Screwworm Count Reaches 50 as New Mexico Confirms a Second Horse Case

The New World screwworm outbreak has reached 50 confirmed U.S. cases — and for the second week in a row, the newest case is a horse. USDA's case-level dashboard confirmed an infestation in a horse in Grant County, New Mexico, on September 17, the state's second case of the outbreak.

Track every confirmed case on our live Texas screwworm tracker and county map.

Forty-eight of the 50 U.S. cases are in Texas. Both New Mexico cases sit just across the state line: a dog in Lea County in early June, and now the Grant County horse. Only two cases nationwide are listed as active under mitigation, with 48 inactive.

Second equine case in two weeks

The Grant County confirmation comes eight days after the outbreak's first equine case, a working ranch horse in Presidio County, Texas, confirmed September 9. Until this month the parasite had been found in cattle, sheep, goats and dogs; it has now struck horses twice in two states within about 200 miles of each other along the border.

New Mexico officials are establishing infested and surveillance zones around the Grant County premise, the same containment pattern TAHC has applied across 17 affected Texas counties. Equine cases carry an added risk: horses travel — to shows, sales and between ranches — and the illegal movement of horses across the border remains a known pathway for spread.

Texas count holds at 48 as a border port prepares to reopen

No new Texas case has been confirmed since September 9, the longest quiet stretch since July. The September slowdown follows TAHC's wave of zone releases, which cut the quarantine map from parts of 19 counties to 14 over the first half of the month.

The new case landed the same week Reuters reported the U.S. is preparing to reopen a border port to Mexican livestock imports, closed since the outbreak crossed the border in June. Agriculture Secretary Brooke Rollins cautioned that the threat has not passed, pointing to Arizona and New Mexico as areas of concern: "We're not out of the woods yet."

USDA says it has released more than 1 billion sterile flies in Texas since February and is aiming to raise production to 500 million flies a week by next summer.