Screwworm found in Texas cow: Can they infect humans? How did they return to US after 60 years?

The New World screwworm, which was eradicated from the United States over 60 years ago, has been found inside a cow in Texas. It is a parasitic, flesh-eating creature that feeds on the living flesh of warm-blooded animals, the American Society for Microbiology (ASM) said. The US Department of Agriculture (USDA) was announced the discovery, triggering alarm about the return of the screwworm, also known as Cochliomyia hominivorax. The screwworms are the larvae, or maggots, of adult C. hominivorax flies.

How do screwworms infest animals?

Adult flies search for open wounds or natural body openings, such as the eyes, ears, nose, mouth, and genitals, where they to lay their eggs. Once the larvae hatch, the maggots burrow deep into the living tissue of the host. They do so in a distinctive, corkscrew-like movement, which lends them the name screwworms. Equipped with sharp mouth hooks, the maggots feed on the flesh, aggressively tearing in which rapidly enlarges the wound. This structural damage causes intense pain, swelling, and hemorrhaging, and leads the host to release a foul smell. Other flies are attracted to this smell, which further worsens the infestation, increasing the risk of fatal secondary bacterial infections.

Once they worms pass this cycle, they leave the animal and burrow into the soil where they "pupate" before maturing into a fly. This maggot infestations are known as myiasis. Regions where the fly species is endemic, economic losses can run into billions of dollars each year. Cows, sheep and horses are most at risk from screwworms. Domestic dogs and wild mammals, such as deer, rabbits, and birds can also fall prey to these worms. Livestock infected by the New World screwworms can be treated with antiparasitic medications.

Can screwworms infect humans?

The chances of humans being infected by the screwworms are extremely low. But the good news is that in humans, the infection can be treated. People in areas where screwworms are commonly found, especially those who work with livestock, are susceptible to the flies laying eggs in their wounds. Symptoms of the C. hominivorax infestation include seeing or feeling maggots move under the skin, ears, nose, eyes, or mouth, with wounds bleeding and emanating a foul smell.

Why have screwworms returned to the US?

For decades, aa strict biological barrier at the Darién Gap in Panama has ensured that the screwworm does not enter the US. Adult screwworm flies can only travel a few kilometres in their lifetime. Their movement through Central America and Mexico was driven by human assistance. The primary reason for it reaching different regions has been the domestic transport and shipping of infested livestock. Smugglers also engage in illegal cattle movement across geographically difficult borders, which lets infected animals to being in the flesh-eating maggots without being detected.