Chapter 31
Viruses and Some Other Proven and
Suspected Foodborne Biohazards
VIRUSES
Much less is known about the incidence of viruses in foods than about bacteria and fungi, for several
reasons. First, being obligate parasites, viruses do not grow on culture media as do bacteria and fungi.
The usual methods for their cultivation consist of tissue culture and chick embryo techniques. Second,
because viruses do not replicate in foods, their numbers may be expected to be low relative to bacteria,
and extraction and concentration methods are necessary for their recovery. Although much research
has been devoted to this methodology, it is difficult to effect more than about a 50% recovery of
virus particles from products such as ground beef. Third, laboratory virological techniques are not
practiced in many food microbiology laboratories. Finally, not all viruses of potential interest to food
microbiologists can be cultured by existing methods (the Norwalk virus is one example). However,
the development of reverse transcription–polymerase chain reaction (RT–PCR) detection methodology
has allowed the direct detection of some foodborne viruses in oyster and clam tissues.
5
The efficacy of the RT–PCR technique to detect viruses in foods has been demonstrated by a
number of researchers. In one study, four concentration and extraction methods were compared for the
recovery of added astrovirus, hepatitis A, and poliovirus from mussels, and the glycine solution and
borate buffer methods were found to be best.
106 Using RT–PCR, several combinations were effective
in allowing detection of the three viruses from the analyzed samples. By using oysters spiked with 10
1
to 10
5 plaque-forming units (pfu) of poliovirus 1 or hepatitis A and concentration with polyethylene
glycol, the combined concentration and purification scheme permitted the detection of poliovirus and
hepatitis A, and 10
5 RT–PCR amplifiable units of the Norwalk agent.
53 In another study, dot-blot
hybridization detection of amplicons from the RT–PCR allowed the detection of as few as 8 pfu of
hepatitis A per gram of oyster meat.
32 The use of other concentration methods for hardshell clams
spiked with poliovirus 1 or hepatitis A at 10
3 pfu allowed the recovery of 7 to 50% of poliovirus 1 and
0.3–8% of hepatitis A.
34 When clam meat was spiked with the Norwalk agent, detection at levels as
low as 450 RT–PCR units/50 g of clam extract was achieved.
34
Because it has been demonstrated that under unsanitary conditions any intestinal bacterial pathogen
may be found in foods, the same may be presumed for intestinal viruses, even though they do not
proliferate in foods. Cliver et al.
30 noted that virtually any food can serve as a vehicle for virus
transmission, and they have stressed the importance of the anal–oral mode of transmission, especially
727
Viruses and Some Other Proven and
Suspected Foodborne Biohazards
VIRUSES
Much less is known about the incidence of viruses in foods than about bacteria and fungi, for several
reasons. First, being obligate parasites, viruses do not grow on culture media as do bacteria and fungi.
The usual methods for their cultivation consist of tissue culture and chick embryo techniques. Second,
because viruses do not replicate in foods, their numbers may be expected to be low relative to bacteria,
and extraction and concentration methods are necessary for their recovery. Although much research
has been devoted to this methodology, it is difficult to effect more than about a 50% recovery of
virus particles from products such as ground beef. Third, laboratory virological techniques are not
practiced in many food microbiology laboratories. Finally, not all viruses of potential interest to food
microbiologists can be cultured by existing methods (the Norwalk virus is one example). However,
the development of reverse transcription–polymerase chain reaction (RT–PCR) detection methodology
has allowed the direct detection of some foodborne viruses in oyster and clam tissues.
5
The efficacy of the RT–PCR technique to detect viruses in foods has been demonstrated by a
number of researchers. In one study, four concentration and extraction methods were compared for the
recovery of added astrovirus, hepatitis A, and poliovirus from mussels, and the glycine solution and
borate buffer methods were found to be best.
106 Using RT–PCR, several combinations were effective
in allowing detection of the three viruses from the analyzed samples. By using oysters spiked with 10
1
to 10
5 plaque-forming units (pfu) of poliovirus 1 or hepatitis A and concentration with polyethylene
glycol, the combined concentration and purification scheme permitted the detection of poliovirus and
hepatitis A, and 10
5 RT–PCR amplifiable units of the Norwalk agent.
53 In another study, dot-blot
hybridization detection of amplicons from the RT–PCR allowed the detection of as few as 8 pfu of
hepatitis A per gram of oyster meat.
32 The use of other concentration methods for hardshell clams
spiked with poliovirus 1 or hepatitis A at 10
3 pfu allowed the recovery of 7 to 50% of poliovirus 1 and
0.3–8% of hepatitis A.
34 When clam meat was spiked with the Norwalk agent, detection at levels as
low as 450 RT–PCR units/50 g of clam extract was achieved.
34
Because it has been demonstrated that under unsanitary conditions any intestinal bacterial pathogen
may be found in foods, the same may be presumed for intestinal viruses, even though they do not
proliferate in foods. Cliver et al.
30 noted that virtually any food can serve as a vehicle for virus
transmission, and they have stressed the importance of the anal–oral mode of transmission, especially
727