Roundworms in Small Animals

The first indication of infection in young animals is lack of growth and loss of condition. Infected animals have a dull coat and often are “potbellied.” Worms may be vomited and are often voided in the feces. In the early stages, migrating larvae may cause an eosinophilic pneumonia, which can be associated with coughing. Diarrhea with mucus may be evident.

In puppies with severe infections, verminous pneumonia, ascites, fatty liver, and mucoid enteritis are common. Cortical kidney granulomas containing larvae may be seen.

Infection in dogs and cats is diagnosed by detection of eggs in feces. Distinguishing the spherical, pitted-shelled eggs of Toxocara spp (T canis 80–90 × 75 μm; T cati 65 × 75 μm) from the oval, smooth-shelled eggs of Toxascaris leonina (75–85 × 60–75 μm) is important because of the public health significance of the former.

In dogs, compounds approved for treatment of roundworm infections include fenbendazole, milbemycin, moxidectin, piperazine, and pyrantel (see Table: Drugs for Intestinal Helminths of Dogs Approved in the USA and UK). In Europe, selamectin is approved to treat T canis infections with a single dose, whereas in Canada approved treatment requires two doses 1 mo apart. Preventive programs for heartworm infection using milbemycin, milbemycin/lufenuron, milbemycin/praziquantel, milbemycin/spinosad, moxidectin/imidacloprid, ivermectin/pyrantel, or ivermectin/pyrantel/praziquantel also control intestinal ascarid infections. In addition, selamectin is approved for this indication in some countries but not in the USA (see Table: Drugs for Intestinal Helminths of Dogs Approved in the USA and UK).

Drugs approved for treatment of ascarid infections in cats include emodepside, fenbendazole, milbemycin, moxidectin, piperazine, pyrantel, and selamectin (see Table: Drugs for Intestinal Helminths of Cats Approved in the USA and UK). Heartworm-preventive programs that use milbemycin, milbemycin/praziquantel, moxidectin/imidacloprid, or selamectin also control ascarid infections in cats (see Table: Drugs for Intestinal Helminths of Cats Approved in the USA and UK).

Environmentally resistant larvated eggs on the ground and somatic larvae in the bitch are the main reservoirs of infection. Perinatal transmission of infection can be greatly reduced by treating bitches with 1) daily doses of fenbendazole (25 mg/kg, PO) from day 40 of gestation to day 2 after whelping (approved in the UK), 2) ivermectin (0.3 mg/kg, SC) on days 0, 30, and 60 of gestation, and 10 days after whelping, 3) ivermectin (0.5 mg/kg) on days 38, 41, 44, and 47 of gestation, or 4) ivermectin (1 mg/kg) on days 20 and 42 of gestation; these uses of ivermectin are extra-label. Otherwise, to minimize egg output, pups should be treated as early as possible; ideally, treatment should be given 2 wk after birth and repeated at 2-wk intervals to 2 mo of age, and then monthly to 6 mo of age. Nursing bitches should be treated at the same times as puppies. In cats, perinatal transmission can be greatly reduced by treating queens with a single dose of emodepside/praziquantel spot-on in the last week of pregnancy. Kittens should be treated with an appropriate anthelmintic at 3, 5, 7, and 9 wk of age, and then monthly to 6 mo of age. Nursing queens should be treated at the same time as kittens. In other animals, the appropriate frequency of preventive treatment for roundworms should be based on a risk assessment of the animal's environment.

Because the eggs adhere to many surfaces and become mixed in soil and dust, strict hygiene should be observed by people, particularly children, exposed to potentially contaminated animals or areas.