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New World Screwworm: A Flesh-Eating Maggot makes a Concerning Comeback
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A decades-long success story in animal health is facing a serious challenge. The New World screwworm, a parasitic fly whose larvae feed on the flesh of warm-blooded animals, is experiencing a notable resurgence in Central america and Mexico, and is now threatening livestock in the United States. This marks a concerning reversal after decades of eradication efforts.
What is New World Screwworm?
The New World screwworm (Cochliomyia hominivorax) is a fly native to the Americas. The female fly lays its eggs in open wounds of livestock – cattle, sheep, goats, horses, and even humans – and the hatched larvae feed on living tissue. The larvae cause myiasis, a painful and economically damaging condition
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lifecycle and Impact
The screwworm lifecycle is relatively speedy. Eggs hatch within 24 hours, and the larvae feed for five to ten days before pupating in the soil. The entire lifecycle, from egg to adult fly, takes approximately two to three weeks. Infestations can lead to reduced weight gain, decreased milk production, secondary infections, and even death in livestock. The economic impact on ranchers and farmers can be substantial.
Did You know? The screwworm was once widespread throughout much of North, Central, and South America, causing an estimated $1 billion in annual losses to the livestock industry.
A History of Eradication and recent Resurgence
Intensive eradication programs, primarily utilizing the sterile insect technique (SIT), were remarkably successful in eliminating the screwworm from the United States by 1983, and from Mexico and much of Central America by the early 1990s. The SIT involves rearing large numbers of sterile male flies and releasing them into the wild to mate with wild females, resulting in infertile eggs.
| Milestone | Date |
|---|---|
| US Eradication Complete | 1983 |
| Mexico Eradication Complete | 1991 |
| First Resurgence Reported (Mexico) | 2016 |
| resurgence Confirmed (Central America) | 2023 |
| US Quarantine Zones Established | 2024 |
However, in 2016, screwworm re-emerged in Mexico, and in 2023, cases were confirmed in several Central American countries, including Panama, Costa Rica, Nicaragua, Honduras, and Guatemala. The resurgence is now threatening the southern United States, prompting quarantine zones in Texas and heightened surveillance efforts.
Factors Contributing to the comeback
Several factors are believed to be contributing to the screwworm’s return. These include reduced funding for eradication programs, increased movement of livestock across borders, climate change potentially expanding the fly’s range, and a decline in wild animal populations that previously served as a barrier to the fly’s spread. The breakdown of coordinated regional control efforts is a major concern
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Pro Tip: Ranchers should practice strict wound care on livestock, including cleaning and disinfecting any injuries, to minimize the risk of screwworm infestation.
Current Control Efforts and Future Outlook
The United States Department of Agriculture (USDA) is working with mexico and central American countries to re-establish eradication programs. This includes releasing sterile flies, implementing quarantine measures, and providing technical assistance to livestock producers. The USDA’s Animal and Plant Health Inspection Service (APHIS) is actively monitoring the situation and responding to reported cases.
The success of these efforts will depend on sustained funding, regional cooperation, and the continued use of the sterile insect technique. The screwworm’s resurgence serves as a stark reminder of the importance of ongoing vigilance in animal health and the potential for eradicated diseases to
