Bull. Environ. Contam. and Toxic. (USA) 58(6), 969-975.. : Association of Africa Universities
Kenya's fast growing human population is expected to reach 35 million by the year 2000. In order to cope with such a rapid rate of growth, efforts must be directed towards adequate agricultural and livestock production to counter the disproportionate increase in demand for food. To provide sufficient animal protein (milk and beef products) attempts must be made to eliminate the current constraints hindering livestock production and expansion in Kenya (KARI,1989). One such constraint (in terms of both health effects and economic losses) is the presence of several important infectious diseases affecting cattle, characterized by the occurrence of parasites in the animal's blood (haemoparasites) (Mutugi et al, 1989).
There are two major groups of haemoparasitic diseases that occur in Kenya: tick-transmitted, and tsetse and non-tsetse transmitted (trypanosomiasis) diseases. Tick-borne diseases are considered to be the most important animal health problem in the high potential areas, while trypanosomiasis is a major threat in the low potential range lands (Mutugi, 1986). These diseases restrict introduction of higher producing but susceptible stock in certain areas of the country; inflict high mortalities in susceptible stock; lead to productivity losses in recovered animals; and necessitate exclusion of highly productive breeds of livestock from locations where there is an outbreak (FAO, 1984).
Tick-borne diseases frequently encountered in Kenya are theileriosis, anaplasmosis, cowdriosis and babesiosis. Theileriosis comprises a group of protozoan parasites of the genus Theileria, which are transmitted by the ixodid ticks. Four different species of this genus are recorded in cattle; clinical theileriosis is associated with one species, Theileria parva transmitted by the brown ear tick, Rhipicephalus appendiculatus. This species causes the notorious East Coast Fever (ECF), a highly fatal disease of cattle. A closely related form, corridor disease (T.parva Tawrencei infection) transmitted by the same tick is a buffalo derived parasite that causes very high mortalities in infected cattle (Mutugi et al, 1989). In Western Kenya, both ECF and anaplasmosis are common practical animal health problems that are seriously affecting the livestock industry. Outbreaks of these diseases are frequent and have continued to pose great challenges in terms of control for over 80 years.
Currently, the most conventional method of controlling ECF and anaplasmosis in cattle involves the use of acaricides. In Western Kenya, many types of acaricides are available but presently, the most commonly used chemical is chlorfenvinphos (ILRAD, 1991). It is frequently applied on cattle either through plunge dips or sprays. Little, however, is known about the fate of this compound and its residual effect in milk and beef. A recent survey in Kenya (KEMRI,1988) suggests that chronic or acute exposure to chlorfenvinphos can result in serious health effects in humans. Residue levels exceeding 8jug/kg of butterfat in cow's milk are currently regarded as dangerous for human consumption (Codex Alimentarius,1993), although concentrations as high as 20/ig/kg have been reported in Australia (Shell, 1969).
The purpose of this project was to establish the levels of chlorfenvinphos typically occurring in Kenyan cow's milk; and to determine the influence of season (climate changes) variation in butterfat content, and method of acaricide application (plunge dip or spray) on the residue content in milk sampled at a range of sites in Western Kenya.
Correspondence to: I. O. Jumba