Most of the lethal diseases in early Europe did not originate there. They came from Asia or Africa.
Small Pox is believed to come from Northeast Africa some 12,000 years ago. It was then carried from ancient Egypt to India along various trade routes. The mummified body of Pharaoh Ramses V, who died in 1157 bce, shows telltale signs of Small Pox on his body. From there it followed the trade routes to Asia and Europe. This Article gives a brief timeline of the disease and early methods of treating it. ANational Geographic article I recently read also gives a similar timeline of the spread of small Pox from Egypt to the Europe and the Americas but says that the disease is about 3,000 years old instead. This article tells us that there is a historical record of people being vaccinated some 2000 years ago in Asia by blowing powdered scabs from infected people up their noses. This knowledge became lost as the virus travelled from Asia to Europe.
In The History of Smallpox and it's Spread Around The World I read that Smallpox was brought back to Europe by the Crusaders and did not show up in Denmark until 1241. If this is true then it could not have appeared in Greenland or North America until well after the Vikings first appeared on this side of the ocean.
The Viking colonies were small as were the Inuit populations of Greenland. This information page from the World Health Organization tells us that smallpox is ..... "The virus which causes smallpox is contagious and spreads through person-to- person contact and saliva droplets in an infected person’s breath. It has an incubation period of between 7 and 17 days after exposure and only becomes infectious once the fever develops. A distinctive rash appears two to three days later. The most infectious period is during the first week of illness, although a person with smallpox is still infectious until the last scabs fall off." so it is probable that these small numbers coupled with the late arrival of smallpox in Northern Europe could very well have insulated early North American natives from major smallpox outbreaks.
While reading about the history of my local area I came across an interesting article in Historylink.org that examined the Smallpox epidemic that hit British Columbia in 1862. It gives us a look at how the Indians themselves reacted to this dreaded disease and an amusing firsthand account by Joseph Crow on how the Indian doctors treated their patients. Joseph Crow's account goes as follows:
"At the time of the small pox epidemic among the Indians in 1864 they used the Tomanus House as a hospital and built little houses along the bay, in which they dug a hole in the ground fille[d] it with rocks and built a fire on them. "When they were red hot they would throw water, put the paitent [patient] in the room and get him to sweating hard and then cause him to jump into the bay, which would always cause death"
"The[y] would then lay the patient out on the ground of the Tomanus House and get two boards laid with blocks at each end and pound the boards with clubs and yell at the top of their voices, keeping this up all day and night making hideous noises."
"The doctor would be working on the patient all the time, biting him on the head and neck to blede [bleed] him, in fact biting al over his body, and would be continually mumbling and would shake his head and spit the blood from his mouth.
"The Doctor was only allowed to have three patients in succession and if the three died the doctor was killed.
"After the epidemic I never saw any more Indian Doctors in Seattle so you can conclude what became of them" (Hilman F. Jones Papers).