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The presence of Dirofilaria immitis excretory-secretory (ES) products was detected in the urine of infected dogs using a coagglutination assay. Urine samples from 30 naturally infected dogs were positive. Seventeen of them were microfilaremic, whereas 13 had become amicrofilaremic after receiving 2 courses of diethylcarbamazine. Urine samples from 20 dogs infected with other parasites, Dipetalonema reconditum (7), Toxocara canis (5), and Ancylostoma caninum (8), and urine samples from 20 healthy dogs were negative. The assay detected 200 ng/ml or more of ES products. This assay is simple, easy to perform with minimum training, and requires no equipment. Therefore it should be useful to detect canine filariasis under field conditions.

The serologic prevalence of Dirofilaria immitis infection in 601 dogs in Washington was investigated in 1989-1990. Blood samples for serum were obtained from dogs approximately 2 yr of age or older in humane society shelters (n = 392) or veterinary clinics (n = 209). Serum samples were tested for heartworm infection using an enzyme-linked immunosorbent assay antigen test. Three (0.5%) dogs were positive for D. immitis infection, all of which were born and lived several years in states other than Washington. Heartworms have not been detected during the last 9 yr in the 1,203 dogs examined at the Washington Animal Disease Diagnostic Laboratory, Pullman, Washington. Consequently, the likelihood of indigenous heartworm infections in dogs in Washington remains low at this time.

Protective immunity to larval Dirofilaria immitis has been demonstrated in both the natural host, the dog, and in an experimental host, the mouse. In the present study, sera were collected and pooled from dogs that had been shown to have protective immunity to larval D. immitis. The pooled serum was inoculated into normal BALB/cByJ mice that then were challenged with third-stage larvae (L3) implanted in diffusion chambers. Two weeks postchallenge no significant difference was seen in either parasite survival or growth. Three weeks postchallenge, there was a significant decrease in parasite survival in mice receiving serum from immune dogs. Living larvae recovered at 3 wk postchallenge were significantly shorter than cohorts recovered from control mice. Antibody responses to L3 and forth-stage larvae (L4) surface antigens, to L3 and L4 aqueous soluble antigens, and to an excretory-secretory antigen fraction were measured. Only antibody responses to L3 surface antigens were elevated in the immune serum as compared to controls, thus suggesting a possible role for antibodies with specificity for surface antigens in protective immunity.

The ferret, Mustela putorius furo, was found to be susceptible to Dirofilaria immitis infection when exposed to low (14) or high (280-420) numbers of infective larvae harvested from Aedes aegypti. Eight ferrets (half of them cortisonized) were inoculated subcutaneously with 14 larvae each. All of them were subsequently found to harbor D. immitis in the heart, and all but one of them had worms of both sexes. Six of these ferrets were examined for microfilaremia at 31 to 35 weeks after inoculation; 3 were positive (one observed only at postmortem examination) and there was evidence that fertilization of female worms had occurred in one other. Females up to 25.5 cm and males up to 16.0 cm were recovered. There was no evidence that the cortisonization of some ferrets had affected the infections. Both male and female ferrets became infected. Four cortisonized ferrets were inoculated with 280 or 420 larvae of D. immitis (divided equally between subcutaneous and intraperitoneal routes). All of them died 16 to 18 weeks after inoculation, yielding 102 to 125 immature D. immitis. In these lethal infections, worms were recovered from the heart and adjoining vessels, and also from vascular and extravascular sites throughout the body.

A study was undertaken to determine the prevalence of Dirofilaria tenuis in raccoons from subtropical southern Florida as compared to the northern part of the state. The results indicate that D. tenuis is more prevalent in southern Florida and suggest that this might be why humans suffer from more D. tenuis infections in southern Florida than in other parts of the state.

The prevalence of canine heartworm (Dirofilaria immitis) was examined in the domestic dog, coyote (Canis latrans), and red fox (Vulpes fulva) populations of southeastern Nebraska. Microfilariae were detected in 21.4% (22 of 103) of the domestic dogs. The average age of infection for dogs was 5.8 yr. Nine of the 22 infected dogs also were positive for Dipetalonema reconditum. Thirty-nine of 443 (8.9%) coyotes were found to have adult heartworms. The average number of male and female worms per heart was 3.7 and 3.9, respectively. The mean age of infected coyotes was 3.6 yr. Red foxes had an infection rate of 4.8% (1 of 21). This fox heart had only 1 immature female worm. A mail survey of 6 veterinary clinics was also conducted. Veterinarians reported infection rates of 0% to 18.8% in domestic dogs for their localities.

Avermectin B1a was found active against the pre-cardiac stage of Dirofilaria immitis in ferrets. The drug was given orally, at 0.2 mg/kg, on days 38--42 of infection. At necropsy, 5 1/2 months after inoculation, worms were almost totally absent from the hearts of these ferrets. The efficacy of melarsoprol against developing Dirofilaria, which has been demonstrated in dogs by other workers, was demonstrated in ferrets given oral doses, at 100 mg/kg, on days 38--42 of infection. The reported efficacy of mebendazole was not evident in the ferret host in this study, probably because the treatment (100 mg/kg, orally, on days 38--42) was shorter and later than that reported for dogs.

Natural and experimental infections of cats with Dirofilaria immitis have been reported. Experimental infections of D. immitis in cats with the subsequent detection of microfilaremia and immediate skin hypersensitivity to antigen to D. immitis were produced. Cutaneous nodules and chylothorax were also detected in some infected cats. Adult worm recoveries were low and dead worms were found in some cats indicating the unsuitability of the cat as a host for D. immitis. However, one successful mosquito passager of D. immitis from a cat to a dog was accomplished.