Several of the new outbreaks have been caused by deadly strains of bacteria that are resistant to most tuberculosis drugs.

The vaccine does not work against the three other, less deadly strains that cause the remaining 5 percent of malaria cases worldwide.

That only a few months ago scientists were tinkering with deadly strains of bird flu in less-than-top-security labs.

Jack was surer than ever that both his captors had the deadly strain of the flu.

A quarter of prisoners catch the deadly multidrug-resistant strain.

But the deadly strep strains have an additional weapon that turns them into the flesh-destroying variety.

In animal studies, he finds that mice infected with the deadly strains of bacteria all die.

But the deadly strains of these bacteria are infected with a virus that directs them to make a toxin.

Experts say the exceptionally deadly strain is almost impossible to find.

And although technology is making the creation of ever more deadly strains possible, the idea of using germs in warfare has a long history.