Discussion

HrCLM is commonly caused by infection with the larvae of the hookworms Ancylostoma caninum, Ancylostoma braziliense and, less commonly, Uncinaria stenocephala.1 The natural hosts of these hookworms are dogs and cats. Interestingly, both U. stenocephala and A. caninum have also been isolated from red foxes;2 in a study to quantify the prevalence of zoonotic-important parasites in the red fox (Vulpes vulpes) in Great Britain, U. stenocephala was isolated from the small intestine of 41.3% of the 588 carcasses collected.3 The risk of HrCLM in humans that is contributed by red foxes is yet to be ascertained. It is feasible that the cases described were due to skin contact with soil contaminated with infected dog/cat faeces; however, wild animals should not be discounted in the transmission of HrCLM.

Humans are incidentally infected when there is skin contact with contaminated soil or sand containing filariform larvae. These develop 5–10 days after the rhabditiform larvae have hatched from eggs passed in the faeces of their infected definitive host.4 Hatching and survival of the larvae are optimised in specific soil conditions: moisture, warmth and shade. For this reason, HrCLM commonly presents in tropical or subtropical climates. HrCLM in the UK is classically diagnosed in the returning traveller; however, cases acquired within the UK in addition to other temperate climates have been reported. Cases within the UK have been attributed to prolonged contact of clothing with infected dog or cat faeces,5 and from skin exposure to sand on a Cornish beach6 and grass on the west coast of Scotland.7 A further case in the UK has been reported following skin contact with faeces from puppies that had not received hookworm infection prophylaxis.8 Six cases in Italy occurred likely after contact with dog or cat faeces that had contaminated floral arranging material.9 Several cases that have presented in Germany, which has a similar climate to the UK, were deemed to be secondary to unusual weather conditions that is, a warm and humid summer, and contact with riverbanks and lakeside soil/sand.10–13 The UK, in 2014, had higher than average temperatures and rainfall over spring and summer.14 ,15 Our patients presented in June and August of that year. This, in addition to the contact with dark and moist areas of soil, likely increased the chance of transmission in our patients.

In our first case, there was a history of travel to South Africa 4 months prior to presentation. Prolonged incubation periods exceeding this time have been reported, however, an incubation time of a few days to a month is more common.16 ,17 A study in Brazil reported that track length was significantly associated with the duration of the infection, with an average increase in length of 2.7 mm per day,18 thus time and place of exposure can be estimated. The length of the track in our first case was approximately 70 mm, suggesting an incubation period of less than a month and hence the presumed location of acquisition to be the UK.

The diagnosis of HrCLM in the two cases we present is based on characteristic clinical findings. Diagnosis is largely clinical through the presence of a pruritic erythematous linear to serpiginous lesion extending from a red itchy papule—the site of larval penetration.1 The lesion is caused by an inflammatory reaction secondary to the migration of the larva through the epidermis.1 Lesions are mainly found on the most exposed areas of the body, that is, the upper and lower extremities and other areas that may come into contact with infected soil/sand, including the buttocks. Biopsy of the lesion followed by histological investigations rarely is of use, as the larva is located further than the visible lesions.6

Although the eruption largely resolves after 2–8 weeks without therapy, for the relief of symptoms and reduction in the risk of recurrence and secondary bacterial infection, treatment with antihelminthic agents is recommended.17 However, the optimal treatment regimen remains controversial, with varying treatment durations of albendazole (1, 3, 5 and 7 days), a single dose of oral ivermectin or topical therapy with thiabendazole or albendazole being recommended in the literature.19–21 When comparing single dose regimens; higher cure rates with ivermectin (81–100%) in comparison to albendazole (46–100%) are reported.20 ,22 In more extensive or multiple lesions, a 7-day course of albendazole (100% cure rate) has been advised.23 The optimum treatment regimen advised appears to be dependent on the extent of the clinical presentation. In our patients who presented with a single lesion uncomplicated by secondary bacterial infection, early resolution of the lesions was achieved with a single 400 mg dose of albendazole, with no relapse within 3 months.