First Confirmed Human Case of New World Screwworm in the U.S. Sparks Concern
A recent development has raised alarms among public health officials and the agricultural sector after a confirmed case of New World screwworm was identified in a person from Maryland who had traveled to the United States from Guatemala. This marks the first human case of the parasite in the U.S. since an outbreak began spreading northward from Central America and southern Mexico late last year.
The individual, who received treatment in Maryland, is now at the center of a growing concern over the potential spread of the disease. Beth Thompson, South Dakota's state veterinarian, shared that she learned about the case through direct communication with someone who had knowledge of the situation. The information was relayed within the past week, highlighting the urgency surrounding this incident.
Another source, who preferred to remain anonymous, mentioned receiving emails from an executive of the Beef Alliance on August 20. These emails informed recipients about the CDC's confirmation of a human case of screwworm in Maryland. State veterinarians were made aware of the case during a call with the CDC, according to one source. A Maryland state government official also confirmed the case, although the CDC deferred questions to the state for further details.
Understanding Screwworms
Screwworms are parasitic flies whose females lay eggs in wounds on warm-blooded animals. Once the eggs hatch, the larvae burrow into living flesh, causing severe damage. If left untreated, this can lead to the death of the host. While rare, infestations in humans can be fatal. Treatment involves removing hundreds of larvae and thoroughly disinfecting wounds, which can be both time-consuming and challenging.
The case in Maryland comes just over a week after USDA Secretary Brooke Rollins and other officials announced plans to build a sterile fly facility in Texas as part of efforts to combat the pest. This facility aims to help control the spread of screwworms, which have been traveling north through Mexico from Central America since 2023.
Impact on the Beef and Cattle Industry
The confirmed case could significantly impact the beef and cattle futures market, which has already seen record-high prices due to tight supplies. The U.S. cattle herd is at its smallest size in seven decades, making the industry particularly vulnerable. The lack of transparency around the case may also pose political challenges for Rollins, who has repeatedly pledged to keep screwworm out of the country.
The USDA has set traps and sent mounted officers along the border, but it has faced criticism for not acting faster to pursue increased fly production. Rollins initially announced plans for a sterile fly facility at Moore Air Force Base in Edinburg, Texas, in June. However, the facility is expected to take two to three years to come online.
International Efforts to Combat Screwworm
Mexico has also taken steps to limit the spread of the pest, which can kill livestock within weeks if not treated. In July, the Mexican government announced the construction of a $51 million sterile fly production facility in the south. Currently, the only operating plant is in Panama City, capable of producing up to 100 million sterile screwworm flies each week.
The USDA estimates that 500 million flies would need to be released weekly to push the fly back to the Darien Gap, the stretch of rainforest between Panama and Colombia. Screwworms are endemic in several countries, including Cuba, Haiti, the Dominican Republic, and nations in South America.
In response to the spread of the parasite, the USDA ordered the closure of livestock trade through southern ports of entry after a new case was reported in Ixhuatlan de Madero, Veracruz, in July. The U.S. typically imports over a million cattle from Mexico annually for processing into beef.
Historical Context and Eradication Efforts
Screwworms were eradicated from the U.S. in the 1960s when researchers began releasing massive numbers of sterilized male flies. This method helped reduce the population significantly. However, the recent resurgence highlights the ongoing need for vigilance and proactive measures.
The USDA has estimated that a screwworm outbreak could cost the economy in Texas, the largest cattle-producing state, approximately $1.8 billion in livestock deaths, labor costs, and medication expenses. As the situation unfolds, the focus remains on preventing further spread and protecting both animal and human health.
