Viruses and Some Other Proven and Suspected Foodborne Biohazards 737
Klebsiella pneumoniae
About 6 hours after consuming a fast-food chain hamburger, an individual complained of not feeling
well. After hospital admission, this organism along with generic E. coli was isolated from leftover
hamburger and from the patient’s blood, and the two matched by cultural methods.
94 The strain of
K. pneumoniae was LT+ and ST−. The coliform count in leftover hamburger was 3.0 × 10
6 /g, and
1.9 × 10
5 /g of bun.
Streptococcus iniae
There have been at least six human infections by this organism traced to a fish product. S. iniae was
first recognized in 1972 as the cause of a disease in Amazon dolphins.
20 It was next recorded in Israel
in 1986 as the cause of disease in tilapia and trout, and later seen in Taiwan and the United States.
89
The first human case was recorded in 1991 in Texas, and the second in 1994 in Ottawa.
20 Four human
cases occurred in Ontario, Canada, in 1995–1996 and the organism was isolated from both fish and
patients. The fish was tilapia that was imported from fish farms in the United States.
S. iniae appears to be a fish pathogen that causes disease in humans. In the Ontario cases, it appeared
that the organism entered the body through hand lesions. It is beta-hemolytic on sheep blood. In humans,
the organism produces fulminant soft tissue infections.
39
PRION DISEASES
Prions are unique proteins in that they can convert other proteins into damaging ones by causing
them to alter their shape. The normal cell prion protein (PrP) exists in the brain cell membrane where
it carries out some vital functions and is then degraded by proteases. However, the pathogenic form is
distorted and is resistant to proteases, and thus it accumulates in brain tissue and gives rise to disease
(see below). It has been postulated that the distorted prion molecule, acting as a template, converts
normal protein to a distorted form.
9 The normal protein (α-helical form) takes on a protease-resistant
β-flat form (PrP
Sc , PrPres) when it becomes pathogenic. The pathogenic forms tend to aggregate into
amyloid fibrils where they cause nerve cell degeneration, which leads to clinical signs of disease.
Although the evidence of a prion etiology of these diseases seems strong, the possibility that a virus
is the agent has been raised.
28
These particles were named around 1982 by Stanley Prusiner, who was awarded the 1997 Nobel
Prize in physiology for his pioneering work.
112 Prions cause the disease scrapie in sheep, goats, and
hamsters; and kuru in humans. Another prion disease of humans is Creutzfeldt-Jakob disease (CJD).
Bovine spongiform encephalopathy (BSE) is a prion disease of cattle and sheep referred to as “mad cow
disease.” All of these belong to a family of diseases called transmissible spongiform encephalopathies
(TSEs).
Bovine spongiform encephalopathy (BSE)
BSE (“mad cow disease”) was first recognized in Great Britain in 1984 and specifically diagnosed
in cattle in 1986. Four years later, over 14,000 confirmed cases out of a population of 10 million cattle
had been recognized in Great Britain. The epidemic seemed to peak around 1,000 new cases per week
in 1993. By February 1998, a total of 172,324 cases were seen in cattle in the United Kingdom.
9 A total
Klebsiella pneumoniae
About 6 hours after consuming a fast-food chain hamburger, an individual complained of not feeling
well. After hospital admission, this organism along with generic E. coli was isolated from leftover
hamburger and from the patient’s blood, and the two matched by cultural methods.
94 The strain of
K. pneumoniae was LT+ and ST−. The coliform count in leftover hamburger was 3.0 × 10
6 /g, and
1.9 × 10
5 /g of bun.
Streptococcus iniae
There have been at least six human infections by this organism traced to a fish product. S. iniae was
first recognized in 1972 as the cause of a disease in Amazon dolphins.
20 It was next recorded in Israel
in 1986 as the cause of disease in tilapia and trout, and later seen in Taiwan and the United States.
89
The first human case was recorded in 1991 in Texas, and the second in 1994 in Ottawa.
20 Four human
cases occurred in Ontario, Canada, in 1995–1996 and the organism was isolated from both fish and
patients. The fish was tilapia that was imported from fish farms in the United States.
S. iniae appears to be a fish pathogen that causes disease in humans. In the Ontario cases, it appeared
that the organism entered the body through hand lesions. It is beta-hemolytic on sheep blood. In humans,
the organism produces fulminant soft tissue infections.
39
PRION DISEASES
Prions are unique proteins in that they can convert other proteins into damaging ones by causing
them to alter their shape. The normal cell prion protein (PrP) exists in the brain cell membrane where
it carries out some vital functions and is then degraded by proteases. However, the pathogenic form is
distorted and is resistant to proteases, and thus it accumulates in brain tissue and gives rise to disease
(see below). It has been postulated that the distorted prion molecule, acting as a template, converts
normal protein to a distorted form.
9 The normal protein (α-helical form) takes on a protease-resistant
β-flat form (PrP
Sc , PrPres) when it becomes pathogenic. The pathogenic forms tend to aggregate into
amyloid fibrils where they cause nerve cell degeneration, which leads to clinical signs of disease.
Although the evidence of a prion etiology of these diseases seems strong, the possibility that a virus
is the agent has been raised.
28
These particles were named around 1982 by Stanley Prusiner, who was awarded the 1997 Nobel
Prize in physiology for his pioneering work.
112 Prions cause the disease scrapie in sheep, goats, and
hamsters; and kuru in humans. Another prion disease of humans is Creutzfeldt-Jakob disease (CJD).
Bovine spongiform encephalopathy (BSE) is a prion disease of cattle and sheep referred to as “mad cow
disease.” All of these belong to a family of diseases called transmissible spongiform encephalopathies
(TSEs).
Bovine spongiform encephalopathy (BSE)
BSE (“mad cow disease”) was first recognized in Great Britain in 1984 and specifically diagnosed
in cattle in 1986. Four years later, over 14,000 confirmed cases out of a population of 10 million cattle
had been recognized in Great Britain. The epidemic seemed to peak around 1,000 new cases per week
in 1993. By February 1998, a total of 172,324 cases were seen in cattle in the United Kingdom.
9 A total