Roundworm
Toxocara canis is the most common roundworm of the domestic dog, and it is not able to infect cats (cats have their own species of roundworm). Its presence can go completely without symptoms although more often it creates diarrhoea, vomiting, poor growth, pot-belly and weight loss in the canine host. Sometimes the sheer volume of infection can cause such poor nutrition, even bowel blockage, and can lead to death.
Its life cycle is complicated – adult worms (they look like spaghetti) live in the intestines and produce eggs which are passed in the faeces. Once ingested by the dog/cat or another temporary host (eg. Rodents) these eggs become larvae and pass through the blood vessels and liver before encysting in the windpipe and being coughed up, then swallowed into the intestines, where they grow into adults and the cycle begins again.
An infection of roundworm can be caught multiple ways:
Consuming infective worm eggs from the soil in the environment (generally through normal grooming/self-licking)
Nursing milk from an infected mother dog
Consuming a prey animal (rodent) that is infected
During embryonic development when an infected mother dog is pregnant (most puppies are infected this way)
Toxocara eggs are passed in the host’s feces where they can be detected if a faecal sample is tested. Given the high levels of infection in young animals, treatment is typically given without evidence. Most veterinary all-wormers are able to kill roundworm infection, though repeated treatments are required in young pets to kill reinfections caused by resistant eggs/larve in the environment. Once adult, we recommend de-worming every 3 months to limit infection.
Human Health Implications
Rarely, infective larvae in the environment can cause infection in humans, typically young children or immune-compromised adults. Because of the complicated life cycle, roundworm infection in humans may lead to organ disease or even blindness when the worms encyst in the tissues. Prevention is the best treatment – regularly deworm your pet, wash hands after pet contact, pick up poo from the environment while it’s still fresh, and prevent children playing in areas where your pet toilets.