Viruses are a type of bacteria that have an irregular life cycle in which they reproduce by division. Like all bacteria they require a living host to live and multiply. They can only infect living things as their name suggests, but viruses can infect non living things also. Unlike most bacteria viruses are unable to be seen by the human eye, only infecting objects where their viral particles are secreted.


When a virus is newly produced it is in a state of inactive waiting to be reactivated and infected by its victim. The name virus comes from the Greek word virusa which means ‘boundless’ and from the verb virus which means ‘to spread.’ A virus can be created in the lab by adding certain bacterium to a culture of infectious bacteria. The exact replication methods depend upon the type of virus. Some viruses reproduce through the use of a protein called the ‘ovary’, producing a fluid within the ovarian capsule (the eggs in a female reproductive organ).

There are two main classes of viruses: those that infect living things and those that infect non living things. Most viruses that infect living things are a type called rickettsia virus, the source of cold sores. Some of these include the herpes simplex virus, shingles and Epstein-Barr virus. The herpes simplex is responsible for approximately half of the cases of cold sores that appear in people of all ages, and the shingles and Epstein-Barr are responsible for about a quarter of all cases of blisters in people of all ages. The third class of viruses that infect non living things is the primate virus, which can be traced back to the Shingles family and is responsible for about a fifth of all cases of paronychia.

There are two types of viruses that affect the living host, these are termed as retroviruses and bacterials. Retroviruses are generally genetic and are passed on from one host cell to another. Examples of retroviruses are HIV, genital warts, and some forms of cytomegalovirus. There are also many bacterials, these are called proviruses. They are passed on by contact with the infected area, and they have their own set of instructions for replication.

There are also a few well known viral diseases that affect the body and these are: malaria, typhoid, lymphomas, AIDS, and caused by insect bites. Some viruses may be able to infect the host in more than one way. These include influenza viruses that can cause a fever and headache, and a strain of hepatitis virus that causes an array of liver problems. The most well-known viruses to affect the body are the various types of transmittable diseases that can be transmitted by direct contact with infected bodily fluids.

Of the viruses that affect living cells, some of the more common ones include: hepatitis A virus, HIV/AIDS, Epstein-Barr virus, and the bacteria Streptococcus viridans. Most viruses require living cells to survive. Without cells to proliferate, viruses cannot grow, reproduce or move through the body. Since many viruses affect the immune system, the body’s defense system tries to fight it off. When too much virus is produced and not enough cells are available to combat it, a condition called autoimmune disease occurs, in which the body attacks itself.