Taxonomy of Trichinella and the epidemiology of infection in the Southeast Asia and Australian regions.

Seven species belonging to the Trichinella genus (five with encapsulated larvae and two with non-encapsulated larvae in host muscles) and three additional genotypes have been described to date: T. spiralis (genotype T1), a cosmopolitan species with a high infectivity to swine and rats; T. nativa (T2), etiological agent of sylvatic trichinellosis in arctic and subarctic areas of the Holarctic region, and its related genotype (Trichinella T6), detected in Alaska, Idaho, Montana, Pennsylvania, Wyoming, and Ontario; T. britovi (T3), etiological agent of sylvatic trichinellosis in temperate areas of Europe and Asia, and its related genotypes Trichinella T9 in Japan and Trichinella T8 in South Africa and Namibia; T. murrelli (T5), etiological agent of sylvatic trichinellosis in temperate areas of the USA; T. nelsoni (T7), etiological agent of sylvatic trichinellosis in Africa south of the Sahara; T. pseudospiralis (T4), a non-encapsulated cosmopolitan species infecting both mammals and birds; and T. papuae (T10), a recently discovered non-encapsulated species in sylvatic swine of Papua New Guinea. In the Southeast Asia and Australian regions, T. spiralis, T. pseudospiralis and T. papuae have been detected in sylvatic and domestic animals and in humans. A focus of human trichinellosis due to T. papuae was recently discovered in Papua New Guinea, with a prevalence of 28.9%. Trichinellosis has also been documented in domestic animals and/or humans in Cambodia, Indonesia (Bali and Sumatra), Lao PDR, Malaysia, Myanmar, Thailand, and New Zealand, and in wildlife of Tasmania.

Molecular identification of food-borne and water-borne protozoa.

Cryptosporidium and Giardia can be transmitted to humans by contaminated food and water, resulting in large outbreaks of diarrheal disease. Sensitive methods for detecting these parasites are needed to control and prevent infection. However, this issue is complicated by the fact that there is still uncertainty about the role played by different species/genotypes with respect to human disease. We are in the process of collecting samples from clinical cases (both sporadic and outbreak-related human infections) and from the environment (tap and waste water samples from different geographic regions), to test the efficacy of methods for detection and genotyping. Concerning Cryptosporidium parvum, we have developed new genotyping methods based on highly polymorphic microsatellite markers. The use of microsatellite markers allows the route of transmission to be traced; these methods can also be used not only to distinguish between anthroponotic and zoonotic transmission but also to identify the source(s) of infection. Regarding Giardia, which was found very frequently in environmental water samples, we are testing the beta-giardin gene as a marker to discriminate among species/genotypes.

Current status of food-borne parasitic zoonoses in Mediterranean and African regions.

Epidemiological data on food-borne parasitic zoonoses of Mediterranean and African regions are fragmentary. Several studies indicate that toxoplasmosis frequently occurs in Africa, but the epidemiological patterns in these countries are far from being complete. Serological investigations have been carried out with different methods and the results are not always comparable. Food habits, presence or absence of domestic and/or synanthropic felines, and environmental characteristics (damp or dry areas) seem to influence the prevalence of infection in man from 15 to over 60%. There are few reports on Sarcocystis infection in man, while its presence in domestic and sylvatic animals is well evidenced. Cysticercosis infection in cattle is widespread in Africa with a prevalence ranging from 2 to 50% in relation to breeding and human habits. In European countries of the Mediterranean area the prevalence of infection is below 2%. Cysticercosis infection in swine has almost disappeared in the Mediterranean area, while it is still present in some African countries. Human paragonimiasis is present in Western Africa with a prevalence ranging from 2 to 31%. Heterophyasis in man is present in Egypt, Tunisia, and Middle East. Sylvatic trichinellosis is widespread in Mediterranean (Trichinella sp.3) and African (T. nelsoni, Trichinella T8) regions. Domestic trichinellosis (T. spiralis spiralis) is present in Spain, France, Yugoslavia, Egypt, Gambia, and Nigeria in domestic and/or sylvatic animals. In Africa human trichinellosis is rare, mostly from religious and food habits. Till now very few control projects against food-borne parasitic zoonoses have been developed in Africa.

General introduction and epidemiology of trichinellosis.

All studies on trichinellosis have been based on the assumption that there is only one cosmopolitan agent of human and animal trichinellosis; Trichinella spiralis (Owen, 1835). In the past, swine and only a few synanthropic animals were considered reservoirs, and the presence of the parasite in sylvatic animals was considered rare. Breeding experiments before, and then biochemical approaches (isoenzymes and DNA analysis), showed the presence of a high genetic variability inside this genus, suggesting it be considered as polyspecific. At present, eight gene pools, named from T1 to T8, have been identified in the genus Trichinella. T1 (T. spiralis s str) is the etiological agent for the domestic cycle, with a cosmopolitan distribution related to swine breeding and human habits. However, in some areas this parasite passes from domestic to sylvatic animals and vice versa. Six gene pools are the agents for the sylvatic cycle at different latitudes, mainly in carnivores. T2 (T. nativa) is present in terrestrial mammals and seldom in sea mammals of arctic and subarctic regions. T3, T5, and T8 are present mainly in Canidae (T3), Ursidae (T5), Hyaenidae and Felidae (T8) of temperate-subtropical areas of Palearctic, Nearctic and South African regions, respectively. T6 is present in carnivores in the subarctic-temperate area of the Nearctic region; and T7 (T. nelsoni) in Hyaenidae and Felidae of Equatorial Africa. Only T4 (T. pseudospiralis) can infect both mammals and birds, and it shows a cosmopolitan distribution. Probably trichinellosis is present world-wide, but unknown in those areas where it has not been sought.