What is Rickettsia Prowazekii?
Rickettsia prowazekii is a type of bacteria that lives inside cells and cannot survive outside a host. It is shaped somewhat like a sphere or rod and doesn’t take up a particular stain that scientists use in the lab, which classifies it as ‘gram-negative’. R. prowazekii belongs to a group, or ‘genus’, of similar bacteria called Rickettsia. It is responsible for causing a disease called epidemic typhus.
The Rickettsia group is made up of gram-negative bacteria and these bacteria are the closest known relatives to a part of our cells called mitochondria. Mitochondria are like power plants of our cells as they generate most of the chemical energy needed to power biochemical reactions.
What Causes Rickettsia Prowazekii?
R. prowazekii is a type of bacterium that belongs to the typhus group. Bacteria of this kind are divided into several groups: the Spotted Fever Group, the Typhus Group, the Transitional Group, and the Ancestral Group. The Spotted Fever Group has two types of outer membrane proteins (basically, components of the bacterium’s surface), and they are most often spread by ticks. The Typhus Group, which R. prowazekii belongs to, doesn’t have these proteins and is spread by fleas and lice.
When it comes to epidemic typhus (a severe infectious disease), R. prowazekii is spread by the human body louse. This bacterium multiplies in the louse’s gut, and eventually causes so much damage that the louse dies. Interestingly, R. prowazekii is the only known bacteria of its kind to kill its spreading agent in this way. However, even after the louse dies, the bacteria survive in the remains and louse feces, and can make a person sick for several months. This is the only known Rickettsia bacterium that can cause a so-called “latent” infection, which means it can reactivate years or even decades later and cause a disease known as Brill-Zinsser Disease.
Risk Factors and Frequency for Rickettsia Prowazekii
Epidemic typhus is a historic disease that affected many soldiers during war times and seen in limited-resource areas during peace times. The disease is transmitted through the human body louse, discovered by Charles Nicole, who won a Nobel Prize for his finding in 1928. During World War II, vaccines were created to protect U.S. soldiers from the disease, but they’re no longer produced today.
Globally, humans are the only hosts of the disease. However, in the U.S., the flying squirrel can carry and potentially transmit the disease, causing a variant known as sylvatic typhus. The exact transmission process from squirrel to human is not fully understood.
Epidemic typhus is not commonly seen among tourists, but can break out within refugee populations infested with body lice, especially during cold months.
- The disease can be fatal, with a mortality rate up to 60% in untreated individuals, typically affecting the elderly and malnourished.
- However, sylvatic typhus and BZD – a related disease – have lower fatality rates.
- BZD usually has milder symptoms and is rarely fatal.
Signs and Symptoms of Rickettsia Prowazekii
If you have a fever and symptoms affecting multiple bodily systems, you might be dealing with a variety of illnesses – not just epidemic typhus. Other potential causes of your symptoms could include typhoid, relapsing fever, infections caused by different rickettsial species, Ehrlichia, Leptospira and malaria. Certain insect-borne diseases, like dengue, could also fit the bill. Murine typhus and epidemic typhus can be especially hard to tell apart, since they share many of the same symptoms. It’s worth noting, however, that murine typhus is more common in summer and fall, while epidemic typhus tends to show up in winter. It’s very important to think about any situations you’ve been in where you might have been exposed to these diseases.
When it comes to epidemic typhus, symptoms usually show up one to two weeks after exposure. This can involve a high fever that can last up to two weeks, severe headache, muscle pain, a dry cough, confusion, and a dull, red rash. This rash typically starts on the body and spreads to the limbs, while usually not affecting the palms and soles. Without medical treatment, the illness can get worse, potentially leading to low blood pressure, shock, and even death.
If you’ve previously been infected with the bacteria R. prowazekii, it’s possible for the infection to reactivate, especially if you’re malnourished, have a chronic illness, or are living in conditions of poor hygiene that enable lice to thrive. This reactivation (known as BZD) can happen years or even decades after you first got sick. BZD has many symptoms overlapping with epidemic typhus, including high fever, chills, severe headache, and a cough. The symptoms are generally milder, though, and there’s often no rash. Despite the milder symptoms, BZD can cause severe problems with the circulatory system, liver, kidneys, and brain. Diagnosing BZD requires a thorough medical history and a high index of suspicion.
Testing for Rickettsia Prowazekii
Epidemic typhus, like other diseases in the rickettsial group, is often diagnosed by a doctor based on a person’s symptoms and then confirmed by blood tests. The main strategy to confirm the diagnosis involves looking for a four-fold or higher increase in some specific substances in your blood, known as ‘titers’.
Various testing methods can be used, such as the indirect fluorescence antibody (IFA) test, different agglutination tests (for example, plate microagglutination and latex agglutination), and enzyme immunoassays. These tests are designed to detect the presence of certain proteins (antibodies) in your body that fight against the disease.
If you have epidemic typhus, your body first sends out a type of protein called immunoglobulin M (IgM) to fight the invader, and then follows up with another protein, immunoglobulin G (IgG). However, in Brill-Zinsser Disease (BZD), the body’s first response is to increase IgG protein levels.
One tricky part is that the proteins your body makes to fight R. prowazekii, the bacteria that cause epidemic typhus, can also respond to R. typhi, the bacteria responsible for murine typhus. These proteins are called antibodies. R. prowazekii can produce a specific type of antibodies known as Weil-Felix antibodies. However, the test to detect these antibodies isn’t used anymore because more accurate tests are available.
Treatment Options for Rickettsia Prowazekii
If you come down with epidemic typhus, a disease transmitted by body lice, the main treatment usually involves taking an antibiotic named doxycycline. It helps fight against the bacteria causing the disease and you take it until your symptoms improve and your fever goes away for at least 24-48 hours. The usual course of treatment span lasts around one to one and a half weeks.
If for any reason you can’t take doxycycline, there is an alternative medication available, which is chloramphenicol. This can be taken either orally (by mouth) or through an IV (a small tube placed in your vein).
In more serious cases of epidemic typhus, you might need extra support, such as receiving fluids through an IV to keep you hydrated and help your body fight off the infection.
Sometimes patients with epidemic typhus could have increased capillary permeability – which means fluids can easily leak out of the tiny blood vessels called capillaries. If this happens, the fluids can build up in the lungs (pulmonary edema) or brain (cerebral edema), which can be quite serious and needs immediate care.
The good thing is that patients usually respond quickly to the treatment. However, there have been cases where patients didn’t get better with a different type of antibiotic called azithromycin, so it’s not normally recommended. Macrolides, another group of antibiotics, are also not recommended for treating this infection.
What else can Rickettsia Prowazekii be?
There are many conditions that may cause certain symptoms which include but are not limited to:
- Epstein-Barr virus
- Fever of unknown origin
- Kawasaki disease
- Leptospirosis
- Malaria
- Meningitis
- Meningococcemia
- Relapsing fever
- Rocky Mountain spotted fever (RMSF)
- Syphilis
- Toxic shock syndrome
- Toxoplasmosis
- Tularemia
- Typhoid fever