Epidemiology of theileriosis (with emphasis on east coast fever) and some aspects of economics of tick control in transmara division, Narok District, Kenya.

Abstract

Tick-borne diseases are by far the most serious source of cattle losses in Eastern Africa. The four main tick-borne diseases, namely; East Coast Fever (ECF), anaplasmosis, babesiosis and heartwater cannot yet be routinely prevented by vaccination. Vector control is the main practical means of controlling these diseases and this has been practised in sore parts of Kenya since 1912. This control method is reported to be expensive due to costs of dio construction, acaricides, and manpower. Complications of tick resistance also constitute an added problem. On the basis of eco-climatic indicators, it has been estimated that 75% of Kenya's land area is best described as rangeland; a land type' whose combination of soil and climate, even potentially, is only capable of supporting pastoralists and wildlife. This study was carried out in Narok, Kenya, where the main type of farming is beef ranching and falls within the 75% rangeland. The purpose of this study was to carry out an epidemiological study on some aspects of theileriosis (with emphasis on ECF) and some aspects of economics of tick control in Narok district, Kenya, in order to institute effective theileriosis control measures in beef ranching areas. A comparative study of three tick control regimes was used under field conditions. Six farmers were randomly chosen; two dipping animals weekly and regularly; two hand spraying or dipping animals irregularly, according to observed heavy tick infestation, but at intervals of ten to twenty days; and two who did not dip or spray their cattle. The weights of these animals were estimated using a weigh band put round the girth. The regularly dipped cattle had better weight increase than the irregularly or non-dipped cattle. Males had better weight gains than females in all tick control regimes, and younger cattle gained more weight than older animals. The highest weight gains were observed in the months of February, May, July and September 1982, while the lowest weight gains were in April and August. Theileriosis period prevalence rates were based on Giemsa stained blood smears and were 82.8% in regularly dipped, 58.7% in irregularly dipped and 77.1% in the non-dipped cattle. Incidence rates of 83.9%, 57.1% and 75.7% were observed in regularly, irregularly and non-dipped cattle, respectively. Theileria spp. were also found in a number of cattle more than once during the one year study period. Older cattle had less Theileria spp. than younger cattle and most Theileria spp. infection in cattle was observed during or following the rainy months. The regularly dipped cattle had few tickp (5.6 ticks/animal), irregularly dipped cattle had more ticks (73.8 ticks/animal) and the non-dipped cattle had the most ticks (100.2 ticks/animal). Therefore, dipping cattle reduced tick loads on cattle. The more regular the dipping (once weekly), the less the tick load on cattle. Older cattle had more ticks than young cattle. There was no difference in tick infestations on male and female cattle in all tick control regimes. Fewer indirect fluorescent antibody (IFA) test reactors were observed in regularly dipped cattle compared to the irregularly and non-dipped cattle. Cumulated positive IFA reactors were 95.3% in regularly dipped, 100% in irregularly dipped and 98.6% in non-dipped cattle. Most positive reactors were observed after peak rise in Theileria spp. The incidence rates of theileriosis based on IFA reactors were 26.6% for regularly dipped, 22.2% for irregularly dipped and 22.9% for non-dipped cattle. On indirect haemagglutination (IHA) test, period prevalence rates of theileriosis were 67.2% for regularly dipped, 88.8% for irregularly dioped and 87.1% for the non-dipped cattle. Regular dipping of animals reduced positive reactors in IFA and IHA tests. In screening sera for antibodies to T. parva infection, the IFA test was found to be more sensitive than the IHA test while the IHA test was found to be more specific than the IFA test. It was, therefore, concluded that in screening field sera for T. parva infection both tests should preferably be used concurrently. The benefit-cost ratios (B/C) for the three tick -control regimes were also estimated. The regularly dipping farms had a B/C ratio of 8.2:1, irregularly dipping farms had a B/C ratio of 9.3:1 while the non-dipping farms had a B/C ratio of 7.6:1, when all factors involved in weight losses and tick control were considered. Therefore, all regimes had some returns for every expenditure incurred. However, there were minor differences in benefit-cost ratios in the three tick control regimes, although the differences were % not statistically significant. Regular dipping, however, reduced the tick load on the animals to very low levels. If one, therefore, considers the aspect of tick control alone without considering the costs and benefits, then regular dipping would be recommended for this area. However, considering the economic aspects of tick control then strategic tick control at the onset and during the rainy season would be recommended for Transmara.