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About viruses and viral disease

Amish

Polio returns to Minnesota

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amishPoliovirus has been isolated from a patient who died last month in Minnesota. Is this incident related to the outbreak of polio in an Amish community in the same state four years ago?

Here are the facts about this case that have been released by the Minnesota Department of Health: the patient, an adult, had paralytic polio, but it is not known if this played a role in death. Apparently the patient had multiple health problems, including a weakened immune system. The virus isolated from this patient is related to the infectious, orally administered poliovirus vaccine, OPV. They speculate that the patient was infected with OPV over nine years ago, because the use of this vaccine in the US was discontinued in 2000.

The fact that OPV use was discontinued 9 years ago in the US does not prove that this patient was infected with a vaccine virus at that time. The only way to answer this question would be to determine the nucleotide sequence of poliovirus isolated from the patient. From this information the number of years that the vaccine-derived virus has been replicating in humans could be determined. However, no sequence information has been reported by the Department of Health. It is likely that the patient was infected with poliovirus at any time in the last 9 years. If in fact the patient had an immunodeficiency, then infection could have persisted for at least nine years, as has been reported in other immunodeficient patients. However, it seems unlikely that the virus would replicate for 9 years in this individual, and then cause paralytic disease only recently.

I believe this individual was a member of a Minnesota Amish community and was therefore not immunized with OPV as an infant. The patient was probably infected recently with a strain of poliovirus derived from OPV. Because OPV has not been used in the US since 2000 and in Canada since 1995-96, the infecting virus was either imported from another country, where OPV is still used, or shed by an immunodeficient individual in the US. Such patients excrete poliovirus for years in the absence of clinical symptoms. A similar scenario has been invoked to explain poliovirus infection in 2005 of children in a Minnesota Amish community.

We will find out whether this speculation is correct when the Centers for Disease Control and Prevention release the complete data on this case.

You might be wondering why poliovirus has been isolated on two separate occasions in Minnesota. It so happens that the former Minnesota State epidemiologist was Dr. Harry Hull,  who previously worked on the polio eradication campaign at the World Health Organization. When he arrived in Minnesota after his WHO stint, he installed an excellent polio surveillance system in the state which remains in place to this day.

Odoom, J., Yunus, Z., Dunn, G., Minor, P., & Martin, J. (2008). Changes in Population Dynamics during Long-Term Evolution of Sabin Type 1 Poliovirus in an Immunodeficient Patient Journal of Virology, 82 (18), 9179-9190 DOI: 10.1128/JVI.00468-08

Polio among the Amish

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amishThe last outbreak of poliomyelitis in the United States occurred in 1979, when a type 1 strain imported from the Netherlands caused 13 paralytic cases among unvaccinated Amish communities in three states. Twenty years later, use of the live, attenuated poliovirus vaccine (OPV) was discontinued in the United States, and was replaced with the inactivated vaccine, IPV.  How do we explain the 2005 outbreak of polio in an Amish community in Minnesota?

The infant in this case was five months old when it was hospitalized for fever, irritability, bloody diarrhea, and recurrent infections. Vaccine-derived poliovirus (VDPV) type 1 was isolated from a stool specimen, but paralysis did not occur. VDPVs are excreted by individuals who receive OPV; they have been shown to circulate for long periods and cause outbreaks of paralytic disease in undervaccinated populations. Similar VDPVs were subsequently isolated from four other children in the same Amish community, none of whom were ill. A total of 8 out of  23 children tested had virologic or serologic evidence of type 1 poliovirus infection.

Sequence analysis of the VDPVs was used to estimate that the virus had probably circulated for 2 months in the community before infecting the infant. Such estimates are based on the known rate of sequence change in the poliovirus genome as it moves through the human population. The origin of the VDPV was not identified, despite extensive virological and serological studies of other communites in the US and Canada which might have had contact with the individuals in Minnesota. The source of the virus is probably a recipient of OPV outside of the US and Canada – these countries stopped using this vaccine in 2000 and 1995-96, respectively.

The infant was subsequently diagnosed with severe combined immunodeficiency, a disease characterized by defects in B and T cell immunity and frequent infections. Poliovirus was detected in her stool until January 2006, after which the immunodeficiency was corrected by bone marrow transplant and the virus was eliminated.

All previous outbreaks of poliomyelitis caused by VDVP were in undervaccinated communities in underdeveloped countries. The outbreak in Minnesota underscores the need to maintain high vaccination coverage: until OPV is replaced with IPV globally, circulating VDPVs pose a threat to unimmunized individuals. The outbreak is a harbinger of what could occur in countries where immunization with OPV is halted after the eradication of poliomyelitis. As the number of susceptible newborns increases, circulating VDVPs could spark an outbreak of poliomyelitis.  Another reason for switching to IPV rather than stopping immunization altogether.

James P. Alexander, Kristen Ehresmann, Jane Seward, Gary Wax, Kathleen Harriman, Susan Fuller, Elizabeth A. Cebelinski, Qi Chen, Jaume Jorba, Olen M. Kew, Mark A. Pallansch, M. Steven Oberste, Mark Schleiss, Jeffrey P. Davis, Bryna Warshawsky, Susan Squires, Harry F. Hull (2009). Transmission of Imported Vaccine‐Derived Poliovirus in an Undervaccinated Community in Minnesota The Journal of Infectious Diseases, 199 (3), 391-397 DOI: 10.1086/596052