Abstract
Despite evidence of both human and animal Leptospira exposures in Uganda, the epidemiology of the disease is still not well-investigated. Contact with animals and their environments have been pointed out as potential source of infection with Leptospira species in humans; and cattle may be an important reservoir in Uganda. In this cross-sectional study, we estimated the prevalence of anti-Leptospira antibodies by the standard microscopic agglutination test (MAT); and associated risk factors among slaughtered cattle. We also compared the performance of the MAT used in this study against a lipL32 based real time PCR (qPCR) assay previously conducted on the kidneys and urine of the same slaughter cattle as tested in this reported study. Of 500 cattle sampled, 27.8% (95% CI 23.9–32.0) tested positive (titer ≥ 100) to at least one Leptospira serovar, with the majority of seropositive cattle reacting to serovars Tarassovi (sg Tarassovi) (11.6%), Sejroe (Sg Sejroe) (7.8%), and Australis (Sg Australis) (5.2%). Older animals had 2.8 times (95% CI 1.0–8.2, p-value 0.055) greater odds of being seropositive than younger ones (<1.5 years). The sensitivity and specificity of the MAT over the qPCR were 65.9% (95% CI 50.1–79.5) and 75.9% (95% CI 71.7–79.7), respectively; with a negative predictive value of 95.8% and positive predictive value of 20.9%. In conclusion, slaughter cattle in this study were significantly exposed to pathogenic Leptospira species of mainly the Tarassovi, Sejroe, and Australis serogroups, with seroprevalence being higher among older cattle. The high specificity and negative predictive value of MAT as used in this study when compared to the qPCR assay may imply a rather strong association between seronegativity and absence of renal Leptospira infection. However, MAT predictability for renal Leptospira infection may be interpreted cautiously since predictive values of diagnostic tests are dependent on prevalence.
Highlights
Leptospirosis is one of the most wide spread zoonotic bacterial diseases that is endemic in subtropical and tropical countries; accounting for a global annual incidence of 1.03 million human cases and 58,900 deaths [1]
Blood samples were collected from a total of 500 randomly selected slaughter cattle, following the same sampling strategy that Alinaitwe et al [11] used to cocurrently collect matching kidney and urine samples from the same cattle population tested in this study
Up to 8.4% of the slaughter cattle were reportedly sourced across the borders of Uganda, while the definite origin of up to 19.0% of the cattle could not be established due to insufficient accompanying documentation from their source markets
Summary
Leptospirosis is one of the most wide spread zoonotic bacterial diseases that is endemic in subtropical and tropical countries; accounting for a global annual incidence of 1.03 million human cases and 58,900 deaths [1]. Cattle have been reported to maintain serovars Hardjo, Sejroe and at times Pomona [3,4,5] Despite evidence of both human and animal leptospirosis in Uganda, the epidemiology of the disease is still not wellinvestigated. Dreyfus et al [10] demonstrated 35% prevalence of anti–Leptospira antibodies in health centre patients in Hoima, Uganda; with skinning of cattle during slaughter being significantly associated with the observed seropositivity. This further implicates cattle as potential sources of Leptospira infections to humans. In order to assess the usefulness of serological tests as tools for surveillance of leptospirosis in cattle herds, we compared the performance of MAT against a lipL32 based real time PCR (qPCR) assay conducted previously on the kidneys and urine of the same slaughter cattle tested in this study
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