Hepatitis

Andrew and granddad Rollosson

This weekend we drove over to Eastern Washington to attend my brother's wedding and visit family. Andrew met his great grandmother, my youngest brother and my new sister-in-law, more of his cousins, and one of Holly's uncles and his family. Andrew usually sleeps through being passed around friends and relatives but, when he ends up back in my arms, he curls up in a ball and grabs ahold of my shirt as if to say, "okay daddy, that's enough!" For me, the best part of this three-day weekend has been the amount of time I've been able to spend with my son.

Andrew received his first hepatitis B vaccine a few minutes after he was born. As I prepared to write an entry on hepatitis B vaccine I realized that this is a topic that I cannot adequately cover in a single post, so I've decided to start by writing an overview on hepatitis. This will also serve as a basis for my entry on hepatitis A vaccine when that time comes.

According to Steadman's medical dictionary, the word hepatitis comes from the Greek words hepar, meaning liver, and the suffix -ites, which commonly refers to inflammation or disease. The symptoms of hepatitis are caused by impairment of normal liver functions; these include breaking down toxins, hormones, drugs, and other substances, making clotting factors, and making albumin, a protein that holds water in the blood vessels. The liver also takes bilirubin, a byproduct of the breakdown or red blood cells, out of the blood and uses it to make bile, which aids in the digestion of fats.

Early symptoms of acute hepatitis include fatigue, malaise, muscle and joint pain, nausea and vomiting, and pain over the liver. Jaundice is yellow discoloration of the skin and sclera (whites of the eyes) from deposition of bilirubin. While jaundice is the most recognizable symptom of acute hepatitis, newborn jaundice is not caused by hepatitis.

There are many causes of hepatitis; both infectious and non-infectious. Non-infectious hepatitis include alcoholic hepatitis, autoimmune hepatitis, drug-induced hepatitis, and ischemic hepatitis. Acetaminophen (Tylenol^®) is a common cause of drug-induced hepatitis. Many cold and allergy preparations contain acetaminophen, so unintentional overdoses can occur when these medications are combined.

• Acetaminophen and children: Why dose matters
• Acetaminophen overdose
• Careful: Acetaminophen in pain relief medicines can cause liver damage

Aside from the hepatotropic viruses, several other viruses can cause hepatitis including cytomegalovirus (CMV), Epstein-Barr virus (EBV), herpes simplex virus (HSV), varicella-zoster virus (VZV), and yellow fever virus. Bacterial causes of hepatitis include brucellosis, leptospirosis, Lyme disease, and syphilis.

Hepatotropic viruses

Hepato, liver + -tropic, having an affinity for (Steadman's).

There are five known hepatotropic viruses that cause disease in humans: hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), and hepatitis E virus (HEV). There is another hepatotropic virus, GB virus type C (formerly known as hepatitis G virus), but it is not known to cause disease in humans. All five hepatotropic viruses can cause acute hepatitis, but only HBV, HCV, and HDV can cause chronic hepatitis.

Like other viruses, hepatotropic viruses invade cells and use the cells' protein synthesis mechanisms to make copies of themselves. However, hepatotropic viruses do not damage the liver directly. Hepatocytes ("liver cells") infected with a hepatotropic virus are targeted and killed by the immune system. In general, infants and young children are more "tolerant" of infection with hepatotropic viruses and are therefore more likely to have no symptoms or only mild symptoms of acute infection than adults. Unfortunately, this also means that people infected with either hepatitis B virus or hepatitis C virus as children, especially during infancy, are much more likely to be chronically infected with those viruses than adults. Adults tend have more severe acute symptoms but clear the infection more effectively than children.

Hepatitis A virus and hepatitis E virus are transmitted by the fecal-oral route. That means that to be infected with either HAV or HEV, something that a person eats, drinks, or otherwise puts in her or his mouth must be contaminated with feces. There are a lot of very common pathogens transmitted by the fecal-oral route. In two weeks, Andrew will have his first dose of rotavirus vaccine. Rotavirus, which causes diarrhea in infants, is transmitted by the fecal-oral route. Norovirus, which causes diarrhea and vomiting and is common called "stomach flu" (pet peeve: it's not the flu!), is also transmitted by the fecal-oral route. HAV, HEV, rotavirus, and norovirus are highly contagious, so it only takes a small inoculum (infecting dose) for a person to become infected and get sick with one of these viruses.

Hepatitis A used to be a very common childhood infection in the U.S. (I had it when I was 6 years old). The incidence of hepatitis A has dropped dramatically since the recommendation for universal childhood immunization with hepatitis A vaccine (CDC, 2006).

There are sporadic outbreaks of hepatitis E in the U.S., but it is much more common in developing countries. Like hepatitis A, HEV infection is usually self-limiting, however, hepatitis E is much more severe in pregnant women and is a significant cause of maternal death.

I had planned to write that there is no hepatitis E vaccine until I saw the table of contents for the September 2012 issue of Emerging Infectious Diseases: Hepatitis E, a vaccine preventable cause of maternal deaths. The State Food and Drug Administration of China approved a hepatitis E vaccine.

Hepatitis B virus, hepatitis C virus, and hepatitis D virus are transmitted by blood and bodily fluids. My next post will be on hepatitis B, so I'll go into more detail about transmission and epidemiology of these viruses as well as the effects of chronic hepatitis.

I'll end by quickly discussing a recent Centers for Disease Control and Prevention (CDC) recommendation. There are an estimated 2.7 to 3.9 million people in the United States infected with hepatitis C virus, most of whom are unaware of their infection. In the U.S., the majority of people infected with hepatitis C virus are between 45 and 65 years of age. The CDC therefore recommends that all persons born between 1945 and 1965 ("baby boomers") be tested for hepatitis C. People who are infected with hepatitis C virus will be advised how to avoid progression to cirrhosis of the liver and hepatocellular carcinoma (liver cancer). There are also treatments available to prevent progression to severe disease.

• CDC Now Recommends All Baby Boomers Receive One-Time Hepatitis C Test

 

 

References:

Centers for Disease Control and Prevention. (2006). Prevention of hepatitis A through active or passice immunization: recommendations of the Advisory Committee on Immunization Practices (ACIP). Morbidity and Mortality Weekly Report, 55(7), 1-23. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5507a1.htm.

Centers for Disease Control and Prevention. (2012). Recommendations for the identification of chronic hepatitis C virus infection among persons born during 1945-1965. Morbidity and Mortality Weekly Report, 61(4), http://www.cdc.gov/mmwr/preview/mmwrhtml/rr6104a1.htm.

Cohen, A. (2000). Liver disease. In L-E. C. Copstead & J. L. Banasik (Eds.) Pathophysiology: biological and behavioral perspectives (2nd ed.). Philadelphia: Saunders.

Curry, M. P. & Chopra, S. (2009). Acute viral hepatitis. In G. L. Mandell, J. E. Bennett, & R. Dolin. (Eds.). Mandell, Douglas, and Bennett’s principles and practice of infectious diseases. (7th Ed.). [Electronic version].

Dienstag, J. L. (2009). Chronic viral hepatitis. In G. L. Mandell, J. E. Bennett, & R. Dolin. (Eds.). Mandell, Douglas, and Bennett’s principles and practice of infectious diseases. (7th Ed.). [Electronic version].

Ferrante, M. A. (2003). Endogenous metabolic disorders. In C. Goetz (Ed). (2003). Textbook of clinical neurology (2nd ed.). Philadelphia: Saunders.

Labrique, A. B., Sikder, S. S., Krain, L. J., West, K. P., Christian, P, Rashid, M., et al. (2012). Hepatitis E, a vaccine-preventable cause of maternal deaths. Emerging Infectious Diseases, 18(9), http://wwwnc.cdc.gov/eid/article/18/9/12-0241_article.htm.

Mast, E. E. & Ward, J. W. (2008). Hepatitis B vaccine. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (5th Ed.) [Electronic version].

Ryder, S. D. (2010). Viral hepatitis. In J. Cohen, S. M. Opal, & W. G. Powderly (Eds.) Infectious diseases (3rd Ed.). [Electronic version].

 

Update: Washington State pertussis epidemic

Andrew received his first dose of hepatitis B vaccine minutes after he was born. My intention had been to write an entry on hepatitis B but, as you can see, I've had my hands full.

In April of this year, Washington State Health Secretary Mary Selecky declared that pertussis (whooping cough) had reached epidemic level in the state. At that time, 640 cases had been reported to the state Department of Health since the beginning of the year.

Last Friday (July 20, 2012), the Centers for Disease Control and Prevention (CDC) published a summary of the current pertussis epidemic in Washington State in the Morbidity and Mortality Weekly Report (MMWR). Between January 1^st and June 16^th, 2,520 cases had been reported – 13 times the number reported during the same time last year. Illinois, New York and Wisconsin have also had dramatic increases in the numbers of pertussis cases compared to last year. In fact, nearly half of all the states have reported more than double the numbers of cases in the first six months of 2012 than their total numbers of cases in 2011 (CDC, 2012a).

Overall, the national incidence of pertussis is increasing. In 2011, a total of 8,284 cases of pertussis were reported in the U.S. So far this year, 17,920 cases have been reported. One notable exception is California. A total of 7,195 cases of pertussis were reported during the 2010 epidemic in California. Last year 1,709 cases were reported in California and, so far this year, 275 cases have been reported.

I included this graph in my previous post on pertussis vaccines:

CDC, 2002

What we see is a sharp decrease in the incidence of pertussis after the introduction of whole-cell pertussis vaccine in the mid-1940's to the lowest point in 1976. Since then, there has been a gradual increase in pertussis incidence.

There are a number of factors that could be contributing to the increase in the number of pertussis cases. One is simply that pertussis is being recognized and diagnosed more frequently. Pertussis used to be thought of as a childhood disease and immunity to pertussis was believed to be life-long. We now know that immunity to pertussis wanes and that adults usually don’t have the severe symptoms that are seen in children.

The epidemiological data from the current pertussis epidemic in Washington State and the 2010 California epidemic suggests that immunity to pertussis from acellular pertussis vaccines wanes more quickly than immunity from whole-cell pertussis vaccines, which are no longer used in the U.S.

Whereas acellular pertussis vaccines contain up to 5 antigens, whole-cell pertussis vaccines contained around 3,000 antigens. Whole-cell vaccines are highly effective; unfortunately, they also have a high occurrence of adverse events ("side effects"). Acellular vaccines have fewer side effects and appear to be highly effective for the first two years after immunization, but immunity seems to wane more quickly than after immunization with a whole-cell pertussis vaccine.

So, why should my child or I receive a pertussis vaccine if I can still get pertussis anyway? There are several reasons. Even though most of the cases of pertussis are in vaccinated people, the attack ratio is much higher in unvaccinated people. Unvaccinated children are eight times more likely to get pertussis than children who have received all of the recommended doses of DTaP (CDC, 2012b). Unvaccinated children with pertussis are more likely to have severe disease, cough longer, and infect other people than vaccinated children (Baptista et al, 2006; Préziosi & Halloran, 2003; Tozzi et al., 2003).

No vaccine is 100% effective. We have known that immunity to pertussis wanes, but it now appears that immunity from acellular vaccines wanes more quickly than we thought. Nevertheless, acellular pertussis vaccines remain our best defense against pertussis.

On a personal note, one of my duties as a nurse epidemiologist in a county health department is to investigate cases of notifiable diseases. State law requires health care providers to report notifiable diseases to their local health jurisdiction (LHJ). Pertussis is one of those diseases. When the health department receives notification of a case of pertussis, one of my colleagues or I contact the parent of the child or the person with pertussis and complete a case report form. We then submit the data that we collect to the Washington State Department of Health and from there it is sent to the CDC. In this case, the CDC published their analysis of Washington State pertussis data in the MMWR cited above. In other words, the CDC report includes data that I collected.

References:

Águas, R., Gonçalves, G., & Gomes, G. M. G. (2006). Pertussis: increasing disease as a consequence of reducing transmission. Lancet Infectious Diseases, 6(2), 112-117. doi.org/10.1016/S1473-3099(06)70384-X.

Baptista, P. N., Magalhães, V., Rodrigues, L. C., Rocha, M. A. W., & Pimentel, A. M. (2006). Pertussis vaccine effectiveness in reducing clinical disease, transmissibility, and proportion of case with positive culture after household exposure in Brazil. Pediatric Infectious Disease Journal, 25(9), 844-846.

Centers for Disease Control and Prevention. (2002). Pertussis – United States, 1997-2000. Morbidity and Mortality Weekly Report, 51(4), 73-76. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5104a1.htm.

Centers for Disease Control and Prevention. (2012). Notifiable diseases and mortality table. Morbidity and Mortality Weekly Report, 61(28), ND-382-ND-395. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6128md.htm.

Center for Disease Control and Prevention. (2012). Pertussis epidemic – Washington, 2012. Morbidity and Mortality Weekly Report, 61(28), 517-522. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6128a1.htm.

Offit, P. A., Quarles, J., Gerber, M. A., Hackett, C. J., Marcuse, E. K., Kollman, T. R. et al. (2002). Addressing parents’ concerns: do multiple vaccines overwhelm or weaken the infants immune system? Pediatrics, 109(1), 124-129. http://pediatrics.aappublications.org/content/109/1/124.full.

Préziosi, M-P. & Halloran, E. (2003). Effects of pertussis vaccination on disease: vaccine efficacy in reducing clinical severity. Clinical Infectious Diseases, 37(6), 772-779. http://cid.oxfordjournals.org/content/37/6/772.long.

Rohani, P. & Drake, J. M. (2011). The decline and resurgence of pertussis in the US. Epidemics, 3(3-4), 183-188. doi: 10.1016/j.epidem.2011.10.001.

Tozzi, A. E., Ravá, L., Ciofi degli Atti, M. L., Salmaso, S., Progetto Pertosse Working Group. (2003). Clinical presentation of pertussis in unvaccinated and vaccinated children in the first six years of life. Pediatrics, 112(5), 1069-1075. http://pediatrics.aappublications.org/content/112/5/1069.full

Witt, M. A., Katz, P. H., & Witt, D. J. (2012). Unexpectedly limited durability of immunity following acellular pertussis vaccination in preadolescents in a North American outbreak. Clinical Infectious Diseases, 54(12), 1730-1735. doi: 10.1093/cid/cis287.

Ladies and gentlemen,

please allow me to introduce Andrew Craig Rollosson.

As he was walking by the Sea of Galilee, he saw two brothers, Simon who is called Peter, and his brother Andrew, casting a net into the sea; they were fishermen. He said to them, “Come after me, and I will make you fishers of men.” At once they left their nets and followed him.
- Matthew 4:18-20

The next day John was there again with two of his disciples, and as he watched Jesus walk by, he said, “Behold, the Lamb of God.” The two disciples heard what he said and followed Jesus. Jesus turned and saw them following him and said to them, “What are you looking for?” They said to him, “Rabbi” (which translated means Teacher), “where are you staying?” He said to them, “Come, and you will see.” So they went and saw where he was staying, and they stayed with him that day. It was about four in the afternoon. Andrew, the brother of Simon Peter, was one of the two who heard John and followed Jesus. He first found his own brother Simon and told him, “We have found the Messiah”
- John 1:35-41

Immunization laws

Our son - nose, lips, chin, and cheek.

I started this blog to discuss childhood immunizations but I've spent the last six months discussing vaccines and pregnancy, adult vaccines, and some immunization principles. Our son will born soon - very soon - so it's time for me to shift gears.

A number of surveys of adults have found that the majority of parents vaccinate their children according to the recommended immunization schedule and consider their health care providers to be reliable sources of immunization information (Gust et al., 2008; Kennedy et al., 2011). Although most parents of young children in the U.S. do not remember epidemics of vaccine-preventable diseases, most parents recognize that vaccines are an important way to prevent diseases (Freed et al., 2010; Gust et al., 2005). I suspect that, other than when they register their children for school and must present their children's immunization records, most parents don't give much thought to school immunization laws. Nevertheless, given some of the comments I hear from parents as well as news stories about mandated vaccines, I think there is some confusion about vaccine laws in the U.S.

First, school immunization laws are state laws. There are no federal immunization laws.

There are two operating divisions of the U.S. Department of Health and Human Services that are involved with regulating and recommending vaccines. The Food andDrug Administration (FDA) approves and licenses vaccines marketed in the U.S. The Center for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) publishes immunization recommendations. Occasionally, there are some differences between what the FDA approves and what the ACIP recommends. For example, the FDA approved herpes zoster (shingles) vaccine for persons 50 years of age and older while the ACIP recommends shingles vaccines for persons 60 years of age and older.

Neither the FDA nor the CDC mandate vaccines. In fact, the CDC is not a regulatory agency.

In Jacobson v. Massachusetts (1905), the U.S. Supreme Court affirmed states' authority to mandate vaccines. The court recognized the duty of the state to preserve the safety of the general public. Each state has its own school immunization laws and the requirements for school entry differ from state to state. In general, the states follow the ACIP recommendations; however, some vaccines recommended by the ACIP are not required by every state. One example is human papillomavirus (HPV) vaccine. The ACIP recommends HPV vaccine for males and females ages 9 through 26 years. Currently, the only state to require HPV vaccination for school entry is Virginia (6^th grade, girls only).

All states require DTaP/Tdap, MMR, polio, and varicella (chickenpox; documentation of immunity from natural infection may be acceptable) immunizations for school entry. The number of doses required varies between states as do the requirements for other vaccines such as hepatitis B, hepatitis A, meningococcal, and pneumococcal vaccines.

Just as the school immunization laws vary between states, immunization exemption laws also vary between states. There are three types of immunization exemptions: medical, religious, and personal/philosophical. Children for whom an immunization is contraindicated may obtain a medical exemption, which usually requires documentation of the reason for the exemption from a medical provider. All 50 states allow medical exemptions. Forty-eight states allow religious exemptions and 20 states allow personal/philosophical exemptions.

The requirements for obtaining an exemption vary between states. Some states require only a parent's signature on an exemption forum to obtain either a religious and/or personal/philosophical exemption. Other states have additional requirements. Last year, the Washington State legislature changed the requirement for obtaining a person/philosophical requirement. Prior to 2011, a parent or guardian could simply sign an exemption form. ESB 5005 requires the signature of a licensed health care professional who has counseled the parent on the benefits of vaccinating and the risks of not vaccinating.

Not surprisingly, states in which exemptions are easily obtained tend to have higher exemption rates (Rota et al., 2001). Several studies have concluded that nonmedical exemptions increase the incidence of vaccine-preventable diseases and increase the risk of those diseases in babies too young to have been immunized, people with medical contraindications to vaccines, and those who received the vaccine but did not develop adequate immunity (primary vaccine failure) or lost their immunity (secondary vaccine failure) (Feikin et al., 2000; Glanz et al., 2009; May & Silverman, 2003; Omer, Engler, et al., 2008; Omer, Pan, et al., 2006; Omer, Salmon, et al., 2009).

Students with immunization exemptions may be excluded from school during an outbreak of a vaccine-preventable disease (NNII, 2011). In Washington State, a local (county) health officer may require non-immunized students to be excluded from school during an outbreak (WAC 246-110-020).

Parents of infants and school-age children should review the immunization requirements for the state in which you live. See additional information below.

The ACIP recommends a dose of hepatitis B vaccine at birth, so that will be the topic of my next post.

Additional information:

Immunization Action Coalition:

• Links to stateimmunization websites

CDC:

• Requirements & Laws

National Network for Immunization Information:

• Indications, Recommendations and Immunization Mandates
 
• Exemptions from Immunization Laws

References:

Feikin, D. R., Lezotte, D. C., Hamman, R. F., Salmon, D. A., Chen, R. T., Hoffman, R. E. (2000). Individual and community risks of measles and pertussis associated with personal exemptions to immunizations. JAMA, 284(24), 3145-3150. http://jama.jamanetwork.com/article.aspx?articleid=193407.

Glanz, J. M., McClure, D. L., Magid, D. J., Daley, M. F., France, E. K., Salmon, D. A. et al. (2009). Parental refusal of pertussis vaccination is associated with an increased risk of pertussis infections in children. Pediatrics, 123(6), 1446-1451. http://pediatrics.aappublications.org/content/123/6/1446.long.

Freed, G. L., Clark, S. J., Butchart, A. T., Singer, D. C., & Davis, M. M. (2010). Parental vaccine safety concerns in 2009. Pediatrics, 125(4), 654-659. http://pediatrics.aappublications.org/content/125/4/654.full.

Gust, D., Brown, C., Sheedy, K., Hibbs, B., Weaver, D., & Nowak, G. (2005). Immunization attitudes and beliefs among parents: beyond a dichotomous perspective. American Journal of Health Behavior, 29(1), 81-92. http://www.ncbi.nlm.nih.gov/pubmed/15604052.

Gust, D. A., Darling, N., Kennedy, A., & Schwartz, B. (2008). Parents with doubts about vaccines: which vaccines and reasons why. Pediatrics, 122(4), 718-725. http://pediatrics.aappublications.org/content/122/4/718.full.

Kennedy, A., Basket, M., & Sheedy, K. (2011). Vaccine attitudes, concerns, and information sources reported by parents of young children: results from the 2009 HealthStyles survey. Pediatrics, 127(Supple. 1). S92-S99. Retrieved June 10, 2011 from http://pediatrics.aappublications.org/content/127/Supplement_1/S92.full.html.

May, T. & Silverman, R. D. (2003). ‘Clustering of exemptions’ as a collective action threat to herd immunity. Vaccine, 21, 1048-1051. http://www.sciencedirect.com/science/article/pii/S0264410X02006278.

National Network for Immunization Information. (2011). Exemptions from immunization laws. Retrieved July 7, 2012 from http://www.immunizationinfo.org/issues/immunization-policy/exemptions-immunization-laws.

Omer, S. B., Enger, K. S., Moulton, L. H., Halsey, N. A., Stokley, S., & Salmon, D. A. (2008). Geographic clustering of nonmedical exemptions to school immunization requirements and associations with geographic clustering of pertussis. American Journal of Epidemiology, 168(12), 1389-1396. http://aje.oxfordjournals.org/content/168/12/1389.long.

Omer, S. B., Pan, W. K. Y., Halsey, N. A., Stokley, S., Moulton, L. H., Navar, A. M. et al. (2006). Nonmedical exemptions to school immunization requirements: secular trends and association of state policies with pertussis incidence. JAMA, 296(14), 1757-1763. http://jama.jamanetwork.com/article.aspx?articleid=203593.

Omer, S. B., Salmon, D. A., Orenstein, W. A., deHart, P., Halsey, N. (2009). Vaccine refusal, mandatory immunization, and the risk of vaccine-preventable diseases. New England Journal of Medicine, 360(19), 1981-1988. http://www.nejm.org/doi/full/10.1056/NEJMsa0806477.

Rota, J. S., Salmon, D. A., Rodewald, L. E., Chen, R. T., Hibbs, B. F. et al. (2001). Process for obtaining nonmedical exemptions to state immunization laws. American Journal of Public Health, 91(4), 645-648. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1446650.

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 1^st: 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:

• Global Polio Eradication Initiative
• The Carter Center: Guinea Worm Disease Eradication

References:

Dowdle, W. A. (1998). The principles of disease elimination and eradication. Morbidity and Mortality Weekly Report, 48(Supple. 1), 23-27. http://www.cdc.gov/mmwr/preview/mmwrhtml/su48a7.htm.

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 (3^rd 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. http://www.sciencemag.org/content/312/5772/384.full.