Influenza: A Tale of Birds, Pigs, and Pandemics
Influenza: A Tale of Birds, Pigs, and Pandemics
If Shakespeare were alive, he would urge caution regarding the “Ides of Influenza.” Recent publicity about global influenza, a result of both potential and real avian and swine flu epidemics, has led to a plethora of theories as well as alarm. How can the primary care practitioner answer questions, educate, prepare, and alleviate anxiety?
What follows is an influenza primer by a professed non-expert. It attempts to provide sketchy information, potentially useful to other professionals who are also non-experts.
Since influenza outbreaks are usually mild, most vaccines protective, and antivirals available—why the heightened alarm?
What was the deadliest plague in history? If you answered the Black Death or AIDs, you were wrong. Estimates today place the death toll of the 1918 flu pandemic somewhere between 50 and 100 million.1 To place that in perspective, the world’s population then was only one-third of what it is now. The pandemic occurred before the world had vaccines, antivirals, and antibiotics for secondary bacterial pneumonias. So, it won’t happen again, will it? Unfortunately, it could.
The H1N1 virus responsible for the 1918 pandemic has been “pieced together” only recently.2 Unlike the viruses that cause common, seasonal influenza, it killed persons in the prime of life at a greater rate than those who were elderly. This occurred because the antigenic determinants leading to lethality were unique and had never been disseminated throughout the global population before 1918. The potent genetic package was a direct result of influenza A’s prolific mutational abilities.
Healthy persons fared the worst. As a result of either an exaggerated “cytokine storm” or other poorly understood mechanisms (for example, lymphoid cell apoptosis), the virus targeted and preferentially killed the young. The problem is, other than the virus’s unique antigenic code, we are still not sure what rendered it so deadly. However, it killed so effectively that contemporary antibiotics would not have helped in many instances, despite the Staphylococcus aureus and Haemophilus influenzae pneumonias that followed.
The recent swine flu virus and the avian viruses waiting in the wings (sorry for the pun) share an ominous characteristic with the 1918 virus. They too can mutate successfully with new antigens to which the global population has no baseline immunity.3 In fact, that is just what appears to have happened during the recent outbreak.
What about antivirals coming to the rescue? Twelve percent of 1155 H1N1 isolates from 2007 to 2008 were resistant to oseltamivir.4 Amantadine has already fallen by the wayside for influenza A treatment.
What are the risks of—and what is the hype about—these myriad viruses living among birds, pigs, and people?
In 1997, an “avian” influenza strain (H5N1) infected humans for the first time.5 It is suspected that previous pandemics also contained hybrid bird and human viruses (eg, the 1957 H2N2 influenza virus). The 1997 virus killed 60% of those it infected; this is a higher rate than that of the notorious 1918 virus. That is why avian flu pandemic scares abound. Thirty-eight countries reported the same dangerous strain. Although human to human transmission did not occur in 1997, that protection against another pandemic may disappear after further mutations.
The recent swine flu outbreak seems not to be as bad as initially predicted. However, some experts offer a caveat.6 The first outbreak of the 1918 pandemic influenza was relatively mild, but it reappeared later with a vengeance. No one knows if this pattern will be repeated with the swine flu virus recently activated.
Watching and waiting: what can we do?
Bookmark relevant sites such as that of the CDC (http://www.cdc.gov/h1n1flu), which have critical information immediately available to the primary care practitioner. This allows you to sift the pertinent facts immediately.
Read The Great Influenza by John Barry.1 It taught me much more about influenza than my medical school, graduate training, and practice ever could. Although the media disseminates information quickly and accessibly, some of it may be too basic, especially for medical professionals.
Although the alarm surrounding avian and swine flu has not been realized to the degree of a 1918 pandemic, danger still lurks.7 We inhabit a global community with potential reservoirs for fatal zoonotic pathogens that can mutate quickly and spread within days. Any advance knowledge packaged for the good of public health—whether it relates to quarantine, antivirals, or multiple vaccinations—is important to primary care practitioners.
Global pandemics can become a reality as recent events have reminded us. We will be the ones who bear the brunt of prevention, questions, and care.
1. Barry JM. The Great Influenza: the Story of the Deadliest Pandemic in History. New York: Penguin Books; 2005:4.
2. Tumpey TM, Belser JA. Resurrected pandemic influenza viruses. Annu Rev Microbiol. 2009;63:79-98.
3. Neale T. IVW: “High risk” of resistant swine flu, researcher says. http://www.MedPagetoday. Accessed May 5, 2009.
4. Dharan N, Gubareva LV, Meyer JJ, et al. Infections with oseltamivir-resistant influenza A (H1N1) virus in the United States. JAMA. 2009;301:1034-1041.
5. Pappaioanou M. Highly pathogenic H5N1 avian influenza virus: cause of the next pandemic? CIMID. 2008;32:287-300.
6. Smith M. Tsunami of swine flu news leaves world awash in questions. http://www.medpagetoday. Accessed May 5, 2009.
7. What you should know about swine flu: Q & A with Dr. Michael Greger. http://www.hsus.org. Accessed May 5, 2009.