New World Screwworm Moves into Northern Mexico

On Tuesday, the Centers for Disease Control and Prevention (CDC) issued a health advisory to share information and notify clinicians, public health authorities, and the public about recent New World screwworm (NWS) animal cases in the Mexican state of Tamaulipas, which shares a border with Texas.

No NWS infestations related to this outbreak have been identified in people or animals in the U.S. as of Jan. 20. However, given the potential for geographic spread, CDC issued the Health Advisory to increase awareness and summarize recommendations for U.S. clinicians and health departments on case identification and reporting, specimen collection, diagnosis, treatment of NWS, and guidance for the public.

NWS is a devastating pest, the CDC said. NWS infections occur when flies lay eggs in wounds or other body cavities with mucus membranes, such as the nose, ears, eyes, or mouth. The eggs develop into parasitic larvae (maggots) that feed on living flesh and burrow into it. Although they primarily affect livestock, such as cattle and horses, the flies can also lay eggs on people and other warm-blooded animals, both domestic and wild. Cases of NWS in people can be fatal if left untreated.

An outbreak of NWS infestations in people and animals has developed across Central America and Mexico. During this outbreak, more than 1,190 cases and seven deaths in people have been reported as of Jan. 20.

Mexico has reported 24 hospitalizations among people and 601 active cases among animals. (An animal case is defined as “active” at the time of diagnosis and becomes inactive if officials verify the absence of new wounds or larvae after 15 days.) The Mexican state of Tamaulipas reported eight active animal cases. Still, the risk to people in the U.S. remains low, the CDC said.

People might be at increased risk for developing NWS if they spend time in geographic areas where NWS flies are present and:

• Have an open wound, including scratches, cuts, insect bites, or surgical wounds.
• Have a medical condition that might affect how quickly a wound heals, or that may cause bleeding or open sores (e.g., skin cancer, psoriasis, or eczema).
• They are very old or very young.
• Experience malnutrition.
• Sleep outdoors, especially during daytime hours when NWS flies are more active.
• Live, work, or spend an extended amount of time near livestock or other warm-blooded animals in these areas.

The treatment of NWS in humans is the removal of all eggs and larvae, which may require surgical extraction if the larvae are deeply embedded in tissues, the CDC said. No studies have proved that any specific medication helps treat humans. Patients with secondary infections or additional symptoms may need supportive care.