Typhus bacterium that causes it: Rickettsia. History-Changing

Typhus fever is arguably the most historically important disease you’ve never heard of. In this lesson, I will attempt to shed some light on this deadly disease and provide some basics on the bacterium that causes it: Rickettsia.

History-Changing Infection

Think about the most infamous diseases you’ve learned about in history class. There was the plague, that scourge of the Middle Ages, and malaria has and continues to kill countless people in the tropics. AIDS is a more contemporary example of a deadly disease that made the rounds on the news programs in the last 30 years. But, we’re leaving out a major killer, one that many of you have probably never even heard of – a disease introduced by the Spanish and was responsible for killing 75% of the population of Mesoamerica in the 1500s, a disease that, before World War II, killed more soldiers during wartime than actual combat, a noteworthy history-changer.

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Anyone have a guess as to the identity of this mystery killer? The disease I’m talking about is called typhus. In this lesson, I will attempt to shed some light on this little-known illness.

Typhus Fevers

Typhus fever is the name given to several similar diseases caused by bacteria in the genus Rickettsia, acquired through the bite of an infected arthropod. The arthropods responsible include fleas, ticks, mites, and lice – all the classic biters that feed on the skin and blood of host mammals. The Rickettsial bacteria live in the salivary glands and gut of arthropods and are excreted in the feces.

When a flea, for example, bites you, it poops as it feeds. In addition to fecal material, the Rickettsia are also deposited. The bacteria enter your body directly through the bite site or can enter through abrasions when you scratch at the flea bite.

Once inside your bloodstream, the Rickettsia invade the cells that line your blood vessels, causing inflammation and leading to an immune response. It is this inflammation and host immune reaction that leads to the symptoms of the disease.Typhus fevers are most common in areas with poor sanitation and in people with poor personal hygiene.

Not surprisingly, outbreaks of typhus are often associated with war, famine, poverty, and areas populated by people with poor quality of life. The typhus fever that decimated the Aztecs was brought to the New World by the body lice infesting the Spanish sailors, who were unable to consistently clean themselves while on the ships. Soldiers typically living in crowded, dirty conditions are especially susceptible to outbreaks of fleas, lice, and mites carrying Rickettsia.

Today, typhus impacts refugee camps and poor, third-world countries.The specifics of the different typhus fevers depend on which species of bacteria you’re infected with. Let’s take a minute to look at the two most common: epidemic typhus and murine typhus.

Epidemic Typhus

Epidemic typhus is caused by the bacteria Rickettsia prowazekii and is transmitted by head and body lice in the genus Pediculus. These lice are natural parasites of humans and are passed from person to person.

They thrive in areas with poor sanitation or where personal hygiene is lacking. Epidemic typhus is the most deadly, history-changing form of typhus. This is the scourge that ravaged the Aztecs and the soldiers in many historic wars.

Symptoms of epidemic typhus usually begin 8-12 days after infection following a louse bite. Initially, the patient will develop a high fever and debilitating headache. This is often accompanied by muscle aches and chills. The fever can be so high that the patient hallucinates or loses consciousness. ‘Typhus’ in Greek literally means ‘stuporous’ after this classic symptom. After several days of these symptoms, the patient will develop a rash that covers nearly the entire body.

A body rash that does not include the face, palms, or soles of the feet is often a key diagnostic tool for typhus fever. This rash is a direct result of the Rickettsial bacteria damaging the capillaries near the skin surface, leading to bleeding beneath the skin. If the disease is allowed to progress untreated, the patient can suffer permanent damage to vital organs, including the heart and blood vessels.When large-scale, poorly treated outbreaks occur, the death rate can be a staggering 75% of those infected! Fortunately, the last major outbreak of typhus in the United States was in 1922. Improved sanitation has nearly eliminated epidemic typhus in the U.S.

, but the disease continues to impact high-risk populations in less-developed countries worldwide.

Murine Typhus

Murine typhus is caused by the bacteria Rickettsia typhi and is transmitted by fleas. The culprit fleas usually live solely on rats and mice, but they have no problem biting a human if the opportunity presents itself. And, everyone living in a major American city can attest to seeing rats in the more unsanitary parts of town. The term ‘murine’ is actually in reference to the phylogenetic subfamily that includes most rats and mice – Murinae.Murine typhus is a much less dangerous disease.

The symptoms are similar to epidemic typhus but on a much more mild scale. Patients develop a low-grade fever with a mild headache. Several days later, the nearly full-body rash develops, but the disease rarely progresses much beyond this and is even more rarely fatal. Murine typhus is a bit more common in the United States than epidemic typhus.

Most cases of murine typhus occur in the south and impact people who work in rodent-infested areas. This is usually limited to large-scale grain producers with grain storage elevators.

Diagnosis and Treatment

Diagnosing typhus fevers can be difficult. The initial symptoms are vague and flu-like. It is not until the appearance of the rash that most doctors will suspect a Rickettsial cause. Usually these symptoms, combined with a possible exposure to lice, fleas, or ticks, is all that is required for a diagnosis and to begin treatment.

Directly identifying the exact species of Rickettsia is often unnecessary because the treatment is the same for all varieties of typhus. The current treatment of choice is the antibiotic doxycycline. Fortunately, doxycycline is very effective, often completely curing the disease with one round of treatment. Even patients with severe, life-threatening infections respond very well to doxy. Relapses can occur after treatment but are usually very mild.

Lesson Summary

Let’s review.Typhus fever is the name given to several similar diseases caused by bacteria in the genus Rickettsia, acquired through the bite of an infected arthropod. Fleas, lice, ticks, and mites commonly transmit the bacteria to humans through bites contaminated by the arthropod feces. Once in the bloodstream, the bacteria invade the cells that line the blood vessels, leading to inflammation and a host immune response.Epidemic typhus is caused by the bacteria Rickettsia prowazekii and is transmitted by head and body lice in the genus Pediculus. This form of typhus fever is the most deadly.

Epidemic typhus manifests as a high fever causing hallucinations, severe headache, and a characteristic red rash. Large-scale outbreaks can devastate a population, but fortunately the disease has nearly been eliminated from the United States.Murine typhus is caused by the bacteria Rickettsia typhi and is transmitted by fleas. This typhus fever is not as deadly as epidemic typhus.

The fever, headache, and rash are usually mild and rarely lead to death.Diagnosis is usually based solely on the symptoms combined with exposure to fleas, ticks, or lice. A positive diagnosis can be difficult and is usually not needed. Treatment is the same regardless of which specific species of Rickettsia is responsible. The antibiotic doxycycline is the treatment of choice and is generally very effective at eliminating the disease completely.

Learning Outcomes

After reviewing this lesson, you’ll have the ability to:

  • Summarize historical outbreaks of typhus
  • Explain how typhus fever is contracted
  • Differentiate between epidemic typhus and murine typhus
  • Describe the diagnosis and treatment of typhus fever

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