Cochliomyia hominivorax Heather Peters Amy Liberio

Aka. New World Screwworm  This species is the most important cause of myiasis (infection by fly larvae) in the world  Adult flies are a deep, greenish-blue metallic color with a yellow, reddish, or orange face, and 3 stripes on the thorax  Adults are about twice the size of a common house fly (between 20-25mm long)  Adult often confused with Cochliomyia macellaria, aka. Secondary screwworm

Comparison Secondary screwworm Feeds on dead tissue only New World screwworm Feeds on both dead and living tissue

Geography  Located throughout the Neotropical region  Normal range: Mexico to northern Chile and Argentina  Has been seen as far north as Minnesota and Montana

Hosts  Definitive hosts: humans, cattle, horses, goats, cats, dogs, along with many other warm- blooded animals  No intermediate hosts

Life Stages  Egg  Larva  Pupa  Adult  Entire life cycle takes place in an average of days

Life Cycle

 Females will lay their eggs ( ) at the edge of an open wound, since larvae cannot penetrate intact skin  The larvae will hatch from the eggs and will embed themselves in the host’s tissue and begin to feed on both dead and living tissue

Life Cycle  After a few days of gorging themselves, the larvae will drop off of the host and bury themselves in the soil  They then develop a dry shell around themselves and enter the pupal stage  During this stage they will undergo metamorphosis and become mature adult flies  Once development is complete, the flies will emerge from their pupae and begin to mate  Males will mate many times, whereas females will only mate once

Pathogenesis  Cutaneous myiasis  Often seen in cattle and other warm- blooded animals  As higher numbers of cattle become infected, chances of humans becoming infected are greatly increased

Pathogenesis  Nasopharangeal myiasis  This type of myiasis is more common in humans  Eggs will be deposited near nasal opening, and larvae will migrate into nasal cavities and pharynx

Symptoms  Formation of wounds  Enlargement of existing wounds  Decaying flesh  Wound discharge  Secondary bacterial infections  Pain in infected area  Edema  Fever  Lethargy  Loss of appetite

Diagnosis  Visualization of larvae in or around wounds  In cattle, infected individual will often separate self from group, display discomfort and depression  No serologic tests available

Treatment  Killing and manual removal of larvae from infected site  Treatment of cutaneous wounds with approved pesticide (Spinosad-aerosol)  Administration of antibiotics to treat secondary bacterial infections

Control  Sterile Insect Technique (SIT)- a process where adult males are raised in a lab and sterilized via radiation and are released into the environment  Since females only mate once, if they mate with a sterile male then females will produce sterile eggs and this will break the cycle  Injections of doramectin has been shown to give some protection to cattle against New World Screwworm infections  Detection of wounds on cattle and other animals, and immediate treatment of the wound with an approved insecticide  Wash and keep any wounds clean  No vaccine available

Economic Importance  Before eradication of Cochliomyia hominivorax an average of 180,000 livestock deaths occurred yearly in Texas alone  Since eradication in the mid-1950s, the United States saves $900 million yearly that before would have been lost due to this parasite

Monsters Inside Me  ters-inside-me-screwworms.html ters-inside-me-screwworms.html

Review  What geographic regions are home to Cochliomyia hominivorax?  What is myiasis?  How is this parasite controlled?  What are the different life stages of this parasite?