{"id":92421,"date":"2026-08-05T09:23:33","date_gmt":"2026-08-05T15:23:33","guid":{"rendered":"https:\/\/www.uchealth.org\/today\/?p=92421"},"modified":"2026-08-05T09:23:33","modified_gmt":"2026-08-05T15:23:33","slug":"new-world-screwworm-flesh-eating-fly","status":"publish","type":"post","link":"https:\/\/www.uchealth.org\/today\/new-world-screwworm-flesh-eating-fly\/","title":{"rendered":"New World screwworm: The frightening tale of the flesh-eating fly infecting cattle in Texas and New Mexico"},"content":{"rendered":"<div style=\"margin-top: 0px; margin-bottom: 0px;\" class=\"sharethis-inline-share-buttons\" ><\/div><figure id=\"attachment_92430\" aria-describedby=\"caption-attachment-92430\" style=\"width: 640px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-92430\" src=\"https:\/\/uchealth-wp-uploads.s3.amazonaws.com\/wp-content\/uploads\/sites\/6\/2026\/08\/05084423\/GettyImages-2231146554-screwworm-web.webp\" alt=\"The New World screwworm. The New World screwworm was considered eradicated in the U.S. in 1966. Recent infections in livestock in Texas and New Mexico have raised concerns about its spread. Photo: Getty Images. \" width=\"640\" height=\"421\" \/><figcaption id=\"caption-attachment-92430\" class=\"wp-caption-text\">A New World screwworm. The screwworm was considered eradicated in the U.S. in 1966. Recent infections in livestock in Texas and New Mexico have raised concerns about its spread. Photo: Getty Images.<\/figcaption><\/figure>\n<p>Agriculture officials have discovered a flesh-eating fly in livestock in the United States for the first time in 60 years, and the alarm bells have been ringing ever since.<\/p>\n<p>The news came from Texas, where investigators from the U.S. Department of Agriculture (USDA), in June, <a id=\"\" href=\"https:\/\/www.aphis.usda.gov\/news\/agency-announcements\/usda-confirms-presence-new-world-screwworm-united-states\" target=\"_blank\" rel=\"noopener\">confirmed <\/a>the presence of what\u2019s known as the New World screwworm in a three-week-old calf.<\/p>\n<p>If you\u2019re not a rancher or a cow, you might be wondering what the big deal is about a bug that has decided to meander northward. The answer is that New World screwworm can affect both people and animals. And unlike the \u2018normal\u2019 maggots we might be unlucky enough to encounter in rotting meat, these little guys will eat<em> living <\/em>flesh. They land on intact mucus membrane (the inside of your lips, nose and other orifices) or a wound as small as a scratch, and lay their eggs. And then the babies, the larvae, burrow their way in, eating healthy flesh.<\/p>\n<p>Think zombie worms. Then try to stop thinking.<\/p>\n<p>The New World screwworm was deemed eradicated from the U.S. in 1966. Since then, the only time these screwworms had come close to getting a toehold in the U.S. livestock population was a brief outbreak ten years ago in<em> wild deer <\/em>in the<a id=\"\" href=\"https:\/\/www.aphis.usda.gov\/sites\/default\/files\/nws-finaloutbreakreport-ppt.pdf\" target=\"_blank\" rel=\"noopener\"> Florida Keys,<\/a> which was quickly eradicated.<\/p>\n<p>The secret to eradicating screwworms is a biological weapon called <a id=\"\" href=\"https:\/\/www.aphis.usda.gov\/sites\/default\/files\/factsheet-eradicating-nws-sit.pdf\" target=\"_blank\" rel=\"noopener\">Sterile Insect Technique<\/a>. Back in 1966, an international consortium of North, Central and South American government representatives got together and set up a biological barrier in the <a id=\"\" href=\"https:\/\/www.aphis.usda.gov\/animals\/animal-health\/livestock-and-poultry-disease\/stop-screwworm\" target=\"_blank\" rel=\"noopener\">Darien Gap <\/a>of Panama. Experts created this barrier by releasing irradiated male flies, which then mated with females and produced non-viable eggs. Since female flies generally only mate once, and a fly\u2019s lifespan is, at most, 30 days, this intervention quickly killed off the population.<div class=\"su-callout-box col-xs-6 col-sm-6 right\" style=\"background-color:#dce4e7; color:#2e3b44;\">\n<h4><strong>Key facts about screwworm<\/strong><\/h4>\n<ul>\n<li>Screwworm is a flesh-eating fly whose larvae feed on living tissue.<\/li>\n<li>The parasite recently infected livestock in Texas and New Mexico.<\/li>\n<li>Humans, dogs, cats and livestock can become infected.<\/li>\n<li>There is no vaccine.<\/li>\n<li>Early treatment prevents serious complications.<\/li>\n<li>Colorado has not reported livestock infections.<\/div><\/li>\n<\/ul>\n<p>But the Darien Gap barrier started to<a id=\"\" href=\"https:\/\/www.newsweek.com\/screwworm-immigration-darien-gap-2088609\" target=\"_blank\" rel=\"noopener\"> weaken in 2022. <\/a>COVID-19 supply-chain issues made it difficult to keep up with the necessary prevention efforts, and record human and animal migration through the Gap meant more fertile male flies were getting through the biological barrier as hitchhikers on clothing and skin.<\/p>\n<p>Health officials determined that the barrier had been completely<a id=\"\" href=\"https:\/\/asm.org\/home-page\/featured\/new-word-screwworm-rise-fall-resurgence\" target=\"_blank\" rel=\"noopener\"> breached in 2023<\/a>, and an explosion of screwworm cases emerged in Mexico and Central America. In May of<a id=\"\" href=\"https:\/\/www.usda.gov\/about-usda\/news\/press-releases\/2025\/05\/11\/secretary-rollins-suspends-live-animal-imports-through-ports-entry-along-southern-border-effective\" target=\"_blank\" rel=\"noopener\"> 2025, <\/a>U.S. Agriculture Secretary Brooke Rollins suspended all livestock trade with Mexico, but it was too late. <a id=\"\" href=\"https:\/\/www.cdc.gov\/new-world-screwworm\/situation-summary\/index.html\" target=\"_blank\" rel=\"noopener\">As of July, 2026, <\/a>there were 185,000 animal cases in Central America and Mexico, and 2,263 human cases in that area. Here in the U.S., that one little Texas calf case in June has given way to 35 animal cases in both Texas and New Mexico, including infections in cows, sheep, goats and, yes, a dog.<\/p>\n<p>USDA officials don\u2019t know if New World screwworm may already be lurking in cattle in Colorado or how soon they could arrive.<\/p>\n<p>To figure out just how worried we should be about potential screwworm cases in both people and our pets, we spoke with <a href=\"https:\/\/www.uchealth.org\/provider\/michelle-barron-md\/\">Dr. Michelle Barron,<\/a> senior medical director of infection prevention and control for UCHealth and a <a id=\"\" href=\"https:\/\/som.ucdenver.edu\/Profiles\/Faculty\/Profile\/8603\" target=\"_blank\" rel=\"noopener\">professor of medicine and infectious diseases<\/a> at the <a id=\"\" href=\"https:\/\/medschool.cuanschutz.edu\/\" target=\"_blank\" rel=\"noopener\">University of Colorado Anschutz School of Medicine<\/a>.<\/p>\n<h2><strong>Why is this fly (or insect or maggot) called the New World screwworm?<\/strong><\/h2>\n<p>\u201cThe scientific name for it is <em>Cochliomyia hominivorax<\/em>, which roughly translates as \u2018man-eater,\u2019\u201d said Barron. \u201cRegular, non-Latin speaking folks started calling it screwworm, because the larvae are shaped like screws, which allows them to burrow deeper and deeper into healthy flesh which they then eat.\u201d<\/p>\n<p>The \u2018New World\u2019 part of the name refers to the Western Hemisphere.<\/p>\n<figure id=\"attachment_92433\" aria-describedby=\"caption-attachment-92433\" style=\"width: 400px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-92433\" src=\"https:\/\/uchealth-wp-uploads.s3.amazonaws.com\/wp-content\/uploads\/sites\/6\/2026\/08\/05084535\/NWS-two-whole-larvae-screwworm-CDC-web.webp\" alt=\"Screwworm larvae are named for their resemblance to screws. Unlike typical flies or maggots that feed on dead tissue, screwworm larvae eat healthy, living flesh. Photo courtesy of the U.S. Centers for Disease Control and Prevention.\" width=\"400\" height=\"226\" \/><figcaption id=\"caption-attachment-92433\" class=\"wp-caption-text\">Screwworm larvae are named for their resemblance to screws. Unlike typical flies or maggots that feed on dead tissue, screwworm larvae eat healthy, living flesh. Photo courtesy of the U.S. Centers for Disease Control and Prevention.<\/figcaption><\/figure>\n<h2><strong>What does the screwworm fly look like?<br \/>\n<\/strong><\/h2>\n<p>It\u2019s very distinctive, with iridescent blue stripes on its back. The run-of-the-mill blow fly has brown or green stripes on its back.<\/p>\n<p>\u201cYou\u2019ll be able to tell,\u201d said Barron, \u201cif you look closely.\u201d<\/p>\n<h2><strong>Is there a vaccine for New World screwworm to prevent infections in animals or people?<\/strong><\/h2>\n<p>\u201cNope,\u201d said Barron. \u201cThis isn\u2019t a virus or a bacteria. It\u2019s a parasite: a little bug that wants something you have, namely your living tissue.\u201d<\/p>\n<h2><strong>What&#8217;s the best way to prevent infections from the New World screwworm?<\/strong><\/h2>\n<p>\u201cThese flies can lay eggs in your mouth, your nose or <a href=\"https:\/\/www.uchealth.org\/services\/wound-care\/\">an open wound<\/a>, even as small as a scrape,\u201d said Barron. \u201cIt\u2019s truly horrifying. I recommend covering all scrapes and cuts no matter how small, and not sleeping outside.\u201d<\/p>\n<p>Barron explains that a maggot infection, such as that caused by the screwworm, is called myiasis.<div class=\"su-pullquote su-pullquote-align-right\">Learn about other <a href=\"https:\/\/www.uchealth.org\/today\/all-about-bugs-keep-your-family-healthy-bugs-that-bug-us\/\">bugs that often get too close for comfort<\/a>, like lice and bedbugs, and how to spot, treat and prevent bites.<\/div>\n<p>\u201cAnd avoid places that have lots of flies, like landfills and livestock feedlots, if you can. Also, use fly and mosquito spray on your clothing and in immediate areas, to try to keep the area clear from flies.\u201d<\/p>\n<h2><strong>What are the symptoms of a screwworm infection?<\/strong><\/h2>\n<p>\u201cFirst, understand that the flies have not made it north of New Mexico as of late July,\u201d said Barron. \u201cBut it\u2019s never too early to be careful. Myiasis can be tricky to spot. Look for pain or movement in intact flesh, wounds that continue to bleed and fail to heal, smelly wounds, and of course, the presence of maggots.\u201d<\/p>\n<h2><strong>Can dogs or cats get screwworm infections?<br \/>\n<\/strong><\/h2>\n<p>\u201cYes, there has already been a report of a canine screwworm infection in Texas,\u201d said Barron. \u201cI wouldn\u2019t allow dogs or cats to sleep outside, and I would check them often for open wounds or scrapes frequently, and cover any if you find them.\u201d<\/p>\n<h2><strong>Is there a medication to prevent or treat screwworm in pets so I can protect my dog or cat?<\/strong><\/h2>\n<p>Officials at the FDA preliminarily approved a handful of anti-parasitic medications for <a id=\"\" href=\"https:\/\/www.fda.gov\/animal-veterinary\/safety-health\/new-world-screwworm-information-veterinarians\" target=\"_blank\" rel=\"noopener\">prevention and \u201ctreatment\u201d <\/a>of screwworm infection, but it is important to understand that these medications are not foolproof. Most of them work by paralyzing the worms or interfering with the gut function, which eventually kills them. But pills alone are not enough to prevent or treat a screwworm infestation, which requires surgically removing the maggots and then treating them with antibiotics.<\/p>\n<p>\u201cIt makes sense to keep pets away from places that have flies (feedlots, trashpiles, cow pens, etc.). In addition, have them sleep indoors and check them frequently for open wounds,\u201d said Barron. \u201cDo give them preventatives, but don\u2019t rely on them.\u201d<\/p>\n<h2><strong>How do doctors treat screwworm infections?<\/strong><\/h2>\n<p>\u201cSurgical debridement is the only treatment, followed by a course of antibiotics to prevent or treat a bacterial <a href=\"https:\/\/www.uchealth.org\/diseases-conditions\/skin-rashes\/\">skin infection<\/a>,\u201d Barron said. \u201cYou\u2019ve got to get the maggots out and clean the wound.\u201d This can be an extensive procedure given that one female fly can lay <a id=\"\" href=\"https:\/\/www.cdc.gov\/new-world-screwworm\/about\/index.html\" target=\"_blank\" rel=\"noopener\">200-300 eggs at a time<\/a>.<\/p>\n<h2><strong>Do people or animals die from New World screwworm?<\/strong><\/h2>\n<p>Yes. Screwworm infections can be fatal but only if the infestation is ignored and allowed to progress.<\/p>\n<p>\u201cAnimals are much more likely to have fatal infections because they can\u2019t talk and tell us that something hurts or feels funny,\u201dsaid Barron.<\/p>\n<h2><strong>Who is at highest risk of getting a New World screwworm infection?<\/strong><\/h2>\n<p>\u201cAt this point, the people at the most risk are those who have open wounds, have been through some kind of trauma and have a lot of exposed flesh,\u201d said Barron. \u201cIn addition, those who work with livestock or horses and those who live in areas with a fair amount of agriculture, and those who sleep outside on a regular basis.\u201d<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Agriculture officials have discovered a flesh-eating fly in livestock in the United States for the first time in 60 years, and the alarm bells have been ringing ever since. The news came from Texas, where investigators from the U.S. Department of Agriculture (USDA), in June, confirmed the presence of what\u2019s known as the New World [&hellip;]<\/p>\n","protected":false},"author":2426,"featured_media":92430,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_relevanssi_hide_post":"","_relevanssi_hide_content":"","_relevanssi_pin_for_all":"","_relevanssi_pin_keywords":"","_relevanssi_unpin_keywords":"","_relevanssi_related_keywords":"","_relevanssi_related_include_ids":"","_relevanssi_related_exclude_ids":"","_relevanssi_related_no_append":"","_relevanssi_related_not_related":"","_relevanssi_related_posts":"","_relevanssi_noindex_reason":"","footnotes":""},"categories":[8],"tags":[392,162],"class_list":["post-92421","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news","tag-infection-prevention","tag-infectious-diseases"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v28.1 (Yoast SEO v28.1) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>Screwworm: The flesh-eating fly infecting cattle in Texas and New Mexico - UCHealth Today<\/title>\n<meta name=\"description\" content=\"Screwworm is a flesh-eating fly whose larvae infect living tissue. 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