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.

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.

This series is the first reported set of travelers with gnathostomiasis. Patterns of international travel suggest that this condition may be seen more often in travelers and immigrants from regions in which the disease is endemic. Moreover, the widening geographic distribution of the infection and increasingly adventurous eating habits of visitors to such regions are likely to contribute to an increase in incidence.

In our patients, the median time from onset of symptoms to diagnosis was 12 months, which reflects both the intermittent, episodic nature of the symptoms and the obscurity of the diagnosis. We do not have data on the time to diagnosis after medical attention was sought, but anecdotally we often and understandably find a considerable delay.

The key to diagnosis of gnathostomiasis is recognition of the highly suggestive clinical history; cases 1 and 2 are the most typical. Once the disease is diagnosed, management is straightforward, but the rarity of the condition in areas in which the condition is not endemic might lead to the diagnosis’ being overlooked. The unusual symptoms, combined with the usual absence of physical signs between episodes, may lead to discounting of the symptoms and erroneous reassurance of the patient by clinicians unfamiliar with gnathostomiasis. Patients may be referred to rheumatology, dermatology, or general medical clinics; the absence of eosinophilia may also prevent due consideration of possible parasitic causes. Eosinophilia was present in only seven of our patients and thus cannot be considered as a screening tool. However, as a marker of treatment response in those with eosinophilia at baseline, this symptom was proven useful; for the three patients requiring a second course of albendazole, residual eosinophilia preceded symptom relapse.

Because of little information about dietary intake, we cannot comment on the sources of infection in our patients. More detailed dietary histories are now recorded routinely at the Hospital for Tropical Diseases, but the notorious inaccuracy of verbal dietary histories and the broad range of potential culprits eaten by many travelers suggest that, for identifying the source in humans, dietary history is usually of limited value.

A number of serologic tests are available for the diagnosis of gnathostomiasis. Our testing is performed at Mahidol University in Thailand by using an immunoblot to detect the specific 24-kDa band considered diagnostic of Gnathostoma infection. In that laboratory, for the four parasite-confirmed cases of Gnathostoma, the immunoblot was 100% sensitive, and antibodies of 15 parasitic diseases and one mixed infection were not cross-reactive, except for 1 of 13 samples from patients with paragonimiasis which gave a weak reaction against this antigen (5). Antibodies from 16 patients with confirmed cases of Gnathostoma were consistently reactive with this 24-kDa antigen. Cross-reactivity was not found in a further extensive study of parasitic and nonparasitic diseases (6).

The reported efficacy of albendazole in the treatment of gnathostomiasis is >90% (7,8), and similar success has been reported for ivermectin (8). Three of our patients required a second course of treatment. The episodic nature of this condition means that an initial determination is difficult as to whether cure has been effected, but the resolution of eosinophilia and lack of symptom recurrence within 12 months were taken as presumptive evidence of cure. Although we used a second course of albendazole for retreatment, ivermectin has also been used successfully (9).

A diagnosis of gnathostomiasis should be considered for patients with a history of transient, migratory cutaneous or subcutaneous swellings, or nonspecific gastrointestinal symptoms for which a potential epidemiologic exposure is identified. Management of the disease thereafter is usually relatively straightforward, although more than one course of treatment may be required to effect a cure.