Economic Impact and Risk Factors Associated With Lumpy Skin Disease Outbreaks in Cattle Farms in Nakuru County, Kenya

Abstract

Lumpy Skin Disease (LSD) is spreading rapidly to previously disease-free areas causing enormous economic losses. The factors that favour its spread are not extensively studied in the tropics. This study was carried out in Nakuru County, Kenya with the aim of identifying the risk factors of LSD outbreaks and estimating the economic impact of the disease. A retrospective case control study was carried out on 205 farms in order to compare the frequency of risk factors in the case and control farms. A frequency of factor that is greater in cases than in controls is judged as a risk factor. Forty-one and 164 case and control herds were assembled. Data from both case and control herds were collected via questionnaires administered through personal interviews. Data collected included herd sizes, age and sex structures, breeds, source of replacement stock, grazing system and costs (direct and indirect) incurred when LSD outbreaks occurred. The data were analysed using STATA 13® and R 3.3.3 for association tests. A mixed model was used with fixed effects on village and the rest of the variables as random. A univariable and multivariable logistic regression analysis of disease outcome and the risk factors was done and model built by backward fitting using likelihood ratio tests. The economic impact was estimated using the framework and methods suggested by Rushton in 1999 and used by Jemberu et al. in 2014 and Molla et al. in 2017 in the estimation of economic impact of Foot and Mouth Disease and LSD respectively in Ethiopia. The factors that were significantly associated with LSD outbreaks on univariable analysis included breed, source of replacement stock and herd size. Farms which replaced their herds with cattle from outside the farm were 8.4 times more likely to experience LSD outbreaks compared to farms that replaced from their own herds (p=0.000), exotic breeds were 14.3 times more likely to experience LSD outbreaks relative to the indigenous breeds (p=0.007), large herds were 3.5 times more likely to experience LSD outbreaks compared to the small herds (p=0.029).. In the multivariable logistic regression model, only breed and source of replacement stock retained their significance indicating that the other variables that lost their significance were confounded by either unmeasured or measured variables. Indigenous breeds of cattle are less susceptible to ectoparasites that include blood feeding arthropods that transmit LSD compared to exotic breeds. Replacement stock from outside the farms could be a source of infection since culling of sick animals is practiced in some farms. Farms with exotic breeds were of cattle were 16.7 times more likely to experience LSD outbreak compared to farms with indigenous breeds of cattle (p=0.01). Farms that sourced their replacement stocks from outside the farm were 8.7 times more likely to experience LSD outbreak compared to farms that did not source their replacement cattle from outside the farms (p<0.001). The direct losses were estimated at an average of Ksh. 2,511 and Ksh. 21,110 per farm keeping indigenous and exotic breeds, respectively. The losses due to milk reduction were estimated at an average of Ksh. 1,890 and Ksh. 11,275 per farm keeping indigenous and exotic breeds of cattle, respectively. Cattle mortalities were estimated at an average of Ksh. 621 and Ksh. 9,835 per farm keeping indigenous and exotic breeds of cattle, respectively. The indirect losses were estimated at an average of Ksh. 4,603 and Ksh. 5,855 per farm keeping indigenous and exotic breeds of cattle. The cost of treatment of secondary infections were estimated at an average of Ksh. 3,715 and Ksh. 5,003 per farm keeping indigenous and exotic breeds of cattle, respectively. The cost of vaccination, whether pre or post LSD, was estimated at average of Ksh. 888 and 852 per farm keeping indigenous and exotic breeds of cattle, respectively. The impact of LSD was higher in farms keeping exotic breeds than indigenous breeds of cattle. Within the farms keeping exotic breeds, direct losses from LSD had a higher impact with the milk loss being the greatest, followed by mortalities. In the farms with indigenous breeds of cattle, indirect losses had a higher impact with treatment being the greatest source of losses. Based on these estimates, the total losses of LSD for farms keeping indigenous cattle was estimated at Ksh 7,114 and Ksh 26,965 for farms keeping exotic breeds of cattle. Yet, if these farms implemented vaccination as a control strategy against LSD, they would save approximately, Ksh 6,226 and 26,113 for farms keeping indigenous and exotic cattle breeds, respectively. These levels of resources can be reallocated to other management functions within cattle farms. It is recommended that the efficacy of LSD vaccine currently used in Kenya be re-evaluated, farmers are trained on LSD control measures such as vaccination, introduction of cattle examined and certified by the veterinary authorities to be free of notifiable diseases such as LSD and cattle gaining entry into the county for market or pasture and water be vaccinated prior to accessing the county. In conclusion, LSD occurs in Nakuru County and is one of the major causes of morbidity and mortality. Control measures of the disease needs to be refined, especially use of vaccines.