The New World Screwworm, aka. NWS or Cochliomyia hominivorax, is a fly native to the Americas. It lays its eggs in the living tissue of fresh wounds in warm-blooded animals. The maggots (larvae) feed on the animal’s flesh, causing severe wounds and often death if left untreated.
The maggots have sharp mouth hooks that tear tissue, causing the wound to enlarge and deepen. The mature larvae are about 2/3 -inch long and have spines that wrap around their body in a spiral, allowing them to “screw” or burrow into an open wound.
This parasitic fly was eradicated in the US in the 1960s, but occasionally reemerges in Central America and Mexico. They are controlled only by releasing sterile male flies, which has worked very well in the past and is expected to work again. The adult fly are metallic blue blow flies, with three stripes that run down the top of the fly, just behind the head, and have large orange eyes.
Currently, NWS are actively affecting livestock in South and Central Texas, as well as New Mexico. One incident of screwworm infection in a pet dog has been reported.
Hopefully, NWS will be confined to Texas and New Mexico, but because of interstate travel, it is important to know what to monitor in our pets. If your pet has a wound, it should be checked out by your veterinarian quickly. Even if we don’t have NWS in our area, we do have flies that could lay eggs on moist skin or open wounds, particularly if your pet spends time outside. These maggots don’t burrow into healthy tissue, but rather feed on dead tissue and eat it, but they do release toxins that can cause more tissue death, sepsis, and shock.
If your pet is licking or biting at a wound, seems restless or lethargic, or has a foul odor (especially in a long-haired pet), please take them in to your veterinarian as quickly as possible.
If you are planning to travel with your pet to a screwworm-affected state, check for travel orders in the destination state. You may require an exam by a USDA-accredited veterinarian specially trained for screwworms.
Dr. Scarlett