The mandibles of the Screwworm are strong enough to chew through human flesh and at a voracious speed. Photo credit:John Kucharski/Wikimedia Commons
The United States has confirmed its first human case of infection with the New World screwworm (Cochliomyia hominivorax) in decades. The case involves a Maryland resident who was diagnosed in early August after returning from El Salvador, where the parasite is still present. According to health authorities, the patient received medical care, including the removal of larvae, and has since recovered.
The New World screwworm is a parasitic fly native to the Americas. It is regarded as particularly dangerous because the larvae feed on the living tissue of warm-blooded animals, unlike other fly species whose maggots consume dead or decaying matter. Adult female flies lay eggs in open wounds, and once hatched, the larvae burrow deeper into the flesh, feeding aggressively and causing extensive tissue damage. If untreated, infestations can be fatal. This parasite has historically been a serious problem in both humans and livestock. The United States eradicated the screwworm in the 1960s through the sterile insect technique, which involved the mass release of sterilised male flies. When these sterile males mated with females, no viable offspring were produced, leading to the collapse of local populations. The strategy was considered one of the most successful pest eradication campaigns in history and was later applied in Central America.
Despite this success, the screwworm has persisted in parts of Latin America and the Caribbean. Occasional outbreaks have been reported in countries such as Panama and the Dominican Republic. The case in Maryland highlights the continuing risk of reintroduction through human or animal movement across borders. Authorities emphasise that the infection was acquired abroad and that there is no evidence of local transmission within the United States.
The US Department of Agriculture (USDA) and state officials have responded by reinforcing surveillance measures. Texas, which would be the most vulnerable state in the event of a cross-border outbreak, is preparing a new high-capacity sterile fly production facility. Reports indicate that the centre will be able to produce and release up to 300 million sterile flies per week. These efforts aim to create a protective barrier along the southern border and prevent the parasite from becoming re-established in US livestock populations. The economic stakes are significant. Screwworm infestations in cattle, sheep, and other animals can lead to serious losses, as infestations not only cause suffering but also reduce productivity and may require culling. The livestock industry in the United States is worth billions of dollars annually, and a reintroduction of the parasite would pose a severe threat to farmers and supply chains.
For humans, cases remain rare. When they do occur, they are generally linked to travel in regions where the parasite is still present. Symptoms can include painful wounds that fail to heal, visible larvae in affected tissue, and secondary infections. Treatment typically involves the physical removal of larvae, wound care, and the administration of medication to prevent reinfestation.
Officials stress that while the appearance of the parasite in a human patient is alarming, the public health risk in the United States remains very low. The detection and rapid treatment of the Maryland case also demonstrate the effectiveness of medical and surveillance systems in place. Nonetheless, the case serves as a reminder of the importance of international cooperation in monitoring and controlling parasitic diseases. As global travel continues to increase, so too does the potential for rare but serious parasites to appear in countries where they were once eliminated.
