On the Radar-What's This About Screwworms?

What's Going On

The Centers for Disease Control and Prevention (CDC) recently activated a formal emergency response to the New World screwworm (NWS).  NWS, formally known as Cochliomyia hominivorax, is a parasitic fly that lays eggs in and on open wounds and mucous membranes of warm-blooded animals, including livestock, pets, wildlife, occasionally birds, and in rare cases, people. An infestation with NWS larvae (maggots) is called myiasis. The maggots burrow into the flesh of animals and eat healthy living tissue, which can cause significant damage or even be fatal. The term "screwworm" relates to the sharp mouth hooks they use to "screw" into healthy tissue.

Cochliomyia hominivorax fly

Cochliomyia hominivorax larva

Background

NWS remains endemic in Cuba, Haiti, the Dominican Republic and some countries in South America. The most recent US outbreak occurred in Florida between 2016 and 2017. The flies were successfully re-eradicated from Florida at that time using the sterile insect technique (SIT), in which sterilized male flies are released into the wild to mate with females.

There are currently at least six cases in Texas involving cattle and a goat, plus an additional case in New Mexico involving a dog.

Adult screwworm flies are about the size of a common housefly (or slightly larger). They have orange eyes, a metallic blue or green body, and three dark stripes along their backs.

How It's Being Handled

Myiasis is treated primarily by physically removing the larvae from the affected tissue, often requiring urgent surgery. Because there are no approved medications to eradicate the infestation within the body, care focuses on extraction and management of secondary bacterial infections. This is also why preventing the spread and attempting to eradicate the NWS is so important.

The Department of Agriculture is leading the response on the animal side by monitoring cattle and livestock and dispersing sterile flies to control the spread of the screwworm. 

The Society's Take

In conclusion, there is minimal risk to humans at this time, but significant risk to animals, who are part of the US food chain. This should remain On the Radar.

References:

https://www.aphis.usda.gov/livestock-poultry-disease/cattle/ticks/screwworm

New World Screwworm Case Reporting for Health Care Providers

Prompt reporting of human cases is essential for an effective response to New World screwworm.

New World ScrewwormCDC