Spatial distribution and risk factors for equine infectious anaemia in the state of Mato Grosso, Brazil

Abstract

The prevalence of equine infectious anaemia (EIA) in the three biomes of the state of Mato Grosso (Amazon, Cerrado and Pantanal) was estimated. Serum samples were collected from 3,858 equines in 1,067 herds between September and December 2014. The agar gel immunodiffusion (AGID) assay was used to detect EIA virus antibodies, and if a herd contained a seropositive animal it was classified as a focus. The prevalence rates were 17.2% (95% confidence interval [CI]: 14.9-19.8%) for herds and 6.6% (95% CI: 5.8-7.5%) for animals. The Pantanal region showed the highest prevalence rates: 36.1% (95% CI: 30.8-41.7%) for herds and 17.0% (95% CI: 14.7-19.6%) for animals. The spatial distribution of relative risk was calculated according to the kernel density, which revealed three major clusters with the highest prevalence rates occurring in the north-western (Amazon biome), north-eastern (Cerrado biome) and southern (Pantanal biome) regions. A high spatial correlation was found among ranches, with high intraherd prevalence rates located in the Amazon and Cerrado biomes, but the highest spatial correlation with EIA foci was found in the Pantanal biome. Variables related to ranch management, reflecting human influence, were associated with positive equines. Based on the results, it can be concluded that EIA is present in all biomes of the state, and that the risk factors are associated with human interference in the transmission process. Given this situation, the EIA control programme should be re-evaluated and more prophylactic measures should be adopted to control the disease.