Fear of a fly eating flesh. The number of cases is increasing

For decades, countries in South and North America have invested billions of dollars to combat the parasite. By the mid-1960s, the screw fly was almost completely eliminated from the southern United States, where it was a serious problem for cattle farmers. In 2006, a special protective barrier was created along the US border with Mexico.

However, since 2023, the number of cases of the South American insect is increasing and spreading north, from Panama to Costa Rica, Nicaragua, Honduras and Guatemala. In Panama, the number of detected cases rose sharply from an average of 25 per year before last year to 22,611 recorded by December 4.

The U.S. Embassy in Costa Rica reported that the country has seen an increase in human infections this year, and one death was confirmed at the beginning of the year.

As reported by the United States Department of Agriculture at the end of November, the insect was also detected again in Mexico, where it was eradicated in 1986.

Due to the risk of the screw fly entering the U.S., imports of livestock from Mexico have been restricted “pending further information from Mexican authorities on the size and scope of the infestation.” There are concerns that infected horses in particular, often illegally imported, could transmit the parasite.

screw fly (Cochliomyia hominivorax) resembles a housefly, but is slightly larger. It mainly infects farm animals, domestic animals, wild animals and, less often, people. Adult females lay eggs most often in open wounds on the skin. The larvae feed on the flesh surrounding the wound, tearing the tissue with their sharp mouth hooks and eating their hosts from the inside. As more larvae hatch from the eggs, the wound becomes larger and deeper. According to a study by the World Health Organization (WHO), the mortality rate in humans is approximately three percent.

According to the US Centers for Disease Control and Prevention (CDC), people living in rural areas who often work with farm animals are most at risk, but infection can occur in anyone with wounds, including those after recent surgery. There is no approved treatment beyond physically removing the larvae from the tissue.

The United States Department of Agriculture has advised pet owners to check their pets for enlarging or oozing wounds and for the presence of insect eggs or larvae.