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General Information -> Pets and humans

Are gordiids dangerous to humans and pets?


    No.  Gordiids do not use humans or any other vertebrate as hosts.  So, they cannot infect humans or your pets.  However, there have been reports of gordiids as pseudoparasites.


    Many of the reports of worms associated with humans are simply due to the spurious presence of worms in or near places of human habitation.  Thus,  reports of gordiids ‘‘infecting’’ humans must be interpreted with great caution. In one unpublished case, a worm was recovered from the underwear of a woman in Lincoln Nebraska (see figure here ). The assumption was that the worm came from inside the patient, but no evidence was given for this assumption. Although exactly how the worm came to be inside the woman’s underclothing is unknown, it is most likely that the worm was carried in by the host. However, it is clear that in some cases gordiids are resident within the digestive systems of humans. However, these cases do not represent real parasitism, but rather pseudoparasitism. 

    Pseudoparasitism is defined as a parasite present in a host due to accidental circumstances.  This host organism is not a natural host and usually the parasite does not thrive (and often does not survive for extended periods) in this foreign environment. Most, if not all, cases reporting ‘‘infection’’ of humans with gordiids are instances of pseudoparasitism.  For example, in a recent case, a girl in Korea was found to have vomited two Gordius sp. worms. It is clear from this report that the girl ate an insect (which looked like a cricket) shortly before she vomited. The most likely scenario for this event is that the cricket eaten by the patient was itself hosting the gordiids, which were subsequently released in the gastric juices of her stomach. 

    Similar reports exist for worms vomited by a domestic cat and by a domestic dog. Numerous reports exist of patients passing worms per rectum and per urethra. In several instances, the infection of the urinary tract was reported. In one case, an adult male was admitted to a hospital in Brazil after having passed worms per urethram. While in the hospital, the patient expelled an additional adult worm, which was found in his chamber pot. These reports are plausible, but since the documentation of most of these cases was less than thorough, it is unknown whether these patients were even suffering from pseudoparasitism. Furthermore, no diagnosis of an active case of infection with gordiids has ever been reported. 

    It is clear that the sole method of infection of humans by gordiids is through the ingestion of the adult form. This could occur through the ingestion of adults in untreated water, or through the ingestion of infected insect-definitive hosts. Several scientists have urged doctors to distinguish between pseudoparasitism from true helminthic infection. Misdiagnoses and ignorance of the benign nature of these worms has caused patients to undergo undue stress and financial burden of unnecessary regiments of antihelminthics.

Gordiids in sources of drinking water

    Numerous reports exist of nematomorphs ‘‘contaminating’’ city water systems. These cases occurred in countries within a wide spectrum of economic development, from Zimbabwe and Malaysia to England and United States. More recently, such cases have been reported from areas such as Bosnia-Herzegovina, Turkey and Australia. Often these reports associate the presence of gordiids in water systems with water quality. For example, in a leading Australian farming magazine, an author wrote that gordiid adults (which do not feed nor have a working mouth) wreak havoc on water systems by eating out water filters. Obviously, this report is utterly untrue. Gordiid worms within water supplies do not pose danger to humans, but are simply an indication that insect definitive hosts are capable of getting into the water source.

Gordiids around the home

    Gordiids are also frequently found in and around the home. Worms often appear in the bathroom, where standing water is typical; examples are toilets, showers, bathtubs and hot tubs.  Often, the worms are carried by their insect-definitive hosts.  In other cases, crickets are disposed of in the toilet after being killed, only to have the worms within the cricket wiggle back up the pipes.  After subsequent use of the facility, by either adults or especially children, people can become unduly alarmed at the sight of undulating worms.  

    In another case, a man recently returned home to Washington State from travel in Australia.  Three days after his return, he was aghast to find a gordiid in his bathtub. The worm was brought into the local health clinic where it was processed.  The serial section revealed a male gordiid worm.  The worm was likely carried into the tub by the insect host, either before or during use, or brought in through the pipes. 

   Pet owners also have reported finding worms within their pet’s water dish, leading to unnecessary trips to the veterinarian. 

Hairworm in pet water bowl

Hairworm found in a pet's water dish after emerging from beetle host.
 This image is a still frame from this movie submitted to us by R. Preston
and collected by E. M. Preston from central California, USA (September 2010).

In addition, worms are often reported from temporary standing water in the yard or the driveways after heavy rains.

If you think you have found a worm, please tell us about your find by following this link and by joining us as a Citizen Scientist.

Copyright 2014 Ben Hanelt, Matt Bolek, and Andreas Schmidt-Rhaesa
Updated: July 2015