Emerging Virus!

NEW AND EMERGING VIRUS
An emerging virus is defined as a disease of infectious origins with an incidence that has increased within the last 2 decades or threatens to increase in the near future by Centres for Disease Control (CDC).
Attention has been given to viruses which cause incurable, fatal disease such as haemorrhagic fever or AIDS. The term ‘emerging disease’ is used for diseases which have historically been rarely seen. The emergence of infections is not new. It has been happening throughout history and it covers the whole range of infections.

Where does emerging virus come from?
There are many ways in which virus can emerge from. A zoonosis is the transfer of infectious agent from an animal to human. Other sources can be mutation of genes, recombination like influenza antigenic shift, geographical contact like smallpox (now eradicated), rabbit haemorrhagic disease and reappearance (shingles). A true zoonosis is poorly transmissible between humans since human borne disease transmission come to dominate spread of the virus. One example is HIV (human immunodeficiency virus) which is zoonotic (transferred from African monkey to human. But even though HIV is a zoonotic origin, it can also be transmitted from human to human. Many viruses have the ability to adapt to co-existing normal host and cause relatively mild disease. Thus a virus may circulate around the animal and be unnoticed. If this virus were to be able to infect human it would be a severe disease. Environmental changes can cause humans to come in contact with animals more.
Dengue Haemorrahgic Fever (DHF) which is under flaviviridae is an arthropod-borne viral zoonosis. It’s endemic to tropical areas which have high rain fall and hot climate throughout the year. The host for DHF is monkey by aedes mosquitoes which is the vector of DHF.

Mutation
While all viruses must have been arisen by mutations at base, the effects of this process in the limited time available to study viruses are necessarily limited. Recently there has been more evidence in virus rising like AIDS. Serological methods prove that this disease is not seen in humans before the second half of 20th century. The appearance of rabbit Haemorrahgic disease or rabbit calicivirus (RCV) also represents an apparent new disease followed by massive and rapid spread of it. Antigenic drift in influenza virus are not easily resolved from parental strains and are not considered as new or emerging viruses. A more relevant example would be appearance of drugs- resistant variants of all viruses that are treated with antiviral drugs. Drug resistance arises from mutations this does not have to occur after the drug is used. It is seen that mutation during normal replication results in viruses which differ in genetic material and physical properties.