Aetiology

So, I'm heading up to the lovely city of Minneapolis in a few hours for this conference. Though a bunch of nerds gathering to talk micro is sure to make local news, it looks like we'll be overshadowed by a real microbiology story in the Twin Cities area: four Amish children infected with polio.

Four children in an Amish community in Minnesota have contracted the polio virus the first known infections in the U.S. in five years, state health officials said Thursday.

Dr. Harry Hull, the state epidemiologist, said the cases do not pose a threat to the general public because most people have been vaccinated against polio and are unlikely to have contact with Amish people. But he said he expects to find more infections within the Amish community because some of its members refuse immunizations on religious grounds.

None of the children have shown any symptoms of the paralyzing disease. About one in 200 people who contract the polio virus suffer paralysis because of it; others typically rid themselves the virus after weeks or months.

None of the four children had been vaccinated. Three are siblings; the fourth is a baby from another family.

The infection came to light when the baby was hospitalized for various health problems and underwent tests. Authorities then began testing other members of the community for the virus.

They also mention this intriguing bit:

Hull said the infections were traced to an oral vaccine that was administered in another country, probably within the past three years.

There are 2 types of polio vaccines. Most of us in the United States get the IPV--injected polio vaccine. This is a killed vaccine, so it cannot cause polio. However, it also is not as immunogenic (therefore, you need multiple doses), and is more expensive to manufacture and distribute than the other type of vaccine--the oral polio vaccine. This is a live, attenuated (weakened) vaccine. In addition to the cheaper cost, since this is a live vaccine, it provokes a stronger immune response and is easier to administer (no needles required). Additionally, since it is live, it can be transmitted to other people who have not been vaccinated. In areas where polio remains endemic, this is an advantage--you get more bang for your buck, and people can be protected without ever being vaccinated. However, the big disadvantage of this type of vaccination is that a small number (~1 in 2 million) of recipients will develop polio. Therefore, this vaccine is no longer used in the United States where polio is no longer endemic, but because of the factors mentioned above, it is still used in developing countries where polio remains endemic. Apparently, this is the strain of polio the children acquired. So the big question is, how did these kids contract these infections?

I won't even get started ranting on the fact that these kids weren't vaccinated in the first place...:( I guess the silver lining is that because it does appear to be the vaccination strain, the kids are unlikely to suffer the worst effects of polio due to their infection.