Academic journal article International Public Health Journal

Intestinal, Lung and Liver Flukes

Academic journal article International Public Health Journal

Intestinal, Lung and Liver Flukes

Article excerpt

Introduction

Of the 50 million people infected with trematodes, most are in China, Japan, Korea, and parts of Southeast Asia including Indonesia, Vietnam, Thailand, Laos and Myanmar (1).

Paramphistomatidae occurs in Africa, Echinostomatidae is endemic in Inda, and Hereophyidae has been reported in Brazil. International travel has also made this a world-wide problem.

People contract this infection by eating raw or undercooked fresh-water fish or water plants such as watercress with encysted metacercaria. Infestation of human trematodes is related to their migration. Intestinal, pulmonary, and liver flukes present distinct clinical and diagnostic problems to physicians and health care workers who care for patients with neglected tropical diseases.

Intestinal flukes

More than 70 species of intestinal flukes have been reported in humans (2). The most common are Fasciolopsis, Echinostoma, Gymnophallidae, and Heterophye species. The cysts of Fasciolopsis are ingested when eating aquatic plants such as water hyacinth, water chestnuts, water bamboo, and water lotuses, many of which are preferred raw. Echinostoma is encysted in fish, mollusks and amphibians which are eaten raw or incompletely cooked. Freshwater fish, carp, and mullet, contain Heterophye cysts. Gymnophallidae contaminate both mollusks and vegetation. The ingested cysts, released in the duodenum, attach to the mucosa and mature into adult worms over a period of 3 months.

Epidemiology

Fasciolopsiasis is endemic to Southeast Asia and the Orient. The disease has the highest prevalence in school-age children (3). Reported prevalence is 57% in mainland China, 25% in Taiwan, 50% in Bangladesh, 60% in India, and 10% in Thailand. Control programs with effective medications have not achieved success due to continued traditions of eating raw aquatic plants and contact with domestic pigs. Change in traditional practices is slow. Athough simply drying plant products kills the parasite, this practice is not acceptable in many local customs, and cooking is thought to destroy the flavor.

Recognition of the disease in Africa and reports of the disease in Brazil, Russia, Spain, Turkey, and the Philippines have raised awareness of this neglected disease. The economic impact of the disease is difficult to assess but clearly affects rural communities depending on subsistence agriculture.

Clinical features

Food-borne trematodes predominantly infect children in endemic areas. Many are asymptomatic but heavy infections produce severe diarrhea, abdominal pain, low-grade fever, and fatigue. High inoculums cause malabsorption due to villous edema and atrophy. When cysts attach to the mucosa in duodenum and jejunum they cause inflammation, ulceration, and micro-abscesses. Eosinophilia occurs as an immunologic response to trematode protein and toxins and is directly related to worm load (4). Children tend to become re-infected after treatment, amplifying the clinical problems and confusing the understanding of which treatments are effective, and when and if eradication occurs with treatment. Flukes mature in 3 months and have an average life span of 1 year in humans (2).

Although a few flukes are asymptomatic, heavy worm burdens, identified as > 500 worms, cause intermittent diarrhea, constipation, anorexia, nausea, and vomiting (5). Diagnosis depends on the detection of Fasciolopsis eggs in stool samples. Morbidity in endemic areas is related to anemia from chronic blood loss, malnutrition due to malabsorption from villous damage, and toxic worm metabolites which are thought to cause a variety of symptoms and immunologic reactions that result in facial as well as generalized edema (6). Mortality is related to malnutrition, intestinal obstruction, and electrolyte abnormalities.

The Heterophyids infect humans eating fish or shrimp infected with viable metacercariae. Infected fish-eating mammals and birds contain the eggproducing heterophyids. …

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