Bird Flu, People Flu, and You
In 1918, a postman went off to deliver mail to Brevig Mission, a small, remote Native Alaskan village, in spite of the fact that he was not feeling well. A week later, 85% of the people in the village, including those in the prime of their life, had died, having been suffocated by their own blood. In this same year and the year that followed, 25 to 50 million people died of influenza (flu) worldwide. The cause of this pandemic was a strain of the avian influenza virus, better known as bird flu. Does the recent increase in the number of cases of bird flu among domestic birds in Southeast Asia signify the possible return of such a devastating scourge?
The causes of viral influenza (flu) among humans are the Type A, Type B and Type C influenza viruses. Type B and C influenza viruses do not infect animals, only humans. Type A influenza viruses include those that infect humans, birds, pigs and horses.. Bird flu viruses are closely related to Type A human flu viruses and it is believed that at least parts of these viruses originated from bird flu viruses.
Viruses are made of DNA or RNA that is encapsulated in a protein shell or capsid. Sub-types of Type A influenza viruses are named for two of the proteins found on the outside of this outer shell that differ in sequence from strain to strain. These are hemagglutinin and neuraminidase and are abbreviated H and N. For example, the bird flu virus that caused the 1918-19 pandemic is now classified as Avian H1N1. The bird flu strains showing up in recent years are H5N1 and H5N2. While the most common human flu sub-types this year are H3N2 and H1N1 (but not the same as the H1N1 bird flu virus that caused the 1918-19 pandemic!). These strains come and go for two reasons: 1. Influenza viruses are genetically unstable and therefore mutate and recombine over time. and 2. New viral strains are selected by the presence of a susceptible population as human (and bird) populations become immune to past strains,.
Will the current bird flu viruses turn on humans the way the H1N1 bird flu virus did in 1918? No one knows the answer because no one knows how this happened in 1918. In an effort to better understand the 1918 bird flu virus, scientists have constructed a flu virus containing the H and N genes of this original 1918 pandemic bird flu virus using genetic material from one of the victims of Brevig Mission, Alaska, which had been preserved by the cold climate. Infection studies in mice have not deciphered why this bird flu virus turned on humans but have reinforced what we already knew - that this was one really nasty virus. One of the major differences between the human bird flu cases of 1918-19 and those of individuals infected by human strains is that the 1918-19 pandemic primarily killed adults in the 25 - 34 year old range (compared to today’s human viruses strains that result in greater fatality rates among the very young and the very old).
So far the numbers of humans infected during recent outbreaks of flu among domestic birds have been relatively small. This is because another difference between current bird flu viruses as compared to human viruses is that they do not transmit well to humans. And even when they do, they do not seem to be capable of spreading from person to person they way that human viruses do. If they ever gain this capability, we could be in deep trouble. However, there are weapons available in 2005 that were not present in 1918 for treating the flu. There are currently four FDA approved medications that block the multiplication of influenza viruses that would likely be effective against bird flu viral strains. The bad news is that there is no current vaccine with which to vaccinate humans against bird flu. This would likely have to be developed after the pandemic is already in progress (because the developers would have to know which strain to use to produce the vaccine). This could take a few months (unlike that movie with Dustin Hoffman where they are able to stop an epidemic overnight – that only happens in Hollywood).
What is the bottom line? Get vaccinated against the current strains of human flu. This vaccine is available in either inactivated or attenuated live forms. If you are younger than 5 years of age or older than 49 years of age or your immune system is comprimised, you have to stick (no pun intended) with the more commonly used inactivated one that you get by needle. Both the inactivated and attenuated vaccines are designed to induce immunity against human Type A H3N2 and H1N1 and the currently prevalent Type B human virus. As far as bird flu goes, all we can do now is watch the news, support public health efforts to prepare for a possible pandemic, and pray that none of the current bird flu viral strains figure out how to spread from human to human.
If you want to know more about influenza, I recommend the US Centers for Disease Control web site: http://www.cdc.gov/flu.
November 30th, 2005 at 1:42 pm
Does the morbity levels in the 24-35 age range suggest that there was a prior flu with similar characteristics that established immunity in the older population?
November 30th, 2005 at 2:54 pm
The possibility you suggested had occurred to me and I think it is very plausible. A prior wave of infection with the same or a related strain of the bird flu virus resulting in immunity among the older population would certainly explain why these individuals were less effected. But it would still be difficult to explain the reduced lethality of the 1918 virus for young children. In direct contrast, it is possible that the 25-34 year old age group over-responsed and this hyper-responsiveness due to prior exposure resulted in the severe and fatal hemorrhaging that occurred in these patients.
December 2nd, 2005 at 2:23 pm
Some sources have suggested that the increased morbidity was a result of a heightened immune response to the virus in essence an allergic reaction would antihistamines be useful in preventing these effects in future outbreaks. Is there any evidence to suggest that the 25-34 group was particularly susceptible to a secondary infection that contributed to its potency. Lastly are there any studies about generation skipping diseases, or generation skipping immunity, because as the speed of a fatality of disease goes up the spreadability goes down but if it skips generations the opportunity for catastrophe increase.
December 2nd, 2005 at 2:25 pm
You might also say that the 24-34 group might have been the first to grow up without regular exposure to birds due to the rapid industrialization of the time.
December 2nd, 2005 at 4:35 pm
You pose some interesting thoughts in your previous comments but I don’t have answers for any of those questions. Your last comment is also interesting. The so called “hygeine hypothesis” could very well apply here. There is no doubt that encountering infectious agents later on in life due to modern hygeine levels can alter the way in which people respond and might have something to do with changes in the effects of specific viruses on particular age groups.