Cutaneous larva migrans (creeping eruption)

The CDC explains that zoonotic hookworms such as Ancylostoma braziliense and A. caninum normally infect dogs and cats. Their eggs pass in animal faeces and hatch in warm, moist soil or sand. The infective larvae then penetrate human skin. In people the larvae cannot mature and cannot complete the life cycle, so they wander within the upper skin layers and eventually die.

That wandering gives the condition its name: larva migrans means migrating larva, and cutaneous means in the skin. The CDC notes that other animal hookworms, including Uncinaria stenocephala in cooler climates, can also cause it.

DermNet lists barefoot beachgoers, children in sandpits, farmers, gardeners and outdoor workers in warm, moist climates as the groups at risk. The CDC places A. braziliense in the south-eastern United States, Latin America, South America and Africa, and notes that beach visitors and anyone with barefoot contact with contaminated soil in tropical and subtropical regions are at risk.

Many UK cases follow a holiday in the Caribbean, South-East Asia, Africa or Latin America, often noticed after returning home. Sitting or lying on sand, not only walking barefoot, can be enough because the larvae can enter any exposed skin.

DermNet describes a tingling or prickling sensation within about 30 minutes of larvae entering, followed by itchy snake-like tracks about 2 to 3 mm wide that advance a few millimetres to a few centimetres a day. The CDC describes intensely itchy, red, serpiginous tracks in the upper skin that occasionally blister.

Typical sites are the feet, toes, hands, knees and buttocks. Because scratching damages the skin, bacterial infection with crusting, pus or spreading redness can follow, and the CDC mentions secondary infection as a known problem. Often the rash begins days to weeks after exposure, so the connection to the beach holiday may not be obvious.

The CDC states that the condition is diagnosed clinically because there are no serological tests for zoonotic hookworm infections. Skin biopsy is generally not helpful, since the larva is usually not within the visible track. The history of recent travel and the shape of the track are enough.

Conditions that can look similar include scabies, a fungal ringworm rash, contact dermatitis and larva currens from Strongyloides, which moves faster and tends to appear on the trunk and buttocks. If the pattern is unusual, a GP may refer to dermatology or a travel medicine service.

DermNet explains that the condition is self-limiting, with lesions typically resolving within 4 to 8 weeks, or sooner with treatment. Options it lists are topical thiabendazole for limited disease, oral albendazole, mebendazole or ivermectin for more widespread involvement, cryotherapy or laser to destroy larvae, and antihistamines or topical steroid creams to ease itching. Which approach is used, and at what dose, is for the prescriber.

Because the larvae are confined to the skin, serious complications are unusual. Keep the area clean, avoid scratching and watch for signs of infection. Freezing is not preferred by every clinician because the larva is not always at the visible end of the track.

DermNet recommends avoiding walking barefoot on contaminated sandy beaches and moist soil where animal faeces may be present. Lying on a towel or wearing footwear reduces contact. At home, picking up dog faeces and regularly deworming pets reduces contamination of public and garden soil, as NHS guidance on worms advises for pets.

See a GP if you have an itchy migrating track after travel, if the area becomes red, swollen or painful, or if you have a fever. Contact NHS 111 if you cannot get an appointment promptly and the rash is spreading or you feel unwell.