The World Health Organization is reporting cases where multiple members of families are testing positive for bird flu. When multiple infections occur in the same family that raises the threatening possibility that the bird flu is mutating into a form that is more capable of human-to-human transmission. The development of that capability could ignite a deadly worldwide bird flu pandemic which could potentially kill tens of millions of people. Some of the bird influenza cases being found in Vietnamese families are strongly suggestive that human-to-human transmission is taking place.
Since the family members are infected with identical or closely related H5N1, distinguishing between a common source and human transmission is heavily dependent on onset dates. Most cases show symptoms 2-4 days after exposure. Therefore, cases involving a common source will develop symptoms at about the same time. If the transmission is from one family member to another, there will be a longer time lag and the onset dates will be bimodal.
As noted above, the latest familial cluster from Thai Binh has a 7 day differential between onset dates suggesting the sister was infected by her brother.
Since primary caregivers for sick family member are most often female another sign of human-to-human transmission is the higher rate of infection of females in cases where multiple family members are diagnosed with bird flu.
However, another way to demonstrate human-to-human transmission in these other familial clusters is to simply compare the gender distribution of the primary cases relative to the secondary. There were 13 index cases in the 12 clusters (in one cluster cousins developed symptoms at the same time). There were 6 females and 7 males indicating the risk to both sexes was similar. In contrast, 11 of the 14 secondaries were female.
Why should we be alarmed by these reports? Karl Nicholson, a professor of infectious diseases at University of Leicester in Britain who currently working on bird flu vaccine development says bird flu has a very high mortality rate.
Based on the current recognized cases of the illness, it seems to have an 80% mortality rate, says Nicholson.
Imagine a virus with such a high mortality rate mutating to become easily transmissible between humans.
The World Health Organization said Tuesday that seven Vietnamese patients who initially tested negative for bird flu have been found to be carrying the virus after their samples were retested.
All seven, who were first tested in January, have since recovered, said WHO regional spokesman Peter Cordingley.
Still, even if some of the current estimate for bird flu mortality rate is overstated it is very unlikely to be overstated by, say, a full order of magnitude.
A 26-year-old male nurse from northern Vietnam who provided bedside care for a 21-year-old bird flu patient now in critical condition has himself tested positive for H5N1 avian influenza, according to media reports from the region.
It is possible the nurse was exposed to the patient's blood or mucus. It is not clear that the nurse got the virus from the patient and even if he did it is not clear that the virus was transmitted by a route that would mean the virus has developed greater ability to move between people.
Whether or not these cases indicate the avian flu is now more able to spread between humans the virus is still over there moving through duck, chicken, and other bird populations. It may still mutate into a massive killer pandemic.
Should the bird flu break out into the general population keep in mind that in my past posts I've listed things we ought to do to reduce our risks of getting the flu in the case of a killer pandemic. If I don't turn out to be one of the early victims when the pandemic starts I'll colllect together all those items and you all can then read my comprehensive list of things you ought to do and ought not do.
One thing you ought to do now: Tell your government to accelerate the development of better flu vaccine production technologies so that when a killer pandemic eventually shows up in the human population we will be able to more quickly and massively manufacture vaccines.
|Share |||Randall Parker, 2005 March 10 01:37 PM Dangers Natural Bio|