Tuesday, September 27, 2005

H5N1 Spreading in the Human Population

Most people know we are in danger, but these sites make it clear just how much danger. In addition to the possibility of H5N1 simply continuing to evolve into a major killer there is also a steadily increasing danger that the more it spreads the more chance it has of infecting a human who is infected with a human flu. The mixing of two flu strains within the cells of a single organism could cause H5N1 to suddenly gain the ability to become a panemic. The biggest danger would be if there are a large increase in H5N1 cases this flu season, which would seem likely considering there is a large increas in the prevalence of other flu strains at this time. Because there would be more H5N1 cases and more human flu cases, the chance of a single person getting both forms of the flu at the same time would be dramatically increased.

Though the danger of such an event occuring has been with us ever since H5N1 reappeared in 2001, the danger is particularly acute this year because contrary to what is publically reported by the WHO, human to human transmission of H5N1 Avian flu has become quite common. And although the WHO grudgingly admits that H5N1 can be transmitted from a person who has been infected by chickens or other foul to another person, but denies that it can be transmitted beyond the first person infected, this may also be false.

Why the lack of accuracy? The simplest explaination is simply lack of data. Not every case gets tested and even when tests are done our weak immune response causes a lot of false negatives. Then again there are positive tests that are not counted because a second corroborating test wasn't performed. For example the official data records no cases of H5N1 in Thailand during 2004, yet there were 12 cases with positive tests for H5N1 that didn't make it into the official numbers. That article also lists multiple cases which due to lack of laboratory testing are not included in the numbers and which appear to indicate human to human transmission that is being reported not to exist.

Then there are cases which were not even initially thought to be flu related. This was due to causing meningitis-like symptoms. Four people attending the wake of a fifth person all died within a span of three days aproximately 1 1/2 weeks later even though they had returned home after the wake to separate cities. At the time H5N1 was not known to cause meningitis-like symptoms without apparent respiratory symptoms. Now it is known to do so. Since none of the victims from the wake were tested we cannot know whether or not this was caused by H5N1. However there are basically only two possible culprits. H5N1 would only have to gain the ability to transmit as efficiently from person to person as it transmits from chicken to checken. Meningitis would have to gain the same ability (and is less likely to do so since it has never been an easily spread illness), and would also have to develop a much higher case fatality rate. Note that the 5 fatalities in this cluster was 2 1/2 times the entire number of cases of Meningitis in the country that year. It is very unlikely that this was caused by Meningitis, thus making a strong case that H5N1 caused the deaths, and thus indicating that it can transmit from human to human with much greater ease than health officials have been willing to admit.

The danger posed by the meningitis form of H5N1 is particularly accute because it is operating completely under the influenza monitoring system's radar. Everyone is looking for a respiratory flu, not meningitis. Furthermore because Meningitis has symptoms that are less obvious than the respiratory symptoms that we associate with flu, others nearby are less likely to avoid contact with infected persons, and people who are infected are less likely to make changes in their behavior that would reduce their contact with others, like calling in sick from work. Thus a meningitis form of flu would be likely to spread more easily than a rispiratory form.

Once sustained human to human transmission begins, it will quickly accelerate. If it is occuring now, it is quite sporadic. However before now H5N1 couldn't improve its ability to transmit from human to human much because the virus died with its victims, so every human to human transmission was an evolutionary dead end. In a concentrated population even if the ability to transmit from human to human multiple times were weak, it would still occur. Thus the viruses able to transmit only once would die with the first victim, those which could transmit only twice would die with their second vicetim, etc. Those viruses that could pass on to new victims indefinitely would be able to survive and possibly be communicated into the community at large. Furthermore those viruses that could transmit from human to human most easily would infect more victims, thus forming a larger portion of each generation than those that could only transmit from human to human with difficulty. This would continue until the most virulent strain was the dominant strain of the flu in the human population. If those viruses were somehow able to re-enter the avian population, for example by a scavenger bird eating flesh from a corpse that had died of H5N1, they might then be able to spread even further.

Changes like these occur because the genome of any Influenza strain is in a constant state of change. This is due to the process of recombination, which occurs continuously as flu viruses infect animals or people who are already infected by another flu virus, and pick up genes from other strains. Viruses also mutate, and then those mutations are added back into the mix. Again, as H5N1 continues to spread, the number of these recombinations will continue to increase. Also as human flus become more common during the flu season, the chance that this mixing will occur between H5N1 and a human flu increases.

2 Comments:

At 10:32 AM, Anonymous Anonymous said...

Need to protect your children from the spread of Avian Flu? Check out the hilarious video you MUST show the kids!

http://collegeguru.blogspot.com/2006/02/burt-flu-bird-with-bird-avian-flu.html

 
At 11:31 PM, Anonymous freepoultryconsultant said...

In retrospect, I consider the brouhaha on bird flu all but negative hype which resulted into deaths, not from bird-flu afflicted persons, but psychological and economical "deaths" afflicted poultry farmers. The poultry industry downturn from the "bird-flu" affected countries were so severe that it became almost impossible for farmers to come out of financial debts when the brouhaha subsided. There are even reports of actual people deaths coming from farmers committing suicides from depression. And come to think about it, the scare is caused just by alarmist scientists who fear that the disease might eventually get transmitted from human to human which might start a disease spread of pandemic proportions! And these alarmists became very palatable for media to devour and broadcast which resulted into widespread fear and non-patronage of poultry products. So sad.

 

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