The summer months are when rabbits are most at risk, especially when it’s warm and humid. These conditions are perfect for the green bottle flies (Lucilia sericata), responsible for laying the tiny eggs which develop into larvae. The flies are attracted to fur contaminated with urine and faeces, where they selectively lay their eggs. These eggs then develop into larvae and maggots, which are themselves attracted to the warm skin and underlying tissues. Most blowfly larvae tend to feed on dead tissue, though some blowflies, including the Lucilia species, are capable of initiating fly strike.
A retrospective study of the electronic health records of veterinary practices in the UK found some important information relating to myiasis;
- Check under the tail - the recorded blowfly strike lesions were overwhelmingly in the perineal area, with over 50% of cases being found in this region.
- Almost half put to sleep - of all cases being recorded as having myiasis, just under half of them (44.7%) were put to sleep or died.
- Unneutered potential – there were more than 3 times as many entire female rabbits recorded with flystrike than neutered females.
- Old age - rabbits aged five years or more were almost 4 times more likely to present with fly strike than younger animals.
- High environmental temperatures - for every 1 °C rise in temperature between 5°C and 18°C, there was a 33% increase in the risk of fly strike.
- Late summer risk – myiasis cases peaked in July and August.
- Location matters - blowfly strike cases started earlier and peaked higher in the south of Great Britain than further north.
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 more flies.
- Overweight or obese pets - rabbits that are unable to clean themselves properly or feed on the normal caecotrophs will be more susceptible. In particular, faecal material may accumulate around the tail base and perineum, providing a strong focus for flies.
- Animals in pain – if a rabbit has pain associated with dental disease, gut stasis or arthritis, it will be less inclined to groom, clean and behave normally. Caecotrophs won’t be eaten and will build up as a smelly, sticky mess under the tail.
- Bladder disease – any animal with bladder stones, sludge or cystitis will end up dribbling urine that will attract the egg-laying flies. Urine scalding may develop on the perineal skin, medial thighs and ventral abdomen, providing a meal for the larvae.
- 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 is at considerable risk.
- Respiratory infections – be vigilant if the rabbit has a chronic purulent nasal or ocular discharge, all of which will appeal to flies.
Differentiating between the 4 stages of myiasis
Stage 1 - fly eggs will have been laid but won’t have hatched and will appear in clumps on the fur. At this stage, rabbits may present with symptoms of an underlying predisposing condition such as dental, respiratory or gastrointestinal disease.
Stage 2 - eggs can hatch within 18 hours, with second stage larvae appearing less than 36 hours later. It’s for this reason that myiasis can progress very quickly and needs to be dealt with urgently. Owners must be advised to be vigilant at all times. First stage maggots measure a few millimetres in length and may be difficult to see.
Stage 3 - As the condition progresses, second and third stage larvae may be present and associated with considerable soft tissue damage and necrosis, the degree of damage being related to the numbers of maggots and their rate of development. Ensure a detailed examination of the tail fold and inguinal glands is made, as these are areas that are often attacked. At this stage the rabbits will be depressed and may show a range of clinical signs, including;
- 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
- Anorexia – most rabbits at this stage will stop eating
Stage 4 - advanced cases where large numbers of second and third stage larvae have attacked the deeper tissues carry a poor prognosis. Euthanasia is often the only viable option.
Managing and treating myiasis – our top tips
- Fluid therapy – this is essential if the rabbit is depressed or dehydrated. Shock fluid rates may be used initially. Subsequent rates will depend on the extent of any dehydration and ongoing fluid losses, which may be significant if large areas are affected. Once immediate life-threatening fluid deficits are replaced, provide additional fluid based on estimated percentage of dehydration and maintenance needs.
- Analgesia - the wounds will be extremely sore and usually become infected. Pain is managed using analgesics such as opiates (buprenorphine, butorphanol) and NSAIDs (meloxicam and carprofen). Failure to treat the pain will put the patient at risk from stress related complications.
- Antibiotics - secondary anaerobic infections can be treated with penicillin. Enrofloxacin and trimethoprim combinations are frequently used to treat general infections, however it’s important to always follow the cascade and choose your antibiotics wisely.
- 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. Second and third stage larvae are considered to be the most damaging and their removal should be prioritised. This requires a thorough approach and is best performed under anaesthesia or heavy sedation. Where possible, eggs and first stage larvae should also be removed to prevent the development of more second and third stage larvae. Eggs are best removed using a flea comb.
- Avoid hypothermia - try not to wet the rabbit’s coat excessively when removing the larvae so as to avoid causing hypothermia. After washing the fur, dry the area using clean soft dry towels and careful use of a hairdryer. Heat from the hairdryer tends to attract maggots and will aid their removal. Drying is also indicated to eliminate excess humidity, a factor which promotes egg and larval development.
- 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). Ivermectin or Imidacloprid are both effective. It’s most important that you don’t use Fipronil as this is potentially lethal to rabbits. See our article on Fipronil toxicity in rabbits >.
- Wound management – open wounds can become contaminated and infected. Healing will be delayed and can result in life threatening complications unless managed carefully. They’ll need to be cleaned, debrided and have appropriate dressings applied to ensure a speedy recovery.
- Nutritional support – for any animal to recover from significant tissue damage, good nutrition is essential. Some animals will be so weak at first that they require help with feeding. Our Excel Dualcare Recovery diet is perfect in this situation. It’s a specially formulated diet which when mixed with water, can be easily syringe fed at times of stress and recovery. It contains long chain fibre, pre-biotics, methionine, tryptophan and Vitamin C – all essential when looking for nutritional and GIT support.
- Investigate the cause - ultimately the underlying reason the animal has become flyblown needs to be found and treated. 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.
Stop myiasis - 10 ways to prevent a problem
Remove soiled bedding – this will reduce the smells and levels of ammonia and so won’t attract flies.
Feed a high fibre diet – always provide lots of good quality feeding hay and limited access to concentrates, and never feed muesli style diets. At Burgess Pet Care we have a range of quality high fibre hay products. See our range here.
Short hair - keep the hair around and under the tail short and clean.
Fly traps – sticky fly traps can be very effective, but ensure they’re placed correctly out of reach of the rabbit.
Screens on doors and windows - these can reduce the number of flies that get into the house.
Apply Rearguard – this product contains Cyromazine, an insect growth regulator, which prevents myiasis through its action on the first larval stage. It can be applied to fur surrounding a wound to prevent the development of first stage larvae. Rabbits should be first treated in early summer before any flies are seen and thereafter at 8-10 week intervals. It’s important to note that it won’t repel flies or kill adult maggots but works by preventing fly eggs from developing.
Health checks – all rabbits suffering from medical conditions likely to result in faecal or urine contamination of the skin should be checked by a vet regularly, and if possible, the underling cause of its problems should be addressed.
Good housekeeping – make sure the rabbit lives in a clean hygienic environment.
Daily inspection – ask the owner to check their pet daily, particularly the perianal region and especially if they are obese, disabled or generally unwell.
Grooming - fur should be combed with a fine-tooth comb to help detect eggs or larvae.