State Veterinarian To Discuss New World Screwworm Outbreak and Response

By Ben Neary/NMWF

The New World screwworm, a parasitic fly whose larvae burrow into living flesh, has returned to the Southwest. 

State and federal officials are working to contain the outbreak now centered in southern Texas, where dozens of infected cattle, sheep and other animals have been found since early June. A dog in Lea County, N.M., was found to be infected but has recovered – the only confirmed case in New Mexico so far.

Dr. Samantha Holeck, New Mexico state veterinarian, will give a free presentation July 8 in Albuquerque to inform the public how to recognize screwworm infestations in wildlife and other animals. Her presentation is part of the New Mexico Wildlife Federation’s “Wildlife Wednesday” series.

“I think we’re easily looking at a couple of years,” Holeck said when asked for her assessment of how long the current infestation will last. “We’ve got a fight ahead of us, let’s put it that way.”

While state and federal agencies are working to track the fly population through trapping and other methods, Holeck said hunters also can play a critical role by reporting any infected animals they encounter.

“Any of our outdoor enthusiasts, they’ll be more likely to encounter wildlife that might be affected out in the field,” Holeck said. “And certainly hunters, if they come across game that might be affected by it, reporting that is going to be critical.”

Female screwworm flies lay hundreds of eggs on any wounds or mucous membranes they can find on warm-blooded animals. They particularly attack the umbilical cord on newborn animals. The eggs quickly develop into larvae in the host body, and proceed to eat the living flesh, causing excruciating pain. Ultimately, the larvae reach over one-half inch long and will fall out of the wound and burrow into the ground before emerging from the ground as an adult fly. 

The adult flies are slightly bigger than common houseflies, about ⅜-inch long. They have a metallic blue or green body with orange to reddish-orange eyes. They have three dark stripes on their backs with the middle stripe slightly shorter than the others

.The U.S. Department of Agriculture has stated that animals suffering from screwworm may exhibit irritated behavior; head shaking; the smell of decay and the presence of fly larvae (maggots) in wounds. An infestation can kill an animal within a week or so.

The New Mexico Department of Wildlife has issued instructions for hunters who believe they’ve encountered a suspected case of screwworm in a game animal:

1. Do not eat, handle or transport the animal.

2. Take a GPS location.

3. Take pictures of the wound, larvae and/or affected animal if possible.

4. If you can, collect a sample safely. Using gloves or tweezers, place several larvae into a sealed container (small jar or plastic vial) with 70 percent alcohol.

5. Label with date, GPS location, species and your contact info.

6. Report and submit immediately to the New Mexico Department of Game and Fish, the New Mexico Livestock Board or the New Mexico Department of Agriculture.

Several New Mexico state agencies including the Department of Wildlife have created a joint website to provide information about screwworm. Click HERE for more information. 

The screwworm is native to the United States but was  eradicated here in the mid-1960s, with the exception of a few small outbreaks. Until recent years, officials have kept the fly population from spreading north from Central America.

The United States has worked closely with Panama to control the spread of the screwworm by raising and releasing millions of sterile male flies to keep the females from breeding successfully. Over recent years, however, officials have tracked the spread of the screwworm north, from central America, through Mexico, heading toward the United States. 

Many Democrats in Congress have blamed the Trump Administration’s budget and staffing cuts in the U.S. Department of Agriculture for the fly’s resurgence. Trump Administration officials, however, have tried to shift blame to the Biden Administration, claiming relatively lax immigration enforcement allowed illegal cattle importations that carried the parasite.

Holeck said she believes that government officials throughout the fly’s territory may have gotten complacent about the screwworm threat after so many decades of keeping it contained in Central America.

Members of New Mexico’s congressional delegation have criticized the federal government’s response to the screwworm threat leading up to the recent outbreak here. U.S. Reps. Gabe Vasquez and Teresa Leger Fernandez, both D-N.M., in recent weeks announced legislation to try to prevent the fly from spreading. The legislation would establish a grant program to train workers how to recognize and respond to infestations.

Whatever the cause for its arrival, it’s clear the screwworm is hurting the cattle industry. The U.S. has banned cattle imports from Mexico since last year. Canada, meanwhile, announced last month that it was banning the importation of cattle from Texas.

Holeck said her office and others in the state have been fielding calls from agricultural producers as well as from pet owners with questions about the screwworm. 

“We’re in pretty good communication with veterinarians,” Holeck said. “We have had several veterinarians who have submitted samples from a variety of species, mostly dogs and a few cats and a few from cattle. I think we also had a sample submitted from a sheep.”

It’s possible that the screwworm will once again infest wildlife populations in the United States, Holeck said. “When you look back historically in the 1960s and 1970s, the whitetail deer population in Texas was heavily affected,” she said. “But also some of the smaller animals, and I think that those are harder to find because it doesn’t take them long to succumb to the infestation, given how sick they become afterward.”

Animals such as rabbits can be affected by the screw worm, but are harder to monitor, Holeck said.

“I think we’re probably looking at least at a couple of years, because we’ve got to wait for the sterile fly production to increase,” Holeck replied when asked how long the current outbreak will last. “Steps are already in place to make that happen.”

New fly-production plants are under construction in Texas and elsewhere. 

Holeck said her Wildlife Wednesday presentation will cover how to identify fly infestations. She said she will address the behavioral changes that can precede the open wounds caused by the feeding larvae. 

“Often you’ll see those behavioral changes first, they can be very subtle when they first start, it’s not until they’re in more advanced stages of infestation that you’ll see these big open, gaping wounds,” Holeck said.

Holeck’s talk will start at 5:30 p.m., Wed., July 8, at Marble Brewery’s Northeast Heights Taproom, located at 9904 Montgomery Blvd NE, in Albuquerque.