From Plague to Leprosy: 7 Diseases We'd Forgotten About

Some cases have received publicity, but the disease tends not to be well known here. Part of the reason is that the disease is very treatable with the administration of antibiotics.

But, while the disease is controlled, it is unlikely to be eliminated completely.

"Getting rid of Yersinia pestis completely from nature, that's unlikely," Markel said. "It's still in the flea population and it's still in the rat populations, and I don't know how you're going to kill all of the fleas and all of the rats."

Spanish and Swine Flu -- H1N1

The outbreak of so-called Spanish flu in the winter of 1918-19 caused tens of millions of deaths. While the current strain, known as swine flu or influenza A, has claimed 1,462 lives to date, according to the most recent numbers from the WHO.

But flu season has yet to arrive, and the possibility of more deaths from the pandemic has many worried. And despite the different names given to the influenza strains, both have the same basic structure, H1N1. The virus has mutated -- and survived -- despite efforts to eliminate it.



"We don't know exactly where these viruses hide in the time that they aren't active in the population," said Dr. Patricia Winokur, a professor of internal medicine at the University of Iowa who is working on developing a vaccine for swine flu. "Somewhere they lay dormant and then get into the human population at different times."

While 1918 marked, perhaps, the most deadly worldwide pandemic of influenza attributed to H1N1, Markel noted that accounts of influenza date as far back as the Renaissance, although it's difficult to determine which strains were responsible.

"We just have these old accounts, but it's not the same kind of data that we'd use today," he said.

But influenza has managed to adapt over time, changing each year to beat the human immune system.

"Each year, they're just a little bit different," Winokur said. "Those proteins have shifted just a little bit over time, and our immune system isn't perfect about capturing those new genetic variants."

She noted that scientists have developed a vaccine to help prevent flu and antivirals to lessen the impact of an infection, but, "They're not flat-out cures."

"This strain will likely stay in our population for quite some time, and eventually it will be replaced by new strains," Winokur said. "A lot of it has to do with this type of virus being able to mutate quite quickly. Each year it mutates and creates a slight variation on itself, and that allows it to survive and continue to infect humans."

Compounding the problems with wiping out influenza is the fact that it can live in animals, such as birds and pigs.

"It's been traditionally very hard to eradicate diseases that have broad animal reservoirs," Winokur said. "We can't vaccinate all birds and all swine the way we could, for example, [vaccinate people against] smallpox."

Polio

Like smallpox, polio has a vaccine and, therefore, many have high hopes that it can be eradicated. It is virtually gone from the United States but is still a problem abroad.

"There is an elimination strategy being led by the World Health Organization," Hotez said. "There was great optimism it could be eradicated just like smallpox."

But polio has some distinctions from smallpox that make such an outcome less likely.



Polio can cause paralysis, in the legs and even the lungs.

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