Prevalence of Dirofilaria immitis and Dipetalonema reconditum infection in dogs: 805 cases (1980-1989).

Clinical records of 6,977 dogs examined at the small animal clinic of the University of Tennessee College of Veterinary Medicine from January 1980 through December 1989 were analyzed to determine the prevalence and changing frequency of Dirofilaria immitis and Dipetalonema reconditum infection. Using the Knott's test on these dogs, 805 (11.54%) tested positive for microfilariae, with D immitis in 430 dogs (6.16%), and Dip reconditum in 375 dogs (5.37%). Statistical analysis confirmed that the prevalence of D immitis and that of Dip reconditum were essentially equal in the population of dogs included in this study. There was a slight decrease in the prevalence of D immitis over the 10 years examined, but the prevalence of Dip reconditum remained constant. The results were not affected by year-to-year variability in the number of examinations performed. On the basis of our findings, in eastern Tennessee, those veterinarians who diagnose heartworm infection by the presence of microfilariae without differentiating the species involved, risk misdiagnosing 50% of the cases. If the patterns of prevalence seen in recent years continue, the chances of error may actually increase.