Economic analysis of rift valley fever control options from a one health perspective in Kenya

Abstract

Since 1931, Rift Valley fever (RVF) epidemics have recurred in Kenya at an average interepidemic period of up to 10 years. The most recent epidemic occurred in 2006/2007. It resulted in losses. Estimated as KES 2.1 Billion. A post epidemic assessment recommended adoption of One Health (OH) approach to RVF management as well as implementation of livestock control strategies that offer highest benefits to both the livestock and public health sectors. Evidence to guide such decisions was inadequate. Costs and benefits analysis (CBA) of RVF control had not been conducted. This study provides the evidence in four sequential steps of data collection and analysis, focusing on RVF high risk areas in Kenya. The steps included, (i) a social network analysis at national and sub-national (Garissa County) levels that identified RVF stakeholders and the extent to which they had institutionalised One Health (OH) approach, (ii) delineation of eleven (1 baseline and 10 alternatives) livestock RVF control strategies (that combined different levels of surveillance, vaccination, and mosquito control) and estimation of the associated control costs for the period 2007-2014. The impacts of the control measures on a hypothetical epidemic 2014/2015 were simulated in a (iii) herd dynamics and RVF modelling to estimate number of animal mortality and morbidity, (iv) animal-human RVF epidemiological modelling to generate human morbidity and mortality that would arise from the animal cases. Human case data was used to estimate disability adjusted life years (DALYs). Quantitative livestock and economic CBA in Excel combined animal simulation outputs, production indices and product prices to estimate value of livestock sector losses under each control strategy. Benefits of alternative strategies represented saved losses, compared to the baseline strategy. The evaluation criteria for the alternate control strategies were net present value of incremental benefits over costs. Social network analysis showed that, at national level, stakeholders had mobilised for and institutionalized OH through formal structures. The reverse was true at sub-national level. Alternate strategies that assumed improved vaccination coverage (3-5 fold) implemented 2-3 years before the hypothetical epidemic, showed the highest benefits ~livestock sector benefit cost ratio of 1.1 to 5.0 and public health sector cost effectiveness of KES 2,847 to KES 3,485 per DALY averted. Considering that RVF outbreaks occur at sub-national level, where both OH has not been institutionalized and the baseline vaccination strategy continues to be adopted, in case of an incursion, the next epidemic would have a similar magnitude as the 2006/2007.