728 Modern Food Microbiology
for viral hepatitis of food origin. Just as nonintestinal bacteria of human origin are sometimes found
in foods, the same may be true for viruses, but because of their tissue affinities, foods would serve as
vehicles only for the intestinal or enteroviruses. These agents may be accumulated by some shellfish
up to 900-fold.
41 Viral gastroenteritis is believed to be second only to the common cold in frequency.
Incidence in Foods and the Environment
A common food source of gastroenteritis-causing viruses is shellfish. Although crustaceans do not
concentrate viruses, molluskan shellfish do because they are filter feeders. When poliovirus 1 was
added to waters, blue crabs were contaminated, but they did not concentrate the virus.
47 Shucked
oysters artificially contaminated with 10
4 pfu of a poliovirus retained viruses during refrigeration for
30–90 days with a survival rate of 10–13%.
33 It has been reported that the uptake of enteroviruses
by oysters and clams is not likely when viruses in the water column are less than 0.01 pfu/ml.
66 The
recovery method employed by the latter authors was capable of detecting 1.5–2.0 pfu per shellfish.
Although the coliform index is of proven value as an indicator of intestinal bacterial pathogens in
waters, it appears to be inadequate for enteroviruses, which are more resistant to adverse environmental
conditions than bacterial pathogens.
90 In a study of more than 150 samples of recreational waters from
the upper Texas gulf, enteroviruses were detected 43% of the time when by coliform index the samples
were judged acceptable, and 44% of the time when judged acceptable by fecal coliform standards.
42
In the same study, enteroviruses were found 35% of the time in waters that met acceptable standards
for shellfish harvesting, and the investigators concluded that the coliform standard for waters does
not reflect the presence of viruses. From a study of hard-shell clams off the coast of North Carolina,
enteric viruses were found in those from open and closed beds.
113 (Closed waters are those not open
to commercial shellfishing because of coliform counts.) From open beds, 3 of 13 100-g samples were
positive for viruses, whereas all 13 were negative for salmonellae, shigellae, or yersiniae. From closed
waters, 6 of 15 were positive for salmonellae, and all were negative for shigellae and yersiniae.
113 The
latter investigators found no correlation between enteric viruses and total coliforms or fecal coliforms
in shellfish waters, or total coliforms, fecal coliforms, “fecal streptococci,” or aerobic plate counts
(APC) in clams. Although enteric viruses may be found in shellfish from open waters, less than 1%
of shellfish samples examined by the Food and Drug Administration (FDA) contained viruses.
67 (See
Chapter 20 for further discussion of safety indicators and intestinal viruses.)
With respect to the capacity of certain viruses to persist in foods, it has been shown that enteroviruses
persisted in ground beef up to 8 days at 23
◦ C or 24
◦ C and were not affected by the growth of spoilage
bacteria.
48 In a study of 14 vegetable samples for the existence of naturally occurring viruses, none
were found, but coxsackievirus B5 inoculated onto vegetables did survive at 4
◦ C for 5 days.
62 In an
earlier study, these investigators showed that coxsackievirus B5 had no loss of activity when added
to lettuce and stored at 4
◦ C under moist conditions for 16 days. Several enteric viruses failed to
survive on the surfaces of fruits, and no naturally occurring viruses were found in nine fruits that were
examined.
63 Echovirus 4 and poliovirus 1 were found in 1 each of 17 samples of raw oysters examined
by Fugate et al.,
38 and poliovirus 3 was found in 1 of 24 samples of oysters. Of seven food-processing
plants surveyed for human viruses, none was found in a vegetable-processing plant or in three that
processed animal products.
64 The latter investigators examined 60 samples of market foods but were
unable to detect viruses in any. They concluded that viruses in the U.S. food supply are very low.
Destruction in Foods
The survival of the hog cholera (HCV) and African swine fever viruses (ASFV) in processed meats
was studied by McKercher et al.
72 From pigs infected with these viruses, partly cooked canned hams
for viral hepatitis of food origin. Just as nonintestinal bacteria of human origin are sometimes found
in foods, the same may be true for viruses, but because of their tissue affinities, foods would serve as
vehicles only for the intestinal or enteroviruses. These agents may be accumulated by some shellfish
up to 900-fold.
41 Viral gastroenteritis is believed to be second only to the common cold in frequency.
Incidence in Foods and the Environment
A common food source of gastroenteritis-causing viruses is shellfish. Although crustaceans do not
concentrate viruses, molluskan shellfish do because they are filter feeders. When poliovirus 1 was
added to waters, blue crabs were contaminated, but they did not concentrate the virus.
47 Shucked
oysters artificially contaminated with 10
4 pfu of a poliovirus retained viruses during refrigeration for
30–90 days with a survival rate of 10–13%.
33 It has been reported that the uptake of enteroviruses
by oysters and clams is not likely when viruses in the water column are less than 0.01 pfu/ml.
66 The
recovery method employed by the latter authors was capable of detecting 1.5–2.0 pfu per shellfish.
Although the coliform index is of proven value as an indicator of intestinal bacterial pathogens in
waters, it appears to be inadequate for enteroviruses, which are more resistant to adverse environmental
conditions than bacterial pathogens.
90 In a study of more than 150 samples of recreational waters from
the upper Texas gulf, enteroviruses were detected 43% of the time when by coliform index the samples
were judged acceptable, and 44% of the time when judged acceptable by fecal coliform standards.
42
In the same study, enteroviruses were found 35% of the time in waters that met acceptable standards
for shellfish harvesting, and the investigators concluded that the coliform standard for waters does
not reflect the presence of viruses. From a study of hard-shell clams off the coast of North Carolina,
enteric viruses were found in those from open and closed beds.
113 (Closed waters are those not open
to commercial shellfishing because of coliform counts.) From open beds, 3 of 13 100-g samples were
positive for viruses, whereas all 13 were negative for salmonellae, shigellae, or yersiniae. From closed
waters, 6 of 15 were positive for salmonellae, and all were negative for shigellae and yersiniae.
113 The
latter investigators found no correlation between enteric viruses and total coliforms or fecal coliforms
in shellfish waters, or total coliforms, fecal coliforms, “fecal streptococci,” or aerobic plate counts
(APC) in clams. Although enteric viruses may be found in shellfish from open waters, less than 1%
of shellfish samples examined by the Food and Drug Administration (FDA) contained viruses.
67 (See
Chapter 20 for further discussion of safety indicators and intestinal viruses.)
With respect to the capacity of certain viruses to persist in foods, it has been shown that enteroviruses
persisted in ground beef up to 8 days at 23
◦ C or 24
◦ C and were not affected by the growth of spoilage
bacteria.
48 In a study of 14 vegetable samples for the existence of naturally occurring viruses, none
were found, but coxsackievirus B5 inoculated onto vegetables did survive at 4
◦ C for 5 days.
62 In an
earlier study, these investigators showed that coxsackievirus B5 had no loss of activity when added
to lettuce and stored at 4
◦ C under moist conditions for 16 days. Several enteric viruses failed to
survive on the surfaces of fruits, and no naturally occurring viruses were found in nine fruits that were
examined.
63 Echovirus 4 and poliovirus 1 were found in 1 each of 17 samples of raw oysters examined
by Fugate et al.,
38 and poliovirus 3 was found in 1 of 24 samples of oysters. Of seven food-processing
plants surveyed for human viruses, none was found in a vegetable-processing plant or in three that
processed animal products.
64 The latter investigators examined 60 samples of market foods but were
unable to detect viruses in any. They concluded that viruses in the U.S. food supply are very low.
Destruction in Foods
The survival of the hog cholera (HCV) and African swine fever viruses (ASFV) in processed meats
was studied by McKercher et al.
72 From pigs infected with these viruses, partly cooked canned hams