Four Cases in August, Forty-Two in Eleven Days: The Screwworm Curve Bent Upward

On Nov. 1 the federal count of confirmed screwworm infestations in the Southwest stood at 79 animals. By Wednesday evening it was 128, an increase of 62 percent in ten days, according to Texas Public Radio's running read of U.S. Department of Agriculture figures.

The map has been the story for most of the fall, and it moved again this week. What has changed is the shape of the curve behind the map, which is now legible in a way it was not a month ago. Broken into months, the domestic caseload ran four in August, three in September, thirty-three in October, and forty-two in the first eleven days of November, according to the figures USDA's Animal and Plant Health Inspection Service updated Wednesday and FOX 4 published Thursday morning.

Put those against the calendar and the acceleration stops being a rhetorical word. September's three cases over thirty days works out to roughly one case every ten days. October's thirty-three over thirty-one days is a little more than one a day. November's forty-two in eleven days is nearly four a day — about three and a half times October's pace and close to forty times September's. The rest of the outbreak, by subtraction from the 128 total, sits in June and July: forty-six animals over roughly two months, a period when the parasite was treated as a West Texas problem confined to a handful of ranches near the New Mexico line.

Two things happened inside the same ten-day window, and they are worth keeping separate. The caseload grew, and the list of animals it grew in widened. Alongside cattle in Reagan and Hudspeth counties, the recent confirmations include a horse in Bandera County, a sheep in Val Verde County and a dog in El Paso County, plus a horse in Cochise County, Arizona and one in Otero County, New Mexico. Sheep are a detail worth noticing: the fly does not care what species it finds a wound on, but a sheep flock is a different operational problem from a cow-calf outfit, with more animals, closer together, and more chances for a lambing wound to go unexamined for a day.

Of the 128 confirmed infestations, 65 remain active and 63 are closed, per the same tracker. The two wildlife cases — elk in Pecos and Jeff Davis counties — are both inactive. Federal surveillance has also caught wild screwworm flies in six traps, four of them in October and one in November, which is a different kind of evidence: a trapped fly means the insect is present somewhere no one has yet found a wounded animal.

There is a small discrepancy in how the Texas side of this gets reported. Wire copy this week still described restrictions in "parts of 21 Texas counties," which was the count before Nov. 10. The Texas Animal Health Commission's own notice, checked Thursday morning, lists twenty-five: Bandera, Brewster, Crockett, Culberson, Edwards, El Paso, Fisher, Hudspeth, Irion, Jeff Davis, Jim Hogg, Medina, Mitchell, Nolan, Pecos, Presidio, Reagan, Reeves, Schleicher, Scurry, Starr, Sutton, Terrell, Val Verde and Zapata. The four newest arrived with the two orders signed Nov. 10 that also produced the Bandera and Reagan detections, and two of them, Medina and Irion, hold no detection of their own — they are drawn around a finding next door.

None of this changes what the response is waiting on. The sterile fly plant at Moore Air Base near Edinburg is due to open in April 2027 at a designed output of 100 million sterile flies a week, with the current supply split between the Panama facility and the newer plant at Metapa, Mexico. The arithmetic of whether that is enough fly to bend the curve back down has been covered here before; the new number this week is what the curve is doing while the concrete cures.

The practical guidance has not moved either. Inspect animals daily, particularly ears, eyes, nose, mouth, navels and any scrape or wire cut, and treat a wound that enlarges or smells wrong as an emergency rather than a wait-and-see. Suspected cases go to a veterinarian first and to the Texas Animal Health Commission at 800-550-8242, which also takes wildlife reports. Any warm-blooded animal leaving a restricted area needs prior authorization, an inspection, a treatment and a movement certificate naming the product used and the animal's official ID.

What to watch next is whether November's rate holds. Cooler weather slows screwworm flies without stopping them, and entomologists have pointed to a mild fall as one reason the parasite is still finding wounds to lay in. If the December series comes in near forty again, the outbreak will have doubled roughly every three to four weeks since the start of October. If it falls back to single digits, the fly releases will have something to claim.