Parasites are a common affliction that affects humans and animals. In developing countries where sanitation is poor and malnutrition is common, human parasites can present a serious health risk, especially to children, the elderly and the immuno-suppressed, such as AIDS sufferers. Intestinal parasites are also common in the developed world and are easily transmitted in various ways. However, human saliva is not an ordinary means of transmission.
Worm infections are common to humans and are often also seen in children. According to Skye Weintraub in his book “The Parasite Menace,” worm infestations in children are more easily identifiable since the low acidity of their stomachs offers a compatible place for the creatures to be and may even be expelled through vomit. In adults, hydrochloric acid in the stomach kills most parasites and their eggs, but a few may pass into the small intestine and grow into adult egg-laying worms.
Transmission from Feces
Worm eggs are passed out of the body via the rectum. Many worms (such as roundworm) lay eggs in the intestine, which are then passed out in feces. Tapeworm segments contain many eggs, and whole segments are also passed out of the host body in feces. Pinworms wriggle out of the body at night and lay eggs around the anus. Parasite eggs infect a new host when they enter the body through the mouth, either by contaminated food, water or direct transmission through poor hygiene (i.e. not washing hands after using the toilet).
The Salivary Glands
Parasite eggs do not travel up the body to be released via the mouth or salivary glands, as the latter are not part of the gastrointestinal tract and do not host intestinal parasites. The only way parasite eggs could be transmitted through saliva is if the eggs entered the mouth and were immediately transmitted to a second host; for example, a dog licking its anus and then immediately licking its owner’s mouth. While not impossible, it is not likely that humans would transmit parasites in this way.
Antibodies in Saliva
A doctor can test bodily secretions, including saliva, for the presence of parasites in the body. It is possible to test saliva for antibodies resulting from intestinal parasite infestation, and studies carried out in St. Lucia and Tanzania have shown that this can be an effective strategy to monitor worm infections among children. However, parasite eggs are found in fecal samples and not saliva. Parasite antibodies in saliva are not sources of infection.
Some parasite hosts, including the tsetse fly and other blood-sucking parasites such as ticks, can transmit secondary parasite infections when their saliva mixes with a host’s blood upon being bitten, although these would be blood-and-tissue parasites rather than intestinal parasites. Fleas can be an intermediate host to tapeworms, but again, these only infect a new host when the flea is ingested, for example by a cat grooming itself with its tongue. Intestinal parasites are not transmitted through saliva.