The US Department of Health and Human Services (HHS) has reported the first human case of travel-associated New World screwworm, a flesh-eating parasite, in the United States. The patient, who has since been treated, returned from travel to El Salvador, according to an HHS spokesperson. However, industry sources have said the individual travelled from Guatemala, creating a discrepancy over the origin of the infection.
The case was confirmed by the US Centers for Disease Control and Prevention (CDC) on 4 August and investigated by the Maryland Department of Health. The CDC reported the case to Maryland health officials and the state veterinarian, but state veterinarians learned of the case through other channels, leading to criticism of the transparency of the notification process. The CDC has described the risk to public health as 'very low'.
The confirmation comes amid heightened alert in the beef industry, as screwworm has moved northwards from Central America and southern Mexico. The US Department of Agriculture (USDA) recently announced plans to build a sterile fly facility in Texas to combat the pest, estimating that an outbreak could cost the state's economy around $1.8bn in livestock deaths, labour and medication expenses. Border closures on Mexican cattle have largely been in effect since November to prevent the arrival of screwworm.
Screwworms are parasitic flies whose females lay eggs in wounds on warm-blooded animals. The larvae burrow through living flesh using sharp mouths, potentially killing the host if untreated. Infestations are rare in humans but can be fatal. Treatment involves removing hundreds of larvae and disinfecting wounds, and is typically survivable if administered early.
No animal cases have been confirmed in the US this year, and the government has emphasised that the risk of introduction remains low. The Beef Alliance, an industry group, informed stakeholders of the human case via email, noting that due to patient privacy laws no further details were available.
