Trop Anim Health Prod (2015) 47:93–101 DOI 10.1007/s11250-014-0690-6
REGULAR ARTICLES
Theileria parva infection seroprevalence and associated risk factors in cattle in Machakos County, Kenya Fred David Wesonga & John Mwangi Gachohi & Philip Mwanzia Kitala & Joseph Mwangi Gathuma & Munene John Njenga
Received: 6 August 2014 / Accepted: 26 September 2014 / Published online: 16 October 2014 # Springer Science+Business Media Dordrecht 2014
Abstract The principle objective of this study was to estimate the infection seroprevalence and identify risk factors associated with Theileria parva infection in cattle on smallholder farms in Machakos County, Kenya. A total of 127 farms were selected by a proportional allocation approach based on the number of farms in four divisions in the county previously selected by stratified random sampling method. Subsequently, a total sample of 421 individual animals was randomly selected from the farms. Information on animal and relevant individual farm management practices was gathered using a standardized questionnaire. Prevalence of serum antibodies was determined using the enzyme-linked immunosorbent assay (ELISA). Multivariable logistic models incorporating random effects at the farm level evaluated the association between the presence of T. parva antibodies and the identified risk variables. The overall estimation of T. parva antibodies in the county was 40.9 % (95 % confidence interval of 36.1, 45.7 %). Seroprevalence to T. parva was F. D. Wesonga Kenya Agricultural Research Institute (KARI), Muguga South, P.O. Box 32, Kikuyu, Kenya J. M. Gachohi Kenya Agricultural Research Institute (KARI) Trypanosomiasis Research Centre, P.O. Box 362, 00902 Kikuyu, Kenya J. M. Gachohi (*) International Livestock Research Institute (ILRI), P. O. Box 30709, 00100 Nairobi, Kenya e-mail: [email protected] J. M. Gachohi e-mail: [email protected] P. M. Kitala : J. M. Gathuma : M. J. Njenga Faculty of Veterinary Medicine, University of Nairobi, P.O. Box 29053, 00625 Nairobi, Kenya
significantly associated with animal age, vector tick infestation in the animal, tick control frequency, and administrative division. Further analyses suggested a confounding relationship between administrative division and both breed and grazing system and the T. parva seropositivity. Random effects model yielded intra-farm correlation coefficient (ICC) of 0.18. The inclusion of farm random effect provided a substantially better fit than the standard logistic regression (P = 0.032). The results demonstrate substantial variability in the T. parva infection prevalence within all categories of the cattle population of Machakos County of Kenya, where East Coast fever is endemic. Keywords Theileria parva infection . Seroprevalence . Epidemiology . Machakos . Kenya
Introduction East Coast fever (ECF) is a cattle disease caused by a parasitic protozoan, Theileria parva, and transmitted by the brown ear tick Rhipicephalus appendiculatus. The disease is the most economically important disease of cattle in east and central Africa including Kenya (Norval et al. 1992; Lawrence et al. 2004). East Coast fever is a major hindrance to the introduction of improved exotic cattle breeds due to their high susceptibility to the disease (Minjauw and McLeod 2003). The disease was reported to be responsible for annual mortality rates of 40– 80 % among unvaccinated Zebu (Bos indicus) calves kept under pastoral management (Homewood et al. 2006). The economic losses due to the disease have the greatest impact on small-scale resource poor farmers through animal morbidity and mortality and the huge costs incurred annually in the control of the disease through tick control and chemotherapy. It is estimated that countries where the disease is prevalent spend up to $315 million a year in
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losses due to treatment, mortality, and control costs (Minjauw and McLeod 2003). A recent review on T. parva infection epidemiology identified the important biological and ecological factors associated with the infection risk (Gachohi et al. 2012). These include the agroecological zone (AEZ), livestock production system (LPS), and both animal breed and age. The principle objective of the current study was to estimate the T. parva infection seroprevalence and identify risk factors associated with the infection. In carrying out the study, we considered the reviewed factors (Gachohi et al. 2012). East Coast fever immunization which involves an elaborate infection-and-treatment strategy (ITM) has recently been implemented in certain districts in Kenya but not in Machakos County (Gachohi et al., 2012). Therefore, we did not anticipate detecting antibodies due to the vaccine. The study was undertaken as a component of a broader study that was carried out from mid-2007 to early 2009 to identify constraints to livestock production in the county and ultimately recommend appropriate interventions for the constraints (Wesonga et al. 2010).
Materials and methods Study site The study was conducted in Machakos County (the former larger Machakos District). The county lies between latitudes 0.45′S and 1.31′S and longitudes 36.45′E and 37.45′E and has a total area of 6850 km2. The average annual rainfall in the county ranges between 500 and 1300 mm, concentrated in two seasons: end of March to May and end of October to December. The mean temperature ranges between 18 and 25 °C. The county spans across the AEZs 2 through to 6 based on a moisture index (Sombroek et al. 1982). The index represents the annual rainfall expressed as a percentage of potential evaporation. Zones 2 and 3 have an index >50 % with potential for substantial vegetation cover. These zones are characterized by smallholder and commercial systems. Areas with an index
REGULAR ARTICLES
Theileria parva infection seroprevalence and associated risk factors in cattle in Machakos County, Kenya Fred David Wesonga & John Mwangi Gachohi & Philip Mwanzia Kitala & Joseph Mwangi Gathuma & Munene John Njenga
Received: 6 August 2014 / Accepted: 26 September 2014 / Published online: 16 October 2014 # Springer Science+Business Media Dordrecht 2014
Abstract The principle objective of this study was to estimate the infection seroprevalence and identify risk factors associated with Theileria parva infection in cattle on smallholder farms in Machakos County, Kenya. A total of 127 farms were selected by a proportional allocation approach based on the number of farms in four divisions in the county previously selected by stratified random sampling method. Subsequently, a total sample of 421 individual animals was randomly selected from the farms. Information on animal and relevant individual farm management practices was gathered using a standardized questionnaire. Prevalence of serum antibodies was determined using the enzyme-linked immunosorbent assay (ELISA). Multivariable logistic models incorporating random effects at the farm level evaluated the association between the presence of T. parva antibodies and the identified risk variables. The overall estimation of T. parva antibodies in the county was 40.9 % (95 % confidence interval of 36.1, 45.7 %). Seroprevalence to T. parva was F. D. Wesonga Kenya Agricultural Research Institute (KARI), Muguga South, P.O. Box 32, Kikuyu, Kenya J. M. Gachohi Kenya Agricultural Research Institute (KARI) Trypanosomiasis Research Centre, P.O. Box 362, 00902 Kikuyu, Kenya J. M. Gachohi (*) International Livestock Research Institute (ILRI), P. O. Box 30709, 00100 Nairobi, Kenya e-mail: [email protected] J. M. Gachohi e-mail: [email protected] P. M. Kitala : J. M. Gathuma : M. J. Njenga Faculty of Veterinary Medicine, University of Nairobi, P.O. Box 29053, 00625 Nairobi, Kenya
significantly associated with animal age, vector tick infestation in the animal, tick control frequency, and administrative division. Further analyses suggested a confounding relationship between administrative division and both breed and grazing system and the T. parva seropositivity. Random effects model yielded intra-farm correlation coefficient (ICC) of 0.18. The inclusion of farm random effect provided a substantially better fit than the standard logistic regression (P = 0.032). The results demonstrate substantial variability in the T. parva infection prevalence within all categories of the cattle population of Machakos County of Kenya, where East Coast fever is endemic. Keywords Theileria parva infection . Seroprevalence . Epidemiology . Machakos . Kenya
Introduction East Coast fever (ECF) is a cattle disease caused by a parasitic protozoan, Theileria parva, and transmitted by the brown ear tick Rhipicephalus appendiculatus. The disease is the most economically important disease of cattle in east and central Africa including Kenya (Norval et al. 1992; Lawrence et al. 2004). East Coast fever is a major hindrance to the introduction of improved exotic cattle breeds due to their high susceptibility to the disease (Minjauw and McLeod 2003). The disease was reported to be responsible for annual mortality rates of 40– 80 % among unvaccinated Zebu (Bos indicus) calves kept under pastoral management (Homewood et al. 2006). The economic losses due to the disease have the greatest impact on small-scale resource poor farmers through animal morbidity and mortality and the huge costs incurred annually in the control of the disease through tick control and chemotherapy. It is estimated that countries where the disease is prevalent spend up to $315 million a year in
94
losses due to treatment, mortality, and control costs (Minjauw and McLeod 2003). A recent review on T. parva infection epidemiology identified the important biological and ecological factors associated with the infection risk (Gachohi et al. 2012). These include the agroecological zone (AEZ), livestock production system (LPS), and both animal breed and age. The principle objective of the current study was to estimate the T. parva infection seroprevalence and identify risk factors associated with the infection. In carrying out the study, we considered the reviewed factors (Gachohi et al. 2012). East Coast fever immunization which involves an elaborate infection-and-treatment strategy (ITM) has recently been implemented in certain districts in Kenya but not in Machakos County (Gachohi et al., 2012). Therefore, we did not anticipate detecting antibodies due to the vaccine. The study was undertaken as a component of a broader study that was carried out from mid-2007 to early 2009 to identify constraints to livestock production in the county and ultimately recommend appropriate interventions for the constraints (Wesonga et al. 2010).
Materials and methods Study site The study was conducted in Machakos County (the former larger Machakos District). The county lies between latitudes 0.45′S and 1.31′S and longitudes 36.45′E and 37.45′E and has a total area of 6850 km2. The average annual rainfall in the county ranges between 500 and 1300 mm, concentrated in two seasons: end of March to May and end of October to December. The mean temperature ranges between 18 and 25 °C. The county spans across the AEZs 2 through to 6 based on a moisture index (Sombroek et al. 1982). The index represents the annual rainfall expressed as a percentage of potential evaporation. Zones 2 and 3 have an index >50 % with potential for substantial vegetation cover. These zones are characterized by smallholder and commercial systems. Areas with an index
