The Centers for Disease Control and Prevention issued a nationwide Health Alert Network Health Advisory on Jan. 20 to share information about the New World screwworm, or NWS, and the recent increase in animal cases in the Mexican state of Tamaulipas, which shares a border with Texas. Although no NWS infestations have been identified in people or animals in the U.S., there is potential for geographic spread. The advisory issued by the CDC is intended to increase awareness of the expanding NWS outbreak and provide recommendations to health departments and doctors in the U.S. as well as guidance for the general public.

NWS is the larvae of a parasitic fly that feeds on the living tissue of warm-blooded animals, including dogs, livestock, wildlife, and, rarely, humans. Female flies lay eggs in open wounds, breaks in the skin, surgical sites, or moist body openings. Within a day the larvae hatch and begin burrowing into healthy tissue, causing painful, rapidly worsening wounds if not treated promptly. Infestations can occur in otherwise healthy animals and humans.

“The risk to military working animals and pets on military installations in the continental United States is low due to the fact that the U.S. is currently free of New World screwworm, which we hope remains the case,” said Lt. Col. Melissa Hehr, deputy chief, Veterinary Services Division, Defense Health Agency-Public Health. “The risk of exposure to NWS is higher in countries where the disease is endemic, so working dog handlers and pet owners should take extra precautions when traveling to or living in endemic areas outside of the U.S.”

One Health 

Military veterinarians play a critical role in supporting the federal interagency One Health efforts to address the resurgence of NWS in the Americas. The CDC and Department of Agriculture are leading the government’s unified response to this threat.

“The Department of War is supporting unified interagency efforts led by USDA to prevent the re-emergence of NWS in the United States,” said Dr. Kristina McElroy, interagency coordinator, Veterinary Services Division, DHA-Public Health in Falls Church, Virginia. “Military veterinary personnel carry out regulatory duties established by USDA and CDC. Army veterinary personnel located at veterinary treatment facilities and at operational Medical Detachment Veterinary Service Support units are vital contributors to DOW’s efforts to ensure this pest does not become established in the United States.”

Hehr explained military veterinarians support homeland defense by maintaining enhanced vigilance to detect diseases specified on the National List of Reportable Animal Diseases, which includes NWS.

“If detected or suspected, these diseases must be reported to the USDA. U.S. Army veterinarians enhance their ability to detect notifiable diseases by maintaining USDA Category II accreditation, which involves completing training on reportable animal diseases,” said Hehr.

McElroy explained the DOW is part of the robust ‘whole-of-government’ response to protect U.S. agricultural stability, public health, and national security.

“DOW service members, beneficiaries, and employees are all part of DOW’s contributions to this effort.”

Guidance for handlers, kennels, and families 

To support military working dog teams, the U.S. Army issued focused guidance last year that reinforces daily animal health checks, rigorous wound care, and strong fly control around kennels and outdoor areas. Similar guidance tailored to military horses was also released.

“The U.S. Army Medical Command, in coordination with DHA Veterinary Services, published a technical communication which addresses precautions that military working dog handlers and kennels should take to reduce the risk of NWS in MWDs and on kennel premises,” said Hehr.

For families, the message is simple and consistent.

“Effective ectoparasite prevention is available,” said Hehr. “MWD handlers and pet owners should consult with their veterinarian to develop a prevention plan and immediately inform their veterinarian if they suspect NWS infestation in an animal.”

This same advice applies when encountering a potential NWS infection.

“Do not wait and do not self-treat,” said Hehr. “Get veterinary care immediately.”

What if an animal does get NWS?

“Early action makes a critical difference if NWS is ever found in a working dog or pet,” said Hehr.

“If a NWS infestation is detected early enough in a patient, and the animal is treated before extensive tissue damage or a secondary infection have occurred, its prognosis for survival and return to duty is good,” said Hehr. “Long-term consequences and treatment depend on the extent the disease has progressed prior to treatment.”

Animals with more advanced infestations may face more extensive care, potential scarring, or functional problems, underscoring why rapid reporting and veterinary evaluation are so important. Untreated cases can also lead to the larvae completing their life cycle, which means more adult flies will enter the environment to spread NWS.

Re-eradication 

The USDA Animal and Plant Health Inspection Service previously developed an effective eradication strategy based on releasing sterile male flies into the environment. Since the female NWS fly mates only once in her 21-day lifespan, mating with a sterile male fly means any resulting eggs are not fertilized, and no larvae will hatch. The CDC points out this strategy was successful in eradicating NWS from the United States, Mexico, and southward through Central America from the 1970s to the early 2000s. The United States successfully used the strategy again in 2017 following a 2016 reintroduction of NWS into Key deer in the Florida Keys.

The USDA APHIS current strategy to control and re-eradicate NWS includes the release of sterile male flies and also incorporates developing and enforcing animal movement controls along with increasing passive and active surveillance, outreach, and education in impacted areas.

Where to find trusted information, and what you can do 

For up-to-date information on NWS, Hehr recommended that handlers and pet owners check http://screwworm.gov and consult with their veterinarian for the latest information and guidelines. http://screwworm.gov/ centralizes government verified‑ updates on the regional situation, federal response actions, and practical advice for animal owners.

For humans, the CDC said prevention is key to protecting yourself and family. The CDC screwworm site also offers information on screwworm in humans.

Families and handlers traveling with dogs from NWS affected countries must also follow U.S. reentry rules. USDA requires that dogs returning from a screwworm endemic country be certified as screwworm-free by a government (or authorized) veterinarian in the country of origin, confirming the dog was inspected within five days before shipment and is either free of screwworm or was treated and cleared before departure.

“Ultimately, every member of the military community has a role,” said McElroy. “By using effective ectoparasite prevention, inspecting animals regularly, following travel and import rules, and contacting a veterinarian immediately if something looks wrong, service members and families help ensure that the nation’s animals, food supply, and economy stay protected.”

DOW veterinarians are focused on helping prevent the NWS threat to U.S. economic security.

“While all warm-blooded animals, including humans, pets, and livestock, are susceptible to NWS infestation, the primary threat to the nation lies in the devastating impact on the livestock industry and food supply, which has profound implications for U.S. economic security,” said McElroy. “DOW veterinarians play a role in protecting U.S. food and agriculture by promoting threat awareness and countering the threat of NWS in multiple animal species.”

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