Typhus fever is a group of bacterial infections spread to humans by fleas, lice, or chiggers. The bacteria invade the cells lining your blood vessels, triggering high fever, severe headache, body aches, and often a distinctive rash. There are three main types, each carried by a different insect and caused by a closely related but distinct bacterium.
The Three Types of Typhus
Though they share a name and similar symptoms, the three forms of typhus differ in their cause, their insect carrier, and their severity.
Epidemic typhus is the most dangerous form. It’s caused by a bacterium called Rickettsia prowazekii and spread through infected body lice. It tends to emerge during wars, famines, and other situations where people live in crowded, unsanitary conditions without the ability to wash clothes or bathe. Outbreaks typically occur in winter, when heavy clothing harbors lice. Without treatment, epidemic typhus can be fatal.
Flea-borne (murine) typhus is the milder and more common form. It’s caused by a related bacterium, Rickettsia typhi, and spread through contact with infected fleas, particularly the Oriental rat flea and the common cat flea. Cases peak in summer and fall and are increasing in parts of southern California, Hawaii, and Texas. Murine typhus is rarely fatal, even without treatment.
Scrub typhus is caused by a different organism entirely, Orientia tsutsugamushi, and is transmitted by the bites of infected chiggers (tiny larval mites). It’s most common in rural and forested areas of Southeast Asia, the Pacific Islands, and northern Australia. Unlike the other two types, scrub typhus often produces a dark scab at the bite site, called an eschar, which helps distinguish it.
How Typhus Spreads
You don’t catch typhus from another person. The bacteria travel from animals (usually rodents) to humans through an insect intermediary. In epidemic typhus, body lice feed on an infected person, pick up the bacteria, then defecate while feeding on a new host. The bacteria in louse feces enter through tiny scratches or when you unknowingly rub the feces into a bite wound or your eyes. In flea-borne typhus, the cycle is similar: fleas feeding on infected rats or opossums pass the bacteria to you the same way.
Scrub typhus works slightly differently. Chigger larvae pick up the bacteria from the soil or from their rodent hosts and transmit it directly through their bite.
Symptoms and Timeline
Symptoms of epidemic typhus appear abruptly 8 to 16 days after exposure to infected lice. Flea-borne typhus follows a similar timeline. The onset often feels like a sudden, severe flu: high fever, intense headache, muscle pain, and chills. Within a few days, a rash typically develops on the trunk and spreads outward toward the arms and legs, though it usually spares the face, palms, and soles.
In flea-borne typhus, fever lasts 12 to 21 days in untreated cases. Many people also experience nausea, vomiting, abdominal pain, or loss of appetite. The illness can range from mild enough to be mistaken for a viral infection to severe enough to require hospitalization. Because epidemic and murine typhus produce nearly identical symptoms, telling them apart without lab tests is difficult.
Complications of Untreated Typhus
Most people with flea-borne typhus recover fully, even without antibiotics. A systematic review of untreated murine typhus cases found an overall fatality rate of just 0.4% across 239 patients. Still, about one in four untreated patients develops complications. The lungs, kidneys, and brain are the organs most often affected. Pneumonia, acute kidney injury, and confusion or seizures from inflammation around the brain are the most serious possibilities.
Epidemic typhus is far more dangerous. Historically, untreated epidemic typhus killed a significant percentage of those infected, particularly older adults and malnourished populations. The bacteria cause widespread damage to small blood vessels, which can lead to gangrene in the fingers and toes, organ failure, and shock.
How Typhus Is Diagnosed
Diagnosis is tricky in the early days of illness because symptoms overlap with many common infections and because lab confirmation takes time. The most common method is a blood test that detects antibodies your immune system produces against the bacteria. The catch is that detectable antibody levels generally don’t appear until 7 to 10 days after symptoms start. To confirm the diagnosis, doctors compare antibody levels from a blood sample taken during acute illness with a second sample drawn 2 to 10 weeks later. A fourfold rise between the two confirms infection.
A faster option is PCR testing, which can detect bacterial DNA in blood during the first week of illness, especially before antibiotics are started. However, PCR isn’t sensitive enough to rule out typhus on its own. A negative result doesn’t mean you’re in the clear. Because of these diagnostic delays, doctors who suspect typhus typically begin treatment right away rather than waiting for lab confirmation.
An additional wrinkle: the bacteria responsible for epidemic and flea-borne typhus produce antibodies that cross-react with each other on standard blood tests. Specialized PCR testing on blood or tissue samples can distinguish between the two species when that distinction matters.
Treatment
Typhus responds well to antibiotic therapy when started early. The standard treatment for adults is a course of doxycycline, typically lasting about seven days. An alternative regimen uses azithromycin for five days. Most people begin to feel noticeably better within 48 hours of starting treatment. Delayed treatment, particularly in epidemic typhus, increases the risk of severe complications, which is why doctors start antibiotics based on clinical suspicion alone.
One unusual feature of epidemic typhus is that the bacteria can remain dormant in your body for years after the initial infection. Decades later, during periods of stress or weakened immunity, the infection can reactivate in a milder form known as Brill-Zinsser disease.
Reducing Your Risk
No vaccine is currently available for any form of typhus. Prevention comes down to avoiding the insects that carry it.
- Control fleas on pets. Animals that spend time outdoors are the most common way fleas enter a home. Flea collars, oral medications, and topical treatments all help. (Permethrin-based products should never be used on cats.)
- Keep rodents and wildlife away from your home. Store food and pet food in sealed containers. Remove brush piles, clutter, and junk from around your property. Seal gaps and holes where rodents can enter.
- Use insect repellent. EPA-registered repellents applied to skin and clothing reduce flea and chigger bites when you’re spending time outdoors. Follow label directions, as some products are designed for skin and others for clothing only.
- Avoid contact with stray or wild animals. Don’t feed or pet strays, and always wear gloves when handling sick or dead animals.
For epidemic typhus, which thrives in overcrowded conditions with poor sanitation, the most effective prevention measures are regular bathing, access to clean clothing, and delousing programs during outbreaks.