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The New World screw-worm fly (Cochliomyia
hominivorax), screw-worm for short, is a species of parasitic
fly that is well known for the way in which its larvae or maggots eat the
living tissue of warm blooded animals. It is present in the New
World tropics. Screwworms
are the larvae (maggots) of a certain fl y species that feed on living tissue
of animals. Although these flies have been eradicated from the United States, Mexico
and Central America, they can still be found in some countries of South
America, the Caribbean, Southeast Asia, India and Africa.
Infestation of a live warm blooded animal by a maggot is technically called
myasis. While the maggots of many
fly species eat dead flesh, screw-worm maggots are unusual because they attack
healthy tissue.
Life cycle
Screw-worm
females lay 250-500 eggs in the exposed flesh of a superficial wound of
warm-blooded animals, including humans and birds. Most cases occur in cattle, goats and sheep. Screwworms
can infest a wide variety of wounds (e.g. tick bites, wire cuts and other
injuries). Navels of newborn mammals are a common site for screwworm
infestation. The larvae hatch and burrow into the surrounding tissue
as they feed. If the wound is disturbed during this time the larvae burrow or
"screw" deeper into the flesh, which is the source of the insect's
name. The maggots are capable of causing severe tissue damage or even death to
the host. Approximately three to seven days after hatching the larvae fall to
the ground to pupate The pupae reach the adult stage about seven days later.
Female screw-worm flies mate four to five days after hatching. The entire life
cycle is approximately twenty days. A female can lay up to 3,000 eggs and fly
up to 200 km (125 miles) during her life.
Control
The Unites
States officially eradicated the screw-worm in 1982 using the sterile insect
technique. This is when not fertile males are introduced in the population.
When these males mate with females they will not produce fertile eggs, thus
making the population smaller. The screw-worm was eradicated in Guatemala and Belize,
but also previously in Curacao and Aruba. The
last infection in Aruba in 2004 lasted approximately
8 months. Eradicating the epidemic was accomplished by using the sterile insect
technique.
A few questions to ask yourself:
What animals get screwworm?
Screwworms can infest all warm blooded
animals, including birds. Most cases occur in cattle, goats and sheep.
style='font-family:"Arial","sans-serif"'>The screwworm eggs lay in the wound
hatch into larval screwworm, which feed on the living tissue of the animal.
Screwworm infestations are difficult to detect at first. Slight movement might
be seen inside a wound, but the larvae feed and the wound gradually enlarges
and deepens. A b
Can I get screwworm?
Yes. Humans can get screwworm (vector)
in the same manner as animals
– by flies depositing larvae on an
open wound.
Who should I contact, if I suspect
screwworm?
In Animals – Contact your veterinarian
immediately.
In Humans – Contact your physician immediately.
How can I protect my animals from
screwworm?
Animals must be carefully examined by their
owner. In cases of suspicion they must be taken to a veterinarian for careful
examination. Wounds should be closely checked for any screwworm eggs or larvae
that could be there. Observe your animal for signs or the presence of screwworms.
Screwworm eggs are creamy and white and deposited in a shingle-like manner on
or near the edges of superficial wounds. The larvae are cylindrical with one
pointed end and one blunt end and have rings of dark brown spines around the
body. Female screwworm flies are larger than a housefly with a dark blue to
blue-green body and reddish-orange head.
How can I protect myself from
screwworm?
While traveling in countries that have
screwworms, pay careful attention to any wounds to help protect yourself from
screwworm infestation.
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