Viruses

Viruses are very small infectious microorganisms. Unlike bacteria, viruses can only multiply inside the living cells of other organisms. However, many viruses show high resistance to stresses such as heat, drying, freezing, UV light, etc. and may survive for long periods in foods or the environment.

The majority of viral foodborne illnesses are caused by a few types of viruses, including:

• Norovirus
• Rotavirus
• Hepatitis A and E

Viral infections make up perhaps one-third of cases of food poisoning in developed countries. In the USA, more than 50% of cases are due to viruses. Noroviruses, which are the most common foodborne illness, caused 57% of outbreaks in 2004. A foodborne viral infection is usually of intermediate (1–3 days) incubation period, causing illnesses that are self-limited in otherwise healthy individuals and are similar to the bacterial forms described above.

Rotavirus is a genus of double-stranded RNA virus in the family Reoviridae. It is the single leading cause of severe diarrhea among infants and young children. By the age of five, nearly every child in the world has been infected with rotavirus at least once. However, with each infection, immunity develops, subsequent infections are less severe, and adults are rarely affected. There are seven species of this virus, referred to as A, B, C, D, E, F, and G. Rotavirus A, which is the most common, causes more than 90% of infections in humans.

The fecal-oral route transmits rotavirus. It infects cells that line the small intestine and produces an enterotoxin, which induces gastroenteritis, leading to severe diarrhea and sometimes death through dehydration. Although rotavirus was discovered in 1973 and accounts for up to 50% of hospitalizations for severe diarrhea in infants and children, its importance is still not widely known within the public health community, particularly in developing countries. In addition to its impact on human health, rotavirus also infects animals and is a pathogen of livestock.

More than 500,000 children under five years of age die from rotavirus infection each year, and almost two million more become severely ill. In the United States, rotavirus causes about 2.7 million cases of severe gastroenteritis in children, almost 60,000 hospitalizations, and around 37 deaths each year. There are global public health campaigns to combat rotavirus, which focuses on providing oral rehydration therapy for infected children and vaccination to prevent the disease.

Hepatitis A is distinguished from other viral causes by its prolonged (2–6 weeks) incubation period and its ability to spread beyond the stomach and intestines into the liver. It often induces jaundice or yellowing of the skin yet rarely leads to chronic liver dysfunction. The virus has been found to cause infection as a result of the consumption of fresh-cut produce, which has fecal contamination.