New World screwworm (NWS) remains a serious animal health threat and has been detected in southern Texas near La Pryor.
NWS is a type of fly that lays eggs in open wounds or around the eyes, ears, nose, and mouth of live, warm-blooded animals. When the eggs hatch, the larvae (maggots) feed on healthy, living tissue, causing painful wounds that can grow larger over time. NWS can affect livestock, pets, wildlife, and, in rare cases, people. If not treated, these infestations can cause severe damage and may even lead to death. Only NWS flies spread this animal health threat.
NWS is not a food safety or foodborne illness issue, it does not spread through meat or food, and infested animals (inspected at slaughter) won’t make it into the human food supply.
USDA Response
To help eradicate NWS, the United States Department of Agriculture (USDA), is releasing sterile male flies in the area of the positive site, in addition to the four million sterile flies already being released each week. They have implemented an infestation zone of 20 km around the detection site and are implementing quarantines, movement controls, and surveillance.
Livestock Producer Information
Livestock producers should be aware that newborn animals (umbilical cords), newly freshened animals, and animals that have been wounded, dehorned, branded, ear-notched, sheared, tail docked or castrated are susceptible to NWS.
If you suspect New World screwworm in an animal, isolate the animal immediately, contact your veterinarian, and report the case to your State Animal Health Official or USDA APHIS.
Livestock infested with NWS will be treated and quarantined until all wounds heal and there is no evidence of re-infestation after 21 days. In rare cases, euthanasia may be necessary for individual animals for humane reasons or in cases when treatment is not possible.
To help prepare for a possible NWS outbreak in the United States, the FDA has issued Emergency Use Authorizations (EUAs) for several products used to prevent and treat NWS infestations, including over-the-counter ointments, wound spray, injectable drugs, and prescription-only topical powder.
FDA-Authorized Drug Treatments for New World Screwworm
Drug Name | Animal | Milk Withdrawal | Meat Withdrawal |
Dectomax®/Dectomax®-CA1 (doramectin injection) | Lactating & non-lactating dairy >20 mos.
| 19.5 Days | 35 Days |
| Beef Cattle |
| 35 Days |
| Veal Calves |
| Not Approved |
| Swine |
| 24 Days |
| Non-lactating Sheep |
| 35 Days |
| Deer |
| 35 Days |
F10® Antiseptic Wound Spray with Insecticide and F10® Antiseptic Barrier Ointment with Insecticide
| Dairy Cattle, Dairy Goats, Dairy Sheep | 10 Days | 30 Days |
| Cattle, non-lactating sheep and goats |
| 30 Days |
| Veal Calves |
| Not Approved |
Negasunt® Powder * | Dairy Animals | Do Not Use |
|
*Prescription only in NWS infested and adjacent surveillance zones | Meat Animals |
| 28 Days |
| Veal Calves |
| Not Approved |
Visit the USDA New World Screwworm site for more information.
The University of Minnesota Extension Office has also issued guidance about the impact of NWS in northern climates.
