Thursday, 22 January 2009

Largest DNA viruses

Orthopoxvirus (Poxvirdae)

The poxviruses are the largest known DNA viruses and are distinguished from other viruses by their ability to replicate entirely in the cytoplasm of infected cells. Poxviruses do not require nuclear factors for replication and, thus, can replicate with little hindrance in enucleated cells. Double-stranded DNA genome and is surrounded by a lipoprotein core membrane. It can remain stable for hours in the air.
Smallpox is caused by the variola virus, a brick-shaped DNA virus in the orthopoxvirus genus. The variola virus is among the largest of all animal viruses and can be seen with a light microscope. The variola virus initially infects the cells in the respiratory tract, then spreads to lymph nodes. The virus enters the bloodstream about 3-4 days after the initial infection.

Eradication of smallpox

The eradication of smallpox occurred with the observation by English physician, Edward Jenner, that milkmaids who developed cowpox, a less serious disease, did not develop the deadly smallpox. In 1796, Jenner took the fluid from a cowpox pustule on a dairymaid's hand and inoculated an 8-year-old boy. Six weeks later, he exposed the boy to smallpox, and the boy did not develop any symptoms. Jenner coined the term "vaccine" from the word "vaca" which means "cow" in Latin. His work was initially criticized, but soon was rapidly accepted and adopted. By 1800 about 100,000 people had been vaccinated worldwide.

No comments: