A longitudinal study of disease incidence and case-fatality risks on small-holder dairy farms in coastal Kenya

Evaluating the efficacy of Mazao Tickoff (Metarhizium anisopliae ICIPE 7) in controlling natural tick infestations on cattle in coastal Kenya: Study protocol for a randomized controlled trial

Ticks and tick-borne diseases cause substantial economic losses to the livestock industry in sub-Saharan Africa. Mazao Tickoff is a novel bioacaricide developed for tick control and is based on the entomopathogenic fungus Metarhizium anisopliae sensu lato (s.l.) isolate ICIPE 7. To date, no randomized controlled study has been undertaken to demonstrate the efficacy of this bioacaricide in reducing natural tick infestation on cattle. To this end, this field trial is designed to evaluate the anti-tick efficacy of Mazao Tickoff on cattle in coastal Kenya compared to a standard chemical tick control protocol. In this prospective, multi-center randomized controlled trial, eligible herds will be randomized by the herd size to the intervention arm in a 1:1:1 ratio to either Triatix® (active ingredient: amitraz); Mazao Tickoff (active ingredient: M. anisopliae ICIPE 7); or placebo (excipients of the Mazao Tickoff), with a total enrollment target of 1,077 cattle. Treatments will be dispensed on Day 0 (defined individually as the day each animal receives the first treatment) and thereafter every two weeks until Day 182. Ticks will be counted on every animal in each herd (herds to be included have at least one animal bearing at least one tick on Day 0), and thereafter on bi-weekly intervals until Day 182. The primary efficacy assessments of Mazao Tickoff will be based on the mean percentage reduction in tick counts at each post-treatment follow-up visit compared to the placebo group and the Triatix® arm. Further, the effect of Mazao Tickoff on the prevalence of common cattle pathogens, Anaplasma marginale and Theileria parva, will be determined by assessing incidence and seroprevalence at four different time points. This protocol describes the first rigorous evaluation of the efficacy of Mazao Tickoff and its potential as a viable alternative non-chemical acaricide tool for tick control in Kenya and elsewhere.

Epidemiological and Comparative Diagnostic Study of Anaplasma Spp. Infection in Goats from North-Eastern Algeria

Anaplasmosis is an infectious disease affecting goats and other ruminants. Our goal was to estimate the prevalence of Anaplasma spp. infections, and to identify different tick species in goa ts along with their associated risk factors. The epidemiology of Anaplasma spp. (A. ovis/A. marginale) was investigated from April to September 2016 in dairy goats from three different agro-ecological areas in the northeast region of Algeria (Guelma and El-Taref). We tested 182 goat sera using a MSP5 competitive ELISA (cELISA) test for IgG antibody screening, and by microscopic examination using the Giemsa (May-Greunwald-Giemsa) stain of 128 blood smears to detect intraerythrocytic inclusions bodies. The results demonstrated a total infection rate of 78.02 % and 42.18 % using cELISA and MGG, respectively. Only two species of ticks collected were identified, i. e. Rhipicephalus sanguineus (85.39 %) and Rhipicephalus bursa (14.60 %). Our study revealed that factors, such as the season, the type of farming, the hygienic status and the climatic conditions of the studied areas were found to be significantly associated with the tick infestation of goats (P < 0.05). The Anaplasma spp. infection prevalence was found to be highly dependent on the climatic conditions, the season (P < 0.05) and most closely related to the type of breeding and herd management (P = 0.000).

The evaluation of the Giemsa technique showed specificity and sensitivity of 60.71 % and 45.16 % respectively. Calculating the concordance between the two techniques revealed Cohen’s Kappa value of 0.038 in the range 0.21—0.40, which corresponded to a very low agreement. The McNemar test results showed that both tests gave significantly different results (P < 0.05). This work provides evidence for Anaplasma spp. in goats from north-eastern Algeria.

Impact of foot-and-mouth disease on mastitis and culling on a large-scale dairy farm in Kenya

Foot and mouth disease (FMD) is a highly transmissible viral infection of cloven hooved animals associated with severe economic losses when introduced into FMD-free countries. Information on the impact of the disease in FMDV-endemic countries is poorly characterised yet essential for the prioritisation of scarce resources for disease control programmes. A FMD (virus serotype SAT2) outbreak on a large-scale dairy farm in Nakuru County, Kenya provided an opportunity to evaluate the impact of FMD on clinical mastitis and culling rate. A cohort approach followed animals over a 12-month period after the commencement of the outbreak. For culling, all animals were included; for mastitis, those over 18 months of age. FMD was recorded in 400/644 cattle over a 29-day period. During the follow-up period 76 animals were culled or died whilst in the over 18 month old cohort 63 developed clinical mastitis. Hazard ratios (HR) were generated using Cox regression accounting for non-proportional hazards by inclusion of time-varying effects. Univariable analysis showed FMD cases were culled sooner but there was no effect on clinical mastitis. After adjusting for possible confounders and inclusion of time-varying effects there was weak evidence to support an effect of FMD on culling (HR = 1.7, 95% confidence intervals [CI] 0.88-3.1, P = 0.12). For mastitis, there was stronger evidence of an increased rate in the first month after the onset of the outbreak (HR = 2.9, 95%CI 0.97-8.9, P = 0.057).

A longitudinal assessment of the serological response to Theileria parva and other tick-borne parasites from birth to one year in a cohort of indigenous calves in western Kenya

Tick-borne diseases are a major impediment to improved productivity of livestock in sub-Saharan Africa. Improved control of these diseases would be assisted by detailed epidemiological data. Here we used longitudinal, serological data to determine the patterns of exposure to Theileria parva, Theileria mutans, Babesia bigemina and Anaplasma marginale from 548 indigenous calves in western Kenya. The percentage of calves seropositive for the first three parasites declined from initial high levels due to maternal antibody until week 16, after which the percentage increased until the end of the study. In contrast, the percentage of calves seropositive for T. mutans increased from week 6 and reached a maximal level at week 16. Overall 423 (77%) calves seroconverted to T. parva, 451 (82%) to T. mutans, 195 (36%) to B. bigemina and 275 (50%) to A. marginale. Theileria parva antibody levels were sustained following infection, in contrast to those of the other three haemoparasites. Three times as many calves seroconverted to T. mutans before seroconverting to T. parva. No T. parva antibody response was detected in 25 calves that died of T. parva infection, suggesting that most deaths due to T. parva are the result of acute disease from primary exposure.

BRONSVOORT BMARK, COETZER JACOBUSA, HANDEL IANG, HANOTTE OLIVIER, JENNINGS AMY, LESOSKY MAIA, KIARA HENRY, THUMBI SAMM, TOYE PHIL, WOOLHOUSE MARKW, PENZHORN BANIEL. The impact of co-infections on the haematological profile of East African Short-horn Zebu calves

The cumulative effect of co-infections between pathogen pairs on the haematological response of East African Short-horn Zebu calves is described. Using a longitudinal study design a stratified clustered random sample of newborn calves were recruited into the Infectious Diseases of East African Livestock (IDEAL) study and monitored at 5-weekly intervals until 51 weeks of age. At each visit samples were collected and analysed to determine the infection status of each calf as well as their haematological response. The haematological parameters investigated included packed cell volume (PCV), white blood cell count (WBC) and platelet count (Plt). The pathogens of interest included tick-borne protozoa and rickettsias, trypanosomes and intestinal parasites. Generalized additive mixed-effect models were used to model the infectious status of pathogens against each haematological parameter, including significant interactions between pathogens. These models were further used to predict the cumulative effect of co-infecting pathogen pairs on each haematological parameter. The most significant decrease in PCV was found with co-infections of trypanosomes and strongyles. Strongyle infections also resulted in a significant decrease in WBC at a high infectious load. Trypanosomes were the major cause of thrombocytopenia. Platelet counts were also affected by interactions between tick-borne pathogens. Interactions between concomitant pathogens were found to complicate the prognosis and clinical presentation of infected calves and should be taken into consideration in any study that investigates disease under field conditions.

Mortality in East African shorthorn zebu cattle under one year: predictors of infectious-disease mortality

BACKGROUND

Infectious livestock diseases remain a major threat to attaining food security and are a source of economic and livelihood losses for people dependent on livestock for their livelihood. Knowledge of the vital infectious diseases that account for the majority of deaths is crucial in determining disease control strategies and in the allocation of limited funds available for disease control. Here we have estimated the mortality rates in zebu cattle raised in a smallholder mixed farming system during their first year of life, identified the periods of increased risk of death and the risk factors for calf mortality, and through analysis of post-mortem data, determined the aetiologies of calf mortality in this population. A longitudinal cohort study of 548 zebu cattle was conducted between 2007 and 2010. Each calf was followed during its first year of life or until lost from the study. Calves were randomly selected from 20 sub-locations and recruited within a week of birth from different farms over a 45 km radius area centered on Busia in the Western part of Kenya. The data comprised of 481.1 calf years of observation. Clinical examinations, sample collection and analysis were carried out at 5 week intervals, from birth until one year old. Cox proportional hazard models with frailty terms were used for the statistical analysis of risk factors. A standardized post-mortem examination was conducted on all animals that died during the study and appropriate samples collected.

RESULTS

The all-cause mortality rate was estimated at 16.1 (13.0-19.2; 95% CI) per 100 calf years at risk. The Cox models identified high infection intensity with Theileria spp., the most lethal of which causes East Coast Fever disease, infection with Trypanosome spp., and helminth infections as measured by Strongyle spp. eggs per gram of faeces as the three important infections statistically associated with infectious disease mortality in these calves. Analysis of post-mortem data identified East Coast Fever as the main cause of death accounting for 40% of all deaths, haemonchosis 12% and heartwater disease 7%.

CONCLUSION

The findings demonstrate the impact of endemic parasitic diseases in indigenous animals expected to be well adapted against disease pressures. Additionally, agreement between results of Cox models using data from simple diagnostic procedures and results from post-mortem analysis underline the potential use such diagnostic data to reduce calf mortality. The control strategies for the identified infectious diseases have been discussed.

Identification of hard ticks (Acari: Ixodidae) and seroprevalence to Theileria parva in cattle raised in North Kivu Province, Democratic Republic of Congo

This study aimed to identify tick species and to determine their relationship with the Theileria parva seroprevalence in cattle raised under an extensive farming system in North Kivu Province, Democratic Republic of Congo in two agro-ecological zones namely medium (1,000-1,850 m) and high (>1,850 m) altitude. Among the 3,215 ticks collected on 482 animals, from February to April 2009, Rhipicephalus appendiculatus (64.26 %), the main vector of T. parva, was the most abundant species followed by Rhipicephalus decoloratus (35.49 %) and Amblyomma variegatum (0.25 %). The mean burden of R. appendiculatus tick per infested animal appeared significantly higher at medium (6.5 ± 0.22 ticks) than at high (0.07 ± 0.3 ticks) altitude (P < 0.05). However, an indirect fluorescent antibody test carried out on 450 blood samples revealed a global T. parva seroprevalence of 43 % (95 % CI: 38-47) which was not significantly (P > 0.05) different between medium (48.4 %; 95 % CI: 38-49) and high (41.9 %; 95 % CI: 35-49) altitude. These relatively low seroprevalences suggest that there is a state of endemicity to T. parva infection in the study area. The presence of the tick vector on animals was associated with an increased risk of being seropositive to T. parva infection (odds ratio = 2.04; 95 % CI: 1.8-2.3; P < 0.001). The results suggest the need for a longitudinal study to investigate the seasonal dynamics of tick species and T. parva infection. The rate of tick infection should also be evaluated in order to determine the intensity of T. parva transmission to cattle.

Epidemiology of East Coast fever (Theileria parva infection) in Kenya: past, present and the future

In this article, we review the epidemiology of East Coast fever (ECF), a tick-borne infection of cattle, in Kenya. The major factors associated with epidemiology of ECF include the agro-ecological zone (AEZ), livestock production system (LPS) and both animal breed and age. These factors appear to influence the epidemiology of ECF through structured gradients. We further show that the gradients are dynamically shaped by socio-demographic and environmental processes. For a vector-borne disease whose transmission depends on environmental characteristics that influence vector dynamics, a change in the environment implies a change in the epidemiology of the disease. The review recommends that future ECF epidemiological studies should account for these factors and the dynamic interactions between them. In Kenya, ECF control has previously relied predominantly on tick control using acaricides and chemotherapy while ECF immunization is steadily being disseminated. We highlight the contribution of ECF epidemiology and economics in the design of production system and/or geographical area-specific integrated control strategies based on both the dynamic epidemiological risk of the disease and economic impacts of control strategies. In all production systems (except marginal areas), economic analyses demonstrate that integrated control in which ECF immunization is always an important component, can play an important role in the overall control of the disease. Indeed, Kenya has recently approved ECF immunization in all production systems (except in marginal areas). If the infrastructure of the vaccine production and distribution can be heightened, large ECF endemic areas are expected to be endemically stable and the disease controlled. Finally, the review points the way for future research by identifying scenario analyses as a critical methodology on which to base future investigations on how both dynamic livestock management systems and patterns of land use influence the dynamics and complexity of ECF epidemiology and the implications for control.

Molecular and serological prevalence of Anaplasma marginale in cattle of North Central Morocco

A cross sectional study was conducted to investigate the epidemiological distribution of Anaplasma marginale in North Central Morocco. Blood samples from five provinces of Morocco were collected from apparently healthy cattle (n=668) and simultaneously analyzed by a nested polymerase chain reaction (nPCR) assay and competitive enzyme-linked immunosorbent assay (cELISA). The overall prevalence of A. marginale was 21.9% by nPCR and 16.5% by cELISA. The Kappa coefficient between nPCR and cELISA indicated a modest level of agreement (0.54). The prevalence of A. marginale varied significantly according to the province and the month of sampling. However age, gender and breed did not have a significant effect on the prevalence of this pathogen. The highest prevalence of A. marginale was found in the Gharb, a sub-humid area while the lowest was reported in the Saiss, a semi-arid area. These results indicate that an A. marginale infection are widespread in the country and suggests that either or both techniques are excellent tools for epidemiological studies and control programs.

East Coast fever immunisation field trial in crossbred dairy cattle in Hanang and Handeni districts in northern Tanzania

East Coast fever (ECF) causes considerable mortality and production losses in the Tanzania smallholder dairy sector and limits the introduction of improved dairy breeds in areas where the disease is present. The infection and treatment method (ITM) was adopted by smallholder dairy farms for ECF immunisation in Hanang and Handeni districts of Tanzania. This study recorded incidence rates for ECF and other tick-borne diseases (TBDs) for ECF-immunised and non-immunised cattle between 1997 and 2000. Approximately 80% of smallholder households from both sites (n = 167) participated in this longitudinal study, with immunisations carried out at the request of the livestock owners. Efficacy of ITM for preventing ECF cases in these crossbred dairy cattle was estimated at 97.6%, while that for preventing ECF deaths was 97.9%. One percent of the cattle developed clinical ECF as a result of immunisation. Since ECF immunisation permits a reduction in acaricide use, an increase in other TBDs is a potential concern. Sixty-three percent of farmers continued to use the same acaricide after immunisation, with 80% of these reducing the frequency of applications. Overall, 78% of farmers increased the acaricide application interval after immunisation beyond that recommended by the manufacturer, resulting in annual savings in the region of USD 4.77 per animal. No statistical difference was observed between the immunised and non-immunised animals in the incidence of non-ECF TBDs. However, immunised animals that succumbed to these diseases showed fewer case fatalities. ITM would therefore appear to be a suitable method for ECF control in Tanzania's smallholder dairy sector.

Epidemiology of bovine anaplasmosis in dairy herds from Costa Rica

Bovine anaplasmosis is endemic and occurs in almost all areas of livestock production of Costa Rica. The aim of this study was to determine the seroprevalence and risk factors of anaplasmosis in dairy farms of Costa Rica by the recombinant truncated MSP-5 (rMSP-5) enzyme-linked immunosorbent assay (ELISA). Serum samples were obtained from 733 cattle from 20 commercial dairy herds of Costa Rica. The overall seroprevalence was 37.2% and herd seroprevalence ranged from 20.0 to 72.0%. The age-specific seroprevalence was 49.3% in young and 33.4% in adult animals. The main risk factors associated with seroprevalence were season of occurrence of clinical cases (rainy season) (OR=22.8), presence of tabanids (OR=9.5) and stable flies (OR=6.2), stable flies control measures (OR=3.2), non-use of ear tattoos (OR=2.8), interval of veterinary visit (≤ 60 days) (OR=2.7), altitude of the farms (<800 masl) (OR=2.6) and age (<2 years) (OR=1.8). The results indicated that exposure of cattle to Anaplasma marginale is common in dairy herds of Costa Rica and endemic instability situation probably is due to inadequate vector control.

Environment and farm factors associated with exposure to Theileria parva infection in cattle under traditional mixed farming system in Mbeere District, Kenya

The objective of this study was to investigate the relationship between seroprevalence to Theileria parva infection in cattle and potential environmental and farm-level effects in 80 farms under traditional crop-livestock system in Mbeere District, Kenya. A standardized questionnaire was used to collect the effects characteristics as related to T. parva infection epidemiology. Serum samples were collected from 440 cattle of all ages for detection of T. parva antibodies by the enzyme-linked immunosorbent assay technique. The association between the variables was assessed using a generalized estimation equation logistic regression model. The overall T. parva seroprevalence, accounting for correlation of responses, was 19.3% (95% confidence interval (CI) 14%, 25%). Two variables, "administrative division" and "presence of the vector tick on the farm", were significantly associated with the T. parva seroresponse. Respectively, cattle from farms in Gachoka, Evurore, and Mwea divisions were (and their 95% CI) 1.3 (0.36, 4.8), 4.4 (1.2, 15.9), and 15.2 (4.9, 47.1) times more likely to be seropositive relative to those from Siakago Division (P = 0.000). Cattle from farms in which the vector tick was present were 2.9 (1.2, 6.7) times more likely to be seropositive (P = 0.011). Results of this study suggested that both environmental and farm factors may be associated with T. parva infection epidemiology in Mbeere District. Under such circumstances, characterization of environmental suitability for the vector tick and corresponding environment-specific farm management practices in the district is required both for improved understanding of the disease and in planning disease control programs.

Systematic review of causes and factors associated with morbidity and mortality on smallholder dairy farms in eastern and southern Africa

This article presents the first systematic review of the causes and factors associated with morbidity and mortality, on smallholder dairy farms in Eastern and Southern Africa. It was conducted in August 2007. Primary studies on causes of morbidity and mortality on smallholder dairy farms in the region were identified, examined and descriptive information extracted. Electronic (CAB Abstracts, PubMed, ScienceDirect and Web of Science) and non-electronic databases were used to identify and retrieve the primary studies. The retrieval process included all types of study designs with no restriction on the year of publication and language. Mastitis, tick-borne diseases (TBDs), tick infestation and diarrhoea were among the most commonly documented causes of morbidity. TBDs, diarrhoea and trypanosomiasis were among the most commonly documented causes of mortality; however, a substantial number of mortalities with undiagnosed causes were also reported. Factors ranked as most negatively associated with mastitis were residual calf suckling and increased water availability on the farm while use of common udder towel was the factor most positively associated with mastitis. Zero-grazing was ranked as the factor most negatively associated with TBDs while age was most positively associated. More intervention studies are recommended in the region to better identify animal health constraints and their associated risk factors.

A longitudinal study on morbidity and mortality in youngstock smallholder dairy cattle with special reference to tick borne infections in Tanga region, Tanzania

The incidence and potential determinants of tick borne diseases (TBDs) were estimated in a longitudinal study that was conducted in cohorts of youngstock animals of less than 3 years kept in smallholder dairy farms in Tanga region, Tanzania. A combination of serological tests, blood and lymph node smears were used as diagnostic tests for TBDs during the study. A total number of 549 youngstock were followed for a total of 532.2 animal years from August 1999 to July 2001. Overall morbidity and mortality rates (due to all causes) were 8.26 and 12.0 per 100 animals year at risk, respectively. Of the total deaths, 56% were attributed to TBDs (37.5%-East Coast fever (ECF) and 18%-anaplasmosis). Specific morbidity and mortality rates for ECF were estimated to be 3.57 and 4.51 per 100 animals year risk, respectively, and for anaplasmosis 2.21 and 2.25 per 100 animals year risk, respectively. Analysis of survival times to death indicated that calves < 6 months of age and those out on pasture had higher death rates than older calves and those kept under zero-grazing systems (relative risk [RR] 3.80, P = 0.001 for pasture-grazed calves). There was no mortality or morbidity arising specifically from cowdriosis (heartwater) or babesiosis during the whole period of monitoring. The study revealed that most farms were applying under strength acaricide and using acaricides at irregular intervals. It is concluded that TBDs namely ECF and anaplasmosis are important diseases in this farming system and reducing morbidity and mortality in smallholder dairy farms in Tanga region is an achievable goal. Both farmers and extension services should target at risk calves with the provision of both strict tick control and optimal husbandry management practices.

Modelling energy metabolism of Friesians in Kenya smallholdings shows how heat stress and energy deficit constrain milk yield and cow replacement rate

The 2002 World Summit on Sustainable Development focussed attention on agricultural sustainability and biodiversity in developing countries. These goals are relevant for livestock production in Kenya, where development agencies encourage resource-poor smallholders to acquire large, exotic, high-yielding dairy cows, despite their poor performance, revealed in recent surveys in the highlands and at the coast. The performance of the cows is not in question. The debate relates to the diagnosis of the causes, their treatment and the prognosis for the production system. To improve our understanding of the dynamics of the system, models of nutrition and energy, modified for the tropics, were used to measure the thermal responses over 24 h of six pure or crossbred Friesians at a mean lactation of 54 (s.d. 21·6) days, in separate zero-grazing units. Four smallholdings were on the hot, humid coast and two in the cooler highlands. The output of the model runs was related to the subsequent lactation, calving interval and profitability of the cows. The model showed that the thermal load caused moderate stress for all cows during the day, which became severe in the sun in the highlands, but the drop in air temperature, from 27 °C to 13 °C, at night dissipated the gain in body heat. At the coast, where the night temperature remained above 24 °C and relative humidity above 0·85, there was no remission of heat stress for cows with a milk yield greater than 11 l/day. The lactation curve, in all cows, declined from an initial peak to a low profile of 5 l/day. Cows in both regions with initial yields above 20 l/day had the steepest decline and longest calving intervals (457 to 662 days). They had the largest lactation yields and lowest direct cost per litre, but their poor breeding record reduced cull sales and increased replacement cost, raising the total cost per litre. By contrast, the cow with the lowest daily and lactation yield had the highest direct cost, but lowest total cost per litre, because she produced 2 heifer calves at an interval of only 317 days. These case studies serve as a reminder that, where heat load depresses appetite or poor food cannot support lactation, the energy deficit and stress reduces cow fertility, fitness, and longevity, so that she fails to breed a heifer replacement during her shortened productive life. The model predicted that food intake, depressed by heat stress, would not support a milk yield above 14 l/day and 3000 l per annum at the coast, and 22 l/day and 5000 l per annum in the highlands. Therefore, although appearing profitable in the short term, the current policy of promoting cows with higher yields than the climate and production system can support, is unsustainable. This outcome has implications for smallholder dairy development policy in Kenya, and probably elsewhere in the tropics. Instead, one should reconsider smaller exotic breeds and crossbreds with improved indigenous dairy cows whose overall productivity from milk yield, fecundity, longevity, and disease tolerance 50 years ago was better than that of the modern Holstein-Friesian in a Kenya smallholding.

Livestock farmers' perception and epidemiology of bovine trypanosomosis in Kwale District, Kenya

We did cross-sectional surveys in Kwale District, Kenya to determine the epidemiology of bovine trypanosomosis and livestock owners' perceptions of the disease. The surveys involved relative importance of trypanosomosis, examination of the current disease constraints, current control practices and drug-use patterns. Informal meetings were held with farmers and cattle census undertaken. Tsetse-fly densities and trypanosomosis prevalences in cattle were determined. A total of 132 farmers were interviewed. Trypanosomosis, anaplasmosis, East Coast fever, foot-and-mouth diseases were reported to be the major constraints to livestock production. Trypanosomosis was the most important compared to other diseases. Chemotherapy was the most widely used method of controlling the disease. Farmer-based tsetse-control technologies were poorly adopted. Respondents were quite knowledgeable on the symptoms, causes and treatment of trypanosomosis. Glossina austeni, G. brevipalpis and G. pallidipes were found in the area; the latter was the most common (0.2-738 flies/trap). Trypanosoma congolense and T. vivax were found in cattle with the former more prevalent. Infection prevalences in cattle varied between 0 and 25% (median: 22%).

Temporal dynamics of dairy health and production in rural smallholder communities in Northern Vietnam

The objective of this field study was to describe the temporal pattern of dairy cattle health and production and associated risk factors in rural small-holder communities in northern Vietnam, one of the target areas of the government's dairy development programme. A total of 99 dairy farms (11 per commune) were recruited from 9 of 32 communes in Ba Vi District, Ha Tay Province, using random two-stage cluster sampling. All dairy cattle present on the selected farms were included. After the initial questionnaire survey was conducted, farms were visited to collect follow-up information at 3-monthly intervals over a period of one year. The results suggest that offtake as well as mortality are important productivity indices because farmers sell or slaughter dairy cattle that are in poor health at low prices during summer months. Changes in relation to the farming operation suggest that for the farmers adopting dairy production it has become one of the main agricultural activities.

Epidemiological studies on Theileriosis and the dynamics of Theileria parva infections in Rwanda

An epidemiological analysis based on three country wide surveys was carried out to determine the prevalence of infections with Theileria spp. in Rwanda. In the 1998 dry season, a total of 264 blood samples were submitted to Theileria spp. characterisation using the 18S species-specific PCR-RFLP assay. The same samples together with 634 samples (317 samples/season) collected during the 2002 dry season and the 2003 wet season were further analysed using the p104 Theileria parva specific PCR. The results from the 18S characterisation showed the presence of four Theileria spp., namely T. parva, T. mutans, T. taurotragi and T. velifera in the field. Half of the animals had multiple Theileria spp. infections. T. parva was the most prevalent and a high correlation (94%) was found between the prevalence results using the 18S and the p104 PCR assays. The prevalence of T. parva infections was stable over time and over season but decreased significantly from the high land to the low land areas. This unexpected trend cannot be explained alone by ecology or the dynamics of the tick population in the different zones, many other components such as breed type, tick control practices and grazing system are likely to play a role. Another important finding was the fact that young animals are infected early in life in all regions except in the high land zone indicating the existence of a particular epidemiological situation in this part of the country.

Prevalence and incidence of tick-borne diseases in smallholder farming systems in the western-Kenya highlands

The prevalence and incidences of tick-borne diseases (TBDs) infections in cattle were studied in the western-Kenya highlands. Serological tests, thick-blood and lymph-node smears were used to quantify TBDs during cross-sectional and longitudinal studies. Four hundred and eight and 192 (wet season) and 114 and 46 (dry season) cattle were bled for serology in the rural and peri-urban areas, respectively. Seroprevalences differed significantly between the two areas (p<0.05). The cattle were monitored for 23 months (259,923 and 126,273 cattle days in the rural and peri-urban areas, respectively) from September 1996 to August 1998. The incidences of babesiosis, anaplasmosis and theileriosis were 0.42%, 4.64% and 4.92% and 1.45%, 32.11% and 39.05% in the rural and peri-urban areas, respectively. The difference in the incidence were significantly different for anaplasmosis and theileriosis (p<0.05). The difference in disease frequencies in two areas in close proximity shows the importance of monitoring disease events in order to understand and advice farmers in different production and farming systems appropriately.

Spatial and management factors associated with exposure of smallholder dairy cattle in Tanzania to tick-borne pathogens

A cross-sectional study of serum antibody responses of cattle to tick-borne pathogens (Theileria parva, Theileria mutans,Anaplasma marginale, Babesia bigemina and Babesia bovis) was conducted on smallholder dairy farms in Tanga and Iringa Regions of Tanzania. Seroprevalence was highest for T. parva (48% in Iringa and 23% in Tanga) and B. bigemina (43% in Iringa and 27% in Tanga) and lowest for B. bovis (12% in Iringa and 6% in Tanga). We use spatial and non-spatial models, fitted using classical and Bayesian methods, to explore risk factors associated with seroprevalence. These include both fixed effects (age, grazing history and breeding status) and random effects (farm and local spatial effects). In both regions, seroprevalence for all tick-borne pathogens increased significantly with age. Animals pasture grazed in the 3 months prior to the start of the sampling period were significantly more likely to be seropositive for Theileria spp. and Babesia spp. Pasture grazed animals were more likely to be seropositive than zero-grazed animals for A. marginale, but the relationship was weaker than that observed for the other four pathogens. This study did not detect any significant differences in seroprevalence associated with other management-related variables, including the method or frequency of acaricide application. After adjusting for age, there was weak evidence of localised (<5 km) spatial correlation in exposure to some of the tick borne diseases. However, this was small compared with the 'farm-effect', suggesting that risk factors specific to the farm were more important than those common to the local neighbourhood. Many animals were seropositive for more than one pathogen and the correlation between exposure to the different pathogens remained after adjusting for the identified risk factors. Identifying the determinants of exposure to multiple tick-borne pathogens and characterizing local variation in risk will assist in the development of more effective control strategies for smallholder dairy farms.

Seroprevalence Estimation and Risk Factors for A. marginale on Smallholder Dairy Farms in Tanzania

A cross-sectional serological survey of A. marginale was conducted on 200 randomly selected smallholder farms in each of the Tanga and Iringa Regions of Tanzania between January and April 1999. Sera, from dairy cattle of all ages, sexes and breeds were tested for antibodies against A. marginale using an indirect enzyme-linked immunosorbent assay. Antibodies to A. marginale were present in cattle throughout the study areas and the overall prevalence was 20% for Tanga and 37% for Iringa. The forces of infection based on the age seroprevalence profile were estimated at 8 for Tanga and 15 for Iringa per 100 cattle years-risk, respectively. In both regions, seroprevalence increased with age (beta = 0.01 and 0.017 per year of age, p < 0.005, in Tanga and Iringa, respectively). Older animals in Iringa were significantly and negatively associated with decreased seropositivity (beta = -0.002, p = 0.0029). Further results of logistic regression models reveal that geographic location of animals in Tanga was associated with seropositivity (odds ratio (OR) = 2.94, p = 0.005, for Tanga Rural and OR = 2.38, p = 0.066, for Muheza). Animals acquired as a gift in Iringa had higher odds for seropositivity than brought-in cattle (OR = 2.44, p = 0.005). Our study has identified and quantified some key risk factors that can guide planners devising disease control strategies.

The incidence of calf morbidity and mortality due to vector-borne infections in smallholder dairy farms in Kwale District, Kenya

An observational longitudinal study was carried out on 92 randomly selected smallholder farms in two coastal lowland zones of Kwale District in Kenya between December 1997 and November 1999. The objective was to estimate the incidence of the main vector-transmitted diseases in pre-weaned calves. From an initial 41 pure or cross-bred Bos taurus calves which were less than 2 months and whose birth and disease histories were known, study calves were recruited progressively and monitored until they were weaned at around 146 days. Overall, 130 calves in 67 farms were monitored and these contributed a total risk period of 30,062 days. Disease parameters were analysed and compared as true annual and age-specific incidence rates. The incidences of East Coast fever (ECF) (23.1%) and trypanosomosis (29.1%) were the highest among the vector-borne diseases. The corresponding mortality incidence rates of ECF and trypanosomosis were 10.9 and 3.6%, respectively. The annual incidence rates of anaplasmosis and babesiosis were 10.9 and 1.2%, respectively. There was no mortality arising specifically from anaplasmosis or babesiosis. Analysis of survival times to natural infection indicated that the field challenge resulting to cases of trypanosomosis was much higher compared to the risk of either ECF or anaplasmosis. It was concluded that these vector-borne diseases constrain production of replacement stock in this coastal lowlands region of Kenya.

Identification of a target population for immunisation against East Coast fever in coastal Kenya

Two experiments were carried out to identify the target population of cattle for immunisation against East Coast fever (ECF) using the infection-and-treatment method. Firstly, a sentinel-calf study was used to determine the age window for ECF immunisation by determining ages at clinical detection of infection with Theileria parva. Six groups of five naive cross-bred (Bos taurus/Bos indicus) male calves, introduced at intervals of 2 months at a mean age of 26 days, were exposed to natural tick challenge on a high ECF-risk, small-holder farm in the coastal lowland, coconut-cassava agro-ecological zone of coastal Kenya. Secondly, a challenge study evaluated the relationship between the presence of T. parva antibodies and immunity. Ten indigenous adult Zebu cattle and nine Zebu young stock purchased from farmers in the same zone, and eight cross-bred calves (survivors of the sentinel-calf study) were challenged with 10 times the immunising dose of T. parva Marikebuni stock. Twenty-four of these 27 cattle had high antibody titres before challenge. Two cross-bred calves, obtained from an ECF-free area and seronegative to T. parva schizont antigen, also were challenged and used as susceptible controls. Twenty-five (83%) of the 30 sentinel calves contracted ECF over an age range of 36-116 days (mean 72 days). The remaining five calves died of other causes within 2 months of arrival on the farm. Fourteen of the 25 calves survived the infection and developed antibodies to T. parva. Despite tick control, seven of these 14 calves had a second episode of ECF and two died. In total, 13 of the 25 calves that contracted ECF died. Only one of 19 indigenous Zebu animals developed clinical ECF when challenged with T. parva Marikebuni (mild clinical signs with spontaneous recovery). Of the eight cross-bred survivors from the first experiment, only one succumbed to ECF when challenged and it died. Both susceptible cross-bred calves developed severe clinical signs of ECF and one died. The experimental studies show that in the high ECF-risk areas of the coconut-cassava zone of coastal Kenya, immunisation against ECF in cross-bred (B. taurus/B. indicus) cattle should be targeted at an early age (preferably within 1-2 months of birth).