SCREWWORM MYIASIS. William Edmiston, DVM Eldorado Animal Clinic Eldorado, Texas

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1 SCREWWORM MYIASIS William Edmiston, DVM Eldorado Animal Clinic Eldorado, Texas

2 Screwworm Myiasis Robert B. Moeller Jr. California Animal Health and Food Safety Laboratory Tulare, CA Nov 2009

3 Screwworms Economic Impact US currently free of screwworms?? (Sept 2007: (NWSW) canine in Mississippi from Trinidad; OCT 2007: (OWSW) canine in Massachusetts from Singapore ) $100 million economic losses to livestock producers in US in Gulf coast region during the first half of the 1900 s Reintroduction into US --- $ million - Losses due to: * Animal treatments and handling (increased manpower) * Loss of meat products due to tissue damage South America estimated losses $3.6 billion annually Eradication effort in case of extensive reintroduction - $1.2 to $1.5 billion in control program cost (Cost are SIT program, increase boarder monitoring and education programs) US benefit from eradication $900 million annual benefit Central America livestock $257 million annual benefit from eradication effort.

4 Screwworms New World Screwworms Cochliomyia hominivorax 8-10mm length Blue to green body 3 dark longitudinal stripes Old World Screwworms Chrysomya bezziana 8-12 mm length Green to blue body 2 dark longitudinal strips

5 Screwworm Distribution Historical range

6 Screwworm Distribution Current range

7 New World Screwworms History in Western Hemisphere 1934 major outbreak in US million animals affected - 200,000 deaths 1937: Knipling and Bushland begin working on fly 1938: Discover that female breeds only once 1950 Sterilization of male flies developed Knipling Bushland

8 History of New World Screwworm Eradication Program Sanibel Island

9 History of New World Screwworms Eradication - Florida US Mexico Central America Puerto Rico Currently free US Virgin Islands and Jamaica - Cuba and Hispaniola have no eradication programs currently

10 SCREWWORM OUTBREAK LIBYA, NORTH AFRICA, INFESTED HIGH RISK LOW RISK

11 Old World Screwworms Chrysomya bezziana

12 Screwworms Transmission Infect any mammal (birds rarely infected) Wildlife tend to be reservoir for livestock infections Female deposits eggs onto wound or mucus membrane (nose, eye, prepuce, vagina) while feeding Female lays 100 to 300 eggs/feeding (female can lay 3000 eggs in lifetime)

13 Screwworm Transmission Eggs hatch in 10 to 20 hours Larva eat flesh and expand wound Larva mature in 4 to 20 days Many female flies can lay eggs into wound (smell attracts more screwworm flies and other flies 2 o screwworm infection can occur - Cochliomyia macellaria (West) - Chrysomya megacephala (East)

14 Screwworm Transmission After feeding for 4 to 12 days larva drop off Burrow into ground Pupate in soil for 3 to 5 days Adults emerge

15 Screwworms Neonatal animals commonly affected, umbilical infections common Wounds invaded by screwworm flies as small as tick or insect bite Gulf coast ear tick (A. maculatum) caused many infected lesions with ear loss in cattle

16 Screwworms in animals Nasal, occular and gingival infestations common

17 Infections of skin primary area of infection Nasal passages second most common site Poor personal hygiene aids in infestations Old people most common individuals infected with larva Screwworms Human infections

18 Screwworm Identification Larval identification is the primary method for mammals Larvae removed from deepest part of wound to avoid non-screwworm larvae (Larva tend to be at the margin of viable and nonviable tissues) Posterior spiracle open for both screwworms Look for pigmentation of dorsal tracheal trunks NWSW: Cochliomyia hominivorax - 2 nd instars larva: dorsal tracheal trunks over ½ of body length, Pigmentation of trunks characteristic - 3 rd instars larva: dorsal; trachea; trunks extend from the 12 th to 10 th segment. OWSW: Chrysomya bezziana - Dorsal tracheal trunks pigmented only at 12 th segment Chrysomya bezziana: anterior spiracle with 4 to 6 lobes separate it from other species

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21 Screwworms: Identification Identification of adult and larva screwworms - Usually deep tissue larva not superficial larva Mab-ELISA testing in development: 97% accurate identified Cochliomyia hominivorax eggs, larva and adults PCR technique - Mitochondrial DNA - Random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) Submit fresh and alcohol fixed larva

22 Screwworms: Detection Physical examination of animals for larva Insect traps Detector dogs trained to sniff for odor given off by infected wounds (one animal)

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31 Screwworm: Treatment Manual removal of larva Flush wound with saline/hydrogen peroxide/antiseptic Chloroform, ether, benzol to evacuate larvae Boric acid and potassium permanganate deodorant and cleaning agent Antibiotics for secondary bacteria

32 Screwworms: Treatment Old treatments - Diphenylamine 35%; Benzol 35%, Turkey red oil 6.7% and lindane 3% - 3% lindane and pine oil - 1% dichlorfenthion and gentian violet New treatments - 1% fipronil pour-on - Doramectin injectable to eliminate larvae - Ivermectin injectable to eliminate larvae

33 Screwworms: Risk to the United States Movement of pets and people from risk countries - Tourist, quest workers, military (pets from screwworm endemic areas) Importation of livestock with infections (horses affected) Air and sea transport carrying flies into US Intentional release

34 Sterile Insect Technique USDA-APHIS participates in International Eradication Programs Against Screwworms Screwworms are mass produced in a production facility in southern Mexico, irradiated, and then mass released from airplanes. New plant open in Panama in 2007 (Pacora, Panama) - $40 million production facility - Able to produce 150 million sterilized flies per week for Panama (Darien Gap region) and eventually Caribbean islands Tuxtla Gutierrez, Mexico Pacora, Panama

35 Colonies of adult screwworms are kept in cages; about 60,000 per cage.

36 When adults are about 6 days old, eggs are collected and prepared for placement in larval media.

37 About 1 gram of eggs are placed in the media of dry blood, dry egg, dry milk, gelling agent and water (kept at about 38 degrees C).

38 Trays of larva are kept on large racks, media is added 3-4 times Mature larvae are removed from the media and pupate (in sawdust) The larval period last about 6 days

39 Mature larvae are placed in containers of sawdust where they pupate. Large numbers of trays of pupae are stored on racks for about 4 days.

40 Pupae are then placed in tubes. 2. The tubes are placed in slots in the wall for irradiation. (use Cesium 137 as source) 3 3. On the other side of the wall are irradiators where the flies are sterilized.

41 Sterile screwworm pupae are kept chilled in large boxes for up to 2 days before loading to planes for dispersal in the eradication program.

42 Pupae are released at a rate of about 3,000 or more per nautical mile.

43 Good Web sites: vetmanual.com

44 Photos Dr Chase Dr Schlater Dr Scoda USDA Grey book

45 Questions