The number of confirmed New World screwworm cases in the United States jumped to 113 this week, as the U.S. Department of Agriculture reported an additional 42 cases since last week.
The latest cases — in Texas, New Mexico and Arizona — involve horses, cattle, sheep, dogs and a chicken, according to the USDA’s Animal and Plant Health Inspection Service. Of the 113 confirmed infestations, 111 have involved domestic animals, including livestock and pets, and two have involved wildlife: elk in Pecos and Jeff Davis counties in Texas, both now classified as inactive. The USDA data show 55 active cases and 58 inactive cases.
The outbreak is accelerating. The total stood at 79 on Sunday, and 34 infestations were added in the days that followed. Sixty-one cases were reported during the 30-day period ending Nov. 4 — more than half of all detections recorded since June — with 36 cases in October and 24 in November through Nov. 4.
The first U.S. case was found in June, when a rancher discovered the parasite in a calf near La Pryor, Texas. Texas and New Mexico reported their first animal infestations in early June; Arizona confirmed its first case on Oct. 28, in a dog in Cochise County, and New Mexico has since confirmed the country’s first case in a domestic cat. USDA surveillance has also detected wild screwworm flies in five traps, four of them in October.
The New World screwworm is a parasitic fly whose larvae feed on the living flesh of warm-blooded animals. Officials eradicated it from the United States in the 1960s and pushed it back to Panama, but the parasite has steadily marched north through Central America and Mexico. All warm-blooded animals are susceptible, including deer and elk, as well as small game and waterfowl.
The U.S. government has started ramping up production of sterile flies to try to keep the parasites from spreading, and New Mexico’s Department of Agriculture has called on hunters to report any suspicious larvae, particularly in Grant and Otero counties. USDA updates its detection data daily, Monday through Saturday, on its screwworm website.
