Search

The present study compared the humoral response of dogs which developed microfilaremic or occult forms of dirofilariasis following experimental infection with Dirofilaria immitis L3 larvae. Quantitative analysis by ELISA revealed that antibody levels to adult somatic (AS), excretory-secretory (ES), and microfilarial (MF) antigens were highest during the patent phase of infection in dogs with either form of dirofilariasis. Patent sera from dogs destined for occult infections contained anti-AS and anti-MF antibody concentrations of 1,572 and 1,004 micrograms/ml, respectively, while microfilaremic-bound dogs contained 1,044 and 906 micrograms/ml, respectively. Chronic sera (430 days post infection) from occult dogs contained anti-AS and anti-MF antibody levels of 982 and 600 micrograms/ml, respectively, which were higher than in microfilaremic dogs. The antibody response to ES antigen was generally 10-fold less in absolute antibody concentrations at all time points tested. Immunoperoxidase staining of antigens transferred to nitrocellulose revealed the presence of several antigenic proteins which were recognized by occult, and to a lesser extent or not at all, by microfilaremic dogs. Sera drawn from occult-bound dogs 280 days post-infection, a time corresponding to microfilarial clearance (transition phase), contained higher antibody activity to microfilarial proteins weighing 47.5, 42.0, 34.2, and 22.4 kilodaltons compared to the microfilaremic dogs. This difference in antigen recognition became more apparent during the chronic phase of infection.

Circulating Dirofilaria immitis antigen was detected in sera from 24 of 24 infected dogs by counterimmunoelectrophoresis (CIE). Parasite antigen was not detected in sera from uninfected dogs or dogs with Dipetalonema reconditum infection. In experimentally infected dogs, the antigen was first detectable 6.5–8.5 months after infection. Preliminary evidence suggests that the antigen is present in male and female adult worms but not in microfilariae. Sera from dogs with microfilaremic and amicrofilaremic infections contained statistically equivalent amounts of D. immitis antigen. However, a significant correlation was observed between serum parasite antigen content and the number of adult worms present in individual dogs at necropsy. Previous studies from several laboratories have shown that microfilarial counts and serum antibody titers are not related to adult worm counts in canine dirofilariasis or other filarial infections. Thus, CIE detection of D. immitis antigenemia represents a significant improvement over previously available diagnostic techniques because it is more sensitive than microfilarial tests, more specific than antibody tests, and the only test that has been related to infection intensity.

Three 7-chlorinated lincomycin derivatives exhibited curative activity against blood-inoculated Plasmodium cynomolgi infection in rhesus monkeys. Acute infections were treated by oral or subcutaneous administration for 5 consecutive days with doses ranging from 6.25 to 100 mg per kg body weight. Cures were obtained when U-21,251F (7-chlorolincomycin) and U-24,729A (7-chloro N-demethyl-4′-pentyllincomycin) were given orally at 50 mg per kg and when U-26,285A (7-chloro N-demethyllincomycin) was given at 100 mg per kg. U-24,729A and U-26,285A were also curative when given subcutaneously at 25 and 50 mg per kg, respectively. With all dosage regimens the blood was cleared of parasites 3 to 6 days after cessation of treatment. The rate of clearance of parasites did not appear to be related to dose. No side-effects due to the antibiotics were observed.