24 Questions
What is the primary source of enteric viruses that contaminate food?
Human feces
What is the current status of cultivating Norwalk-like viruses in cell cultures?
The method has not yet been successful
What is the main source of both hepatitis A and NLV outbreaks?
Food contaminated with fecal matter of infected people
What is the minimum dose level required for enteric viruses to cause infection?
Low dose level
What is the ranking of viral foodborne infection in terms of the number of cases affected in the US between 1986 and 1987?
Third
How long can NLV symptoms last?
1 to 2 days
What is the purpose of pasteurization in preventing foodborne virus infections?
To kill the viruses in contaminated foods
What is the effect of pasteurization on enteric viruses?
It can effectively kill the enteric viruses
Why are shellfish implicated in many outbreaks of both types of viruses?
Because they are harvested from water polluted with sewage
What is unique about hepatitis A virus compared to Norwalk-like viruses?
HAV can be grown in cell cultures, but NLVs cannot
What is the size range of hepatitis A and Norwalk-like viruses?
27-28 nm
When do symptoms of hepatitis A typically occur?
After 4 weeks, with a range of 2 to 7 weeks
What may or may not occur after ingesting hepatitis A viruses through contaminated food or other sources?
An individual may or may not develop symptoms
What is a major preventative method of foodborne virus infections?
Killing the viruses in contaminated foods
How are NLVs typically transmitted?
Through contaminated food and water
What is the purpose of using oxidative agents such as hypochlorite?
To kill viruses in contaminated equipment or in water
In what year was Vibrio parahaemolyticus first recognized as a foodborne pathogen in the U.S.?
1971
What is the optimal temperature range for the growth of Vibrio parahaemolyticus?
30 to 37oC
What is the characteristic of Vibrio parahaemolyticus that makes it sensitive to drying?
It is extremely sensitive to drying
What is the name of the toxin produced by Vibrio parahaemolyticus?
Thermostable direct hemolysin (TDH)
What is the characteristic of Vibrio parahaemolyticus that allows it to grow in the presence of salt?
It is halophilic
What is the seasonal variation of Vibrio parahaemolyticus in estuarine environments?
It is present in higher numbers during summer months
What is the characteristic of Vibrio parahaemolyticus that makes it vulnerable to pasteurization?
It is sensitive to heat
What is the characteristic of Kanagawa-positive strains of Vibrio parahaemolyticus?
They can cause hemolysis
Study Notes
Viral Foodborne Infections
- Viral foodborne infections are rarely examined for contamination, but they were the fifth leading cause of foodborne disease outbreaks in the US between 1973 and 1987.
- Between 1986 and 1987, viral infections ranked third in the number of cases affected by foodborne disease outbreaks.
- Hepatitis A and Norwalk-like viruses are the most commonly associated viruses with foodborne infections.
Characteristics of Viral Infections
- Foodborne viral infections can only occur from enteric pathogenic human viruses.
- Hepatitis A and Norwalk-like viruses are small RNA viruses, with sizes of 27-28 nm.
- Hepatitis A viruses can be grown in cell cultures and used to produce vaccines, while Norwalk-like viruses have not been successfully cultivated in cell cultures.
Habitat of Viral Infections
- Enteric viruses are excreted in high numbers in human feces and do not multiply outside the human body, including contaminated foods.
- Pasteurization can effectively kill enteric viruses.
Disease and Symptoms of Viral Infections
- Enteric viruses can cause infection at a low dose level.
- Symptoms of hepatitis A virus infection occur 2-7 weeks after ingestion and include fever, malaise, nausea, vomiting, abdominal discomfort, and liver inflammation.
- Symptoms of Norwalk-like virus infection appear 12-24 hours after ingestion and include vomiting and diarrhea.
Food Association of Viral Infections
- Food contaminated with fecal matter of infected people, either directly or indirectly, is the main source of viral outbreaks.
- Infected food handlers, even without symptoms, can contaminate ready-to-eat food with fecal matter.
- Shellfish harvested from polluted water and eaten raw or improperly heated have been implicated in many outbreaks.
Prevention of Viral Infections
- Killing viruses in contaminated foods through proper heat treatment, such as pasteurization, is a major preventative method.
- Good sanitation and personal hygiene habits, such as washing hands, can control contamination.
- Keeping suspected individuals away from handling ready-to-eat food can also prevent viral infections.
Vibrio parahaemolyticus
- Vibrio parahaemolyticus are Gram-negative, nonsporulating, motile, curved rods that are catalase and oxidase positive.
- They grow in a medium containing glucose without producing gas, but are unable to ferment lactose and sucrose.
Habitat of Vibrio parahaemolyticus
- Vibrio parahaemolyticus strains are halophilic bacteria distributed in coastal waters worldwide, with a seasonal variation and highest numbers during the summer months.
Toxin and Toxin Production of Vibrio parahaemolyticus
- Not all strains of Vibrio parahaemolyticus are pathogenic, but foodborne pathogenic strains can cause hemolysis due to the presence of a heat-stable hemolysin (thermostable direct hemolysin, TDH).
This quiz covers the importance of examining food for contamination by enteric viruses, and the prevalence of viral foodborne infections in the US.
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