outbreaks of mycotoxin poisoning have on economics through losses in
productivity.
Recognition of the potential to cause harm in humans, by the impo-
sition of maximum tolerated levels of mycotoxins such as aflatoxin, can
also have a major impact on economics by rendering a commodity
unacceptable in national or international trade. Thus, a major problem
occurred for Turkey, the world’s most important exporter of dried figs,
during the Christmas of 1988.
Several European countries imposed a ban on the import and sale of
dried figs following the demonstration of aflatoxin in 30% of samples of
figs analysed. Fearing the loss of 50 000 jobs in the fig-drying and
packing industry, Turkey was vigorous in her diplomatic efforts to have
the bans lifted. This was done fairly soon after they had been imposed
and an international symposium on ‘Dried Figs and Aflatoxins’ was held
in Izmir, Turkey, in April 1989. More recently, in 1996, the first reports
of aflatoxin contamination of pistachios imported into Europe caused
some concern, but the producing country has taken appropriate action to
reduce the level of contamination.
In 1980, nearly 66% of random samples of maize from North Carolina
had concentrations of aflatoxins in excess of 20mgkg^1 giving rise to an
estimated loss to producers and handlers of nearly 31 million dollars. It is
rare that the losses and costs arising from mycotoxin contamination can
be calculated but these three isolated and very different examples indicate
that on a world-wide basis they must be considerable. In at least two of
these examples aflatoxin was probably formed in the commodity during
growth and development in the field. Under these conditions aflatoxin
formation is usually relatively low and in neither case was there any
evidence of harm to human beings. However, it is when commodities are
improperly stored that really high concentrations of mycotoxins may be
formed and it is in these situations that human suffering can occur.
8.5 Foodborne Viruses
Viruses differ profoundly from other types of micro-organism. They have
no cellular structure and possess only one type of nucleic acid (either
RNA or DNA) wrapped in a protein coat or capsid. They are also
extremely small, with diameters generally in the range 25–300 nm
(1 nm¼ 10 ^3 mm), so that most are invisible using conventional light
microscopy and can only be viewed with the electron microscope. Some
viruses (for example HIV) are enveloped by an outer lipid membrane,
but these cannot be transmittedviafood since they are relatively fragile
and are destroyed by exposure to bile and acidity in the digestive tract.
As obligate intracellular parasites, viruses cannot multiply other than
in a susceptible host cell whose machinery and metabolism they hijack
300 Non-bacterial Agents of Foodborne Illness