Calliphoridae

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Pollenia rudis (Calliphoridae) - Richard Bartz, Munich - Wikimedia Commons
Lucilia cuprina - Wikimedia Commons
Blowfly Head Close Up - Martin Pot - Wikimedia Commons
  • The Calliphoridae family are facultative parasites
  • Cause blowfly strike
  • If the fly lays eggs on an animal, the animal is said to be blown
  • The damage the larvae cause to the animal is known as strike
  • Worldwide distribution
  • Affects sheep mostly
    • Rabbits can also be affected


Species of veterinary importance in Europe

  • Lucilia sericata; Greenbottle
  • Phormia terra-novae; Blackbottle
  • Calliphora erythrocephala; Bluebottle
  • Calliphora vomitoria; Bluebottle


Species of veterinary importance in the Tropics

  • Lucilia cuprina; South Africa and Australia
  • Chrysomya spp.; Africa, Asia and Australia
  • Wohlfahrtia; Fleshfly


Recognition of Adults

  • Medium sized flies under 10mm long
  • Metallic sheen to abdomen
    • Colour depends on species
  • Clear wings


Recognition of Larvae

  • Smooth maggots
  • 10-15mm long
  • Spiracles and stigmatic plates on the tail can be used for species differentiation


Life cycle

  • Eggs laid in wounds, soiled fleece and on carrion
    • Females attracted by the odour emitted
    • Clusters of yellow-cream eggs laid
  • Larvae hatch 24 hours later and crawl down onto the skin
    • Feed rapidly
    • Grow rapidly
    • Moult twice before becoming full maggots
    • Process takes 1-2 weeks
  • Larvae fall to the ground to pupate
  • Adult emerges in under 1 week (during summer)
  • The female reaches sexual maturity after a protein meal
    • Lays eggs in batches of 100-200
  • Adult flies survive for 1 month
  • Four generations can develop between May and September
    • In warmer climates, up to 9 or 10 generations can develop per year
  • Flies can survive the winter as pupae and emerge the next spring


Epidemiology
Blowflies are divided into categories depending on their ability to initiate strike

  • Primary flies are capable of initiating a strike on living sheep. Larvae can penetrate intact skin
    • Lucilia
    • Phormia
    • Calliphora spp.
  • Secondary flies cannot initiate a strike. Larvae attack an area already struck or damaged, extending it
    • Calliphora spp.
    • Chrysomya spp. (in warmer climates)
  • Tertiary flies attack lesions on carcasses which have become dry
    • Musca
    • Sarcophaga spp.


Predisposing factors to flystrike

  • Temperature
    • Temperature in the spring will determine when the overwintering larvae hatch
    • High temperature and humidity will create a microclimate in the fleece, attracting adult flies to lay eggs
  • Rainfall
    • Persistent rainfall will make the fleece microclimate attractive to adult flies. Females lay eggs after the rain ceases
    • Breeds with long, fine wool are the most susceptible
  • Host susceptibility
    • This is increased when putrefactive odours develop on the fleece due to bacterial decomposition of organic matter following soiling with urine or faeces
    • Merino sheep have a narrow breech area with excessive wrinkling making them more susceptible to soiling
    • A narrow opening of the penile sheath in rams and wethers may result in accumulation of urine and increase blowfly strike in this area
    • Cuts during shearing, fighting and barbed wire will also increase the incidence of blowfly strike


Blowfly season

  • Temperate regions in June to September
    • Mostly in unshorn sheep in June
    • Lambs from July to September
  • Warmer regions have a more prolonged season due to greater number of blowfly generations


Pathogenesis

  • Severe skin damage
    • Larvae lacerate skin with oral hooks and liquefy host tissue by secreting proteolytic enzymes
  • Skin lesions are extended and deepened
    • Secondary blowfly attack
    • Flies attracted to odour of decomposing tissue
  • Secondary bacterial infection
  • Production losses
    • Irritation and distress associated with skin lesions
    • Poor weight gain (often the first clinical sign)
  • Risk of strike is highest in warm, moist weather


Clinical signs

  • Anorexia
  • Listlessness
  • Animals standing apart from flock
  • Fleece may appear darker, be damp and have a foul smell


Control

  • Prophylactic insecticide treatment
    • Must kill larvae and remain in fleece to prevent flies from laying eggs
    • Applied by spraying, dipping, spray race or jetting
  • Insect growth regulators
    • Pour-on
    • 2-4 month protection depending upon the product used
  • Effective worm control
    • To minimise diarrhoea and therefore soiled fleece
  • Crutching to prevent soiling
  • 'Mule's operation'
    • Surgical removal of breech skin in Merino breeds
  • Tail docking of lambs
  • Proper carcass disposal
    • Eliminates fly breeding sites
  • Vaccination
    • Experimental use against Luculia cuprina in Australia