New World Screwworm Detected Near US-Mexico Border: How to Stay Safe

The dangerous screwworm parasite, once eradicated in the United States, has been detected in northern Mexico, near the American border. Confirmed by Mexico’s agriculture ministry, an 8-month-old cow in Nuevo León tested positive for New World screwworm – showing signs of infestation. According to the authorities, while the cow has been treated, other cattle in the group have been given ivermectin, an antiparasitic medication. The case was reported from Sabinas Hidalgo, a small city less than 70 miles from Texas. It is the northernmost detection so far, moving much closer to the US border than earlier outbreaks in other parts of Mexico. In August, the flesh-eating parasite was detected in a person in the US, who had travelled from Guatemala.

Screwworm causes serious injury in livestock

Screwworm causes serious injury in livestock by laying eggs in wounds, and its larvae feed on living tissue. According to health officials, the parasite was completely eradicated from the US in the 1960s by mass-producing and releasing sterile flies to contain the flies’ range, but recent outbreaks in Central America and Mexico have caused concerns again. US Agriculture Secretary Brooke Rolling said it is a “national security priority”. The U.S. Department of Agriculture (USDA) and multiple other agencies are "executing a phased response strategy that includes early detection, rapid containment and long-term eradication efforts," the statement said. Thousands of fly traps have also been placed along the border, with no infected flies detected so far.

What are screwworms?

Doctors say New World screwworms are parasitic flies whose females lay eggs in wounds on any warm-blooded animal. Once the eggs hatch, screwworm larvae use their extremely sharp mouths to burrow through living flesh, eventually killing their host if left untreated. The feeding of maggots is similar to a screw being driven into wood, giving the pests their name. Infestations begin when a female fly lays eggs on open wounds or other parts of the body of live, warm-blooded animals. It primarily affects livestock but can also infest birds and people. The smell of a wound or an opening, such as the nose, mouth, or eyes, the umbilical cord of a newborn animal, or genitals, will attract the female flies. Experts say that when animals get infested, it leads to a loss of appetite, infection, and severe weakness or death. The only treatment is the removal of the larvae.

Signs and symptoms of screwworm

According to the CDC, the NWS infestations are extremely painful. If you have an infestation, you may see maggots around or in an open wound. A few signs and symptoms of NWS include:

• Unexplained skin lesions that do not heal
• Skin wounds or sores that worsen over time
• Painful skin wounds or sores
• Bleeding from open sores
• Feeling larvae movement within a skin wound or sore, nose, mouth, or eyes
• Seeing maggots around or in open sores
• A foul-smelling odour from the site of the infestation
• Secondary bacterial infections sometimes occur and may cause high fever or chills.

What are the risk factors?

Experts say you may be at a high risk for NWS if you travel to areas where the flies are present, or

• You have an open wound from a scratch or cut or from an insect bite.
• You have low immunity.
• You have a medical condition that leads to bleeding or open sores.
• You live or work at a place near livestock or other warm-blooded animals.