Bird Flu in Americans – how likely is it?

Some of my students asked me whether we should be worried about the report of a Colorado man testing positive for the H5 bird flu virus.

  • Before I answer that question, let’s go through what an H5 bird flu virus is.
    • Bird flu aka avian influenza caused by the H5 subtype is highly pathogenic and can cause severe disease and death in infected flocks of poultry (a better target than humans).
    • What does H5 mean?
      • To be explained soon.
  • Another question would be: is this virus contagious?
    • It is highly contagious, which means these viruses can spread rapidly through poultry flocks and also spill back into wild aquatic birds, which is where Influenza A viruses naturally circulate.

There are four main types of Influenza (aka flu) viruses, A, B, C, and D, of which, only A and B cause
notable human disease.
There is one important distinction between A and B:

  • A is able to infect multiple animal species, including waterfowl such as ducks, geese, swans, gulls, and terns, and shorebirds, such as storks, plovers, and sandpipers.
  • A can also infect pigs, chickens, and horses.
  • B, on the other hand, infects mostly humans.

Poultry and wild birds infected with bird flu A viruses allow these viruses access to their guts and respiratory tracts.

  • Once inside the gut and respiratory tract, these viruses can start reproducing (making millions of new viruses) and spread through bird droppings, bird snot (nasal secretions) and saliva.
  • Rarely, poultry workers can get infected with bird flu when they inhale these viruses or pick them up from contaminated surfaces and subsequently touch their eyes, nose, or mouth – essentially, self-infecting with unclean hands.

In the rare instance that Influenza A of the H5N1 type does infect humans, the resulting flu can end up being really severe.

  • In fact, H5N1 shows greater than 50% mortality in humans – i.e. more than half of those infected have died from it.

Good news:

  • Even in these high severity cases, it is extremely rare for bird flu viruses to spread from an infected person to other people.

Even more good news:

  • To monitor the possibility of bird flu viruses mutating to a form that spreads rapidly through humans, influenza surveillance centers across the globe engage in 24/7 surveillance.
  • For this mutant scenario to be probable, the virus would need to undergo “reassortment,” which is the mixing together of pieces of virus genome.
    • More on this soon.

Over the last two years, we’ve heard a lot about SARS-CoV-2 and its RNA genome.

  • The SARS-CoV-2 genome is on a continuous piece of RNA.

Influenza viruses, on the other hand, carry their RNA genome in pieces (scientific term: segments), kind of like matchsticks in a matchbox.

  • Let’s say there are 2 different strains of Influenza viruses:
    1. the not-so-deadly, but common and seasonal human flu virus (Influenza A virus)
    2. the deadly, but rare bird flu virus (also Influenza A)
  • Let’s say these 2 strains infect the exact same cell inside ONE human body
    • Once inside the body, these 2 strains of flu viruses will start making more copies of themselves (reproduce).
    • Once both viruses are inside the same cell, it is possible that some of the genomic segments from Strain 1 will become part of Strain 2, and vice versa.
      • This is “reassortment.”
      • This would be an error. But, it could happen.
  • Let me repeat this:
    • As a result of “reassortment,” there could be new seasonal flu viruses carrying segments of bird flu viruses, and vice versa.
    • IF this were to happen, we would want to know whether this mutant is contagious like seasonal flu as well as lethal like bird flu.
    • Is this possible?
      • The experts seem to think YES.
  • This possibility is why influenza surveillance centers monitor flu activity all across the world, year-round. This is also why the federal government maintains a stockpile of vaccines against Influenza A viruses H5N1 and H7N9 (another highly pathogenic bird flu virus).

The vaccines are for general use if these bird flu viruses start spreading person-to-person.

  • Let’s get back to the Colorado man who tested positive for bird flu.
  • At this time, we do not know if this is H5N1, the highly pathogenic strain (form) of bird flu virus. 
    • We do know that the virus has the H5 part of this bird flu virus.

What does this mean for others? 

  • While surveillance for more human cases is ongoing, there are a few protective measures
    we can take to protect ourselves from bird flu:
    1. avoid contact with wild birds – these birds may be carry flu viruses and not look sick;
    2. wear gloves, a medical facemask, and eye protection while handling poultry that are
      sick or have died; discard the gloves and facemask; change your clothes, and
      wash hands well with soap and water;
    3. avoid touching surfaces that may have come in contact with wild birds or poultry flocks.

At this time, what should poultry workers with a possible infection with bird flu viruses, know?

  • Humans infected with bird flu viruses (again, a rare scenario) may show either
    • no symptoms, or
    • mild illness such as
      • pink eye and/or colds, or
    • severe pneumonia, that could get fatal.

The CDC recommends prompt treatment with antiviral drugs for humans who show symptoms of bird flu.

  • Coming back to the our original question of worry over “bird flu in Americans,” I would say No. And the major reason for that is our public health infrastructure, which includes surveillance.

I will finish with one last thought:

  • given the possibility of antiviral resistance, and our heightened awareness of hand hygiene, strict adherence to hand hygiene and not touching our faces until our hands are clean will definitely help protect against a variety of viruses.

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