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Happy Holidays! I give you the gift of terror. What made six of the ten age group categories for the CDC's top ten causes of death in 2010? What killed over 300 kids in 2009, and killed over 100 Americans last year? [1] What has to be contained in a Biohazard Safety Level 4 facility, and killed anywhere from 20 million to 50 million people in 1918? [2] Well, it's not chickens, but they are relevant to the topic. The topic at hand is actually the respiratory virus Influenza. If you raised your eyebrows, you aren't alone.
Influenza is everywhere- you can find Influenza A viruses in dogs, seals, people, bats, ferrets, pigs, horses, and birds. Mainly, the viruses that can jump into people are found in pigs and birds, since we either are susceptible to the same Hemagglutinin (the H in H1N1 or H4N1) proteins, or their Hemagglutinin is close enough to fit our Sialic Acid (lung cell) receptors. When you then consider that influenza has a mutation rate just above one mutation per genome replication (1 in 10,000 base pairs mutate in a genome of roughly 13,000), and each infection of a complex organism results in billions of virus particles, it's pretty easy to imagine how easy it would be for a human-competent virus to arise from an animal infection. That same process of mutation contributes to antigenic drift, which essentially boils down to the idea that the virus I give you isn't the same virus I caught. Rinse and repeat a few hundred times, and you've got a virus that's different enough that last year's vaccine or immune memory can't touch it.
It gets better. Influenza has a segmented genome, which means that each of the segments undergoes transcription separately, and while it isn't totally random, the virus isn't guaranteed to package its segmented genome correctly when it leaves the cell. So what happens when you get two different influenza viruses infecting the same cell- like, say, a pig and bird influenza infecting the same pig lung tissue? You get antigenic shift, caused by reassortment. You get some of your genome from the bird flu- maybe the part that contributes to how pathogenic the virus is- and you get some of your genome from the pig flu- the part that makes it competent for spread in humans- and you've got a brand new virus that nobody's immune system knows how to handle.
It gets even better. Animal agriculture practices aren't really great anywhere, not even the US. Pigs, chickens, and other animals susceptible to infection with influenza are kept in the thousands in very close proximity to one another. You might suggest that they'd cull the sick ones, but, at least in people, not all contagious infected exhibit symptoms. At that, those that will exhibit symptoms can be contagious one day before they show any signs of infection. What that means is that poor ag practices can contribute to the mutation, spread, or rise of a pandemic influenza. That's pretty big revenge for such little chickens.
So, we've got modern medicine, you say, who's afraid of the big bad flu? You have a small point for the moment- there's suspicion that a large number of the deaths from the 1918 Spanish Influenza were actually due to secondary bacterial pneumonia induced by the viral infection. We have antibiotics today, but maybe not for long. Antimicrobial resistance is another topic for another day, but to put it bluntly, in an interview with PBS, an associate director at the CDC stated in October 2013 that "We're in the post-antibiotic era."[3] So, we're at real risk for secondary pneumonias. So far, we've gotten lucky with bird influenzas like H7N9 or H4N1, which seem to sacrifice their ability to spread for pathogenicity, demonstrating only stuttering chains of transmission among family or persons with very close contact. Our luck is eventually going to run out, if history is any lesson.
Fight the Fear
So, now that you're thoroughly alarmed, let's talk about what we've got fighting in our corner. First, and foremost, influenza itself. It may come as something of a surprise, but the virus typically has a pretty low R0 (R-naught, also known as the reproductive number, indicates how many subsequent infections arise on average from each infection) somewhere near 1.4 [4]. For example, if there's 100 infected with a disease with an R0 of 1.4, they'll create 140 new infections during the course of their own infection. For reference, any virus with an R0 below 1 will fail in a population, and smallpox had an R0 around 3. What that means is that, with the proper application of pharmaceutical an public health interventions, containing a pandemic influenza might be within our grasp.
In the realm of pharmaceutical interventions, we have a few tools at our disposal. We have antivirals that we can use to reduce the impact and duration of an influenza infection, but not all strains are susceptible to currently available therapies, and it is possible to cause a pandemic flu to develop resistance to antivirals if they're overused or deployed inappropriately. We also have vaccines available, but their efficacy is often variable due to antigenic drift, which can allow the virus to escape a vaccine-induced immunity. Unlike with antivirals, however, vaccines are generally believed to be more effective the more they're used, because they limit the spread- thus, the opportunities the virus has to mutate- of a pathogen through a population. If you reduce the number of available hosts for a virus, you reduce the R0, and if you bring it below 1, you can bring the epidemic to a halt. However, if vaccine compliance in a population is poor, it can contribute to a pathogen escaping vaccine induced immunity by exposing the vaccinated population to viable mutants, and those among the vaccinated population who do not develop lasting immunity and would otherwise be protected through a phenomenon known as herd immunity.
Our biggest aid in preventing the rise of pandemic influenza is research and public health monitoring programs, such as the NIH and the CDC, respectively. Researchers are currently in the process of developing a vaccine that targets fundamental parts of the virus that don't tolerate mutation very well [5]. They're also doing basic research to find out what parts of the virus contribute to infectivity and pathogenesis, in hopes that we'll be able to use that information to develop drugs to target them. Public health programs monitor for new infections, and have multiple measures at their disposal- such as quarantines, isolation, travel restrictions, culling livestock, and mass media announcements- to try and slow or shut down an epidemic. Wikipedia has a wonderful timeline detailing the various public health measures that were taken to bring the 2003 SARS epidemic to a halt here.
What Can I Do?
Get vaccinated. The numbers aren't phenomenal for seasonal flu vaccine success rates, usually hovering somewhere around 70%, but that's still better than no protection at all. Even if you do get sick, it can still help lessen your symptoms and shorten the duration of your infection. More importantly, it helps limit the spread of seasonal flu through the rest of the population, which will afford protection to children, the elderly, the infirm, and the immunocompromised (like AIDS, some cancer, and transplant patients). If you think you have the flu, stay home, wear a mask if you have to go out in public, and sneeze into the pit of your elbow to keep from launching influenza particles up to six feet away from you. Washing your hands with soap and water frequently (or using hand sanitizer) and teaching yourself not to touch your face can also be effective ways to reduce your risk of catching, and thus, spreading the Flu. Also, don't go to your doctor demanding antibiotics, because they won't help. The Flu is a virus, not a bacteria, and isn't affected in the slightest. You wouldn't take Benadryl for a sprained ankle, and you don't take antibiotics for a viral illness- the only thing you'll be doing is contributing to the growing antibiotic resistance problem.
You can also help by promoting healthy agriculture practices. There's a number of good organizations out there that aren't PETA, and actually get things done by working with- not against- people. A good place to start is the FAO. You can write to your local legislature or support politicians or bills that seek to improve agricultural standards. If you're going to buy a pet bird, try to verify that the animal came from a local breeder instead of overseas. There's a large black market for exotic animals, and we're throwing the dice every time one of these animals gets imported without the proper quarantine measures. Try eating some vegetables once in a while, or buying from farmer's markets- if demand for meat slows, fewer livestock will be required to meet the demand, which will hopefully translate to less cramped conditions for livestock, like chickens. If our feathered overlords are pleased with these offerings, we may delay a pandemic a little while longer.
You can push for more funding to public health and research programs, and donate to science projects you believe in through crowdfunding sites, such as indiegogo. The biggest impact here comes from sharing the knowledge. Get educated on the flu at http://www.cdc.gov/flu/index.htm and share what you've learned here.
Sources & Citations
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