Water and Food Associated Viruses and Emerging Pathogens of Concern

Polio The genus Enterovirus is made up of small (28 nm), single-strandedRNA 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.

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.

ASTROVIRUSES Astroviruses are spherical, positive-sense, single-stranded RNA viruses belonging to the family Astroviridae. Astrovirus infections are mainly spread by person-to-person transmission via the faecal–oral route, however, a very small percentage of infections are estimated to be foodborne.

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.

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.

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.

Although HAV is most commonly spread by direct person-to-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.

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.

The infective dose for the HAV is unknown 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.

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.

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.

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.

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.

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 non-A 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.

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.

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.

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.

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.

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.

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’’).

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.

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.

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.

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.

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).

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%.

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.

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.

NOROVIRUSES Noroviruses is the name given to a group of related non-enveloped, 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).

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.

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 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 parvovirus-like 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.

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.

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.

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.

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.

SAPOVIRUSES The sapoviruses are a group of single-stranded, positive-sense, 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.

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.

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.

THANK YOU