USDA Logs 61 New World Screwworm Cases in 30 Days

Sixty-one animal cases of New World screwworm were confirmed in the United States during the 30-day period ending Nov. 4, according to the U.S. Department of Agriculture. That single month accounts for more than half of all U.S. detections since the first case appeared on June 3.

The cumulative total now stands at 113 confirmed animal cases across Texas, New Mexico and Arizona. Of those, 111 involved domestic animals and two involved wildlife. The acceleration is recent and steep: USDA recorded four domestic cases in August, three in September, 36 in October and 24 in November through Nov. 4.

For livestock producers in the Southwest, the trajectory matters more than the total. Detection counts that doubled and then multiplied within eight weeks signal an establishing fly population rather than isolated incursions. Ranchers in affected counties should inspect wounds on livestock frequently, since screwworm larvae infest open injuries and the fly spreads through animal movement.

Where are the newest cases?

The Nov. 4 case report listed domestic detections in Greenlee County, Arizona; Eddy and Otero counties in New Mexico; and Starr County, Texas. The report also listed an inactive wildlife case involving an elk in Jeff Davis County, Texas.

Additional domestic cases reported Nov. 3 included sheep in Greenlee County, Arizona, and cattle in Dona Ana County, New Mexico.

How does USDA classify counties?

USDA's dashboard separates active counties from inactive counties. Active counties have at least one current active animal case. Inactive counties have no current active animal cases.

The same Nov. 4 data reflect that distinction at the case level. Of the 59 domestic cases reported during the 30-day window, 55 were classified as active and four as inactive. Both wildlife cases in the period were inactive. No active wildlife cases appeared in the latest update.

What is tracked beyond animal cases?

USDA also tracks wild NWS flies captured in traps, separately from confirmed animal cases. A fly trap detection means at least one wild fly was found in a trap and does not represent an additional confirmed animal case. Producers reading the dashboard should therefore avoid adding trap detections to case counts when assessing local risk.

The agency updates its NWS detection data daily, Monday through Saturday, through the screwworm.gov website maintained by USDA APHIS.

What should producers watch next?

The November figure of 24 cases in just four days points to a pace that could exceed October's 36. Producers in Greenlee, Eddy, Otero, Starr and Dona Ana counties, and in adjacent areas, should monitor the daily dashboard and treat and report any suspicious wounds promptly. The next weeks of daily updates will show whether the October surge marks a seasonal peak or a continued expansion of the outbreak zone.