Relationship of abomasal histology and parasite-specific immunoglobulin A with the resistance to Haemonchus contortus infection in three breeds of sheep

Mucosal Immunity of Major Gastrointestinal Nematode Infections in Small Ruminants Can Be Harnessed to Develop New Prevention Strategies

Gastrointestinal parasitic nematode (GIN) infections are the cause of severe losses to farmers in countries where small ruminants such as sheep and goat are the mainstay of livestock holdings. There is a need to develop effective and easy-to-administer anti-parasite vaccines in areas where anthelmintic resistance is rapidly rising due to the inefficient use of drugs currently available. In this review, we describe the most prevalent and economically significant group of GIN infections that infect small ruminants and the immune responses that occur in the host during infection with an emphasis on mucosal immunity. Furthermore, we outline the different prevention strategies that exist with a focus on whole and purified native parasite antigens as vaccine candidates and their possible oral-nasal administration as a part of an integrated parasite control toolbox in areas where drug resistance is on the rise.

Understanding Animal-Plant-Parasite Interactions to Improve the Management of Gastrointestinal Nematodes in Grazing Ruminants

Grazing systems have great potential to promote animal welfare by allowing animals to express natural behaviours, but they also present risks to the animals. Diseases caused by gastrointestinal nematodes are some of the most important causes of poor ruminant health and welfare in grazing systems and cause important economic losses. Reduced growth, health, reproduction and fitness, and negative affective states that indicate suffering are some of the negative effects on welfare in animals infected by gastrointestinal nematode parasitism. Conventional forms of control are based on anthelmintics, but their growing inefficiency due to resistance to many drugs, their potential for contamination of soil and products, and negative public opinion indicate an urgency to seek alternatives. We can learn to deal with these challenges by observing biological aspects of the parasite and the host’s behaviour to develop managements that have a multidimensional view that vary in time and space. Improving animal welfare in the context of the parasitic challenge in grazing systems should be seen as a priority to ensure the sustainability of livestock production. Among the measures to control gastrointestinal nematodes and increase animal welfare in grazing systems are the management and decontamination of pastures, offering multispecies pastures, and grazing strategies such as co-grazing with other species that have different grazing behaviours, rotational grazing with short grazing periods, and improved nutrition. Genetic selection to improve herd or flock parasite resistance to gastrointestinal nematode infection may also be incorporated into a holistic control plan, aiming at a substantial reduction in the use of anthelmintics and endectocides to make grazing systems more sustainable.

Immunization with thiol-binding proteins from Haemonchus contortus adult worms partially protects goats against infection during prepatency

To contribute of the knowledge of the immune mechanisms underlying the response to the immunization of goats with thiol-binding proteins fractions (PBS-TSBP) from Haemonchus contortus (H. contortus) adult worms, this study analyzed the degree of protection and the immune responses developed against the parasite after vaccination with this antigenic complex during the time-elapsing between challenge with L3 of the parasite and the development of adult worms, evidenced by the appearance of first faecal eggs (prepatent period or prepatency). Goat kids immunized with PBS-TBSP generated an immune response during the prepatency which translates into a reduction in the number of worms, as well as a lower reduction on packed cell volume and plasma protein levels in relation to the non-vaccinated animals. As previously described in other studies carried out after the prepatent period, this protection was associated with a systemic humoral response. At the local level, a specific humoral response was also observed, together with an immune-inflammatory infiltrate in the gastric mucosa of MCH-II + cells and CD4⁺ lymphocytes, whose number was associated with a reduction in the number of worms and an increase in plasma proteins. A high peripheral eosinophilia was detected, but no corresponding increased infiltration of the gastric mucosa by eosinophils or globular leukocytes was observed. In agreement with previous data on the immunolocalization of the antigens used here, the results obtained contribute to the idea that these may be excretion/secretion (E/S) products necessary for parasite survival, whose inactivation during the larval and/or pre-adult stages may have contributed to immunoprotection.

Antibody response and abomasal histopathology of lambs with haemonchosis during supplementation with medicinal plants and organic selenium

We evaluated the effects of dietary supplementation with medicinal plants (Herbmix) or organic selenium (Selplex) on the immune responses and histopathology of lambs infected with Haemonchus contortus. Twenty-seven lambs were infected and reinfected with approximately 11,000 third-stage larvae of H. contortus during the experiment (on days 0, 49 and 77). Lambs were divided into two supplemented experimental groups (Herbmix and Selplex) and unsupplemented group (Control). The abomasal worm counts at necropsy on day 119 were lower for Herbmix (4230) and Selplex group (3220) than to the Control (6613) which resulted in 51.3% and 36.0% of reduction, respectively. The mean length of adult female worms was in the order Control > Herbmix > Selplex (2.1, 2.08, and 2.01 cm, respectively). The specific IgG response against adults was significantly affected by time (P < 0.001). Serum-specific and total mucus levels of IgA in the Herbmix group were highest on day 15. Mean levels of serum IgM against adults were influenced by treatment (P = 0.048) and time (P < 0.001). The Herbmix group had strong local inflammation in the abomasal tissue, with the formation of lymphoid aggregates and the infiltration of immune cells, but the tissues of the Selplex group had higher numbers of eosinophils, globule leukocytes, and plasma cells. The lymph nodes of each animal had reactive follicular hyperplasia due to the infection. Dietary nutritional supplementation with a mixture of medicinal plants or organic selenium could improve local immune responses and thus enhance the resistance of animals to this parasitic infection.

Effect of commercial tannins on parasitic infection and immunity of lambs naturally infected with Haemonchus contortus

This study aimed to evaluate the effects of different doses of quebracho extract tannins (Schinopsis lorenzii) (EQ) included in the basal diet (DB) on the count of eggs per gram of feces (EPG), count of parasites in the abomasum, hematological, and immunological parameters in lambs naturally infected with Haemonchus contortus. Forty-eight lambs were evaluated for 42 days and divided into four groups (n = 12): CONT- lambs that received DB without EQ supplementation; G1%- DB with EQ at 1% of dry matter intake (DMI) level; G3%- DB with EQ at the 3% of DMI level; G6%- DB with EQ at the 6% DMI level. For EPG counts, feces were collected weekly. For counting abomasal parasites, at the end of the experiment (D42) half of the lambs in each group were slaughtered. For hematological and immunological analysis, venous blood samples were collected at D0, D21, and D42 to perform the erythrocyte count, mean cell volume (MCV), hematocrit, differential leukocyte count, total plasma protein dosage, and serum IgA class anti-H. contortus using an indirect enzyme immunoassay (ELISA). In the EPG count, there was no significant difference (p > 0.05) between the groups compared with the control. Analysis of the abomasal parasite count showed Haemonchus contortus in its entirety; however, there was no significant difference (p > 0.05) in the number of males, females, and total parasites. No differences (p > 0.05) were observed in erythrocyte count, MCV, hematocrit, and total plasma protein. The average total leukocyte, monocyte, eosinophil, and basophil counts showed no difference (p > 0.05). However, the averages of segmented neutrophils in the G1% and G3% groups presented a reduction in the percentage of cells (p < 0.05) between D21 and D42. Regarding the lymphocyte count, a difference was observed in the CONT and G3% groups at D21 and D42 (p < 0.05), when compared to D0. The analyses of the average absorbance of anti-Haemonchus contortus serum IgA showed no difference (p > 0.05), when the groups were analyzed over time or when compared between them. It can be concluded that the inclusion of different doses of tannins from EQ did not alter the parasitological, hematological, and immunological parameters of lambs infected with H. contortus.

Characterization of interferon gamma gene in relation to immunological responses in Haemonchus contortus resistant and susceptible Garole sheep

Garole sheep exhibits within-breed difference in resistance to natural gastrointestinal nematode infection predominated by Haemonchus contortus. In the present study, interferon gamma gene (IFN-γ) was characterized in relation to parasitological, haematological, and immune response against H. contortus in resistant and susceptible Garole sheep. Resistant and susceptible Garole sheep were selected from the field based on consistent low faecal egg counts (FEC) for one year and single nucleotide polymorphisms (SNPs) in the IFN-γ gene. The partial amplification of IFN-γ gene (1282 bp) revealed 4 SNPs exclusively in resistant sheep and 3 SNPs were shared between resistant and susceptible Garole sheep. The selected resistant and susceptible Garole sheep were challenged with H. contortus infection. The parasitological, haematological, immunological responses, and expression of IFN-γ gene were compared between the resistant and susceptible Garole sheep. The FEC of resistant sheep was significantly (P < 0.05) lower than the susceptible sheep infected with H. contortus. There was spontaneous elimination of H. contortus from 28 to 33 days post infection (DPI) in resistant sheep. Haemoglobin and packed cell volume were significantly (P < 0.05) higher in resistant sheep than the susceptible sheep. The serum concentration of immunoglobulin (Ig)G₁ and IgA and cytokine IFN-γ activity and also the expression of IFN-γ gene were significantly (P < 0.05) higher in the infected resistant sheep from 14 to 28 DPI compared to the susceptible sheep. In resistant sheep, IgA and IgG₁ and cytokine IFN-γ positively correlated with expression of IFN-γ gene, and the SNPs recorded in the resistant sheep only might play an important role in conferring resistance against H. contortus. Further studies are required to elucidate the role of IFN-γ gene in H. contortus resistance in Garole sheep.

The role of IgA in gastrointestinal helminthiasis: A systematic review

Immunoglobulin-A (IgA) is an important mediator of immunity and has been associated with protection against several pathogens, although its role in gastrointestinal infections remains unclear. Then, the aim of this systematic review was to synthesize qualitative evidence in respect of IgA as mediator of protective immunity against gastrointestinal helminths. Following recommended guidelines, we searched for articles published between January 1990 and October 2019 that evaluated IgA levels and their association with gastrointestinal helminth infections. Twenty-five articles were included after screening 1,546 titles and abstracts, as well as reading in full 52 selected articles. Consistent associations between higher IgA levels and lower parasitological parameters were only found in mice, rats, and sheep. However, the role of IgA in other host species remains uncertain, making it difficult to create a consensus. Therefore, it is too soon to claim that IgA is an effective protective factor against gastrointestinal helminths, and further studies are still needed.

Hepatocellular carcinoma-associated antigen 59 and ADP-ribosylation factor 1 with poly (lactic-co-glycolic acid): A promising candidate as nanovaccine against haemonchosis

Haemonchus contortus (H. contortus) ADP-ribosylation factor 1 (Hc-ARF1) and Hepatocellular carcinoma-associated antigen 59 (Hc-HCA59) are recognized to largely regulate the immune responses of host cells. However, studies about the protective efficacy of the two molecules are poorly unknown. In this research, combinations of recombinant Hc-HCA59 (rHc-HCA59) and Hc-ARF1 (rHc-ARF1) proteins were amalgamated with poly (lactic-co-glycolic acid) (PLGA) nanoparticles adjuvant in order to investigate their protection potential against H. contortus in goats. The results demonstrated that the levels of IgG, IgA, IgE, and IL-4 were noticeably enhanced in the rHc-HCA59 and rHc-ARF1 (rHc-HCA59+rHc-ARF1) group before H. contortus third-stage larvae (L3) challenge. After the L3 challenge, the levels of IL-17, IL-9, and TGF-β were considerably upregulated in the rHc-HCA59+rHc-ARF1 group. In the meantime, the abomasal worm burdens and the fecal eggs were reduced by 63.2% and 69.4% respectively in the rHc-HCA59+rHc-ARF1 group. According to the studies, PLGA nanoparticles immobilized with rHc-HCA59 and rHc-ARF1 proteins conferred partial protection and were expected to be a potential candidate for developing nano vaccines to combat goat haemonchosis.

A Review: Haemonchus contortus Infection in Pasture-Based Sheep Production Systems, with a Focus on the Pathogenesis of Anaemia and Changes in Haematological Parameters

Simple Summary

Infection with Haemonchus contortus parasites (haemonchosis) is an important cause of anaemia in sheep. Haemonchosis is a global problem, although sheep that are kept in warm, high rainfall environments are at the greatest risk of infection due to the favourable conditions for H. contortus survival. Following ingestion, the parasites develop in the abomasum of sheep. Various factors such as age, breed, health, nutritional status, and larval challenge influence the severity of clinical disease. Hyperacute, acute, and chronic haemonchosis are reviewed, focusing on the pathophysiology of haemonchosis, associated clinical signs, and haematological and biochemical findings.

Abstract

Haemonchosis is an important cause of anaemia in sheep worldwide, particularly those that are kept in pasture-based systems in warm, high rainfall environments. Potential outcomes vary based on the severity of infection and the sheep’s immune response, however, in some sheep infection can lead to death. The consequences of Haemonchus contortus infection mean that it has been well-studied in a range of different farming systems. However, to our knowledge, there has not been a recent review focused on the pathophysiology of anaemia caused by haemonchosis. Thus, this review provides an in-depth discussion of the literature related to the pathophysiology of haemonchosis and associated clinical signs for hyperacute, acute, and chronic haemonchosis. Additionally, haematological and biochemical findings are presented, and various diagnostic methods are assessed.

Immunization With Recombinant Haemonchus contortus Y75B8A.8 Partially Protects Local Crossbred Female Goats From Haemonchus contortus Infection

Haemonchus contortus Y75B8A.8 (Hc8) derived from H. contortus excretory–secretory (ES) products was identified as a functional inhibitor of goat interleukin 2 (IL-2). It may act as a vaccine candidate for the development of therapeutic strategies against H. contortus infection. In this research, recombinant Hc8 (rHc8) and goat anti-rHc8 polyclonal antibodies were employed to evaluate the protective capacities of Hc8 antigen against H. contortus infections via active and passive immunization trials, respectively. In both trials, local crossbred female goats aged 9–12 months old were randomly divided into three groups, five in each group, respectively. Parasitological examinations, including fecal egg counts (FEC), cumulative FEC (cFEC), and worm burdens, were performed. In addition, antibody levels in mucosal homogenate (MH) samples and hematological and immunological parameters were detected. In the passive trial, goats were intravenously immunized with 5 mg total IgG containing anti-rHc8 goat polyclonal antibodies. After twice immunization, compared with the challenged control group, cFEC was reduced by 39%. In addition, there was a 46% reduction of worm burdens compared with the challenged controls. In the active immunization trials, 500 μg of recombinant Hc8 protein was given subcutaneously twice to 9–12-month-old local crossbred female goats with a 2-week interval, resulting in the generation of high levels of antigen-specific circulating antibodies. Besides, cFEC and abomasal worm burden were reduced by 70 and 55%, respectively, compared with the challenged control group. In addition, immunized goats had higher mucosal homogenate IgA and hemoglobin levels than the challenged controls in both passive and active immunization trials. These preliminary results demonstrated the immunoprophylactic effects of Hc8 antigen and will inform new studies on ES proteins in developing subunit recombinant vaccines against H. contortus.

Impact of Sainfoin (Onobrychis viciifolia) Pellets on Parasitological Status, Antibody Responses, and Antioxidant Parameters in Lambs Infected with Haemonchus contortus

Our study analyzed the parasitological status, antibody responses, and antioxidant parameters of lambs experimentally infected with a gastrointestinal nematode during the consumption of sainfoin pellets (SFPs) for 14 d. Twenty-four lambs infected with Haemonchus contortus were separated into two groups: untreated animals (control) and animals treated with SFPs (600 g dry matter/d). SFP treatment began on day (D) 30 post-infection. The number of eggs per gram (EPG) of feces was quantified on D18, D23, D26, D30, D33, D37, D40, and D44. The mean reductions in EPG on D40 and D44 were 33.6 and 36.7%, respectively. The number of abomasal worms was lower for the SFP than the control group (p < 0.05). SFP treatment did not significantly affect either the total or the local antibody response (p > 0.05). The blood activity of glutathione peroxidase was affected by the treatment (p < 0.022). Adult worms were selected for scanning electron microscopy after necropsy, but surface structures of adult H. contortus females did not differ between the groups. The treatment of lambs with SFPs directly affected the dynamics of infection, probably indirectly by mobilizing the antioxidant defensive system and antibody response thus improving animal resistance.

Ovarian activation delays in peripubertal ewe lambs infected with Haemonchus contortus can be avoided by supplementing protein in their diets

BACKGROUND

The ewe lamb nutritional and physiological state interfere with the ovarian environment and fertility. The lack or excess of circulating nutrients reaching the ovary can change its gene expression. A protein deficiency in the blood caused by an Haemonchus contortus abomasal infection is detrimental to the organism's development during puberty. The peripubertal period is a time of intensive growth that requires a high level of nutrients. An essential feature controlling pubertal arousal and female reproductive potential is ovarian follicle growth activation. Protein supplementation improves the sheep's immune response to helminthic infections. We aimed to determine if supplementing protein in infected ewe lambs' diet would impact the ovarian environment leading to earlier ovarian follicle activation than in infected not supplemented animals.

METHODS

We fed 18 Santa Ines ewe lambs (Ovis aries) - bred by the same ram - with either 12% protein (Control groups) or 19% protein (Supplemented groups) in their diets. After 35 days of the diet, they were each artificially infected or not with 10,000 Haemonchus contortus L3 larvae. Following 77 days of the diet and 42 days of infection, we surgically collected their left ovaries and examined their genes expression through RNA sequencing.

RESULTS

We found that protein supplementation in infected animals led to an up-regulation of genes (FDR p-values < 0.05) and biological processes (p-value cut-off = 0.01) linked to meiotic activation in pre-ovulatory follicles and primordial follicle activation, among others. The supplemented not infected animals also up-regulated genes and processes linked to meiosis and others, such as circadian behaviour. The not supplemented animals had these same processes down-regulated while up-regulated processes related to tissue morphogenesis, inflammation and immune response.

CONCLUSION

Diet's protein supplementation of peripubertal infected animals allowed them to express genes related to a more mature ovarian follicle stage than their half-sisters that were not supplemented. These results could be modelling potential effects of the interaction between environmental factors, nutrition and infection on reproductive health. When ovarian activation is achieved in a timely fashion, the ewe may generate more lambs during its reproductive life, increasing sheep breeders' productivity.

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.

Haemonchus contortus hepatocellular carcinoma-associated antigen 59 with poly (lactic-co-glycolic acid): A promising nanovaccine candidate against Haemonchus contortus infection

Hepatocellular carcinoma-associated antigen 59 (HCA59), one of significant excretory/secretory products of Haemonchus contortus (HcESPs), is identified to have immunomodulatory eff ;ects on host cells. However, protection potential of the molecule in H. contortus remains poorly understood. In this study, H. contortus recombinant HCA59 protein amalgamated with poly (lactic-co-glycolic acid) (PLGA) nanoparticle adjuvant was tested for its protection against H. contortus infection in goats. Fifteen goats were allocated into three groups. On days 0 and 14, rHCA59 group was immunized with PLGA nanoparticles encapsulated with recombinant protein HCA59 (rHCA59-PLGA) respectively. Positive control group was unvaccinated, but challenged with H. contortus third stage larvae (L3). Negative control group was unvaccinated and unchallenged with L3. Goats in rHCA59 group and positive control group were challenged with 8000 H. contortus L3 after 14 days of the second immunization. Following immunization, high level of sera IgG, IgA, and IgE, as well as significantly high production of IL-4 and IL-9 was produced in rHCA59 group. After L3 challenge, the level of IL-17 and TGF-β in rHCA59 group increased obviously. Meanwhile, the fecal eggs and the abomasal worm burdens in rHCA59 group was reduced by 44.1 % and 54.6 %, respectively. The studies suggested that rHCA59-PLGA nanoparticles conferred partial protection and could be a good candidate for the development of nanovaccines against H. contortus infection in goats.

Effect of Artemisia absinthium and Malva sylvestris on Antioxidant Parameters and Abomasal Histopathology in Lambs Experimentally Infected with Haemonchus contortus

This study evaluated the effect of Artemisia absinthium and Malva sylvestris on antioxidant response and histopathological changes in the abomasa of the Haemonchus contortus infected lambs. Twenty-four lambs were divided into four groups: unsupplemented lambs (UNS), lambs supplemented with A. absinthium (ART), lambs supplemented with M. sylvestris (MAL), and lambs supplemented with both plants (ARTMAL). Lambs were infected orally with approximately 5000 third-stage (L3) larvae of H. contortus. The experiment was conducted for 75 d (days), all animals were then slaughtered; and the abomasal tissues were examined for antioxidant parameters and histopathology. The concentration of malondialdehyde in the abomasal mucosa was lower in ARTMAL (p < 0.05), and the total antioxidant capacity was higher in MAL (p < 0.05), than in UNS. Increased mucus production was observed in the ARTMAL. The number of mast cells in UNS and ART was significantly higher than the number in MAL (p < 0.01 and p < 0.05). Plasma cell numbers were higher in ARTMAL than the number in MAL (p < 0.05). Abomasal tissue regenerated more frequently in ARTMAL. These results represent the first report of the impact of A. absinthium and M. sylvestris on antioxidant parameters and local immune responses of abomasal mucosa of lambs infected with a GIN parasite.

Interaction between abomasal blood feeder Haemonchus contortus and intestinal mucosal browser Trichostrongylus colubriformis during co-infection in Boer goats

This study was conducted to investigate potential interactions between the abomasal blood feeder Haemonchus contortus and the intestinal mucosal browser Trichostrongylus colubriformis among deliberately infected Boer goats. Faecal and blood samples were collected twice a week for eight weeks from 25 parasite-naïve goats. Correlation analysis and multiple linear regression models were conducted to explore the association between phenotypic variables and variables taken at necropsy. Positive associations were identified between total FEC and log T. colubriformis number (r = 0.62, p < 0.05) as well as between IgA and peripheral eosinophil counts (r = 0.65, p < 0.05). A negative correlation was observed between T. colubriformis and log H. contortus number (r=-0.56, p < 0.05). Multiple linear regression models show that H. contortus and T. colubriformis interacted with each other. T. colubriformis appeared to contribute more significantly to the variation of FEC than H. contortus. Co-infection induced an IgA response which was only effective against T. colubriformis but not protective against H. contortus infection. This could be seen via significant associations of IgA with both nematode species but with the effect of IgA differing for H. contortus and T. colubriformis. In this study, H. contortus infection was not detrimental to the goats with no observed impact on PCV. This could be because the growth of T. colubriformis as represented by its length was associated with reduced number and composite burden of H. contortus during co-infection, or possibly due to low infection dosage. Improved understanding of the impact of H. contortus and T. colubriformis and their interaction from natural co-infection studies is beneficial for a better understanding of the goat-parasite interaction and its potential impacts on the health and productivity of animals.

Parasitological and immunological response to Haemonchus contortus infection: Comparison between resistant Garole and susceptible Sahabadi sheep

Parasitological and immunological responses to the experimentally induced Haemonchus contortus infection were compared between Garole and Sahabadi breeds of sheep. The experiment was conducted in a 2 (breed) × 2 (infection status) factorial arrangement with a completely randomised design. Two breeds of sheep were divided into infected (n = 10) and control (n = 6) groups, and the infected groups were orally infected with H. contortus (500 stage 3 larvae per kilogram of body weight). Faecal egg counts (FEC) were determined from 18 days post infection (DPI) at 3-day intervals until 42 DPI. Average daily body weight gain, packed cell volume (PCV), concentrations of serum immunoglobulin (Ig) G₁, IgG₂, IgE and peripheral eosinophil count were measured at 14-day intervals from 0 to 42 DPI. Lymphocyte proliferation in response to somatic antigen of H. contortus was determined by in vitro lymphoproliferation assay, and concentrations of interferon gama (IFN-γ) and interleukin 4 (IL-4) in lymphocyte culture supernatant were measured at 14-day intervals until 42 DPI. Variables were analysed using the repeated measures mixed model procedure over DPI. Faecal egg count was significantly (p < 0.01) lower in Garole sheep than Sahabadi sheep and no faecal eggs were detected in the infected Garole sheep on 30 DPI. Infected Garole sheep had significantly (p < 0.05) higher body weight gain and PCV% than the infected Sahabadi sheep. In the infected Garole sheep, serum Ig except IgE increased significantly (p < 0.05) compared to infected Sahabadi sheep. On 28 DPI, peripheral eosinophil number, in vitro lymphoproliferation as well as concentrations of IFN-γ and IL-4 in culture supernatant were significantly (p < 0.05) higher in the infected Garole sheep than in the infected Sahabadi sheep. Parasitological observations indicated that Garole sheep were resistant to H. contortus and they exhibited greater cellular as well as humoral immune responses compared to Sahabadi sheep.

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.

HcFAR, a functional inhibitor of goat TGF-β1 identified from excretory and secretory products of Haemonchus contortus

Haemonchus contortus has developed complexed and multifaceted mechanisms of immune evasion to enable the survival in the host. Generating excretion and secretion products (ESPs) to subvert or suppress the functions of host cytokines is a newly immune regulatory pattern found during recent years. Transforming growth factor-β (TGF-β) has critical immune regulatory functions in nematode infections. In this study, co-immunoprecipitation (co-IP) assay was used to identify the goat TGF-β1 binding proteins from HcESPs. The interaction between TGF-β1 and nematode fatty acid retinoid binding domain containing protein of H. contortus (HcFAR) was analyzed by glutathione S-transferase (GST)-pull down assay. The suppressive effect of rHcFAR on TGF-β1-induced immunoglobulin A (IgA) secretion was observed by co-incubation of rHcFAR and TGF-β1 with goat peripheral blood mononuclear cells (PBMCs). The IgA concentrations were determined using enzyme linked immunosorbent assay (ELISA) kit. Meanwhile, the suppressive effect of rHcFAR on TGF-β1-induced T helper (Th) 9 differentiation was investigated by co-incubation of rHcFAR, TGF-β1 and interleukin (IL)-4 with goats PBMCs. In parallel, IL-4 was replaced by IL-6 to determine the effects on the Th17 differentiation. The transcriptions of IL-9 and IL-17 in PBMCs were then evaluated by real-time PCR. Finally, we found that HcFAR from HcESPs could bind to goat TGF-β1 in vitro. The ELISA results of IgA showed that 40 μg/mL rHcFAR could suppress the IgA secretion of PBMCs induced by TGF-β1. Additionally, rHcFAR (at 10 μg/mL and 20 μg/mL) could inhibit the mRNA transcription of IL-9 induced by TGF-β1 and IL-4. Meanwhile, rHcFAR could also downregulate the transcription of IL-17 induced by TGF-β1 and IL-6 in a dose-dependent manner. These results indicated that HcFAR was a functional inhibitor of goat TGF-β1 and this information may help contribute to understanding of the relationship between the ESPs and host cytokines.

Gastrointestinal nematode infections in goats: differences between strongyle faecal egg counts and specific antibody responses to Teladorsagia circumcincta in Nera di Verzasca and Alpine goats

Strongylida are gastrointestinal nematodes (GIN) of greatest importance in small ruminants throughout the world. Differences in resistance and resilience to GIN among goat breeds were reported. This study aims to investigate the mechanism underlying the breed-associated differences using a cosmopolitan (Alpine, AB) and an autochthonous (Nera di Verzasca, NV) goat breed. At first, fifteen goats from the same herd (NV = 7, AB = 8) at day 0 were infected with infective larvae (L3) of mixed GIN. From the 15th day post-infection (DPI), individual parasite egg excretion (faecal egg counts, FEC) was performed on all goats, once per week, until the 63rd DPI. Afterwards, in goats under field conditions (30 AB and 30 NV reared on the same farm), individual faecal and blood samples were collected; FEC-specific antibody and PCV levels were explored. In goats with experimental GIN infection, mean eggs per gram of faeces (EPG) values were consistently lower in NV goats. In goats with natural GIN infection, EPG and prevalence values showed high variability in both breeds; among individual variables, breed had a significant influence on EPG. Further, PCV and anti-T. circumcincta IgA levels were influenced by the breed. Lower PCV values were also associated with higher strongyle EPG in AB goats, and anti-T. circumcincta IgA levels were influenced by both strongyle EPG and breed, with IgA levels being higher in AB vs. NV goats and positively associated with EPG. Neither EPG nor breed had any influence on IgE levels. Both studies on experimental and natural infection confirmed that goats of NV are more resistant to infection with gastrointestinal nematodes.

Immunoglobulins as Biomarkers for Gastrointestinal Nematodes Resistance in Small Ruminants: A systematic review

The rise of anthelmintic resistance worldwide has led to the development of alternative control strategies for gastrointestinal nematodes (GIN) infections, which are one of the main constraints on the health of grazing small ruminants. Presently, breeding schemes rely mainly on fecal egg count (FEC) measurements on infected animals which are time-consuming and requires expertise in parasitology. Identifying and understanding the role of immunoglobulins in the mechanisms of resistance could provide a more efficient and sustainable method of identifying nematode-resistant animals for selection. In this study we review the findings on immunoglobulin response to GIN in the literature published to date (june 2019) and discuss the potential to use immunoglobulins as biomarkers. The literature review revealed 41 studies which measured at least one immunoglobulin: 35 focused on lamb immune response (18 used non-naïve lambs) and 7 on yearlings. In this review we propose a conceptual model summarizing the role of immunoglobulins in resistance to GIN. We highlight the need for more carefully designed and documented studies to allow comparisons across different populations on the immunoglobulin response to GIN infection.

Haemonchus contortus transthyretin domain - containing protein (HcTTR): A promising vaccine candidate against Haemonchus contortus infection

Haemonchus contortus transthyretin domain-containing protein (HcTTR) with 136 amino acids belongs to a transthyretin-like (TTL) family member. In our previous study, it was reported that HcTTR was a novel antagonist of the goat cytokine Interleukin 4 (IL-4), and was involved in the regulation of host immune responses, implying that it might be applied for therapeutic strategies or vaccine development against the infection of H. contortus. Thus, the protective capacities of HcTTR against H. contortus infections via active and passive immunization trials were examined. For the passive protection trials, H. contortus-infected goats were intravenously immunized twice with 5 mg of total IgG containing anti-rHcTTR goat polyclonal antibodies. The results showed that the significant rates of reduction in egg shedding and worm burden was 58.12% and 64.61%, respectively, as compared with the positive control group. For the active protection trials, local goats were vaccinated twice with 500 μg of recombinant HcTTR to generate antigen-specific circulating antibodies, resulting in 63.7% reduction in eggs shedding and 66.4% reduction in worm burdens after H. contortus challenge. In both passive and active trials, the immunized goats displayed higher mucosal IgA levels and less anaemic compared to the challenged positive controls. Pen trials indicated that HcTTR generated partial immune protective effects against H. contortus challenge and it could be a promising vaccine candidate for development of effective strategy to control H. contortus.

Saccharomyces cerevisiae (YT001) supplementation for the control of Haemonchus contortus and modulation of the immune response of sheep

Studies aiming at the development and evaluation of alternative methods to minimise losses caused by the gastrointestinal nematode Haemonchus contortus are extremely important. Such research is essential, given the high morbidity rates among sheep and the significant mortality rates of lambs, allied to the low efficacy of commercial products for the control of this parasite. The purpose of this study was to evaluate the effect of the Saccharomyces cerevisiae (YT001 - YEASTECH) on the control of H. contortus and its modulation of the immune response in experimentally infected sheep. Eighteen sheep were divided into two groups. Group 1, the control group, comprised animals infected with H. contortus and supplemented with distilled water, while Group 2, the treated group, consisted of animals infected and supplemented with S. cerevisiae (400 million cfu/day of suspension for 49 days). The following parasitological parameters were evaluated: number of eggs per gram of faeces, number of infective larvae (L3) recovered per faecal culture, and parasitic load of the abomasum. The following immunological parameters were quantified: immunoglobulin (Ig)A in the mucous secretions and serum IgG; cytokines interleukin (IL)-4, IL-5 and IL-10; number of eosinophils in the abomasal mucosa and groups of cells positive for the markers: MHCII, CD4⁺CD25⁺, CD5⁺CD8⁺, WC4, CD5⁺CD4⁺, CD8⁺CD11b⁺ and CD5⁺WC1 by whole blood flow cytometry. The results revealed a significant decrease (P<0.05) in the number of larvae and significantly higher serum IgG levels (P<0.05) in the group supplemented with S. cerevisiae. The supplemented animals showed significantly larger numbers of eosinophils (P<0.05), as well as more cells positive for MHCII, CD4⁺CD25⁺, CD5⁺CD8⁺ than the control animals. This study confirmed the beneficial action of S. cerevisiae on the host immune response to H. contortus, as evidenced mainly by the smaller number of L3 recovered from the faeces of sheep supplemented with S. cerevisiae.

Immunization of Goats with Recombinant Protein 14-3-3 Isoform 2(rHcftt-2) Induced Moderate Protection against Haemonchus contortus Challenge

A previous study identified that isoform 2 (Hcftt-2) of the 14-3-3 protein of Haemonchus contortus (H. contortus) could suppress immune functions of goat peripheral blood mononuclear cells (PBMCs) and might be a potential vaccine target, as neutralization of the protein function may enhance anti-parasite immunity. In this research, the recombinant Hcftt-2 was evaluated for its immunoprotective efficacy against H. contortus infection in goats. Five experimental goats were immunized twice with rHcftt-2 along with Freund’s adjuvant. The five immunized goats and five nonimmunized goats (adjuvant only) were challenged with 5000 L3-stage H. contortus larvae after 14 days of second immunization. Five nonimmunized and uninfected goats (adjuvant only) were set as the uninfected group. A significant increase in the serum immunoglobin G(IgG) and serum IgA levels were identified in the rHcftt-2 immunized animals. The mean eggs per gram in feces (EPG) and the worm burdens of rHcftt-2 immunized group were reduced by 26.46% (p < 0.05) and 32.33%, respectively. In brief, immunization of goats with rHcftt-2 induced moderate protection against H. contortus challenge.

Resistance to Haemonchus contortus in Corriedale sheep is associated to high parasite-specific IgA titer and a systemic Th2 immune response

Gastrointestinal nematode infections, including Haemonchus contortus, are one of the main causes of economic losses to ovine farmers worldwide. In order to contribute to the control of nematode infections and avoid parasite spreading we generated divergent resistant and susceptible sheep breeds and evaluated the adaptive immunity of these animals developed upon experimental infection against H. contortus. The selection of resistant or susceptible animals from the Corriedale Breed has been based on Expected Progeny Differences for faecal egg counts per gram. Furthermore, animals from the resistant Corriedale line were inseminated with imported semen from Australian Rylington Merino rams. Thus, the objective of this work was to analyze the adaptive immune response in both susceptible and resistant obtained lambs. Our results indicate that there is a potent parasite-specific local and systemic immune response in resistant animals and that although susceptible lambs can produce high levels of IgA antibodies during the infection, their antibody response is delayed which, together with an impaired specific-Th2 response, does not contribute to initial parasite elimination. Our results shed light into the immune mechanisms that mediate resistance to H. contortus and could constitute important assets to sheep farmers, not only as a means to detect resistance, but also to enhance the efficiency of selection in stud flocks.

Differences in immune responses to Haemonchus contortus infection in the susceptible Ile de France and the resistant Santa Ines sheep under different anthelmintic treatments regimens

Understanding the immunological basis of resistance to gastrointestinal nematode infections in livestock is important in order to develop novel methods of parasite control such as vaccination or genetic selection for parasite resistance. The present study aimed to investigate differences in immune response between parasite resistant Santa Ines and susceptible Ile de France sheep breeds to natural Haemonchus contortus infection. Parasitological parameters, humoral immunity, local and circulating cellular immune responses were evaluated in 19 Santa Ines and 19 Ile de France lambs undergoing different anthelmintic treatments regimens: suppressive treatments (SUP) or targeted selective treatments (TST) over a 5-month grazing period. Santa Ines lambs had significantly lower Haemonchus faecal egg count and worm burden compared to Ile de France regardless of treatment regime. In addition, circulating blood eosinophils count and parasite-specific IgG levels were significantly higher and more rapidly induced in Santa Ines lambs. Abomasal immune responses were generally greater in the resistant breed, which had significantly higher levels of parasite-specific IgA in mucus, and elevated number of globule leukocytes and CD3+ T cells within the abomasal mucosal. Furthermore, numbers of POU2F3+ epithelial cells, a tuft-cell specific transcription factor, were also elevated in the Santa Ines breed, suggesting that this breed is better able to initiate T-helper type 2 immune responses within the abomasum. In conclusion, the differential immunological responses detailed here are relevant to understanding resistance to gastrointestinal nematodes in other host breeds, as well as to resistance breeding as a sustainable control approach for parasitic infections.

Transcriptome variation in response to gastrointestinal nematode infection in goats

Gastrointestinal nematodes (GIN) are a major constraint for small ruminant production. Due to the rise of anthelmintic resistance throughout the world, alternative control strategies are needed. The development of GIN resistance breeding programs is a promising strategy. However, a better understanding of the mechanisms underlying genetic resistance might lead to more effective breeding programmes. In this study, we compare transcriptome profiling of abomasal mucosa and lymph node tissues from non-infected, resistant and susceptible infected Creole goats using RNA-sequencing. A total of 24 kids, 12 susceptible and 12 GIN resistant based on the estimated breeding value, were infected twice with 10,000 L3 Haemonchus contortus. Physiological and parasitological parameters were monitored during infection. Seven weeks after the second infection, extreme kids (n = 6 resistant and 6 susceptible), chosen on the basis of the fecal egg counts (FEC), and 3 uninfected control animals were slaughtered. Susceptible kids had significantly higher FEC compared with resistant kids during the second infection with no differences in worm burden, male and female worm count or establishment rate. A higher number of differentially expressed genes (DEG) were identified in infected compared with non-infected animals in both abomasal mucosa (792 DEG) and lymph nodes (1726 DEG). There were fewer DEG in resistant versus susceptible groups (342 and 450 DEG, in abomasal mucosa and lymph nodes respectively). ‘Cell cycle’ and ‘cell death and survival’ were the main identified networks in mucosal tissue when comparing infected versus non-infected kids. Antigen processing and presentation of peptide antigen via major histocompatibility complex class I were in the top biological functions for the DEG identified in lymph nodes. The TGFβ1 gene was one of the top 5 upstream DEG in mucosal tissue. Our results are one of the fist investigating differences in the expression profile induced by GIN infection in goats.

Effect of Ovar-DRA and Ovar-DRB1 genotype in small ruminants with haemonchosis

The effect of Ovar-DRA and Ovar-DRB1 genotypes on faecal egg count (FEC) was determined in sheep and goats infected with Haemonchus contortus. One hundred and forty-three sheep from 3 different breeds (St. Croix, Katahdin and Dorper) and 150 goats from three different breeds (Spanish, Boer and Kiko) were used. Parasitological (FEC), haematological (packed cell volume) and immunological (IgA, IgG and IgM) parameters were measured. Sheep populations showed a higher FEC and humoural response than goat breeds. Genotypes were determined by high-resolution melting assays and by conventional PCR. For Ovar-DRA, sheep and goats carrying the AA genotype showed significant lower FEC than AG and GG genotypes. The additive effect was found to be 115.35 less eggs per gram of faeces for the A allele for goats. For Ovar-DRB1, only in sheep, the GC genotype was associated with low FEC. The additive effect was 316.48 less eggs per gram of faeces for the G allele, and the dominance effect was 538.70 less eggs per gram of faeces. The results indicate that single nucleotide polymorphisms within Ovar-DRA and Ovar-DRB1 could be potential markers to be used in selection programmes for improving resistance to Haemonchus contortus infection.

Boer goats appear to lack a functional IgA and eosinophil response against natural nematode infection

Gastrointestinal nematode infection is one of the major diseases affecting small ruminants. Although some breeds of goats are quite resistant, many breeds of goats are relatively susceptible. This study used a combined parasitological, immunological, bioinformatic and statistical approach to examine the role of goat IgA and eosinophils in protection against Teladorsagia circumcincta. Molecular modelling suggested that the transmembrane domain of the high affinity IgA receptor was dysfunctional in goats. Statistical analyses failed to find any association in naturally infected goats between high IgA or eosinophil responses and low faecal egg counts. Together these results indicate that IgA and eosinophil responses against T. circumcincta are less effective in goats than sheep.

Systemic oxidative stress in Suffolk and Santa Ines sheep experimentally infected with Haemonchus contortus

The mechanisms responsible for the imbalance between oxidants and antioxidants in sheep infected with Haemonchus contortus are not well established. This study aimed to prove the hypothesis that oxidative stress occurring during infection by H. contortus varies according to breed, and that the parasite burden correlates with hypoalbuminaemia and anaemia. Thus, after deworming and confirming the absence of infection, two different sheep breeds, Suffolk (n = 15) and Santa Ines (n = 22), were orally inoculated with a single dose of 5,000 L3 of H. contortus. The egg counts per gram of faeces (EPG), packed cell volume (PCV) and concentrations of several plasma markers of oxidative stress (lipid peroxidation, albumin, uric acid, total bilirubin, total antioxidant capacity [TAC], total oxidant concentration [TOC] and the oxidative stress index [OSI]) were quantified before (control group) and during the experimental infection (28, 34 and 42 days post-inoculation). In both breeds, TOC increased at 28 days and TAC increased at 42 days. In Suffolk sheep, there was a positive correlation of EPG with oxidant components (28 days) and a negative correlation of EPG with PCV (42 days). In Santa Ines sheep, there was a positive correlation of EPG with bilirubin (r = 0.492; p = 0.020). H. contortus infection caused oxidative stress, which varied according to the breed. Parasite burden was not associated with hypoalbuminaemia, whereas there was a negative correlation with PCV. This research provides the first evidence that the antioxidant status contributes more to the resilience to H. contortus in Santa Ines sheep compared to Suffolk sheep.

Immune response in goats vaccinated with thiol-binding proteins from Haemonchus contortus

The experimental protocol of immunization tested here confirms its protective effect against Haemonchus contortus in goats. This protection translated into a 65.5% mean reduction in adult worm burden after a homologous challenge, and a significant decrease (73.2%) in cumulative faecal egg counts (FECs). These parasitological findings were consistent with the levels of some biopathological parameters. Thus, the reduction in adult worms and FEC observed in immunized animals were associated with increased levels of packed cell volume as well as plasma proteins. This response seems to be related to an important increase in specific antibodies (in serum and gastric mucus) and eosinophilia in response to challenge. At the local level, a cellular response was also observed in which CD4⁺ lymphocytes and globule leucocytes played a predominant role. Finally, it should be noted that the study of immunolocalization of proteins used in the vaccination trial suggests that these antigens have an internal location (at intestinal and reproductive tissues) in the adult worm. This observation, in conjunction with the kinetics of specific antibody levels after the challenge, suggests that these antigens may be part of excretory/secretory (E/S) products.

Vaccination of lambs against Haemonchus contortus with the recombinant rHc23. Effect of adjuvant and antigen dose

Haemonchus contortus is the most pathogenic gastrointestinal helminth of small ruminants. Natural or experimental repeated infections and several native antigens confer a partially protective immune response but vaccination with subunit antigens has been elusive. Promising results have been obtained with a recombinant form of a somatic antigen (rHc23). In this paper we present the results obtained in vaccination trials in lambs using two dosages of rHc23 and standard adjuvants. Six-months old Manchego females lambs were vaccinated with rHc23 (50 or 200 μg/dose) adjuvanted with 1mL aluminum hydroxide on days -42, -28 and -14 or with 200 μg/dose rHc23 and 5 mg Quil A on days -49, -28 and -7. Control lambs were kept receiving only the adjuvants the same days or no treatment. Moreover one group did not receive any treatment or infection. On day 0 vaccinated lambs, untreated animals and those receiving the adjuvant were infected per os with a monospecific single infection of 4000 L3 of H. contortus. Infection was kept for 58 days and follow-up included the determination of serum specific antibody response (ELISA, WB), hematological parameters (eosinophil counts, hematocrit) and fecal egg counts (epg). Absence of hematocrit alterations, reduction of helminth's eggs output and abomasal parasite burden at the end of the experiment were the efficacy criteria of vaccination with the recombinant. Immunization with both adjuvants and antigen dosages elicited strong antibody responses particularly with Quil A. Vaccinated groups showed significant reduction of fecal egg excretion and abomasal helminth burdens. Highest protection of lambs against challenge was achieved with aluminum hydroxide and 200 μg/dose rHc23 with a reduction of over 70% of the abomasal burden and over 80% of fecal egg output. Results suggest that rHc23 could be a valuable recombinant candidate for vaccination against haemonchosis. No clear relationship was found between antibody levels and protection this pointing towards involvement of both humoral and cellular components in the protective response elicited by rHc23.

Galectins and collectinis expression are increased in Haemonchus contortus-infected corriedale sheep

Galectins and collectins are proteins classified in the lectin family that have the ability to recognize molecular patterns associated with pathogens. Studies on cattle have demonstrated high expression of these proteins during infection with gastrointestinal nematodes. The aim of this study was to investigate whether the level of Haemonchus contortus infection would alter the expression of galectins (Gal11 and Gal14) and collectins (SPA and CGN) in sheep. Twelve Corriedale sheep exposed to natural infection with nematodes were divided into two groups: group 1 (G1, n = 7) and group 2 (G2, n = 5), with low and high parasite burdens, respectively, based on fecal egg counts and abomasal parasite counts. The fecal egg counts and abomasal parasite counts were significantly different (p < 0.05) between the groups. Galectin and collectin gene expression was observed in all sheep abomasal samples. However, animals with lower infection levels showed lower expression of the genes Gal14, SPA and CGN (p < 0.05). Expression of lectins was associated with the abomasal H. contortus burden, thus suggesting that these proteins may have a role in controlling of this infection.

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.

Diagnosis, Treatment and Management of Haemonchus contortus in Small Ruminants

Haemonchus contortus is a highly pathogenic, blood-feeding nematode of small ruminants, and a significant cause of mortalities worldwide. Haemonchosis is a particularly significant threat in tropical, subtropical and warm temperate regions, where warm and moist conditions favour the free-living stages, but periodic outbreaks occur more widely during periods of transient environmental favourability. The clinical diagnosis of haemonchosis is based mostly on the detection of anaemia in association with a characteristic epidemiological picture, and confirmed at postmortem by the finding of large numbers of H. contortus in the abomasum. The detection of impending haemonchosis relies chiefly on periodic monitoring for anaemia, including through the 'FAMACHA' conjunctival-colour index, or through faecal worm egg counts and other laboratory procedures. A range of anthelmintics for use against H. contortus is available, but in most endemic situations anthelmintic resistance significantly limits the available treatment options. Effective preventative programmes vary depending on environments and enterprise types, and according to the scale of the haemonchosis risk and the local epidemiology of infections, but should aim to prevent disease outbreaks while maintaining anthelmintic efficacy. Appropriate strategies include animal management programmes to avoid excessive H. contortus challenge, genetic and nutritional approaches to enhance resistance and resilience to infection, and the monitoring of H. contortus infection on an individual animal or flock basis. Specific strategies to manage anthelmintic resistance centre on the appropriate use of effective anthelmintics, and refugia-based treatment schedules. Alternative approaches, such as biological control, may also prove useful, and vaccination against H. contortus appears to have significant potential in control programmes.

Potential role for mucosal IgA in modulating Haemonchus contortus adult worm infection in sheep

Haemonchus contortus (H. contortus) is a haematophagous parasite which causes important economic losses in small ruminants. On the island of Gran Canaria, two sheep breeds coexist which differ in their susceptibility to the infection with H. contortus; the resistant Canaria Hair Breed (CHB) sheep and the susceptible Canaria Sheep (CS) breed. The major target of resistance mechanisms in CHB sheep are directed to the adult parasite stage, reducing the worm burden, and decreased length and fecundity of surviving worms. Mucosal IgA (mIgA) has been shown to be an important regulator of immunity in Haemonchus and Teladorsagia infections; through correlations with larval stages where such mechanisms as antibody-dependent cell cytotoxicity and enzyme inhibition may mediate resistance. Here for the first time, we demonstrate a significant negative correlation between mIgA and adult worm length and fecundity only in the resistant CHB sheep. In contrast, and as reported in other sheep breeds, mIgA was only negatively correlated against the larval stage in the more susceptible CS breed. This study suggests mIgA may play a role in resistance to both larval and adult stages.

Relative resistance of Menz and Washera sheep breeds to artificial infection with Haemonchus contortus in the highlands of Ethiopia

The aim of this study was to evaluate the relative resistance of Menz and Washera sheep breeds to artificial infection with Haemonchus contortus. The challenge trial was conducted at the Debre Berhan Agricultural Research Center in Ethiopia. A total of 39 (Menz = 21, Washera = 18) lambs of about 6 months old were used for the trial. All lambs were initially treated against internal parasite using albendazole and Fasinex to free them from internal parasites and kept indoors. H. contortus third-stage larvae (L3) were prepared according to standard procedure from adult female parasite collected from abattoirs and recovered using the Baerman technique. Approximately 5000 infective larvae were inoculated to the experimental lambs at about 5 weeks after deworming. Fecal egg count (FEC), packed cell volume (PCV), FAffa MAlan CHArt (FAMACHA) score, lamb body weight, and survival of lambs were recorded at 28, 35, and 42 days after challenge. Breed effect was not significant (P > 0.05), whereas time of measurement and the interaction of breed and time had significant (P < 0.05) effects on FEC and PCV. At 28 days after challenge, Menz sheep had lower FEC than Washera sheep, whereas at days 35 and 42, the Washera sheep had lower FEC than Menz lambs. The PCV decreased significantly throughout the post-challenge period. Despite their parasite burden, Menz sheep were able to maintain live weight during the 42 days of challenge. Chi-square tests for breed differences in lamb survival were not significant at any time (28, 35, and 42 days after challenge). Lower FEC at 28 days and delayed rise in FEC after infection in Menz lamb would allow in delaying anthelmintic treatment. In addition to maintain body weights during the infection period, sheep of both breeds exhibited substantial variability in PCV and FEC, suggesting opportunity to consider parasite resistance in selection program.

Effect of condensed tannins supplementation through leaf meal mixture on voluntary feed intake, immune response and worm burden in Haemonchus contortus infected sheep

The study was carried out to assess the effect of condensed tannins (CT) supplementation through leaf meal mixture (LMM) on feed intake, humoral [Immunoglobulin G (IgG)], cell mediated immune response (CMI) and faecal egg counts in Haemonchus contortus infected sheep. Eighteen sheep were randomly divided into three groups (negative control-NC, infected control-C and Infected treatment-T) of six animals in each group in a completely randomized block design for a period of 90 days. Twelve H. contortus infected adult sheep were allocated into two equal groups C and T, supplemented with 0 and 1.5 % of CT, respectively. Six non-infected sheep of similar age and body weight of NC group were included in this study to compare their immune response with H. contortus C and CT supplemented T groups. Intake of dry matter and organic matter (g day(-1) and % live weight) was statistically similar (P < 0.05) among the three groups. The anti-Haemonchus IgG and CMI response was higher in T group as compared to C group. The mean faecal egg counts was significantly (P < 0.001) higher in C group as compared to T group. It may be concluded that dietary supplementation of CT (1.5 %) through LMM improved humoral and CMI immune response and decreased worm load in H. contortus infected sheep.

Immunization with Eimeria ninakohlyakimovae-live attenuated oocysts protect goat kids from clinical coccidiosis

Caprine coccidiosis, affecting mainly young goat kids around the weaning period, is worldwide the most important disease in the goat industry. Control of caprine coccidiosis is increasingly hampered by resistances developed against coccidiostatic drugs leading to an enhanced need for anticoccidial vaccines. In the current study we conducted an oral immunization trial with live attenuated sporulated Eimeria ninakohlyakimovae oocysts. Sporulated E. ninakohlyakimovae oocysts were attenuated by X-irradiation technique. The experimental design included a total of 18 goat kids divided into the following groups: (i) animals immunized with attenuated E. ninakohlyakimovae oocysts at 5 weeks of age and challenged 3 weeks later with non-irradiated homologous oocysts (group 1); (ii) animals infected with non-attenuated E. ninakohlyakimovae oocysts at 5 weeks of age and challenged 3 weeks later with non-attenuated homologous oocysts (group 2); (iii) animals primary-infected with untreated E. ninakohlyakimovae oocysts at 8 weeks of age (control of the challenge infection, group 3); (iv) non-infected control animals (group 4). Goat kids immunized with live attenuated E. ninakohlyakimovae oocysts (group 1) excreted significantly less oocysts in the faeces (95.3% reduction) than kids infected with non-attenuated ones (group 2). Furthermore, immunization with live but attenuated oocysts resulted in ameliorated clinical coccidiosis compared to goat kids infected with untreated oocysts (group 2) and resulted in equally reduced signs of coccidiosis after challenge infection compared to acquired immunity driven by non-attenuated oocysts. Overall, the present study demonstrates for the first time that live attenuated E. ninakohlyakimovae oocysts orally administered showed almost no pathogenicity but enough immunogenicity in terms of immunoprotection. Importantly, vaccinated animals still shed low amounts of oocysts, guaranteeing environmental contamination and consecutive booster infections to sustain ongoing immunity.

Vaccination of goats with DNA vaccine encoding Dim-1 induced partial protection against Haemonchus contortus: a preliminary experimental study

Disorganized muscle family member (Dim-1) belongs to immunoglobulin superfamily, and is a structural protein localized to the region of the muscle cell membrane around and between the dense bodies. Strong immunogenicity to host's immune system was induced by Dim-1 from Ascaris suum, which indicated that Dim-1 could be a potential candidate for vaccine. The homologues of Dim-1 were also detected in nematodes Brugia malayi and Trichostrongylus colubriformis. However, information on the complete coding sequence and protection potential of this molecule in Haemonchus contortus is lacking. In this study, full length of Dim-1 cDNA was cloned using a rapid amplification of cDNA ends (RACE) strategy and the DNA vaccine encoding Dim-1 open reading frame (ORF) was tested for protection against experimental H. contortus infections in goats. Fifteen goats were allocated into three trial groups. The animals of Dim-1 group were vaccinated with the DNA vaccine encoding Dim-1 on day 0 and 14, and challenged with 5000 infective H. contortus third larval stage (L3) on day 28. An unvaccinated positive control group was challenged with L3 at the same time. An unvaccinated negative control group was not challenged with L3. The results indicated Dim-1 DNA vaccines were transcribed at local injection sites and expressed in vivo post immunizations respectively. Following L3 challenge, the mean eggs per gram feces (EPG) and worm burdens of Dim-1 group were reduced by 45.7% and 51.1%, respectively. Significantly high levels of serum IgG, serum IgA, mucosal IgA, CD4(+) T lymphocytes and B lymphocytes of Dim-1 group were produced. While compared with the negative control group, increased numbers of blood eosinophils and lymphocytes and declined haemoglobin level were observed in the Dim-1 group after L3 challenge. The preliminary study suggest that recombinant H. contortus Dim-1 DNA vaccine induced partial immune response and has protective potential against goat haemonchosis.

Evaluation of two Iranian domestic ovine breeds for their pathological findings to gastrointestinal infection of Haemonchus contortus

The generally warm, moist environmental conditions in the Northwestern Iran are ideal for survival and growth of the egg and larval stages of Haemonchus contortus and other gastrointestinal nematodes (GIN) of sheep and goats.A total of 2,421 animals were slaughtered and examined from July 2010 to July 2011 in Urmia abattoir. In case of sheep, 225 out of 2,421 were positive and prevalence of H. contortus infestation was 9.3 %. Sex wise prevalence of H. contortus in sheep was 33.08 % (76/229) in male and 66.22 % (149/225) in female. The females indicated significantly (P < 0.05) higher prevalence (66.22 %) as compared to males (33.08 %). The highest prevalence was recorded in the spring (April) and the lowest was in summer (July), respectively. On microscopic examination, infiltration of mononuclear cells and eosinophils in gastric glands, periglandular hyperemia and hemorrhage, mucous gland hyperplasia, connective tissue proliferation and necrosis was observed. Also, in mixed abomasal infection with Haemonchus and Ostertagia species, mucosal hyperplasia and increased mucous glands and sometimes cystic glands were seen. Statistical analysis using SPSS software, and Chi-square test, demonstrated a non-significant difference between ages and abomasal PH values of infected and healthy sheep (P < 0.05). But the difference between sexes, seasons and abomasal lesions was significant (P > 0.05).