Flystrike occurs when larvae (maggots) of blow flies hatch on the skin and feed on tissues of live animals. Adult flies lay eggs in wool moistened from a range of causes such as urine or faecal staining, skin wounds, weeping from eyes, or the lesions of footrot, fleece rot or lumpy wool.
Affected animals may lose condition and be predisposed to secondary bacterial infections and septicaemia or toxaemia.
Warm, wet weather increases the likelihood of flystrike. If the weather is too hot or too dry, the eggs and maggots do not survive. Flystrike is rare in goats because they are hairy rather than wooly and have few skin folds. Fly strike in the live export process is uncommon because animals are crutched and shorn, conditions are usually dry, and they are closely monitored for much of the time.
Affected animals may be first noticed showing signs of depression, anorexia, and separation from flock or herd mates. Affected animals may be irritated and attempting to bite or kick at the struck area. The animal may have a distinct smell coming from the struck area. Close examination reveals maggots burrowing or tunneling under and into tissues.
Screw worm fly should always be considered where maggots are found in wounds. Specimens can be submitted in 70% alcohol to the laboratory for identification.
Cut away matted hair and wool, remove accessible maggots and apply insecticide or larvicide to kill remaining maggots. Individual animals showing signs of toxaemia should be treated with antibiotics (procaine penicillin, or oxytetracycline).
Reduce attractiveness of animals to flies by shearing, crutching, treating wounds and preventing diarrhoea and foot infections.
Under favourable environmental conditions fly numbers can increase and lead to multiple animals being affected with flystrike. It is important to detect and treat affected animals promptly and consider applying prophylactic treatments (jetting or dipping) at strategic times to prevent further cases. A range of insecticidal and larvicidal preparations are available for individual or group prophylaxis during fly waves.