Explain the term Viruses
Viruses was demonstrated by Iwananowski in 1892, bacteria were considered the lowest forms of life. Viruses are called as 'obligate intracellular parasites', since they are unable to carry out any of the typical life functions until they are inside a host cell. Once inside the host cell, they thrive and direct the host cell to produce more viruses. As long as the virus is outside the host cell, it is known as 'vision'.
The viruses are minute when compared to bacteria. Except for a few, viruses like the cow pox virus, used in vaccination against small pox is 0.3 pm, whereas, the smallest type, like the foot and mouth disease virus is about 0.01 pm. Note, they are so small that they cannot be seen under an electron microscope.
The viruses consist of a protein layer, capsid, surrounding nucleic acid comprising either RNA or DNA. The important characteristic of viruses is that they are host- specific. Most viruses infect only one species, either animal or plant or else only very closely related species. The mammalian viruses do not affect any prant e.g. the polio virus infects humans and monkey and does not affect other animals, whereas, the tobacco mosaic virus, which attacks plants, does not affect humans. Viruses are killed in a few minutes under pasteurization temperature i.e. 62°C for 30 minutes. They are affected by general disinfectants like phenols, formaldehyde, halogens and cresols. To a certain extent, soaps and detergents inactivate them and UV light destroys all viruses. They are not affected by antibiotics unlike bacteria.
Viruses are known to cause illness although they do not grow on foods or produce toxins in foods. Food items merely act as a vehicle for their transfer. They are the intestinal or enteric type and are food borne. They spread from the hands of human carriers and from water to foods. The presence of viruses in foods, especially the shell fish grown in sewage polluted water, could be the significant route of illness in man. Other foods like hits and vegetables contaminated by faces and salad preparations using contaminated vegetables have been implicated in several outbreaks of food borne diseases. The hepatitis A virus, which causes jaundice, spreads through Food