Affects: Dogs
Toxocara canis (T. canis, also known as dog roundworm) is a worldwide-distributed helminth parasite that primarily infects dogs and other canids, but can also infect other animals including humans. The name is derived from the Greek word toxon 'bow, quiver' and the Latin word caro 'flesh'. T. canis live in the small intestine of the definitive host. This parasite is very common in puppies and somewhat less common in adult dogs. In adult dogs, infection is usually asymptomatic but may be characterized by diarrhea. By contrast, untreated infection with Toxocara canis can be fatal in puppies, causing diarrhea, vomiting, pneumonia, enlarged abdomen, flatulence, poor growth rate, and other complications.
As paratenic hosts, a number of vertebrates, including humans, and some invertebrates can become infected. Humans are infected, like other paratenic hosts, by ingestion of embryonated T. canis eggs. The disease (toxocariasis) caused by migrating T. canis larvae results in two syndromes: visceral larva migrans and ocular larva migrans. Owing to transmission of the infection from the mother to her puppies, preventive anthelmintic treatment of newborn puppies is strongly recommended. Several anthelmintic drugs are effective against adult worms, for example fenbendazole, milbemycin, moxidectin, piperazine, pyrantel, and selamectin.
Transmission To Humans: Humans can be infected by T. canis, resulting in a condition called toxocariasis. Consumption of eggs from feces-contaminated items is the most common method of infection for humans, especially in children and young adults under the age of 20 years. Although rare, being in close contact with an infected animal (e.g., stroking the fur of an infected animal) or with soil that contains infectious eggs can also cause human infection, especially handling soil with an open wound or accidentally swallowing contaminated soil, as well as eating undercooked or raw meat of an intermediate host of the parasite such as lamb or rabbit. Although the risk of being infected by petting a dog is extremely limited, a single infected puppy can produce more than 100,000 roundworm eggs per gram of feces.
Toxocariasis can result in complications such as hepatomegaly, myocarditis, respiratory failure and vision problems, depending on where the larvae are deposited in the body. In humans, this parasite can infect organs including the lungs, liver, and the back of the eye (which can result in blindness).
Treatment: Humans suffering from visceral infection of T. canis, the drugs albendazole, mebendazole and thiabendazole are highly effective. For other treatments, refer to the disease pages: visceralis larva migrans and ocularis larva migrans.
Anthelminthic drugs are used to treat infections in dogs and puppies for adult worms. Treatment protocol will vary based on the dog's age, production level and activity level. There are different treatment paths for puppies, pregnant bitches, lactating bitches, dogs with increased risk of infection, professional dogs, and dogs sharing homes with young children or immunocompromised individuals.
Puppies: from the age of two weeks, then every 14 days up to two weeks after weaning with fenbendazole/febantel, flubendazole, pyrantel, or nitroscanate, followed by monthly treatments for up to six months of age.
Pregnant bitches: to prevent transmission to the puppies, pregnant females can be given macrocyclic lactones on the 40th and 55th day of pregnancy or genbendazole daily from the 40th day of pregnancy continuing until the 14th day postpartum.
Prevention: There are several ways to prevent a T. canis infection in both dogs and humans. Regular deworming by a veterinarian is important to stop canine re-infections, especially if the dog is frequently outdoors. Removing dog feces from the yard using sealed disposable bags will help control the spread of T. canis. Good practices to prevent human infections include: washing hands before eating and after disposing of animal feces, teaching children not to eat soil, and cooking meat to a safe temperature in order to kill potentially infectious eggs.