Gnathostomiasis: an emerging imported disease - Research

Emerging Infectious Diseases, June, 2003 by David A.J. Moore, Janice McCroddan, Paron Dekumyoy, Peter L. Chiodini

As the scope of international travel expands, an increasing number of travelers are coming into contact with helminthic parasites rarely seen outside the tropics. As a result, the occurrence of Gnathostoma spinigerum infection leading to the clinical syndrome gnathostomiasis is increasing. In areas where Gnathostoma is not endemic, few clinicians are familiar with this disease. To highlight this underdiagnosed parasitic infection, we describe a case series of patients with gnathostomiasis who were treated during a 12-month period at the Hospital for Tropical Diseases, London.

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The ease of international travel in the 21st century has resulted in persons from Europe and other western countries traveling to distant areas of the world and returning with an increasing array of parasitic infections rarely seen in more temperate zones. One example is infection with Gnathostoma spinigerum, which is acquired by eating uncooked food infected with the larval third stage of the helminth; such foods typically include fish, shrimp, crab, crayfish, frog, or chicken. Previously, most disease related to Gnathostoma was reported from Southeast Asia, particularly Thailand and Japan, because of the dietary habits of those living there. In recent years, however, gnathostomiasis has become an increasing problem in Central and South America, most notably in Mexico (perhaps related to consumption of ceviche) (1,2). In cats and dogs, which serve as important reservoirs of infection in regions where Gnathostoma is endemic (3), the ingested third-stage larva matures into the adult worm in approximately 6 months (Figure 1). However, because the larva cannot mature into the adult form in humans, the third-stage larva can only wander within the body of the host; clinical symptoms of gnathostomiasis then occur because of the inflammatory reaction provoked by these migrating larvae (Figure 2).

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Traditionally the disease has been divided into cutaneous and visceral forms, depending on the site of larval migration and subsequent symptoms. Another form of gnathostomiasis, which is quite rare, includes the dangerous complication of central nervous system involvement (4). This form is manifested by painful radiculopathy, which can lead to paraplegia, sometimes following an acute (eosinophilic) meningitic illness.

We describe a series of patients in whom G. spinigerum infection was diagnosed at the Hospital for Tropical Diseases, London; they were treated over a 12-month period. Four illustrative case histories are described in detail. This case series represents a small proportion of gnathostomiasis patients receiving medical care in the United Kingdom, in whom this uncommon parasitic infection is mostly undiagnosed.

Methods

The case notes of patients in whom gnathostomiasis was diagnosed at the Hospital for Tropical Diseases were reviewed retrospectively for clinical symptoms and confirmatory serologic results for the period April 1, 2000, to March 31, 2001. Clinical and laboratory data gleaned from case notes are described in the following sections.

Definitions

The definition of clinical Gnathostoma infection is: 1) a history of intermittent, migratory skin and subcutaneous swellings (localized or not localized) with or without peripheral blood eosinophilia (eosinophil count >0.4 x [10.sup.9]/L), or 2) otherwise undiagnosed eosinophilia with nonspecific symptoms. Plausible epidemiologic risk is defined as travel to an area in which gnathostomiasis had been reported previously (i.e., Southeast Asia and Central and South America). We did not impose a time limit on previous travel in our study. Positive Gnathostoma serologic results were defined as the presence on immunoblot of the specific 24-kDa band diagnostic of Gnathostoma infection (5,6). All serologic testing for gnathostomiasis was performed in the Department of Helminthology of the Faculty of Tropical Medicine at Mahidol University in Bangkok, Thailand. For patients at risk of Loa loa infection (because of previous travel to regions in central or West Africa where the infection is endemic), day-blood tests (samples taken between 12:00-2:00 p.m.) were performed to check for microfilaria and a filaria enzyme-linked immunosorbent assay was performed to exclude this diagnosis (Calabar swellings, indicative of Loa loa infection, may mimic gnathostomiasis).

Results

During the 12-month study period, we identified 16 patients who had clinical symptoms consistent with Gnathostoma infection, a plausible epidemiologic risk, and positive serologic results. Seven patients were referred by their general practitioner (primary care physician) and four by consultant physicians working elsewhere in London. Median time from onset of symptoms to diagnosis was 12 months (range 3 weeks-5 years). A dietary history was recorded for three patients who reported eating (among other things) raw fish and watercress (patient 1); mutton, fish, and chicken in Bangladesh (patient 3); and fish and a variety of crustacea from market stalls in Southeast Asia (patient 13). Eosinophilia was noted in seven patients and was usually modest, always declining after treatment. Median erythrocyte sedimentation rate (available for 12 patients, data not shown) was 10 (range 1-62). The countries visited most frequently by our 16 patients were India (n=4), Bangladesh (n=3), China (n=2), and Thailand (n=2). Standard treatment during the period of study was albendazole (400 mg twice a day for 21 days). Three patients required a second course for recurrence of symptoms and incomplete resolution of eosinophilia.