Biology Reference
In-Depth Information
associated illnesses are very common. Each year 20,000 to 30,000 cases
are reported to the Center of Disease Control (CDC) in the U.S. (Ahmed,
1991), and one of the largest outbreaks of foodborne illness ever reported,
is the outbreak of hepatitis involving 290,000 cases in China in 1988. The
investigation revealed that the source and mode of transmission were the
consumption of contaminated and inadequately cooked shellfi sh (Tang
et al., 1991).
The survival of viruses in the environment and in food is dependent
on a number of factors such as temperature, salinity, and solar radiation,
presence of organic solids as reviewed by Gerba (1988). Thus, enteric
viruses are able to survive for several months in seawater at temperatures
< 10°C, which is much longer than, e.g., coliform bacteria (Melnick and
Gerba, 1980). Thus, there is little or no correlation between the presence
of virus and the usually applied indicator bacteria for fecal pollution. All
enteric viruses are also resistant to acid pH, proteolytic enzymes and bile
salts in the gut. Hepatitis type A virus, being one of the more heat stable
viruses, has an inactivation time of 10 min at 60°C (Eyles, 1989). Thus virus
is able to survive some commonly used culinary preparations (steaming,
frying). Enteric viruses are also resistant to some common disinfectants
(e.g., phenolics, quaternary ammonium compounds, ethanol) while the
halogens (e.g., chlorine, iodine) inactivate enteric viruses in water and on
clean surfaces. Ozone is highly effective in clean water (Eyles, 1989).
Contamination by food handlers can be prevented by introducing good
personal hygiene and health education. Food handlers must not handle
food while suffering from intestinal infections and for at least 48 h after
symptoms have disappeared. In cases of doubt, disposable gloves should
be worn in critical operations, as viruses are diffi cult to remove from hands
by washing and are resistant to many skin disinfectants (Eyles, 1989).
PARASITE
The presence of parasites in fi sh is very common, but most of them are
of little concern with regard to economics or public health. However,
more than 50 species of helminth parasites from fi sh and shellfi sh are
known to cause disease in humans (Healy and Juranek, 1979; Higashi,
1985; and Olson, 1987). Most are rare and involve only slight to moderate
injury but some pose serious potential health risk. The most important
pathogenic parasites are listed in Table 4.7. All the parasitic helminths have
complicated life cycles. They do not spread directly from fi sh to fi sh but
must pass through a number of intermediate hosts in their development.
Very often sea-snails or crustaceans are involved as fi rst intermediate host
and marine fi sh as second intermediate host, while the sexually mature
parasite is found in mammals as the fi nal host. In between these hosts, one
