Strain W family’ found in Russian prisons
A bad actor made worse by drug resistance
The same family of TB strains that produced strain W — the agent that wreaked havoc during the multidrug-resistant TB outbreak earlier this decade — appears to be widespread throughout prison systems in the former Soviet Union, says Barry Kreiswirth, PhD, director of the Tuberculosis Center at the Public Health Research Institute (PHRI) in New York City.
That discovery is the result of two kinds of research, he says. By examining the molecular "fingerprints" of hundreds of isolates over recent years, PHRI has identified similarities among types of the strain W family, he says, allowing investigators to develop a sense of what features have persisted over time in the strain family.
At the same time, researchers have been scrutinizing hundreds of isolates supplied by Russia’s national TB laboratory in Moscow. (See related stories, pp. 55-56.) Since those isolates represent a cross-section of isolates from penal colonies all over Russia, PHRI researchers have concluded that the same sorts of features they’ve spotted in the 10 or so versions of strain W that have turned up in the United States also are present in the cultures from the Moscow lab.
That’s not good news, says Kreiswirth. "All we can say for sure is that when you see strains like this, you should be worried," he says.
The strain W family is clustered throughout the prison system in Russia and is widespread across the entire country, he adds. "We’re seeing the same strain types scattered across 19 oblasts [the equivalent of provinces], all the way from the Sea of Japan in the East, to Chechnya and Georgia in the West."
Along the way, PHRI researchers also have decided that there is something inherent in the nature of the strain W family that makes it unusually successful in humans, Krieswirth says. That contradicts previous thinking on the subject, he adds. At one time, TB experts surmised that strain W spread quickly chiefly because clinicians, not suspecting it was resistant to so many frontline agents, weren’t treating patients effectively soon enough, so patients remained infectious for longer periods of time. Plus, the thinking went, the strain spread especially fast because many hosts were immune-compromised by HIV.
Now, it appears that along with those two factors, there is a third reason, still unknown, for strain W’s success, Kreiswirth says. "We have yet to figure out what makes these strains unique and what causes them to spread so rapidly. What we do know is that these strains are more able to cause disease and that they’re more able to spread rapidly. No wonder we had such a disaster in the early ’90s."
The discovery that the strain W family is wide spread throughout Russia and other countries in the former Soviet Union also contradicts previous assumptions about the family’s epidemiology, he says. The strain family has long been known to Europeans as "the Beijing family" and is found throughout Asia, including China, Singapore, Thailand, and Tibet. Now, PHRI researchers are finding the family has made itself at home in Russia as well, probably over a long time span of "who knows how many generations," he says.
Tools available to PHRI researchers are refined enough that investigators can detect subtle similarities common to evolving variations of a strain over time, Kreiswirth says. "In just four years, we’ve seen about 10 types of the W strain. So it’s not surprising that over thousands of years, it looks very different. Still, we have the tools to follow all the little components. In effect, we’re following a moving target."
Public health implications for the United States are clear, he adds. "It’s bad enough that we’re spreading TB. By creating multidrug-resistant strains, we’re adding even more ammunition."