Understanding the New World Screwworm

1. What is the New World Screwworm?

The New World screwworm is a flesh-eating parasitic fly, Cochliomyia hominivorax. Its larvae (maggots) infest wounds of warm-blooded animals and humans, feeding on living tissue.

2. Where is it found?

It is mainly found in South America and the Caribbean. Sporadic outbreaks have been reported in Central America and rare cases in the United States.

3. How does it infect humans?

Female screwworm flies lay eggs on open wounds or soft tissue points. The eggs hatch into larvae, which burrow into the flesh, causing painful infestation.

4. How many eggs does a female lay?

One female can lay up to 300 eggs at a time and up to 3,000 eggs in her lifetime (10–30 days).

5. What are the symptoms of infestation?

• Painful wounds or sores that do not heal
• Bleeding and pus discharge
• Sensation of movement under the skin
• Foul odour from the wound
• Risk of severe infection or sepsis if untreated

6. Why are they called “screwworms”?

The larvae screw themselves into flesh in a spiral manner, causing deep tissue damage.

7. How is it controlled?

The US eradicated screwworms in 1966 using the Sterile Insect Technique (SIT)—releasing sterilized male flies so that females produce no offspring. This method has been reapplied in later outbreaks.

8. Why are they spreading again?

Recent cases in Central America suggest:

• Movement of infested cattle across borders
• Reduced effectiveness of sterilisation measures compared to earlier times

9. How dangerous is it for humans?

Human infestations are rare but can be life-threatening if untreated due to rapid tissue destruction and infection.