PROF. KITALA PHILIP M

The primary objective of this study was to assess the impact of Rhipicephalus appendiculatus tick presence (exposure variable) on Theileria parva infection seroprevalence (outcome variable) in a group of cattle belonging to a farm using population attributable fractions (PAF). The analyses were based on a representative sample of 80 traditional smallholder mixed farms. The farms were selected by first stratifying the population administratively and implementing a multistage random sampling in Mbeere district in Kenya. The PAFs were estimated using the stratified, Bruzzi, and sequential partitioned PAF approaches. A secondary objective was, thus, to evaluate the impact of the approaches on the PAF estimates. The stratified and Bruzzi approaches estimated proportion of T. parva infection cases directly attributable to the exposure after controlling for confounding by agro-ecological zone (AEZ). The sequential partitioned PAF approach estimated a PAF associated with exposure after adjusting for any effect that the AEZ may have had by influencing the prevalence of the exposure. All analyses were carried out at the farm level where a farm was classified as infested if the tick was found on cattle on a farm, and infected if at least one animal on a farm was positive for T. parva antibodies. Variance estimation for PAFs was implemented using ‘delete-a-group’ jackknife re-sampling method. The stratified PAF (26.7% [95% CI: 9.0%, 44.4%]) and Bruzzi PAF (26.4% [95% CI: 9.6%, 43.2%]) were consistent in estimating a relatively low impact of farm vector tick presence with a relatively high level of uncertainty. The partitioned PAF (15.5% [95% CI: 1.5%, 29.6%]) suggested that part of the impacts estimated using the stratified PAF and Bruzzi approaches was driven by AEZ effects. Overall, the results suggested that under endemic instability in Mbeere district, (1) presence of R. appendiculatus was not a good indicator of T. parva infection occurrence on a farm; (2) ecological variation could play a role in determining infection impacts. This study provides a preliminary basis for evaluating the potential value and utility of estimating PAFs for variables amenable to control in tick-borne diseases (TBDs) epidemiological studies.

Bovine cysticercosis is a zoonosis that is mainly of socioeconomic ,H1(1 public health impor, ranee. A survey of this disease was.carried ou t in Northern Turkana District, Kenya to estimate the prevalence through both serology and meat inspection. to determine the prevalence or the adult tapeworm in the human definitive 11Ost, and to determine risk factors for cattle seropositivity. This information is of public health importance and will be of use inassessing economic losses due to downgrading, refrigeration or condemnation of infested carcasses. The study area was stratified into the three livestock grazing regions of Oropoi to the south, Lokichoggio--Mogilla centrally and Kibish in the north for the purposes of rhe serological and questionnaire (n = 53 herd owners) data. Five ada/wars (grazing units) were selected and 34, 63. 49, 75 and 571 cattle serum samples obtained from these. The slaughter slabs of Lokichoggio and Kakurna were visited and 188 serum samples were obtained from slaughter cattle and compared to results of meat inspection. Human stool samples were collected in each of the three grazing areas and 66, 97 and 78 samples were obtained. The seroprevalence of cysticercosis in cattle was estimated at 16.7% (95% CI 13-20,9%) using a secretory-excretory antigen detection ELISA. There was poor agreement between meat inspection and serology (I< = 0.025; P = 0.2797). The prevalence of taeniasis was estimated as 2.5% (95% CI 0.8-5.6%) by microscopy. A backwards elimination logistic regression analysis indicated that the grazing unit (Ada/war), the deworrning history of household members and the distance (>2km) of gl-azing fields from the homestead were significant expla-natory variables for cattle being found to be positive on serology. An intra-cluster correlation coefficient (ICC) of 0,07 (0.02-0.12); P < 0.0001 was calculated for bovine cysticercosis in this area

East coast fever (ECF) is the most important tick-borne disease (TBD) of cattle in Kenya. A cross-sectional survey was carried out in the cattle population raised under traditional crop-livestock production system in Mbeere district, Kenya. The objective was to estimate ECF seroprevalence and identify associated risk factors for planning ECF control strategies in the district. A total of 440 cattle of all ages from 80 farms were selected by multistage random sampling. Prevalence of serum antibodies to ECF was determined by enzyme-linked immunosorbent assay (ELISA). Risk factor information was collected at three levels: animal-, farm-(herd) and division-levels. The relationship between ECF seropositivity and the risk factors was assessed by multivariable analysis using logistic regression models. The overall ECF seroprevalence was 19.3% (range: 3.9% to 48% across divisions) in the district [95%CI: 13.7%, 24.9%]. Regression analysis found four major factors associated with seropositivity: presence of the vector tick on the farm (OR=3.8), frequency of calf tick control before 6 months of age (for frequency of >5 times, OR=3.9 relative to frequency of ≤5 times), herd size (OR for herd size category 6-10 cattle = 2.7; OR for over 10 cattle = 0.95 relative to herd size category 1-5 cattle) and division (ORs for Siakago, Gachoka and Mwea divisions = 0.3, 0.21 and 5.1 respectively relative to Evurore division). The low ECF seroprevalence indicates that ECF occurs in the district in an endemic instability state. The significant herd management factors possibly arose out of differential perceptions of ECF occurrence and importance across the district while the wide variation in seroprevalence across divisions was thought to be due to a gradient in vector tick environmental suitability habitats. These findings suggest that ECF seroprevalence in Mbeere district is mainly influenced by herd and environmental factors.

Rabies is still prevalent in most parts of the developing WOrld, with approximately 4 million people in Asia, Africa, and South America receiving post-exposure treatment and over 30 000 dying after being bitten by rabid dogs (WHO, 1992). In Kenya, rabies has been common in Machakos District for at least 40 years. We have undertaken several studies in recent years to collect information on dog ecology, dog population dynamics and rabies epidemiology required to improve rabies control in this district (Kitala et aI., 1993; Kitala and McDermott, 1995). Given this baseline data, mathematical models, often quite simple ones, can serve as a useful tool for predicting disease incidence under different natural and disease control scenarios (Anderson and May, 1991) and have been used to advantage in assessing rabies epidemiology, particularly in fox populations in Europe and North America (e.g. Anderson et al., 1981; Voigt et al., 1985). In this paper, we describe a simple deterministic model of rabies which incorporates both transitions between the main rabies disease states and dog populaton parameters. particularly thresholds for dog density. We compare model predictions to observed patterns of rabies in Machakos District and also explore the potential efficacy of different rabies control programmes.

This paper presents the results of a study conducted in a pastoral community in Kenya using partici¬patory appraisal approaches. The objective of the study was to assess the socio-economic impact of camel trypanosomosis (surra) according to the perceptions of the pastoralists. Four livestock grazing units were conveniently selected and in each of them, three groups of key informants comprising five to eight persons were selected for the participatory exercises. Five camel diseases were listed in or¬der of importance according to their severity and frequency of occurrence including trypanosomosis, mange, non-specific diarrhoea, tick infestations and haemorrhagic septicaemia. The losses listed as incurred due to the five diseases were: losses in milk, meat, blood, fats and hides, dowry payments, and depreciation in sale of animals, losses due to infertility and abortions, and losses due to the cost of treatment. There was good agreement (P < 0.05) between the informant groups on the losses in¬curred as a result of the diseases for all the selected loss indicators. Surra and mange were given high median scores on all the indicators while non-specific diarrhoea, tick infestations, and haemor¬rhagic septicaemia received moderate median scores. Based on the study findings it is concluded that the camel plays a central role in the lives of Turkana pastoralists and that surra has a devastating social and economic impact. There is a need for veterinary and policy decision-makers to focus more attention on the control of surra in this arid and semi-arid area of Kenya.