Trypanotolerance in small ruminants of sub-Saharan Africa

Recent advances in the genomic resources for sheep

Sheep (Ovis aries) provide a vital source of protein and fibre to human populations. In coming decades, as the pressures associated with rapidly changing climates increase, breeding sheep sustainably as well as producing enough protein to feed a growing human population will pose a considerable challenge for sheep production across the globe. High quality reference genomes and other genomic resources can help to meet these challenges by: (1) informing breeding programmes by adding a priori information about the genome, (2) providing tools such as pangenomes for characterising and conserving global genetic diversity, and (3) improving our understanding of fundamental biology using the power of genomic information to link cell, tissue and whole animal scale knowledge. In this review we describe recent advances in the genomic resources available for sheep, discuss how these might help to meet future challenges for sheep production, and provide some insight into what the future might hold.

Performance of diagnostic tests for Trypanosoma brucei brucei in experimentally infected pigs

Animal African trypanosomosis is an important vector-borne disease of livestock in sub-Saharan Africa. Pigs seem relatively tolerant to trypanosome infection and could act as a reservoir of trypanosomes affecting animals and humans. Our ability to reliably detect trypanosome infection in pigs depends on the performance of diagnostic tools, which is not well known. In pigs experimentally infected with Trypanosoma brucei brucei, we evaluated the performance of parasitological Buffy Coat Technique (BCT), two molecular (TBR and 5.8S PCR) and four serological tests (CATT, HAT Sero-K-Set rapid diagnostic test-RDT, indirect ELISA, immune trypanolysis). Most diagnostic tests showed high specificity, estimated at 100% (95% CI = 74-100%) with the exception of CATT and RDT whose specificity varied between 100% (95% CI = 74-100%) to 50% (95% CI = 7-93%) during the experiment. The sensitivity of each test fluctuated over the course of the infection. The percentage of positive BCT over the infection (30%) was lower than of positive PCR (56% and 62%, depending on primers). Among the serological tests, the percentage of positive tests was 97%, 96%, 86% and 84% for RDT, ELISA, immune trypanolysis and CATT, respectively. Fair agreement was observed between both molecular tests (κ = 0.36). Among the serological tests, the agreement between the ELISA and the RDT was substantial (κ = 0.65). Our results on the T.b. brucei infection model suggest that serological techniques are efficient in detecting the chronic phase of infection, PCR is able to detect positive samples several months after parasites inoculation while BCT becomes negative. BCT examination and RDT are useful to get a quick information in the field, and BCT can be used for treatment decision. ELISA appears most suited for epidemiological studies. The selection of diagnostic tests for trypanosomosis in pigs depends on the context, the objectives and the available resources.

Prevalence of blood and skin trypanosomes in domestic and wild fauna from two sleeping sickness foci in Southern Cameroon

Although studies on African Trypanosomiases revealed a variety of trypanosome species in the blood of various animal taxa, animal reservoirs of Trypanosoma brucei gambiense and anatomical niches such as skin have been overlooked in most epidemiological settings. This study aims to update epidemiological data on trypanosome infections in animals from human African trypanosomiasis (HAT) foci of Cameroon. Blood and skin snips were collected from 291 domestic and wild animals. DNA was extracted from blood and skin snips and molecular approaches were used to identify different trypanosomes species. Immunohistochemical analyses were used to confirm trypanosome infections in skin snips. PCR revealed 137 animals (47.1%) with at least one trypanosome species in the blood and/or in the skin. Of these 137 animals, 90 (65.7%) and 32 (23.4%) had trypanosome infections respectively in the blood and skin. Fifteen (10.9%) animals had trypanosome infections in both blood and skin snip. Animals from the Campo HAT focus (55.0%) were significantly (X2 = 17.6; P< 0.0001) more infected than those (29.7%) from Bipindi. Trypanosomes of the subgenus Trypanozoon were present in 27.8% of animals while T. vivax, T. congolense forest type and savannah type were detected in 16.5%, 10.3% and 1.4% of animals respectively. Trypanosoma b. gambiense infections were detected in the blood of 7.6% (22/291) of animals. No T. b. gambiense infection was detected in skin. This study highlights the presence of several trypanosome species in the blood and skin of various wild and domestic animals. Skin appeared as an anatomical reservoir for trypanosomes in animals. Despite methodological limitations, pigs, sheep, goats and wild animals were confirmed as potential reservoirs of T. b. gambiense. These animal reservoirs must be considered for the designing of control strategies that will lead to sustainable elimination of HAT.

Infection of West African dwarf rams with Trypanosoma brucei brucei and Trypanosoma congolense significantly alter serum electrolytes, redox balance, sperm parameters, and gonadal morphology

Trypanotolerance of the West African dwarf (WAD) breeds may not rule out significant pathophysiological changes that may affect productivity. In this study, the effects of infection of WAD rams with Trypanosoma brucei brucei (Tbb) and Trypanosoma congolense (Tc) on their serum levels of electrolytes [calcium, phosphorus, sodium, potassium]; oxidative stress markers [superoxide dismutase (SOD), malondialdehyde (MDA)]; and sperm parameters [sperm count, motility, vitality, and morphology] were investigated. Fifteen WAD rams, assigned to 3 groups (A, B & C) of 5 rams each, were used for the study. Group A rams were infected with Tbb, while Group B rams were infected with Tc, both intraperitoneally, at the dose of 10⁶ trypanosomes/animal. Group C rams served as the uninfected control. The infections were monitored for 70 days. Serum calcium levels were significantly (p < 0.05) lower in Tbb and Tc infected rams compared to the control throughout the study. Serum sodium was significantly (p < 0.05) higher in the Tb infected rams compared to the Tc infected and control rams on days 14 and 28 PI. Serum SOD activity decreased while MDA levels increased in both infected groups of rams. Tbb infected rams were azoospermic, while Tc infected rams had lower sperm motility, vitality and concentration, and higher number of abnormal sperm cells compared to the control. Necrotic and inflammatory lesions occurred in the testis and epididymis of both infected rams. These results suggest that despite trypanotolerance, trypanosome infections in the WAD rams significantly impact on health and reproduction.

Identification and Characterization of Copy Number Variations Regions in West African Taurine Cattle

A total of 106 West African taurine cattle belonging to the Lagunaire breed of Benin (33), the N’Dama population of Burkina Faso (48), and N’Dama cattle sampled in Congo (25) were analyzed for Copy Number Variations (CNVs) using the BovineHDBeadChip of Illumina and two different CNV calling programs: PennCNV and QuantiSNP. Furthermore, 89 West African zebu samples (Bororo cattle of Mali and Zebu Peul sampled in Benin and Burkina Faso) were used as an outgroup to ensure that analyses reflect the taurine cattle genomic background. Analyses identified 307 taurine-specific CNV regions (CNVRs), covering about 56 Mb on all bovine autosomes. Gene annotation enrichment analysis identified a total of 840 candidate genes on 168 taurine-specific CNVRs. Three different statistically significant functional term annotation clusters (from ACt1 to ACt3) involved in the immune function were identified: ACt1 includes genes encoding lipocalins, proteins involved in the modulation of immune response and allergy; ACt2 includes genes encoding coding B-box-type zinc finger proteins and butyrophilins, involved in innate immune processes; and Act3 includes genes encoding lectin receptors, involved in the inflammatory responses to pathogens and B- and T-cell differentiation. The overlap between taurine-specific CNVRs and QTL regions associated with trypanotolerant response and tick-resistance was relatively low, suggesting that the mechanisms underlying such traits may not be determined by CNV alterations. However, four taurine-specific CNVRs overlapped with QTL regions associated with both traits on BTA23, therefore suggesting that CNV alterations in major histocompatibility complex (MHC) genes can partially explain the existence of genetic mechanisms shared between trypanotolerance and tick resistance in cattle. This research contributes to the understanding of the genomic features of West African taurine cattle.

Brain and pituitary-adrenal lesions of Trypanosoma brucei brucei and Trypanosoma congolense infections in the West African Dwarf rams: Is trypanotolerance overrated?

Trypanosomosis of the West African Dwarf (WAD) sheep is often neglected due to emphasis on trypanotolerance. Nevertheless, significant pathological changes may occur in tissues of infected WAD sheep. The purpose of this study was to evaluate the brain, pituitary, and adrenal lesions of Trypanosoma brucei brucei (Tbb) and Trypanosoma congolense (Tc) infections in WAD rams. Fifteen WAD rams were infected intraperitoneally with Tbb or Tc (10⁶ trypanosomes/animal) or were uninfected controls (5 rams per group). Adrenocorticotrophic hormone (ACTH) and cortisol were assayed in serum by enzyme immunoassay technique. The brain, pituitary, and adrenal glands were processed for histopathology. Serum ACTH levels of infected rams were significantly (P < .05) higher than that of controls on days 14 and 70 post infection (PI). Serum cortisol levels of infected rams were significantly (P < .05) higher than that of controls only on day 14 PI. Mortality was 60% in Tbb- and 40% in Tc-infected rams. The brain of the infected groups showed chromatolysis of cortical neurons and Purkinje cells with severe encephalitis. Degenerative, necrotic, and inflammatory changes were seen in the pituitary and adrenal glands of the infected rams. Adrenal corticomedullary ratio was significantly (P < .05) higher in Tc-infected rams than controls. Based on the high mortality levels, likely due to severe encephalitis, the WAD sheep may not be regarded as trypanotolerant.

Breeding of African sheep reared under low-input/output smallholder production systems for trypanotolerance

Trypanosomiasis is a disease caused by unicellular protozoan parasites. Small ruminants succumb to trypanosomiasis in areas of high tsetse fly challenge, resulting in serious economic loss often to farmers in low-input smallholder systems. At present, trypanosomiasis is treated with trypanocidal drugs, but access to these can be limited, and increasing parasite resistance raises questions about their efficacy. The development of trypanotolerance in small ruminant flocks through targeted breeding strategies is considered a sustainable and economical option for controlling African trypanosomiasis. Recently, quantitative trait loci (QTLs) associated with trypanotolerance traits in sheep have been reported. The results of these studies form the basis for more studies to identify QTLs associated with trypanosomiasis resistance, particularly in African livestock species. For example, signatures of positive selection for trypanotolerance have been identified using genome-wide single-nucleotide polymorphism data. However, there are several challenges in performing genetic analyses using data from low-input smallholder systems, including a lack of recorded pedigree and production records and the need for large sample sizes when flock sizes are often fewer than 50 animals. Breeding strategies to improve trypanotolerance should also preserve existing genetic diversity as well as minimize excessive genetic introgression by trypanosusceptible breeds. This review discusses the possibilities of breeding for trypanosome tolerance/resistance in low-input/low-output small ruminant production systems. Potential challenges are outlined, and potential available genetic resources are described as a foundation for future work.

Ancient autozygous segments subject to positive selection suggest adaptive immune responses in West African cattle

Small-sized and trypanotolerant West African taurine (Bos taurus) cattle are a unique case of human-mediated process of adaptation to a challenging environment. Extensive gene flow with Sahelian zebu (B. indicus), bigger and with some resistance to tick attack, occurred for centuries and allowed the apparition of stable crossbred populations (sanga) having intermediate characteristics. Up to 237 individuals belonging to 10 different taurine, zebu and sanga cattle populations sampled in Benin, Burkina Faso and Niger were typed using the BovineHD BeadChip of Illumina to identify signatures of selection, assessed using three different Extended-Haplotype-Homozygosity-based statistics, overlapping with ancient, originated 1024 or 2048 generations ago, Homozygosity-By-Descent segments in the cattle genome. Candidate genomic regions were defined ensuring their importance within cattle type and using zebu as reference. Functional annotation analysis identified four statistically significant Annotation Clusters in taurine cattle (from ACt1 to ACt4), one (ACs1) in sanga, and another (ACz1) in zebu cattle, fitting well with expectations. ACt1 included genes primarily associated with innate immunity; ACt2 involved bitter taste receptor genes of importance to adaptation to changing environments; ACt3 included 68 genes coding ATP-binding proteins, some of them located on trypanotolerance-related QTL regions, that can partially underlie immune response and the additive mechanism of trypanotolerance; ACt4 was associated with growth and small size (NPPC gene); ACs1 included genes involved in immune response; and ACz1 is related with ectoparasite resistance. Our results provide a new set of genomic areas and candidate genes giving new insights on the genomic impact of adaptation in West African cattle.

Search for Selection Signatures Related to Trypanosomosis Tolerance in African Goats

Livestock is heavily affected by trypanosomosis in Africa. Through strong selective pressure, several African indigenous breeds of cattle and small ruminants have acquired varying degrees of tolerance against this disease. In this study, we combined LFMM and PCAdapt for analyzing two datasets of goats from West-Central Africa and East Africa, respectively, both comprising breeds with different assumed levels of trypanotolerance. The objectives were (i) to identify molecular signatures of selection related to trypanotolerance; and (ii) to guide an optimal sampling for subsequent studies. From 33 identified signatures, 18 had been detected previously in the literature as being mainly associated with climatic adaptations. The most plausible signatures of trypanotolerance indicate the genes DIS3L2, COPS7B, PD5A, UBE2K, and UBR1. The last gene is of particular interest since previous literature has already identified E3-ubiquitin ligases as playing a decisive role in the immune response. For following-up on these findings, the West-Central African area appears particularly relevant because of (i) a clear parasitic load gradient related to a humidity gradient, and (ii) still restricted admixture levels between goat breeds. This study illustrates the importance of protecting local breeds, which have retained unique allelic combinations conferring their remarkable adaptations.

Epidemiology of Trypanosomiasis in Wildlife-Implications for Humans at the Wildlife Interface in Africa

While both human and animal trypanosomiasis continue to present as major human and animal public health constraints globally, detailed analyses of trypanosome wildlife reservoir hosts remain sparse. African animal trypanosomiasis (AAT) affects both livestock and wildlife carrying a significant risk of spillover and cross-transmission of species and strains between populations. Increased human activity together with pressure on land resources is increasing wildlife–livestock–human infections. Increasing proximity between human settlements and grazing lands to wildlife reserves and game parks only serves to exacerbate zoonotic risk. Communities living and maintaining livestock on the fringes of wildlife-rich ecosystems require to have in place methods of vector control for prevention of AAT transmission and for the treatment of their livestock. Major Trypanosoma spp. include Trypanosoma brucei rhodesiense, Trypanosoma brucei gambiense, and Trypanosoma cruzi, pathogenic for humans, and Trypanosoma vivax, Trypanosoma congolense, Trypanosoma evansi, Trypanosoma brucei brucei, Trypanosoma dionisii, Trypanosoma thomasbancrofti, Trypanosma elephantis, Trypanosoma vegrandis, Trypanosoma copemani, Trypanosoma irwini, Trypanosoma copemani, Trypanosoma gilletti, Trypanosoma theileri, Trypanosoma godfreyi, Trypansoma simiae, and Trypanosoma (Megatrypanum) pestanai. Wildlife hosts for the trypansomatidae include subfamilies of Bovinae, Suidae, Pantherinae, Equidae, Alcephinae, Cercopithecinae, Crocodilinae, Pteropodidae, Peramelidae, Sigmodontidae, and Meliphagidae. Wildlife species are generally considered tolerant to trypanosome infection following centuries of coexistence of vectors and wildlife hosts. Tolerance is influenced by age, sex, species, and physiological condition and parasite challenge. Cyclic transmission through Glossina species occurs for T. congolense, T. simiae, T. vivax, T. brucei, and T. b. rhodesiense, T. b. gambiense, and within Reduviid bugs for T. cruzi. T. evansi is mechanically transmitted, and T. vixax is also commonly transmitted by biting flies including tsetse. Wildlife animal species serve as long-term reservoirs of infection, but the delicate acquired balance between trypanotolerance and trypanosome challenge can be disrupted by an increase in challenge and/or the introduction of new more virulent species into the ecosystem. There is a need to protect wildlife, animal, and human populations from the infectious consequences of encroachment to preserve and protect these populations. In this review, we explore the ecology and epidemiology of Trypanosoma spp. in wildlife.

Functional characterization of Copy Number Variations regions in Djallonké sheep

A total of 184 Djallonké (West African Dwarf) sheep of Burkina Faso were analysed for Copy Number Variations (CNV) using Ovine 50 K SNP BeadChip genotyping data and two different CNV calling platforms: PennCNV and QuantiSNP. Analyses allowed to identify a total of 63 candidate Copy Number Variations Regions (CNVR) on 11 different ovine chromosomes covering about 82.5 Mb of the sheep genome. Gene-annotation enrichment analysis allowed to identify a total of 751 potential candidate ovine genes located in the candidate CNVR bounds. Functional annotation allowed to identify five statistically significant Functional Clusters (FC; enrichment factor > 1.3) involving 61 candidate genes. All genes forming significantly enriched FC were located on ovine chromosome (OAR) 21. FC1 (22 genes including PAG4 and PAG6) and FC5 (three genes: CTSC, CTSW and CTSF), coding proteases (peptidases and cathepsins, respectively), were involved in reproductive performance and modulation of gestation. Both FC3 and FC4 were involved in inflammatory and immunologic response through coding serum amyloid A and B-box-type zinc finger proteins, respectively. Finally, FC2 consisted of 27 genes (including OR10G6 and OR8B8) involved in olfactory receptor activity, key for animals adapting to new food resources. CNVR identified on at least 15% of individuals were considered CNVR hotspots and further overlapped with previously reported quantitative trait loci (QTL). CNVR hotspots spanning genes putatively involved with lipid metabolism (SKP1, TCF7, JADE2, UBE2B and SAR1B) and differential expression in mammary gland (SEC24A and CDKN2AIPNL) on OAR5 and dairy traits (CCDC198 and SLC35F4) on OAR7 overlapped with QTL associated with lipid metabolism, milk protein yield and milk fat percentage. Information obtained from local sheep populations naturally adapted to harsh environments contributes to increase our understanding of the genomic importance of CNV.

Haemoparasites-Challenging and Wasting Infections in Small Ruminants: A Review

Haemoparasites include bacteria, mycoplasma, protozoa and flagellates inhabiting the bloodstream of living hosts. These infections occur worldwide and are transmitted by vectors, especially ticks and tsetse flies. Geographical distribution varies due to movements of animals and vectors between geographical areas, and even between countries and continents. These changes may be caused by climate change, directly and indirectly, and have a huge effect on the epidemiology of these microbes. Active and ongoing surveillance is necessary to obtain reliable maps concerning the distribution of these infections in order to do proper risk assessment and efficient prophylactic treatment. Genera Anaplasma, Ehrlichia, Mycoplasma, Babesia, Theileria and Trypanosoma include common haemoparasite species in small ruminants causing a variety of clinical manifestations from high fatality rates to more subclinical infections, depending on the species or strain involved. These infections may also cause ill-thift or long-lasting wasting conditions. Life-long infections are a common feature of these pathogens. The present review will focus on haemoparasites in small ruminants, especially related to challenging and wasting infections.

Ancient Homozygosity Segments in West African Djallonké Sheep Inform on the Genomic Impact of Livestock Adaptation to the Environment

A sample of Burkina Faso Djallonké (West African Dwarf) sheep was analyzed to identify stretches of homozygous segments (runs of homozygosity; ROH) overlapping with ancient homozygosity-by-descent (HBD) segments. HBD segments were considered ancient if they were likely to be inherited from ancestors living from 1024 to 2048 generations ago, roughly coinciding with the time in which sheep entered into West Africa. It is hypothesized that such homozygous segments can inform on the effect of the sheep genome of human-mediated selection for adaptation to this harsh environment. PLINK analyses allowed to identify a total of 510 ROH segments in 127 different individuals that could be summarized into 124 different ROH. A total of 32,968 HBD segments were identified on 119 individuals using the software ZooRoH. HBD segments inherited from ancestors living 1024 and 2048 generations ago were identified on 61 individuals. The overlap between consensus ROH identified using PLINK and HBD fragments putatively assigned to generations 1024 and 2048 gave 108 genomic areas located on 17 different ovine chromosomes which were considered candidate regions for gene-annotation enrichment analyses. Functional annotation allowed to identify six statistically significant functional clusters involving 50 candidate genes. Cluster 1 was involved in homeostasis and coagulation; functional clusters 2, 3, and 6 were associated to innate immunity, defense against infections, and white blood cells proliferation and migration, respectively; cluster 4 was involved in parasite resistance; and functional cluster 5, formed by 20 genes, was involved in response to stress. The current analysis confirms the importance of genomic areas associated to immunity, disease resistance, and response to stress for adaptation of sheep to the challenging environment of humid Sub-Saharan West Africa.

The continental atlas of tsetse and African animal trypanosomosis in Nigeria

Tsetse-transmitted trypanosomosis remains a major animal health problem in Nigeria, in a context where changes in land cover, climate and control interventions are modifying its epidemiological patterns. Evidence-based decision making for the progressive control of the disease requires spatially-explicit information on its occurrence and prevalence, as well as on the distribution and abundance of the tsetse vector. In the framework of the continental Atlas of tsetse and African animal trypanosomosis (AAT), a geo-referenced database was assembled for Nigeria, based on the systematic review of 133 scientific publications (period January 1990 - March 2019). The three main species of trypanosomes responsible for the disease (i.e. Trypanosoma vivax, T. congolense and T. brucei) were found to be widespread, thus posing a national-level problem. Their geographic distribution extends beyond the tsetse-infested belt, owing to the combined effect of animal movement and mechanical transmission by non-tsetse vectors. T. simiae, the major trypanosomal pathogen in pigs, T. godfreyi and the human-infective T. brucei gambiense were also reported. AAT was reported in a number of susceptible host species, including cattle, sheep, goats, pigs, camels, horses, donkeys and dogs, while no study on wildlife was identified. Estimates of prevalence are heavily influenced by the sensitivity of the diagnostic techniques, ranging from an average of 3.5% for blood films to 31.0% for molecular techniques. Two riverine tsetse species (i.e. Glossina palpalis palpalis and G. tachinoides) were found to have the broadest geographical range, as they were detected in all six geopolitical zones of Nigeria. By contrast, the distribution of savannah species (i.e. G. morsitans submorsitans and G. longipalpis) appears to be highly fragmented, and limited to protected areas. Very little information is available for forest species, with one single paper reporting on G. fusca congolensis and G. nigrofusca nigrofusca in the Niger Delta region. The future development of a national Atlas of tsetse and AAT, relying on both published and unpublished information, could improve on the present review and provide further epidemiological evidence for decision making.

Noninvasive Biological Samples to Detect and Diagnose Infections due to Trypanosomatidae Parasites: A Systematic Review and Meta-Analysis

Unicellular eukaryotes of the Trypanosomatidae family include human and animal pathogens that belong to the Trypanosoma and Leishmania genera. Diagnosis of the diseases they cause requires the sampling of body fluids (e.g., blood, lymph, peritoneal fluid, cerebrospinal fluid) or organ biopsies (e.g., bone marrow, spleen), which are mostly obtained through invasive methods. Body fluids or appendages can be alternatives to these invasive biopsies but appropriateness remains poorly studied. To further address this question, we perform a systematic review on clues evidencing the presence of parasites, genetic material, antibodies, and antigens in body secretions, appendages, or the organs or proximal tissues that produce these materials. Paper selection was based on searches in PubMed, Web of Science, WorldWideScience, SciELO, Embase, and Google. The information of each selected article (n = 333) was classified into different sections and data were extracted from 77 papers. The presence of Trypanosomatidae parasites has been tracked in most of organs or proximal tissues that produce body secretions or appendages, in naturally or experimentally infected hosts. The meta-analysis highlights the paucity of studies on human African trypanosomiasis and an absence on animal trypanosomiasis. Among the collected data high heterogeneity in terms of the I2 statistic (100%) is recorded. A high positivity is recorded for antibody and genetic material detection in urine of patients and dogs suffering leishmaniasis, and of antigens for leishmaniasis and Chagas disease. Data on conjunctival swabs can be analyzed with molecular methods solely for dogs suffering canine visceral leishmaniasis. Saliva and hair/bristles showed a pretty good positivity that support their potential to be used for leishmaniasis diagnosis. In conclusion, our study pinpoints significant gaps that need to be filled in order to properly address the interest of body secretion and hair or bristles for the diagnosis of infections caused by Leishmania and by other Trypanosomatidae parasites.

Genomic scan of selective sweeps in Djallonké (West African Dwarf) sheep shed light on adaptation to harsh environments

The Djallonké (West African Dwarf) sheep is a small-sized haired sheep resulting from a costly evolutionary process of natural adaptation to the harsh environment of West Africa including trypanosome challenge. However, genomic studies carried out in this sheep are scant. In this research, genomic data of 184 Djallonké sheep (and 12 Burkina-Sahel sheep as an outgroup) generated using medium-density SNP Chips were analyzed. Three different statistics (iHS, XP-EHH and nSL) were applied to identify candidate selection sweep regions spanning genes putatively associated with adaptation of sheep to the West African environment. A total of 207 candidate selection sweep regions were defined. Gene-annotation enrichment and functional annotation analyses allowed to identify three statistically significant functional clusters involving 12 candidate genes. Genes included in Functional Clusters associated to selection signatures were mainly related to metabolic response to stress, including regulation of oxidative and metabolic stress and thermotolerance. The bovine chromosomal areas carrying QTLs for cattle trypanotolerance were compared with the regions on which the orthologous functional candidate cattle genes were located. The importance of cattle BTA4 for trypanotolerant response might have been conserved between species. The current research provides new insights on the genomic basis for adaptation and highlights the importance of obtaining information from non-cosmopolite livestock populations managed in harsh environments.

Some Biochemical Perturbations May Modify the Understanding of Trypanotolerance in the West African Dwarf Sheep Infected With Trypanosoma brucei brucei and Trypanosoma congolense

Trypanosomes are single-celled protozoa that cause severe diseases in both humans and livestock in sub-Saharan African countries. The disease in the West African Dwarf (WAD) sheep is often neglected due to the issue of trypanotolerance. The current study is aimed to evaluate some biochemical changes in this breed that may modify the understanding of trypanotolerance. Fifteen WAD sheep were assigned into 3 groups (A, B, and C). Baseline (day 0) values of the parameters assayed were obtained before groups A and B were infected with Trypanosoma brucei brucei and Trypanosoma congolense, respectively, by intraperitoneal inoculation with 106 trypanosomes per animal. Standard procedures using Quimica Clinica Applicada (Spain) and Randox (UK) test kits were used to evaluate serum levels of AST, ALT, ALP, total protein, albumin, total cholesterol, urea, and creatinine on days 0, 14, 28, 42, 56, and 70 post infection. The infections caused sustained pyrexia, hypoproteinaemia, hypocholesterolaemia, weight loss, hepatitis, and mortalities although parasitaemia was greatly controlled especially in the T congolense infected rams. The findings suggest that the WAD rams are not just passive reservoirs of trypanosomes for human and animal infections, but experience active host-parasite interactions with huge price for resilience, biochemically.

Analysis of pooled genome sequences from Djallonke and Sahelian sheep of Ghana reveals co-localisation of regions of reduced heterozygosity with candidate genes for disease resistance and adaptation to a tropical environment

BACKGROUND

The Djallonke sheep is well adapted to harsh environmental conditions, and is relatively resistant to Haemonchosis and resilient to animal trypanosomiasis. The larger Sahelian sheep, which cohabit the same region, is less well adapted to these disease challenges. Haemonchosis and Trypanosomiasis collectively cost the worldwide animal industry billions of dollars in production losses annually.

RESULTS

Here, we separately sequenced and then pooled according to breed the genomes from five unrelated individuals from each of the Djallonke and Sahelian sheep breeds (sourced from Ghana), at greater than 22-fold combined coverage for each breed. A total of approximately 404 million (97%) and 343 million (97%) sequence reads from the Djallonke and Sahelian breeds respectively, were successfully mapped to the sheep reference genome Oar v3.1. We identified approximately 11.1 million and 10.9 million single nucleotide polymorphisms (SNPs) in the Djallonke and Sahelian breeds, with approximately 15 and 16% respectively of these not previously reported in sheep. Multiple regions of reduced heterozygosity were also found; 70 co-localised within genomic regions harbouring genes that mediate disease resistance, immune response and adaptation in sheep or cattle. Thirty- three of the regions of reduced heterozygosity co-localised with previously reported genes for resistance to haemonchosis and trypanosomiasis.

CONCLUSIONS

Our analyses suggest that these regions of reduced heterozygosity may be signatures of selection for these economically important diseases.

Phenotypic resistance of indigenous goat breeds to infection with Haemonchus contortus in northwestern Nigeria

Two studies at the National Animal Production Research Institute (NAPRI), Zaria, Nigeria, compared Red Sokoto (RS), Sahelian (SG), and West African Dwarf (WAD) goats after experimental or natural infection with Haemonchus contortus. In the first study, 20 RS, 17 SG, and 14 WAD kids were challenged at 6 months of age with 5000 L₃ larvae of H. contortus. Fecal egg counts (FEC), packed cell volumes (PCV), and body weights (BW) were recorded 0, 28, 35, and 42 days after infection. The FEC and PCV were affected only by time of measurement. In the second study, 322 RS and 97 SG kids were produced at NAPRI over 3 years, weaned at 4 to 6 months of age, dewormed, returned to contaminated pastures, and evaluated 28 and 35 days later. Effects of breed, year, breed × time interaction, and breed × year interaction were observed for PCV and BW; FEC was only affected by time of measurement, year and breed × year interaction. The FEC were larger and PCV were smaller on day 35 compared to day 28 and in year 2 compared to years 1 and 3. The SG kids were notably smaller than RS kids in year 2, with higher FEC and lower PCV, but FEC were larger for RS kids in years 1 and 3. Differences in parasite resistance among these Nigerian goat breeds were therefore small and likely reflected underlying differences in growth, development, and disease history.

Leveraging Available Resources and Stakeholder Involvement for Improved Productivity of African Livestock in the Era of Genomic Breeding

The African continent is home to diverse populations of livestock breeds adapted to harsh environmental conditions with more than 70% under traditional systems of management. Animal productivity is less than optimal in most cases and is faced with numerous challenges including limited access to adequate nutrition and disease management, poor institutional capacities and lack of adequate government policies and funding to develop the livestock sector. Africa is home to about 1.3 billion people and with increasing demand for animal proteins by an ever growing human population, the current state of livestock productivity creates a significant yield gap for animal products. Although a greater section of the population, especially those living in rural areas depend largely on livestock for their livelihoods; the potential of the sector remains underutilized and therefore unable to contribute significantly to economic development and social wellbeing of the people. With current advances in livestock management practices, breeding technologies and health management, and with inclusion of all stakeholders, African livestock populations can be sustainably developed to close the animal protein gap that exists in the continent. In particular, advances in gene technologies, and application of genomic breeding in many Western countries has resulted in tremendous gains in traits like milk production with the potential that, implementation of genomic selection and other improved practices (nutrition, healthcare, etc.) can lead to rapid improvement in traits of economic importance in African livestock populations. The African livestock populations in the context of this review are limited to cattle, goat, pig, poultry, and sheep, which are mainly exploited for meat, milk, and eggs. This review examines the current state of livestock productivity in Africa, the main challenges faced by the sector, the role of various stakeholders and discusses in-depth strategies that can enable the application of genomic technologies for rapid improvement of livestock traits of economic importance.

Livestock Genomics for Developing Countries - African Examples in Practice

African livestock breeds are numerous and diverse, and typically well adapted to the harsh environment conditions under which they perform. They have been used over centuries to provide livelihoods as well as food and nutritional security. However, African livestock systems are dynamic, with many small- and medium-scale systems transforming, to varying degrees, to become more profitable. In these systems the women and men livestock keepers are often seeking new livestock breeds or genotypes - typically those that increase household income through having enhanced productivity in comparison to traditional breeds while maintaining adaptedness. In recent years genomic approaches have started to be utilized in the identification and development of such breeds, and in this article we describe a number of examples to this end from sub-Saharan Africa. These comprise case studies on: (a) dairy cattle in Kenya and Senegal, as well as sheep in Ethiopia, where genomic approaches aided the identification of the most appropriate breed-type for the local productions systems; (b) a cross-breeding program for dairy cattle in East Africa incorporating genomic selection as well as other applications of genomics; (c) ongoing work toward creating a new cattle breed for East Africa that is both productive and resistant to trypanosomiasis; and (d) the use of African cattle as resource populations to identify genomic variants of economic or ecological significance, including a specific case where the discovery data was from a community based breeding program for small ruminants in Ethiopia. Lessons learnt from the various case studies are highlighted, and the concluding section of the paper gives recommendations for African livestock systems to increasingly capitalize on genomic technologies.

Combatting African Animal Trypanosomiasis (AAT) in livestock: The potential role of trypanotolerance

African Animal Trypanosomiasis (AAT) is endemic in at least 37 of the 54 countries in Africa. It is estimated to cause direct and indirect losses to the livestock production industry in excess of US$ 4.5 billion per annum. A century of intervention has yielded limited success, owing largely to the extraordinary complexity of the host-parasite interaction. Trypanotolerance, which refers to the inherent ability of some African livestock breeds, notably Djallonke sheep, N'Dama cattle and West African Dwarf goats, to withstand a trypanosomiasis challenge and still remain productive without any form of therapy, is an economically sustainable option for combatting this disease. Yet trypanotolerance has not been adequately exploited in the fight against AAT. In this review, we describe new insights into the genetic basis of trypanotolerance and discuss the potential of exploring this phenomenon as an integral part of the solution for AAT, particularly, in the context of African animal production systems.

Long-term spatiotemporal stability and dynamic changes in the haemoparasite community of spiny mice (Acomys dimidiatus) in four montane wadis in the St. Katherine Protectorate, Sinai, Egypt

BACKGROUND

Long-term field studies of parasite communities are rare but provide a powerful insight into the ecological processes shaping host-parasite interactions. The aim of our study was to monitor long-term trends in the haemoparasite communities of spiny mice (Acomys dimidiatus) and to identify the principal factors responsible for changes over a 12 year period.

METHODS

To this end we sampled four semi-isolated populations of mice (n = 835) in 2000, 2004, 2008 and 2012 in four dry montane valleys (wadis) located in the Sinai Massif, Egypt.

RESULTS

Overall 76.2 % of spiny mice carried at least one of the five haemoparasite genera (Babesia, Bartonella, Haemobartonella, Hepatozoon, Trypanosoma) recorded in the study. Prevalence of haemoparasites varied significantly between the sites with the highest overall prevalence in Wadi Tlah and the lowest in W. El Arbaein, and this changed significantly with time. In the first two surveys there was little change in prevalence, but by 2008, when the first signs of a deepening drought in the region had become apparent, prevalence began to drift downwards, and by 2012 prevalence had fallen to the lowest values recorded from all four sites over the entire 12-year period. The overall mean species richness was 1.2 ± 0.03, which peaked in 2004 and then dropped by more than 50 % by 2012. Species richness was highest among mice from Wadi Tlah and peaked in age class 2 mice (young adults). Site was the most significant factor affecting the prevalence of individual parasite species, with Trypanosoma acomys and Hepatozoon sp. occurring mainly in two wadis (W. Tlah & W. Gharaba). In four of the five genera recorded in the study we observed a significant drop in prevalence or/and abundance since 2004, the exception being Hepatozoon sp.

CONCLUSIONS

During the 12-year-long period of study in the Sinai, we observed dynamic changes and possibly even cycles of prevalence and abundance of infections which differed depending on parasite species. Although the exact reasons cannot be identified at this time, we hypothesize that the effects of a 15-year-long scarcity of rainfall in the local environment and a fall in host densities over the period of study may have been responsible for a drop in transmission rates, possibly by a negative impact on vector survival.

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.

Long-term spatiotemporal stability and dynamic changes in the haemoparasite community of bank voles (Myodes glareolus) in NE Poland

Long-term field studies on parasite communities are rare but provide a powerful insight into the ecological and evolutionary processes shaping host-parasite interactions. The aim of our study was to identify the principal factors regulating long-term trends in the haemoparasite communities of bank voles, and to this end, we sampled three semi-isolated populations of bank voles (n = 880) in 1999, 2002, 2006 and 2010 in the Mazury lake district region of NE Poland. Overall, 90.8 % of the bank voles harboured at least one of the species of haemoparasites studied. Whilst overall prevalence (all species combined) did not vary significantly between the surveys, different temporal changes were detected among voles in each of the three sites. In voles from Urwitałt, prevalence increased consistently with successive surveys, whereas in Tałty, the peak years were 2002 and 2006, and in Pilchy, prevalence oscillated without a clear pattern. Across the study, bank voles harboured a mean of 1.75 ± 0.034 haemoparasite species, and species richness remained stable with no significant between-year fluctuations or trends. However, each of the five constituent species/genera showed a different pattern of spatio-temporal changes. The overall prevalence of Babesia microti was 4.9 %, but this varied significantly between years peaking in 2006 and declining again by 2010. For Bartonella spp., overall prevalence was 38.7 %, and this varied with year of study, but the temporal pattern of changes differed among the three sites. The overall prevalence of Haemobartonella (Mycoplasma) was 68.3 % with an increase in prevalence with year of study in all three sites. Hepatozoon erhardovae had an overall prevalence of 46.8 % but showed a marked reduction with each successive year of the study, and this was consistent in all three sites. The overall prevalence of Trypanosoma evotomys was 15.4 % varying significantly between sites, but showing temporal stability. While overall prevalence of all haemoparasites combined and species richness remained stable over the period of study, among the five haemoparasites, the pattern of spatiotemporal changes in prevalence and abundance of infections differed depending on parasite species. For some genera, host age was shown to play an important role, but a significant effect of host sex was found only for Haemobartonella spp.

Natural selection on individual variation in tolerance of gastrointestinal nematode infection

A 25-year study of wild sheep shows that individuals vary in how quickly they lose weight as parasite infections increase, and that those who lose the least weight when heavily infected produce more offspring.

Hosts may mitigate the impact of parasites by two broad strategies: resistance, which limits parasite burden, and tolerance, which limits the fitness or health cost of increasing parasite burden. The degree and causes of variation in both resistance and tolerance are expected to influence host–parasite evolutionary and epidemiological dynamics and inform disease management, yet very little empirical work has addressed tolerance in wild vertebrates. Here, we applied random regression models to longitudinal data from an unmanaged population of Soay sheep to estimate individual tolerance, defined as the rate of decline in body weight with increasing burden of highly prevalent gastrointestinal nematode parasites. On average, individuals lost weight as parasite burden increased, but whereas some lost weight slowly as burden increased (exhibiting high tolerance), other individuals lost weight significantly more rapidly (exhibiting low tolerance). We then investigated associations between tolerance and fitness using selection gradients that accounted for selection on correlated traits, including body weight. We found evidence for positive phenotypic selection on tolerance: on average, individuals who lost weight more slowly with increasing parasite burden had higher lifetime breeding success. This variation did not have an additive genetic basis. These results reveal that selection on tolerance operates under natural conditions. They also support theoretical predictions for the erosion of additive genetic variance of traits under strong directional selection and fixation of genes conferring tolerance. Our findings provide the first evidence of selection on individual tolerance of infection in animals and suggest practical applications in animal and human disease management in the face of highly prevalent parasites.

Animals can defend themselves against parasites through either resistance (reducing parasite numbers, for example, by killing them) or tolerance (maintaining health as infections levels increase, for example, by repairing damage). Resistance has been well-studied in wild animals, but tolerance has been less so. We analysed data on body weight collected over 25 years on a natural population of Soay sheep, infected with parasitic gut worms. As parasite burden increased, sheep lost weight. Crucially, there was variation among individuals: some lost weight rapidly with increasing infections (i.e., showed “low tolerance”), whereas others lost weight slowly (i.e., showed “high tolerance”). The least tolerant individuals lost 4.5 kg of body weight across the range of parasite burdens that we saw, whereas the most tolerant lost only around 0.36 kg. However, variation in tolerance did not have a heritable genetic basis, so that although tolerance varied between individuals, this was not due to genetic differences. Further analysis revealed that there was natural selection on tolerance. Individuals who were more tolerant of infection produced more offspring over the course of their lives. This study shows that natural selection can act upon resistance and tolerance simultaneously in nature, a result that has implications for both human health and livestock management.

An analysis of the ruminal bacterial microbiota in West African Dwarf sheep fed grass- and tree-based diets

AIMS

To measure the impact of supplementing a forage diet with tree-based browse on the ruminal bacterial communities of Nigerian West African Dwarf (WAD) sheep.

METHODS AND RESULTS

Fifteen WAD sheep were fed a control diet of forage (Panicum maximum), with 12 animals shifted in groups of three to one of four browse-supplemented diets (Albizia saman, Bridelia micrantha, Ficus sur, or Gmelina arborea). These browse plants were shown in a concurrent but separate study to be reasonably nutritious (based on chemical composition and fibre constituents) and nontoxic (based on tannin, phytate, saponin, alkaloid and oxalate levels). Rumen liquids and solids for DNA extraction were collected via intubation from two animals in each group before and after dietary shift. Bacterial 16S rRNA gene regions V6-V8 were sequenced by 454 pyrosequencing. All communities were highly diverse and dominated by the phyla Firmicutes, Bacteroidetes, Tenericutes, Actinobacteria and Proteobacteria. All communities shared members of the genera Butryivibrio, Prevotella and Ruminococcus. Our analysis defined a core sets of bacteria shared by all animals, forage-fed animals and browse-fed animals. Community structure shifted dramatically in animals fed A. saman or G. arborea.

CONCLUSIONS

The impact of tree-based browse on the ruminal bacterial community of Nigerian WAD sheep varies by browse species, likely due to differences in browse composition.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study describes the first neotropical small ruminant bacterial microbiome and supports diet supplementation with specific tree-based browse for WAD sheep.

Coxiella burnetii seroprevalence in small ruminants in The Gambia

Background

Q fever is a zoonosis caused by Coxiella burnetii, a Gram negative bacterium present worldwide. Small ruminants are considered the main reservoirs for infection of humans. This study aimed to estimate the extent of C. burnetii infection among sheep and goats in part of The Gambia.

Methodology/Principal Findings

This survey was carried out from March to May 2012 at two areas in The Gambia. The first area comprised a cluster of seven rural villages situated 5–15 km west of Farafenni as well as the local abattoir. A second sampling was done at the central abattoir in Abuko (30 km from the capital, Banjul) in the Western Region. Serum samples were obtained from 490 goats and 398 sheep. In addition, 67 milk samples were obtained from lactating dams. Sera were tested with a Q fever ELISA kit. C. burnetii DNA was extracted from milk samples and then detected using a specific quantitative multiplex PCR assay, targeting the IS1111a element. A multivariable mixed logistic regression model was used to examine the relationship between seropositivity and explanatory variables. An overall seroprevalence of 21.6% was found. Goats had a significantly higher seroprevalence than sheep, respectively 24.2% and 18.5%. Seropositive animals were significantly older than seronegative animals. Animals from the villages had a significantly lower seroprevalence than animals from the central abattoir (15.1% versus 29.1%). C. burnetii DNA was detected in 2 out of 67 milk samples, whereas 8 samples gave a doubtful result.

Conclusion/Significance

A substantial C. burnetii seroprevalence in sheep and goats in The Gambia was demonstrated. People living in close proximity to small ruminants are exposed to C. burnetii. Q fever should be considered as a possible cause of acute febrile illness in humans in The Gambia. Future studies should include a simultaneous assessment of veterinary and human serology, and include aetiology of febrile illness in local clinics.

Traditional breeding objectives and practices of goat, sheep and cattle smallholders in The Gambia and implications in relation to the design of breeding interventions

This paper describes the traditional breeding objectives and practices of West African Dwarf goat, Djallonke sheep, and N'dama cattle keepers in The Gambia and discusses the implications of these on the design of breeding-related interventions to improve livestock productivity. Data were collected via surveys implemented within three study sites in The Gambia, where traditional mixed crop-livestock smallholder farming predominates. The surveys comprised a participatory rural appraisal conducted in nine communities and a household questionnaire targeting 238 households. Livestock-keeping households were classified as 'poorer' or 'wealthier' based on the number of cattle owned. The most important objectives for keeping all species of livestock for the poorer groups (0 to 10 cattle) was 'savings and insurance', followed by 'income' and 'ceremonial/dowry' for the small ruminants and 'manure' and 'draught' for both cows and bulls. In contrast, for the wealthier group (more than 10 cattle), savings and insurance was the fourth to seventh ranked production objective (depending on species), with the most important production objectives being ceremonial/dowry for goats, income for sheep and manure for cows and bulls. An analysis of breeding practices indicated that breeding animals are selected on criteria which partially align to the breeding objectives, animals are rarely purchased for the purpose of breed improvement, knowledge of the cause and consequence of inbreeding is low and breeding decision makers may not necessarily be the livestock owner, particularly if the livestock owner is a women. Given this, it is suggested that capacity building on breeding-related issues, particularly in relation to the selection of breeding animals and specifically targeted at the different socioeconomic groups of livestock keepers, may be an appropriate, effective and relatively low-cost breeding intervention.

Ascertaining gene flow patterns in livestock populations of developing countries: a case study in Burkina Faso goat

Background

Introgression of Sahel livestock genes southwards in West Africa may be favoured by human activity and the increase of the duration of the dry seasons since the 1970’s. The aim of this study is to assess the gene flow patterns in Burkina Faso goat and to ascertain the most likely factors influencing geographic patterns of genetic variation in the Burkina Faso goat population.

Results

A total of 520 goat were sampled in 23 different locations of Burkina Faso and genotyped for a set of 19 microsatellites. Data deposited in the Dryad repository: http://dx.doi.org/10.5061/dryad.41h46j37. Although overall differentiation is poor (F_ST = 0.067 ± 0.003), the goat population of Burkina Faso is far from being homogeneous. Barrier analysis pointed out the existence of: a) genetic discontinuities in the Central and Southeast Burkina Faso; and b) genetic differences within the goat sampled in the Sahel or the Sudan areas of Burkina Faso. Principal component analysis and admixture proportion scores were computed for each population sampled and used to construct interpolation maps. Furthermore, Population Graph analysis revealed that the Sahel and the Sudan environmental areas of Burkina Faso were connected through a significant number of extended edges, which would be consistent with the hypothesis of long-distance dispersal. Genetic variation of Burkina Faso goat followed a geographic-related pattern. This pattern of variation is likely to be related to the presence of vectors of African animal trypanosomosis. Partial Mantel test identified the present Northern limit of trypanosome vectors as the most significant landscape boundary influencing the genetic variability of Burkina Faso goat (p = 0.008). The contribution of Sahel goat genes to the goat populations in the Northern and Eastern parts of the Sudan-Sahel area of Burkina Faso was substantial. The presence of perennial streams explains the existence of trypanosome vectors. The South half of the Nakambé river (Southern Ouagadougou) and the Mouhoun river loop determined, respectively, the Eastern and Northern limits for the expansion of Sahelian goat genes. Furthermore, results from partial Mantel test suggest that the introgression of Sahelian goat genes into Djallonké goat using human-influenced genetic corridors has a limited influence when compared to the biological boundary defined by the northern limits for the distribution of the tsetse fly. However, the genetic differences found between the goat sampled in Bobo Dioulasso and the other populations located in the Sudan area of Burkina Faso may be explained by the broad goat trade favoured by the main road of the country.

Conclusions

The current analysis clearly suggests that genetic variation in Burkina Faso goat: a) follows a North to South clinal; and b) is affected by the distribution of the tsetse fly that imposes a limit to the Sahelian goat expansion due to their trypanosusceptibility. Here we show how extensive surveys on livestock populations can be useful to indirectly assess the consequences of climate change and human action in developing countries.

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.