Implications of blowfly strike

HI_RES_Page_09_Image_0005BLOWFLY strike in the UK results in the opportunistic invasion of living tissues by the larvae of Lucilia sericata (greenbottles), Phormia terrae-novae (blackbottles) and Calliphora erythrocephala (bluebottles).

Economic impact

The incidence of disease is estimated between 1.5 – 3 per cent but this may be an underestimate when no control measures are adopted. Cutaneous myiasis is a major economic concern for farmers:

  • Considerable prevention costs involved for all atrisk sheep
  • Sheep affected with blowfly strike have disrupted grazing patterns and rapidly lose weight
  • Death occurs in neglected sheep.

It is legal requirement to inspect all sheep on low ground and upland farms daily. Blowfly strike is easily detected by observing sheep whilst grazing.

HI_RES_Page_09_Image_0004Clinical signs

  • Become isolated from the group
  • Spend long periods lying down with the head on the ground
  • Show disrupted grazing; often running off for no reason
  • Nibble around the anus (perineum)

Adult flies are attracted to areas

  • Adjacent to faecal staining surrounding the perineum
  • Foot lesions with exposed corium/exuberant granulation tissue
  • lumpy wool lesions on the skin
  • Urine scalding around the prepuce.

Diagnosis

large numbers of adult flies are seen on the fleece with maggots on the blackened skin once the surrounding fleece has been lifted clear. There is an associated putrid smell. Skin, previously damaged by fly strike, grows black wool.

Welfare implications

  • Blowfly strike is a major welfare concern and infested sheep are greatly affected especially after several days
  • Death can result in neglected cases

BLOWFLY STRIKE AROUND THE PREPUCE WITH FLIES ATTRACTED BY URINE SCALDING IN THIS CASTRATED MALE LAMB.

  • Fly strike of foot lesions causes severe non-weight bearing lameness.

Treatment

  • Apply dip wash directly to the struck area after first clipping away overlying wool.
  • Antibiotics and NSAIDs should be given to severely affected sheep – consult your veterinary surgeon.

Prevention and control

Prevention of blowfly strike will be an integral part of the veterinary flock health plan. Before preventive measures using various chemicals are considered, much can be done to reduce the attraction of blowflies:

  • Reduce diarrhoea caused by high parasite burdens
  • Remove wool contaminated with faeces (‘dagging’ or ‘crutching’).
  • Shear adult sheep at the correct time.

DISEASE CONTROL AND PREVENTION SHOULD BE PART OF YOUR VETERINARY HEALTH PLAN – CONSULT YOUR VET

The main aim of NADIS is to highlight the importance of better animal health through veterinary health planning and to encourage dialogue between farmers/livestock handlers and their veterinary practitioner. NADIS provides a valuable learning resource and revision guide for everyone interested in animal health and welfare. www.nadis.org.uk

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