Pneumonic Plague: The Siberia Case and California's Own Record
Pneumonic Plague: The Siberia Case and California's Own Record
LodiEye — October 2026
A laboratory technician in Siberia died on October 2 of a pneumonia that Russian authorities have not identified, and because she worked at an anti-plague research institute, the World Health Organization and the U.S. Centers for Disease Control and Prevention both opened files on the case. The word plague carries six centuries of weight, and it is worth separating that weight from what the disease actually is now. Plague never left California. It lives in ground squirrels and chipmunks across the Sierra and the coastal ranges, it produces a handful of human cases in the state each decade, and it is curable with antibiotics that have been available since the 1940s. It is also the reason Los Angeles saw the last urban plague epidemic in the United States, in 1924, and the last person-to-person transmission of the disease this country has recorded. San Joaquin County sits outside the zone where plague circulates, and no human case has ever been recorded here.
What the disease is
Plague is caused by Yersinia pestis, a bacterium that lives among wild rodents and the fleas that feed on them. Bubonic, septicemic and pneumonic plague are three forms of one disease, not three diseases. Which form a person gets depends on how the bacteria entered the body.
Bubonic plague follows a flea bite and produces the swollen, painful lymph nodes called buboes. It accounts for more than 80 percent of U.S. cases. Septicemic plague is bloodstream infection, with fever and sepsis. Pneumonic plague is infection of the lungs, and it arrives two ways: by inhaling the bacteria, or when untreated bubonic or septicemic infection spreads into the lungs on its own.
Two things make the lung form the one public health agencies watch. It is the only form that passes from person to person, through respiratory droplets. And it moves quickly, with pneumonia developing within roughly 24 to 36 hours. An influenza-like illness with bloody sputum is the warning sign. Without prompt antibiotics, patients progress to respiratory failure and death, and untreated pneumonic plague is almost always fatal.
Transmission requires close, sustained contact. CDC's clinical guidelines estimate that a person with pneumonic plague will on average infect about one other person. That is a different category of contagion from measles or COVID-19.
In the United States, the most common route to a human pneumonic case is not another person. It is a cat. House cats that hunt in country where plague circulates can bring the infection home, and a sick cat with respiratory symptoms can transmit it by droplet to the person handling it. That is how the most recent U.S. death happened.
How it is treated
Before antibiotics, fatality rates across all forms of plague ran between 66 and 93 percent. Sulfonamide drugs in the 1930s changed that, and patients with pneumonic plague who had been considered beyond help began surviving. The disease has been curable for about eighty years.
CDC published updated treatment guidelines in 2021, replacing recommendations a private working group had issued in 2000. The older guidance offered essentially two first-line drugs. The 2021 version widens the list.
| Use | Agents |
|---|---|
| First-line treatment | Streptomycin, gentamicin, ciprofloxacin, levofloxacin, moxifloxacin |
| Alternative treatment | Doxycycline; chloramphenicol where there is meningeal involvement |
| Post-exposure prophylaxis | Doxycycline is the first choice; fluoroquinolones are also used |
Source: CDC, Antimicrobial Treatment and Prophylaxis of Plague, MMWR Recommendations and Reports, 2021.
Timing governs the outcome. Antibiotics need to start within about 24 hours of the first symptoms, which is why clinicians in endemic areas are instructed to treat on suspicion rather than wait for a laboratory result. The Arizona case described below illustrates what happens when the diagnosis arrives late.
For people who have been exposed, CDC recommends seven days of prophylaxis. Exposure means close contact, under six feet and sustained, with a pneumonic patient or animal, or direct contact with infected fluids or tissues. Pre-exposure prophylaxis is not considered necessary for first responders and health care workers as long as standard and droplet precautions hold. Isolation for a pneumonic case uses negative pressure, droplet precautions and N-95 respirators.
Two limits are worth stating plainly. There is no vaccine of proven effectiveness against primary pneumonic plague. And there is no evidence of meaningful antibiotic resistance among the strains circulating in natural foci.
How often it happens in the United States
The United States averages seven human plague cases a year, with a range from zero to seventeen. Since 2000, about fifteen cases have been fatal. The last decade shows no trend upward or downward.
Plague arrived in this country through San Francisco in 1900, on rat-infested steamships. Early epidemics hit port cities. After the last of them, the bacterium moved from urban rats into rural rodent species and became permanently established across the western states. CDC places current cases in two regions: northern New Mexico, northern Arizona and southern Colorado; and California, southern Oregon and far western Nevada.
The high-water mark of the last decade was 2015, with eleven cases across six states by September and three deaths, two of them tied to exposure at Yosemite National Park. Nothing since has come close.
| Date | Location | Form | Outcome |
|---|---|---|---|
| August 2015 | Yosemite National Park, California | Bubonic, two cases | Both recovered |
| 2020 | El Dorado County, California | Bubonic | Recovered |
| July 2025 | Coconino County, Arizona | Pneumonic | Fatal |
| August 2025 | South Lake Tahoe, California | Bubonic | Recovered |
| April 2026 | Apache County, Arizona | Not specified | Not reported |
| June 2026 | Santa Fe County, New Mexico | Not specified | Fatal |
Sources: CDC, Arizona Department of Health Services, New Mexico Department of Health, El Dorado County Public Health.
The Arizona death is the one that matters for understanding the pneumonic form. A young man died in July 2025, and the diagnosis came only after his death. CDC published the case report on October 1, 2026. He had work-related contact with two sick indoor cats, both showing respiratory symptoms consistent with pneumonic plague. It was Arizona's first pneumonic plague death since 2007, in a state that had reported only eight human plague cases in the twenty-five years from 2000 through 2024.
New Mexico carries the highest rates in the country. State health officials reported in June 2026 that a Santa Fe County woman in her fifties had died, the state's first human case of that year. New Mexico recorded three human cases in 2025 and one fatal case in 2024.
How often it happens worldwide
Global plague incidence has fallen sharply over twenty-five years and has been roughly flat for the last decade. WHO published updated figures on September 29, 2026. Between 2019 and 2025, ten countries reported suspected human plague cases and six reported confirmed cases, for a total of 3,847 suspected cases and 423 deaths. That is a case fatality rate of 11 percent. Most cases came from the Democratic Republic of the Congo and Madagascar, where plague remains endemic in some areas.
Average annual reported plague cases worldwide, by period
Calculated from WHO totals: 2,334 cases annually on average from 1999 through 2008; 2,886 cases total across 2013 through 2018; 3,847 suspected cases total across 2019 through 2025. WHO notes that plague also occurs in countries that do not report cases, so these figures reflect surveillance capacity as well as disease activity.
Africa accounts for more than 90 percent of global human plague cases. Peru is the other country where the disease is permanently established, though its numbers are small, roughly 40 cases across the 2013 to 2018 period, the same as the United States over that span.
The annual totals move with individual outbreaks rather than with any underlying trend. One year dominates the last decade.
Reported plague cases by outbreak, 2016 through 2023
Source: WHO African Region plague surveillance. Mad. is Madagascar; DRC is the Democratic Republic of the Congo. Deaths by outbreak, in the same order: 26, 238, 9, 1, 31, 19, 7, 15. The 2017 Madagascar epidemic is the outlier on the chart and the reason the case fatality rate varies so widely between outbreaks.
Madagascar's 2017 epidemic is the relevant one for pneumonic plague. It was urban, and roughly 70 percent of its cases were the pneumonic form, which is unusual. Madagascar's near-annual outbreaks are normally bubonic and rural. WHO recorded 2,348 confirmed, probable and suspected cases with 202 deaths, a case fatality rate of 8.6 percent. The outbreak ran through the capital, spread to Seychelles in one traveler, and was brought under control with antibiotics and contact tracing.
California's record
California has the deepest American record of pneumonic plague, and it is where the last person-to-person transmission in the United States occurred.
The disease entered through San Francisco in 1900. Those first outbreaks involved domestic rats, rat fleas and people. The bacterium then crossed into wild rodents, and was first isolated from native ground squirrels and woodrats in California in 1908. That jump created the permanent reservoir the state still has.
Oakland, 1919
A pneumonic outbreak traced to an index patient who hunted and skinned ground squirrels. Thirteen of the fourteen human cases were fatal.
Los Angeles, 1924
A second pneumonic outbreak, thirty-two cases with thirty-one fatal, running from late September to containment in mid-November. The California Department of Public Health ties it to an outbreak among domestic rats, with infected squirrels found near San Luis Obispo County as late as July of that year pointing to squirrels as the original source. This was the last urban plague epidemic in the United States and the last documented human-to-human plague transmission in the country.
The 1924 outbreak is also a difficult chapter in public health history. It centered on Mexican-American residents of the Macy Street district. The disease was not referred to by name even after city health officers confirmed it, and the response involved physically isolating Hispanic neighborhoods from white ones.
After 1924
California has had no primary pneumonic outbreak since. What it has had is occasional secondary plague pneumonia and a small number of cat-associated cases. In March 1984 a Claremont veterinarian developed bubonic plague with secondary plague pneumonia, the first person since 1924 to acquire plague pneumonia in Los Angeles County. One of his patient cats had symptoms consistent with pneumonic plague. CDC noted at the time that since 1959 four veterinarians and one veterinary assistant had confirmed plague infections, and that a veterinarian in Santa Clara County died.
Where plague lives in California now
The California Department of Public Health's plague compendium is the authoritative statement, and it is specific: plague is found in many foothill and mountainous regions of the state but is absent from the Central Valley and the southeastern desert regions. Since 1970, plague-positive rodents have been found in 34 of California's 58 counties. From 1927 through 2019, 63 human plague cases with exposure in California were reported, almost all of them connected to rodent activity in the wild and most commonly to California ground squirrels.
Recent human cases in the state have all been bubonic and all have survived. Two people were exposed in Yosemite in 2015, the state's first cases since 2006. An El Dorado County resident was infected in 2020, likely in South Lake Tahoe. In August 2025 another South Lake Tahoe resident tested positive, probably from a flea bite while camping.
The state runs animal surveillance every year, and the 2024 results are the most recent published. CDPH reported no human plague cases and no domestic pet cases in 2024. It tested 533 wild rodents and 140 carnivores and feral pigs from 31 counties, and detected plague activity in nine: Alpine, El Dorado, Inyo, Lassen, Mariposa, Mono, Plumas, Sierra and Siskiyou.
Share of California specimens testing positive for plague exposure, 2024
Source: California Department of Public Health, Vector-Borne Disease Section Annual Report 2024. Sample sizes: 533 wild rodents, of which 8 were positive across six counties; 140 carnivores and feral pigs, of which 18 were positive across five counties; 669 fleas collected from wild rodents across nine counties, none positive. Carnivores test positive more often because a coyote or bear that eats infected rodents is exposed repeatedly and survives, which makes them useful sentinels for where the bacterium is active.
San Joaquin County
No human plague case of any form has ever been recorded in San Joaquin County. The documented record here is thin, and that is itself the finding.
A U.S. Public Health Service county-by-county survey from the plague-prevention campaign of the early 1900s states flatly that there is no record of human plague in San Joaquin County. Nothing in the state record since has changed that.
There is one historical rodent finding. During the federal ground-squirrel eradication program, Public Health Reports for the week ending January 14, 1911 recorded plague-infected ground squirrels found on January 4 and January 9 of that year at the Hughes ranch, one mile southwest of Ripon. That appears to be the only plague detection in the county in the primary record. It came during the brief window when infected squirrels were spreading outward from the Bay Area, before the valley foci died out.
The county sits almost entirely on the valley floor, inside the zone CDPH describes as free of plague. San Joaquin County does not appear in the state's 2024 plague testing table; no rodents, carcasses or carnivores from the county were submitted that year. The San Joaquin County Mosquito and Vector Control District lists plague among the vector-borne diseases within its mandate, and the district participates in other state surveillance programs. In 2024 it submitted four western blacklegged ticks for Lyme disease testing, and four deer mice have been tested for hantavirus across the 2015 to 2024 window, all negative.
The closest confirmed plague activity in recent years is Mariposa County, in the Yosemite area, roughly 90 miles southeast, and El Dorado County in the Tahoe Basin, roughly 100 miles northeast. Both are foothill and mountain habitat. Calaveras and Tuolumne counties, immediately east, submitted samples to the state in 2024 — ten carnivores from Calaveras, and 97 rodents plus four carnivores from Tuolumne — with no positives reported.
One gap in the public record is worth naming. The CDPH compendium maps the 34 counties with plague-positive rodents since 1970 in a figure rather than a list, and that figure is not reproducible from the document's text. Whether San Joaquin is formally inside or outside the 34-county count is therefore unconfirmed from publicly available material.
What this means for people here
The exposure group is people who hike, camp or hunt in the Sierra foothills and above, not people at home in the valley. California ground squirrels are abundant across San Joaquin County, but abundance is not infection, and the county has no record of Y. pestis in its rodent population in more than a century.
The route that has produced pneumonic cases in California and Arizona is worth knowing for anyone who takes an outdoor cat to the foothills or has one that roams there. A cat that catches and eats an infected rodent can develop pneumonic plague and transmit it to the person caring for it. Standard advice from state and county health departments covers the rest: avoid contact with wild rodents dead or alive, keep pets away from rodent burrows, use flea control, and seek veterinary care promptly for a sick pet after a trip to plague country.
The Siberia case
Darya Shipilova, a 28-year-old laboratory technician at the Irkutsk Anti-Plague Research Institute of Siberia and the Far East, was hospitalized on September 29 and died early on October 2. The institute's own materials say it was founded in 1934 to combat plague and later expanded to other dangerous diseases including cholera and anthrax.
Rospotrebnadzor, Russia's consumer and public health watchdog, diagnosed her with pneumonia of unknown etiology. It said tests of biological material found no microorganisms linked to her professional activity, and that no accidents involving pathogenic microorganisms had been recorded at the institute. About 200 contacts were placed under medical observation or isolation. Parts of the hospital where she died were cordoned off, more than 60 colleagues remained isolated inside the institute building, and a mask mandate was imposed at the Irkutsk Aluminium Plant in Shelekhov.
Several things have been reported but not confirmed. The independent Russian outlet People of Baikal reported she may have contracted pneumonic plague from a broken test tube while collecting samples, attributed to unnamed sources close to regional security services. Alexei Tsydenov, head of the neighboring republic of Buryatia, posted that she had died of plague, then edited the post to add the word possibly. On October 6 the Daily Mail reported a second unidentified death at an Irkutsk district hospital; that claim has not been independently confirmed and Russian authorities have not acknowledged it.
WHO spokesman Christian Lindmeier told a United Nations briefing there is no indication of anything resembling a pandemic, and noted that the institute studies dangerous pathogens in a part of Siberia where plague occurs naturally in wild animals. Russia has not requested a WHO expert deployment. On October 6, Russian officials told WHO under the International Health Regulations that no case of plague had been recorded in Irkutsk, in her or in anyone else; that roughly 200 contacts had tested negative for dangerous pathogens; and that medical monitoring of contacts had concluded. WHO rates the risk moderate to low for Irkutsk, low for Russia and very low for Europe. The European Centre for Disease Prevention and Control reported no secondary cases. A U.S. State Department spokesperson said there had been reports of a fatal case of suspected pneumonic plague in Irkutsk oblast, and CDC said it is monitoring reports while the circumstances remain unconfirmed.
What remains unknown is whether she was infected with plague at all, and if she was, whether it came from the lab or from the wild. Irkutsk sits in country where the bacterium circulates naturally in rodents, so a natural infection is not implausible. Lisa Morici, a microbiologist at the Tulane University School of Medicine, has noted that her death may turn out to be unrelated to her workplace entirely. There is no evidence that any strain involved would resist antibiotics, and no evidence that the institute does biological weapons work.
Two things make the case hard to read from outside. Russian officials have been evasive: one authority issued a travel warning for Shelekhov on October 3 and deleted it less than two hours later, and several Russian media reports on the situation have disappeared from news websites. Mongolia, Kyrgyzstan and Uzbekistan tightened health controls in response.
The most useful signal available is the absence of secondary cases. Pneumonic plague has a short incubation period. More than a week after the death, anyone infected by close contact with her would be showing symptoms. None have been reported.
Sources
- CDC, Antimicrobial Treatment and Prophylaxis of Plague: Recommendations for Naturally Acquired Infections and Bioterrorism Response, MMWR Recommendations and Reports, 2021.
- CDC, Plague: Maps and Statistics.
- CDC, Plague: Clinical Care.
- CDC, Notes from the Field: Fatal Pneumonic Plague — Coconino County, Arizona, July 2025, MMWR, October 1, 2026.
- CDC, Plague Pneumonia — California, MMWR, 1984.
- California Department of Public Health, California Compendium of Plague Control.
- California Department of Public Health, Vector-Borne Disease Section Annual Report 2024.
- El Dorado County, Resident Tests Positive for Plague, August 2025.
- New Mexico Department of Health, New Mexico reports first case of human plague in 2026, June 11, 2026.
- World Health Organization, WHO reports latest global trends in cholera, meningitis and plague, September 29, 2026.
- WHO African Region, Plague in the African Region.
- U.S. Public Health Service, Public Health Reports, Vol. XXVI, February 3, 1911.
- Radio Free Europe/Radio Liberty, Siberian Anti-Plague Institute Staff Isolated After Worker's Death, October 5, 2026.
- PBS NewsHour, How Russia and the world are responding to a possible case of pneumonic plague after lab worker death, October 2026.
- The Conversation, The death of a Russian plague researcher, explained by a microbiologist, October 6, 2026.
- San Joaquin County Mosquito and Vector Control District, sjmosquito.org.
LodiEye performs a news-media function for Lodi and San Joaquin County, alongside the Lodi News-Sentinel, Stocktonia, The Sacramento Bee and CalMatters. It reports on public records, government proceedings and matters of community concern, and publishes that reporting for a general readership.
This report was produced with AI assistance under the editorial direction of the founder. AI systems were used in five capacities.
Source Discovery
Locating primary documents, agency publications and contemporaneous news coverage relevant to the subject, including CDC and WHO publications, California Department of Public Health surveillance reports, and historical Public Health Service records.
Credibility Validation
Checking claims against the originating agency or publication rather than secondary summaries, and separating confirmed facts from reported but unverified claims, particularly in the coverage of the Irkutsk case.
Analysis and Synthesis
Comparing figures across jurisdictions and time periods, calculating rates and averages from published totals, and identifying where the public record is incomplete.
Presentation
Drafting, structuring and charting, including the data visualizations in this report.
Final Review
Verification of figures, sources and framing by the editor before publication.
The AI systems used were Claude, from Anthropic, and Perplexity.
Corrections and additions are welcome. Write to editor@lodi411.com.