New World Screwworm Meeting Notes 7-23-25

These are my personal notes from the New World Screwworm meeting that was held in Uvalde, TX that was held by the TAHC, USDA, TPWD, Texas A&M Extension Service, and East Foundation.

Disclaimer, these are my personal notes that I was typing as fast as I could. I tried to get as much helpful information as I could. There was a lot of info that I don't believe is helpful to the average producer such as: what level of radiation is necessary to sterilize a fly, what a damaged ovary looks like, in-depth statistical models that have so many variables that I simply don't have faith in them, plus lots and lots ... and lots of historical information. I tried to distill the information down to what I felt was most important. 

Also check out my New World Screwworm Article for more information.

Screwworm Meeting - Uvalde 7-23-2025

Personal Notes by Sam Wilkinson DVM

The Wildlife Vet

Dr David Anderson - Economics Model

• Costs to hire cowboys to monitor daily
• $50 per head medicine costs
• 10% rate of incidence (50% mortality of affected)
• Estimates it would cut the total farm income by approximately 80%
• Wildlife: Predict 80% fawn mortality

 Dr Luisa Collins

• No evidence of spread north of the most recent report (approximately 400 miles south of Brownsville.
• USA funding the conversion of a Mexican fly facility in addition to the establishment of a facility in south TX. Timeline TBD.
• Currently, Southern Border is closed and will remain closed until further noticed for cattle, horse, and bison imports.
• Wildlife are known to cross without restriction = Concerning, but unavoidable.
• Dogs and cats require a Mexican health certificate from vet stating they are screwworm free within 5 days of crossing the southern US border.
• Steps if you suspect screwworm infestation:
  • Contact your vet ASAP
  • Seek treatment ASAP
  • Do not move the animal so we don’t spread the disease It is preferred that the animal stays at whatever location the worms were found at.
  • Store worms in container with alcohol (isopropyl or ethanol)

Dr. Sandra Leyendecker

• Must contact TAHC and USDA
• Report any live animal with maggots on them. Do not move the animal.
•  When treating
  •  Permethrin product (example Catron, Co-Ral)
  •  Do not leave any maggots on the animal and do not let them fall on the ground.
  •  Collect some of the maggots in alcohol for ID.
  • You must kill all the maggots.
• USDA is working hard to get a confirmed, effective treatment protocol
• Quarantine: If NWS is found on your property, you will be quarantine. Animals must be inspected and treated before movement (Animals can be moved and sold post-inspection.)
• Quarantine Zone Proposal: 
  • 3 mile zone
  • 6 mile zone
  • 10 mile zone
  • Does not have exact quarantine protocol yet.
• Private Owner Reporting: Essential to the eventual eradication of NWS.
• TAHC and your local vet will help you monitor and get through this.

Dr. Roel Lopez

• Florida Key Deer = subspecies of whitetail deer.
• July 2016 first case
• Sep 2016 USDA confirms screwworm
• Oct 2016 full response mobilized.
• Techniques: sterile insect technique was primary focus. They also used injectable, oral, and topical dormection
• Dormectin: So far unclear if helpful or not in this case to use dormectin.
• Cost $3.15 million on this key that is isolated with a very small road in and out.
•  Highest loss in mature adult males.
  •  Due to fighting in rut season.
  • ~15% of total population of deer died from NWS.
• Infestation was officially contained in April 2017. 
• The delay in identification of NWS (June 2016 to Sep 2016helped the disease spread and get worse than it should have.
• USDA, TPWD, and FDA do not currently have a published treatment protocol either. Working on it.

Dr Jason Sawyer

• Prevention and Husbandry
• (Lot’s of numbers… Hard to follow.)
• His opinion is it could hit South Texas in 6 months or less unless something changes.
•  Herbicides: EPA.
  • No off label use allowed = Illegal.
•  Drugs: FDA.
  • Some off label use allowed under veterinary direction only. However, it cannot ever be done in feed. (There are not drugs currently labeled for screwworm prevention or treatment)
  • Most of our modern drugs have been developed after the NWS eradication (1982) so there has not been a need to get NWS indication on the label.
• Resistance: (parasites being resistance to drug) (dosing too low, continuous exposure, persistent use of a single drug)
• East Foundation current TX protocol: Co-Ral and Catron. A feed through IGR does not help with NWS at all. 
• Moxidectin - lower efficacy against insects than in worms. Does not work for NWS. (Do not use for NWS)
•  Ivermectin and dormectin are currently the recommended options. However there is a lot of documentation of significant resistance
• In endemic areas, the local people apply ivermectin every 28 days. This has cause increased resistance of the NWS to pesticides and ivermectin.
• Eprinomectin has no reports on its efficacy. It might help. Unknown.
• Furalaner not approved in USA in cattle. Bravecto Effective in pets.

Panel Discussion

• Most important things people need to know is they need to know there is a fly larva (worm) that is moving up through Mexico. The worm is unique because it eats live tissue.
• All animals that have live maggots on them need to be assumed they have NWS. Quarantine the animal. Collect the worm. Place it in alcohol. 
•  Steps to Treat NWS
  •  Kill and collect all worms on the animal with Co-Ral or Catron.
  •  Clean the wound with antiseptics.
  •  Cover the wound when possible.
  •  Administer ivermectin or dormectin.
  •  Repeat: Must remove all worms from the wound.
  •  Treat the wound with topical and/or injectable antibiotics.
  • Regularly treat with topical fly treatments until healed.
• The current goal is for producers to recognize the presence of NWS in their herd as fast as possible. It seems like this is a race to be first to recognize NWS as the first ones are going to be the one that get the most help. Many people are scared they are going to be treated like they have
•  Regarding Adding Ivermectin to feed as some industry leaders have suggested.
  •  There is no data to support the idea of feeding oral ivermectin in food would help to slow, prevent, or treat NWS.
  •  This disease is not the same as fever tick.
  •  Widespread use of ivermectin in the feed would would dramatically increase intestinal parasite resistance due to 1) long term duration of feeding, 2) wide-spread rather than targeted use, 3) consistent underdosing of animals because they are not eating full meals with a full dose.
  •  Also you must stop feeding ivermectin at least 56 days before consuming the meat of the animal.
  •  There are also a lot of animals that do not eat corn = Would not help those.
  •  Mass killing of non-target insects like dung beetles.
  •  Would cause a false sense of biosecurity.
  • Cost would be significant. Value is very, very limited.
• NWS does not like cold weather. It does better in moderate temps and wetter weather.
• All of the currently produced NWS flies in the world are owned by the USA.
• Starting on 7/28/25, the USDA are setting up fly traps on the southern US border to monitor.
• If there is a case confirmed in the US, flies will taken from Mexico and be dropped on that location the next day. All government agencies will respond 

Check out my NWS article: Here - NWS Article