Background: Surra, a vector borne disease caused by Trypanosoma (T.) evansi, affects the health, productivity and working capacity of camels. Since clinical signs are not pathognomonic, diagnosis must be confirmed by laboratory methods. This is a first study on the prevalence of surra in Cholistan Desert, Pakistan using a broad variety of diagnostic tests thereby emphasizing it as a risk for the dromedaries of Pakistan.
Methods: In a cross sectional study, 1005 dromedary camels from three districts in the Cholistan Desert were sampled to assess the prevalence of trypanosomosis due to T. evansi by means of parasitological (Giemsa stained thin smear), serological (formol gel test, CATT/T. evansi, ELISA/VSG RoTat 1.2, immune trypanolysis) and molecular tests (TBR1/2 PCR and RoTat 1.2 PCR). Kappa was calculated to assess the degree of agreement between different tests whereas chi-square test along with odds ratios and their 95% confidence intervals were used to study influence of breed, gender, age and locality on disease prevalence.
Results: Overall prevalence was 0.7% with Giemsa stained thin smears (GST), 40.1% with formol gel test (FGT), 47.7% with CATT/T. evansi, 44.2% with ELISA/VSG RoTat 1.2, 39.9 % with immune trypanolysis (TL), 31.9 % with TBR1/2 PCR and 30.5% with RoTat1.2 PCR. Based on these results, the Cholistan Desert appears to be a high risk area for surra. According to TL and TBR1/2 PCR, camels at Bahawalpur are approximately two times more likely to be infected than those in Bahawalnagar (OR = 1.8; 95% CI: 1.38-2.42) and Rahim Yar Khan (OR = 1.9; 95% CI: 1.30-2.75). Test agreement of TL was moderate with CATT/T. evansi (k = 0.43; 95% CI: 0.378-0.489) and ELISA/VSG RoTat 1.2 (k = 0.54; 95% CI: 0.489-0.594) and poor with the other tests. Test agreement between TBR1/2 PCR and RoTat1.2 PCR was almost perfect (k = 0.96; 95% CI: 0.950-0.984). We didn't find evidence for the presence of T. evansi type B in the studied population.
Conclusion: Our study supports using antibody detection tests, rather than parasitological and molecular examination, to assess surra prevalence in camels. It also calls for implementation of measures to control surra in the Cholistan Desert.