Fascioliasis and other plant-borne trematode zoonoses

Abstract

Fascioliasis and other food-borne trematodiases are included in the list of important helminthiases with a great impact on human development. Six plant-borne trematode species have been found to affect humans: Fasciola hepatica, Fasciola gigantica and Fasciolopsis buski (Fasciolidae), Gastrodiscoides hominis (Gastrodiscidae), Watsonius watsoni and Fischoederius elongatus (Paramphistomidae). Whereas F. hepatica and F. gigantica are hepatic, the other four species are intestinal parasites. The fasciolids and the gastrodiscid cause important zoonoses distributed throughout many countries, while W. watsoni and F. elongatus have been only accidentally detected in humans. Present climate and global changes appear to increasingly affect snail-borne helminthiases, which are strongly dependent on environmental factors. Fascioliasis is a good example of an emerging/re-emerging parasitic disease in many countries as a consequence of many phenomena related to environmental changes as well as man-made modifications. The ability of F. hepatica to spread is related to its capacity to colonise and adapt to new hosts and environments, even at the extreme inhospitality of very high altitude. Moreover, the spread of F. hepatica from its original European range to other continents is related to the geographic expansion of its original European lymnaeid intermediate host species Galba truncatula, the American species Pseudosuccinea columella, and its adaptation to other lymnaeid species authochthonous in the newly colonised areas. Although fasciolopsiasis and gastrodiscoidiasis can be controlled along with other food-borne parasitoses, fasciolopsiasis still remains a public health problem in many endemic areas despite sustained WHO control programmes. Fasciolopsiasis has become a re-emerging infection in recent years and gastrodiscoidiasis, initially supposed to be restricted to Asian countries, is now being reported in African countries.

Introduction

The importance of food-borne trematode infections and the need to implement control measures against them have been emphasised by the World Health Organization (WHO) (1995b). Plant-borne trematodes have recently been included in the list considered by the Institute of Food Technologists' Expert Panel on Food Safety and Nutrition (Orlandi et al., 2002). More recently fascioliasis and other food-borne trematodiases were added to the list of important helminthiases with a great impact on human development, at the Third Global Meeting of the Partners for Parasite Control held in WHO Headquarters Geneva in November 2004 (Anonymous, 2004). Moreover, present climate and global changes appear to increasingly affect those snail-borne helminthiases, which are heavily dependent on the environment for dissemination. Fascioliasis is a good example of an emerging/re-emerging parasitic disease in many countries as a consequence of many phenomena related to both environmental change and man-made modifications.

Six plant-borne trematode species have been found to affect humans: Fasciola hepatica, Fasciola gigantica, Fasciolopsis buski, Gastrodiscoides hominis, Watsonius watsoni and Fischoederius elongatus. Whereas F. hepatica and F. gigantica are hepatic parasites, the four other species are intestinal parasites. The fasciolids and the gastrodiscid cause important zoonoses distributed throughout many countries, while W. watsoni and F. elongatus have only been accidentally detected in humans.

Watsonius watsoni has been reported only twice in humans. The first finding took place during the autopsy of an emaciated West African who had died of severe diarrhoea in Liberia in 1904. Many worms were recovered from the intestine, some attached to the duodenal and jejunal wall, others free in the lumen of the colon. The second case, also affected by diarrhoea, was detected in Nigeria and shed numerous specimens too. Various species of primates in eastern Asia and Africa are natural hosts of this parasite. The complete history of those two cases and a study on the parasite and its symptomatology and pathology in primates were described by Pick, 1964, Pick, 1967. The morphology of the parasite was described by Stiles and Goldberger (1910). Its life cycle is unknown, but infection is probably acquired by ingesting vegetation on which the metacercariae have encysted (Yu and Mott, 1994).

Fischoederius elongatus is a parasite of ruminants infected by ingesting aquatic plants or snails (Lymnaea acuminata, Lymnaea succinea, Gyraulus euphraticus) carrying attached, encysted metacercariae. It is transmitted by lymnaeid snails, such as Lymnaea luteola, in Asia (Yamaguti, 1975). The first human infection was reported from Guangdong, China (Li, 1991). A 35-year-old woman complained of epigastric pain for months and vomited a worm of this species one morning while brushing her teeth, after which the symptoms disappeared. It is unknown how the patient became infected.