Eight trials were conducted in dogs to document the efficacy of ivermectin (6 micrograms/kg of body weight) and pyrantel pamoate (5 mg of active pyrantel/kg) in a beef-based chewable formulation against Dirofilaria immitis, Ancylostoma caninum, Uncinaria stenocephala, Toxocara canis, and Toxacaris leonina. Three studies involved induced infection with D immitis, and 5 studies involved induced or natural infection with hookworms and ascarids. In 3 intestinal parasite trials, the efficacy of the combination chewable tablet was compared with each of its components. Results indicated that 1 component did not interfere with the activity of the other. In 1 heartworm and 2 intestinal parasite trials, the efficacy of pyrantel, ivermectin/pyrantel combination, or ivermectin with pyrantel dosage of 10 mg/kg was evaluated. The ivermectin/pyrantel combination was 100% effective in preventing development of D immitis larvae. Efficacy of the combined product against T canis, Toxascaris leonina, A caninum, and U stenocephala was 90.1, 99.2, 98.5, and 98.7%, respectively. In the intestinal parasite trials, each individual component was found not to interfere with the anthelmintic action of the other. Increasing the dosage of pyrantel to 10 mg/kg (2 X that in the combination) did not interfere with the efficacy of ivermectin against heartworm or increase the activity of pyrantel against intestinal parasites.

Eight trials were conducted in dogs to document the efficacy of ivermectin (6 micrograms/kg of body weight) and pyrantel pamoate (5 mg of active pyrantel/kg) in a beef-based chewable formulation against Dirofilaria immitis, Ancylostoma caninum, Uncinaria stenocephala, Toxocara canis, and Toxacaris leonina. Three studies involved induced infection with D immitis, and 5 studies involved induced or natural infection with hookworms and ascarids. In 3 intestinal parasite trials, the efficacy of the combination chewable tablet was compared with each of its components. Results indicated that 1 component did not interfere with the activity of the other. In 1 heartworm and 2 intestinal parasite trials, the efficacy of pyrantel, ivermectin/pyrantel combination, or ivermectin with pyrantel dosage of 10 mg/kg was evaluated. The ivermectin/pyrantel combination was 100% effective in preventing development of D immitis larvae. Efficacy of the combined product against T canis, Toxascaris leonina, A caninum, and U stenocephala was 90.1, 99.2, 98.5, and 98.7%, respectively. In the intestinal parasite trials, each individual component was found not to interfere with the anthelmintic action of the other. Increasing the dosage of pyrantel to 10 mg/kg (2 X that in the combination) did not interfere with the efficacy of ivermectin against heartworm or increase the activity of pyrantel against intestinal parasites.

Although cats are less susceptible to infection with Dirofilaria immitis than are dogs, the possibility of severe consequences from infection or adulticidal treatment renders preventive treatment a desirable alternative in endemic areas. To evaluate the efficacy of milbemycin oxime as a chemoprophylactic agent in cats, 48 cats were inoculated with infective D immitis larvae. Single oral treatment with 2.3 mg of milbemycin oxime (0.5 to 0.9 mg/kg of body weight) at 30 or 60 days after inoculation with infective larvae gave strong but incomplete protection. Treatment at 60, as well as 90, days after inoculation with infective larvae was completely effective in preventing development of infection. A control group of inoculated, but untreated, cats was monitored biweekly for hematologic changes and for changes in parasite-specific serum antigen and antibody concentrations. Pronounced increases in total leukocyte counts and eosinophil numbers were associated with the estimated time of in vivo molting from fourth- to fifth-stage larvae. Antibody reactivity correlated with infection status, but serum antigen concentrations through 161 days after inoculation were undetectable.

The occult dirofilariasis is considered a great diagnostic problem and may be related to: a) pre-patent infections; b) infections caused by worms of one only sex; c) parasites sterility due to the age or induced by drugs action; d) iirmune mediate response. The present study estimated the prevalence of the dirofilariasis in dogs in São Paulo State by means R TM of the ELISA test (CITE^R Semi-Quant ^TM Canine Heartworm Antigen Test Kit) as well as it tried to caracterize the cause of the circulating microfilaraemia absence using subsidiary exams. From 244 examined sera, 35 (14.34%) showed to be positive. From these, 20 presented one or more alternations (radiographic/ haematologic/eletrocardiographic), besides the positive ELISA test, which were compatible with dirofilariasis diagnosis. In the 15 animals left, which were assintomatic and seropositive by means of the ELISA test, no pre-patent infection was possible in spite of being to the infection risk for 6 months. Also the parasite sterility in consequence to drugs action was no observed | <p>A dirofilariose oculta constitui-se num grande problema diagnóstico e pode estar relacionada a: a) infecções pré-patentes; b) infecções causadas por vermes de um único sexo; c) esterilidade dos parasitas devido à idade ou induzida por ação de drogas; d) resposta imune mediada. Avaliou-se, no presente trabalho, a prevalência de dirofilariose em cães do Estado de São Paulo, através do teste de ELISA (CITE^R Semi-Quant ^TM Canine Heartworm Antigen Test Kit), bem  como se tentou caracterizar a causa da ausência de microfilaremia circulante, com auxílio de exames subsidiários. De 244 soros examinados, 35 (14,34%) mostraram-se positivos. Destes, 20 apresentaram, além do teste de ELISA positivo, una ou mais alterações (radiográficas /eletrocardiográficas), compatíveis com o diagnóstico de dirofilariose canina; e, nos demais 15 animais, assintomáticos, também soropositivos pelo teste de ELISA, descartou-se a forma de infecção prépatente, pois haviam sido expostos ao risco da infecção há mais de 6 meses, e também a esterilidade dos parasitas conseqüentemente à ação de drogas.</p>