VetZone, vet zone, veterinary, Kayla Wells DVM, Christopher Lee DVM, veterinary medicine, veterinarian, education, preventive medicine, diplomate, ACVPM, DACVPM, zoonosis, zoonotic, New World screwworm, Old World screwworm, myiasis, Chrysomya bezziana, Cochliomyia hominivorax,  Order Diptera, Family Calliphoridae, India, Africa, Asia, South America, Caribbean, maggots, larvae, flesh, insecticides, eradication

Maggots are gross.  No two ways about it.  Tiny little creatures with a voracious appetite consuming flesh.  But, did you know that there are different types of maggots? 

The type we have in the US consume dead flesh.  This can be in the form of a dead carcass, or in a wound that is heavily infected, and the tissue is dying.  But, in parts of South America, Asia, India, and Africa, the maggots have upped their gruesome game.  Screwworm maggots consume living tissue.  A small wound on an animal or human can become infested, attracting more flies, and eventually causing death.  As scary as that sounds, we are not safe here.  An invasion of New World screwworms in Florida in the fall of 2016 served as a grim reminder that we are susceptible.  It is not clear how the infestation arrived in Florida.  Importation of animals from Caribbean islands remains suspect.

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New World and Old World species

Screwworms are divided into Old World (OWS) (Chrysomya bezziana) and New World (NWS) (Cochliomyia hominivorax) screwworms.  Both genera are in the Order Diptera (true flies), Family Calliphoridae (blow flies) As the names imply, OWS are found in India, Africa and Asia.  NWS are found in South America and the Caribbean.  Both species prefer similar environments, and either could thrive in the other’s home regions.  Both prefer temperatures of 77-86°F and 30-70% relative humidity.  Ranges of adults vary from 6-12 miles in humid areas, and nearly 200 miles in arid regions.

 

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Maggots are NOT picky eaters!

While rare in birds, any warm-blooded animal can serve as host to screwworms.  Wounds as small as tick bites or wire cuts attract flies.  Infestation (myiasis) begins with a female laying eggs in an animal’s wound.  The eggs hatch, and larvae begin to feed on living flesh.  As the wound grows, more flies are attracted and lay more eggs.  The animal begins to show signs of systemic illness from secondary infections.  If left untreated, myiasis can be fatal.  Infestation is not contagious between host animals.       

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Good husbandry is the key to prevention

Prevention of screwworm myiasis in endemic regions boils down to good livestock husbandry.  Timing of wounding procedures (parturition, dehorning, tail docking, shearing, etc.) should avoid times of highest fly activity.  Through inspection of any animals leaving endemic areas is critical.  Any wounds should immediately be treated with an approved insecticide (organophosphates, carbamates, or pyrethroids).   

We will discuss the lifecycle of both species in the next post. Eradication is possible, using a multi-faceted approach. 

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