Hello Science in the News members!
We want to thank you again for making the 2005 “Science in the News” seminar series such a success. We hope that you enjoyed it as much as we did and we also hope that you join us for a brand new series of seminars beginning in September 2006. In the meantime, our monthly newsletter resumes with the article below about a topic that has been making headlines around the world. If you have any questions you'd like us to address about the science behind the bird flu or other topics in biology or medicine, please visit our Science in the News question and answer page for details on how to submit your question (http://sitn.hms.harvard.edu/).
Happy New Year from all of us at Science in the News!
One Flu Over the Cuckoo's Nest
Usually the flu is just a passing nuisance that we hope to avoid for the sake of not feeling miserable for a few days. However, every so often, a strain of the flu is particularly nasty. What does this have to do with poultry? Birds like chickens and ducks, both wild and domesticated, have flu viruses of their own. When bird flu starts infecting humans the outcome can be deadly. Why this occurs and what can be done to prevent millions of human deaths are the concerns of public health officials worldwide and the subject of this SITN newsletter.
The last serious flu pandemic occurred in 1918, and two less deadly pandemics occurred in 1957 and 1968. A pandemic is an epidemic that affects a wide geographic area and a large percentage of the population. A normal death toll for the flu is about 36,000 American lives each year. In 1918 there were over 50 million deaths, and the 1957 and 1968 pandemics resulted in a total of about 2 million deaths. Researchers have some ideas about what makes these flu strains so deadly and why the 1918 strain was especially deadly.
Although other infectious diseases such as polio and chicken pox require only one vaccine to confer immunity, the flu requires a new vaccine to be made and administered each year. The flu virus is able to mutate rapidly and therefore, every new flu season there may be a new strain of the virus. Usually the mutations are minor and therefore previous exposure to a related virus or vaccination can aid in keeping the infection under control. However, if a new flu virus comes from a completely different source, such as a bird, most of the human population will be very vulnerable if infected because they lack previous exposure to the virus. On the other hand, the fact that the virus comes from a completely different source also means that it will be more difficult for the virus to infect humans in the first place. The virus must first find a way to go from infecting birds to infecting humans.
In a process called reassortment, strains from two different species (ex. a human and a bird) infect the same animal and are able to swap genes. The result is a hybrid virus that has characteristics of the bird flu, but maintains the ability to infect and spread in the human population. This is what most likely happened in 1957 and 1968. However, it appears that the 1918 virus had no human origin and instead was the result of a bird flu mutating and acquiring the ability to infect, and spread within, the human population.
This is what makes the recent reports of the bird flu strain, H5N1, so serious. H5N1, named for the H and N proteins on the virus, is completely non-human. So far, H5N1 has only a very limited ability to infect people and has had even less success at spreading from person to person. Currently all human infection with H5N1 can be traced to infected birds. Although H5N1 is quite dangerous to the individuals it infects, a serious public health crisis would result only if it mutates to become more successful at human infection and transmission.
Fortunately, we are not completely defenseless if a pandemic occurs. The antiviral drug, Tamiflu, is effective in slowing the replication of the H5N1 strain during an infection and vaccines are being developed to prevent a massive outbreak. If an outbreak does occur, the easiest way to avoid infection is to stay clear of infected people and to monitor yourself and your family for symptoms. These precautions are applicable during every flu season, but they are especially important if a particularly deadly strain of flu emerges. Will H5N1 cause the next flu pandemic? No one knows, but some feel that an eventual flu pandemic is inevitable. Governments worldwide recognize the risk and are preparing by increasing supplies of antiviral drugs as well as putting more effort into vaccine development.
