Endemic status of tick-borne infections and tick species diversity among transhumant zebu cattle in Karamoja Region, Uganda: Support for control approaches

Abstract

We conducted a study to investigate tick species diversity, seroprevalence of antibodies to Anaplasma marginale and Theileria parva, and the risk factors for these infections among cattle under a transhumant production system in Karamoja Region, Uganda, from November 2013 through January 2014. Twenty herds were randomly selected from 20 purposively-selected superherds. Semi-structured interviews and piling for annual proportion of tick-borne disease (TBD) cases in different age groups, with pastoralist groups, clinical examinations and field observations were employed to obtain information related to the epidemiology of TBDs. Ticks were collected and identified from whole body inspections of at least seven systematically selected cattle in each herd. Concurrently, serum was collected from 397 cattle. Antibodies to A. marginale were detected by MSP-5 competitive inhibition enzyme-linked immunosorbent assay, and to T. parva by indirect fluorescent antibody test. Clinical examinations and informant interviews showed that TBDs affected all age groups of cattle. Tick species that have not been reported in recent studies from other parts of Uganda were collected, namely Amblyomma lepidum, Hyalomma truncatum, Amblyomma gemma, and Rhipicephalus pulchellus. Out of the 10,923 ticks collected, Rhipicephalus appendiculatus (54.4%) was the most abundant species followed by Rhipicephalus (Boophilus) decoloratus (17.7%), Amblyomma variegatum (12%) and A. lepidum (11.6%). Two-thirds of the sampled cattle had moderate (37.3%, 11-50 ticks) to abundant (28.6%, >50 ticks) numbers of ticks. Seroprevalence of A. marginale was high (86.6%, 95% confidence interval [CI] 80.8%-91.8%), while that of T. parva was low (14.6%, 95% CI 7.1%-22.4%). Cattle of 5-12months (18.3%, Odds ratio [OR]=4.1) and 13-24months (30.3%, OR=8.0) were more likely to be seropositive for T. parva than those >24months. For A. marginale, cattle of 13-24months (92.4%, OR=2.7) and >24months (89.7%, OR=2.0) were more likely to be seropositive than those 5-12months. There was a significant difference (p<0.001, OR=6.5) in the proportion of T. parva seropositive animals between Moroto (24.5%) and Kotido districts (4.8%), but not for A. marginale. In conclusion, the low seroprevalence for T. parva, possibly due to limited exposure in calves, may suggest a high likelihood of ECF in cattle. High seroprevalence for A. marginale suggests that a high proportion of cattle were exposed to infection. The findings provide knowledge of epidemiology of TBDs in Karamoja cattle and support for strategic control and improvement of cattle productivity.

Keywords: Anaplasma marginale; East Coast fever; Pastoralist; Seroprevalence; Theileria parva.