Flystrike In Rabbits
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).
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. It is routine to hospitalise the rabbit for intensive therapy and monitoring for a few days. Rapid removal of the eggs and maggots is imperative to stop any further damage and this requires sedation / anaesthesia. If the larvae have migrated far under the skin, then surgery is needed to explore and remedy this. However, such a heavy burden does not have a good prognosis and often euthanasia is the kindest option for severe cases.
The fur will need to be shaved off of the affected areas and then use forceps to carefully remove the larvae and a flea comb can be used to remove unhatched eggs. 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. Multi modal pain relief and fluid therapy are vital to help the rabbit combat shock. You will also need to assess the rabbit’s nutritional status as often these patients have not eaten for a few days. If the rabbit is too unwell to be syringe fed, then place a naso-gastric feeding tube and use an easy to feed solution such as Emeraid by Lafeber.
Once complete, the rabbit will need to be dried well and placed in a clean, warm and quiet area. It is recommended to use a hairdryer on a low heat setting to dry the fur (but be very careful not to burn the skin or over heat the rabbit). This drying action reduces humidity which results in a reduced ability of any remaining eggs and larvae to develop further.
Once clean, F10 Wound Spray with Insecticide / F10 Wound Cream with Insecticide can be used on the skin to treat mild to moderate cases. Sometimes the use of topical creams like Dermisol (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. More severe cases will need more intensive treatment. Intensive nursing will also be vital to the success of the case. The rabbit will need regular syringe feeding, medicating and cleaning along with trying to keep its environment warm and as stress free as possible.
It is very important to kill or halt the growth of any eggs and larvae that may still be on the rabbit. There are licensed topical products that can be used (Xenex Ultra by Gentrix etc) however, injections of ivermectin work very well. Regardless of what is used, the patient must be very closely monitored as the dying larvae excrete toxins that can be fatal.
It is vital that the underlying condition is also treated once the rabbit has stabilised and recovered otherwise there is the risk of relapse of the myiasis. Assess the rabbit for obesity, arthritis, dental disease, renal problems etc and treat as needed.
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 recognise 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 flystrike.
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 number of flies that can enter the area. 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 number of flies entering the room.
Lastly, a topical treatment can be applied to the rabbit to help prevent fly strike. Rearguard (Novartis) is an example of one of these topical treatments. The main ingredient 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 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. However, this product should not be used on sore or broken skin, so it would be better to use the F10 Wound Spray with Insecticide on a weekly basis for these cases.