Causes of Threadworm Infection (Strongyloidosis)
Dogs can become infected with threadworms through a number of different routes. Most threadworm eggs and larvae are passed out of infected dogs in their stool (in their “poop”). Other dogs can become infected by licking or eating fertile eggs, or the larvae hatched from them. Infective threadworm larvae are motile, or mobile, meaning that they are capable of moving independently. In the environment, these larvae have a unique ability to penetrate the unbroken skin of their mammalian hosts; this is called “transdermal transmission.” This occurs with greater frequency in areas with poor sanitation and hygiene, such as some high-density kennels, rescue facilities and pet stores, where fecal material is allowed to build up. Hot temperatures and high humidity increase the risk of transdermal transmission of threadworm larvae. Infection can also be transferred to newborn puppies through their mother’s milk, especially if the bitch becomes infected late in her pregnancy or while she is lactating. This is called “transmammary transmission”.
Fertile eggs that are not expelled in fecal matter can hatch inside the dog’s gastrointestinal tract, causing what is known as “auto-infection of the host.” This can happen in the large intestine (colon), where threadworm eggs in unexpelled stool hatch into motile larvae, which then penetrate the large intestinal lining and become re-routed back to the dog’s small intestine. This can lead to persistent infection and re-infection of the same animal, without any contact with outside sources of the parasite.
Regardless of the route of transmission, once they enter a host, threadworm larvae migrate through the bloodstream and tissues of the throat (pharynx), windpipe (trachea) and lungs. Eventually, they end up in the dog’s small intestine, where they mature into adults. At maturity, adult threadworms are only about 0.7 to 2.2 millimeters in length. They are tiny.
Preventing Threadworm Infection (Strongyloidosis)
Because threadworms usually are transmitted through a fecal-oral or a fecal-skin route, the best way to prevent infection is to keep dogs away from the stool of infected dogs. Especially in tight housing situations, the facilities should be cleaned and disinfected daily. Routine de-worming protocols may also be helpful in preventing the spread of these parasites.