Trypanosomosis in The Gambia: prevalence in working horses and donkeys detected by whole genome amplification and PCR, and evidence for interactions between trypanosome species

<p>Abstract</p> <p>Background</p> <p>The Gambia has an increasing population of <it>equidae </it>largely used for agriculture and transportation. A review of cases at The Gambian Horse and Donkey Trust (GHDT) indicated that a common reason for presentation is a poorly defined medical condition often attributed to trypanosomosis. There are few reports describing the prevalence or the range of clinical signs associated with infection with different species of trypanosomes in horses and donkeys, but given the importance of these animals, the role of trypanosomosis requires investigation.</p> <p>Results</p> <p>In total 241 animals from the Central River Division in The Gambia (183 horses and 58 donkeys) were screened using Whole Genome Amplification (WGA) followed by trypanosome species identification using polymerase chain reaction (PCR). The results indicated overall trypanosome prevalence of 91%; with an infection rate of 31% for <it>Trypanosoma congolense </it>Savannah, 87% for <it>Trypanosoma vivax </it>and 18% for <it>Trypanosoma brucei </it>sp. Multiple species were present in 43% of infections. Microscopy had a good specificity (100%) and positive predictive value (100%) for trypanosome detection, but the sensitivity (20%) and negative predictive value (10.5%) were low relative to PCR-based diagnosis.</p> <p>Infection with <it>T congolense </it>showed the greatest negative effect on packed cell volume (PCV), while infection with <it>T. brucei </it>sp also had a significant, although lesser, negative effect on PCV. In addition, cases positive by microscopy were associated with significantly lower PCV. However, concurrent infection with <it>T. vivax </it>appeared to cause less effect on PCV, compared to animals infected with <it>T. congolense </it>alone.</p> <p>Conclusion</p> <p>The prevalence of Trypanosomosis was high in both horses and donkeys. Infection with <it>T. congolense </it>appeared to have the greatest clinical significance, while <it>T. vivax </it>infection may be of limited clinical significance in this population. Indeed, there is evidence of <it>T. vivax </it>co-infection ameliorating the pathology caused by <it>T. congolense</it>. WGA and PCR allowed a more comprehensive analysis of field infections with the detection of infections below the threshold of microscopy, and provided indications of interactions between parasite species that would otherwise remain undetected. The study raises important questions about the epidemiology of trypanosome infection in relation to disease that require a full scale longitudinal analysis.</p