A strange case of oral transmission of polio becomes

Pedro Plaza, a veteran health care worker at a clinic in Sao Paulo, Brazil, noticed some strange things at his desk. His work computer had a smudge of what looked like a shiny silver…

A strange case of oral transmission of polio becomes

Pedro Plaza, a veteran health care worker at a clinic in Sao Paulo, Brazil, noticed some strange things at his desk. His work computer had a smudge of what looked like a shiny silver substance near the letter “i.” But his co-workers had never seen such an odd trend, so Plaza took it to a lab to get it tested. The tests revealed he had cavities left in his teeth, caused by the foreign object in his mouth.

When he took his report to his employer, though, he was assured that he hadn’t broken any rules. And when he asked whether he could purchase dental dams to replace his corrupted teeth, the answer he got was no. The first known case of a poliovirus in Europe since 2006 appeared to be a case of bad hygiene rather than the spread of the virus itself.

“We were initially afraid we would see other cases, but no one reported anything,” said Mario Rezende, a spokesman for the Sao Paulo Public Health Department. In reality, though, that probably just meant the contamination in Plaza’s mouth wasn’t spread, based on how easily it was decontaminated.

Poliovirus is now eradicated from developed countries and, if not extinct, almost certainly long gone. It was first reported in 1962 in the United States. It causes a range of problems, from respiratory illness to nervous system damage to paralysis.

In humans, transmission is almost completely controlled by basic hygiene: Wash your hands frequently. If you have an increased risk of getting the virus, get vaccinated.

So, pretty straightforward to resolve. Still, it’s jarring to have a new case of polio in an industrialized country. As a result, that question of whether to recommend a vaccine to millions of people remains unanswered.

“We don’t really have a health emergency at this point,” said Robert Booyens, president of the Institute for Health Metrics and Evaluation.


Still, there was something in the way the virus was transmitted that seemed very unlike routine dental therapy.

One day, Plaza visited his dentist, just like every other time in his life. While going over his dental history, he noticed that her utensils were dirty. His dentist, it turned out, had performed dental procedures where patients coughed, hung out, and coughed and iced down the metal table. Fluids from one mouth travelled to the other, and pushed out the foreign substance that Plaza had transferred to his teeth.

The virus carried by germs and viruses is known as a sporozoite. It’s usually spread from one human to another via coughing or sneezing, or by handling contaminated surfaces. So when veterinarians refer patients to infectious disease specialists, they’re talking about it the way doctors talk about the flu. They see thousands of cases each year.

Those diseases, of course, don’t cause polio in western Europe.

Because polio was only reported in epidemiological literature—that is, from scientific studies—it was impossible to say whether it was spread from one human to another through dental practice. However, infection control experts do think that one-to-one transmission happens when people touch surfaces that are contaminated, even if they don’t breathe in the particles.

“We believe the poliovirus can be transmitted one-to-one when you reach the desk,” said Marco Machado, an infectious disease specialist at Brazil’s Federal University of Rio Grande do Sul.

With two multiple sclerosis patients infected with the same virus, he didn’t need hard evidence of one-to-one transmission, he said. But the oral transmission was definitely enough to merit investigation.

“We’re concerned and we ask that we proceed with caution,” Machado said. He hopes the infection will get its own report for the first time.

Still, thanks to flimsy dental hygiene, a polio case was never in the cards in Europe. And since public health professionals know that dental care tends to worsen oral hygiene among Brazilians who haven’t been vaccinated, the fact that poliovirus isn’t now spread there means that it isn’t circulating in the population at large.

Poliovirus remains a problem in China, which has about 1,000 known cases of poliovirus, and in Afghanistan, where 2,000 cases have been reported. But for the first time in years, there’s not much of a public health concern there. So even if the United States were to experience its first-ever case of the disease in the future, it wouldn’t be a problem for the CDC.

*This is an update from December 2015, to reflect that the ban on dental dams was lifted in 2015

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