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Lecture Overview

• Mechanical Transmission – Filth Flies and Cockroaches

• Myiasis – Infestation with Fly Larvae

• Forensic Entomology

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Mechanical Transmission of PathogensMechanical Transmission of Pathogens

The transfer of pathogens from an infected host or a contaminated substrate to a susceptible

host - a biological association between biological association between pathogen and vector is not necessarypathogen and vector is not necessary.

The vector can be an arthropod or: bird, rat, mouse, animal, human.

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General characteristics of General characteristics of mechanical infection of a mechanical infection of a pathogen:pathogen:

• No development or multiplication in the vectorNo development or multiplication in the vector

• Usually multiple routes of infectionUsually multiple routes of infection

• Infection may also occur by food and/or water Infection may also occur by food and/or water contaminationcontamination

• Multiplication of the pathogen may occur in the Multiplication of the pathogen may occur in the original host AND in environmental mediaoriginal host AND in environmental media

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Examples of Arthropods Associated with Examples of Arthropods Associated with DirectDirect Mechanical Transmission: Mechanical Transmission:

• Eye Gnats - Yaws from host secretions - Insects feeding on wounds

• Tabanid Flies - Vesicular stomatitis virus and equine infectious anemia from blood - Insects feeding on blood

• Mosquitoes - Fowlpox virus from blood - Insects feeding on blood

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Examples of Arthropods Associated with Examples of Arthropods Associated with IndirectIndirect Mechanical Transmission: Mechanical Transmission:

• Maggots - Botulism toxin from carcasses - Ingestion of maggots

• Flies - Enteric disease from carcasses or feces - Eating contaminated food

• Ants, Roaches, Flies - Nosocomial infection from host secretions - Eating contaminated food or other substances

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Casu Marzu – “walking cheese”

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Important parameters in mechanical transmission:

•Presence of setae on arthropod integument

•Type of feeding behavior (pool or vessel feeding)

•Regurgitation behavior

•Association with human dwellings

•Defecation patterns

•Stability of the pathogen in the environment

•Titer and infectiousness of the pathogen

•Number and type of arthropods

•Host immunity

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COCKROACHESCOCKROACHES• Order Dictyoptera, formerly Orthoptera (most

closely related to praying mantises)• Suborder Blattaria• Some 4000 species, but <1% are medically important

as domestic pests (50 sp.)• Among the most ancient winged insects - little

change from fossils of 250 mya• Primarily tropical and subtropical, but have adapted

to pseudo-tropical situations associated with humans

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COCKROACHESCOCKROACHES

• Medically important species infest two different types of habitats:

homes, shops and food handling establishments sewers and rubbish or trash dumps Movement of cockroaches between these two

habitats, specifically from sewers or dumps to food handling establishments, can lead to mechanical transmission of pathogens

Additional health problem in urban areas:

cockroach allergies

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Cockroaches - AdultsCockroaches - Adults

• Large, oval, dorsoventrally flattened insects• Head with compound eyes and ventral

chewing mouthparts - omnivores (not blood-sucking)

• Two pairs of wings, but may be reduced• Segmented abdomen with paired cerci at end• Coloration - light brown to black in pest forms,

but some tropical species orange, green, etc.• Cockroaches vs. beetles: crossed wings vs.

elytra

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Cockroaches - Biology ICockroaches - Biology I• Simple Metamorphosis:» ootheca (egg case) with 12-50 eggs» 5-12 nymphal instars (depends on species and

sex)» adult (typically winged)• Ootheca - desiccation-resistant, may be carried 2-

3 days or weeks, depending on species• Life span >2 years under poor conditions, need

H2O

• Flight dependent on warm temps - flight muscles need hi temps to activate; fast-running, nocturnal

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Cockroaches - Biology IICockroaches - Biology II

• Recent expansion of species with high reproductive capacity (ex. - Blattella germanica replacing Blatta orientalis in many regions)

• Habit of regurgitation while feeding and of defecating while moving or feeding increases potential for pathogen transmission

• Infestation occurs from infested housed to adjoining ones via water pipes, etc. Also spread in furniture, boxes, and other moved items

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Cockroaches - CompareCockroaches - Compare

14American Cockroach - Periplaneta americana

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German Cockroach Oriental Cockroach

Blatella germanica Blatta orientalis

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Cockroaches - Pathogen Transmission

• Transmission is mechanical, either through feeding/regurgitation, defecation, or body hairs

• Pathogens isolated in nature:» bacteria (E. coli, Pseudomonas, Salmonella,

Shigella)» fungus (Aspergillus)» helminths (Ancylostoma, Ascaris, Necator,

Trichuris)» protozoa (Entamoeba histolytica)» viruses (Hepatitis and poliomyelitis viruses)

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Cockroaches - Control

• Three components: Hygiene - reduce potential food sources Structural alterations to building to reduce

access Chemical control - organophosphates,

carbamates, and pyrethroids; boric acid powder.Other - Traps with or without bait or

insecticide “roach motels”

Flies and Mechanical Pathogen

Transmission

19Forensic Entomology, 2001. Byrd and Castner, Eds.

20Forensic Entomology, 2001. Byrd and Castner, Eds.

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House-flies, Stable-flies, Latrine-fliesHouse-flies, Stable-flies, Latrine-flies

• Musca domestica - house-fly

mechanical transmission of many pathogens, accidental myiasis

• Muscina stabulans - greater house-fly

mechanical transmission, accidental myiasis• Stomoxys calcitrans - stable fly

biting pest (human and veterinary pest)• Fannia sp. - lesser house-fly and latrine fly

mechanical transmission, accidental myiasis

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Control of House-flies, Control of House-flies, Stable-flies, Latrine-fliesStable-flies, Latrine-flies

• Physical and Mechanical Control• Environmental Sanitation• Insecticidal Control

– Larvicides– Adult spraying– Insecticidal cords– Toxic baits

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MyiasisMyiasis• Infestation of the organs and tissues

of humans or animals by fly larvae that for some period of time, feed upon the living or dead tissues or the ingested food of the host

• Accidental = Facultative Myiasis (includes enteric, recto/urogenital and cutaneous)

• Obligatory Myiasis

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Facultative MyiasisFacultative Myiasis• Enteric Myiasis - accidental ingestion

• 50 species reported - most Muscidae and Sarcophagidae

• Passive transport of larvae - no development in host digestive tract

• Severity depends on fly species, number, location

• Genera commonly involved: Musca, Fannia, Muscina

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Facultative MyiasisFacultative Myiasis• Rectal/Urogenital Myiasis

• Access to intestine via anus; larvae feed on excrement

• Immature stages may be completed in rectum or terminal part of intestine

• Can occur in humans under unsanitary conditions

• Primary genera - Fannia, Musca, Sarcophaga

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Facultative MyiasisFacultative Myiasis

• Cutaneous myiasis - usually around wounds

• Larvae normally found in meat or carrion occasionally adapt to a parasitic existence

• Usually do not invade healthy tissues

• Typically blow flies: species of Calliphora (bluebottles), Lucilia (greenbottles), Phormia, Sarcophaga and Wohlfahrtia (flesh flies), Cochliomyia macellaria (secondary screw-worm), and others

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Sarcophaga Species

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Obligatory MyiasisObligatory Myiasis

• Calliphorids (non-metallic): Cordylobia anthropophaga - tumbu or

mango fly (Africa); larvae attach and burrow into skin leaving spiracles exposed - boil-like swelling results [cover with paraffin or oil to extract]

Auchmeromyia senegalensis - Congo floor-maggot (Africa); adult looks like tumbu fly, but larvae do not remain attached; feed nightly from people sleeping on the floor

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Obligatory MyiasisObligatory Myiasis

• Calliphorids (metallic): Cochliomyia hominivorax - New World screw-

worm; eradicated from US and Mexico, but outbreaks possible

Chrysomya bezziana - Old World screw-worm

• Sarcophagids (flesh flies): Wohlfahrtia magnifica - ear, eye, nose • Oestrids (bot flies): Gasterophilus, Hypoderma, Oestrus, Cuterebra

sp., and Dermatobia hominis (human bot fly)

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Dermatobia hominis

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Dermatobia hominis larva

(human bot fly)

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Bot flies and damage

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Control of Myiasis SpeciesControl of Myiasis Species

• Control or eradication of the fly population - through environmental sanitation or chemical control

• Avoidance of infestation (mechanical control) - do not sleep outdoors or on the ground during fly activity, dress or cover wounds to avoid fly strikes, use screening

• Treatment of infestation (remove larvae - antibiotic follow-up may or may not be necessary)

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Medicinal MaggotsMedicinal Maggots

• Using first instar larvae of flies to heal wounds

• Larvae work continually to remove the dead tissue and cleanse it of bacteria while leaving the viable cells alone

• Larval therapy gained acceptance and was widely used until the discovery of antibiotics in the 1940's

• With the emergence of antibiotic-resistant strains of microbes, larval therapy is again being investigated as a viable treatment of wounds

• Fly larvae can be used to heal ulcerative lesions, burns, certain types of benign and malignant tumors, abscesses, and osteomyelitis when conventional treatments fail or are inappropriate

• They are easy to apply, relatively inexpensive, and do not destroy normal gastrointestinal flora or leave violative residues as do systemic antibiotics

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Medicinal Maggots - 2Medicinal Maggots - 2• Not all fly maggots are suitable for use in larval therapy.

• Among those which should not be used are members of the family Sarcophagidae (flesh flies) and the species Cochliomyia hominovorax (screw worm) since they will devour living tissue

• The most commonly used larvae belong to the family Calliphoridae, specifically Lucilia (Phaenicia) sericata (greenbottle blowfly) and Phormia regina (blackbottle blowfly) which will only feed on necrotic tissue

• It was reported in 1933 that for successful larval therapy, the maggots should be free of bacteria before being placed into wounds

• Larvae should be removed from the wound after 3 days, and can be used in conjunction with antibiotic therapy or X-rays

Hinshaw, J. Larval therapy: A review of clinical human and veterinary studies. World Wide Wounds, Oct 2000. www.worldwidewounds.com/2000/oct/Janet-Hinshaw/Larval-Therapy-Human-and-Veterinary.html

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Many of the fly species involved in accidental myiasis are also important in

Forensic Entomology