The Homely Scientist

When looking at the world of infectious diseases, once of the huge questions is how fast it spreads and lethal it is (both in terms of number of people who die and how quickly).  The Spanish Flu of 1918, there hasn’t been a flu that deadly since, why?  Ebola, pretty much 100% lethal, very infectious, but because people die so quickly (not to mention horribly) it tends to burn out quickly.  Scientists looking at West Nile Virus have found that a minor change in the amino acids of the virus can have profound effects:

The amino acid change in question alters the sequence of a protein called a helicase that’s involved in the process of making copies of the virus. A scan of WNV sequences from around the world show that this appears to be the only site in the entire viral genome that’s under positive selective pressure. As a result, the amino acid change found in the North American strain appears to have arisen at least three times in the virus’ history.

Typically, viruses that rapidly kill their host have a very short history, as they rapidly run out of places to reproduce. The authors suggest that the Kenyan WNV strain is actually at a reproductive disadvantage, however, in that the amount of circulating virus in the blood is so low that it is unlikely to be picked up by the mosquitos that spread it. In contrast, the lethal strain not only hits levels in the blood that are five orders of magnitude higher, but it causes its victims to become feverish and lethargic, making them easy targets for mosquitos. These mosquitos then help the virus hop to species where it is less deadly, such as blue jays, sparrows, and humans, which can act as reservoirs for WNV. Source: Single amino acid change turns West Nile Virus into a killer

Applying this knowledge gives epidemiologists another way to both track viruses and potentially a way to combat them as well.

I keep putting Germs, Guns, and Steel on my reading list, but if this post interests you, this book might as well:

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This entry was posted on Tuesday, August 14th, 2007 at 9:46 pm and is filed under Science outside. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.