The Special Brand of Horror that is the New World Screwworm

By Rebecca Kreston | July 22, 2013 1:20 pm

“During her hospital stay, a total of 142 larvae were manually extracted, aided by the application of raw bacon which served as an attractant and petroleum jelly occlusion.”

You might be surprised to know that finding interesting articles on infections and infestations is a thankless and occasionally banal job. It is rare, as you find yourself trawling through the dusty and dense annals of Pubmed and Jstor, that you stumble upon a really good paper, the true gold twinkling among the pyrite of multisyllabic articles on viral proteomics, immunology and dull epidemiological trends in diseases. When you discover a treasure that renders you mute, like the one I recently discovered on a screwworm infestation that was wrangled by physicians with processed pork products, it’s like chancing upon a chupacabra in your backyard. The sight is both rare and awful, but also mesmerizing to behold. Also, you need to tell everyone about the chupacabra that you found.

An illustration of the dorsal view of the New World screwworm fly, Cochliomyia hominivorax.

A dorsal view of the New World screwworm fly, Cochliomyia hominivorax, a member of the family Calliphoridae. Adult flies are the size of a housefly with a greenish-blue metallic body color and an orange face. The larvae are obligate parasites of living flesh in warm-blooded animals  including humans, and can cause a parasitic illnes known as myaisis. Image: CDC.

And so here we are, reader. I found this magnificent article that I need to share out of scientific obligation, gross-out internet commiserating and out-and-out FYI. Let’s do this.

In 2007, a 12 year-old girl arrived in an emergency room in Connecticut complaining of an extraordinary pain in her scalp (1). She had just returned from a trip to Colombia with her family and speculated that the pain was due to “sun poisoning.”  Previous efforts to diagnose her scalp pain and what appeared as “fluid-filled bumps” at a local clinic in Colombia identified cellulitis, a bacterial skin infection, and she was given antibiotics and sent on her way. Yet the pain persisted and upon returning to Connecticut, the young patient and her family immediately went to the ER directly from the airport .

It is disingenuous to simply say that this young girl was in serious pain: to examine her scalp, to shift the strands of her hair and palpate the affected region, physicians had to administer intravenous morphine to bypass her discomfort and suffering. On the right side of her scalp was a “5×5-cm area of swelling with multiple punched-out lesions oozing a foul-smelling, purulent exudate (4).” A computed tomography (CT) scan of her head confirmed the swelling.

The poor thing underwent “a blunt haircut,” every prepubescent teenage girl’s nightmare, and “mobile larvae were identified,” every living person on earth’s nightmare. The larvae were sent to the Connecticut Agricultural Experiment Station and were identified as the New World screwworm. The Latin name of this bug is Cochliomyia hominivorax. For those of us rusty on our Latin, “hominivorax” is roughly translated as “eater of man.”

A dorsal view of the white, bristly larva of the New World screwworm Cochliomyia hominovorax

The larva of Cochliomyia hominivorax. Note it’s spiral, screw-like shape with bristly ridges that it uses to barrel into living tissue. Image: CDC. Click for source.

I know, I know: there you sit terrified, pondering what kind of world we live in where scientists could possibly ever think of christening an insect “eater of man.” It’s a heartless place we live in that plays pranks on you in the form of flesh-eating insects and I just don’t have an answer that would adequately explain the slings, arrows and screwworms of daily life. But let me tell you more about this little man-eater and get this day thoroughly ruined for ya.

The New World screwworm is an obligate parasite of animals and is a unique brand of pest in Central and South America where it infects the wounds and mucous membranes of cattle, sheep and horses (2). Female adult flies lay their eggs and in 8 to 15 hours the 2-centimeter length larva hatch forth causing excruciating pain and itchiness. The larva’s body shape is encircled by bristly ridges along the length of its body, resembling a fat, white screw used to burrow into living flesh.

This form of maggot infestation is considered a secondary form of myiasis – the flies have stumbled upon a human with an existing wound and invade accordingly. Primary myiasis is caused by the screwworm’s fly cousins and involves a deliberate breach of skin and tissue by larvae. Secondary myiasis is considered “generally trivial or even beneficial … [and is] used therapeutically to this day, because the larvae clean pus and necrotic tissue from difficult wounds (2).”

A view of the black teeth of a standing larva Cochliomyia hominivorax with a red background.

Hello there! A close-up of the larva of the New World screwworm Cochliomyia hominivorax showing its tusklike mandibles protruding from its mouth which is used to tear and then macerate the flesh of living warm-blooded animals. Image: Agricultural Research Service of the U.S. Department of Agriculture. Click for source.

C. hominivorax can be distinguished from other myiasis-causing buggies by a traveler’s history and by its propensity to lay hundreds of eggs. Other awful flies that take this “let’s-infest-this-human” route include the human botfly, Dermatobia hominis, and the tumbu fly, Cordylobia anthropophaga (another “eater of man,” incidentally), which tend to lay a single larva in a wound or lesion (3). C. hominivorax is the nastier bug of the three: it has cutting jaws that it uses to drill down to bone and nerves, and enter the bloodstream, necessitating the use of imaging technologies such as CAT scans and MRIs to see the “extent of larval migration and proximity to vital structures (1).” The infestation and resulting infections and abscesses can be deadly; it has a known 8% mortality rate (4).

(In an extraordinarily clever move, the US agricultural office dealt with the issue of screwworms in the American South by sterilizing the males with radiation and then releasing them to mate unprofitably with their female counterparts. The short lifespan of the females, and the valuable time wasted screwing around with a sperm-bereft screwworm, quickly eliminated the fly from the North American landscape (5).)

There are a few methods to tackle these buggers. One of the treatments is – yes, you already know, don’t you? – bacon. “Bacon therapy” stems from a traditional Central American tactic of sorting out human bot fly larvae by jamming pieces of raw meat or pork into the worm’s breathing hole, known as the punctum (6). The larvae vacate the premises either enticed by these culinary meat products or to avoid suffocation by meat, a most ignoble death. As noted in one paper, it may be necessary to employ “hours of bacon therapy” to entice all of the infested worms.

Back to this Connecticut girl’s worst hospital visit ever. Her myiasis stemmed from an untreated case of psoriasis that had undergone lesions due to scratching; the female screwworm found an existing wound and a temporary home for her offspring in the form of this skin disorder. Using a petroleum jelly occusion and bacon therapy, 142 larvae were extricated from her scalp and she was treated with antibiotics for an infection of the wound with Staphylococcus aureusShe was the unfortunate victim of one of the fourth most common travel-associated skin disease, but thankfully only emerged with scar tissue, an unfashionable haircut and a helluva travel story (7).

Resources

A very thorough review from 2012 at Clinical Microbiology Reviews on myiasis.

The Daily Mail is here for the rescue with a personal story of myiasis!

A great resource from the CDC on myiasis-causing flies. The link won’t let me send you there directly, but click on “Clinical Features,” then “Microscopy” to see all the images of the various species of flies.

References

1) M Langhan (2008) The 2007-2008 Photo Competition Award Winner: A Painful Scalp Rash: Cutaneous Myiasis Secondary to New World Screwworm. Pediatr Emerg Care; 24(7): 502-504

2) P Weinstein (1992) The New World screw-worm and other exotic myiases in Australia. Med J Aust157(3): 216.

3) D Despommier, RW Gwadz, PJ Hotez & CA Knirsch ( 2006) Parasitic Diseases. 5th ed. New York: Apple Trees Production

4) IE Sweis et al (1997) Souvenirs from Belize: the botfly and the screwworm fly. Plast Reconstr Surg99: 868-870

5) A Stewart (2011) Wicked Bugs: The Louse That Conquered Napoleon’s Army & Other Diabolical Insects. New York City, New York, USA:  Algonquin Books

6) J Goddard (2007) Physician’s Guide to Arthropods of Medical Importance. 5th ed. Boca Raton: CRC Press

7) K Robbins K & A Khachemoune (2010) Cutaneous myiasis: a review of the common types of myiasis. Int J Dermatol; 49(10): 1092-8

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Body Horrors

Body Horrors looks at the history, anthropology and geography of infectious diseases and parasites.

About Rebecca Kreston

Rebecca Kreston is an infectious disease scholar trained in microbiology and epidemiology. She obtained her Biology degree from Reed College and her Masters of Science in Tropical Medicine from Tulane University. She's lived in tropical jungles, beaches and deserts around the world and has been exposed to several of the diseases that she studies. She currently lives in New Orleans, is a second year medical student and regularly battles insects of the Diptera, Siphonaptera and Hymenoptera orders.

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