Fishborne zoonotic parasitic (FZP) diseases in Southeast Asia, including Vietnam, are receiving increasing attention as information on their diversity and prevalence emerges. Humans are infected with FZPs when raw or inadequately cooked fish are consumed. Humans excrete the FZP larvae in eggs, which then infect and multiply in snails (intermediate hosts). Fish then become infected when free-swimming stages of the FZPs are released from the snails. An illustration of a simplified life cycle of the parasite can be seen in the figure below.

These zoonoses are especially troublesome for Vietnam because of certain climate, social and economic conditions that favour their development and transmission.

The emergence of FZPs infections as a severe public health problem has made action imperative (WHO 1995). A report from the Southeast Asian Ministers of Education Organization – Tropical Medicine Public Health Project (SEAMEO – TROPMED) includes comprehensive documentation on the health significance of FZPs and other foodborne trematode and nematode infections. FZPs are especially prevalent in Asia and are the most important of all zoonotic parasites infecting humans. All of the important FZPs are helminths, the majority of which are trematodes (flukes), that parasitize either the liver or in intestines of the final host. Among the liver flukes, most prevalent are Clonorchis sinensis and Opisthorchis viverrini.

The World Health Organization (WHO) estimated in 1995 that about 7 million people were at risk for liver flukes in Vietnam and that in Vietnam at least 1 million people were infected. However, based on recent human prevalence figures in the Red River Delta provinces the number of infected individuals is likely to be much higher (infection rates of 15 to 20%) (De et al 2003). The diseases that are of most concern in the endemic areas are, according to WHO: cholangiocarcinoma and gallstones (liver trematodes infections due to Opisthorchis and Clonorchis) and diarrhea and peptic ulcers (intestinal trematodes such as Haplorchis and Metagonimus).

Overall, there are few reliable economic impact assessments for FPZs in Asia. The most detailed studies have been carried out on opisthorchiasis for only the most endemic region, northeast Thailand where 60% of the workforce population is infected. The estimated annual impact, based on loss of wages and productivity and on medical treatment is a cost of $ 100 million. Economic costs related to food safety and qualities in fish production are apparently unknown in the region.

There are strong linkages of FZPs to poverty, pollution and population growth. For example, in some areas, shortage of fuel in poor homes may permit only partial cooking of raw fish. Increasing population pressures in the endemic areas lead to deterioration of the environment and increased pollution of surface waters with sewage, night-soil, and animal excreta. Development can also create increased risks; for example, dams create reservoirs highly favourable for snail vectors, as well as fish, which are the major transmitters of fishborne trematodes.

The importance of fish produced in aquaculture is increasing and the sector has in recent years shown steadily increasing production figures. It is well accepted that increased aquaculture production contributes significantly to the country’s socio-economic development – and that increased on-farm production of animal proteins will be to the direct benefit of the women and children within the targeted populations. At the same time, there seems to be little if any significant negative impact of small-scale aquaculture on the environment. Thus, aquaculture is and will remain very important as a major source of protein consumed nationally. It is therefore of utmost importance that consumption of cultured fish be safe and not present a risk to human health, e.g. through infection with FZPs caused by consumption of raw or inadequately prepared fish dishes.

Thus, the main justification for initiating a research capacity building project on FZPs is that their frequent occurrence in Vietnam presents a significant risk not only to the nation’s public health, but also to the economic well being of its aquaculture industry.