Viruses, Food Safety and Sprouts

Virus

A virus is a non-cellular particle that consists minimally of protein or nucleic acid (DNA or RNA). Except for a few cases, viruses are not surrounded by a membrane. In order to survive, it must replicate inside another cell, such as a bacterium or a plant and animal cell.

Depending on their host species, viruses are distinguished between plant viruses multiplying almost exclusively within plant cells, bacterial viruses (bacteriophages) that depend on living bacteria, and animal viruses.  For the sake of discussion I will refer to animal viruses as "human viruses."

Human viruses cannot grow in foods. Since viruses are very host-specific, a human virus will rarely multiply even in foods that are still alive (like oysters). However, they can persist for a long time.

The cell walls of plants are tough and plant viruses have no specific mechanism for entering the host cell. Plant viruses depend therefore on a mechanical breach (injury) of the integrity of a cell wall to directly introduce a virus particle into a cell or on transmissionvia invertebrates (insects, nematodes, etc.).  While bacterial and fungal diseases are common in sprouts, plant virus diseases of sprouts are relatively rare.  Infection is scarcely strong enough to kill the plant.
 

Food Safety Implication

Although human viruses don't grow on food, food serves as a transportation device to get viruses from one host to another. Once the contaminated food is eaten, a virus can multiply in living cells and cause foodborne illness in humans. Sprouts can become contaminated with viruses in a number of ways, such as:

  • A Production Worker - who handles seed or sprouts and is shedding (excreting the virus in their stool). If the person practices poor hygiene, he or she may transfer the virus to sprouts or other foods.
  • Contaminated Water - used to irrigate or wash sprouts.
  • Cross-Contamination - of sprouts by contaminated food.
  • Insects - can transport viruses as they move about.
  • Seeds - may transmit virus infection either due to external contamination of the seed with virus particles, or due to infection of the living tissues of the embryo.  The latter only occurs in plant pathogens.  Chlorine is ineffective as a sanitizer against viruses.
     

How It Causes Disease

A free virus particle may be thought of as a packaging device by which viral genetic material can be introduced into appropriate host cells, which the virus can recognize by means of proteins on its outermost surface. A bacterial virus generally infects the cell by attaching fibers of its protein tail to a specific receptor site on the bacterial cell wall and then injecting the nucleic acid into the host, leaving the empty capsid outside.

Within the cell the virus nucleic acid uses the host machinery to make copies of the viral nucleic acid as well as enzymes needed by the virus and coats and enveloping proteins, the coat proteins of the virus. Release of virus particles from the host may occur by lysis of the host cell, as in bacteria, or by budding from the host cell's surface that provides the envelope of membrane-enveloped forms.

More simply put, viruses cause disease in humans by tricking healthy cells into duplicating the virus's nucleic acid instead of its own, which lets the virus multiply. Once the virus is duplicated, the healthy cell usually dies.

A retrovirus (HIV) is thought to cause AIDS, several viruses cause particular forms of cancer in humans, and many have been shown to cause tumors in animals. Other viruses that infect humans cause measles, mumps, smallpox, yellow fever, rabies, influenza, and the common cold. 

Some Examples of Human Viruses:

  • Influenza (causes the flu)
  • HIV (causes AIDS)
  • Polio (causes poliomyelitis)
  • Rhinovirus (causes colds)
  • Rubella (causes German measles)

Some Examples of Foodborne Human Viruses:

  • Norwalk Virus and other Norwalk-like viruses
  • Hepatitis A
  • Rotavirus (mainly affects young children)

Some Examples of Plant Viruses:

  • Mosaic virus
  • Mottle virus
  • Ringspot virus
     

What's the difference between viruses and bacteria?

The differences between viruses and bacteria are numerous. Viruses are the smallest and simplest life form known. They are 10 to 100 times smaller than bacteria. The biggest difference between viruses and bacteria is that viruses are parasites, so they must have a living host - like a plant or animal - to multiply, while most bacteria can grow on non-living surfaces.

Also, unlike bacteria, which attack the body like soldiers mounting a pitched battle, viruses are guerilla fighters. They don't attack so much as infiltrate. They literally invade human cells and turn the cell's genetic material from its normal function to producing the virus itself.

In addition, bacteria carry all the machinery needed for their growth and multiplication, while viruses carry mainly information - for example, DNA or RNA, packaged in a protein and/or membranous coat. Viruses harness the host cell's machinery to reproduce. In a sense, viruses are not truly "living," but are essentially information (DNA or RNA) that float around until they encounter a suitable living host.
 

Which sprouts are especially "friendly" to viruses?

  • Sprouts that are grown in uncompensated manure or unsanitary soil.
  • Sprouts irrigated with contaminated water.
  • Sprouts harvested by production workers with poor hygiene practices.

The complex, multi-layered surfaces of sprouts are more difficult to clean than, for example, the surface of an apple or potato. Finally, because many sprouts are eaten raw, there is no heating step that would inactivate the viruses.