Risk factors associated with Theileria parva infection in cattle in smallholder dairy farms in Muranga District, Kenya. A longitudinal study

In Kenya, the vast majority of dairy farms are owned and run by smallholder farmers. These farms are estimated to produce 75-90 percent of the milk sold in Kenya (Mbogoh, 1984a, b); about 65 percent of dairy cattle in the smallholder farms are stall-fed for the greater part of the year (Gitau et al., 1994). Dairy farming provides an income through the sale of milk and meat and tends to be a more consistent source of income than many other farming enterprises, in the medium to high potential farming areas. A number of factors limit the further Development of the dairy industry, including diseases, poor management, inadequate nutrition and lack of farm inputs (Goldson and Ndeda, 1985). Among the diseases, tick-borne infections, in particular East Coast fever (ECF) caused by Theileria parva and transmitted by the tick Rhipicephalus appendiculatus, are the most important. A one and a half year longitudinal study was conducted in Murang'a District to estimate the incidence of T. parva infections among the smallholder dairy farms. Three agroecological zones were selected. The results showed that T. parva infection status was different across the agroecological zones and was associated with feeding management. Calves raized in the lower altitude zones were at a higher risk of T. parva infection than those raised in higher altitude zones

The epidemiology of Theileria parva infections on smallholder dairy farms in Kenya

The purpose of the study was to characterize the differences in epidemiology (risks of infection. morbidity. mortality) and potential control of East Coast fever (ECF) between the selected strata. Evidence of Theileria parva infection was assessed by increased antibody levels as measured in an indirect ELISA test by the percent positivity (PP) of serum samples relative to a strong positive reference serum. A prospective cohort study was conducted in five purposively sampled agroecological zone (AEZ)-grazing system strata in Murang’a District. Kenya, between March 1995 and June 1996. The study strata were selected to represent the widest range of ECF risks in the district and included, zero-grazing and open-grazing farms in the Upper Midlands (UM) one and four AEZs and zero-grazing farms in the UM2 AEZ. In total. 225 calves from 188 smallholder farms were examined from birth to age six months. Calves were recruited into the study at birth and visited within the first two weeks of life and thereafter at biweekly intervals for up to 14 visits. Important differences were observed between the different AEZ-grazing strata. Seroconversion risks of T. parva were highest in the UM4-open grazing stratum. Antibody prevalence in adult cattle and ECF morbidity and mortality risks were also highest in this stratum. In the open-grazing strata, particularly in the lower elevation AEZ, UM4, there was stronger challenge and a greater impact of ECE. There is likely to be an expansion of smallholder dairy farming into this area so that it is likely to be the most important target production system for ECF control in the central highlands of Kenya

Differences in the epidemiology of theileriosis on smallholder dairy farms in contrasting agro-ecological and grazing strata of highland Kenya

Tick-borne diseases are considered a major constraint to dairy farming among the smallholder dairy farms in Kenya, which account for an estimated 75-90% of all milk produced in the country. The most important tick-borne disease in Kenya is East Coast fever (ECF) caused by Theileria parva and transmitted by the brown ear tick Rhipicephalus appendiculatus, which has been associated with high mortality in cattle, especially among the exotic breeds of cattle. In Kenya, there is considerable recent evidence that the prevalence of T. parva infections and Reported ECF morbidity, mortality and case-fatality can vary significantly by agro-ecological zone and grazing system. These differences have important implications for both the impact and control of ECF. A paradigm for evaluating production systems for theileriosis based on the epidemiological states i.e. degree of endemic stability or instability has been developed. In endemically stable systems, there is an equilibrium between Theileria parasites and hosts so that ECF impact is minimal despite high infection challenge. In unstable situations, ECF impact can be considerable, either through direct losses from ECF or in costs associated with its control. The prevalence, sero-conversion risk and morbidity/mortality risks of ECF for female calves up to 6 months of age in 5 contrasting agro-ecological zone (AEZ)-grazing system strata in Murang a District, Kenya has been previously described. This paper uses the indicators of theileriosis infection quantified in that study to characterise the epidemiological states of ECF in the 5 AEZ-grazing strata studied in Muranga District, Kenya

The persistence of Theileria parva infection in cattle immunised using two stocks which differ in their ability to induce a carrier state: Analysis using a novel blood spot PCR assay

An improved Theileria parva DNA detection assay based on the polymerase chain reaction (PCR) using primers derived from the 104 kDa antigen (p104) gene was developed to detect parasite DNA in blood spots on filter paper. The specificity of the assay was validated using DNA from a wide range of cattle-derived and buffalo-derived stocks of T. parva. DNA of T. annulata, T. buffeli, T. lestoquardi, T. mutans and T. taurotragi was not amplified using the p104 primers. The detection threshold of the assay was approximately 1-2 parasites/microl of infected blood. PCR amplification using the p104 primers was applied to sequential samples from groups of cattle experimentally infected with either the T. parva Marikebuni stock that induces a long-term carrier state or the Muguga stock, which does not induce a carrier state. The study extended for up to 487 days post-infection and PCR data from defined time points were compared with parasitological microscopy and serological data, together with xenodiagnosis by experimental application of ticks. Microscopy first detected piroplasms between days 13 and 16 after infection whereas all cattle became PCR +ve between days 9 and 13. Animals infected with the Muguga stock of T. parva had parasite DNA in the peripheral blood, which could be detected by PCR, for between 33 and 129 days post-infection in different animals. By contrast parasite DNA in the blood of cattle infected with the Marikebuni stock could be detected consistently from day 9 up to 487 days, when the study terminated. The data suggest that the nature and persistence of the carrier state may differ markedly between different T. parva parasite stocks