Calliphoridae

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