A cross-sectional survey to establish Theileria parva prevalence and vector control at the wildlife-livestock interface, Northern Tanzania

Abstract

East Coast fever (ECF) in cattle is caused by the protozoan parasite Theileria parva, transmitted by Rhipicephalus appendiculatus ticks. In cattle ECF is often fatal, causing annual losses >$500 million across its range. The African buffalo (Syncerus caffer) is the natural host for T. parva but the transmission dynamics between wild hosts and livestock are poorly understood. This study aimed to determine the prevalence of T. parva in cattle, in a 30 km zone adjacent to the Serengeti National Park, Tanzania where livestock and buffalo co-exist, and to ascertain how livestock keepers controlled ECF and other vector-borne diseases of cattle. A randomised cross-sectional cattle survey and questionnaire of vector control practices were conducted. Blood samples were collected from 770 cattle from 48 herds and analysed by PCR to establish T. parva prevalence. Half body tick counts were recorded on every animal. Farmers were interviewed (n = 120; including the blood sampled herds) using a standardised questionnaire to obtain data on vector control practices. Local workshops were held to discuss findings and validate results. Overall prevalence of T. parva in cattle was 5.07% (CI: 3.70-7.00%), with significantly higher prevalence in older animals. Although all farmers reported seeing ticks on their cattle, tick counts were very low with 78% cattle having none. Questionnaire analysis indicated significant acaricide use with 79% and 41% of farmers reporting spraying or dipping with cypermethrin-based insecticides, respectively. Some farmers reported very frequent spraying, as often as every four days. However, doses per animal were often insufficient. These data indicate high levels of acaricide use, which may be responsible for the low observed tick burdens and low ECF prevalence. This vector control is farmer-led and aimed at both tick- and tsetse-borne diseases of livestock. The levels of acaricide use raise concerns regarding sustainability; resistance development is a risk, particularly in ticks. Integrating vaccination as part of this community-based disease control may alleviate acaricide dependence, but increased understanding of the Theileria strains circulating in wildlife-livestock interface areas is required to establish the potential benefits of vaccination.

Keywords: Acaricide; East Coast fever; Rhipicephalus appendiculatus; Theileria parva; Vector; Wildlife-livestock interface.

Fig. 1

Location of sampled villages and T. parva prevalence. Villages shown in shades of red, representative of T. parva prevalence, as detailed in the legend. Villages were selected from those close to the protected area boundaries in Serengeti District. Protected wildlife areas are shown in green and comprise Serengeti National Park, Ngorongoro Conservation Area and Grumeti, Ikorongo and Maswa Game Reserves.

Fig. 2

a) Time intervals of acaricide spraying and b) Time intervals of acaricide dipping. Values shown were reported by farmers selected as part of a randomised cross-sectional study (blue) and by farmers participating in a non-randomised longitudinal study (red). N/A = Non-responses. Error bars indicate 95% confidence intervals.

Fig. 3

Control methods being used by farmers in each village. The proportions of farmers reporting application of insecticides on their cattle by spraying, using a dip tank, both or neither are shown. Villages that have a dip tank are indicated with an asterisk. Numbers indicate the median frequency of application in days.

Fig. 4

Scatterplots showing dilution, volume used and dose per cow for four acaricide products: a) Albadip; b) Paranex; c) Cybadip; and d) Tantix. The value for each herd is shown as a proportion (log scale) of the correct dose, where values <1.0 (grey dashed line) represent underdosing; different coloured points represent different herds and lines connect individual herds.

Fig. 5

Herd size in relation to farmer awareness of ECF. Error bars indicate 95% confidence intervals.