An animal specie can be the unwilling host for a virus or other pathogen. It then serves as a reservoir from which the virus can expand, survive and thrive. When working with the World Animal Health Organization, also known as the OIE a Paris based IGO, I actually learned a lot about this subject. The fact that there are such diseases as the West Nile Virus, Avian influenza, foot and mouth disease or the Henza virus for example that have the capacity to infect humans, is a cause of great concern. This happens when the disease breaks or jumps the species barrier. Rabies is a typical example.
|Source American Society for Microbiology http://mmbr.asm.org/content/72/3/457/F5.expansion.html|
See this article about the Hendra virus found in bats.
For certain diseases such as malaria for example the host specie can be both human or animal (apes) and the disease transmission vector is the mosquito. A good site about malaria , its origins, treatments etc is found here.
The WHO publishes reported malaria cases on a per country basis here. The reduction of the disease is part of the UN millennium development goals (#6C).
|Source US CDC|
The United States Centers for Disease Control (CDC) reports WHO estimates of mortality ranging from 708,000 - 1,003,000 deaths for 2008. Current treatments are derived from plant species according to the CDC site. Take a look here for the malaria's parasite life cycle.
The micro organism responsible is called Plasmodium and there exist over a hundred species of them, four of which are known to infect humans (Source USCDC visited 2101-05-31).
A limiting factor for the spread of the disease appears to be cold temperatures (below 20 deg. C) as it prevents the completion of the anopheles mosquito's growth cycle.
So beware of global warming, for over the coming years the boundaries of the disease may spread well beyond its current areas of occurrence. Genetic mutations and viral recombination too make it possible to break the species barrier. One more reason to keep a close eye on what is happening, via animal research, with the evolution of these micro organisms and to get a vaccine ready for a potential outbreak. Aren't we all worth it?