15 July 2020

Tongue worms, they’re not just for reptiles…..humans too!

Posted by Shane Hanlon

This is part of a student blog series as part of the University of Pittsburgh’s Disease Ecology Class that our own Shane M Hanlon is currently teaching. Find out more about the series and read all the posts here!   

By Chelsea Prescott

Tongue worm disease caused by the parasite Linguatula serrata is a blood sucking parasite that belongs to the group Pentastomida. This species generally inhabits the upper respiratory tract of terrestrial, carnivorous vertebrates. It is mainly found in reptiles and bird species.

This parasite has intermediate hosts like sheep, cattle, and rodents. Rodents being intermediate hosts would explain why snakes can get the pathogen so easily. But how do hosts get L. serrata? Well they ingest the eggs, the larva will hatch in their intestines, penetrate the mucosa, enter into the tissue where it will encyst and molt to a third larval stage.

So where do humans play a role? Well they can serve as aberrant final hosts or accidental intermediate hosts. They serve as aberrant final hosts if they infest raw or poorly cooked viscera (lungs, liver and trachea) of intermediate hosts. It often causes a nasopharyngeal infection. To us, eating this kind of viscera sounds absurd, but it can be normal in other cultures. Now humans can also be accidental intermediate hosts if they somehow ingest the eggs. This kind of infection is extremely rare and only 5 cases have been described; 2 in the southern US, 1 from Portugal, 1 from Israel, and 1 from Ecuador.

Microscopic image of the parasite. Source: Koehsler et al. 2011

A study was done in Europe on a 14 year old girl with an unknown parasite in here eye. She had redness, pain, and progressive vision loss in the infected eye. The only regular animal contact she had was with dogs, cats, and a turtle. Surgical removal of the parasite was not an option because the parasite was very mobile. Eventually, they had to remove her lens, and perform a complete vitrectomy to remove the parasite. One month later, irritation subsided and an artificial lens was implanted. The parasite was examined microscopically and subjected to DNA testing. After examinations, the parasite was indeed identified as L serrata tongue worm. Researchers think eggs were passed into the eye by contact with one of the dogs, which is often a final host for the parasite.

So tongue worm can strangely occur in humans, but it is very rare! Source: Linguatula serrata Tongue Worm in Human Eye, Austria