Lindsay A. Starkey, DVM, PhD, DACVM-Parasit & Stephanie R. Ostrowski, DVM, MPVM, DACVPM

Four score and seven years ago, screwworms were a common pest of the livestock industry in the United States. These flies, known as New World screwworms or Cochliomyia hominivorax, and their parasitic larvae were once common in the Southeastern portions of the United States and resulted in millions of dollars lost to producers annually. Throughout subsequent decades, the USDA developed and utilized a novel method of control for this fly—sterile-male release—and by 1966, screwworms were considered eliminated from the U.S. Populations of this fly continued to be eradicated in our neighboring countries to the south and in the Caribbean, and the current barrier exists between Panama and Colombia, with sporadic reports north of that barrier.

In the past decade, there have been a couple of case-reports of the parasitic larvae of this fly infesting dogs in the U.S., but both of those dogs had recently traveled outside of the U.S. to either Trinidad and Tobago or Venezuela.

The cases recognized this summer, starting in endangered Key deer in Big Pine Key and spreading to other Key deer throughout the Florida Keys, are different. These deer are permanent residents in the Keys and therefore would have acquired the infestation locally. According to the World Organization for Animal Health (OIE) and the World Animal Health Information Database (WAHIS interface), the nearest country to the U.S. with recent reports of C. hominivorax activity is Cuba, where screwworms were reported in 2015 and early 2016.  Other animal species in the Keys with suspected or confirmed screwworm infestations now include dogs, cats, rabbits, pigs, and a tortoise.

Screwworms will infest and feed on the living tissue of a variety of mammals, including livestock, pets, and humans. Producers, animal owners, veterinarians, and public health officials play a key role in initially recognizing this parasite and implementing proper control strategies in order to prevent the spread of this screwworm outbreak to other areas of the Southeastern U.S.

Emergency control and eradication efforts recently implemented in the Keys include active surveillance for infested animals and adult flies, an animal health checkpoint in Key Largo to prevent the movement of infested animals out of the area, sterile-male fly release in the affected regions, prophylactic oral treatment of some herds with an insecticide/ dewormer combination drug to prevent infestation, and communication to the public to increase awareness of this parasite. Public education announcements about this parasite as well as surveillance in neighboring states such as Alabama and Georgia have been intensified. As of Nov. 9, this outbreak is responsible for the death of 130 endangered Key deer (out of a total population of approximately 1,000), but Fish and Wildlife officials stated that the number of new cases identified was decreasing and they were optimistic that the numbers of affected deer would continue to decrease. READ MORE here and here.