairy Cattle: An Immunogenetic Perspective

Johne's disease (JD), also known as paratuberculosis, is a severe production-limiting disease with significant economic and welfare implications for the global cattle industry. Caused by infection with Mycobacterium avium subspecies paratuberculosis (MAP), JD manifests as chronic enteritis in infected cattle. In addition to the economic losses and animal welfare issues associated with JD, MAP has attracted public health concerns with potential association with Crohn's disease, a human inflammatory bowel disease. The lack of effective treatment options, such as a vaccine, has hampered JD control resulting in its increasing global prevalence. The disease was first reported in 1895, but in recognition of its growing economic impact, extensive recent research facilitated by a revolution in technological approaches has led to significantly enhanced understanding of the immunological, genetic, and pathogen factors influencing disease pathogenesis. This knowledge has been derived from a variety of diverse models to elucidate host-pathogen interactions including in vivo and in vitro experimental infection models, studies measuring immune parameters in naturally-infected animals, and by studies conducted at the population level to enable the estimation of genetic parameters, and the identification of genetic markers and quantitative trait loci (QTL) putatively associated with susceptibility or resistance to JD. The main objectives of this review are to summarize these recent developments from an immunogenetics perspective and attempt to extract the principal and common findings emerging from this wealth of recent information. Based on these analyses, and in light of emerging technologies such as gene-editing, we conclude by discussing potential future avenues for effectively mitigating JD in cattle.

The Paratuberculosis Paradigm Examined: A Review of Host Genetic Resistance and Innate Immune Fitness in Mycobacterium avium subsp. Paratuberculosis Infection

Paratuberculosis, or Johne's Disease (JD) is a debilitating chronic enteritis mainly affecting ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). This organism causes worldwide economic losses to the livestock industry, and is of public health importance due to the potential zoonotic risk between MAP and Crohn's disease (CD) in humans. Without economical treatments, or a vaccine capable of preventing infection without causing cross-reactions with bovine tuberculosis, test-and-cull methods for disease control are imperative. Unfortunately, difficulties in diagnostics and long subclinical stage hinder adequate control and is further complicated by variation in MAP exposure outcome. Interestingly, the majority of infections result in asymptomatic presentation and never progress to clinical disease. One contributing factor is host genetics, where polymorphisms in innate immune genes have been found to influence resistance and susceptibility to disease. Candidate genes identified across studies overlap with those found in CD and tuberculosis including; Solute carrier family 11 member 1 gene (SLC11A1), Nucleotide-binding-oligomerization domain containing gene 2 (NOD2), Major histocompatibility complex type II (MHC-II), and Toll-like receptor (TLR) genes. This review will highlight evidence supporting the vital role of these genes in MAP infection outcome, associated challenges, and implications for the future of JD research.

Integrated Analysis of lncRNAs, mRNAs, and TFs to Identify Regulatory Networks Underlying MAP Infection in Cattle

Johne’s disease is a chronic infection of ruminants that burdens dairy herds with a significant economic loss. The pathogenesis of the disease has not been revealed clearly due to its complex nature. In order to achieve deeper biological insights into molecular mechanisms involved in MAP infection resulting in Johne’s disease, a system biology approach was used. As far as is known, this is the first study that considers lncRNAs, TFs, and mRNAs, simultaneously, to construct an integrated gene regulatory network involved in MAP infection. Weighted gene coexpression network analysis (WGCNA) and functional enrichment analysis were conducted to explore coexpression modules from which nonpreserved modules had altered connectivity patterns. After identification of hub and hub-hub genes as well as TFs and lncRNAs in the nonpreserved modules, integrated networks of lncRNA-mRNA-TF were constructed, and cis and trans targets of lncRNAs were identified. Both cis and trans targets of lncRNAs were found in eight nonpreserved modules. Twenty-one of 47 nonpreserved modules showed significant biological processes related to the immune system and MAP infection. Some of the MAP infection’s related pathways in the most important nonpreserved modules comprise “positive regulation of cytokine-mediated signaling pathway,” “negative regulation of leukocyte migration,” “T-cell differentiation,” “neutrophil activation,” and “defense response.” Furthermore, several genes were identified in these modules, including SLC11A1, MAPK8IP1, HMGCR, IFNGR1, CMPK2, CORO1A, IRF1, LDLR, BOLA-DMB, and BOLA-DMA, which are potentially associated with MAP pathogenesis. This study not only enhanced our knowledge of molecular mechanisms behind MAP infection but also highlighted several promising hub and hub-hub genes involved in macrophage-pathogen interaction.

Identification of Long Non-coding RNA Isolated From Naturally Infected Macrophages and Associated With Bovine Johne's Disease in Canadian Holstein Using a Combination of Neural Networks and Logistic Regression

Mycobacterium avium ssp. paratuberculosis (MAP) causes chronic enteritis in most ruminants. The pathogen MAP causes Johne's disease (JD), a chronic, incurable, wasting disease. Weight loss, diarrhea, and a gradual drop in milk production characterize the disease's clinical phase, culminating in death. Several studies have characterized long non-coding RNA (lncRNA) in bovine tissues, and a previous study characterizes (lncRNA) in macrophages infected with MAP in vitro. In this study, we aim to characterize the lncRNA in macrophages from cows naturally infected with MAP. From 15 herds, feces and blood samples were collected for each cow older than 24 months, twice yearly over 3–5 years. Paired samples were analyzed by fecal PCR and blood ELISA. We used RNA-seq data to study lncRNA in macrophages from 33 JD(+) and 33 JD(–) dairy cows. We performed RNA-seq analysis using the “new Tuxedo” suite. We characterized lncRNA using logistic regression and multilayered neural networks and used DESeq2 for differential expression analysis and Panther and Reactome classification systems for gene ontology (GO) analysis. The study identified 13,301 lncRNA, 605 of which were novel lncRNA. We found seven genes close to differentially expressed lncRNA, including CCDC174, ERI1, FZD1, TWSG1, ZBTB38, ZNF814, and ZSCAN4. None of the genes associated with susceptibility to JD have been cited in the literature. LncRNA target genes were significantly enriched for biological process GO terms involved in immunity and nucleic acid regulation. These include the MyD88 pathway (TLR5), GO:0043312 (neutrophil degranulation), GO:0002446 (neutrophil-mediated immunity), and GO:0042119 (neutrophil activation). These results identified lncRNA with potential roles in host immunity and potential candidate genes and pathways through which lncRNA might function in response to MAP infection.

Genome-wide association analysis identified both RNA-seq and DNA variants associated to paratuberculosis in Canadian Holstein cattle 'in vitro' experimentally infected macrophages

Background

Mycobacterium avium ssp. paratuberculosis (MAP) is the causative agent of paratuberculosis, or Johne’s disease (JD), an incurable bovine disease. The evidence for susceptibility to MAP disease points to multiple interacting factors, including the genetic predisposition to a dysregulation of the immune system. The endemic situation in cattle populations can be in part explained by a genetic susceptibility to MAP infection. In order to identify the best genetic improvement strategy that will lead to a significant reduction of JD in the population, we need to understand the link between genetic variability and the biological systems that MAP targets in its assault to dominate macrophages. MAP survives in macrophages where it disseminates. We used next-generation RNA (RNA-Seq) sequencing to study of the transcriptome in response to MAP infection of the macrophages from cows that have been naturally infected and identified as positive for JD (JD (+); n = 22) or negative for JD (healthy/resistant, JD (−); n = 28). In addition to identifying genetic variants from RNA-seq data, SNP variants were also identified using the Bovine SNP50 DNA chip.

Results

The complementary strategy allowed the identification of 1,356,248 genetic variants, including 814,168 RNA-seq and 591,220 DNA chip variants. Annotation using SnpEff predicted that the 2435 RNA-seq genetic variants would produce high functional effect on known genes in comparison to the 33 DNA chip variants. Significant variants from JD(+/−) macrophages were identified by genome-wide association study and revealed two quantitative traits loci: BTA4 and 11 at (P < 5 × 10^− 7). Using BovineMine, gene expression levels together with significant genomic variants revealed pathways that potentially influence JD susceptibility, notably the energy-dependent regulation of mTOR by LKB1-AMPK and the metabolism of lipids.

Conclusion

In the present study, we succeeded in identifying genetic variants in regulatory pathways of the macrophages that may affect the susceptibility of cows that are healthy/resistant to MAP infection. RNA-seq provides an unprecedented opportunity to investigate gene expression and to link the genetic variations to biological pathways that MAP normally manipulate during the process of killing macrophages. A strategy incorporating functional markers into genetic selection may have a considerable impact in improving resistance to an incurable disease. Integrating the findings of this research into the conventional genetic selection program may allow faster and more lasting improvement in resistance to bovine paratuberculosis in dairy cattle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07487-4.

Identification of loci associated with susceptibility to bovine paratuberculosis and with the dysregulation of the MECOM, eEF1A2, and U1 spliceosomal RNA expression

Although genome-wide association studies have identified single nucleotide polymorphisms (SNPs) associated with the susceptibility to Mycobacterium avium subsp. paratuberculosis (MAP) infection, only a few functional mutations for bovine paratuberculosis (PTB) have been characterized. Expression quantitative trait loci (eQTLs) are genetic variants typically located in gene regulatory regions that alter gene expression in an allele-specific manner. eQTLs can be considered as functional links between genomic variants, gene expression, and ultimately phenotype. In the current study, peripheral blood (PB) and ileocecal valve (ICV) gene expression was quantified by RNA-Seq from fourteen Holstein cattle with no lesions and with PTB-associated histopathological lesions in gut tissues. Genotypes were generated from the Illumina LD EuroG10K BeadChip. The associations between gene expression levels (normalized read counts) and genetic variants were analyzed by a linear regression analysis using R Matrix eQTL 2.2. This approach allowed the identification of 192 and 48 cis-eQTLs associated with the expression of 145 and 43 genes in the PB and ICV samples, respectively. To investigate potential relationships between these cis-eQTLs and MAP infection, a case–control study was performed using the genotypes for all the identified cis-eQTLs and phenotypical data (histopathology, ELISA for MAP-antibodies detection, tissue PCR, and bacteriological culture) of 986 culled cows. Our results suggested that the heterozygous genotype in the cis-eQTL-rs43744169 (T/C) was associated with the up-regulation of the MDS1 and EVI1 complex (MECOM) expression, with positive ELISA, PCR, and bacteriological culture results, and with increased risk of progression to clinical PTB. As supporting evidence, the presence of the minor allele was associated with higher MECOM levels in plasma samples from infected cows and with increased MAP survival in an ex-vivo macrophage killing assay. Moreover, the presence of the two minor alleles in the cis-eQTL-rs110345285 (C/C) was associated with the dysregulation of the eukaryotic elongation factor 1-α2 (eEF1A2) expression and with increased ELISA (OD) values. Finally, the presence of the minor allele in the cis-eQTL rs109859270 (C/T) was associated with the up-regulation of the U1 spliceosomal RNA expression and with an increased risk of progression to clinical PTB. The introduction of these novel functional variants into marker-assisted breeding programs is expected to have a relevant effect on PTB control.

Association of genetic variability in CD209 gene with bovine paratuberculosis disease: a case-control study in the Indian cattle population

This study aimed to explore the association of single nucleotide polymorphisms (SNPs) in CD209 gene with the occurrence of bovine paratuberculosis (PTB) disease caused by Mycobacterium avium subspecies paratuberculosis (MAP) in Indian cattle. A total of 213 animals were preliminarily selected on the basis of physical body condition score, which was then screened by a panel of diagnostic tests viz. Johnin, ELISA, fecal microscopy, and fecal culture, for the establishment of a case-control resource population. A total of four SNPs viz. rs208222804, rs211654540, rs208814257, and rs210748127 in CD209 gene were genotyped by PCR-RFLP. All SNPs, except rs210748127, were polymorphic in our population. Genotypic-phenotypic associations were assessed by the PROCLOGISTIC procedure of SAS 9.3. The SNP rs208814257 yielded three genotypes viz. CC, CG, and GG, which were significantly (p < 0.05) different in case as compared to the control population. The odds of CC and CG in comparison to GG genotype were 1.21 and 0.40, respectively. The CG genotype was significantly higher in control population, indicating that this genotype may provide resistance against PTB in our resource population. Upon validation in an independent, larger test population and following biological characterization, SNP rs208814257 can be incorporated in marker panel for selection of animals with greater resistance to MAP infection.

Correlations between single nucleotide polymorphisms in bovine CD209, SLC11A1, SP110 and TLR2 genes and estimated breeding values for several traits in Spanish Holstein cattle

Little is known about the correlations between the genetic susceptibility/resistance to Mycobacterium avium subsp. paratuberculosis (Map) infection and the estimated breeding values for type, production and functional traits. Previously, we identified 70 combinations of five single nucleotide polymorphisms (SNPs) in four bovine innate immune genes (SLC11A1, SP110, TLR2, CD209) that are associated with the genetic risk of paratuberculosis (PTB) or Johne's disease progression, which can be graded as low (LOWIN), latent (LATIN), or patent (PATIN) risk. Other possible combinations of these 5 SNPs were grouped in the average group (AVERIN). In the current study, differences in estimated breeding values (EBVs) for several traits were analyzed using linear models in a large cohort of Holstein cows (N = 15656) genotyped across Spain in 2016 or 2017. After the assignment of each genotyped cow to a risk group, cows within the PATIN risk group (N = 1448) had a superior combined genetic index (2797.57), type genetic index (524.62), milk yield (653.92 kg), protein yield (21.77 kg), fat yield (24.82 kg) and economic merit index (125 Euros) compared with the other three risk groups. Statistically significant differences in the longevity scores between the cows that were included in the PATIN risk group (108.85) and the LOWIN (107.82) and AVERIN (107.92) groups were also observed. The associations between the genetic risk groups and PTB diagnostic results were validated in a population of 99 cows from a Spanish farm with a high prevalence of PTB. Significant differences in ELISA readings between the PATIN (65.49 %) and the AVERIN (15.97 %), LATIN (2.11 %), and LOWIN (3.27 %) groups were observed. In addition, significant differences in Map DNA copies/gram of feces were observed between the PATIN and the other three risk groups. These results together with the substantial economic impact of PTB in dairy cattle support the selection of the animals with less susceptibility to PTB in the Spanish breeding program.

Genetic association of polymorphisms in bovine TLR2 and TLR4 genes with Mycobacterium avium subspecies paratuberculosis infection in Indian cattle population

Toll like receptors (TLRs) are pattern recognition molecules involved in cellular recognition of Mycobacterium avium subspecies paratuberculosis (MAP), the infectious agent causing Paratuberculosis (PTB), a notified disease of domestic and wild ruminants. The present study was undertaken to investigate the presence of single nucleotide polymorphisms (SNPs) in TLR2 and TLR4 gene and to evaluate association of these SNPs with occurrence of PTB in Indian cattle. A total of 213 cattle, were subjected to multiple diagnostic tests viz. Johnin PPD, ELISA test (Indigenous and Parachek kit method), fecal microscopy and fecal culture for detection of MAP infection. Based on screening results 51 animals each were assigned to case and control population. Two SNPs viz. rs55617172, rs41830058 in TLR2 gene and two SNPs viz. rs8193046, rs8193060 in TLR4 gene and were genotyped by PCR-RFLP method. All SNPs were found to be polymorphic except rs41830058 in the case-control population. Both SNPs in TLR4 gene but none in TLR2 genes were significantly associated with the occurrence of PTB in our population. The genotypes in SNP rs8193046 and SNP rs8193060 were significantly (P < 0.01) different in case-control population. These findings suggest that SNPs rs8193046 and rs8193060 are likely a potential marker against MAP infection and a selection programme eliminating AG genotype for rs8193046 and CT genotype for rs8193060 might be beneficial in conferring resistance to MAP infection in Indian cattle population.

Genome-wide association study of Mycobacterium avium subspecies Paratuberculosis infection in Chinese Holstein

Background

Paratuberculosis is a contagious, chronic and enteric disease in ruminants, which is caused by Mycobacterium avium subspecies paratuberculosis (MAP) infection, resulting in enormous economic losses worldwide. There is currently no effective cure for MAP infection or a vaccine, it is thus important to explore the genetic variants that contribute to host susceptibility to infection by MAP, which may provide a better understanding of the mechanisms of paratuberculosis and benefit animal genetic improvement. Herein we performed a genome-wide association study (GWAS) to identify genomic regions and candidate genes associated with susceptibility to MAP infection in dairy cattle.

Results

Using Illumina Bovine 50 K (54,609 SNPs) and GeneSeek HD (138,893 SNPs) chips, two analytical approaches were performed, GRAMMAR-GC and ROADTRIPS in 937 Chinese Holstein cows, among which individuals genotyped by the 50 K chip were imputed to HD SNPs with Beagle software. Consequently, 15 and 11 significant SNPs (P < 5 × 10^− 5) were identified with GRAMMAR-GC and ROADTDRIPS, respectively. A total of 10 functional genes were in proximity to (i.e., within 1 Mb) these SNPs, including IL4, IL5, IL13, IRF1, MyD88, PACSIN1, DEF6, TDP2, ZAP70 and CSF2. Functional enrichment analysis showed that these genes were involved in immune related pathways, such as interleukin, T cell receptor signaling pathways and inflammatory bowel disease (IBD), implying their potential associations with susceptibility to MAP infection. In addition, by examining the publicly available cattle QTLdb, a previous QTL for MAP was found to be overlapped with one of regions detected currently at 32.5 Mb on BTA23, where the TDP2 gene was anchored.

Conclusions

In conclusion, we identified 26 SNPs located on 15 chromosomes in the Chinese Holstein population using two GWAS strategies with high density SNPs. Integrated analysis of GWAS, biological functions and the reported QTL information helps to detect positional candidate genes and the identification of regions associated with susceptibility to MAP traits in dairy cattle.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5385-3) contains supplementary material, which is available to authorized users.

Structural characterization and molecular dynamics simulations of the caprine and bovine solute carrier family 11 A1 (SLC11A1)

Natural Resistance-Associated Macrophage Proteins are a family of transmembrane divalent metal ion transporters, with important implications in life of both bacteria and mammals. Among them, the Solute Carrier family 11 member A1 (SLC11A1) has been implicated with susceptibility to infection by Mycobacterium avium subspecies paratuberculosis (MAP), potentially causing Crohn's disease in humans and paratuberculosis (PTB) in ruminants. Our previous research had focused on sequencing the mRNA of the caprine slc11a1 gene and pinpointed polymorphisms that contribute to caprine SLC11A1's susceptibility to infection by MAP in PTB. Despite its importance, little is known on the structural/dynamic features of mammalian SLC11A1 that may influence its function under normal or pathological conditions at the protein level. In this work we studied the structural architecture of SLC11A1 in Capra hircus and Bos taurus through molecular modeling, molecular dynamics simulations in different, functionally relevant configurations, free energy calculations of protein-metal interactions and sequence conservation analysis. The results of this study propose a three dimensional structure for SLC11A1 with conserved sequence and structural features and provide hints for a potential mechanism through which divalent metal ion transport is conducted. Given the importance of SLC11A1 in susceptibility to PTB, this study provides a framework for further studies on the structure and dynamics of SLC11A1 in other organisms, to gain 3D structural insight into the macromolecular arrangements of SLC11A1 but also suggesting a potential mechanism which divalent metal ion transport is conducted.

Serum lipidomics of bovine paratuberculosis: Disruption of choline-containing glycerophospholipids and sphingolipids

OBJECTIVES

Bovine paratuberculosis is a devastating infection with Mycobacterium avium subspecies paratuberculosis that ultimately results in death from malnutrition. While the infection is characterized by a long (2-4 years) subclinical phase with immune activation, ultimately host defense mechanisms fail and the bacteria spread from the small intestine to other organs. Since both the gastrointestinal tract and liver are essential for the biosynthesis of structural glycerophospholipids, we investigated the circulating levels of these lipids in field infections and experimentally infected cattle.

METHODS

Serum lipidomics of control and M. avium subspecies paratuberculosis-infected cattle were performed utilizing high-resolution mass spectrometry.

RESULTS

In M. avium subspecies paratuberculosis-positive cattle, demonstrating clinical signs, we monitored large decreases in the levels of circulating phosphocholine-containing lipids. These included phosphatidylcholines, choline plasmalogens, and sphingomyelins. Next, we monitored the time course of these lipid alterations in experimentally infected calves and found that altered lipid levels were only detected in cattle with clinical signs of infection.

CONCLUSIONS

Our data indicate that altered availability of choline-containing lipids occurs late in the disease process and is most likely a result of malnutrition and altered biosynthetic capacities of the liver and gastrointestinal tract. Alterations in the bioavailability of these critical structural lipids presumably contributes to the demise of M. avium subspecies paratuberculosis-infected cattle. In light of increasing concern that M. avium subspecies paratuberculosis may be a zoonotic bacterium that contributes to the development of Crohn's disease and multiple sclerosis, our data also have human clinical relevance.

Genomic selection signatures in sheep from the Western Pyrenees

BACKGROUND

The current large spectrum of sheep phenotypic diversity results from the combined product of sheep selection for different production traits such as wool, milk and meat, and its natural adaptation to new environments. In this study, we scanned the genome of 25 Sasi Ardi and 75 Latxa sheep from the Western Pyrenees for three types of regions under selection: (1) regions underlying local adaptation of Sasi Ardi semi-feral sheep, (2) regions related to a long traditional dairy selection pressure in Latxa sheep, and (3) regions experiencing the specific effect of the modern genetic improvement program established for the Latxa breed during the last three decades.

RESULTS

Thirty-two selected candidate regions including 147 annotated genes were detected by using three statistical parameters: pooled heterozygosity H, Tajima's D, and Wright's fixation index F_st. For Sasi Ardi sheep, chromosomes Ovis aries (OAR)4, 6, and 22 showed the strongest signals and harbored several candidate genes related to energy metabolism and morphology (BBS9, ELOVL3 and LDB1), immunity (NFKB2), and reproduction (H2AFZ). The major genomic difference between Sasi Ardi and Latxa sheep was on OAR6, which is known to affect milk production, with highly selected regions around the ABCG2, SPP1, LAP3, NCAPG, LCORL, and MEPE genes in Latxa sheep. The effect of the modern genetic improvement program on Latxa sheep was also evident on OAR15, on which several olfactory genes are located. We also detected several genes involved in reproduction such as ESR1 and ZNF366 that were affected by this selection program.

CONCLUSIONS

Natural and artificial selection have shaped the genome of both Sasi Ardi and Latxa sheep. Our results suggest that Sasi Ardi traits related to energy metabolism, morphological, reproductive, and immunological features have been under positive selection to adapt this semi-feral sheep to its particular environment. The highly selected Latxa sheep for dairy production showed clear signatures of selection in genomic regions related to milk production. Furthermore, our data indicate that the selection criteria applied in the modern genetic improvement program affect immunity and reproduction traits.

Association between combinations of genetic polymorphisms and epidemiopathogenic forms of bovine paratuberculosis

Control of major mycobacterial diseases affecting livestock is a challenging issue that requires different approaches. The use of genetic markers for improving resistance to Mycobacterium avium subsp. paratuberculosis infection in cattle has been explored as a promising population strategy We performed paratuberculosis epidemiopathogenic phenotypic and genotypic characterization involving 24 SNPs in six candidate genes (NOD2, CD209, SLC11A1, SP110, TLR2 and TLR4) on 502 slaughtered Friesian cows. In the current study, we investigate whether recently proposed paratuberculosis (PTB) epidemiopathogenic (EP) forms (apparently free-AF, latent-LAT and patent-PAT) could be associated with some combination of these 24 SNPs. Best EP form grouping was obtained using a combination of 5 SNPs in four genes (CD209: rs210748127; SLC11A1: rs110090506; SP110: rs136859213 and rs110480812; and TLR2: rs41830058). These groups were defined according to the level of infection progression risk to patent epidemiopathogenic forms and showed the following distributions: LOWIN (low) with 39 (8%) cases (94.9% AF/5.1% LAT/0% PAT); LATIN (low) with 17 (3%) cases (5.9% AF/94.1% LAT/0% PAT); AVERIN (average) with 413 (82%) cases (52.1% AF/38.5% LAT/9.4% PAT) and PATIN (patent) with 33 (7%) cases (36.4% AF/24.2% LAT/39.4% PAT). Age of slaughter was significantly higher for LATIN (88.3 months) compared to AVERIN (65.3 months; p = 0.0007) and PATIN (59.1 months; p = 0.0004), and for LOWIN (73.9 months) compared to PATIN (p = 0.0233), and nearly significant compared to AVERIN (p = 0.0572) These results suggest that some selected genetic polymorphisms have a potential use as markers of PTB EP forms and thus add a new tool for the control of this widespread infection.

Association between SLC11A1 (NRAMP1) polymorphisms and susceptibility to tuberculosis in Chinese Holstein cattle

We investigated the associations between SLC11A1 polymorphisms and susceptibility to tuberculosis (TB) in Chinese Holstein cattle, using a case-control study of 136 animals that had positive reactions to TB tests and showed symptoms and 96 animals that had negative reactions to tests and showed no symptoms. Polymerase chain reaction (PCR) sequencing and the restriction fragment length polymorphism (RFLP) technique were used to detect and determine SLC11A1 polymorphisms. Association analysis identified significant correlations between SLC11A1 polymorphisms and susceptibility/resistance to TB, and two genetic markers for SLC11A1 were established using PCR-RFLP. Sequence alignment of SLC11A1 revealed seven single-nucleotide polymorphisms (SNPs). This is the first report of MaeII PCR-RFLP markers for the SLC11A1-SNP3 site and PstI PCR-RFLP markers for the SLC11A1-SNP5 and SLC11A1-SNP6 sites in Chinese Holstein cattle. Logistic regression analysis indicated that SLC11A1-SNP1, SLC11A1-SNP3, and SLC11A1-SNP5 were significantly associated with susceptibility/resistance to TB. Two genotypes of SLC11A1-SNP3 were susceptible to TB, whereas one genotype of SLC11A1-SNP1 and two genotypes of SLC11A1-SNP5 were resistant. Haplotype analysis showed that nine haplotypes were potentially resistant to TB. After Bonferroni correction, three of the haplotypes remained significantly associated with TB resistance. SLC11A1 is a useful candidate gene related to TB in Chinese Holstein cattle.

Phenotype definition is a main point in genome-wide association studies for bovine Mycobacterium avium ssp. paratuberculosis infection status

Paratuberculosis caused by Mycobacterium avium ssp. paratuberculosis (MAP) causes economic losses and is present in dairy herds worldwide. Different studies used different diagnostic tests to detect infection status and are the basis of genome-wide association (GWA) studies with inconsistent results. Therefore, the aim of this study was to identify and compare genomic regions associated with MAP susceptibility in the same cohort of cattle using different diagnostic tests. The GWA study was performed in German Holsteins within a case-control assay using 305 cows tested for MAP by fecal culture and additional with four different commercial ELISA-tests. Genotyping was performed with the Illumina Bovine SNP50 BeadChip. The results using fecal culture or ELISA test led to the identification of different genetic loci. Two single-nucleotide polymorphisms showed significant association with the ELISA-status. However, no significant association for MAP infection could be confirmed. Our results show that the definition of the MAP-phenotype has an important impact on the outcome of GWA studies for paratuberculosis.

Mycobacterium avium ss. paratuberculosis Zoonosis - The Hundred Year War - Beyond Crohn's Disease

The factitive role of Mycobacterium avium ss. paratuberculosis (MAP) in Crohn's disease has been debated for more than a century. The controversy is due to the fact that Crohn's disease is so similar to a disease of MAP-infected ruminant animals, Johne's disease; and, though MAP can be readily detected in the infected ruminants, it is much more difficult to detect in humans. Molecular techniques that can detect MAP in pathologic Crohn's specimens as well as dedicated specialty labs successful in culturing MAP from Crohn's patients have provided strong argument for MAP's role in Crohn's disease. Perhaps more incriminating for MAP as a zoonotic agent is the increasing number of diseases with which MAP has been related: Blau syndrome, type 1 diabetes, Hashimoto thyroiditis, and multiple sclerosis. In this article, we debate about genetic susceptibility to mycobacterial infection and human exposure to MAP; moreover, it suggests that molecular mimicry between protein epitopes of MAP and human proteins is a likely bridge between infection and these autoimmune disorders.

Exploring genetic polymorphism in innate immune genes in Indian cattle (Bos indicus) and buffalo (Bubalus bubalis) using next generation sequencing technology

Activation of innate immunity initiates various cascades of reactions that largely contribute to defense against physical, microbial or chemical damage, prompt for damage repair and removal of causative organisms as well as restoration of tissue homeostasis. Genetic polymorphism in innate immune genes plays prominent role in disease resistance capabilities in various breeds of cattle and buffalo. Here we studied single nucleotide variations (SNP/SNV) and haplotype structure in innate immune genes viz CHGA, CHGB, CHGC, NRAMP1, NRAMP2, DEFB1, BNBD4, BNBD5, TAP and LAP in Gir cattle and Murrah buffalo. Targeted sequencing of exonic regions of these genes was performed by Ion Torrent PGM sequencing platform. The sequence reads obtained corresponding to coding regions of these genes were mapped to reference genome of cattle BosTau7 by BWA program using genome analysis tool kit (GATK). Further variant analysis by Unified Genotyper revealed 54 and 224 SNPs in Gir and Murrah respectively and also 32 SNVs was identified. Among these SNPs 43, 36, 11,32,81,21 and 22 variations were in CHGA, CHGB, CHGC, NRAMP1, NRAMP2, DEFB1 and TAP genes respectively. Among these identified 278 SNPs, 24 were found to be reported in the dbSNP database. Variant analysis was followed by structure formation of haplotypes based on multiple SNPs using SAS software revealed a large number of haplotypes. The SNP discovery in innate immune genes in cattle and buffalo breeds of India would advance our understanding of role of these genes in determining the disease resistance/susceptibility in Indian breeds. The identified SNPs and haplotype data would also provide a wealth of sequence information for conservation studies, selective breeding and designing future strategies for identifying disease associations involving samples from distinct populations.

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Sequencing of exonic regions of 10 selected innate immune genes, 895.60 Mb data was generated.

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Variant analysis using GATK pipeline revealed 278 SNPs, 32 SNVs and from these 24 were found to be reported.

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43, 36 and 11 SNPs were observed in chromagranin genes viz. CHGA, CHGB and CHGC respectively.

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32 and 81 SNPs were identified in NRAMP genes viz. NRAMP1 and NRAMP2 respectively.

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21 and 22 SNPs were observed in β-defensin genes viz. DEFB1 and TAP respectively.

Mycobacterium paratuberculosis as a cause of Crohn's disease

Crohn's disease is a chronic inflammatory bowel disease of unknown cause, affecting approximately 1.4 million North American people. Due to the similarities between Crohn's disease and Johne's disease, a chronic enteritis in ruminant animals caused by Mycobacterium avium paratuberculosis (MAP) infection, MAP has long been considered to be a potential cause of Crohn's disease. MAP is an obligate intracellular pathogen that cannot replicate outside of animal hosts. MAP is widespread in dairy cattle and because of environmental contamination and resistance to pasteurization and chlorination, humans are frequently exposed through contamination of food and water. MAP can be cultured from the peripheral mononuclear cells from 50-100% of patients with Crohn's disease, and less frequently from healthy individuals. Association does not prove causation. We discuss the current data regarding MAP as a potential cause of Crohn's disease and outline what data will be required to firmly prove or disprove the hypothesis.

Genetic association analysis of paratuberculosis forms in holstein-friesian cattle

A genetic susceptibility to Mycobacterium avium subsp. paratuberculosis (MAP) infections in ruminants has been longtime suspected to exist. Recently, natural infections in cattle have been reclassified into latent and patent forms based on histopathological findings and their associations with immunological and microbiological variables. This study aims to explore whether these newly defined phenotypes are associated with twenty-four single-nucleotide polymorphisms (SNPs) in six bovine candidate genes: nucleotide-binding oligomerization domain 2 (NOD2), solute carrier family 11 member A1 (SLC11A1), nuclear body protein SP110 (SP110), toll-like receptors (TLRs) 2 and 4, and CD209 (also known as DC-SIGN, dendritic cell-specific ICAM3-grabbing nonintegrin). SNPs were genotyped for 772 Holstein-Friesian animals (52.6% apparently free; 38.1% latent; 9.3% patent) by TaqMan OpenArray technology. Genotypic-phenotypic associations were assessed by logistic regression analysis adjusted for age at slaughter, under five models (codominant, dominant, recessive, overdominant, and log-additive), and corrected for multiple testing. The rs208222804 C allele (CD209 gene) was found to be associated with latent paratuberculosis (log-additive model: P < 0.0034 after permutation procedure; OR = 0.64, 95% CI = 0.48–0.86). No significant association was detected between any SNP and the patent phenotype. Consequently, CD209 gene may play a key role in the pathogenesis of bovine paratuberculosis.

Genome-wide association analysis and genomic prediction of Mycobacterium avium subspecies paratuberculosis infection in US Jersey cattle

Paratuberculosis (Johne’s disease), an enteric disorder in ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP), causes economic losses in excess of $200 million annually to the US dairy industry. To identify genomic regions underlying susceptibility to MAP infection in Jersey cattle, a case-control genome-wide association study (GWAS) was performed. Blood and fecal samples were collected from ∼5,000 mature cows in 30 commercial Jersey herds from across the US. Discovery data consisted of 450 cases and 439 controls genotyped with the Illumina BovineSNP50 BeadChip. Cases were animals with positive ELISA and fecal culture (FC) results. Controls were animals negative to both ELISA and FC tests that matched cases on birth date and herd. Validation data consisted of 180 animals including 90 cases (positive to FC) and 90 controls (negative to ELISA and FC), selected from discovery herds and genotyped by Illumina BovineLD BeadChip (∼7K SNPs). Two analytical approaches were used: single-marker GWAS using the GRAMMAR-GC method and Bayesian variable selection (Bayes C) using GenSel software. GRAMMAR-GC identified one SNP on BTA7 at 68 megabases (Mb) surpassing a significance threshold of 5×10⁻⁵. ARS-BFGL-NGS-11887 on BTA23 (27.7 Mb) accounted for the highest percentage of genetic variance (3.3%) in the Bayes C analysis. SNPs identified in common by GRAMMAR-GC and Bayes C in both discovery and combined data were mapped to BTA23 (27, 29 and 44 Mb), 3 (100, 101, 106 and 107 Mb) and 17 (57 Mb). Correspondence between results of GRAMMAR-GC and Bayes C was high (70–80% of most significant SNPs in common). These SNPs could potentially be associated with causal variants underlying susceptibility to MAP infection in Jersey cattle. Predictive performance of the model developed by Bayes C for prediction of infection status of animals in validation set was low (55% probability of correct ranking of paired case and control samples).

Polymorphism of cytokine and innate immunity genes associated with bovine brucellosis in cattle

Genetic susceptibility to brucellosis is multifactorial, and it is known that impairment of the immune system could contribute to risk for getting brucellosis. The aim of the study was to find association of bovine brucellosis with 20 SNPs pertaining to bovine cytokine (IFNG, IFNGR1, IFNGR2, TNFA) and innate immunity (SLC11A1, TLR1, TLR4, and TLR9) genes using PCR-RFLP genotyping technique and it was observed that SLC11A1 (+1066 C/G), TLR1 (+1446 C/A), TLR1 (+1380 G/A), TLR4 (+10 C/T) and TLR4 (+399 C/T) loci were significantly (P≤0.05) associated with bovine brucellosis. The odds ratios (OR) of CG and CC genotypes versus GG genotype were 0.31 (0.12-0.82; 95% CI) and 0.18 (0.03-1.06; 95% CI) at SLC11A1 (+1066 C/G) locus in cases of brucellosis affected cattle. For TLR1 (+1380 G/A) locus, the OR for AG and AA genotypes versus GG genotypes were 0.15 (0.05-0.44; 95% CI) and 0.26 (0.04-1.47; 95% CI) which indicated that proportion of GG homozygote was significantly higher in brucellosis affected animals as compared to control. At TLR1 (+1446 C/A) locus the OR of AC genotype versus CC genotype was 0.24 (0.08-0.68; 95% CI) which revealed that relative proportion CC genotypes was significantly higher in case population. The TLR4 (+10 C/T) locus had three genotypes (TT, CT and CC) where OR of CT and CC genotypes versus TT genotype were near to zero. The OR of CT genotypes versus CC genotypes was 8.25 (0.94-71.92; 95% CI) at TLR4 (+399 C/T) locus and indicated that CT genotype had higher odds of bovine brucellosis than control animals.

Bovine CLEC7A genetic variants and their association with seropositivity in Johne's disease ELISA

Mycobacterium avium ssp. paratuberculosis (MAP) infection in cattle causes significant economic losses to the dairy and beef industries resulting from reduced productivity, premature culling and mortality. Bovine Dectin-1, an important pattern recognition molecule that is able to generate a proinflammatory response by acting alongside Toll like receptor (TLR) signaling, is known to co-operate with TLR2 to specifically activate a macrophage proinflammatory response against mycobacterial infections. Therefore, the goal of this study was to identify single nucleotide polymorphisms (SNPs) in the gene encoding bovine Dectin-1 (CLEC7A) and to assess their association with susceptibility to MAP infection in dairy cattle. Blood and milk samples, collected from commercial dairy operations, were tested for MAP infection using blood and milk ELISAs and a resource population consisting of 197 infected and 242 healthy cattle was constructed. Pooled DNA was used for sequencing and eight single nucleotide polymorphisms (SNPs) were identified. Identified SNPs were genotyped on the resource population using the iPLEX MassARRAY system and statistical analysis was performed using logistic regression fitting the additive and dominance effects of each SNP in the model. Out of a total of eight identified SNPs, five were successfully genotyped, and three out of these five SNPs were found to be in complete linkage. Statistical analysis revealed a strong association between a non-synonymous SNP c.589A>G (p=0.008), and MAP infection status of the resource population inferred by seropositivity in MAP antibody specific ELISAs. This SNP c.589A>G was located in the geneic region that encodes the carbohydrate recognition domain of bovine Dectin-1. Therefore, further investigation of its functional relevance is warranted.

Evaluation of age-dependent susceptibility in calves infected with two doses of Mycobacterium avium subspecies paratuberculosis using pathology and tissue culture

The longstanding assumption that calves of more than 6 months of age are more resistant to Mycobacterium avium subspecies paratuberculosis (MAP) infection has recently been challenged. In order to elucidate this, a challenge experiment was performed to evaluate age- and dose-dependent susceptibility to MAP infection in dairy calves. Fifty-six calves from MAP-negative dams were randomly allocated to 10 MAP challenge groups (5 animals per group) and a negative control group (6 calves). Calves were inoculated orally on 2 consecutive days at 5 ages: 2 weeks and 3, 6, 9 or 12 months. Within each age group 5 calves received either a high - or low - dose of 5 × 10⁹ CFU or 5 × 10⁷ CFU, respectively. All calves were euthanized at 17 months of age. Macroscopic and histological lesions were assessed and bacterial culture was done on numerous tissue samples. Within all 5 age groups, calves were successfully infected with either dose of MAP. Calves inoculated at < 6 months usually had more culture-positive tissue locations and higher histological lesion scores. Furthermore, those infected with a high dose had more severe scores for histologic and macroscopic lesions as well as more culture-positive tissue locations compared to calves infected with a low dose. In conclusion, calves to 1 year of age were susceptible to MAP infection and a high infection dose produced more severe lesions than a low dose.

A Sardinian map for multiple sclerosis

Multiple sclerosis (MS) is a complex autoimmune disease of the CNS. At present, MS etiology remains unknown, but it is believed to be caused by environmental factors acting on a genetic predisposition. Several studies suggest that different microorganisms could play a role in triggering autoimmunity, through immunological cross-reactivity or molecular mimicry. An overview of the knowledge regarding the bacteria involved in MS is given, placing emphasis on the newest candidate proposed: Mycobacterium avium subsp. paratuberculosis. This review will focus on discussing several arguments that might support a causal role for Mycobacterium avium subsp. paratuberculosis as an etiologic agent in MS. Additionally, a possible mechanism is postulated attempting to explain how the bacteria could initiate autoimmunity.

M. paratuberculosis Heat Shock Protein 65 and Human Diseases: Bridging Infection and Autoimmunity

Mycobacterium avium subspecies paratuberculosis (MAP) is the known infectious cause of Johne's disease, an enteric inflammatory disease mostly studied in ruminant animals. MAP has also been implicated in the very similar Crohn's disease of humans as well as sarcoidosis. Recently, MAP has been associated with juvenile sarcoidosis (Blau syndrome), autoimmune diabetes, autoimmune thyroiditis, and multiple sclerosis. While it is intuitive to implicate MAP in granulomatous diseases where the microbe participates in the granuloma, it is more difficult to assign a role for MAP in diseases where autoantibodies are a primary feature. MAP may trigger autoimmune antibodies via its heat shock proteins. Mycobacterial heat shock protein 65 (HSP65) is an immunodominant protein that shares sequential and conformational elements with several human host proteins. This molecular mimicry is the proposed etiopathology by which MAP stimulates autoantibodies associated with autoimmune (type 1) diabetes, autoimmune (Hashimoto's) thyroiditis, and multiple sclerosis. This paper proposes that MAP is a source of mycobacterial HSP65 and acts as a trigger of autoimmune disease.

Genome-wide association study to identify chromosomal regions associated with antibody response to Mycobacterium avium subspecies paratuberculosis in milk of Dutch Holstein-Friesians

Heritability of susceptibility to Johne's disease in cattle has been shown to vary from 0.041 to 0.159. Although the presence of genetic variation involved in susceptibility to Johne's disease has been demonstrated, the understanding of genes contributing to the genetic variance is far from complete. The objective of this study was to contribute to further understanding of genetic variation involved in susceptibility to Johne's disease by identifying associated chromosomal regions using a genome-wide association approach. Log-transformed ELISA test results of 265,290 individual Holstein-Friesian cows from 3,927 herds from the Netherlands were analyzed to obtain sire estimated breeding values for Mycobacterium avium subspecies paratuberculosis (MAP)-specific antibody response in milk using a sire-maternal grandsire model with fixed effects for parity, year of birth, lactation stage, and herd; a covariate for milk yield on test day; and random effects for sire, maternal grandsire, and error. For 192 sires with estimated breeding values with a minimum reliability of 70%, single nucleotide polymorphism (SNP) typing was conducted by a multiple SNP analysis with a random polygenic effect fitting 37,869 SNP simultaneously. Five SNP associated with MAP-specific antibody response in milk were identified distributed over 4 chromosomal regions (chromosome 4, 15, 18, and 28). Thirteen putative SNP associated with MAP-specific antibody response in milk were identified distributed over 10 chromosomes (chromosome 4, 14, 16, 18, 19, 20, 21, 26, 27, and 29). This knowledge contributes to the current understanding of genetic variation involved in Johne's disease susceptibility and facilitates control of Johne's disease and improvement of health status by breeding.

Crohn's disease and the mycobacterioses: a quarter century later. Causation or simple association?

It has been more than 25 years since Mycobacterium paratuberculosis was first proposed as an etiologic agent in Crohn's disease based on the isolation of this organism from several patients. Since that time, a great deal of information has been accumulated that clearly establishes an association between M. paratuberculosis and Crohn's disease. However, data are conflicting and difficult to interpret and the field has become divided into committed advocates and confirmed skeptics. This review is an attempt to provide a thorough and objective summary of current knowledge from both basic and clinical research from the views and interpretations of both the antagonists and proponents. The reader is left to draw his or her own conclusions related to the validity of the issues and claims made by the opposing views and data interpretations. Whether M. paratuberculosis is a causative agent in some cases or simply represents an incidental association remains a controversial topic, but current evidence suggests that the notion should not be so readily dismissed. Remaining questions that need to be addressed in defining the role of M. paratuberculosis in Crohn's disease and future implications are discussed.

Genetic susceptibility to paratuberculosis

Multiple studies indicate that host animal genetics play a role in susceptibility to Mycobacterium avium subsp. paratuberculosis (MAP) infection. However, due to differences in methods used to define MAP-infected animals and controls and differences in methods of genetic analysis, there is as yet no clear consensus on the genes or markers to reliably define the MAP infection susceptibility of any animal species. Meta-analysis of combined studies and larger studies will help resolve the situation in the coming years.

Genetic variation of toll-like receptor genes and infection by Mycobacterium avium ssp. paratuberculosis in Holstein-Friesian cattle

Toll-like receptors (TLR) are membrane proteins that play a key role in innate immunity, by recognizing pathogens and subsequently activating appropriate responses. Mutations in TLR genes are associated with susceptibility to inflammatory and infectious diseases in humans. In cattle, 3 members of the TLR family, TLR1, TLR2, and TLR4, are associated with Mycobacterium avium ssp. paratuberculosis infection, although the extent of this association for the TLR1 and TLR4 receptors has not yet been determined. Moreover, the causal variant in the TLR2 gene has not yet been unequivocally established. In this study, 24 single nucleotide polymorphisms (SNP) in the bovine TLR1, TLR2, and TLR4 genes were selected from the literature, databases, and in silico searches, for a population-based genetic association study of a Spanish Holstein-Friesian sample. Whereas previous results regarding the TLR1 gene were not corroborated, a risk haplotype was detected in TLR2; however, its low frequency indicates that this detected association should be interpreted with caution. In the case of the TLR4 gene, 3 tightly linked SNP were found to be associated with susceptibility to M. avium ssp. paratuberculosis infection. Moreover, one of these SNP, the SNP c.-226G>C, which is localized in the 5'UTR region of the TLR4 gene, has been reported to be able to alter TLR4 expression, raising the possibility that this mutation may contribute to the response of the individual to infection.

Candidate gene and genome-wide association studies of Mycobacterium avium subsp. paratuberculosis infection in cattle and sheep: a review

Paratuberculosis (Johne's disease), caused by Mycobacterium avium subspecies paratuberculosis, is responsible for significant economic losses in livestock industries worldwide. This organism is also of public health concern due to an unconfirmed link to Crohn's disease. Susceptibility to paratuberculosis has been suggested to have a genetic component. In livestock, a number of candidate genes have been studied, selected on their association to susceptibility in other mycobacterial diseases, their known role in disease pathogenesis or links to susceptibility of humans to Crohn's disease. These genes include solute carrier family 11 member 1 (SLC11A1, formerly NRAMP1), toll-like receptors, caspase associated recruitment domain 15 (CARD15, formerly NOD2), major histocompatibility complex (MHC) and cytokines (interleukin-10 and interferon-gamma) and their receptors. Genome wide association studies have attempted to confirm associations found and identify new genes involved in pathogenesis and susceptibility. There are a number of limitations and difficulties in these approaches, some peculiar to paratuberculosis but others generally applicable to identification of genetic associations for complex traits. The technical approaches and available information for paratuberculosis have expanded rapidly, particularly relating to sheep and cattle. Here we review the current published evidence for a genetic association with paratuberculosis susceptibility, technological advances that have progressed the field and potential avenues for future research.