The Emergence of Gnathostomiasis in Mexico
Abstract & Commentary
Synopsis: Alter the environment near a well-established resort center by the construction of new dams, then seed rivers with parasite-infected fish, and you have an emerging infectious disease in the most unlikely of places. Then again, it may not be so unlikely once the pieces fall into place.
Source: Gnathostomiasis, an emerging foodborne zoonotic disease in Acapulco, Mexico. Rohas-Molina N, et al. Emerg Infect Dis 1999;5:264.
Between 1993 and 1997, 98 cases of gnathostomiasis were clinically identified at an outpatient dermatology referral hospital in Acapulco, Mexico. Intermittent cutaneous migratory swellings were the most common clinical manifestations and were described as edema of variable size accompanied by a burning sensation and pruritus. Recurring edema developed mainly in the upper and lower extremities (gluteus, thorax, and face). The duration of edema varied from one day to two weeks. The median value of percent blood eosinophils was 12% and serum IgE levels elevated. Larvae were identified in 26 cases, while, in 72 cases, final diagnoses were made on the basis of epidemiologic data, food habits, and positive ELISA/Western blot serological results.
Comment by Michele Barry, MD
Gnathostomiasis is a food-borne zoonotic disease caused by several species of Gnathostoma nematodes. The life cycle of this parasite involves the feces of dogs and cats; feces-containing ova reach water and free-swimming first-stage larvae are ingested by the copepod of the species, Cyclops, and then become second-stage larvae. Freshwater fish then eat copepods and third-stage larvae develop in the fish muscle. Consumption of this fish by cats, dogs, and other mammals completes the cycle. Humans acquire the infection by eating undercooked, infected fish. When larvae are ingested by a human host, no further development occurs, but the larva migrates through subcutaneous tissue causing the subcutaneous edema described in this article. What is not described in patients from this dermatology referral clinic are the painful radiculomyelopathies that can occur or the fatal eosinophilic meningoencephalitis caused by aberrant migrating larvae.
With its highest prevalence in southeast Asia, gnathostomiasis has now become an emerging public health problem in Peru, Ecuador, and, since 1970, Mexico—the latter emergence thought to be due to new dams built on rivers leading to the Pacific Ocean coast and the introduction of infected fish. Travelers to Acapulco should be warned against eating sushi or ceviche, the popular raw lime-marinated fish salad. Treatment with albendazole will cause outward migration of the worms to the dermis, permitting surgical removal and identification of larvae. Serological testing by the ELISA method and Western blot are described in this report, but larvae identification and characteristic clinical manifestations usually clinch the diagnosis.