Saturday, June 9, 2012

Disease eradication

First, Holly had another ultrasound on last week – it's a boy! (but I'm not going to show you that picture).

Next, Mary had surgery three weeks ago. The neurosurgeon removed about 90 to 95 percent of the tumor. Mary transferred out of the hospital into a skilled nursing facility yesterday. She is enthusiastically participating in her therapies and has regained some strength in her left side. Thanks for your prayers.

I forgot to mention that I became a published author May 1st: Improving Immunization Coverage in a Rural School District in Pierce County, Washington. I wrote the article but, since I wasn't directly involved in the study, I'm the last author listed. Now I need to get my cerebral malaria paper published!

Disease eradication

As I discussed in my post on diseases that have been eliminated from the U.S. by vaccines, the difference between disease elimination and eradication is that elimination is the reduction of the incidence of a disease to zero within a geographic region and elimination is the global incidence of a disease to zero. Another important distinction is that once a disease has been eradicated, further efforts to control that disease are no longer necessary.

So far, smallpox is the only disease that has been eradicated, so smallpox vaccination is no longer recommended for the general population. I'm a baby boomer with a smallpox vaccination scar. Holly is Generation X and does not have a smallpox vaccination scar.

There are currently two ongoing disease eradication initiatives: poliomyelitis ("polio") and dracunculiasis (Guinea worm disease).

For a disease to be considered eradicable it must meet a number of biological, economic, political, and societal criteria. Walter Dowdle outlined three primary indicators:
  • There must be an effective intervention to interrupt transmission
  • There must be a diagnostic tool that is sensitive and specific enough to detect the infection
  • Humans must be essential to the lifecycle of the infecting agent
For most eradicable diseases, a vaccine is the intervention used to interrupt transmission, but that's not the case for dracunculiasis.

For smallpox, the diagnostic tool used to detect infection was clinical presentation: a person infected with the variola (smallpox) virus had the characteristic lesions of that disease. Unlike some other infections, there was no asymptomatic carriage of variola virus. People who were infected got the disease. For polio, the diagnostic tool is clinical presentation and detection of poliovirus in stool.

In general, for humans to be essential to the lifecycle of the infecting agent means that there can be no non-human reservoirs. Two examples of diseases for which there are non-human reservoirs that come to mind are yellow fever, which infects humans and monkeys, and influenza, which infects other mammals and birds.

I won't go into the details of the economic/political/societal requirements for disease eradication. The short version is that there must be sustained political will to eradicate a disease. Since disease eradication is a global effort, you can imagine the complexities of arriving at an agreement that eradication of a disease is a worthwhile goal.

Removing a Guinea worm
CDC/ The Carter Center
The strategies used to eradicate a disease will vary with the disease and its mode of transmission. There is no vaccine for Guinea worm disease, which is transmitted through water. Instead, filtering or boiling drinking water are two of the techniques used to prevent transmission.

Polio eradication relies on three vaccination strategies:
  • High routine coverage with oral polio vaccine
  • National Immunization Days
  • Supplemental "mop-up" campaigns

As the immunization outreach coordinator at the Chiri Health Center in Ethiopia, I was involved with achieving and maintaining high routine immunization coverage in the neighboring villages. During National Immunization Days, our clinic staff would be recruited to go door-to-door to administer oral polio vaccine to all of the infants and young children within those households. I recall spending part of a day walking around Addis Ababa looking for chalk for the vaccinators to mark the doors of houses they had visited. Fortunately, there were no outbreaks of polio in our area that required mop-up immunization.

In addition to immunization, the clinic staff were responsible to report any new cases of acute flaccid paralysis (AFP) that might have been paralytic polio. Surveillance is an integral part of an eradication program. Had we seen a case of AFP in the clinic, we would have been required to send a stool specimen from the child to Addis Ababa to test for the presence of poliovirus.

Transmission of one of the three wild poliovirus types has not been detected anywhere in the world since 1999. Wild poliovirus transmission has been interrupted in all but four countries: Afghanistan, India, Nigeria, and Pakistan. Poliovirus transmission had ceased, but has been reestablished in Angola, Chad, and the Democratic Republic of the Congo. Outbreaks of polio occur in countries where poliovirus has been reimported.

Until polio has been eradicated, there is a continuing threat of importation from countries where poliovirus continues to be transmitted.

I'll spend more time talking about polio and polio vaccines in a few months when our baby is due for his first dose of polio vaccine.

More information:


Dowdle, W. A. (1998). The principles of disease elimination and eradication. Morbidity and Mortality Weekly Report, 48(Supple. 1), 23-27.

Fine, P. E. M. & Mulholland, K. (2008). Community immunity. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (5th Ed.) [Electronic version].

Hadler, S. C., Dietz, V., Okwo-Bele, J. M., & Cutts, F. T. (2008). Immunization in developing countries. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (5th Ed.) [Electronic version].

Heymann, D. L. (2011). Disease eradication and control. In R. L. Guerrant, Walker, D. H., & Weller, P. F. (Eds.) Tropical infectious diseases, principles, pathogens and practice (3rd Ed.). [Electronic version].

Olsen, B., Munster, V. J., Wallensten, A., Waldenström, J., Osterhaus, A. D. M. E., Fouchier, R. A. M. (2006). Global patterns of influenza A virus in wild birds. Science, 21(312), 384-388.