Heterogeneous distribution of Dirofilaria immitis in dogs in St. Kitts, West Indies, 2014-2015.

In the Caribbean region, Dirofilaria immitis (heartworm) has been detected on almost all of the islands. While it is assumed to be endemic throughout the region, there is a lack of baseline data from the Leeward Islands (north-east of the Caribbean region). The objective of this study was to estimate the prevalence and the spatial distribution of heartworm disease in dogs on St. Kitts, a small 174km island which is part of the Leeward Islands. A cross-sectional study was conducted in 2014 with 100 dogs tested using a commercial antigen test. Dogs were from all regions of the island except the southeastern region, which differs socio-economically from the rest of the island. Heartworm was not detected in these 100 dogs. To complete the survey, in 2015, fifteen dogs from the southeast region were tested, eight of which were positive for heartworm. Prevalence was estimated at 7.0% (95% confidence interval: 4.6-11.6). Data from two other sources were added to complete the report: data from dogs enrolled in a free spay and neuter program and tested against heartworm (164 dogs with 3 positive for heartworm), and the data from positive dogs diagnosed at the Ross University Veterinary Clinic in 2014 and 2015 (3 dogs). Most of the heartworm positive dogs (10/14) lived in a delimited area in the southeast of the island. These results indicate an overall low prevalence of Dirofilaria immitis in St. Kitts, lower than that observed in the other Caribbean islands. Heterogeneity in the spatial distribution of the parasite was observed, with the majority of cases residing in the southeast of the island. Previous spatial models focused on the spread of the parasite over large geographical areas and long distances, but not within a restricted area. Our results indicate the presence of local factors which may have limited spread of the disease over short distances. Further studies are needed to understand this markedly heterogeneous distribution.