Return Of The Screwworm: Can The Flesh-Eating Parasite Found In US Cattle Infect Humans?
Return Of The Screwworm: Can The Flesh-Eating Parasite Found In US Cattle Infect Humans? Published By, Last Updated: June 05, 2026, 17:27 IST A parasite
Return Of The Screwworm: Can The Flesh-Eating Parasite Found In US Cattle Infect Humans? Published By, Last Updated: June 05, 2026, 17:27 IST A parasite once pushed out of the US has been detected again in livestock, prompting quarantine measures and a wider containment push in cattle-rich Texas. Rapid Read A herd of cattle graze a pasture, a day after the US Department of Agriculture confirmed that New World screwworm was detected in a Texas calf, near Zavala County, Texas, U.S. (REUTERS) A flesh-eating parasite that had been eradicated from the United States decades ago has returned to American livestock, setting off alarms in one of the country’s most important cattle-producing regions. The US Department of Agriculture has confirmed a case of New World screwworm in a 3-week-old calf in La Pryor, Texas, about 100 miles southwest of San Antonio and around 50 miles from the US-Mexico border. According to AP, this is the first confirmed case in Texas since 1966. The case matters because Texas is the top cattle-producing state in the US, with cattle worth about $17 billion. The wider US cattle industry is valued at about $113 billion. While officials have stressed that screwworm does not infest food and is not a food safety issue, it can become a serious food production problem if it spreads among livestock. The confirmed infestation has led to quarantine measures, surveillance, movement restrictions and an expanded sterile fly release programme in South Texas. US Agriculture Secretary Brooke Rollins said the current threat to human health in the US is extremely low, but warned there is “no doubt that this is a very, very serious threat to our livestock." What Is The New World Screwworm? The New World screwworm is a parasitic fly found in the Western Hemisphere. Its Old World cousin is found in parts of Africa and Asia.
What makes these flies unusual and dangerous is that their larvae, or maggots, feed on live flesh and fluids rather than dead tissue. Female flies lay eggs in open wounds or mucous membranes of warm-blooded animals. Once the eggs hatch, the larvae feed on the host’s living tissue. This can damage vital organs, trigger serious bacterial infections and, if left untreated, even kill the animal. Screwworm is not a contagious disease that spreads directly from one animal to another. The risk comes from adult female flies laying eggs in wounds. Even a small break in the skin can attract them. Stephen Diebel, a Texas rancher and president of the Texas & Southwestern Cattle Raisers Association, told AP that wounds “as small as a tick bite" can put cattle at risk. Why Are Cattle At High Risk? Livestock are especially vulnerable because routine handling can leave them with cuts or wounds. Lee Haines, an associate research professor of biological sciences at the University of Notre Dame, told AP that standard cattle practices such as shearing, de-horning, ear tagging, or moving animals in and out of corrals can cause scrapes and breaks in the skin. Birth can also make both the mother and calf vulnerable. That is significant because the confirmed Texas case involved a 3-week-old calf. The parasite can infest any warm-blooded animal. Can Humans Also Be Infected? Human cases are rare, but they can be serious and, in some cases, fatal. CNN reported that the last known US human case was a travel-related infection in Maryland in August, after the person had travelled to El Salvador. The patient recovered. According to the US Centers for Disease Control and Prevention, people at higher risk include those who work with livestock or other warm-blooded animals in affected areas, those who spend a lot of time outdoors, especially if they sleep outside, and people with medical conditions that cause bleeding or open sores.
Outside the US, the scale has been much larger. AP reported that as of June 2, the parasite had sickened more than 171,700 animals and 2,000 people across Central America and Mexico, according to the CDC. The CDC says there have been 10 human deaths. Why Has This Case Alarmed US Officials? The US had eradicated the New World screwworm decades ago through a major programme involving sterile flies, public awareness and international control efforts. For years, the pest had been contained near the southern end of Panama. That barrier has weakened in recent years. AP reported that an outbreak in Panama prompted a state of emergency in early 2023, after which cases moved to Costa Rica and Nicaragua. A case was confirmed in southern Mexico in November 2024, pushing US officials and the cattle industry to sound public alarms as the parasite moved closer to the American border. The flies reproduce quickly and can be carried across wide areas by hosts, including wild animals such as deer. Edward Burgess, a University of Florida entomologist who studies the fly, told AP, “It’s hard to stay ahead of it because of how fast that fly is able to move and regenerate." How Is The US Trying To Contain It? The USDA’s Veterinary Services Laboratories in Ames, Iowa, confirmed the Texas case after testing a sample from the calf. Following the detection, officials activated response teams in Texas, created an infested zone of 20 kilometres and imposed quarantines, movement controls and surveillance. The USDA has also moved to expand sterile fly releases in South Texas. According to AP, it has been dropping sterile flies in the region since February and is now releasing them twice a week, for a total of 4 million flies. It is also putting 4 million more pupae in the ground each week.
How Do Sterile Flies Help Stop Screwworm? The sterile fly method is central to the US response because female screwworm flies mate only once. Scientists rear flies in factories, sterilise males and release them in large numbers. If a fertile female mates with a sterile male, her eggs do not hatch. Over time, if enough sterile males are released, the population declines and can die out. This method helped the US eradicate the pest decades ago. What Next? For now, US officials are trying to prevent the single confirmed livestock case from becoming an established outbreak. The response includes quarantine enforcement, animal inspections, treatment protocols, surveillance and sterile fly releases. “If we all work together and follow the animal treatment protocols and movement restriction guidance, there is no reason to believe that this incursion will result in an establishment of the pest in our country," Rollins said during a briefing. News18 Newsletter Handpicked stories, in your inbox A newsletter with the best of our journalism submit About the Author Karishma Jain Karishma Jain, Chief Sub Editor at News18.com, writes and edits opinion pieces on a variety of subjects, including Indian politics and policy, culture and the arts, technology and social change. Follo... Read More First Published: June 05, 2026, 17:27 IST News world Return Of The Screwworm: Can The Flesh-Eating Parasite Found In US Cattle Infect Humans? Disclaimer: Comments reflect users’ views, not News18’s. Please keep discussions respectful and constructive. Abusive, defamatory, or illegal comments will be removed. News18 may disable any comment at its discretion. By posting, you agree to our Terms of Use and Privacy Policy Loading comments...
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