New World Screwworm Update: What the CDC Wants Veterinarians Need to Know

New World screwworm (NWS) infestations remain a serious animal health concern across parts of Central America and Mexico. Caused by the larvae of Cochliomyia hominivorax, these maggots invade open wounds and feed on living tissue, creating painful, foul-smelling lesions that can rapidly worsen. If not identified and treated early, infestations can lead to extensive tissue destruction, secondary infection, and even death.

Current Situation

In 2023, Panama and Costa Rica reported a re-emergence of New World screwworm. Since then, cases have spread throughout Central America and Mexico, including areas where the parasite had previously been controlled or eradicated.

As of February 3, 2026:

• More than 150,000 animal cases have been reported across affected countries.

• Over 1,240 human cases have also been documented.

There has been one confirmed human case in a traveler returning to the United States from El Salvador. At this time, the NWS fly has not been detected in the United States, and there is no evidence of local transmission.

Federal agencies, including the CDC and USDA, are actively monitoring the situation and working with partners to prevent spread. Control efforts include sterile fly release programs, movement controls for animals, enhanced surveillance, and education in affected regions.

Why This Matters for Veterinary Professionals

Veterinarians play a critical role in early detection and rapid response. New World screwworm larvae infest wounds, surgical sites, umbilici of newborn animals, and mucous membranes. Lesions may initially appear minor but can deteriorate quickly as larvae feed on viable tissue.

Clinical signs in animals may include:

• Painful, enlarging wounds that fail to heal

• Foul odor and serosanguinous discharge

• Visible larvae within lesions

• Behavioral changes due to discomfort

• Tissue destruction in severe or untreated cases

Any suspicious wound, especially in animals with recent travel history or exposure to imported animals from affected regions, should be examined closely.

Reporting Requirements

Immediate reporting is essential to prevent potential spread.

• Veterinarians who suspect a case in an animal should contact their State Animal Health Official and the USDA APHIS office without delay.

• Prompt reporting supports rapid investigation, containment, and protection of the broader livestock and companion animal populations.

Preventive Considerations to Share with Clients and Producers

In regions where NWS is present, prevention focuses on minimizing fly exposure and protecting wounds:

• Keep all wounds clean, treated, and covered.

• Promptly manage surgical and traumatic lesions.

• Use insect control measures where appropriate.

• Monitor animals closely for signs of wound deterioration or unusual discharge.

Zoonotic Awareness

While primarily an animal health issue, NWS can infest humans. Clients traveling to affected regions should be advised to protect open wounds, use insect repellent, and seek medical care immediately if they notice maggots, persistent wound pain, or unusual odor from a lesion.

Ongoing Vigilance

Although there is currently no detection of the screwworm fly in the United States, the scale of the outbreak in Central America and Mexico underscores the importance of awareness, surveillance, and rapid reporting. Early recognition remains the most important tool in preventing re-establishment and protecting both animal and public health.

Read more here: https://www.cdc.gov/new-world-screwworm/situation-summary/index.html