A surprising triumph in the fight against polio

Source: polioeradication.org

The last case of polio in India occurred exactly one year ago, on January 13, 2011.  In the decades-long battle against this devastating disease, this is one of the best pieces of news in a long time.  Just two years ago, health officials counted 741 polio infections in India, and it seemed that the battle was far from over.  It may yet be, but in 2010 the cases dropped dramatically, to just 42, and last year there was only one, on January 13.


As recently as the 1950s, polio was a dreaded, incurable disease that killed or paralyzed millions of children each year.  The U.S. alone had 58,000 cases in 1952. Then came the invention of a vaccine by Jonas Salk, one of the great medical breakthroughs of the 20th century.  By the 1960s, widespread vaccination campaigns had virtually eliminated polio from Europe and the U.S.  Polio lingered in the U.S., mainly in the Amish population who refused to accept vaccinations, but it finally disappeared in 1979.

The worldwide campaign to eliminate polio started in 1988, when 350,000 infections were recorded.  Polio is extremely difficult to control, because a large majority of infected people show no symptoms, but they can still spread the virus.  Vaccination campaigns need to treat everyone who comes in contact with an infected individual in order to break the cycle of transmission.  This is especially hard to do in remote areas of poor countries, especially when the populace is suspicious and uncooperative.

The greatest challenge in India came in the desperately poor, crowded regions of the north, where health care, hygiene, and education are all very poor.  The vaccination efforts were made even more difficult by conspiracy theories among the Muslim population.  As Simon Denyer wrote in the Washington Post this week:

"Rumors spread among the region's numerous Muslims that the polio vaccination campaign was an American conspiracy to wipe them out, by making their sons impotent and their daughters infertile.... Vaccinators were stoned as they approached Muslim neighborhoods. 'The general mind-set was that the immunization campaign was aimed at ending our lineage,' said Anwar Ahmad, the head of a madrassa in a Muslim neighborhood in the city of Meerut."

The campaign turned around after UNICEF and Rotary international launched a major education effort that first convinced Muslim leaders, and then everyone else, that the vaccine would benefit their communities.  With this success in India, polio is now endemic in only three countries in the world: Afghanistan, Pakistan, and Nigeria.  The same rumors and conspiracy theories that plagued India have spread within Muslim populations in these countries as well, but India shows that the misinformation - and polio - can be defeated.

Unfortunately, even here in the U.S. we have our own conspiracy theorists: the anti-vaccination zealots over at Age of Autism, where Dan Olmsted and Mark Blaxill recently posted a series of articles claiming that polio is "a harmless intestinal bug" that only causes disease when triggered by pesticides or by arsenic.  Never mind that there is no evidence to back this truly wacky assertion; these two anti-vaxxers seem happy to invent facts to support their single-minded campaign against all vaccines, even when the vaccines are demonstrably saving tens of thousands of lives.

Polio is still with us, and it could return.  Besides the 3 countries with endemic polio, 9 other countries continue to suffer polio cases that were imported from endemic countries.  Without widespread vaccination in those countries, polio could re-establish itself in any of them.

If polio stays out of India, we can thank the thousands of health care workers who traveled to remote villages, in extremely difficult conditions, to dispense lifesaving vaccines.  Their heroic efforts have paid off for everyone.  We should also thank the combined efforts of the WHO, UNICEF, Rotary International, the Gates Foundation, and the CDC, all of whom are backing the worldwide effort to eradicate polio.  Let's root for humanity to win this one.

The black death is dead

Evolution tells us a lot about death. Of course it's about life too, but it's really about survival, which involves both life and death.

As most people know, the Black Death was a horrible plague that swept through Europe, Asia, and Africa in the 1300's, killing tens of millions of people at a time when there weren't so many people to begin with. The world's population prior to the plague, about 450 million, dropped to 350 million. About one-third of the entire population of Europe, and half the population of China, may have died. Centuries earlier, the Plague of Justinian in 541-542 C.E. may have killed even more, up to half of Europe and untold millions elsewhere around the world. In ancient and medieval times, people thought the plague was caused by rats, but the true cause wasn't discovered until 1894, when Alexandre Yersin of France and Kitasato Shibasaburo of Japan finally traced it to a bacterium now called Yersinia pestis, which is transmitted by fleas, which in turn are carried around by rats.

The plague kills all of its hosts, even the fleas:

"The bacteria multiply inside the flea, sticking together to form a plug that blocks its stomach and causes it to starve. The flea then bites a host and continues to feed, even though it cannot quell its hunger, and consequently the flea vomits blood tainted with the bacteria back into the bite wound. The bubonic plague bacterium then infects a new victim, and the flea eventually dies from starvation. " Source: Wikipedia

Gross, I know. But the original plague, the Black Death, has never returned. Why not? A study last year and another one published just this week provide the answer.

Last year, Barbara Bramanti and colleagues collected DNA from mass graves dating to the Black Death, and showed conclusively that the victims were infected with Yersinia pestis. Until this study, some scientists were uncertain about whether Yersinia pestis was the true cause, but Bramanti's research should settle that question once and for all. They also showed that at least two distinct strains of plague bacteria infected Europe, each arriving via a different route.

Further evidence appears in a remarkable new study published this week by Hendrik Poinar and colleagues. They exhumed over 100 skeletal remains from victims of the Black Death, collected from a ancient London cemetery, East Smithfield, which has been conclusively dated to the plague years, 1348-1350. Using the latest DNA sequencing methods, they identified Yersinia pestis DNA in 20 of the 109 victims.

Both studies collected enough DNA to show that the strain of Yersinia pestis from 1350 C.E. is unlike any modern strain. In other words, the original plague died out, probably long ago. The likely explanation is just this: the Black Death was simply too deadly to persist. Evolutionary theory tells us that a pathogen that kills all its victims will eventually run out of victims, leading to its own extinction. The plague bacteria needed to evolve into something less virulent, and that seems to be what happened. A bug that doesn't kill its host is far more successful evolutionarily. (Just look at the common cold, which we can't seem to get rid of.)

The same thing happened to the "Spanish" flu virus, the one that cause the terrible 1918 flu pandemic. It too evolved into a milder pathogen, and it is still with us today - the 2009 influenza pandemic was caused by a direct descendant of the 1918 virus.

The Black Death was so widespread that it even affected human evolution. In 1998, Stephen O'Brien and colleagues showed that a mutation that confers resistance to HIV first appeared in the human population in the 1300's. They concluded that this mutation can best be explained by "a widespread fatal epidemic"; in other words, the Black Death. I should be careful to explain that the plague didn't actually cause the mutation: the mutation occurred naturally. The Black Death selectively killed more people without the mutation, leaving us with a population of humans that tended to have the mutation.

In light of these new results about evolution, I can't help pointing out that, finally, that evolution has been in the news recently for another reason. Several U.S. politicians, some campaigning for President, have been attacking evolution, saying that it has "got some gaps in it" and even supporting the teaching of creationism. Scientific facts aren't affected by political statements, of course, but the future of the U.S. is. Politicians who attack evolution, whether from ignorance or from some political or religious agenda, only hurt our future potential as a technology leader. I can only hope that the public won't support these anti-science positions.