Swamp fever in wild horses from the Pantanal, Brazil

Abstract

The Pantanal is a large wetland with an area of 140,000 km2, located in the center of South America. In the Pantanal some very large ranches (usually over 40,000 ha) have populations of wild horses. The objective of this study was to evaluate the occurrence of equine infectious anemia (EIA) in a population of wild horses in an EIA-endemic region. In this study seropositivity to EIA was 5.6% in wild horses and 34.1% in domestic horses belonging to the same ranch. The observed prevalence rates were 5.7% in wild male horses and 5.3% in wild females. The observed prevalence rate in domestic male horses was 34.1%. Mean ages of domestic seropositive and domestic seronegative horses were 9 and 5.8 years old, respectively. Mean ages of wild seropositive and wild seronegative horses were 3.2 and 1.7 years old, respectively. No sex influence was observed in the wild animals. There was a very significant (P < 0.001) difference between the EIA prevalence in wild and domesticated horses in the studied farm. The hypothesis formulated by the authors is that man had played an important role in the EIA virus transmission to domesticated horses in the Pantanal. On the other hand, in wild populations insect vectors probably played a fundamental role in EIA transmission in the region.