Optimizing risk-based disease control strategies through network analysis: Case insights from FMD in Sri Lanka

Foot and mouth disease (FMD) is an endemic disease in Sri Lanka. The disease spreads among cattle and buffaloes via direct and indirect contact. Management of FMD is challenging given its endemicity and the largely extensive grazing management practices. This situation is further exacerbated by the difficulty in controlling animal movement. In this study, we describe livestock movement networks in an FMD high-risk area in Sri Lanka and the impact of implementing various control measures on FMD outbreaks. Cattle and buffalo movement networks were created based on the information obtained from the farmers regarding grazing patterns and the veterinary officers regarding animal movement, responding to a pretested questionnaire. In-person questionnaires were administered to each veterinarian in the Eastern province in Sri Lanka and 10 selected farmers from each veterinary range (administrative regions within districts). Static, directed and undirected networks representing grazing and inter-VS range movements were constructed and analyzed for structure, connectivity and communities. Network fragmentation index was used to test the effect of iterations of targeted disrupting potential network-based transmission in the population through animal vaccination. Forty out of the total 46 veterinary range representatives and 294 farmer responses to the questionnaire were collected between January and December 2017. Animal movements primarily occurred within the province and in each district three different network communities were observed, and a fourth community combined the three districts. Targeting high-centrality farms during an outbreak and conducting biannual vaccinations in veterinary ranges with high network centrality could reduce outbreaks significantly compared to applying random control measures. In conclusion, targeted interventions appear to offer a more cost-effective approach for controlling contagious diseases like FMD in Sri Lanka. Informal patterns may contribute meaningfully to disease spread and should therefore be considered in the design of control strategies.