Furuncular myasis

Furuncular myiasis is a temporary cutaneous parasite infestation in which a fly larva develops and burrows into the human host’s dermo-hypodermic tissue. It is the fourth most common travel-related skin disease and is prevalent in numerous regions worldwide (Table I).

Its pathophysiology and clinical diagnosis are described in tables II and III, respectively.

Two flies, Dermatobia hominis and Cordylobia anthropophaga are the most common culprits (Table II).

Furuncular myiasis is diagnosed mainly on the basis of the clinical appearance of the lesions and travel history (Table III). An ultrasound examination may be helpful.

Cutaneous leishmaniasis, tungiasis or cutaneous larva migrans are easy to diagnose in most cases.

The prognosis is good. The only exception is cerebral myiasis caused by D. hominis subsequent to fontanel infestation in neonates.

1 - TREATMENT

The larva can be extracted from the skin by various methods dictated by local custom - sometimes extremely ancient – (Mayas) – or by the experience – often case-specific – of a given team. Three techniques are generally proposed:

– application of products known to be toxic for the eggs and larvae: tobacco juice, lidocaine injected under the furuncle or at its extremities or 1% ivermectin in a propylene glycol solution;

– occlusion, since the larva needs air to breathe and will migrate out of the skin within a few hours (3 to 24 hours): oily products (paraffin, petrolatum, and bacon), nail varnish, sticky tape, aniseed essence, chewing gum, foundation, etc. Preference is given to the oily substances since this limits the risk of the larva dying in the furuncle and being more difficult to extract;

– manual evacuation after application of mineral turpentine or surgical removal through a cruciform incision after administration of a local anaesthetic under the lesion. During surgical removal of the larva, care must be taken to remove it entirely as retained parts may lead to foreign body granuloma formation.

The utility of systemic ivermectin has not yet been clearly defined.

The indications are:

– for D. hominis: occlusion with a fatty substance and/or local anaesthesia under the nodule with a small "episiotomy" followed by extraction of the larva with forceps;

– for C. anthropophaga: application of a fatty substance followed by manual squeezing of the furuncle to extract the larva.

Systemic antibiotics are only recommended in cases of secondary infection (rare).

Once the parasite has been extracted, the empty cavity must be irrigated with an antiseptic (iodinated povidone).

It is important for patients to be up to date in their tetanus vaccination.

2 - PREVENTION

Prevention is essential:

– for D. hominis : the anti-mosquito measures (repellents, mosquito nets and closely woven clothing) recommended for the prevention of other infectious diseases (leishmaniasis, etc.) apply;

– for C. anthropophaga: sleeping directly on a sandy floor is to be avoided; and washing should be dried away from flies and clothing and household items (particularly sheets) should be ironed on both sides.

According to MAIER et al. [ 2]