U.S. Closes Border with Mexico to Livestock Amid New World Screwworm Threat
To protect the U.S. from a renewed threat of New World Screwworm (NWS), the U.S.-Mexico border was closed on May 11 to cattle, bison and horses entering from Mexico. NWS was eradicated from the U.S. in 1966 and eliminated as far south as Panama by 2000. However, this pest began re-emerging above the biological barrier in Panama in 2022 and has steadily moved through Central America into Mexico. NWS is a serious threat to animal and human health with potential economic losses in the U.S. This Market Intel report examines the re-emergence of NWS and its implications for animal health, public safety and food security.
What is the New World Screwworm?
The New World Screwworm is a fly endemic to Cuba, Haiti, the Dominican Republic and several South American countries. In recent years, it has spread northward to Costa Rica, Guatemala, Nicaragua, Belize, El Salvador, and more recently, Mexico. The fly lays its eggs on or near a wound on a warm-blooded animal. Once hatched, the larvae feed on the surrounding flesh as they burrow into the wound—a process that gave the pest its name. NWS can infect livestock, poultry, wildlife, domestic animals and, though rarely, humans.
NWS is typically endemic to warmer climates. In fact, the larvae cannot survive temperatures below 46 degrees Fahrenheit. However, a cold climate doesn’t eliminate the threat. Livestock and wildlife movement can transfer NWS to the northern regions of the country in the summer months where they can find hosts and spread until temperatures cool off during fall and winter. NWS flies can travel up to 12 miles in search of a suitable host. This pest does not discriminate among warm-blooded hosts, and wildlife such as deer, feral hogs and even birds can quickly spread NWS. If untreated, NWS infestations are often fatal. Affected animals can die of trauma, toxicity or secondary infections within two weeks. Staff Contact: Steven Fenaroli, sfenaroli@cfbf.com
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