Flies are not just a buzzy pest….they can cause serious damage to your bunnies!
Fly strike is also known as Myiasis and is defined as “the presence of larvae of dipterous flies in tissues and organs of the living animal, and the tissue destruction and disorders resulting there from” (Boden, 2001). All very scientific…but basically, flies can lay eggs on bunnies and these quickly hatch out into maggots which eat the bunnies skin and organs 🙁
Initially, rabbits can hide fly strike quite well as the eggs and maggots are usually buried deep in the fur. “Bluebottles (Calliphora) and greenbottles (Lucilla) are attracted to soiled fur or infected skin to lay their eggs” (Harcourt Brown, 2002). The most common site for this to happen is around the rabbit’s anus and scent glands. A rabbit that is overweight, unwell or suffers from joint problems will struggle to keep this area clean. This can then lead to the fur being matted with urine and faeces, which attracts the flies. The eggs that are laid will hatch into larvae (maggots) in approximately 12 hours and will start feeding on external debris. Once this has been consumed, the maggots will continue to eat sound skin and tissue, often tunnelling under the skin layers. Aberrant migration brings the maggots deep under the rabbit’s skin, infiltrating vital organs and can even occlude the rabbit’s airway. This is very uncomfortable for the rabbit and will progressively get more painful as the condition progresses. Initially the rabbit will be very restless, however as time goes on it will become unwell, inappetent and lethargic.
The combination of the sore skin and the maggots creates a very pungent ammonia smell. This is because the maggots release proteolytic enzymes into the tissues to cause cell death and decomposition. These toxins can cause serious shock, septicaemia and if left untreated, will often be fatal.
For treatment to be successful, the rabbit needs to be seen by a Veterinarian as soon as possible. Depending on the severity of the case, the rabbit may have to be hospitalised for intensive therapy and monitoring for a few days. Rapid removal of the eggs and maggots is imperative to stop any further damage. This can be done by shaving the fur off the affected areas and then carefully using forceps to remove the contamination. This can be very time consuming and will need to be repeated a few times to ensure all of the eggs and maggots have been removed. The skin needs to be flushed and cleaned with a sterile saline solution and an antiseptic solution (such as povodine-iodine) and any wounds will need flushing and exploring to make sure that they are also clear of contamination. Non-steroidal pain relief and fluid therapy are vital to help the rabbit combat shock. Not all patients will be well enough to endure a sedation or anaesthetic at this point so care needs to be taken and close monitoring performed. The rabbit will need to be dried well and placed in a clean, warm and quiet area. Sometimes the use of topical creams like Dermasol (by Pfizer) is advised as it promotes healing of areas impaired by the presence of necrotic tissue because it activates the sloughing of devitalised tissue. Intensive nursing will also be vital to the success of the treatment. The rabbit will need regular syringe feeding, medicating and cleaning along with trying to keep its environment warm and as stress free as possible. F10 wound spray with insecticide can be used on the area – helping the wound and protecting from further fly problems too. This can be used daily and is good for disabled rabbits that need daily clean ups (thus washing off any Rearguard etc).
If there is a heavy maggot burden, injections of Ivermectin can be given to kill the maggots but the patient must be very closely monitored as the dying larvae excrete toxins that can be fatal. The final treatment option is surgery for when the maggots have migrated far under the skin. However, such a heavy burden does not have a good prognosis and often euthanasia is the kindest option for severe cases.
WARNING! F10 wound spray is TOXIC to cats. Do NOT use on cats or in households where cats and rabbits have direct contact.
As always, prevention is better than cure and there are a number of things that owners can do to help reduce the risks. Owner awareness of fly strike is vital and they must be able to recognize the signs and know that this is an emergency that needs Veterinary attention as soon as possible.
In general, it is very important that the rabbit is kept in good physical condition. This means that it is fed a balanced diet consisting mainly of good quality hays with a small amount of commercial rabbit pellet and fresh vegetables and herbs. By feeding the correct diet, it reduces the risk of the rabbit becoming overweight and also reduces the risk of over producing caecotrophs which get stuck around the anus. Rabbits that are very young, very old or have health problems such as dental, gut or paralysis issues are more susceptible to fly strike.
Next, it is important that the rabbit is kept in clean, spacious living conditions. Any build up of urine or faeces will attract flies. The rabbit should also have plenty of space to move around and exercise away from its toileting area and uneaten fresh vegetables etc should be removed daily. If housed outdoors, mosquito netting can be used over the hutch and run areas to help reduce the amount of flies that can enter the area. It can also be attached to windows / door areas too. Sticky fly paper can be used outside the hutch but never in an area that the rabbit has access to as it can stick to them and cause terrible damage. If the rabbit is housed indoors, an electric insect killer can be used in the same room as the rabbit is housed and net curtains can be used in the windows to reduce the amount of flies entering the room.
Lastly, a topical treatment can be applied to the rabbit to help prevent fly strike. F10 wound spray with insecticide and Rearguard are examples of these topical treatments. F10 wound spray needs to be applied weekly to the rump and genital area. It is TOXIC to cats so don’t use on cats or in households where the cats and rabbits interact.
The main ingredient in Rearguard is Cyromazine (an insect growth regulator). It is recommended by many Veterinary practices and is widely available in pet shops and online. It should be applied at the start of summer before any flies are seen and gives approximately 8-10 weeks of protection. This product does not repel flies or kill maggots but works by preventing any eggs laid on the rabbit from hatching into maggots. Rearguard can also be applied on rabbits that have been successfully treated for fly strike to help prevent re-occurrence.
The bottle comes with a sponge applicator but I find this often has a sharp spike in the middle. So I wear a pair of disposable latex / nylon gloves and apply the liquid to my hands. I then rub this into the rabbits fur from the middle of the back to the tail and the same on the underside. Its important to get the fur quite wet and apply well around the back legs and genitals.
DO NOT APPLY TO SORE OR BROKEN SKIN.
The bottle says to use the whole bottle per rabbit but I have found that you can often get 2-3 applications out of one bottle for small / medium bunnies. As long as the target area is covered and the fur quite wet then this should be fine.
Re-apply every 8-10 weeks.
See here for more info (WARNING! some contain graphic images):