Flystrike (Myiasis)

by **Happy Hoppers** Sun Jun 22, 2008 11:32 am

What is it?
Flystrike is a condition where flies lay their eggs in the soiled or damp fur of rabbits (or any animal). When these eggs hatch into maggots they begin feast on the rabbit’s flesh, releasing toxins as they go and literally eat the animal alive. The condition can develop incredibly quickly, especially during warmer weather, and an apparently healthy rabbit can go into shock within hours.

Flystrike is a very serious condition and, if left untreated, will result in death.

How does it develop?
Flies are attracted to damp, smelly areas but they do not lay their eggs here. You will find fly eggs stuck to the normal fur surrounding the area – they look like a white mush. When these eggs hatch they will head for the area that attracted the flies and begin to feast. You will often see a writhing mass of maggots in flystrike, much like on rotten food. Be aware that if there are maggots on the surface of the skin there are more than likely maggots under the skin too. You can often observe them ‘rippling’ just underneath the skin.

There are two distinct types of flies that cause flystrike: the ordinary, household flies as mentioned above; and bot flies (flies of the subfamily Cuterebra).

Bot flies look a bit like wasps – yellow and black striped bodies and what appears to be a sting on the abdomen. The ‘sting’ is in fact an ovipositor which deposits small, yellow, seed-like eggs on the fur of the rabbit. Unlike houseflies, bot flies are attracted to the rabbit itself, not just the soiled, damp areas. Warmth and moisture cause these eggs to hatch and when they do, the larvae crawl down the hair and begin to burrow inside the rabbit’s skin where they will consume it before reappearing approximately 30 days later. When the larva reach maturity they reappear from the wound and drop to the ground. By this time they will have changed in appearance, forming a black ‘shell’ over their bodies and will be up to an inch in length (larger than the adult fly). Once burrowed under the skin, all you will most likely see is a raised lump with inflamed edges and a hole in the centre, possibly with black edges. This would is left open so that the emerging maggot has a ready-made exit when it emerges later.

Who is at risk?
Any rabbit with a damp bottom, loose stools or caked-on faeces can be affected. Flystrike is most prevalent during the warm summer months so make sure you are extra watchful when the weather is fine.

Rabbits at risk include those who are:

Elderly – they may not be able to clean themselves properly
Incontinent – resulting in a damp bottom
Arthritic – as for elderly buns. Mobility is limited in arthritic rabbits resulting in an inability to wash properly (if at all)
Overweight/Obese – chubby bunnies may be unable to reach their rear to clean it
Suffering from diarrhoea – a soiled, damp behinds attract flies
Suffering from a urinary tract infection – may lead to incontinence
Suffering from dental problems – your rabbit might find it too painful to wash properly
Producing too many caecotrophs – these can easily become caked to the rear if not consumed straight away. Your bunny may be on a diet containing too much protein, may have a sensitive stomach or may just have eaten too many greens!
Sporting an oversized dewlap (unneutered females) – this makes it very difficult for a bunny to reach her bottom to clean it.
Nursing open wounds – these are damp areas and will also attract flies.

It is not just outdoor rabbits who are affected. Flies can find their way into houses too so be on the lookout even if your rabbit is a houserabbit.

How is it treated?
If you do find maggots on your rabbit it important to act immediately. A rabbit with flystrike can easily go into shock and so you need get the rabbit to the vet as quickly as possible. Do not worry if you don’t have an appointment (though it is always best to try to ring ahead and warn them) – flystrike is an emergency and should be treated as such when you arrive.

If for any reason you cannot get to the vets straight away, or if the infestation is very advanced and there are many maggots it may be necessary to provide your rabbit with some preliminary treatment at home.

The best thing to do would be to tweeze off each individual maggot that you can find. This is often a gruesome task but it is important to get rid of as many maggots as possible as soon as possible. If the maggots have burrowed into the flesh or if you are too squeamish for tweezers you can encourage them to the surface with heat – using either a hot water bottle (or heat pack) or a hairdryer. Be warned though, a hairdryer may well distress your rabbit more if it is noisy or if they are unused to it! Do NOT try to dig into the flesh or squeeze the skin in the hopes of removing burrowed maggots – this could cause the maggots to become squashed and break apart, leading to infection and possibly anaphylactic shock. We also do not recommend using warm water if you can help it as, not only will this encourage any bot fly eggs present to hatch, but it will make it harder for the vet to clip away the hair when you do manage to get your bunny seen.

Often a vet will just flush out the burrowed maggots but sometimes they will need to be surgically removed, especially in the case of Cuterebra. Once the maggots have been successfully removed your vet will ensure there are no remaining fly eggs attached to your rabbit, who will most probably need fluids, a course of antibiotics and pain relief.

**Please note, even if you do manage to remove all maggots and eggs yourself your rabbit will still need to see a qualified vet as he/she may well go into shock or have an infection developing. ALWAYS see a vet for flystrike.**

How is it prevented?
First and foremost, make sure your bunny’s behind is dry! It is vital to clean off any stuck faeces or stained fur as the smell will only attract flies. The best things you can do are:

Clean the hutch regularly – a bunny sitting around on damp bedding will find it very difficult to keep clean and dry
Spot check daily – make sure your rabbit’s rear is not soiled
Remove any soiled fur/faeces – this ensures that any areas that your rabbit has missed or is unable to clean will not become infested.
Trim long fur – if your rabbit often has a wet behind it is acceptable to trim (or even shave) any fur around the area. This will make it harder for faeces to stick and will dry much quicker.
Tend to wounds – make sure there is no infection or discharge as this will attract flies more. Be extra careful with bunnies with open wounds/sores and if possible keep them indoors.
Keep bunny dry! – don’t completely submerge your rabbit’s rear in water. Spot cleaning is safer as you are only allowing the bare minimum to become wet. If your bunny does have a wet behind ensure you dry it properly.
Keep flies away – harder than it sounds as chemical repellants and insecticides are usually harmful to your rabbit. You can try fly paper or fly traps, mosquito netting or even bug zappers but you are unlikely to completely rid your rabbit’s environment of flies.
“Rearguard” – this is a medication that a vet can prescribe to help prevent flystrike. It lasts approximately 10 weeks and is applied to the rabbit's hind quarters in liquid form.

Be vigilant – check your bunny twice daily between April and October and be sure to remove soiled fur and faeces immediately. If your rabbit displays any signs of listlessness, lack of energy, seizure or stupor then check them over for signs of flystrike and consult a vet.

The information contained in this article is represented in this rather chilling video,
produced for the Happy Hoppers You Tube channel

References

Marinell Harriman ‘Fly Strike’ http://www.rabbit.org/journal/2-12/fly-strike.html

Galen’s Garden (2006) ‘Fly strike (myiasis)’ http://www.galensgarden.co.uk/herbivores/health/flystrike.php

[size=9]MU College of Veterinary Medicine (2002) ‘Dermatologic Diseases’ http://www.radil.missouri.edu/info/dora/RABBPAGE/derm.html

Joy Gioia ‘Fly Strike Emergency’ http://www.rabbit.org/journal/4-3/maggots.html

“Charky & Ash” (2005) ‘Rabbit References’ http://homepage.mac.com/mattocks/morfz/rabrefs.html[color=black]

Wright & Morten Veterinary Surgeons 'New Products' http://www.maccvets.co.uk/new_products/main.htm#Rear%20Guard

This Document is Copyright © Helen Coulson, HappyHoppers Forums Uk. June 2008.UK. ALL RIGHTS RESERVED.