Myiasis (with special reference to Waterfowl, Hedgehogs, Elephants, Bears, Lagomorphs and Ferrets)

Hedgehog photos:

Lagomorph photos: 

Video Clip: Myiasis

Disease Summary

Alternative Names (Synonyms)

• Blowfly strike
• Fly larvae infestation
• Maggot infestation
• Flystrike

See also: 

• Bots (Gastric Myiasis) in Elephants
• Elephant Foot Fly Infection
• Old World Screw-worms in Elephants
• Skin Warbles in Elephants
• Cuterebra (Warble) Infection in Lagomorphs (with notes on Ferrets)
• Hypoderma bovis (Warble) Infection in Ferrets

Disease Type

Infectious/Non-Infectious Agent associated with the Disease

• Flesh fly Wohlfahrtia opaca, black blowfly Phormia regina
• Calliphorid flies (Bluebottles, screw-worms etc.) which lay eggs on wounds, infected skin or skin dampened or soiled with normal discharges or faeces (B46, B208.2.w2)
• Lucilia spp. (J15.21.w1, B224, B228.9.w9, B291.12.w12); Lucilia sericata in wounds of two hedgehogs in Austria. (J192.71.w1)
• Calliphora spp. (J15.21.w1)
• Sarcophagidae blowflies: Calliphora vicina R.D and Lucilia illustris (Mg.) as causes of primary myiasis, also Lucilia ampullacae, Lucilia caesar and Sarcophaga melanura. (J158.46.w1)
• Hemipyrellia fernandica in Kenya and South Africa. (J157.82.w1)
• In a Ursus arctos - Brown bear in a zoo in New Mexico, the larvae were not identified but the possibility of Callitroga hominovorax (true screw-worm) was suggested. (J196.54.w1)
• Cochliomyia hominivorax (screwworm) was reported in one Ursus americanus - American black bear in Marion County in Florida, USA, but the fly was eradicated from Florida in the late 1950s/early 1960s. (B419.14.w14)
• Blowflies
  • Most blowflies (e.g. Lucilia, Calliphora, Phormia and Protophormia species) will usually feed on dead tissue or decaying matter.
  • The majority of parasitic blowflies are actually facultative parasites and are able to complete their life cycle on dead tissue, other organic matter, and living tissue. 
  • Some blowflies, including the Lucilia species, are able to initiate fly strike and are therefore described as primary flies. Secondary flies, however, cannot initiate myiasis, but attack areas that are already struck or otherwise damaged. 
  • Many flies are attracted to soiled skin and fur. "Activation, upwind orientation and landing appear to occur in response to putrefactive sulphur-rich volatiles originating from the products of bacterial decomposition. Oviposition is elicited primarily by the presence of ammonia-rich compounds, although moisture, pheromones and tactile stimuli are also reported to be attractive". 

  (J15.28.w2) 

In Lagomorphs

In rabbits (Leporidae (Family))

• In the UK
  • Lucilia spp. including Lucilia sericata. This greenbottle fly is reportedly the main cause of flystrike in rabbits. (B600.9.w9, B601.13.w13, B610.23.w23, J15.28.w2)
  • Calliphora spp. The bluebottle fly is also responsible for flystrike. (B600.9.w9, J15.28.w2)
  • Flies don't usually attack normal rabbit skin instead they lay their eggs on skin/fur that is soiled, damp and inflamed. (B600.9.w9, B603.4.w4)
• In North America
  • Wohlfahrtia vigil:
    • Also known as the flesh fly, this is common in the USA. (B602.19.w19, B610.23.w23, P62.7.w1)
    • This is the most common cause of flystrike in rabbits. (B601.13.w13, B610.23.w23, J213.4.w4)

Other species of flies reported to cause myiasis in rabbits:

• In Sylvilagus floridanus - Eastern cottontail:
  • Cochliomyia hominivorax
  • Cochliomyia macellaria 

(P62.7.w1)

• In Texas jack-rabbit Lepus californicus texianus (Lepus californicus - Black-tailed jackrabbit) has been reported to be affected by:
  • Cochliomyia hominivorax
  • Cochliomyia macellaria

  • Lucilia sp.

  • Lucilia coeruleivirdis

  • Synthesiomyia nudiseta

  • Blaesoxipha plinthopyga

  • Sarcophaga sulcata

  • Sarcophaga sp. 

(P62.7.w1)

In pikas (Ochotona - (Genus))

• Cuterebra spp. has been found in Ochotona princeps - American pika. (J1.15.w13)
  • Species unknown but the Cuterebra larvae that were found were thought to be rodent bot fly larvae because they had multiple-pointed spines rather than the single pointed spines of rabbit bot fly larvae. The posterior spiracular arrangement and cuticular spine structure of the larvae were similar to larvae of Chipmunks that were in the same area. The American pika was not thought to be the normal host of this species of Cuterebra. (J1.15.w13)
    
• Oestromyia spp.
  • Oestromyia leporina: Ochotona alpina, and Ochotona dauurica. 
  • Oestromyia prodigiosa: Ochotona pallasi and Ochotona dauurica in central Asia. 
• Oestroderma spp. 
• Portschinskia spp. 

(B208.3.w3, B336.42.w42)

In hares (Leporidae (Family))

• Cynomya mortuorum (P62.7.w1)

In Ferrets

• Ferrets (Mustela putorius furo - Ferret) have been commonly infected by Wohlfahrtia vigil. (B602.10.w10, B631.24.w24) 
  • Otherwise known as flesh fly. (P20.1992.w7)
  • This is a larviparous species. (B24)

Further information on Disease Agents has only been incorporated for agents recorded in species for which a full Wildpro "Health and Management" module has been completed (i.e. for which a comprehensive literature review has been undertaken). Only those agents with further information available are linked below:

Infective "Taxa"

• Wohlfahrtia opaca
• Wohlfahrtia vigil (Wohlfahrtia sp.)
• Phormia regina
• Calliphoridae - (Family)
• Sarcophagida - (Family)

Non-infective agents

Physical agents

References

Disease Author

Referees

Major References / Reviews

Code and Title List

• B11.3.w10, B15, B32.32.w12, P4.1992.w1.
• B208.2.w2, J15.21.w1, B212.w26, B224, B228.9.w9, B228.11.w11, B259.w7, B291.12.w12, B337.3.w3

Lagomorphs:

• B187.20.w20, B208.3.w3, B272.11.w11, B284.10.w10, B336.42.w42, B600.4.w4, B600.9.w9, B601.13.w13, B602.19.w19, B603.4.w4, B604.5.w5, B606.4.w4, B608.21.w21, B610.23.w23, B614.11.w11, B615.6.w6
• J15.28.w2, J29.5.w1, J213.4.w4, J213.7.w2, J513.4.w1
• P62.7.w1

Ferrets:

• B232.10.w10, B602.10.w10, B627.16.w16, B631.24.w24
• J213.12.w2
• P20.1992.w7

Other References

Code and Title List

Bears:
B419.14.w14, J196.54.w1

Ferrets:
B629.13.w13

Detailed Clinical and Pathological Characteristics

General

• Larvae may infest wounds, weeping skin or normal orifices (eyes, nose, ears, anus, vulva, prepuce) (B208.2.w2, J15.21.w1, B224, B228.9.w9)

• Larvae may infest wounds or 'weeping' skin and move into living flesh; larvae may also enter newly-hatched downies at umbilicus or even through the cracked eggshell during hatching (B15, B32.32.w12, P4.1992.w1).

• Larvae may be found in body orifices or associated with wounds. (J15.21.w1, J192.71.w1, B156.7.w7, B228.9.w9, B259.w7, B291.12.w12)

• Larvae may be found in neglected wounds of Elephas maximus - Asian Elephant. (B212.w26)

• Larvae on wounds. (J196.54.w1)

• Lucilia spp.
  • This type of flystrike is frequently primary (i.e. intact skin).
  • Flies are attracted by the accumulation of caecotrophs around the perineum particularly the folds each side of the genitals.
• Wohlfahrtia vigil
  • Eggs are laid at the edges of wounds. 

(B601.13.w13, B610.23.w23)

• Wohlfahrtia vigil can infect young kits and adults around their face and neck. (B602.10.w10, B627.16.w16)
  • The flies may lay their larvae in wounds or the surface of the ferret's skin. (J213.12.w2)

Clinical Characteristics

• Fly eggs/maggots visible in the tissue of a living animal; usually associated with wounds or with normal body orifices in a debilitated animal. (B224, B208.2.w2)

• Maggots in tissues of a living bird, often associated with open wounds or weeping skin (B15, B32.32.w12, P4.1992.w1).

• Maggots or eggs of blowflies may be found in and around normal orifices (eyes, nostrils, mouth, ears, anus, vagina, prepuce), wounds, infected areas of skin or damp areas of skin e.g. skin folds of the axilla).
  • May cause direct damage to superficial and deeper tissues and may also lead to secondary infection..
  • Severe infestation, involving deep tissues, may be fatal or require euthanasia on welfare grounds.

(J158.46.w1,V.w44, J15.21.w1, J192.71.w1, B156.7.w7, B228.9.w9, B259.w7, B291.12.w12)

• Maggots may be found in neglected skin wounds of Elephas maximus - Asian Elephant. (B212.w26)
  • There is often a thin, offensive discharge and a fetid odour associated with the infected wound. (B212.w26)

• Hundreds of maggots were seen infesting a raw open fight wound (about 15 cm long by 10 cm wide) on the nape of an adult grizzly bear (Ursus arctos - Brown bear) in a zoo in New Mexico. (J196.54.w1)
• Recurrent infestation with fly larvae in chronic foot lesions in an Ursus maritimus - Polar bear.(P1.1979.w3)

Blow fly infestation

• Pathogenesis
  • Flies lay eggs on contaminated or inflamed rabbit skin. When the eggs hatch out, maggots may be concealed by soiled, matted fur and may not be particularly obvious until the rabbit becomes unwell. (B600.9.w9)
  • Each female Lucilia sericata can deposit around 200 eggs in one batch. (J15.28.w2)

  • Maggots may cause extensive lesions by feeding on the dead tissue of their host. Lucilia sericata larvae can penetrate through epidermal and dermal layers of the rabbit's skin due to the effects of the proteolytic enzymes that they excrete. The resultant enzymatic "burns" may be very extensive. (J15.28.w2)

  • Preexisting wounds are not needed for maggot infection. (B602.19.w19) See the susceptibility section. 
• Clinical examination findings
  • Signs first become apparent four days after the eggs hatch and they are dependent on:
    • Number of maggots present; (B610.23.w23) 
      • Hundreds of larvae can colonise a single skin area. (B602.19.w19)
    • Time of year of infestation. (B610.23.w23)
  • Depression, lethargy, anorexia, weight loss, dehydration. (J15.28.w2)
  • Presence of eggs and larvae (J15.28.w2)
  • Moist dermatitis which exudes a characteristic fetid smell. (B600.9.w9, B602.19.w19, B608.21.w21)
  • Perineal soiling (J15.28.w2)
  • Fur matting (B602.19.w19, B608.21.w21)
  • Hair loss (J15.28.w2)
  • Erosion of the skin (B610.23.w23, J15.28.w2)
  • Ulcers (B610.23.w23)
  • Extensive tissue damage (B610.23.w23)
  • The maggots are thought to secrete a local anaesthetic and so the tissue damage is rarely observed to be causing pain to the rabbit. (B601.13.w13, B610.23.w23)
  • Death may occur if there is an overwhelming number of maggots and the patient has gone into shock. (B604.5.w5)
    
• Distribution of lesions
  • Primarily the perineal region is affected. (B601.13.w13, B602.19.w19, B603.4.w4, B608.21.w21, B610.23.w23, J513.4.w1)
    • particularly the folds each side of the genitals. (B601.13.w13, B610.23.w23, J513.4.w1)
  • The area between the tail and the dorsum, at the base of the spine, is the commonest area for flystrike in the rabbit. It is a difficult area to groom particularly if the rabbit is obese or has back problems. (B600.9.w9)
    • This is a common area. (J513.4.w1)
  • The lesions may spread dorsally over the rump. (B602.19.w19, B608.21.w21)
  • Face. (B602.19.w19)

Wohlfahrtia vigil

• The larvae of this species are subcutaneous parasites of young, healthy mammals. These hosts have skin that is soft and thin enough to allow larval penetration. Older animals are rarely affected unless they are debilitated due to disease or injury. (P62.7.w1)
• "Female flies larviposit live maggots on unbroken skin which then burrow through the skin into subcutaneous tissues for feeding. Often, a boil-like lesion (2-4 mm) with a small opening develops at the point of entry in the skin. Each lesion may contain 1-5 larvae, with up to 40 larvae found in a single animal". (P62.7.w1)
• The hair around the opening of the maggot entry may be moist and matted from exudation or their may be erection of the hair due to swelling of the site. (P62.7.w1)
• Larvae will remain in the host for seven to fourteen days before leaving to pupate. 
• Larva liquefy and ingest tissues and this results in extensive lesions. (J213.4.w4)
• A characteristic matting of the fur occurs where the larvae penetrate the host. (J1.6.w7)
• The host may experience intense pain and irritation caused by the penetration and feeding of the maggots. (P62.7.w1)
• Infested young may stop nursing and have a slightly raised temperature. They can become emaciated and secondary bacterial infection may occur in the lesions. (P62.7.w1)

• Parasitized nestling cottontail rabbits Sylvilagus floridanus mearnsii (Sylvilagus floridanus - Eastern cottontail) lost weight and became emaciated despite continuing to nurse; infection can be fatal. (J1.6.w7)

• Distribution of lesions:
  • Face, neck, axillary, flank and perineal regions. (J213.4.w4, P62.7.w1)
  • Lesions occured on the head, back, flank and paws. (J1.6.w7)

• Flystrike has been seen in ferrets. (B602.10.w10, B631.24.w24)

Distribution of lesions:

• Mink kits Mustela vison and ferrets become infected on their face, neck or flanks. (B602.10.w10, B627.16.w16)
• In ferrets, larvae are commonly found down their back, axillary, cervical and inguinal region. (J213.12.w2)

Clinical examination

• Abscess lesions, 6 to 20 mm in diameter. (B602.10.w10, B627.16.w16, P20.1992.w7)
  • Lesions are generally 1 to 3 cm in diameter. (J213.12.w2)
• The kits may be restless. (B627.16.w16, P20.1992.w7)
• Reduced appetite. (B627.16.w16)
• The kits may whimper. (B627.16.w16)

Incubation

Lagomorphs

• Eggs may hatch into L1 maggots within twelve hours. 
• The maggots that cause the extensive tissue damage are L2 and L3 maggots that will appear within 3 days when the L1 larvae moult. 
• The larvae require conditions of at least 60% humidity and a temperature of 9-11ºC to be able to develop.

(B601.13.w13, B610.23.w23)

• During a warm summer (temperature of 27°C): eggs will hatch out within eighteen hours; L1 maggots will spend twenty hours before becoming L2 maggots and then it takes a further twelve hours before L3 (mature maggots) occur. 
• In colder weather (temperature of 16°C): eggs will hatch within 41 hours.

(J15.28.w2)

Mortality / Morbidity

• Deaths in newly-hatched ducklings reported. (B15)

• Maggots and eggs are commonly found on e.g. casualty animals and orphaned animals in warm weather.
• Mortality associated with myiasis in hedgehogs has been reported, also severe infection may require euthanasia on welfare grounds.
• (B208.2.w2, J15.21.w1, B224, B228.9.w9, B259.w7, V.w44)

• Wohlfahrtia maggot invasion can be fatal in cottontails in three days. (B272.11.w11, J1.6.w7)

Morbidity

• Ferrets are rarely affected. (J213.12.w2)

Mortality

• Early diagnosis and treatment will increase the survival rate. (P20.1992.w7)
• Mothers will often move the infected kits from the nest, which results in death. (B627.16.w16, P20.1992.w7)

Pathology

• Fly larvae (maggots) in subcutis area (under skin), and deeper into tissues, or in wounds (P4.1992.w1, B15).
• Large amounts of soft tissue may be consumed in a few hours (B11.3.w10)

Wohlfahrtia vigil

Gross pathology

• Subcutaneous lesions varying from a raised abscess at the larval penetration site to separation of large areas of skin from the underlying muscle. (J1.6.w7)

Histopathology

• Areas of necrosis, containing cellular debris, red blood cells, macrophages and eosinophils adjacent to the larval paths. Often haemorrhagic and eosinophilic infiltration between muscle fibres. Beneath the necrotic areas, proliferating fibroblasts. (J1.6.w7)

Human Health Considerations

Disease / Agent has been reported in either the wild or in captivity in:

• Any mammal or bird which is debilitated or has damage to the skin is susceptible to flystrike - Myiasis.
• Newly-hatched Northern shoveler Anas clypeata and blue-winged teal Anas discors ducklings; attacked by Flesh fly Wohlfahrtia opaca (B15).
• Geese (wound infection with Phormia regina, black blowfly)(B32.32.w12).

In Hedgehogs:

• In 18 hoglets about 8-14 days old, two older juveniles and one adult (caught in a wire fence) hedgehog Erinaceus europaeus in Denmark, mid-August to early September 1977 in Denmark. (J158.46.w1)
• Common in hedgehogs in the UK. (B228.9.w9)
• Occasionally found on young and sick hedgehogs. (B214.3.26.w11)
• Juvenile hedgehogs Erinaceus europaeus found by members of the public abandoned/accidentally separated from their mother and which did not survive. (J180.26.w1)
• In juveniles and adult: in wounds and in body orifices (mouth, nose, ears), requiring euthanasia in severe cases. (V.w44)
• Lucilia sericata in wounds of two hedgehogs in Austria. (J192.71.w1)
• In hedgehogs with wounds, also in hoglets without obvious injuries. (B259.w7)

In Elephants:

• Occurs in Elephas maximus - Asian Elephant in Asia. (B212.w26)

In Bears:

• Cochliomyia hominivorax (screwworm) was reported in one Ursus americanus - American black bear in Marion County in Florida, USA, but the fly was eradicated from Florida in the late 1950s/early 1960s. (B419.14.w14)
• Unidentified fly larvae, possibly Callitroga hominovorax (true screw-worm) were found on a Ursus arctos - Brown bear in a zoo in New Mexico. (J196.54.w1)

In Lagomorphs

• Lepus californicus texianus Texas jack-rabbit (Lepus californicus - Black-tailed jackrabbit) has been reported to be affected by Cochliomyia hominivorax , Cochliomyia macellaria, Lucilia sp., Lucilia coeruleivirdis, Synthesiomyia nudiseta, Blaesoxipha plinthopyga, Sarcophaga sulcata and Sarcophaga sp. (P62.7.w1)

• Wohlfahtia vigil parasitize nestling cottontail rabbits Sylvilagus floridanus mearnsii (Sylvilagus floridanus - Eastern cottontail). (J1.6.w7)

• Myiasis is common in domestic rabbits. (J15.28.w2)
• Note: rare in wild rabbits in the UK; may be seen secondary to traumatic injuries or Myxomatosis. (V.w121)

In Ferrets

• Wohlfahrita vigil has been reported in farmed ferrets and mink Mustela vison. (B602.10.w10, B631.24.w24)

Further information on Host species has only been incorporated for species groups for which a full Wildpro "Health and Management" module has been completed (i.e. for which a comprehensive literature review has been undertaken). Host species with further information available are listed below:

 Host Species List

• Anas clypeata - Northern shoveler
• Anas discors - Blue-winged teal
• Anser anser domesticus - Domestic goose

MAMMALS:

• Bears (Ursidae - Bears (Family))
• Elephants (Elephantidae - Elephants (Family))
• Elephas maximus - Asian Elephant
• Erinaceus europaeus - West European Hedgehog
• Ursus americanus - American black bear
• Ursus arctos - Brown bear
• Mustela putorius furo - Ferret

(List does not contain all other species groups affected by this disease)

Disease / Agent has been specifically reported in Free-ranging populations of:

• Any mammal or bird which is debilitated or has damage to the skin is susceptible to flystrike - Myiasis.
• Newly-hatched Northern shoveler Anas clypeata and blue-winged teal Anas discors ducklings; attacked by Flesh fly Wohlfahrtia opaca (B15).

In Hedgehogs:

• In 18 hoglets about 8-14 days old, two older juveniles and one adult (caught in a wire fence) hedgehog Erinaceus europaeus in Denmark, mid-August to early September 1977 in Denmark. (J158.46.w1)
• Common in hedgehogs in the UK. (B228.9.w9)
• Occasionally found on young and sick hedgehogs. (B214.3.26.w11)
• Juvenile hedgehogs Erinaceus europaeus found by members of the public abandoned/accidentally separated from their mother and which did not survive. (J180.26.w1)
• In juveniles and adult: in wounds and in body orifices (mouth, nose, ears), requiring euthanasia in severe cases. (V.w44)
• In hedgehogs with wounds, also in hoglets without obvious injuries. (B259.w7)

In Bears:

• Cochliomyia hominivorax (screwworm) was reported in one Ursus americanus - American black bear in Marion County in Florida, USA, but the fly was eradicated from Florida in the late 1950s/early 1960s. (B419.14.w14)

In Lagomorphs

• Lepus californicus texianus Texas jack-rabbit (Lepus californicus - Black-tailed jackrabbit) has been reported to be affected by:
  • Cochliomyia hominivorax
  • Cochliomyia macellaria

  • Lucilia sp.

  • Lucilia coeruleivirdis

  • Synthesiomyia nudiseta

  • Blaesoxipha plinthopyga

  • Sarcophaga sulcata

  • Sarcophaga sp. 

(P62.7.w1)

• Wohlfahtia vigil parasitize nestling cottontail rabbits Sylvilagus floridanus mearnsii (Sylvilagus floridanus - Eastern cottontail). (J1.6.w7)

• Note: rare in wild rabbits in the UK; may be seen secondary to traumatic injuries or Myxomatosis. (V.w121)

Further information on Host species has only been incorporated for species groups for which a full Wildpro "Health and Management" module has been completed (i.e. for which a comprehensive literature review has been undertaken). Host species with further information available are listed below:

Host Species List

• Anas clypeata - Northern shoveler
• Anas discors - Blue-winged teal

MAMMALS:

• Bears (Ursidae - Bears (Family))
• Erinaceus europaeus - West European Hedgehog
• Ursus americanus - American black bear

(List does not contain all other species groups affected by this disease)

General Information on Environmental Factors/Events and Seasonality

In hedgehogs:

• In summer. (V.w44)

In lagomorphs:

• Lucilia spp
  • In summer. (B601.13.w13, B610.23.w23, J15.28.w2)
  • The larvae of Lucilia spp. require conditions of at least 60% humidity and a temperature of 9-11 ºC to be able to develop. (B601.13.w13, B610.23.w23, J15.28.w2)
• Rabbits that are housed outdoors in warm weather may be affected by Lucilia spp. (B602.19.w19)
• Damp dirty bedding increases the risk of fly strike. (B600.9.w9)

In Ferrets:

• Mink kits Mustela vison and ferrets may become infected with Wohlfahrtia vigil - Flesh flies(Wohlfartia sp.) at four to five weeks of age, during the summer. (B602.10.w10, B627.16.w16)
• Ferrets kept outdoors are more likely to become infected. (J213.12.w2)

Regions / Countries where the Infectious Agent or Disease has been recorded

• In Erinaceus albiventris in Kenya and Erinaceus frontalis in Africa, with Hemipyrellia fernandica identified as the fly involved. (J157.82.w1)
• In Elephas maximus - Asian Elephant in Asia. (B212.w26)

Lagomorphs

• UK. Common in domestic rabbits. (J15.28.w2)
  • Note: rare in wild rabbits in the UK; may be seen secondary to traumatic injuries or Myxomatosis. (V.w121)
• North America
  • Not uncommon in domestic rabbits. (B187.20.w20)
  • Note: Cochliomyia hominivorax (screwworm) previously was an important parasite in Florida, USA but the fly was eradicated from the United States in the late 1950s/early 1960s by using irradiated male flies. (B419.14.w14, J213.4.w4)
• Asia. (J1.15.w13)

Ferrets

• Wohlfahrtia vigil (Wohlfahrtia sp.) is found in Canada and in the northern USA. (B24)

Regions / Countries where the Infectious Agent or Disease has been recorded in Free-ranging populations

• Rare in wild rabbits in the UK; may be seen secondary to traumatic injuries or Myxomatosis. (V.w121)
• Note: Cochliomyia hominivorax (screwworm) previously was an important parasite in Florida, USA but the fly was eradicated in the late 1950s/early 1960s. (B419.14.w14)

General Information on Investigation / Diagnosis

• Presence of larvae on the eyes, within natural orifices (ears, nose, mouth, anus, prepuce, vulva, cloaca) or on open wounds or within tissues. Check carefully using a good light source. (B15, B224, B291.12.w12).

Lagomorphs

• To detect early cases of myiasis a thorough examination is necessary, paying particular attention to the tail fold and the inguinal glands. (J15.28.w2)
• Diagnosis is based on the clinical signs. (B610.23.w23)
  • Lucilia spp: First stage maggots are only a few millimetres in length and can be difficult to see. In established cases of myiasis, second and third (mature) larvae will be present and there is likely to be considerable soft tissue damage. (J15.28.w2) These maggots are found more superficially than are Cuterebra larvae (Cuterebra (Warble) Infection in Lagomorphs). (B604.5.w5)
• Investigation of underlying causes (B603.4.w4) - see susceptibility section.

Ferrets

• Clinical examination will show lesions or abscesses around the neck or flanks. (B602.10.w10, J213.12.w2)

• Environmental Assessment
• History & Documentation
• Physical Examination of Mammals
• Physical Examination of Birds - General
• Necropsy of Mammals
• Necropsy of Birds - General
• Clinical Pathology of Lagomorphs
• Clinical Pathology of Ferrets
• Treatment and Care
• Environmental and Population Management
• Preventative Medicine for Mammals
• Chapter 2 - B36 Field Manual of Wildlife Diseases - Specimen Collection and Preservation
• Chapter 3 - B36 Field Manual of Wildlife Diseases - Specimen shipment
• Appendix A - B36 Field Manual of Wildlife Diseases - Sample specimen history form

Similar Diseases (Differential Diagnosis)

• If found on a carcass, must be distinguished from infestation by larvae after death. (V.w5)
• See also: 
  • Cuterebra (Warble) Infection in Lagomorphs (with notes on Ferrets)
  • Elephant Foot Fly Infection
  • Old World Screw-worms in Elephants
  • Hypoderma bovis (Warble) Infection in Ferrets

Specific Medical Treatment

• Direct application of an appropriate insecticide:
  • e.g. coumaphos (Negasunt, Bayer) (J15.21.w1, B259.w7)
  • Coumaphos (Negasunt, Bayer) may be used on adults. (B156.7.w7)
    • Negasunt may cause toxicity in hedgehogs. (B151)
  • Topical application of Ivermectin (Ivomec Injection for Cattle, Merial) diluted 1:9 with water just prior to use, up to (maximum) 1 mL of the mixture. (B151)
  • Fenthion (Tiguvon 10%, Bayer), applied at one drop per 100 g bodyweight to the back of the hedgehog has been found effective. (B291.12.w12)
  • For myiasis in the ears, one or two ear drops (GAC Ear Drops, Arnold's Veterinary Products) may be useful after physical removal of eggs and maggots in case any have been missed. (B151)
  • For the eyes, a chloramphenicol eye ointment may be applied following physical removal of eggs or recently-hatched maggots, to suffocate any which remain. (B151)
• Parenteral Ivermectin may be given in case one or two maggots have been missed during physical removal. (B151)
• Parenteral antibiotics (e.g. long-acting Amoxycillin) should be given to avoid secondary bacterial infection. (B151, B259.w7)
• Flunixin meglumine may be given to individuals from which large maggot burdens have been removed (analgesic, anti-inflammatory and anti-toxic). (B151)
• In an Ursus arctos - Brown bear, when circumstances did not allow restraint, an organophosphate insecticide in appropriate dilution was thrown over the wound on two successive days. This was apparently successful, with the wound closing and healing well. (J196.54.w1)

Treatment involves:

1. Intravenous fluid therapy.
2. Supportive nutritional care (see General Nursing & Surgical Techniques below).
3. Analgesia.
4. Antibiotics.
5. Removal of all the second and third stage of larvae (see General Nursing & Surgical Techniques below).
6. Removal of as many first stage larvae and eggs as possible (see General Nursing & Surgical Techniques below).
7. Treatment to kill, or inhibit the development of, any remaining larvae and eggs.
8. Wound management including debriding and dressing the wound (see General Nursing & Surgical Techniques below).
9. Identification and treatment of underlying causes.

"The majority of rabbits presenting with fly strike will be in a state of profound shock. Initial treatment must deal with this shock and provide appropriate analgesia to eliminate the pain that is likely to arise as a result of the considerable damage to the epidermal, dermal and subdermal tissues".

(J15.28.w2)

Supportive therapy for endotoxic shock in severe cases

Intravenous Fluid Therapy (B601.13.w13, B610.23.w23, B615.6.w6)

• To replace the losses that have occurred - extensive damage from flystrike is akin to thermal burns. (B603.4.w4)
• Sites: Cephalic or saphenous veins should be used for prolonged intravenous therapy because they are better tolerated than catheters that are placed in marginal ear veins. (J15.28.w2)
• Rates: 
  • Shock fluid rates up to 90 mL/kg/hour may be necessary initially. (J15.28.w2)
  • Subsequent rates depend on the extent of ongoing losses (may be significant is large areas of skin have been affected) and dehydration. (J15.28.w2)
  • Continuous infusion should be continued at 5 to 10 mL/kg/hour, using a small volume infuser or a syringe pump, until the patient is voluntarily drinking fluids. Continuous infusion of fluids is preferable to bolus injections in rabbits that are suffering from shock. However, bolus injections (up to one percent bodyweight) are well tolerated if they are given slowly in the sedated rabbit. (J15.28.w2)
• Intravenous Nutrition: "Duphalyte", Fort Dodge, is a useful addition to the fluid therapy in rabbits that have been ill and anorexic for a few days. (J15.28.w2)

Analgesia

• It is necessary to provide analgesia for this condition. (B602.19.w19)
• NSAIDs (B601.13.w13, B603.4.w4, B610.23.w23)
  • Carprofen (B602.19.w19)
    • 1 - 2 mg/kg by subcutaneous or intravenous injection every 24 hours. (J15.28.w2)
  • Meloxicam 0.2 - 0.3 mg/kg by intravenous or subcutaneous injection or orally every 12 to 24 hours. (J15.28.w2)
  • Flunixin meglumine
    • 1.1 mg/kg by intramuscular injection. (B606.4.w4)
    • 1.1 mg/kg by subcutaneous injection every twelve hours. (B600.4.w4)
    • This medication may also provide anti-endotoxic properties although the benefits of this have yet to be evaluated in rabbits. (J15.28.w2)
    • NOTE: use with care in dehydrated, hypotensive or shocked animals whose renal perfusion may be impaired. (B600.4.w4, V.w128)
• Opioid analgesia (B603.4.w4)
  • Buprenorphine 0.01 - 0.05 mg/kg by subcutaneous or intravenous injection every 6 to 8 hours. (J15.28.w2)

Antibiotics

• Lucilia sericata is a facultative feeder and therefore likely to spread environmental bacterial contaminants leading to a secondary bacterial infection of the necrotic tissue. (B601.13.w13, B610.23.w23, J15.28.w2)
• Clostridial secondary infection may be responsible for the death of those rabbits with extensive maggot infestation that initially appear stable after surgery but then deteriorate. (B602.19.w19, J15.28.w2)
• Treatment of secondary anaerobic bacterial infections:
  • Penicillin G procaine
    • 30000 to 60000 IU/kg by subcutaneous injection every 24 hours for 5 days. (B602.19.w19, J15.28.w2)
• Enrofloxacin 
  • 5 - 15 mg/kg by subcutaneous or intramuscular injection or orally twice a day. (J15.28.w2)
  • 10 mg/kg orally once daily. (B606.4.w4)
  • Safe choice (B600.9.w9, J15.28.w2)
• Trimethoprim-sulfa
  • 30 mg/kg orally twice a day. (J15.28.w2)
  • Safe choice (B600.9.w9, J15.28.w2)
  • Good skin activity (B602.19.w19)
• Oxytetracycline
  • 30 mg/kg by injection every 3 days. (B606.4.w4)

Sedation or Anaesthesia

• Sedation:
  • Midazolam at 2 mg/kg intravenously with Buprenorphine 0.03 mg/kg intravenously. This is a useful combination particularly if repeat procedures are needed. (J15.28.w2)
  • Fentanyl/fluanisone 
    • At 0.2 - 0.5 ml/kg by intramuscular injection. (J15.28.w2)
    • Provides good sedation and analgesia. (B600.9.w9, J15.28.w2)
• Anaesthesia:
  • "The sedated rabbit can be anaesthetised using gaseous anaesthesia (isoflurane or sevoflurane), ideally via an induction chamber as face masks can be poorly tolerated and require the rabbit to be physically restrained". (J15.28.w2)
  • General anaesthesia is often the best method for the initial intervention because the wounds can be explored thoroughly. (J15.28.w2)

Treatment to inhibit the development or kill remaining eggs and larvae

• Ivermectin
  • One dose at 0.4 mg/kg by subcutaneous injection. (B284.10.w10, B600.9.w9, B601.13.w13, B602.19.w19, B608.21.w21, B610.23.w23, J213.4.w4)
  • Give the above dose every 14 days for two treatments. (B602.19.w19, B615.6.w6, J15.28.w2)
  • This will kill any internal or subcutaneous maggots and also any that subsequently hatch. (B610.23.w23)
  • Distributed throughout the body unlike Permethrin. (J15.28.w2)
  • Note: In Cuterebra infections, ivermectin has been used experimentally in cases of aberrant migration; however, the reaction to the dead larva can be fatal, necessitating the concurrent use of corticosteroids. (B604.5.w5)
• Selamectin (B603.4.w4)
  • Used safely in rabbits. (J15.28.w2)
  • Distributed throughout the body unlike permethrin. (J15.28.w2)
• Nitenpyram (B603.4.w4)
  • "there are only anecdotal reports about its efficacy when used topically". (J15.28.w2)
• Cyromazine
  • Licensed for use in rabbits. 
  • Prevents myiasis by preventing the development of the first stage larvae to second stage larvae. 
  • It does not repel flies. 
  • Apply to fur surrounding the wound.
  • Control is maintained for up to ten weeks. 
  • Contraindications: Do not apply to broken skin 
    (J15.28.w2)
• Permethrin and cypermethrin
  • Indicated for prevention and treatment of myiasis. 
  • Xenex Ultra Spot on (Genetrix) contains permethrin and is licensed in the UK for use in rabbits to prevent myiasis. 
  • Good kill rates of first stage larvae and second stage larvae, in vitro, have been demonstrated by the manufacturer. However permethrin is only likely to act superficially because it will not penetrate beyond the skin's sebaceous layer. 
    (J15.28.w2)
• Contraindications:
  • Fipronil: not licensed for use in rabbits and its use has been associated with death in this species. (J15.28.w2)
  • Coumaphos (Negasunt; Bayer): provokes Organophosphates toxicity in rabbits. (J15.28.w2)

Topical medication

• Topical silver sulfadiazine cream (B601.13.w13, B610.23.w23)
  • Use daily until healed. (J213.4.w4)
• Dermisol (B603.4.w4, B606.4.w4)- Only use this product if there is necrotic debris to be removed. (V.w103)
• Intrasite
• Flamazine
• Nu-gel
• Manuka honey

(B603.4.w4)

Address the underlying cause of perineal faecal soiling or urine scalding

Cases for euthanasia

• Rabbits that have extensive soft tissue damage due to the activity of the maggots, including:
  • Areas of extensive tissue necrosis
  • Body cavity involvement
  • Large wounds that extend beyond the dermis (this is the equivalent of a third degree burn)
• Moribund (seriously injured or terminally ill) rabbits that have succumbed to an attack by blowflies.

Note: Rabbits that have significant numbers of second and third stage larvae are likely to have been ill for a number of days and therefore may carry a poor prognosis. 

(J15.28.w2)

• Apply insecticide to the ferret. (B602.10.w10)
• Give systemic antibiotics where necessary. (B602.10.w10, B627.16.w16)

Note: Early treatment will increase the survival rate. (P20.1992.w7)

• Treatment and Care
• Oral Medication and Syringe Feeding of Ferrets
• Subcutaneous Injection in Ferrets (Techniques)

General Nursing and Surgical Techniques

• Keep wounds cleaned.
• Physically remove visible larvae from wounds, eyes, ears and other orifices. (B214.3.26.w11, B228.11.w11)
  • Forceps and a tooth brush may be useful for removing maggots from the hair and spines. (B291.12.w12)
  • Careful manual removal is important for eye infestations.
  • Flushing of wounds and orifices may assist in completing the removal of small larvae. (B259.w7)
    • A sterile non-irritant fluid should be used for flushing maggots from the eyes. (B337.3.w3)
  • A glass pipette and bulb may be used to gently suction maggots away. (B224)
  • A dilute antiseptic solution may be used to flush out the ears. (B259.w7)
• A hair drier may be used to gently heat and dry the skin to encourage maggots to move out of a wound. (B228.11.w11, B259.w7)
• Fingertip pressure from behind the eye socket may be used to expel fly eggs from the eye socket. (B151)
• Dripping 30% alcohol into the ears encourages maggots to crawl out. (B228.11.w11, B291.12.w12)
• Hydrogen peroxide (H₂O₂) may be used on less sensitive areas. (B291.12.w12)
• A fine "nit comb" may be used to remove fly eggs and very small maggots from the hair coat. (B337.3.w3)
• If a chemical has been used to kill maggots infecting wounds it is important to make sure that all the dead maggots are removed, for example using tweezers, to ensure that they do not remain in the wound and rot. (B337.3.w3)
• If, following removal of maggots, the hedgehog continues scratching at one area of its body (e.g. an ear) check that site in case some maggots are still present. (B337.3.w3)

• Physical removal of maggots using forceps is recommended. It is important to remember that there may be pockets of the wound, not immediately visible, in which more maggots may be present, therefore the wound should be inspected for the following two or three days for any maggots which were not removed initially. (B212.w26)

Treatment involves:

1. Intravenous fluid therapy (see Specific Medical Treatment section above).
2. Supportive nutritional care.
3. Analgesia (see Specific Medical Treatment section above).
4. Antibiotics (see Specific Medical Treatment section above).
5. Removal of all the second and third stage of larvae.
6. Removal of as many first stage larvae and eggs as possible.
7. Treatment to kill, or inhibit the development of, any remaining larvae and eggs (see Specific Medical Treatment section above).
8. Wound management including debriding and dressing the wound.
9. Identification and treatment of underlying causes.

"The majority of rabbits presenting with fly strike will be in a state of profound shock. Initial treatment must deal with this shock and provide appropriate analgesia to eliminate the pain that is likely to arise as a result of the considerable damage to the epidermal, dermal and subdermal tissues".

(J15.28.w2)

Supportive nutritional care

• Any rabbit that is anorexic or has signs of gastrointestinal disturbance, requires intensive supportive care. This is particularly important in obese rabbits that are at risk of hepatic lipidosis. Provide a positive energy balance by syringe feeding high fibre recovery foods and by the inclusion of dextrose within the intravenous fluid therapy plan. Motility stimulants may also be useful. (B600.9.w9, J15.28.w2)

Removal of all the second (L2) and third (L3) stage larvae

• L2 and L3 larvae are the most damaging and therefore should be removed first. (J15.28.w2)
• Heavy sedation or general anaesthesia is necessary to minimise the discomfort and stress. (B600.9.w9, J15.28.w2, J213.7.w2) See the medications section. 
• Clip the fur to examine the area more easily. (B603.4.w4, B610.23.w23)
• Clean the area:
  • manually remove the maggots with forceps; (B284.10.w10, B600.9.w9, B601.13.w13, B603.4.w4, B610.23.w23, J15.28.w2)
  • flush the area with dilute antiseptic solution, e.g. povidone-iodine (Iodophors) (B600.9.w9, B601.13.w13, B610.23.w23, J15.28.w2) by using one of the following:
    • syringe; (B603.4.w4)
    • dental machine; (B603.4.w4)
    • ear cleaning flushing unit; (B603.4.w4)
    • introduce a tube proximal (deep to) the maggots if flushing out cavities. (B603.4.w4, J15.28.w2)
  • Make sure all organic material is removed from the rabbit including urinary and faecal contamination to prevent attraction of more flies. (J15.28.w2)
  • An insecticidal shampoo containing 1% Permethrin, may be used to kill significant numbers of larvae but this may be toxic to rabbits and is not necessary if all maggots have been manually removed. (B600.9.w9, J15.28.w2)
  • Debride any necrotic tissue. (B603.4.w4, J15.28.w2)

Removal of as many first stage (L1) larvae and eggs as possible

• Eggs can be removed using a flea comb. (J15.28.w2)
• Drying: Warm air from a hairdryer may draw the maggots to the surface and is also necessary to dry the coat if the fur has been washed to remove faecal or other forms of contamination; drying will also eliminate excess humidity that would promote larval and egg development. (B284.10.w10, B600.9.w9, B603.4.w4, J15.28.w2)
• Provide warmth if the patient is in shock. (B601.13.w13, B610.23.w23)

Wound management

• Third degree "burns" need protection from ongoing fluid loss and infection. These wounds must be covered. (J15.28.w2)
• The wounds do not usually benefit from suturing. (B603.4.w4)
• Allow to heal by second intention. (B602.19.w19)
• Apply hydrogels (see Specific Medical) to the wound and then use a moisture vapour permeable dressing such as Opsite; Smith and Nephew, to cover the area. Check the wound every six to eight hours to remove any new larvae. (J15.28.w2)
• Clean the wound daily before applying any more topical medication. (B602.19.w19)
• Non dusty bedding should be used during the healing period but make sure the rabbit still receives adequate long fibre in its diet. (J15.28.w2)
• A more permanent dressing may be applied once all the eggs and larvae have been removed. It is necessary to protect the exposed nerve endings and also to provide a moist environment in the wound for the development of granulation tissue. This dressing may be sutured in place over the wound. Suitable dressings include: 
  • Granuflex (ConvaTec)
  • Duoderm Extra Thin (ConvaTec) 
    (J15.28.w2)
• A healthy granulation bed will lead to rapid healing of the wound by second intention. (J15.28.w2)
• Also see: Treatment and Care - Wound Management

Specific Wohlfahrtia information

• Use saline to flush into the small openings made by the maggots then apply gentle pressure on the skin to force the maggots to the opening and remove with forceps. (P62.7.w1)
• Larvae which are placed shallowly may be reached with forceps; those which are deeper will come to the surface if their exit hole is filled with water, and can then be removed with forceps. (J1.6.w7)

Removal of larvae

• If cutaneous myiasis is present, removal of the intact larva is recommend. (B602.10.w10, B629.13.w13)
  • It is recommended to remove the whole larva, to prevent infection occurring or a systemic response. (B602.10.w10, J213.12.w2)
• An anaesthetic is recommended for this procedure. (J213.12.w2)
  • An incision should be made over the bore site that has been made by the larva. (J213.12.w2)

Wound management

• Clean and flush the wound out. (B232.10.w10)
• Debride the wound, use topical (B629.13.w13) and possibly systemic antibiotics (B627.16.w16). The wound should be left to heal by secondary intension. (B602.10.w10)

Nutrition

• Nutritional support should be given to ferrets that are anorexic. (B627.16.w16, V.w143)

• Treatment and Care
• Oral Medication and Syringe Feeding of Ferrets

Preventative Measures

• Carefully inspect wounds/lesions and natural orifices of weak/juvenile animals for fly eggs/larvae, particularly in the warmer months, and remove these.
• Keep wounds clean.
• Apply topical insecticides to wounds/lesions

(B11.3.w10, B208.2.w2)

Lagomorphs

• Prompt treatment of problems which may lead to myiasis. (B603.4.w4, J213.7.w2)
• Daily inspection of the animal
  • Inspect the underside of the rabbit twice daily ideally (B603.4.w4, J15.28.w2)
• Deterrence of flies
  • Use insect deterrents nearby. (B603.4.w4)
  • UV/electrocution grids (B603.4.w4, J15.28.w2)
  • Mosquito netting (B600.9.w9, B603.4.w4, J15.28.w2)
  • Fly traps (J15.28.w2)
  • Keep rabbits housed away from anything that is likely to attract flies e.g., compost, household rubbish and manure. (J15.28.w2)
• Insecticides
  • Cyromazine (B603.4.w4)
    • Insect growth inhibitor that is licensed in rabbits for prevention of flystrike. (B601.13.w13, B610.23.w23)
    • It does not repel flies but works by preventing the L1 to L2 moult. (B601.13.w13, B610.23.w23)
  • Dichlorvos strips can be used in the shed. (B606.4.w4)
  • Household flea spray: Vet-Kem Acclaim Plus (Sanfoni Animal Health Ltd.) can be used to spray the hutch. This product contains 0.09 % w/w S-methoprene and 0.58 % permethrin. (B606.4.w4)
• Permethrin spot-on products
  • Can be used every two weeks as a preventative measure. (B601.13.w13, B610.23.w23)
  • Some products available may also contain a fly repellent. (B601.13.w13, B610.23.w23)
    • Xenex Ultra Spot On (Genitrix) acts as a repellent and is also reported to kill adult flies and larvae. (J15.28.w2)
• Insect repellents
  • Xenex (Genitrix): a plant-based insect repellent that contains octanoic and decanoic acid. (J15.28.w2)
  • Citronella is a natural fly repellent and may be of some value. (B606.4.w4)

• Apply insecticide to the ferret, during the warm seasons. (B602.10.w10)

• Treatment and Care
• Preventative Medicine for Birds - General
• Preventative Medicine for Mammals

Environmental and Population Control Measures

Lagomorphs

• Clean bedding. (B600.9.w9)
• Fly control measures:
  • screened windows. (B600.9.w9, B604.5.w5, J15.28.w2)
  • fly traps (B604.5.w5)
  • proper disposal of manure (B604.5.w5)
  • proper disposal of carcases (P62.7.w1)
  • Safe insecticides and fly repellents (B604.5.w5)
• Avoid sources of injury (poor housing etc.) (P62.7.w1)
• Pet rabbits: groom prophylactically to remove fly eggs and restrict access to the outdoors during the fly season. (B604.5.w5)

Ferrets

• The owner should be checking their ferrets on a regular basis, so that flystrike is caught earlier or prevented. (B602.10.w10)
  • Note: Especially if open wounds are present. (B602.10.w10)

• Preventative Medicine for Birds - General
• Preventative Medicine for Mammals
• Environmental and Population Management