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.

Global distribution, host range and prevalence of Trypanosoma vivax: a systematic review and meta-analysis

BACKGROUND

Trypanosomosis caused by Trypanosoma vivax is one of the diseases threatening the health and productivity of livestock in Africa and Latin America. Trypanosoma vivax is mainly transmitted by tsetse flies; however, the parasite has also acquired the ability to be transmitted mechanically by hematophagous dipterans. Understanding its distribution, host range and prevalence is a key step in local and global efforts to control the disease.

METHODS

The study was conducted according to the methodological recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. A systematic literature search was conducted on three search engines, namely PubMed, Scopus and CAB Direct, to identify all publications reporting natural infection of T. vivax across the world. All the three search engines were screened using the search term Trypanosoma vivax without time and language restrictions. Publications on T. vivax that met our inclusion criteria were considered for systematic review and meta-analysis.

RESULT

The study provides a global database of T. vivax, consisting of 899 records from 245 peer-reviewed articles in 41 countries. A total of 232, 6277 tests were performed on 97 different mammalian hosts, including a wide range of wild animals. Natural infections of T. vivax were recorded in 39 different African and Latin American countries and 47 mammalian host species. All the 245 articles were included into the qualitative analysis, while information from 186 cross-sectional studies was used in the quantitative analysis mainly to estimate the pooled prevalence. Pooled prevalence estimates of T. vivax in domestic buffalo, cattle, dog, dromedary camel, equine, pig, small ruminant and wild animals were 30.6%, 6.4%, 2.6%, 8.4%, 3.7%, 5.5%, 3.8% and 12.9%, respectively. Stratified according to the diagnostic method, the highest pooled prevalences were found with serological techniques in domesticated buffalo (57.6%) followed by equine (50.0%) and wild animals (49.3%).

CONCLUSION

The study provides a comprehensive dataset on the geographical distribution and host range of T. vivax and demonstrates the potential of this parasite to invade other countries out of Africa and Latin America.

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.

A meta-analysis of the prevalence of African animal trypanosomiasis in Nigeria from 1960 to 2017

BACKGROUND

African animal trypanosomiasis is an economically significant disease that affects the livestock industry in Nigeria. It is caused by several parasites of the genus Trypanosoma. National estimates of the disease prevalence in livestock and tsetse flies are lacking, therefore a systematic review and meta-analysis were performed to understand the trend of the disease prevalence over the years.

METHODS

Publications were screened in Web of Science, Ovid MEDLINE, Global Health, EMBASE and PubMed databases. Using four-stage (identification, screening, eligibility and inclusion) process in the PRIMSA checklist, only studies that met the inclusion criteria for AAT and tsetse infections were analysed. Point estimates prevalence and subgroup analyses based on diagnostic techniques in livestock were evaluated at 95% confidence interval (CI).

RESULTS

A total of 74 eligible studies published between 1960 and 2017 were selected for meta-analysis. This covers the six geopolitical zones, involving a total of 53,924 animals. The overall prevalence of AAT was 16.1% (95% CI: 12.3-20.3%). Based on diagnostic techniques, the prevalence of AAT in cattle was highest in PCR followed by serology and microscopy while the highest prevalence in pigs was observed with serology. Out of 12,552 tsetse flies examined from 14 eligible studies, an overall prevalence of 17.3% (95% CI: 4.5-36.0%) and subgroup prevalence of 49.7% (95% CI: 30.7-68.8%), 11.5% (95% CI: 6.1-18.5) and 4.5% (95% CI: 1.8-8.8%) in G. morsitans, G. tachinoides and G. palpalis, respectively, were observed using the random effects-model.

CONCLUSIONS

The prevalence of trypanosomes in both vectors and animal hosts was high in Nigeria. Therefore, further research on risk factors, seasonal and transhumance effects, vectoral capacity and competence are warranted for an effective control of AAT in Nigeria.

Bovine and small ruminant African animal trypanosomiasis in Nigeria - A review

Despite extensive attempts over many decades to control African Animal Trypanosomiasis (AAT) across the tsetse fly belt of Nigeria, AAT persists as major animal health problem causing severe morbidity and mortality in livestock. The large agricultural losses in turn have severe adverse impacts on sustainable agricultural development. Despite this, in the past 50 years there have been no significant national control programs against AAT. This review explores the history of AAT control in Nigeria, examining the successes and failures in measures adopted in Nigeria to control AAT and the changing disease epidemiology.

Animal African Trypanosomiasis in Nigeria: A long way from elimination/eradication

Animal African Trypanosomiasis (AAT) is a disease of livestock that directly hinders livestock production and therefore impedes the socio-economic development of sub-Saharan Africa. The establishment of the Pan-African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC) was to enhance the goal of elimination and eradication of tsetse flies and AAT from endemic countries in Africa. In order to achieve AAT eradication, a five-step progressive control pathway (PCP) model has been proposed. The data presented in this report demonstrates that Nigeria is highly endemic of AAT and that it is yet to comprehensively approach the process of eradication as it is at the infancy stage of data gathering and processing. This review is thus presented to serve as a wake-up call to all relevant stakeholders to intensify efforts in approaching the painstaking process of AAT eradication in Nigeria.

Serum biochemical parameters and cytokine profiles associated with natural African trypanosome infections in cattle

Background

Animal African trypanosomiasis (AAT) greatly affects livestock production in sub-Saharan Africa. In Ghana prevalence of AAT is estimated to range between 5 and 50%. Studies have reported serum biochemical aberrations and variability in cytokine profiles in animals during infection. However, information regarding the biochemical parameters and cytokine profiles associated with natural infections are limited. This study was therefore aimed at investigating changes in the levels of serum biochemical parameters and inflammatory cytokines during a natural infection.

Methods

Nested internal transcribed spacer (ITS)-based PCR and sequencing were used to characterise trypanosome infection in cattle at two areas in Ghana (Adidome and Accra) of different endemicities. The cattle were sampled at four to five-week intervals over a period of six months. Levels of serum biochemical parameters, including creatinine, cholesterol, alkaline phosphatase (ALP), alanine aminotransferase (ALT), total bilirubin and total protein and cytokines (interleukin 10, interleukin 4, interleukin 12, interferon gamma and tumor necrosis factor alpha) were measured in serum samples and then compared between infected cattle and uninfected controls.

Results

The predominant trypanosome species detected in Accra (non-endemic) and Adidome (endemic) were Trypanosoma theileri and Trypanosoma vivax, respectively. Serum biochemical parameters were similar between infected and uninfected cattle in Accra. Infected cattle at Adidome however, had significantly higher levels of ALP, creatinine, total protein and total bilirubin (P < 0.05) and significantly lower levels of cholesterol (P < 0.05) at specific time points. At basal levels and during infection, significantly higher pro-inflammatory to anti-inflammatory (Th1/Th2) cytokine ratios were observed in cattle at Adidome compared to Accra (P < 0.05), indicating a shift towards Th1 immune response in Adidome. Levels of IL-10 were, however, significantly elevated in infected cattle in Accra (P < 0.05), suggesting high anti-inflammatory cytokine response in Accra.

Conclusion

These results suggests that cattle in an endemic area repeatedly infected with trypanosomes of different species or different antigenic types demonstrate high pro-inflammatory (Th1) immune response and biochemical alterations whereas cattle in a non-endemic area with predominantly chronic T. theileri infections demonstrate high anti-inflammatory response and no biochemical alterations.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2255-9) contains supplementary material, which is available to authorized users.

Genetic diversity among Trypanosoma vivax strains detected in naturally infected cattle in Nigeria based on ITS1 of rDNA and diagnostic antigen gene sequences

Trypanosoma vivax (sub-genus Duttonella) is largely responsible for non profitable livestock production in sub-Sahara Africa. In Nigeria, no study has addressed the molecular characteristic of T. vivax except Y486. Hence, we characterized and assessed the genetic diversity among T. vivax detected in naturally infected cattle in Nigeria using internal transcribed spacer 1 (ITS1) of ribosoma DNA (rDNA) and diagnostic antigen gene (DAG) sequences. The length of ITS1 and DAG sequences range from 215-220 to 257-338 bp, respectively and the mean G-C contents were 60 and 61.5 %. Homology search revealed 93-99 and 95-100 % homologies to T. vivax DAG and ITS1 sequences from GenBank. Aligned sequences revealed both ITS1 rDNA and DAG to be less polymorphic but DAG sequences of the Y486 strain and its clone showed marked variation from autochthonous strains. Phylogenetic analysis yielded tree that grouped T. vivax ITS1rDNA gene and DAG sequences into two main clades each. Considering the ITI1 rDNA sequences, clade A contained autochthonous T. vivax within which the South American sequences clustered, clade B contained the sequences of T. vivax from East Africa. Analysis of DAG revealed that the clade A contains autochthonous T. vivax sequences but clade B contained the Y486 and its clones. In conclusion, the diagnostic antigen gene sequences of the T. vivax detected in this study may have undergone considerable gene recombination through time and suggests that more than one strain of T. vivax exist among cattle population in Nigeria.

Comparative hematological analysis of Morada Nova and Santa Inês ewes in all reproductive stages

ABSTRACT: Hematologic analysis provides reliable information on the health status of animals. It is an important variable in the assessment of adaptive and productive capacity of breeds under unfavorable environmental conditions. It is an assessment that combined with other genetic and environmental factors and management can become useful for the future sustainability of mainstream agriculture in a hot environment. Adaptive capacity is affected by some factors such as breed, pregnancy and lactation. Therefore, hematological profile is an important indicator of animal health and production. The objective of this study was to perform the comparative hematological analysis of Santa Inês and Morada Nova breeds (native ewes from Brazil) in all different reproductive stages. Twenty Santa Ines and 20 Morada Nova sheep distributed in a completely randomized design in a split-plot arrangement over time were used. To obtain blood counts, blood samples were collected by jugular venipuncture every 14 days, always in the morning, before the animals were released into the pasture. The Morada Nova breed had higher hemoglobin and total leukocyte count than Santa Inês breed. Regarding the influence of pregnancy and puerperium on the eritrogram, there was an increment in red blood cell, hemoglobin and packed cell volume of both breeds in middle pregnancy. However, had a reduction in late pregnancy. There were a reestablishment of the blood cell counts during the puerperium period. It was verified an increase on neutrophil: lymphocyte ratio indicated that ewes in the late pregnancy, postpartum and puerperium were under stress conditions compared to others reproductive stages. The total plasma proteins also increased during this period to compensate for the high nutritional requirements of the fetus, and these levels remained high until the end of the puerperal phase, when the lambs were weaned. The pregnancy and puerperium influenced all erythrocyte indices and changed the total leukocyte count.

Association of SNP variants of MHC Class II DRB gene with thermo-physiological traits in tropical goats

Host defense in vertebrates depend on many secreted regulatory proteins such as major histocompatibility complex (MHC) class II which provide important regulatory and effector functions of T cells. Gene polymorphism in the second exon of Capra-DRB gene in three major Nigerian goat breeds [West African Dwarf (WAD), Red Sokoto (RS), and Sahel (SH)] was analyzed by restriction fragment length polymorphisms (RFLP). Four restriction enzymes, BsaHI, AluI, HaeIII, and SacII, were utilized. The association between the polymorphic sites and some heat tolerance traits were also investigated in a total of 70 WAD, 90 RS, and 50 SH goats. Fourteen different types of alleles identified in the Nigerian goats, four of which were found in the peptide coding region (A57G, Q89R, G104D, and T112I), indicate a high degree of polymorphism at the DRB locus in this species. An obvious excess (P < 0.01) of non-synonymous substitutions than synonymous (dN/dS) in this locus is a reflection of adaptive evolution and positive selection. The phylogenetic trees revealed largely species-wise clustering in DRB gene. BsaHI, AluI, HaeIII, and SacII genotype frequencies were in Hardy-Weinberg equilibrium (P > 0.05), except AluI in RS goats and HaeIII in WAD goats (P < 0.05). The expected heterozygosity (H), which is a measure of gene diversity in the goat populations, ranged from 0.16 to 0.50. Genotypes AA (BsaHI), GG, GC and CC (AluI) and GG, GA, AA (HaeIII) appeared better in terms of heat tolerance. The heat-tolerant ability of SH and RS goats to the hot and humid tropical environment of Nigeria seemed better than that of the WAD goats. Sex effect (P < 0.05) was mainly on pulse rate and heat stress index, while there were varying interaction effects on heat tolerance. Variation at the DRB locus may prove to be important in possible selection and breeding for genetic resistance to heat stress in the tropics.

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.

Field and experimental symptomless infections support wandering donkeys as healthy carriers of Trypanosoma vivax in the Brazilian Semiarid, a region of outbreaks of high mortality in cattle and sheep

Background

The Brazilian Semiarid is the home of the largest herd of donkeys in South America and of outbreaks of Trypanosoma vivax infection of high mortality in dairy cattle and sheep. For a comprehensive understanding of the underlying mechanisms of these outbreaks and epidemiological role of donkeys, we surveyed for T. vivax in wandering donkeys and follow the experimental infection of donkeys and sheep with a highly virulent isolate from the Semiarid.

Methods

Blood samples from 180 randomly selected wandering donkeys from the Brazilian Semiarid region were employed for PCV and parasitemia assessments and tested using the T. vivax-specific TviCATL-PCR assay. PCR-amplifed Cathepsin L (CATL) sequences were employed for genotyping and phylogenetic analysis. Four wandering donkeys were experimentally infected with a T. vivax isolate obtained during an outbreak of high mortality in the Semiarid; the control group consisted of two non-inoculated donkeys.

Results

We detected T. vivax in 30 of 180 wandering donkeys (16.6 %) using TviCATL-PCR. The prevalence was higher during the dry (15.5 %) than the wet season (1.1 %) and more females (23.1 %) than males (8.9 %) were infected. All the PCR-positive donkeys lacked patent parasitemia and showed normal values of body condition score (BCS) and packed cell volume (PCV). To evaluate the probable tolerance of donkeys to T. vivax, we inoculated five donkeys with a highly virulent isolate (TviBrRp) from the Semiarid. All inoculated donkeys became PCR-positive, but their parasitemia was always subpatent. A control goat inoculated with TviBrRp showed increasing parasitemia concurrently with fever, declining PCV, tachycardia, mucous membrane pallor, enlarged lymph nodes and anorexia. None of these signs were observed in donkeys. However, T. vivax from wandering donkeys shared identical or highly similar genotypes (identified by Cathepsin L sequences) with isolates from cattle and sheep outbreaks of acute disease in the Semiarid.

Conclusions

This is the first report of T. vivax in donkeys in Brazil and, to our knowledge, the first experimental infection of donkeys with T. vivax. The symptomless field and experimental infections corroborated that donkeys are more tolerant to T. vivax than other livestock species as shown in African countries. Therefore, farmers, veterinaries and control programmes should be aware of healthy carrier donkeys as a possible source of T. vivax for susceptible livestock species in the Brazilian Semiarid.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-1169-7) contains supplementary material, which is available to authorized users.