Flystrike – it’s that time of year again

Whenever it gets warm during the UK summer, we all need to be on the look out for myiasis in rabbits. May to September are the times they are most at risk, though in recent years the trend has been to see the season start earlier and end later. Flies are attracted to damp fur, urine and faeces where they lay eggs. These eggs then develop into larvae and maggots, which are attracted to skin and underlying tissues.

Posted: 26 June 2018

Flystrike – it’s that time of year again

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Green bottles (Lucilia sericata) are the most common cause of fly strike in the UK. Studies have shown that he incidence of fly strike is directly proportional to the numbers of green bottle flies, which are themselves influenced by patterns of higher temperature and rainfall.

Myiasis – it’s an emergency

Remember, this condition needs urgent attention, so don’t be tempted to leave it until the next day.

Which rabbits are at risk?

Potentially all animals are at risk from this condition, but we tend to find that it affects rabbits with one or more of the following problems.

  • Dirty coats – any animal with wet or soiled fur will attract flies
  • Overweight or obese pets - rabbits that are unable to clean themselves properly or feed on the normal caecotrophs will be more susceptible
  • Animals in pain – if a rabbit has pain associated with dental disease, gut stasis or arthritis, it will be less inclined to behave normally. Caecotrophs won’t be eaten, so these will build up as a smelly, sticky mess under the tail, so attracting flies
  • Bladder disease – any animal with bladder stones, sludge or cystitis will end up dribbling urine that will attract the egg-laying flies
  • Arthritic – any animal with pain associated with the spine or hind legs will be less able to clean itself
  • Elderly – older animals will be less active and attentive. If they move less, they tend to stay close to where they have defecated or urinated, and so will be in close proximity to egg laying flies
  • Injuries – any animal with an open wound
  • Respiratory infections – be vigilant if the rabbit has a chronic purulent nasal or ocular discharge

What are the signs?

  • Lethargy and depression – rabbits will be quiet
  • Dehydration – check mucous membranes, skin tenting and heart rate
  • Toxic shock – these cases will require urgent fluid therapy
  • Putrid smell – this is very characteristic and unpleasant
  • Larvae visible – when small they can be easily missed

Managing and treating myiasis

Remove eggs, larvae and maggots - pick off as many of the external larvae as you can by washing in warm water. Remove the stubborn maggots using tweezers or forceps. Any maggots that have burrowed into the flesh can be encouraged to the surface of the skin by using a warm, damp towel.

Antibiotics and analgesia - the wounds will be extremely sore, and usually become infected. Failure to manage the pain will put the patient at risk from stress related complications such as gut stasis.

Investigate the cause - ultimately the underlying reason the animal has been affected needs to be found and treated to fully and effectively treat the condition. Often the cause is pain that prevents the animals from eating caecotrophs, grooming or moving about. We suggest X-rays to look for signs of arthritis or dental disease to try to identify and resolve the problem.

Don’t use Fipronil – it must be emphasised that you avoid the use of any preparations containing fipronil, as this is potentially lethal to rabbits.

Spot on or injectable treatments – these are used to kill the maggots (not all of them may be removed by washing and picking as they can burrow quite deep). Ivermectin or Imidacloprid are both effective.

Avoid hypothermia - try not to wet the rabbit’s coat excessively when removing the larvae, as you don’t want to cause hypothermia. Dry the area afterwards using clean soft dry towels.

Fluid therapy – this is essential if the rabbit is depressed or dehydrated. Give an initial bolus of 10ml – 15ml/ kg of crystalloids (Hartmann’s).

Preventing myiasis

Myiasis is a distressing and potentially fatal condition. Whilst we can’t eliminate flies from the environment, you can encourage your clients to check their pet daily.

Prevention checklist:

  • Remove all soiled bedding – this will reduce the smells and levels of ammonia and so won’t attract flies.
  • Feed a high fibre diet – lots of hay and only limited access to concentrates. Never feed muesli style diets - overfeeding carbohydrates can result in diarrhoea, leading to a dirty groin.
  • Short hair - keep the hair around and under the tail short and clean.
  • Fly traps – these may be helpful but check they are safe to use
  • Screens on doors and windows - these may reduce the number of flies that get into the house
  • Rearguard – it’s safe and effective

Rearguard

Rearguard contains Cyromazine, and is used for the prevention of blowfly strike (Lucilia sericata) in domestic rabbits for up to 10 weeks after dosing. Rabbits should be first treated in early summer before any flies are seen. Note: It won’t repel flies or kill adult maggots but works by preventing fly eggs from developing. Rabbits should be treated at 8-10 week intervals.

 

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