Dangerous Disease ‘As Old As The Plague’
Reaches Record Levels In California

A disease that has plagued humanity since ancient times is making a disturbing modern comeback — and California is at the epicenter. Flea-borne typhus, a bacterial illness that shares its flea vector with the bubonic plague, has reached record-breaking levels in Los Angeles County and across the state in 2025 and 2026, alarming public health officials who say the numbers reflect a worsening urban wildlife problem that poses a real and growing risk to residents.

What Is Flea-Borne Typhus — And Why Is It Rising?

Flea-borne typhus, also known as murine typhus, is caused by the bacterium Rickettsia typhi. It is transmitted to humans through the bites of infected fleas — the same type of flea responsible for spreading bubonic plague. While typhus and plague are entirely different diseases, their shared vector means they often circulate in the same wildlife populations, particularly among rodents, opossums, and stray cats and dogs.

The disease is not new. Health experts describe it as being “as old as the plague,” with documented outbreaks stretching back centuries. What is new is the scale of its resurgence in 21st-century California. Public health officials point to several intersecting factors driving the surge: the growth of urban homeless encampments that create ideal flea habitats, increasing opossum populations in suburban and urban areas, and a rising number of unvaccinated stray animals. In L.A. County, the 220 cases recorded in 2025 surpassed the previous record of 187 set just the year before — a troubling acceleration that has officials deeply concerned.

Record Numbers: How Bad Is the 2025–2026 Outbreak?

The scale of this outbreak is unprecedented in the modern record. Los Angeles County’s 220 confirmed cases in 2025 represent a roughly 18% increase over the prior year’s record, and California’s statewide total of 277 cases is the highest ever documented in the modern era. Health officials note that these numbers likely underrepresent the true case count, as mild or atypical presentations may go undiagnosed or unreported.

The severity of this outbreak is particularly alarming: nearly 90% of patients required hospitalization, a rate that underscores how aggressively this bacterium can progress when not caught and treated early. Flea-borne typhus, while treatable with antibiotics, can cause serious complications including organ failure if diagnosis is delayed — which it often is, because the early symptoms closely mimic the flu.

Where Outbreaks Are Concentrated

Health officials have identified three primary clusters in the current L.A. County outbreak: Santa Monica, Willowbrook, and the Central City area of Los Angeles. These neighborhoods share common characteristics — high densities of stray animals, significant wildlife activity (particularly opossums), and in some cases, large encampments or areas with inadequate sanitation where flea populations can thrive.

Opossums are a particularly important reservoir for the disease in California’s urban environment. Unlike rodents, opossums can carry large numbers of fleas without dying from the bacteria, making them highly effective hosts. As opossum populations have expanded into suburban neighborhoods across L.A., so too has the geographic reach of the disease.

📍 Los Angeles, California — the epicenter of the 2025–2026 flea-borne typhus outbreak. Photo: Unsplash

Symptoms, Diagnosis, and Treatment

One of the most dangerous aspects of flea-borne typhus is how easily it is mistaken for other illnesses in its early stages. Initial symptoms typically appear within one to two weeks of a flea bite and include fever, headache, chills, body aches, and fatigue — a presentation virtually indistinguishable from influenza or other common viral infections.

A telltale rash often develops several days into the illness, typically appearing on the torso before spreading to the limbs. However, the rash does not always appear, and its absence can delay diagnosis further. Blood tests can confirm infection, and the disease responds well to antibiotic treatment — particularly doxycycline — when caught in time. The danger lies in delay: untreated cases can progress to involve the liver, kidneys, lungs, and central nervous system.

The Plague Connection: What You Need to Know

While flea-borne typhus and bubonic plague are entirely different diseases caused by different bacteria, they share the same flea vector — a fact that has drawn increased attention in 2025 as California wildlife agencies confirmed that rodents in the Tahoe Basin also tested positive for Yersinia pestis, the bacterium responsible for plague.

To be clear: the current outbreak in Los Angeles is typhus, not plague. Plague transmission to humans in the U.S. is extremely rare and occurs almost entirely through direct contact with infected animals or their fleas in wilderness settings, not urban environments. However, the co-circulation of both pathogens in California wildlife serves as a stark reminder that flea control is not a trivial public health concern — and that the conditions enabling typhus could, under different circumstances, enable other flea-borne diseases as well.

How to Protect Yourself and Your Family

Public health officials have issued clear guidance for residents of affected areas. The good news: flea-borne typhus is largely preventable with straightforward precautions that focus on eliminating the flea-to-human transmission pathway.