Overview
New World Screwworm (NWS) is a serious parasitic pest that can affect livestock, companion animals, wildlife, and, less commonly, humans and birds. NWS infestations are caused by the larval stage of the New World screwworm fly (Cochliomyia hominivorax), which lays eggs in open wounds and natural body openings such as eyes, ears, nose, mouth, and genitals.
Once the eggs hatch, the larvae (maggots) burrow into and feed on living tissue of warm-blooded animals, causing severe tissue damage, pain, and potentially life-threatening infections if not appropriately treated.
Although NWS is not currently widespread in the United States and historically has been limited by its sensitivity to cold weather, recent detection in Texas punctuates the importance of vigilance and preparedness among animal care organizations.
Why Rescues and Shelters Should Be Alert
Animal shelters, rescue organizations, boarding facilities, and transport programs play a critical role in early detection and prevention.
Pets Can Be Affected
Dogs and cats are susceptible to NWS infestation, particularly if they have:
- Open wounds
- Recent injuries
- Surgical incision sites
- Chronic skin conditions
- Exposure to areas where NWS has been detected
Rapid Disease Progression
NWS eggs typically hatch within 12-14 hours. Once hatched, larvae quickly penetrate living tissue, causing rapidly worsening wounds that are painful, foul smelling, and difficult to treat without prompt veterinary intervention.
Risk Associated with Animal Transport
The movement of animals across state or international borders can increase the risk of introducing NWS into facilities, particularly when animals originate from or travel through affected regions.
Clinical Signs to Watch For
Staff and volunteers should immediately report any animal exhibiting:
- Wounds that worsen rapidly despite treatment
- Swelling, inflammation, or increased pain around a wound
- Foul odor emanating from a wound
- Bleeding or abnormal discharge
- Visible larvae within a wound
- Apparent movement within a wound
- New or worsening wounds following travel from affected areas
Recommended Precautions
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Screen all incoming animals carefully
- Conduct thorough intake examinations on all animals
- Delay group housing or communal placement for animals with open wounds until evaluated
- Pay particular attention to animals arriving from or traveling though areas with known NWS activity
- Document travel history, wound status, and any medical concerns during intake
-
Educate Staff and Volunteers
- Provide training on NWS biology, transmission, and clinical signs
- Ensure personnel understand the importance of immediate reporting and response
- Reinforce wound-monitoring procedures for all animals in care
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Follow Reporting Requirements
- Contact a veterinarian immediately if NWS is suspected
- Report suspected cases to appropriate state animal health officials in accordance with regulatory guidance
- Maintain detailed records of affected animals and potential exposures
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Maintain Strong Wound-Care Practices
- Promptly clean, treat, and monitor all wounds
- Follow veterinary recommendations for wound management
- Utilize veterinary-approved insecticidal or antiparasitic products when appropriate
- Minimize environmental conditions that attract flies
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Coordinate with Veterinary Partners
- Establish a relationship with a veterinarian who can provide rapid consultation and treatment
- Develop an emergency response plan for suspected NWS cases
- Consider maintaining access to approved treatment products and necessary medical supplies as recommended by your veterinarian
Key Takeaway
Early detection and rapid veterinary intervention are the most effective tools for preventing severe disease and limiting the spread of NWS. Any suspicious wound should be treated as urgent until evaluated by a veterinarian. Facilities should exercise heighted vigilance when admitting animals with recent travel history or wounds originating from areas where NWS has been detected. Maintaining strong intake screening, wound-care protocols, staff education, and veterinary partnerships will help protect animals and support broader disease prevention efforts.
Resource Library
Screwworm.gov | Unified Government Response To Protect the United States (USDA)
New World Screwworm: Veterinary Considerations for Dogs and Cats that Travel Internationally (USDA)
New World Screwworm Prevention for Animals (USDA)
Current Status of New World Screwworm (USDA)
New World Screwworm Outbreak (CDC)
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