Occurrence and Risk Factors Associated With Foot and Mouth Disease in Smallholder Dairy Farms of Nakuru County, Kenya

Abstract

Foot-and-Mouth Disease (FMD) is a highly transmissible viral infection of cloven-hoofed animals caused by an Aphthovirus of the family Picornaviridae. In Kenya, the disease is endemic with outbreaks typically occurring throughout the year. A cross-sectional study of smallholder dairy farmers in Nakuru County was conducted with the objectives of identifying the risk factors for FMD and estimating the 6-month period prevalence (May/June 2016 to November/December 2016). A secondary objective was to analyse retrospective data on FMD occurrence in Nakuru County for the previous 7 years (2010 to 2016) to determine temporal trends in infection. Semi-structured questionnaires were administered via personal interviews to 220 smallholder farmers, selected using random spatial sampling in November 2016. The retrospective study was conducted using data available from the Directorate of Veterinary Services for FMD occurrence in Nakuru for the period 2010-2016. Univariate and multivariate logistic regression models were used to assess the association of risk factors and the occurrence of FMD for the cross-sectional study with occurrence of FMD in the previous 6 months being the outcome variable. In addition, a spatial Bernoulli model was used to detect and quantify clusters of infection in the study area. Descriptive statistics and generalized linear models were used to analyse data for the retrospective study with the outcome variable being sample positivity. xvi The average size of farms was 11.0 acres (5.69-16.26, 95% CI) and the average number of cattle kept was 5.5 (4.75-6.20, 95% CI). A total of 132/220 (60%) of the respondents also owned sheep with 15% (33/220) owning goats. The majority of respondents, 94.1% (207/220), knew of FMD and 80.2% (166/207) could correctly identify the disease based on clinical signs. About 20% (45/220) farmers had vaccinated their livestock against FMD in the previous six months. FMD had reportedly occurred in 5.9% of the surveyed farms within the previous six months. The overall morbidity rate on affected farms in outbreaks occurring on farms in the previous 6 months was 58.0% (95% CI 38.3-77.6). Spatial clustering of FMD cases was identified in the northern part of the study area. This single disease cluster (radius = 5.32 Km) was 38.1 times more likely than any other part of the study area to experience FMD (p<0.001). Univariate logistic regression analysis provided evidence that clinical FMD at the household level was statistically associated with the use of a shared bull, the number of cattle restocked in the previous 12 months, the restock source (with an increased risk if buying from livestock markets), grazing sheep either within towns or the compound, grazing cattle within towns, the use of a communal dip and the number of sheep present within the household (p<0.05). Vaccination in the previous six months (May 2016 – November 2017) was associated with a decrease in the risk of FMD at the household level. xvii On multivariate analysis, the use of a shared bull [OR=28.1 (95% CI 3.3-241.3); p=0.002], the number of sheep owned [for each additionally sheep owned OR=1.1 (95% CI 1.0-1.2); p=0.006] and the number of restocked susceptible species of animals bought in the last one year [OR=1.2 (95% CI 1.0-1.4); p=0.030] were associated with whether a farm experienced a case of FMD in the previous six months. In the retrospective study, high proportions (63.74%) of the samples (171) were positive for FMD for the period 2010 – 2016. Serotypes detected from the samples in the seven-year period were O (25.2%, n=43/171), SAT 2 (17.5%, n=30/171), A (11.7%, n=20/171), and SAT 1 (9.4%, n=16/171). These serotypes caused multiple outbreaks within the study period (2010-2016) and occurred simultaneously. A generalized linear model revealed evidence of seasonal variability in FMD with positivity being highest in the dry season. This study provides a clearer picture of smallholder dairy farming within Nakuru and reports on risk factors associated with FMD at the farm level in a densely populated smallholder farming area of Kenya. The results provided can be used to inform the development of a risk-based FMD control strategy and as a baseline for evaluating future interventions used in FMD management programmes.