1978- caused by people receiving tainted blood products. Loss of helper T cells causes a complete breakdown of the immune defense, this opens up the body for any opportunistic pathogen to devastate. All the most deadly viruses known to man originated in the rain forest. The virus then is introduced to man through rodent excrement or bites. With the destruction of the rain forest and the pollution of the atmosphere, global warming is forcing many vectors to find a more hospitable habitat which brings the virus into a closer proximity to the industrialized and overcrowded world.
Viruses have the ability to infect more than one species of animal.
With this recombination can occur, but this new virus recombinant needs to have the opportunity to infect a new host. An example of this is the Influenza pandemic of the early 1900's. A strain of Influenza from a duck combine with a strain from a human in a pig with swine flu. This new recombinant then infected an immunocompromised person. This new strain of the virus killed 20 million people around the world in six months.