Linguatula serrata also known as “tongue worm”, is a pentastomid, more closely related to arthropods (an invertebrate animal of the large phylum Arthropoda, such as an insect, spider, or crustacean) than true worms.
Its unusual name is due to its shape rather than where it resides; the adult parasite is an elongated tongue-shape and does not reside in or around the tongue! It is actually a nasopharyngeal (relating to the nasopharynx = the upper part of the throat, behind the nose) parasite of dogs widely distributed in the Middle East, Africa and Asia.
Tongue worm as an adult parasite are large, with females typically 30 to 130mm in length. Infection occurs through the ingestion of nymphs in raw offal of infected intermediate hosts, such as ruminants, rabbits and horses. It is found in the nasal cavities or sinuses of dogs and foxes, although the parasite has been reported in UK foxes, it is thought to be rare, and its current endemic status is unknown. Eggs are immediately infective and are passed from the adult parasite in the faeces or nasal secretions of infected dogs.
Although still uncommon there has, however, been a sharp in-crease in clinical cases reported in UK dogs imported from eastern Europe and the Middle East where raw meat is routinely fed. In recent years, the number of pets entering the United Kingdom from abroad has increased, with a coinciding increase in the number of L. serrata infections diagnosed in UK veterinary clinics. This is a concern due to the zoonotic potential of the parasite. Although in endemic countries zoonotic infection occurs primarily through the ingestion of raw or undercooked viscera, it can also occur through ingestion of eggs in the environment or in mucoid discharge from infected dogs’ noses.
The letter in the Vet Record is particularly interesting, as an untraveled dog and after a detailed history it seems plausible that the source was from imported meat fed raw that has been the source of infection. Although adequate pre freezing of raw diets will kill the parasite, potential infection is another reason why we should be vigilant when sourcing, handling and feeding raw meat to pets, and adds to the other zoonotic health concerns we have.
The parasite can cause a variety of clinical presentations, including nasopharyngitis (inflammation of the nasopharynx), blocked nasal passages, visceral pain and aberrant larval migration to the anterior chamber of the eye.
Unless dogs have a travel history to endemic areas, the diagnosis can initially be tricky. The clinical signs mean that the parasite will likely be on of numerous differentials.
Having said that, Ian Wright recommends that any imported dogs expulsing adult parasites or presenting with rhinitis, gagging or chronic upper airway signs should ideally be examined by endoscopy to check for infection.
Another alternative to this is testing of the nasal discharge, by flotation methods for eggs; this can also be performed on faeces but with a much lower sensitivity.
There are reports of infections being successfully treated with oral milbemycin or moxidectin/imidacloprid spot on solution. Parasites may also be physically removed by endoscopy. Infections should be treated promptly and good hand hygiene maintained by owners, due to the risk of spread to humans in contact with the pet or their upper airway secretions.