Introduction

• Cause: fly larvae causing tissue damage. In the UK it is commonly caused by Lucilia spp (greenbottle fly) and in the USA Wohlfahrtia vigil, the flesh fly. Cuterebra spp can also cause myiasis.
• Signs: depression, collapse, presence of fly larvae, open wounds, death. Early stages of fly strike may go undetected in prey species such as guinea pigs, especially in outdoor housed animals and in long haired breeds such as Peruvian guinea pigs.
• Diagnosis: observation of fly larvae/maggots.
• Treatment: fluid therapy, analgesia, supportive care, remove maggots, flush wounds, systemic antibiosis, address underlying causes.
• Prognosis: depends on the severity; good if treated very early on.

Pathogenesis

Etiology

• Fly larvae causing tissue damage. In the UK it is commonly caused by Lucilia spp (greenbottle fly) and in the USA Wohlfahrtia vigil, the flesh fly. Cuterebra spp can also cause myiasis.

Predisposing factors

General

• Warm, humid weather.
• Animals kept outdoors in suboptimal conditions and health.
• True diarrhea and/or urine scalding accumulation around back end.
• Unobserved/untreated diarrhea or excessive fecal soiling in guinea pigs, especially in long-haired breeds.
• Lack of cecotrophy and accumulation, especially in older boars with soft feces impacted within the anus Anal impaction. Can be associated with dental disease Dental disease, obesity Obesity, spondylosis, pododermatitis Pododermatitis.
• Wounds/broken skin Traumatic injuries.

Specific

• Environmental conditions of at least 60% humidity and 9-11°C/48.2-51.8°F for fly larva development.

Pathophysiology

Myiasis by Lucilia spp

• Flies lay eggs in open wounds or soiled skin/fur.
• Eggs → L1 larvae. L1 maggots do not cause tissue damage.
• L1 larvae → L2 → L3.
• Larvae bury deeper into tissues.
• Extensive tissue damage, secondary infections, and potentially fatal toxin release.

Myiasis by Cuterebra flies

• Flies lay eggs on skin.
• Developing larvae migrate through subcutaneous tissues or enter the subcutis through body openings.
• Subdermal cysts seen with breathing hole caused by botfly.
• Larvae 1-3 cm in length can be visualized within the lesion.

Timecourse

Myiasis by Lucilia spp

• Eggs → L1 larvae (within 12 h). These are not harmful.
• L1 larvae → L2 → L3 (within 3 days).

Diagnosis

Treatment

Prevention

Outcomes