Flystrike

Anyone who has seen a flyblown rabbit has no wish to see another, and yet in summertime many vets see at least one or two every week.

What is flystrike?

Flystrike - myiasis - occurs when flies lay their eggs on another animal, be it sheep or rabbit. The eggs hatch into maggots which then eat away at the surrounding flesh. Certain species of fly (notably bluebottles) produce maggots capable of eating through intact skin. However, if the rabbit already has a break in the skin then any kind of maggot will be able to eat into the wound.

In warm conditions, the whole process from eggs being laid to maggots emerging can take just a few hours, so it is vitally important that rabbits are checked twice daily. In the worst cases, there may be severe tissue loss where maggots have literally eaten the rabbit alive: sometimes maggots eat down to the bone in the hind legs or even into the abdomen.

Most cases of flystrike are preventable, but occasionally even the best kept bunny is afflicted. Prompt action is then vital to save the rabbit.

Is my rabbit at risk?

Flies aren't interested in clean, dry fur. They are attracted to damp or dirty fur, which is why mucky rabbit bottoms + flies = trouble.

Most rabbits keep their bottoms very clean and dry, but it only takes one squished caecal poop to trigger problems! This is why even perfectly healthy rabbits need frequent bottom checks. Far and away the most common part of the body to be affected by flystrike is the bottom, but it can occur on other parts of the body. There are even cases reported in healthy rabbits who have managed to soil the fur on their back or flanks.

The bunnies at greatest risk of flystrike are those who can't attend to their personal hygiene; produce loose droppings; or have breaks in the skin:

• Obesity
• Arthritis
• Old, frail rabbits or those with poor balance
• Large dewlap or folds of loose skin or fat on abdomen
• Dental problems
• Long haired rabbits
• Previous fly strike
• Wounds or draining abscesses

If your bunny falls into one of these high risk groups, seek veterinary input as soon as possible. You need a strategy both for tackling the underlying problem (for example, pain killers for arthritic rabbits and weight loss for fat rabbits) and also to minimise the risk of flystrike in the meantime.

Preventing flystrike

• Recognise if your rabbit falls into a high risk category
• Don't allow your rabbit to get fat
• Be careful putting rabbits out on the lawn - scoffing unaccustomed grass may lead to loose droppings and soiled bottoms on high risk warm summer days! Any change of diet should take place over at least 1-2 weeks.
• High risk rabbits are safer indoors but daily bottom checks are still required
• Insect proof hutches and runs (e.g. by stapling net curtains over hutch fronts)
• Even houserabbits need to have their bottoms checked twice daily in warm weather
• If you find fly eggs on your rabbit, pick them off; check for concealed maggots; and step up your prevention programme
• Some vets use a special horse wound powder (Negasunt) which is both larvicidal and bacteriostatic. This may be worth considering as an aid to prevention in high risk animals. As it is not licensed for use in rabbits you'll need to talk to your vet about the risk/benefit balance for your bunny

Treatment

If you find maggots on your rabbit:

This is an emergency, day or night: seek immediate veterinary attention.

Remove obvious maggots with tweezers. Remember that there will probably be concealed maggots that have already eaten their way under the skin.

Once at the vets, the severity of the situation can be assessed. Very bad cases (where large amounts of tissue has been eaten away) are best put to sleep immediately to prevent further suffering. Less severe cases may survive, but there are many problems to be overcome and intensive treatment will be required.

Flyblown rabbits are usually very unwell and shocked. They are at high risk of severe infection and will be in pain. Add to this any underlying problem (as we've already said, most flystruck rabbits have underlying medical problems) and the situation can be complex and treatment extremely challenging.

Treatment consists of clipping away the fur, then dunking the affected area in warm water to remove external maggots, and removing any dead tissue. This often requires a sedative or general anaesthetic, which carries a much higher risk than normal because flyblown rabbits are so sick. Most fly-struck rabbits need intravenous or subcutaneous fluids; antibiotics to try and prevent infection; and anti inflammatory drugs which double up as pain killers. Some vets also use ivermectin (the same drug used to kill fur mites) in the hope that it will penetrate the tissues and reduce further invasion by any remaining concealed maggots.

If the rabbit survives, there may be a large area of skin loss which will take weeks to heal. During the time the bunny will remain at high risk of infections and further bouts of flystrike. Careful nursing will be required as well as a full assessment of any underlying problems and an obsessive prevention strategy.

This article originally appeared in Rabbiting On (journal of the British Houserabbit Association) in Summer 2000. It was written by Dr Linda Dykes and Owen Davies BVSc MRCVS. This version was revised by Linda Dykes in November 2001.