Detection of Trypanosoma evansi in camels using PCR and CATT/ T. evansi tests in Kenya

Abstract

Camel trypanosomosis (Surra) causes high morbidity and is an impediment to the camel husbandry in Kenya. The lack of a sensitive diagnostic test has hindered the collection of accurate epidemiological data and institution of control programmes. A cross-sectional study was conducted in three districts of Kenya to estimate the prevalence of Trypanosoma evansi ( T. evansi) and to compare four diagnostic tests: polymerase chain reaction (PCR), card agglutination test (CATT/ T. evansi), microhaematocrit centrifugation technique (MHCT) and mouse inoculation (MI). A total of 549 camels were randomly sampled. The overall prevalence of Surra was 5.3% using MHCT, 26.6% using PCR and 45.9% using CATT/ T.evansi. There was a significant difference ( P < 0.001) between PCR and CATT/ T.evansi test, MHCT and MI in detection of T. evansi. The prevalence of T. evansi was 39.8% in Samburu, 24.7% in Nanyuki and 14.4% in Isiolo districts using PCR. A male camel was 2.6 times more likely to be infected with T. evansi compared to a female camel (OR = 3.0% CI: 1.6, 4.1), while an adult camel was 2.2 times more likely to be infected compared to non-adults (OR = 2.2; 95% CI: 1.2, 5.0). There was a poor association between the presence of the published clinical signs and seropositivity ( κ = 0.12), PCR ( κ = 0.11) and MHCT ( κ = 0.05). However, there was a higher agreement between farmers’ classification of disease with the PCR test ( κ = 0.5, n = 61). The mean PCV varied with age, presence of infection, locality and gender, with the lowest mean PCV being recorded in MHCT-positive animals (20.97 ± 0.5) and from infected calves (19.5 ± 1.2). This study shows that PCR was more sensitive in detecting T. evansi than other tests used. Further, the prevalence of T. evansi in the camel herds sampled is higher than that previously reported in Kenya, and that the judgment by camel keepers may be a reliable “pen-side” diagnostic test for Surra. Considering the low sensitivity of parasitological techniques in detection of chronic T. evansi infection and high cost of PCR, development of a sensitive pen side diagnostic test, with a low cost is still a priority.