Cochlyomyia hominivorax

Sandra ThorbusAbbi Miller

Introduction

• Cochlyomyia hominivorax – “man-eater” fly.

• Species of parasitic fly that preys on all warm-blooded animals, including humans (sometimes causing nasopharyngeal myiasis)

• Related and very similar to Cochliomyia bezziana (the Old World Screwworm) and difficult to differentiate from C. macellaria, the secondary screwworm which is not an important myiasis-causing insect

• Obligate parasite

Introduction

•Common name is New World screwworm.

• Comes from appearance of larvae and the way they burrow (screw) into the host’s flesh. New World screwworms are found in the western hemisphere, whereas Old World screwworms are found in the Eastern hemisphere.

Hosts

• All warm-blooded animals

• Humans

• Mostly found in livestock

Geographic Range

Currently found in:

• Tropical Areas including:

*Mexico

*South & Central America

*Nicaragua

*Costa Rica

*Panama

*Jamaica

Eradicated from:

• United States

• Guatemala

• Belize

• El Salvador

• Honduras

Geographic Range

• The new world screwworm cannot survive winter in cold climates but summer migrations have brought it as far north as Montana and Minnesota

• Severe epizootics have occurred in Texas cattle• More than 1.2 million cases were recorded in

1935 in that state alone

Screwworm Morphology

• Eggs:• Creamy, white color• Oblong shape• Deposited in a shingle –like

pattern on edges of wound.

• Larvae:• Tapered body with mouth

hooks at narrow end and breathing spiracles at wide end.

• Body segments ringed with spines, “woodscrew” appearance and shape.

• Fully-grown larvae can be as long as 1.5 cm

• Adult Flies:• Bluish to bluish green in

color.

• Reddish orange head and eyes.

• Approx. 2 times larger than a house fly.

• Have 3 dark stripes on their backs.

LifecycleAdult female fly mates and lays her eggs (250-

500) along the edges of flesh wounds on host

• Female flies mate only once during their lifetime, storing sperm for future egg production.

Under ideal conditions, the larvae hatch from their eggs within 12 hours and begin to embed themselves into the wound

• The screwworms feed on living tissue and fluids from the wound site for 5-7 days.

• Feeding screwworms enlarge the wound, and attract more female flies to deposit more eggs in the wound.

• If the wound is disturbed, the larvae will burrow deeper into the flesh.

Lifecycle cont.After 5-7 days of feeding the larvae drop to the

ground and burrow into the soil to pupate• The pupal stage varies from 7 days to 2 months, depending

on temperature. Higher temps. = quicker development.• Pupae are killed in soil temperatures less than 46˚F.

Pupae undergo metamorphosis into adult flies

New adult females usually mate within 3-4 days, and are ready to lay eggs around 6 days old, thus starting the cycle over again.

- Females can lay up to 3,000 eggs in her lifetime.

- Males are usually found near flowering shrubs, where they feed on flower nectar.

Lifecycle

Symptoms/Pathogenesis

• Screwworms infect a wide variety of wounds including: tick bites, cuts, branding or dehorning wounds.

• Very common to find in navels of newborn animals.

• Infested wounds often have a discharge and sometimes a distinctive odor.

• Discomfort, decreased appetite, and lower milk production are common.

• Infested animals usually separate from the herd, lying down in shaded areas.

Symptoms/Pathogenesis

• Causes Myiasis, infection of tissue by fly larvae.

• Maggots (larvae) can cause severe tissue damage to host.

• Persistent lesions on host.

• Weight loss

• Death may occur due to secondary bacterial infections.

Diagnosis/Treatment

• Treatment involves removal of the larvae

• Irrigation with either chloroform or ether is advocated

• Surgery is often required.

• For identification, the larvae should be hatched to adult flies, or first killed by immersion in nearly boiling water, then cooled and preserved in 80% ethanol.

• Secondary bacterial infections should be treated with local wound care and administration of antimicrobial agents.

Control

• The United States officially eradicated the screw-worm in 1982 using the sterile insect technique.

• The screw-worm was eradicated in Guatemala and Belize in 1994, El Salvador in 1995, and Honduras in 1996.

• Campaigns against the flies continue in Mexico, Nicaragua, Costa Rica, Panama and Jamaica with financial assistance from the United States Department of Agriculture.

References

• http://en.wikipedia.org/wiki/Cochliomyia_hominivorax

• http://www.nt.gov.au/d/Primary_Industry/index.cfm?Header=Disease%20Surveillence%20programs%20-%20Screw%20Worm%20Fly

• http://www.cdc.gov/ncidod/eid/vol10no1/02-0825.htm

• Roberts, Larry S., & Janovy, John (2005). Gerald D. Schmidt & Larry S. Roberts' Foundations of Parasitology (8th ed.). New York NY: McGraw-Hill.