Further Mystery Surrounds Plague Death of Scientist

A follow up Story to the Death of a Chicago Scientist caused by Plague - Previous Story

Before Malcolm Casadaban died on September 13, the 60-year-old microbiologist at the University of Chicago had been suffering from flu-like symptoms.

Another victim of swine flu? Perhaps - but an autopsy revealed he had plague bacteria in his blood.

Casadaban was reported to have been working with a weakened vaccine strain of Yersinia pestis, intended for the development of vaccines against plague.

However, doctors are not sure the bacilli in Casadaban's blood were the cause of death, or how they got there. So what's going on?

Y. pestis has been linked to the medieval Black Death, though proof has been elusive. We do know that it kills several thousand a year by causing bubonic plague, and it is considered a potential biological weapon.

The University of Chicago has not revealed which strain the Yersinia was, but says it should have been safe:

This strain is not known to cause illness in healthy adults and has been used in some countries as a live-attenuated vaccine to protect against plague. It has been approved by the Centers for Disease Control and Prevention (CDC) for routine laboratory studies. The weakened strain does not require the special safety precautions required for work with virulent strains.

But the case reminds me of misgivings that have been voiced about weakened strains, which might not be as safe as they seem.

The strain seems likely to have been EV76, which is used as a vaccine in Russia and Madagascar. It is considered unlikely to revert to the virulent strain - but even without reverting, it kills some mice immunised with it.

Worse, up to a fifth of people vaccinated with EV76 develop flu symptoms such as fever, headache, weakness and malaise, according to Rick Titball of the University of Exeter, UK, a leading Yersinia expert. Some even need hospitalisation, he says, though no deaths have ever been reported that we know of.

Of course, we don't yet know whether these findings have any bearing on Casadaban's tragic death. For that we'll need to which strain was in his blood and whether it was the bacteria that killed him.