Cutaneous gnathostomiasis in Vietnam

Clinical record

A 33‐year‐old male tour guide presented at our clinic with rash and swelling on the anterior upper arms. He was not alcohol or drug dependent and had no relevant medical and family history. He never walked barefoot. His symptoms developed 3–4 weeks after he had last eaten grilled frog. His physical examination was unremarkable other than the rash. He developed raised, erythematous and serpiginous skin lesions accompanied by pruritus, mild pain, redness and hot feeling on the middle‐third forearms for 10 days (Box 1). The rash spread distally and caused formication. He was well and had no fever or other specific symptoms.

Differential diagnosis included gnathostomiasis, cutaneous larva migrans, toxocariasis and larva currens (Strongyloides). Stool microscopy, complete blood count and enzyme‐linked immunosorbent assay (ELISA) were carried out at our clinic to detect antibodies against Toxocara spp., Gnathostoma spp. and Strongyloides stercoralis. His stool sample was normal. His peripheral leucocyte count was 8830/mm³ (reference interval, 4000–10 000/mm³), and his absolute eosinophil count was elevated at 940/mm³ (reference interval, 0–500/mm³). Only Gnathostoma serological results were positive. Skin biopsy showed third‐stage Gnathostoma spinigerum larvae (Box 2). Polymerase chain reaction (PCR) testing reconfirmed the parasite species. Details regarding the use of PCR in identifying Gnathostoma spp. are discussed elsewhere.1

He was treated with a single dose of 200 μg ivermectin per kilogram of body weight.2 Skin lesions responded well to treatment and normal eosinophil levels were reached after 2 weeks. Follow‐up every 3 months until 1 year after treatment found no relapse. He was advised to avoid raw or undercooked food.

Discussion

Raised, serpiginous skin lesions in a systemically well patient may suggest an infection caused by helminth species. Our patient's rash could have been a symptom of cutaneous larva migrans caused by the migration of zoonotic nematode larvae (eg, Ancylostoma ceylanicum) through the skin.3 Such a rash usually occurs in the lower extremities, especially the feet, and is associated with walking barefoot. Although our patient lived in Vietnam, where cutaneous larva migrans is endemic, his symptoms and habits helped exclude this diagnosis. Larva currens caused by transdermal migration of Strongyloides larvae may induce serpiginous cutaneous lesions. The rashes are usually linear and recurrent with an intervening symptom‐free period.3 Our patient's Strongyloides serology results were negative, and his rashes did not have the typical characteristics of migrating Strongyloides larvae. Nodular migratory panniculitis, which is usually located at the trunk or upper limbs, is the typical symptom of cutaneous gnathostomiasis.4 These lesions are ill defined and can be pruritic, painful or erythematous.2 The appearance of our patient's rash suggested cutaneous gnathostomiasis. His Gnathostoma serological test result was positive, and Toxocara serology was negative.

Gnathostoma serological testing includes immunoblot and ELISA.2,5 ELISA, which is easier to perform and has good sensitivity (98%) and specificity (88%), should be used.5 However, it can only detect IgG and cross‐reactivity with other parasitic infections, so its specificity is not high.4 Diagnosing the causative agent based on clinical symptoms is not always reliable — especially in countries such as Vietnam, where multiple helminth species are endemic — because different species can cause overlapping cutaneous manifestations.3 The typical cutaneous manifestations of parasitic infections are also uncommon. Only 0.5–3.4% of patients present with the typical symptoms of zoonotic nematode larvae, Strongyloides larvae (1.9–8.3%) and Gnathostoma spp. infections (0.5–3.8%) (unpublished data, Institute of Malariology Parasitology and Entomology Quy Nhon annual report, January 2018). Moreover, the chances of detecting the larva are low.2 Therefore, antihelminthic therapy can be instituted if the patient has epidemiological history (eg, eating raw or undercooked fish, eels, frogs or chickens in endemic areas4) and develops clinical presentation plus suggestive serological testing and either blood or tissue eosinophilia, although the definitive diagnosis of the causative agent remains unknown.2 Our patient fully met all the criteria. Third‐stage G. spinigerum larvae were molecularly and microscopically detected in his skin sample. He was definitely diagnosed with cutaneous gnathostomiasis caused by G. spinigerum.

If left untreated, gnathostomiasis may last up to 12 years.2 Visceral gnathostomiasis, including ocular gnathostomiasis, can also develop with only cutaneous impairment.2 Although surgical removal of larvae is the best treatment for cutaneous gnathostomiasis, this is difficult when larvae are in inaccessible areas or cannot be located.2 Complete removal of larvae also depends on the clinician's surgical skills and experiences. Therefore, our patient was subsequently treated with ivermectin and fully recovered. Current antihelminthic therapy includes oral albendazole or ivermectin (Box 3).2 Relapses can be treated using the same antihelminthic therapy.2 Since relapses are not rare, patients should be symptom‐free 12 months after treatment to indicate sufficient evidence of cure.4 However, an optimal follow‐up interval remains unknown. Our patient was monitored 3‐monthly up to 12 months and had no relapse.

Given the increased number of travellers worldwide, cutaneous gnathostomiasis is not restricted to endemic countries where diagnostic error is common due to atypical skin lesions and low probability of obtaining the parasite. Non‐endemic countries such as Australia have also experienced diagnosis and treatment difficulties.5 Travellers and physicians need to be aware of gnathostomiasis.

Box 1 – Movable skin lesions on the middle third of the patient's right and left arms

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Note: Blue colour is due to the application of methylene blue.

Box 2 – Microscopic observation of third‐stage larva of Gnathostoma spinigerum in skin sample

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