Screwworm flies (a.k.a. “screw-worm flies” and “New World screwworm flies”) belong to the genus Cochliomyia. Within this genus, there are four different species, but only one of the species is a screwworm fly, which is known as Cochliomyia hominivorax. A reader recently wrote to us regarding the screwworm fly, asking how a human can rid him or herself of this parasitic worm. First, we will give a brief overview of the screwworm, explaining what it is, and then we will address the reader’s question specifically.
Screwworm flies are best known for the damage they cause in the larvae stage of their life cycle (i.e., when the screwworm flies are still maggots). It is in this stage that screwworm larvae feed on the living tissue of endothermic (colloquially called “warm-blooded”) animals. The infestation of a vertebrate animal that is alive is called “myiasis,” which is a serious problem for the livestock industry. However, as our reader’s question implies, myiasis can also affect humans, and indeed this occurs with relative frequency in rural and tropical regions of the world. The disturbing thing about screwworm maggots is that they attack living tissue, whereas other types of maggots tend to consume dead flesh. (Lots of us have probably seen those disturbing pictures of animal corpses being disintegrated by hordes of maggots. Buy hey, at least the animal is dead.)
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Screwworm flies lay around 200-250 eggs in the exposed flesh (e.g., an open wound) of animals and humans. The larvae quickly hatch and begin to consume the flesh of the host animal. If the wound is disturbed (perhaps by getting stitches, e.g.), the larvae will burrow deeper into the flesh; in other words, the larvae will “screw” themselves into the host, and hence the name “screwworm flies.”
Fortunately, screwworm flies have been eradicated from some parts of the globe, including the United States, Mexico, and Central America, but they remain in other parts of the world, such as Africa and India. And this brings us back to our reader’s question: if you are infected by the larvae of a screwworm fly, how do you go about addressing the problem?
If a person or animal is confirmed to have a screwworm infestation (which can be recognized by a number of symptoms, such as a reddish-brown excretion leaking from the infected wound), the first step, not surprisingly, is to go to a medical professional so that he or she can remove the screwworm larvae with tools like tweezers or forceps. After all the screwworm larvae have been removed, a topical antibiotic is applied to the wound, and this is often accompanied by an antibiotic that is taken orally. Necrotic (i.e., dead) tissue that results from the infestation may need to be removed, which can be painful. The dressing of the wound will need to remain loose so that fluid can continue to drain from the wound. If the infestation is treated professionally and thoroughly, positive results are common, but unfortunately there is high rate of secondary infection if the initial infection is not rigorously addressed.
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Of course, it is preferable to avoid infestation in the first place, and the best method to achieve this end is to make sure that any wound on an animal or person is dressed properly with an antibiotic ointment and a bandage. It is also essentially to examine wounds frequently so that any infestation symptom can be spotted early.