H5N1 is a highly pathogenic avian (bird) flu virus that has caused serious outbreaks in domestic poultry in parts of Asia and the Middle East. Highly pathogenic refers to the virus’s ability to produce disease. Although H5N1 does not usually infect humans, nearly 650 cases of human cases of H5N1 have been reported from 15 countries since 2003.
http://www.flu.gov/about_the_flu/h5n1/
650 H5N1 deaths in a period of 12 years? Ebola has killed 1552 so far this year and is still spreading.
http://www.cdc.gov/vhf/ebola/outbreaks/guinea/
I still say do the math.
The high path and low path designations typically refer to the ability of an avian flu virus to cause disease in birds, not humans. Most avian influenzas, whether high or low path, do not cause disease in humans at all.
H5N1 causes severe disease in humans, but is minimally contagious--that is, it does not pass from person to person. The reason for both the severity of disease and the lack of human to human infectivity is that this virus binds to cell surface receptors that exist in bird guts and deep in human lungs. The inflammation of deep lung tissues sometimes has fatal consequence, but the virus cannot escape the lower lung spaces. Controversial research carried out independently by Fouchier and by Kawaoka showed that 5 mutations in H5N1--4 in the hemagglutinin, one in the viral polymerase--will cause it to switch from infecting the lower lungs to binding cells in the upper respiratory tract (bronchia, throat). This causes the virus to be highly contagious, but will also (most likely) decrease disease severity. The fear that causes health organizations to continue to watch this virus is that it will undergo those mutations in the wild and cause a pandemic. Even with a decreased death rate due to the different area of infection, it could still have a very high death rate. The 1918 flu had about a 1-2% case fatality rate--enough to kill millions. Contagious influenza viruses can spread through aerosols, and are contagious in the absence of symptoms.
The spread of Ebola is not caused by any virus changes, and we have no reason to think that the virus is even capable of changing to a form that could be spread by aerosolization from upper respiratory tissues. The spread is caused by human behavior--for instance, by people getting sick and hiding, while infecting their caregivers through exposing them to highly infectious fluids. Burial customs that involve washing corpses, giving them enemas, and handling them during funerals also spread Ebola. Since human behavior, not virus biology, is really responsible for the spread of Ebola, there is no reason to think that it will become a local epidemic, much less a pandemic.
For perspective, over 600,000 African children die from malaria every year. About 5,000 people in that part of Africa die from Lassa fever every year--in fact, the reason it took so long to recognize the Ebola outbreak was that Lassa is a hemorrhagic fever with symptoms very like Ebola. Only about 1% of those who get Lassa die. There are many other diseases, far more prevalent in that part of the world, that cause many more deaths annually than have died from Ebola since this outbreak started.