Flies and Myiasis Flashcards
Flies background
Diptera - two winged
Synanthropic - live in close association with man and human settlements
Some species cause myiasis in man and domestic animals whilst others are biting nuisance
enormous reproductive potential
What diseases do flies transmit
bacteria and viruses
Important house flies
Musca domestica - common housefly - indoors and shade
Musca sorbens - bazaar fly or bush fly - outdoors and open
Fannia - lesser housefly - latrines and poultry excreta
Muscina - greater housefly - greater housefly - stables and farms
Musca domestica - common housefly - morphology
Four dark stripes on grey thorax
Wing vein 4 bends to meet vein 3
Musca domestica - housefly behaviour
Feeds on human food, garbage, excreta, decayed plant and animal matter
Feeding sites 100-500m from breeding sites
Breeds often in same decaying organic matter on which it feeds
Found by day near food sources and breeding sites
Musca domestica - housefly
Eggs 0.8-1.0mm, 75-100 at a time and up to 5 batches
Larvae - 3 instars
Puparium
Adults
Musca domestica - housefly breeding sites
Animal manure Grass cuttings Latrines Household garbage Prawn meal Refugee camps Chicken farms - more usually Fannia - lesser housefly
Housefly development is dependent on what
Dependent on temperature
Pupal optimum around 29 C and larval optimum around 36 C
Medical importance of Musca domestica
Omnivorous - faeces and food
Enteric bacteria - Shigella, Salmonella, E.coli
Cholera
Enteroviruses - including polio
Helminth eggs
Major routes of transmission are defecation, regurgitation and transport on the body surface
What do houseflies feed on
Feeds on liquid and semi-liquid food
How do houseflies feed
Undigested food is stored in the crop and vomited where it is digested in the mid-gut
feeds with soft, fleshy and suctorial mouthparts
Defecates every 5 minutes
Features of Fannia larvae
Larva with prominent lateral processes
Fly control in pakistan
Fly control using ULV Deltamethrin resulted in elimination of fly population and reduction of diarrhoea
No reduction outside the fly season
Fly control in Israel
Fly control using traps placed around latrines, kitchens and mess areas in military camps with high compliance
After 11 weeks clinical visits for diarrhoeal disease reduced by 42% as well as shigella incidence down by 85%
Antibody conversion for shigella down by 76% and coli down by 57%
Musca sorbens - Bazaar fly
Breeds particularly in human faeces but less frequently
Attracted to discharge from the eyes and or nose
May be common in refugee camps
What does Musca sorbens - The Bazaar fly transmit
Transmit trachoma - Chlamydia trachomatis
Trachoma control in The Gambia
Fly control using ULV Deltamethrin resulted in
Decrease in Musca population by 75%
75% decrees in incidence of trachoma
22% less diarrhoea in children
Incrimination of Musca sorbens as a vector
Mass oral azithromycin treatment resulted in a drastic reduction in fly carriage
Issue with using insecticides on flies
Insecticide resistance develops incredibly quickly - failure to control
needs to be reliant on prevention of breeding and not on insecticide use
How can breeding be prevented
good waste disposal practice - cover refuse with >25cm of soil, keep only the working edge of a tip exposed and make sure tip is tightly packed, increased temp kills larvae
disposal of human and animal excreta - ventilated pit latrine and manure piles
Control of houseflies and blowflies
Screen premises - kitchens and hospitals
Traps and insecticidal control - stripes, baits, space sprays, tip dressings, animal medication
Biological control - sterile insects and Bacillus thurngiensis in chicken mash
What is myiasis
The invasion of living tissues of humans and other animals by the larvae of dipterous insects
Clinical classifications of myiasis
cutaneous -
furuncular - boil like swellings with one fly larvae per boil (tumbu)
other invasive traumatic (screw worms)
non-invasive (Lucilia, Calliphora etc.)
Nasopharyngeal, ocular - oestrus
urogenital - fannia
intestinal
obligate myiasis
essential for larvae to live on the host for one part of the life cycle - cordylobia, cochliomyia, chrysomya, dermatobia
facultative - normally free living (dead tissues) but will grow on open wounds and sores - calliphora, lucilia, sarcophaga
accidental (pseudomyiasis) - enteric, urinary tract - Musca, Fannia and Sarcophaga
Myiasis pathology
Irritation, discomfort, pruritus (itching), tissue damage, haemorrhaging, secondary bacterial infections, anaphylaxis and shock toxaemia
Tumbu fly - Cordylobia anthropophaga
Obligate parasite from Africa
Eggs laid on urine soaked clothes or sandy soil
Normal host is the rat
Grub shaped larva which from boil like swellings
Common around the buttocks, genitalia and the back
Merge from the skin after 8 days
Pupate in the soil
Adult inconspicuous brown coloured fly
How to remove tumbu fly
lubricate the wound e.g. with paraffin wax and gently prise out
Tumbu fly control
iron clothes
Dermatobia (human botfly
causes new world myiasis
Eggs attached to a biting insect e.g mosquito or stomoxys
Burrow into the skin to form a boil like swelling
Dermatobia (human botfly) larvae
possess stout rose-thorn spines
Screw-worms species
Chrysomya in the old world
Cochliomyia in the new world
Adults are a metallic blue-green colour
Screw worms
obligate parasites of living tissues
very serious as they consume living tissue which causes severe tissue trauma and pain
can invade the natural orifices - nose, mouth, eyes and genitals
larvae with spines giving a screw-thread appearance
Fleshflies - Sarcophagidae
Common in refuse, butchers shops etc
Larvae occasionally cause myiasis
Feed mostly on necrotic tissue
Non invasive myiasis (blowflies)
Blue bottles (Calliphora)
Green bottles (Lucilia)
usually breed in similar habitats to houseflies
Will infest and consume necrotic tissue e.g. foul smelling wounds, ulcers etc. - sometimes found under bandages
Usually do not cause harm since they feed on dead and decaying tissue/ Baer’s maggot therapy
Larvae without screw thread of spines
Maggot therapy for chronic wounds
Uses non invasive species
Larval movement stimulates serous exudate which flushes bacteria from the wound
Larvae consume the necrotic tissue and bacteria
Larvae lower pH
Larvae secrete therapeutic agents - urea ammonium bicarbonate, bactericidal proteins, allantoin
Useful where antibiotic resistance, limited drugs or surgery
