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Water and Food Associated Viruses and Emerging
Pathogens of Concern
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Polio
The genus Enterovirus is made up of small (28 nm), singlestrandedRNA viruses, and includes poliovirus, which was at
one time the only virus known to be foodborne.
Polio can be a transient viraemia with an incubation
period of 3-5 days and characterized by headache, fever
and sore throat, but in a minority of cases it can progress
to a second stage where the virus invades the meninges
causing back pain and headaches.
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In the worst cases the virus may spread to neurons in the
spinal chord causing cell destruction and various degrees
of paralysis.
Previously, contaminated milk had been the principal
source of foodborne polio but this route of infection had
been controlled by improvements in hygiene.
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ASTROVIRUSES
Astroviruses are spherical, positive-sense, single-stranded
RNA viruses belonging
to the family Astroviridae.
Astrovirus infections are mainly spread by person-toperson transmission via
the faecal–oral route, however, a very small percentage
of infections are estimated to be foodborne.
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Evidence of astroviruses in naturally grown oysters has
been reported in Japan,particularly in product sampled
during the winter season.
A food handler infected with astrovirus could potentially
contaminate almost any foodstuff. This could present a
risk of infection if it is consumed without a further heating
step.
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Sources
Humans are the reservoir for human astroviruses and
infected individuals can excrete very high numbers of
viruses.
Infections are usually spread via the faecal–oral route.
Faecally contaminated-water sources (both drinking
and recreational), shellfish from contaminated water
and foods contaminated by infected food handlers can
also be sources of human astroviruses.
The control of astroviruses should focus on the
implementation of strict persona hygiene by food handlers.
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HEPATITIS A VIRUS
The hepatitis A virus (HAV) is an enteric virus, which
causes a liver disease in humans now known as hepatitis
A (previously known by other names including
infectious jaundice, viral hepatitis and infectious
hepatitis).
There are a number of different hepatitis viruses but
only the HAV, and possibly the hepatitis E virus, can
cause foodborne disease.
HAV is a single-stranded RNA virus belonging to the
Picornaviridae family and the genus Hepatovirus.
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Although HAV is most commonly spread by direct personto-person contact via the faecal–oral route.
Foodborne outbreaks can often be traced back to an
infected food handler or foods that have come into
contact with faecally contaminated water.
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In recent years fresh produce, such as salads, fresh fruits
and vegetables, has increasingly been implicated in
foodborne outbreaks of hepatitis A.
These products are likely to be consumed raw or lightly
cooked, and can become contaminated with faecal
matter at almost any point during growing, harvesting,
transport and packing.
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The infective dose for the HAV is unknown. However, it
is thought that as few as 10–100 virus particles could
cause disease.
The incubation time for symptoms to appear is on
average about 4 weeks, but it can vary from 2–6 weeks.
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Many cases of HAV infection are asymptomatic,
particularly in children.
When disease is evident, hepatitis A infection is usually a
mild illness. Initial symptoms include headache, fatigue,
fever, poor appetite, abdominal discomfort, nausea and
vomiting. After a week or so, viraemia (where the virus
can be detected in the blood stream) and liver disease in
the form of jaundice, or liver enzyme elevation, occurs.
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Hepatitis A is usually a self-limiting disease lasting for up
to 2 months, but in a small group of affected people, the
HAV can cause long or recurring illness lasting up to 6
months.
Infection can be fatal, particularly in people over 50
years old.
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Sources
The human intestine is the main reservoir for the HAV
and asymptomatic infected individuals, especially
children, are an important source of the virus.
Transmission can occur by the faecal–oral route by direct
person-to-person contact, or from the ingestion of
faecally contaminated food or water.
It has been reported that transmission of the virus can
occur as the result of using viruses contaminated drinking
glasses.
Infected food handlers with poor hygiene are potential
source of the virus in food.
The virus could potentially be present in any water source
or soil that is faecally contaminated.
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HAV can survive in the environment in water or soil for
at least 12 weeks at 25 1C.
The HAV has a high resistance to many chemicals and
solvents and it is more resistant to heat and drying than
other enteroviruses. It can survive refrigeration and
freezing for up to two years and it is resistant to acid (pH
1 for 2 h at room temperature).
The HAV is resistant to low levels of free chlorine (0.5–1
mg free chlorine/l for 30 min). It is also resistant to
perchloroacetic acid (300 mg/l) and chloramines (1 g/l)
for 15 min at 20 1C.
The virus can be inactivated on surfaces with a 1:100
solution of sodium hypochlorite, or household bleach in
tap water.
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The hepatitis E virus (HEV) is an enteric virus, which
causes a liver disease in humans now known as hepatitis
E (other names for the disease include, enterically
transmitted non-A non-B hepatitis and faecal-oral nonA non-B hepatitis).
The HEV is distinctly different from the hepatitis A virus
and is a single-stranded RNA virus, which has recently
been classified in the family Hepeviridae and the genus
Hepevirus.
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The virus is most often associated with pigs, and surveys
to determine the frequency of the HEV in pig
populations and in pork livers have been conducted
in a number of countries. Pigs carrying the HEV do not
show any signs of disease and the virus is now known to
be present in most pig populations throughout the
world.
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Although all individuals are susceptible to contracting
hepatitis E, the disease is most frequently seen in the 15–
40-year-old age group.
The infective dose for the HEV is unknown and the
incubation time for the disease can vary from 2 to 9
weeks. Many HEV infections are asymptomatic, cause no
sign of disease, and where hepatitis E does occur it is
usually a mild illness lasting 3–4 weeks.
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The symptoms for this mild form of the disease include
general fatigue, jaundice, production of darker urine and
pale stools, abdominal pain, vomiting
and nausea.
However, the virus can occasionally cause a severe
disease with complete liver failure and even death,
especially amongst individuals who are pregnant or
immunocompromised, suffering from chronic liver disease,
or from older age groups. In pregnant women the disease
may also cause a miscarriage.
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Sources
In developing regions the main source of the virus is
drinking water contaminated with human faecal
material.
In developed countries the main source of the virus is
from direct or indirect contact with animals.
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The virus is known to survive frozen storage for extended
periods and is also able to survive in the gastrointestinal
tract, indicating that it is relatively resistant to acid
conditions. It does appear, however, to be very sensitive
to high salt concentrations and is inactivated in
chlorinated water.
Control
Strategies to reduce the risk of foodborne outbreaks of
hepatitis A should focus on preventing foods from
becoming contaminated.
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Highly pathogenic avian influenza (HPAI) viruses belong
to the family Orthomyxoviridae, and within this family
these viruses are in the group known as influenza type-A
viruses.
Influenza type-A viruses are classified into subtypes,
and are named according to two main surface proteins,
haemagglutinin (‘‘HA’’) and neuraminidase (‘‘NA’’).
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Although influenza A viruses can infect many animals
including birds, humans, pigs, dogs, cats and horses, wild
birds are the natural hosts for these viruses.
Some avian influenza viruses can be transmitted to
humans and cause illness.
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There have been concerns that humans may become
infected with the H5N1 virus by the handling and
consumption of contaminated poultry and poultry
products, and this has led to research into the virus and
its potential as a foodborne pathogen.
However, it is important to note that, although there is a
theoretical potential for foodborne transmission of the
virus, this has not yet been conclusively demonstrated.
Most public health authorities, including the World
Health Organization (WHO), do not currently consider
HPAI H5N1 to be a food safety hazard.
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Poultry, such as chickens and turkeys are particularly
susceptible to HPAI viruses such as H5N1. All parts of the
infected bird, including blood, meat and bones, are
potentially contaminated with virus.
The virus is also present in the saliva, nasal excretions
and faeces of infected birds resulting in the
contamination of feathers.
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The HPAI H5N1 virus is also present on the inside and on
the surface of eggs laid by infected birds.
To date, there is no evidence to suggest that humans
have contracted the H5N1 virus through the
consumption of eggs or egg products.
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There are many strains of avian influenza A viruses,
however, only four subtypes (H5N1, N7N3, H7N7 and
H9N2) are known to cause illness in humans.
Usually these viruses cause mild influenza-like symptoms
such as fever, muscle aches, a cough and a sore throat or
sometimes conjunctivitis.
It is thought that the incubation period for the H5N1 virus
in humans is between 2–8 days but may be as long as 17
days (the WHO advises that an incubation time of 7 days
be used to monitor patient contacts for the disease).
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Initial effects may include influenza-like symptoms, a
temperature of greater than 38 1C, or acute encephalitis.
Sometimes, watery diarrhoea without blood,
vomiting, chest pain, abdominal pain, and bleeding
from the nose and gums have been described.
Typically initial symptoms are followed around 5 days
later by lower respiratory tract illness such as breathing
difficulties, respiratory distress, a hoarse voice, a crackling
sound when inhaling and sometimes the production of
sputum, which may contain blood. Deterioration is rapid
with the development of acute respiratory distress and
possibly multiorgan failure.
The disease has an associated mortality rate of 55%.
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Sources
Wild water birds are thought to be the main reservoir for
the H5N1 virus, and some species, particularly ducks, are
thought to act as asymptomatic carriers.
Pigeons may also play a role in the spread of the virus.
Mammals such as cats have also been infected with H5N1
virus and have died from the disease.
Other mammals, such as dogs, have also tested
serologically positive for the virus in outbreak areas,
indicating that they too can become infected.
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If the H5N1 virus is present in poultry meat, it can
survive in this environment under chilling and freezing
conditions with little affect on levels or the viability of
the virus. In general, low temperatures actually
prolong the survival of the virus in poultry tissue.
Control
Control of HPAI viruses currently focuses on containing
outbreaks in poultry by culling infected birds,
implementing strict biosecurity measures and limiting
movement of poultry within designated areas.
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NOROVIRUSES
Noroviruses is the name given to a group of related nonenveloped, singlestranded RNA viruses that have recently
been classified in the family Caliciviridae, genus Norovirus.
Food vehicles for noroviruses are thought to include
sewage-contaminated bivalve shellfish, foodstuffs that
are contaminated by an infected handler, fruits and
vegetables contaminated during irrigation or washing,
and water (including drinking water and ice).
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Infected food handlers can contaminate any foodstuff,
and outbreaks of NoV infections can be associated with
any food that is handled and will be eaten without a
further cooking step.
Contamination can occur during the preparation of
foods as well as during the harvesting of fresh produce
such as oft fruits.
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Sources
Humans are the only known reservoir for noroviruses.
Faeces or vomit from infected individuals can lead to the
environmental contamination of soil, water and surfaces.
Airborne droplets produced during vomiting are a
particularly effective method of distribution for viruses.
Noroviruses can accumulate and concentrate in the guts
of bivalve molluscs such as oysters and mussels, growing
in sewage-contaminated waters.
Control
To reduce the risk of foodborne transmission of noroviruses,
controls should focus on ensuring the use of potable water
for food processing, strict hygiene control, and using
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shellfish from approved waters.
PARVOVIRUSES
The parvoviruses are very small, single-stranded DNA
viruses belonging to the family Parvoviridae.
Data is very limited, although parvovirus or parvoviruslike particles have been linked to a number of outbreaks
associated with the consumption of shellfish.
Gastroenteritis caused by parvovirus has been described
as ‘‘winter vomiting virus’’, suggesting similarities with
norovirus infections.
During some outbreaks it has been found that large
numbers of virus particles are excreted in the faeces of
many patients.
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Parvoviruses causing gastroenteritis in humans are likely
to be found in environments that are faecally
contaminated.
Control
To reduce the risk from viral gastroenteritis associated
with the consumption of shellfish it is important to ensure
that shellfish are harvested from approved waters and
that these products are properly cooked prior to
consumption.
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ROTAVIRUSES
Rotaviruses are non-enveloped, double-stranded RNA
viruses, which are classified as belonging to the family
Reoviridae, genus Rotavirus.
There are seven described species or ‘‘serotypes’’ of
rotavirus (known by the letters A–G).
The name rotavirus is derived from the characteristic
wheel like appearance of
the viruses when viewed under an electron microscope.
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Potentially, an infected food handler could contaminate
any food prepared and consumed without a subsequent
heating step. Salads, cold foods (such as sandwiches and
hors d’oeuvres), fruits and contaminated water
(including ice cubes) have all been implicated in cases of
foodborne rotavirus infections.
Rotaviruses have also been detected in shellfish.
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In developing countries rotaviruses cause an estimated
125 million cases annually in infants and young children.
Sources
Infected individuals act as a reservoir for human
rotaviruses. Individuals suffering from the disease, as
well as asymptomatic cases, excrete high numbers of the
virus into the environment in their faeces.
Control
Strategies to reduce the risk of foodborne outbreaks of
rotavirus infections should focus on preventing foods
from becoming contaminated by the use of clean water
for the irrigation, washing and processing of foods, and
preventing shellfish-harvesting areas from becoming
contaminated withsewage.
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SAPOVIRUSES
The sapoviruses are a group of single-stranded, positivesense, RNA viruses recently classified in the family
Caliciviridae, genus Sapovirus.
Human caliciviruses, including sapoviruses, could
potentially be present in any food or water supply where
faecal contamination is present.
Sapoviruses usually cause infections in infants and young
children, although in neonates infections are often
subclinical.
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The incubation time for sapovirus infections is 1–3 days,
and symptoms persist for about 4 days.
Typically, the illness is characterised by watery stools,
mild or acute diarrhoea, vomiting, nausea, stomach
cramps and sometimes a low fever.
Transmission of sapoviruses generally occurs via the
faecal–oral route. Secondary infections between close
contacts (person-to-person transmission) such as in
schools and child-care settings are also common.
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Sources
Humans are the reservoir for sapoviruses and infected
individuals can excrete very high numbers of virus
particles.
Contaminated environmental sources such as sewage
and water (both drinking and recreational) could also
be potential sources of sapoviruses, as could foods
contaminated by infected foo handlers.
Control
The control of sapoviruses should focus on the
implementation of strict personal hygiene by food
handlers.
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