Fly Strike, Myiasis, ‘Brommers’
By Dr Mackie Hobson BSc(Agric),BVSc

1. Diseases

Fly strike, although more of a problem in sheep, does occur in Angora goats in South Africa.

The green blowfly ‘Groenbrommer’ (Lucilia cuprina) is responsible for most fly strikes (about 90%) in Angora goats.

Chrysomyia chloropyga the Copper tailed blowfly also known as ‘Koperstert-skaapbrommer’ is responsible for about 10% of cases.

‘Bloubrommers’ Chrysomyia marginalis do not cause fly strike in goats that are alive but feed on dead animals. 

Chrysomya chloropyga  Copper tailed Blow fly.

The striped blowfly ‘Gestreepte groenbrommer’, Chrysomyia albicans, is a secondary blowfly maggot as it feeds on the primary maggots. It only lays its eggs once the primary strike has occurred.

General life cycle of Blowfly

• After hatching the adult flies feed on the nectar of certain plants or the breakdown protein ‘soup’ of carcases. The flies may live for a month or more. The adult flies lay eggs in batches of 100-150 (total 3000).
• These eggs hatch in 8-12 hours.
• The larvae feed off the carcase, moult twice, and drop off to pupate in the soil (may be as short as 3 days)
• The pupation period may be 7-10 days in summer but several months in winter.

What causes Fly Strike?

Fly strike occurs in Angora goats that are attractive to the blowfly. The attraction is the rotting organic material which may be due to:

• Rotting hair around breech caused by diarrhoea (as kids in photo)
• Rotting hair around the vulva or prepuce from wet urine
• Any wound (shearing, crutching, castration or trauma such as base of horns in fighting rams)

What do the maggots feed on?

The primary maggots feed on the superficial skin of the goat. These maggots secrete a proteolytic enzyme which leads to a certain amount of liquefaction of the superficial tissue causing inflammation and exudation. This attracts further Blowfly which lay eggs and these maggots then enlarge the wound and burrow more deeply.

What clinical signs do the goats show?

The goats do not eat properly. If the strike is in the breech the tail will is waggled and the hind feet are sometimes stamped. The goat may bite at the area of blowfly strike. There area is clearly visible and will have a distinctive smell.

The goat will ultimately die due to the high ammonia content of the maggot’s saliva which will cause a toxaemia.

Treatment options

GREEN is the list of products recommended by SAMGA to avoid residues in Mohair.

What preventative treatment can be done?

• Crutching
• Burning carcases or treating with insecticide in winter (This will not help in summer as cuprina , the green blowfly, can’t use the carcases I winter)
• Treat wounds with insecticide
• Prophylactic treatment such as Click

References:

Ticks, mites and insects infesting domestic animals in South Africa: Howell, Jane B, Walkert and Nevill

Horack, University of Pretoria, Dept Veterinary Tropical diseases

IDR 2017/18