Enzyme-linked immunosorbent assay for measurement of antibody responses to Dirofilaria immitis in experimentally infected dogs.

The chronology of the antibody response to Dirofilaria immitis was measured in 2 groups of experimentally infected Beagle dogs. An enzyme-linked immunosorbent assay (ELISA), using a semipurified, adult D immitis-derived antigen was used to quantitate antibody levels. Group A consisted of 4 dogs inoculated once with D immitis infective larvae, 4 dogs inoculated twice with D immitis infective larvae, and 4 noninoculated dogs. Group B consisted of 26 dogs which were all infected with D immitis; however, 16 of these were given daily prophylactic concentrations of diethylcarbamazine (DEC) beginning 5 days before inoculation. Significant levels of antibody were demonstrable 16 weeks after inoculation of group A dogs and remained significantly increased throughout the study. There were no significant differences in antibody levels in dogs inoculated once or twice. Nontreated and diethylcarbamazine-treated dogs in group B developed significant antibody titers 11 weeks after inoculation. Significant differences in antibody titers between treated and nontreated dogs were first observed 13 weeks after inoculation; these differences remained for the duration of the investigation. There was no apparent correlation between antibody levels and either adult worm numbers or microfilaria counts.