Last updated on April 18, 2014 at 7:49 EDT

Dog Roundworm, Toxocara canis

The dog roundworm (Toxocara canis) is a species of parasitic worm that infects canid species. It is yellowish white in color and can reach an average length between 3.5 and 7 inches, with females typically growing large than males.

The dog roundworm can be transmitted in four different ways. The most common form of transmission occurs when an egg containing second stage larvae is released onto the ground in feces. Once the egg has been ingested, it will move through the small intestines and into the blood stream until it has reached its destination of the liver or lungs of its host. The egg will molt once more within these areas, developing into its third stage form and will then return to the intestines through the trachea, where two more molts will occur. This first method of infection typically occurs in puppies that are up to three months of age.

The second method for transmission of the dog roundworm occurs in dogs that are typically six months of age or older. The stage two larvae will move through the lungs and liver, as well as the heart, skeletal muscles, and the brain. If a pregnant female becomes infected, the worms may move into her developing puppies, where they will molt into their stage three forms just before the mother dog gives birth. Once the pups are born, the stage three larvae will molt once more in the intestinal lumen. It is common for all litters of an infected breeding female to become infected with these round worms, even if the mother never becomes infected again.

Another method of transmission of the dog roundworm occurs when puppies nurse from their mother during the first three weeks of their life. In this method, stage three adults are transmitted to the pup and no internal transportation is needed. The last method of transmission occurs when an infected animal is eaten by a canid species, but in this method, all stages of life for the worms are limited to the intestines.

The dog round worm is not only found in dogs, but can be transmitted to humans. This infection is known as toxocarosis and is easily spread from dogs by a simple stroke of the fur. Despite this, a study conducted in 2004 showed that out of fifteen dogs, only seven held eggs in their coats and only one egg was found on each of the seven dogs. Four percent of these eggs were not capable of transmitting the worms to humans, so it is thought that the eggs were accidently moved there by means of fecal transference. The round worms found in humans develop in the liver, lungs, or eye, which can cause blindness in some human hosts. The most common method of transmission from dogs to humans occurs when humans encounter a puppy’s feces, which can contain over 100,000 round worm eggs.

Treating dog round worms in dogs or humans is relatively simple, as there are many affordable treatments in the market that prevent and eradicate roundworm infections. Visceral toxocariasis is the easiest form of this infection to cure, with medicines such as mebendazole and albendazole often being combined with anti-inflammatory drugs for an optimum effect. However, ocular toxocariasis is more difficult to treat, because doctors must be careful not to damage the eye of the infected host.

Image Caption: Toxocara canis (canine roundworm) from a puppy. Credit: Joel Mills/Wikipedia (CC BY-SA 3.0)

Dog Roundworm Toxocara canis