Deadly parasite returns to US after 60 years: Can screwworms infect humans and are they contagious?

The United States has reported the first human case of New World screwworm after it was eradicated from the country nearly 60 years ago. The Maryland Department of Health and the US Centers for Disease Control and Prevention confirmed that the New World screwworm was detected in a person in Maryland who had travelled to El Salvador, HHS spokesman Andrew G. Nixon told Reuters. However, earlier, the agency reported beef industry sources as saying that the CDC said the World screwworm case was in a person who had travelled to Guatemala. The disagreement over which country it comes from is likely to add to the panic in the country. Screwworms can cause major devastation in the cattle industry. According to the USDA, in Texas alone, a screwworm outbreak can cause a loss of $1.8 billion.

Also Read: New human screwworm case in US traced to person in Maryland who traveled from Guatemala, sources say

What is a screwworm?

Screwworms are parasitic fly larvae that can infect any warm-blooded animal. Cattle are highly prone to it, and even humans can carry the parasite, as proven by the Maryland case. The female screwworm fly deposits hundreds of eggs on a wound, sore, or mucous membrane, which later hatch, releasing larvae. Using their sharp mouths, the larvae dig through living flesh. The maggots screw through the flesh, hence giving them the name screwworm. After some time, a few of them fall out into the soil from which new screwworms emerge, and the cycle repeats. If left untreated, screwworms eventually kill their hosts. To treat the condition, the larvae need to be removed in a rigorous process that involves thoroughly cleaning the wound. However, it only works if this is done in the early stages of infestation.

Can screwworms infect humans, and are they contagious?

Human infestation is possible, but only in rare cases. However, if it happens, the wound festers just like it does in an animal. A patient in this case should seek immediate medical attention. The good news is that it is not directly transferable from one human to another. But the female screwworm can spread the eggs and larvae to humans in the same manner as in cattle and wildlife. This mostly happens in tropical and subtropical regions.

Are screwworms found in US?

Screwworms have been present in the north through Mexico from Central America since 2023. They are endemic in Cuba, Haiti, the Dominican Republic and countries in South America, according to the USDA. In the US, screwworms were eradicated in the 1960s. Researchers released sterilised male screwworm flies that mated with wild female screwworms, resulting in infertile eggs.