Viruses are microorganisms primarily composed of nucleic acid (DNA or RNA) strands and an outside capsid, or a coat of protein. They are extremely small (0.004 to 0.1 micron in diameter) at about 1/100 the size of bacteria. Generally considered a parasite, they are incapable of growth without a host and are commonly referred to as a “parasitic infectious microbe”.
Viruses are simple in structural composition and vary widely in appearance. Some have very complex shapes and resemble spiked balls or lunar landing spacecraft. On their outside surface are receptor sites which are highly adept at recognizing specific host cells suitable for supporting the growth of particular viruses. Although there are a few viruses that cross the species barrier, these receptors make viruses largely specific to humans, plants or animals.
Replication of viruses can only take place in a living host cell. Once inside the human host, viruses are either engulfed into a host cell or effectively inject their nucleic acid into the cell wall. The virus genetic material takes over the host cell's mechanics, forcing it to create more virus parts. Following replication, virus parts are assembled and released from the cell, which are now able to invade neighboring cells and repeat the process. Because one virus can enter a single cell and thousands may leave that same cell, virus infections can spread very rapidly throughout the body.
Commonly found in our environment on surfaces, in the air, and in food and water, viruses can also be transmitted via insects. Most viruses “of concern” in food and water are known as enteric viruses. These viruses occur in the intestines and include enteroviruses, adenoviruses, rotavirus, hepatitis A virus and caliciviruses. They are spread by fecal/oral route, commonly via contaminated food and water.
Infection of a cell by a virus is often debilitating to the cell's regular functions. Viral infections may be asymptomatic or may cause acute or chronic illness. Among many types of viruses, more notable and potentially deadly viruses include: Norwalk-like viruses (gastroenteritis); hepatitis A and E (hepatitis), poliovirus (paralysis); rotavirus (gastroenteritis); echovirus (meningitis and encephalitis); coxsackie virus A (meningitis, respiratory disease, fever); and coxsackievirus B (myocarditis, congenital heart disease).
In water, there are several proven treatment methods to effectively remove a significant level of virus. These methods are chlorination, Ultraviolet (UV), ozonation, distillation, iodinated resin and electro adhesion. Reverse osmosis, nano-filtration, and other forms of ultrafiltration have also been used to significantly purify water by reducing/removing viruses from a contaminated water supply.
A safe method of emergency water filtration, along with supplies for good hygiene, are critical components of a survival plan – both to avoid exposure and to prevent the spread of a virus. Once a virus has infected a species, options are limited and typically involve treating the symptoms rather than the infection itself with antibiotics being generally not effective. Antiviral agents have been developed to slow the progress of the viruses, but are rarely a fast or complete cure.