The modulatory influence of Trypanosoma brucei on challenge infection with Haemonchus contortus in Nigerian West African Dwarf goats segregated into weak and strong responders to the nematode

Association of single nucleotide polymorphism in NLRC3, NLRC5, HIP1, and LRP8 genes with fecal egg counts in goats naturally infected with Haemonchus contortus

Haemonchus contortus is a common, intractably pathogenic and economically important gastrointestinal nematode for goat producers worldwide, especially in tropical and subtropical regions. The objective of this study is to identify single nucleotide polymorphisms (SNPs) of 12 candidate goat genes mainly related to the innate immune response associated with fecal egg counts (FECs) of Haemonchus contortus in goat as an indicator of the level of parasite infection. Phenotypic data including FEC and blood traits were recorded in 189 native goats from China and 191 ones from Bangladesh, respectively. Bangladeshi goats had significantly (P < 0.01) lower FEC compared to that of Chinese goats, suggesting higher susceptible and infection rates in Chinese goat populations. FEC was significantly positive correlated with body weight (r = 0.64, P < 0.01) and hemoglobin (r = 0.49, P < 0.01) value, but negative with pack cell volume (r = - 0.63, P < 0.05) in goats. Genotyping of SNPs was performed using a matrix-assisted laser desorption ionization time of flight mass spectrometry assay and a generalized linear model was used to evaluate the association between each SNP and goat FEC trait. Eleven novel SNPs in the NLRC3, NLRC5, HIP1, and LRP8, out of 46 variants from these 12 genes, were significantly associated with FEC of goats with a nominal significance level of P < 0.05. Of these 11 SNPs, linkage disequilibrium were revealed among SNPs in LRP8 (r² = 0.87 to 1), between SNPs in NLRC3, NLRC5, and HIP1 (r² = 0.96 to 0.99), respectively. Further, haplotypes within NLRC3, NLRC5, and HIP1 were significantly associated (P < 0.001) with FEC. In artificial challenge trail, quantitative real-time PCR exposed that the relative expression of mRNA was higher in the resistant group for NLRC3 (P < 0.01), LRP8 and HIP1 (P < 0.001) but lower in the resistant group for NLRC5 (P < 0.0001), compared to the susceptible group. The possible SNP markers and genes identified in this study could be potentially used in marker-assisted selection for breeding local goats breeds resistant to gastrointestinal nematode parasite particularly for Haemonchus contortus, and then for improving health and productivity of goat.

Single nucleotide polymorphisms in candidate genes are significantly associated with resistance to Haemonchus contortus infection in goats

BACKGROUND

Haemonchosis is a major economic problem in goat production in humid, tropical and subtropical regions. The disease is caused by an abomasal nematode, Haemonchus contortus, which is highly pathogenic in small ruminants. The aim of this study was to identifying single-nucleotide polymorphisms (SNP) that were associated with fecal egg counts (FEC) and could be used as markers to identify resistance to H. contortus in goats.

RESULTS

Ten novel variants in the CIITA, ATP2A3, HSPA8, STAT5B, ESYT1, and SERPING1 genes were associated with FEC in goats with a nominal significance level of P < 0.05. Two missense mutation in the exon region of the caprine CIITA gene resulted in replacement of arginine with cysteine at position 9473550 (R9473550C) and aspartic acid with glutamic acid at position 9473870 (D9473870E). Chinese goat breeds had significantly higher FEC than Bangladeshi goat breeds within their respective genotypes. Polymorphism information content (PIC), effective allele number (Ne), and heterozygosity (He) were greatest for the STAT5B_197_A > G SNP locus in all goat breeds. Pairwise coefficients of linkage disequilibrium (D´, r 2) revealed complete LD (r 2 = 1) between significant SNP polymorphisms in CIITA and SERPING1 and strong LD (r 2 = 0.93 and 0.98) between polymorphisms in HSPA8 and ATP2A3, respectively. Correlation coefficient (r) between FEC and body weight (BW) was significantly positive (r = 0.56***, P < 0.001) but that between FEC and packed cell volume (PCV) was negatively significant (r = - 0.47**, P < 0.01) in the total population of goats. On the other hand, correlation coefficient (r) between BW and PCV was not significant in total population of goats. Association analysis revealed that haplotypes within ATP2A3, HSPA8, and SERPING1 were significantly associated with FEC. Quantitative real-time PCR revealed that the relative expression of mRNA was higher (P < 0.001) for resistant, compared to susceptible, groups of goats for all candidate genes except CIITA.

CONCLUSIONS

This study identified SNP markers that can potentially be used in marker-assisted selection programs to develop goat breeds that are resistant to H. contortus.

Response of outbred albino mice to concomitant Heligmosomoides bakeri, Plasmodium berghei and Trypanosoma brucei infections

To investigate the response of mice to concomitant infections with Trypanosoma brucei (Tb), Plasmodium berghei (Pb) and Heligmosomoides bakeri (Hb) infections. Each group of 6 mice was either infected with Pb + Tb + Hb, Pb + Tb, Pb + Hb, Tb + Hb, Pb, Tb, Hb or remained as uninfected controls. Hb infected mice each received 200 infective larvae (L3) of Hb orally, Tb infected mice each received 2 × 10^-6 organisms through the intraperitoneal route while Pb infected mice received 1 × 10^-5 parasitized red blood cells through the intraperitoneal route. PCV, body weights (BW), faecal egg counts (FEC), Tb parasitaemia, Pb parasitaemia, clinical signs and worm burdens (WB) were determined. FEC were highest in Pb + Tb + Hb and least in Hb group and the difference was significant (P < 0.05). WB was significantly higher in mice with concurrent infections. PCV of infected mice was lower than that of uninfected controls and the difference was significant between Pb + Tb + Hb infected and uninfected controls. The difference in weight loss was significant between Pb + Tb + Hb infected and controls. Mortalities occurred in Pb + Tb + Hb, Tb + Hb and Pb + Hb infected mice. Mortalities and low PCV and low BW were indications that concomitant infections were more pathogenic to the mice than single infections, pathogenicity increasing with increasing number of parasite species involved.

Variation in faecal worm egg counts of experimentally infected goats and mice with time of day and its implications in diagnosis of helminthosis

Faecal worm egg counts (FEC) are very important indicators in assessing the intensity of helminth infections in animal hosts and inform decisions taken in parasite control programmes. FEC are however affected by many factors which include the dose level of larval challenge, species composition of the worms, worm burden, female worm fecundity and concurrent infections to name but these few. The relevance of time of collection of faecal sample for FEC is not fully known and in most cases faeces for analysis is collected whenever feasible for the researcher on sample collection days. The significance of the time of collection of faeces on FEC was therefore investigated at two different periods of the day, morning and afternoon. Faecal samples were collected at 7-8 a.m. (morning) and at 2-3 p.m. (afternoon) on same sampling days from 6 mice and 10 West African Dwarf goat kids experimentally infected with Heligmosomoides bakeri and Haemonchus contortus respectively. FEC were conducted using the flotation and modified McMaster techniques. Overall, the 2-3 p.m. FEC tended to be higher than the 7-8 a.m. FEC in both animal species but the difference was not significant (P > 0.05). The time of collection of faecal samples for faecal worm egg counts is therefore not a crucial factor that may significantly affect FEC in H. bakeri and H. contortus infected mice and goats respectively although it would be advisable to maintain particular periods for collection of faeces in particular experiments for best results of FEC to be obtained.

Comparative Response of the West African Dwarf Goats to Experimental Infections with Red Sokoto and West African Dwarf Goat Isolates of Haemonchus contortus

Response of the West African Dwarf (WAD) goats to two different isolates of Haemonchus contortus, the Red Sokoto (RS) goat isolate (RSHc) and the WAD goat isolate (WADHc) (isolated from WAD goats), was studied by experimental infections of 4–6-month-old male WAD goat kids. Group 1 and Group 2 goats were each infected with 4500 infective larvae (L3) of RSHc and WADHc, respectively. Group 3 animals served as uninfected control. Prepatent period (PPP), faecal egg counts (FEC), worm burden (WB), body weight (BW), packed cell volume (PCV), and body condition score (BCS) were determined. WAD goats infected with RSHc isolate and the ones infected with WADHc isolate had mean PPP of 19.63 ± 0.26 and 19.50 ± 0.19, respectively. Goats infected with WADHc isolate had significantly higher FEC (P = 0.004) and WB (P = 0.001). BW were significantly higher (P = 0.004) both in the controls and in Group 2 goats infected with WADHc isolate than in Group 1 goats infected with the RSHc isolate. BCS of animals in both infected groups dropped significantly (P = 0.001). There was a significant drop in PCV (P = 0.004) of both infected groups in comparison. Both isolates of H. contortus were pathogenic to the host.

Haemonchotolerance in West African Dwarf goats: contribution to sustainable, anthelmintics-free helminth control in traditionally managed Nigerian dwarf goats

West African Dwarf (WAD) goats are extremely important in the rural village economy of West Africa, but still little is known about their biology, ecology and capacity to cope with gastrointestinal nematode (GIN) infections. Here, we summarise the history of this breed and explain its economic importance in rural West Africa. We review recent work showing that Nigerian WAD goats are highly trypanotolerant and resist infections with Haemonchus contortus more effectively than other breeds of domestic goat (haemonchotolerance). We believe that haemonchotolerance is largely responsible for the generally low level GIN infections and absence of clinical haemonchosis in WADs under field conditions, and has contributed to the relatively successful and sustainable, anthelmintics-free, small-scale system of goat husbandry in Nigeria's humid zone, and is immunologically based and genetically controlled. If haemonchotolerance can be shown to be genetically controlled, it should be possible to exploit the underlying genes to improve GIN resistance among productive fibre and milk producing breeds of goats, most of which are highly susceptible to nematode infections. Genetic resistance to GIN and trypanosome infections would obviate the need for expensive chemotherapy, mostly unaffordable to small-holder farmers in Africa, and a significant cost of goat husbandry in more developed countries. Either introgression of resistance alleles into susceptible breeds by conventional breeding, or transgenesis could be used to develop novel parasite-resistant, but highly productive breeds, or to improve the resistance of existing breeds, benefitting the local West African rural economy as well as global caprine livestock agriculture.

Correlates of resistance to gastrointestinal nematode infection in Nigerian West African dwarf sheep

OBJECTIVE

To investigate correlates of resistance to GI nematode infection in Nigerian West African dwarf (WAD) sheep.

METHODS

Thirty three sheep were randomly assigned to two groups, A (n=27) which were used for experimental infections, and B (n=6) which served as uninfected control. Each infected animal received weekly escalating infections with infective larvae (60%Haemonchus contortus (H. contortus) and 40%Trichostrongylus colubriformis (T. colubriformis) for 4 weeks. The responses of all the infected and control sheep were assessed by faecal egg count (FEC), worm burden (Wb), packed cell volume (PCV), body weight (Bwt), and body condition score (BCS). On the basis of their individual faecal egg output, Lambs in group A with epg ≤1,000 on any sampling day were classified as low faecal egg count (LFEC) phenotype (n=16), those with epg between 1,000 and 10,000 as intermediate (n=5) and lambs with epg > 10,000 as high feacal egg count (HFEC) phenotype (n=6).

RESULTS

The difference between the FEC classes was highly significant (P=0.001). The BCS and weight gained at the end of the experiment by the control and LFEC sheep was significantly higher (P≤0.05) than those of the intermediate and HFEC phenotypes. There was a significant and negative correlation between the parasitological measures and the trio of BCS, PCV and Bwt of sheep.

CONCLUSION

The result of the study indicated that the FEC, weight gain, PCV, and BCS are correlates and potential selection criteria of GI nematode resistant WAD sheep.

Changes in the body condition scores of Nigerian West African Dwarf sheep experimentally infected with mixed infections of Haemonchus contortus and Trichostrongylus colubriformis

Weekly changes in body condition scores and body weights were determined in West African Dwarf sheep following trickle exposure to weekly escalating mixed infections with Haemonchus contortus and Trichostrongylus colubriformis starting with single doses of 500 infective larvae (L(3)) at wk1, 1000 L(3) at wk2, 2000 L(3) at wk3 and 4000 L(3) at wk4. Thirty-three animals were randomly assigned to two groups namely, Group 1 (n=27) and Group 2 (n=6). Group 1 animals were used for experimental infections and Group 2 animals served as uninfected controls. Body condition scores (BCS), body weights (BW), faecal egg counts (FEC) per gram of faeces and worm burden (Wb) were determined using standard procedures. Lambs in group 1 with epg ≤ 1000 were classified as strong responders (n=16), those with epg between 1000 and 10,000 as intermediate (n=5) and lambs with epg>10,000 on any sampling day were classified as weak responders (n=6). Based on this classification, the mean epg of lambs classified as strong responders was significantly lower (P<0.001) than the epg of lambs classified as weak responders. The body condition scores and body weights of the strong responder lambs were comparable with those of the uninfected control and they were significantly higher than those of the weak and intermediate responders from wk5 till the end of the experiment. There was an inverse and significant relationship between the average BCS of days 56 and 59 and the average FEC of days 56 and 59 (r(s)=-572; P=0.017; n=27) as well as with Wb (r(s)=-531; P=0.028; n=27). We concluded that changes in the body scores are good indicators of the intensity of gastrointestinal nematode infection in the Nigerian WAD sheep.

Responses of the humid zone ecotype of the Nigerian West African Dwarf sheep to mixed infections with Haemonchus contortus and Trichostrongylus colubriformis

The responses of the Nigerian West African Dwarf sheep to experimental infections with two of its most important gastrointestinal (GI) nematodes, namely, Haemonchus contortus and Trichostrongylus colubriformis were studied by means of two measures of parasitological response, namely, faecal egg count (FEC) and worm burden (Wb), and three measures of host pathology, namely, packed cell volume (PCV), body weight (Bwt) and body condition score (BCS). Following exposure to weekly escalating infections (60% H. contortus and 40% T. colubriformis) starting with single doses of 500 infective larvae (L(3)) at week 1, 1,000 L(3) at week 2, 2,000 L(3) at week 3 and 4,000 L(3) at week 4, two distinctive worm burden response phenotypes were readily recognisable, namely, low Wb (LWb) and high Wb (HWb) phenotypes. The percentage of inoculums (adults and immature stages) recovered at necropsy were 3.75% and 33.08% respectively for H. contortus and T. colubriformis. The results showed that the FECs of the lambs belonging to the LWb phenotype were significantly lower than the FECs of their HWb counterpart. Among the measures of host pathology tested, the LWb phenotype sheep had similar Bwt, PCV and BCS to the uninfected control sheep, whereas the HWb phenotype sheep had significantly lower values than their LWb counterparts and the control sheep towards the end of the experiment. There was a highly significant positive correlation between worm burden transformed as log(10) (Wb + 10) and the average of D56 and D59 FECs. A highly significant negative correlation also was obtained between log(10) (Wb + 10) and the PCV, Bwt and BCS. The low percentage of H. contortus inoculums recovered at necropsy suggested that the sheep may be resistant to their most important GI nematode, H. contortus but less so to T. colubriformis.

The unique resistance and resilience of the Nigerian West African Dwarf goat to gastrointestinal nematode infections

Background

West African Dwarf (WAD) goats serve an important role in the rural village economy of West Africa, especially among small-holder livestock owners. They have been shown to be trypanotolerant and to resist infections with Haemonchus contortus more effectively than any other known breed of goat.

Methods

In this paper we review what is known about the origins of this goat breed, explain its economic importance in rural West Africa and review the current status of our knowledge about its ability to resist parasitic infections.

Conclusions

We suggest that its unique capacity to show both trypanotolerance and resistance to gastrointestinal (GI) nematode infections is immunologically based and genetically endowed, and that knowledge of the underlying genes could be exploited to improve the capacity of more productive wool and milk producing, but GI nematode susceptible, breeds of goats to resist infection, without recourse to anthelmintics. Either conventional breeding allowing introgression of resistance alleles into susceptible breeds, or transgenesis could be exploited for this purpose. Appropriate legal protection of the resistance alleles of WAD goats might provide a much needed source of revenue for the countries in West Africa where the WAD goats exist and where currently living standards among rural populations are among the lowest in the world.

Resistance and resilience of traditionally managed West African Dwarf goats from the savanna zone of northern Nigeria to naturally acquired trypanosome and gastrointestinal nematode infections

A survey was conducted of gastrointestinal nematode infections and trypanosomosis in Nigerian West African Dwarf (WAD) goats from the savanna region of the country. Animals were screened at two markets, Gboko and Akpagher, from the beginning of April until the end of September, coinciding with the end of the dry season and the first 5 months of the wet season. Of 1054 goats that were examined, 80.5% carried gastrointestinal (GI) nematodes belonging to the genera Haemonchus (61.0%), Oesophagostomum (21.0%) and Trichostrongylus (17.9%). Faecal egg counts (FEC) increased very slowly but significantly from April to maximum levels in September, and varied marginally between the two market sources. The majority of goats (68.8 and 70.1% at the two markets) had low FEC not exceeding 50 eggs/g (epg). FEC did not differ significantly between the sexes or between age classes. Packed cell volume (PCV) also declined significantly with month of the study, but was affected by host sex (a significant month × sex interaction) being generally higher in male animals throughout the period. There was a highly significant negative correlation between log10(FEC+1) and PCV, when all other factors had been taken into account. Body condition scores (BCS) also declined with month of the study, but there was a marked difference between the two sexes, with male animals generally showing a greater stability of BCS across the months compared with females. Trypanosome infections were found in only 4% of the goats and only during the rainy season. Most infections (92.86%) were caused by Trypanosoma brucei alone although T. vivax and T. congolense were occasionally detected. Overall, the majority of goats sampled each month maintained generally good body condition (BCS 3.0–5.0), normal or slightly reduced PCV, even when concurrently infected with trypanosomes and GI nematodes. However, four concurrently infected goats showed signs of overt anaemia during periods of peak infection, during the late rainy season, with marked reductions in PCV ( < 15%). Two of the infected goats were also in poor body condition with BCS of < 2.0. There was no evidence of additive or synergistic pathogenic effects of the two parasites. These results are discussed in the context of the unexpectedly strong resistance and resilience of the savanna WAD ecotype to its native strains of GI nematode and trypanosome parasites.

Trypanosomosis in Goats

Trypanosomosis is a major constraint on ruminant livestock production in Africa, Asia, and South America. The principal host species affected varies geographically, but buffalo, cattle, camels, and horses are particularly sensitive. Natural infections with Trypanosoma congolense, T. vivax, T. brucei, and T. evansi have been described in goats. Trypanosomosis in goats produces acute, subacute, chronic, or subclinical forms, being T. vivax, T. congolense, and T. evansi, the most invasive trypanosomes for goats. However, the role of goats in the epidemiology of trypanosomosis is largely discussed and not well understood. Thus, it has commonly been assumed that trypanosomosis presents a subclinical course and that goats do not play an important role in the epidemiology of the disease. This can partially be due to parasitemia caused by trypanosomes which has been considered low in goats. However, this assumption is currently undergoing a critical reappraisal because of goats may also serve as a reservoir of trypanosome infection for other species, including the human beings in the case of T. brucei rhodesiense. The present article describes the current status of trypanosomosis in goats in Africa, Asia, and South America. Pathogenesis, clinical features, diagnosis, and treatment of the different trypanosomes are also described. The possible role in the epidemiology of the disease in the different areas is also discussed.

Naturally occurring variability in some phenotypic markers and correlates of haemonchotolerance in West African Dwarf goats in a subhumid zone of Nigeria

West African Dwarf (WAD) goats of the Nigerian subhumid zone generally show strong resistance and resilience to Haemonchus contortus in laboratory experiments, although a relatively small proportion are susceptible to infection. Little is known about these extremes of response phenotype in nature. Therefore, a survey was carried out of gastrointestinal nematode infections in WAD goats, with emphasis on abomasal worms, at three goat markets in Southern Nigeria during the rainy season. Faecal samples (n=1070) were collected weekly from goats between April and September, and 352 abomasa and small intestines from local abattoirs were examined. Total strongyle (prevalence=65.0%) and H. contortus (prevalence=64.3%) faecal egg counts (FEC) varied between the three markets, being highest throughout at Opi. FEC increased from April to peak in August. Based on raw FEC, 76.1% of goats had FEC of <100, and 4.7%>500. Adjustment of these figures for monthly and between-market differences, gave figures of 78.8 and 3.4%, respectively. H. contortus worm burdens (WB) showed a similar pattern with 67.9% of goats harbouring <200 worms and 8.2% >1000, and after adjustment 69.6 and 6.0%, respectively. Fecundity, based on eggs in the uterus, did not vary between markets or monthly, but fell with increasing WB. Trichostrongylus colubriformis was less frequent (prevalence=42.4%) but goats from Opi also carried higher WB, and worms were similarly highly aggregated in hosts. When the between-market and monthly differences for both species were controlled, a highly significant positive correlation between the species emerged. Therefore, although a small subset of goats, highly susceptible to H. contortus, exists in this breed, the majority show resistance under field conditions and the resistant phenotype is also resistant to T. colubriformis. Both species are highly aggregated in the susceptible subset of the population. While, we cannot yet exclude alternative explanations, our data are compatible with a strong genetic basis for this phenomenon.