Researcher Had Bacteria for Plague at His Death

[newmum35]

http://www.nytimes.com/2009/09/22/us/22chicago.html

CHICAGO — A weakened and ordinarily harmless strain of the bacteria that cause plague may have led to the death of a University of Chicago researcher.

The researcher, Malcolm Casadaban, 60, had a weakened strain of the bacteria Yersinia pestis in his blood when he died from an infection on Sept. 13, university officials said. An autopsy showed no obvious cause of death except the presence of the bacteria, they said. Dr. Casadaban, an associate professor at the university, was studying the bacteria to create a better vaccine for plague.

IF what they say is true, and people (researchers, indeed) "rarely die from being infected with an ordinarily harmless strain of the bacteria or viruses they are studying" then why in the world are they even wasting time trying to create a vaccine for it? Is it intended to be an animal vaccine or something? I just don't get it.

[JohnBozz]

NewMum35,

Many vaccines against harmful microorganisms are developed using attenuated strains. For example, the polio vaccine is a live vaccine made from the polio virus that was attenuated to make it relatively safe to give to humans. When the weakened strain is taken orally, it will replicate in the body (in the intestine of humans) and the body will generate an immune response against it by making antibodies. These antibodies will neutralize not only with the weakened (attenuated) strain of polio but also the virulent strain that causes paralysis.

The goal of vaccine researchers is to find the right type of attenuated strain that will cause no (or little) harm to the human but still induce a strong immunological response that will protect the human. There are not a lot of live bacterial vaccines (most use killed organisms) so it is proving quite difficult to find just the right combination of safety and effectiveness.

A more modern approach to making a bacterial vaccine is NOT to use the entire bacterial cell (even a weakened one) but to make a sub-component vaccine derived from a part of the cell. For example, there is a vaccine against tetanus that is prepared by taking the extremely potent toxin from the bacteria and inactivating the toxin (with formaldehyde). Next, the inactivated toxin (called toxoid) can be used to immunize a human since it is no longer toxic but will induce an immunological response that will neutralize the toxin. So, when you receive the DTP vaccine, the "T" component is the tetanus toxoid, the "D" component is the diphtheria toxoid (inactivated toxin), while the "P" is an "acellular" vaccine. The acellular pertussis vaccine is much safer than the older pertussis vaccine that used killed, whole cells. The new vaccine employs purified components from bacterial cells that were broken open.

I hope this answers your question. If not, please follow up.

Cheers,

[newmum35]

I think I get it. I must have misunderstood (or perhaps it was poorly worded)... so they were trying to create a vaccine for a bacteria that was naturally deadly. But it was the artificial strain they work with that rarely causes death (which in this case caused death anyway). I got it now.