1. Lecture Overview Mechanical Transmission – Filth Flies and Cockroaches
Myiasis – Infestation with Fly Larvae
Forensic Entomology

2. Mechanical Transmission of Pathogens
The transfer of pathogens from an infected host or a contaminated substrate to a susceptible host - a biological association between pathogen and vector is not necessary.
The vector can be an arthropod or: bird, rat, mouse, animal, human.

3. General characteristics of mechanical infection of a pathogen:
No development or multiplication in the vector
Usually multiple routes of infection
Infection may also occur by food and/or water contamination
Multiplication of the pathogen may occur in the original host AND in environmental media

4. Examples of Arthropods Associated with Direct 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

5. Examples of Arthropods Associated with Indirect 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

6. Casu Marzu – “walking cheese”

7. 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

8. COCKROACHES
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

9. COCKROACHES
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

10. Cockroaches - 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

11. Cockroaches - Biology I
Simple Metamorphosis:
ootheca (egg case) with 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

12. Cockroaches - 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

13. Cockroaches - Compare

14. American Cockroach - Periplaneta americana

15. German Cockroach Oriental Cockroach
Blatella germanica Blatta orientalis

16. 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)

17. 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”

18. Flies and Mechanical Pathogen Transmission

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

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

21. House-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

22. Control of House-flies, Stable-flies, Latrine-flies
Physical and Mechanical Control
Environmental Sanitation
Insecticidal Control
Larvicides
Adult spraying
Insecticidal cords
Toxic baits

23. Myiasis
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

24. Facultative 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

25. Facultative 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

26. Facultative 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

27. Sarcophaga Species

28. Obligatory 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

29. Obligatory 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)

30. Dermatobia hominis

31. Dermatobia hominis larva
(human bot fly)

32. Bot flies and damage

33. Control 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)

34. Medicinal 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

35. Medicinal 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

36. Many of the fly species involved in accidental myiasis are also important in Forensic Entomology