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By Joseph Ramon
Devine News Intern
Over 65 cattle ranchers and farmhands gathered at Graff 7A ranch in Hondo Texas to hear updates from the Medina County Farm Bureau and Texas A&M Agrilfe Extension on New World Screwworms.

Dr. T.R. Lansford, the deputy executive director and assistant state veterinarian for Texas Animal Health Commission, gave the presentation explaining what New World Screwworms (NWS) are, why they are a threat, how they can be combated and what is being done to prevent the spread to Texas.
Screwworm maggots are the larvae of the fly that attack living flesh of mammals. Livestock and deer are most susceptible but there are reported cases of NWS attacking birds, companion animals, other wildlife, and on very rare occasions humans.
The life cycle of the NWS begins with adults aged 10-14 days which will lay eggs in the cattle. Eggs can be laid in an open wound, reproductive tract, sinuses or even ear canals. Within hours these eggs will hatch into larvae which will start burying themselves into the tissue. Larvae spend about 5-7 days inside the animal or in the tissue and then they come out, and pupate into the ground. After 6-8 days, they emerge from their cocoon into adult flies and repeat the process. The entire cycle is normally 18 days in hot climates, but in colder areas it can slow down and take as long as 60 days.
When it comes to transmission of this disease it is not contagious from animal to animal through contact. For this disease to spread, it requires a fly. The NWS can be masked by other types of maggots or flies that enter the wound to feed on tissue that has become necrotic as a result of damage done by the screwworms.
The primary method of eradication is the Sterile Insect Technique. This method is done by releasing sterilized adult male flies into female populations. Female NWS only mate once, so through this method NWS have been eradicated before during the 60’s in the United States.
It would be very impactful to the economy of livestock production, wildlife production and the general economy at large if there was a reintroduction of the NWS into the United States. The U.S. has made substantial efforts to remain NWS free such as financially supporting the creation of a sterile NWS plant in Mexico to eradicate the populations that appear there and prevent the spread into the U.S.. The estimated benefits of remaining free of NWS are $3.7 billion to the general economy in the United States.
There would potentially be a large amount of livestock and deer deaths. In 1935, there was an approximate loss of 180,000 cattle in Texas alone, according to Lansford . During the infestation, it was estimated that 80-90% of fawns died from NWS infections. The estimated impact on the Texas economy if there is another infestation is $1.8 billion based on the losses incurred during the infestation in 1976, adjusted for inflation.
When checking for screwworm infestations one of the signs is a strong foul odor. Monitor behavior, frequent head shaking could also indicate an infestation in the sinuses or ear canals. If these infections are not treated they typically result in death in 7-10 days, according to the presentation.
If there is an infestation discovered there are several forms of treatment to remove the infestation. There is a topical treatment that can be applied called permethrin pesticides. Systemic options are only available through a veterinarian. In addition, consider treating with betadine and otodine solutions. These will help dry up the wound and heal faster.
There are 2,200 confirmed cases of infestation in Mexico, the closest being an infestation in Oaxaca as of the week before this presentation. To prevent the spread U.S. Secretary of Agriculture, Brook Rollins, has closed the borders for importation of cattle, horses and bison into the U.S.. The USDA announced a five pronged approach to stopping the spread into the U.S. which includes: stopping the pest from spreading in Mexico and ensure we are full partners in eradication, protect the U.S border at all costs, maximize our readiness, take the fight to the screwworm, and innovate our way to eradication.
“We need to inform all the cattle producers and the wildlife people that the screwworm situation was bad back in the ‘60s. I mean, it’s devastating to the livestock industry. And now to the wildlife industry. People need to be aware of what’s out there and what might be coming, and what to do about it if it gets here.” said Ronnie Muennink, president of the Medina County Farm Bureau. “ I grew up when screwworms were around, and the treatment is a daily thing. You have to watch your animals constantly, and treat immediately, because the death rate is in 7-14 days.”
If you have a suspicious case, contact the Animal Health Commission, USDA, or your veterinarian.
For more resources on screwworm information go to the USDA, Agrilfe Extension, and the Animal Health Information websites.