Dirofilaria immitis and Dipetalonema reconditum in dogs of East Central Indiana
The four objectives of this study were to determine: 1) the incidence of Dirofilaria immitis and Dipetalonema reconditum in dogs of East Central Indiana, 2) the variables significantly affecting the incidence of each parasite, 3) the correlation of heartworm infections with clinical symptoms, and 4) to determine whether Dirofilaria immitis and Dipetalonema reconditum are endemic in Indiana.From December, 1973 to April, 1974, blood samples were taken from 335 dogs in East Central Indiana and were examined for microfilariae using the direct smear and the modified Knott concentration techniques. At the same time, complete information on each dog was collected on a "SURVEY INFORMATION” form. The data was statistically analyzed by crosstabulation of each variable with the results of the blood tests for each parasite. Levels of significance were computed using chi square values with appropriate degrees of freedom. Values of 0.05 were considered to be significant.In this study, the overall incidence of Dirofilaria immitis was found to be 3°% which included one dog infected with both parasites. Of the 131 hunting dogs, 6.1% were infected, while only 1% of the 204 non-hunting dogs were infected. Furthermore, all of the dogs infected with heart-worms were those which were principally outdoor dogs. These differences were significant and they reflect thehigher exposure risk of hunting dogs and dogs living out-doors to the mosquito vectors.The incidence of Dipetalonema reconditum was 6% overall with 11.5 % of the hunting dogs and 2.5% of the non-hunting dogs infected. It was most prevalent in dogs three to six years of age. After age seven the prevalence declined sharply. This decrease with age may be the result of an immune response to the infective larvae which prevents reinfection.Clinical symptoms could not be correlated with infections with Dirofilaria immitis since 90% of the dogs infected with heartworms had no symptoms of the disease. This indicates that most of the heartworm infections in dogs of this area are light, probably involving few adult worms. The results of this study indicate that Dirofilaria imnitis and Dipetalonema reconditum are endemic in Indiana, as 60% of the dogs with heart-worms and 35% of the dogs with Dipetalonema reconditum had never been out of the state.