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No suspect cases have been reported in Kentucky. To report abnormal wounds and potential cases of NWS in wildlife, click the button below. See below for common clinical signs associated with NWS infestations.
Report a suspected case
The New World Screwworm (NWS) is an invasive parasitic fly. The name "screwworm" comes from the spiral shape of the larvae (maggots) which bore into wounds in a screw-like motion when the larvae infest and feed on the living tissue of mammals and birds. This differs from typical maggots, which feed on the decaying tissue of carcasses. The fly larvae cause a severe condition known as myiasis, in which they invade and consume the host's flesh, leading to painful and life-threatening infestations. Due to the serious threat it poses to wildlife, livestock, pets and human health, NWS is considered a Foreign Animal Disease (FAD). FADs have mandatory reporting requirements at the state and federal level.
The USDA previously eradicated New World Screwworm from the United States in 1966 and again in 2017 using the Sterile Insect Technique (releasing sterile male flies that mate with females, thereby resulting in unviable eggs and stopping reproduction). It slowly began its northern progression from Central America in 2023 and on 06/03/2026, NWS was found in a calf in southern Texas. This marks the first detection of NWS in the United States in 9 years.
Infestation begins when a female screwworm fly lays her eggs in open wounds or natural body openings- such as the eyes, nose, umbilicus or genetalia- of live, warm-blooded animals. Even minor injuries like tick bites or surgical incisions can attract flies. Drawn by the odor of wounds, the female lays up to 400 eggs at one time, which hatches into larvae that burrow into healthy live tissue within a few hours. Multiple female flies can lay eggs in wounds, which leads to massive quantities of larvae in the wounds, numbering in the thousands.
Life Cycle of a Screwworm, USDA APHIS.
As the larvae feed, they cause wounds that fail to heal or worsen over time. Symptoms of infestation include a foul odor from the wound, visible maggots or egg masses, lethargy, and signs of distress or depression. In severe cases, untreated infestations may cause secondary infections and can lead to death in livestock and wildlife. Larvae will stay attached to the host for 5-7 days and then drop off to the ground and burrow into the soil for the next stage of development. In as soon as 7 days, they emerge as adult flies capable of reproducing, which starts the life cycle over again.
Larvae cannot survive in soil temperatures below 45° F and adults cannot survive in air temperatures below 20° F. This means that in Kentucky, NWS would be a seasonal issue. However, in southern states like Texas and Florida, NWS could develop established populations if not eradicated.
The New World Screwworm spreads primarily through the movement of infested animals, which can include livestock, pets and wildlife. Cross-border animal trade and natural migration also contribute towards its spread. Although the USDA successfully eradicated New World Screwworm from the United States in 1966 using the Sterile Insect Technique, there remains a constant risk of reintroduction and sporadic outbreaks have occurred. In October 2016, NWS was found in the Florida Keys, which affected livestock and other domestic animals. NWS was also detected in the endangered Key Deer, which further threatened the isolated population that was already greatly reduced by hunting and habitat loss. Using a multi-pronged approach implemented by multiple federal, state and local agencies, NWS was successfully eradicated from the Florida Keys in March of 2017. Additional efforts in Central and South America pushed back NWS to a maintained sterile fly barrier between Panama and Columbia until July 2023, when the range slowly began expanding again into Costa Rica.
New World Screwworm, USDA.
June 8. 2026- Additional New World Screwworm cases confirmed in multiple counties in Texas.
June 3, 2026- New World Screwworm confirmed in a 3-month old calf in Zavala County, Texas. This is the first detection inside the U.S. since 2017. A 20-km infested zone was established around the detection to guide quaranties, stop movement orders, and properly surveill the immediate area.
June 3, 2026- New World Screwworm detected in a goat in northern Mexico, approx. 25 miles from the U.S. border.
September 2025- New World Screwworm detected in northern Mexico, approx. 70 miles from the U.S. border.
July 2025- New World Screwworm confirmed in Ixhuatlan de Madero, Veracruz in Mexico, aprroximately 160 miles from the U.S. border. In response, the plan to re-open ports following a phased, risk-based strategy was cancelled when U.S. Secretary of Agriculture Brooke L. Rollins ordered the closure of livestock trade through southern ports of entry.
May 2025- New World Screwworm confirmed again on remote farms with minimal cattle movement in Mexico, approx. 700 miles from the U.S. border. In response, U.S. Secretary of Agriculture Brooke L. Rollins suspended imports of live cattle, horses and bison on May 11, 2025, as a precautionary measure to protect animal and public health. On June 30, 2025, the USDA announced a plan for risk-based port re-openings starting on July 7, 2025.
November 2024- New World Screwworm first detected in southern Mexico, prompting the USDA to shut down the U.S. border for live animal trade. USDA resumed imports in February 2025 following implementation of a pre-clearance inspection and treatment protocol.
Adult NWS flies are similar in size to a common housefly and have orange eyes and a metallic blue-green body with three dark stripes on their backs. Identification of adult flies is difficult, so diagnosis typically requires the identification of the larvae found in a wound to differentiate between NWS and other maggots from native fly species. At this time, larvae cannot be identified in the field and must be sent to USDA APHIS National Veterinary Service Laboratory for confirmation.
New World Screwworm Larvae. Photo by USDA.
New World Screwworm Fly. Photo by USDA.
The Food and Drug Administration (FDA) has approved several topical and injectable drugs for the treatment of NWS in livestock and domestic species, but options for free-ranging wildlife are limited and can only be administered by a licensed veterinarian. Additionally, administration of drugs to free-ranging wildlife is prohibited under 301 KAR 4. 110 to prevent accidental exposure to non-target species and to protect human health due to consumption safety concerns.
Initial detection and identification of larvae can be very difficult in wildlife, and the later-stage NWS infestations can be very painful. By the time that cases are detected, treatment options for free-ranging wildlife are not effective. Humane euthanasia should be considered to prevent spread and the further degradation of the animal's quality of life. Licensed veterinarians may administer drugs for the treatment of sick or injured captive wildlife. Veterinarians should reach out to KDFWR's Wildlife Veterinarian for guidance.
If you see a live wild animal with:
- Egg masses or maggots on orifices or open wounds
- Large, gaping wounds
- Foul odors coming from open wounds
Please report IMMEDIATELY to Kentucky Fish and Wildlife's sick and dead reporting form. Do NOT touch or transport the infested animal to a wildlife rehabilitation facility to prevent the spread of NWS to humans or other animals.
FL Key Deer infested with New World Screwworm in 2017, USDA.
New World Screwworm can cause severe, debilitating wounds in both captive and free-ranging wildlife. Wounds caused in the later stages of a NWS infestation can be painful and can disrupt an animal's normal behavior. Eventually, the wound and possible secondary infections may impact an animal's quality of life and eeven lead to death. In addition to the individual impacts, NWS can have population-level impacts, especially during highly vulnerable times for wildlife. These can include birthing young, antler development and during the rut for Kentucky's deer and elk populations. These times are when wounds are more likely to occur, which then facilitates the dispersal of flies and the spreading to new areas or species. This then impacts survival and recruitment in local wildlife populations and increases the risk for threatened and endangered species.
New World Screwworms infest humans, birds, wildlife, livestock and domestic animals like cats and dogs. Currently, the only treatment option for NWS infestations in people is manual removal of larvae from infested tissue and supportive care, which includes prescribing antibiotics to prevent secondary infections after removal.
If you observe possible infestations on livestock, report it to the Kentucky Department of Agriculture. For suspected infestations in pets, contact your veterinarian.
Controlling the spread of screwworms focuses on eliminating populations of NWS from the environment. This can be achieved through the Sterile Insect Technique, which involves exposing NWS pupae (stage between larvae and adult), then releasing the sterile male flies into areas where NWS are present. These sterile males mate with local females, which then produce unviable eggs and halts further reproduction. This has been a highly effective tool in the prevention and eradication of this condition because the female flies only mate once in their lifetime.
For more information about the USDA's sterile fly production and dispersal efforts, visit their website.
U.S. Department of Agriculture
Centers for Disease Control and Prevention
Kentucky Department of Agriculture
University of Kentucky
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