The truth of what happened in Sverdlovsk was ultimately revealed not by politicians, but by scientists holding DNA evidence.
It was April 1979 in the Soviet city of Sverdlovsk when the first patients began arriving at hospitals with alarming symptoms: high fever, blue lips, choking, and difficulty breathing. Many died within hours of admission. The official explanation was swift—tainted meat from infected livestock had caused gastrointestinal anthrax. Yet for years, Western intelligence agencies suspected a far more sinister truth: an accidental release of weaponized anthrax spores from a secret military facility. The controversy would simmer for over a decade until a groundbreaking scientific investigation, using the then-novel technique of PCR analysis, would finally uncover what really happened by examining the victims' tissues years later. This is the story of how molecular biology solved a Cold War mystery.
In late April 1979, an unusual epidemic of anthrax struck Sverdlovsk (now Ekaterinburg), a city of 1.4 million people located 1,400 kilometers east of Moscow 1 . The outbreak resulted in at least 66 human deaths from inhalational anthrax, making it one of the largest known human inhalational anthrax outbreaks in history 2 .
Soviet officials attributed the outbreak to natural causes, claiming contaminated meat from an anthrax epizootic south of Sverdlovsk had caused 96 cases of human anthrax—17 cutaneous and 79 gastrointestinal infections 1 . However, U.S. intelligence agencies believed the outbreak resulted from inhalation of spores accidentally released from Military Compound 19, a secret microbiology facility in the city 1 3 .
Epidemiological data later showed that most victims worked or lived in a narrow zone extending from the military facility to the southern city limit, with livestock deaths from anthrax occurring even farther south along the same axis 3 .
This zone paralleled the northerly wind that prevailed shortly before the outbreak, suggesting an aerosol plume of anthrax spores had originated from the military facility 3 .
The Sverdlovsk outbreak occurred during a period of heightened Cold War tensions, following the Soviet invasion of Afghanistan 5 . The incident became a major point in U.S. accusations that the Soviet Union was violating the 1972 Biological Weapons Convention, which both nations had signed 1 5 .
The Soviet government maintained its "tainted meat" story for over a decade, despite mounting evidence to the contrary 5 . The truth only began to emerge after the collapse of the Soviet Union, when Russian President Boris Yeltsin—who had been the Communist Party chief in Sverdlovsk at the time of the outbreak—admitted that the KGB and military had lied about the true explanation 1 5 .
By the early 1990s, the political truth about Sverdlovsk was becoming clear, but scientific questions remained. How many strains of anthrax were involved? Could the presence of multiple strains support the natural outbreak hypothesis? Or would the evidence point to a single weapons strain?
Answering these questions was tremendously challenging. The outbreak had occurred 15 years earlier, and the only biological evidence available came from formalin-fixed tissue samples collected during autopsies of the victims 2 4 . Formalin preservation damages and fragments DNA, making genetic analysis extremely difficult.
In 1998, a team of scientists published a groundbreaking study using polymerase chain reaction (PCR) analysis to examine tissue samples from 11 Sverdlovsk victims 4 . PCR allows researchers to amplify specific DNA sequences from tiny amounts of starting material, effectively acting as a molecular time machine that can recover genetic information from historical samples.
They developed methods to efficiently extract high-quality total DNA from these precious samples and used "nested primers" to significantly increase the sensitivity of their assays 4 . This double-PCR approach involved two consecutive rounds of amplification, first with outer primers, then with inner primers that bound inside the first amplified region.
Amplifying specific DNA sequences from tiny amounts of starting material
The analysis yielded unexpected results. While all victims contained the full set of B. anthracis virulence genes, the vrrA gene analysis revealed multiple strain categories present in different victims 4 .
| Strain Category | Presence in Samples | Significance |
|---|---|---|
| Multiple vrrA genotypes | Found in tissue samples | Indicated infection by different B. anthracis strains |
| At least 4 of 5 known categories | Detected across victim tissues | Suggested diverse bacterial population |
| One category per single strain | Normally expected in a point source outbreak | Contrasted with findings |
The researchers concluded: "PCR analysis using primers that detect the vrrA gene variable region on the B. anthracis chromosome demonstrated that at least four of the five known strain categories defined by this region were present in the tissue samples" 4 . This was surprising because only one category is typically found in a single B. anthracis strain.
Interactive chart showing distribution of different B. anthracis strains among the 11 victims analyzed
The presence of multiple B. anthracis strains in different victims initially seemed to support the Soviet Union's natural outbreak hypothesis. If multiple strains were present, perhaps the outbreak really did come from various natural sources rather than a single weapons strain.
However, subsequent research provided a more nuanced explanation. Later genomic analysis revealed that what appeared to be "multiple strains" might actually represent natural diversity within a single weaponized strain. A single batch of anthrax produced for weapons could contain subpopulations with minor genetic differences that had arisen during laboratory cultivation 7 .
Further phylogenetic studies placed the Sverdlovsk strain into a specific evolutionary group (the A.Br.008/009 subgroup) closely related to the Russian Tsiankovskii vaccine strain 2 7 . This Soviet production strain was consistent with a wild-type strain from Russia that showed no evidence of genetic engineering, despite known Soviet efforts to create antibiotic-resistant and vaccine-evading variants 2 .
| Reagent/Technique | Function in the Investigation |
|---|---|
| PCR Primers | Target specific bacterial DNA sequences for amplification |
| Nested Primers | Increase sensitivity through two rounds of amplification |
| DNA Extraction Kits | Isolate DNA from degraded formalin-fixed samples |
| Whole Genome Amplification | Amplify tiny amounts of DNA for comprehensive analysis |
| vrrA Gene Markers | Identify strain variations through tandem repeats |
| canSNP Analysis | Place strains in phylogenetic context using canonical SNPs |
The Sverdlovsk investigation pioneered techniques for analyzing historical outbreaks that are now standard in microbial forensics. The methods developed to extract and amplify DNA from formalin-fixed tissues 4 created a roadmap for investigating historical disease outbreaks when fresh samples are unavailable.
The research demonstrated that molecular genotyping could resolve long-standing controversies about disease origins, providing objective evidence where political narratives had previously dominated 4 7 . This approach has since been applied to numerous other historical outbreaks and biocrime investigations.
The technical challenges overcome in the Sverdlovsk analysis drove innovations in working with degraded DNA, including:
While the PCR analysis revealed multiple strains, the overall scientific evidence ultimately supported the accidental weapons release theory. The geographic pattern of cases, the inhalational form of the disease, and the political admissions all pointed to an accident at Compound 19.
President Boris Yeltsin ultimately acknowledged this truth, stating that the outbreak resulted from an accident at a Soviet biological warfare installation 1 5 . The research had provided the scientific evidence to confirm what intelligence agencies had long suspected.
| Year | Event | Significance |
|---|---|---|
| 1979 | Anthrax outbreak in Sverdlovsk | Beginning of the mystery |
| 1980 | U.S. intelligence reports suggest weapons accident | Initial political controversy |
| 1994 | Epidemiological study published | Scientific evidence for aerosol release |
| 1998 | PCR analysis of victim tissues | Multiple strains discovered |
| 2016 | Whole-genome sequencing of Sverdlovsk strain | Phylogenetic placement and engineering assessment |
Anthrax outbreak in Sverdlovsk marks the beginning of the mystery
U.S. intelligence reports suggest weapons accident
Epidemiological study provides scientific evidence for aerosol release
PCR analysis of victim tissues reveals multiple strains
Whole-genome sequencing provides phylogenetic placement
The Sverdlovsk anthrax investigation represents a remarkable convergence of molecular biology, epidemiology, and political history. What began as a Cold War cover-up became a testament to science's ability to uncover truth long after the fact.
The researchers who developed PCR methods to analyze those precious tissue samples could not have known they were creating a playbook for future biocrime investigations. Their work established that evidence preserved in tissue blocks could wait decades for the right technology and the right questions.
As the 1998 study concluded, their PCR analysis "demonstrated that the entire complement of B. anthracis toxin and capsular antigen genes required for pathogenicity were present in tissues from each of these victims" 4 —a definitive molecular diagnosis made nearly twenty years after the victims' deaths.
The story of the Sverdlovsk anthrax outbreak serves as both a warning about the dangers of biological weapons and a promise that scientific inquiry can eventually reveal the truth, no matter how powerful the forces attempting to conceal it.