What kind of bacteria is Rickettsia typhi?

Rickettsia typhi is a small, rod shaped, Gram – negative bacteria. Ricketssias have a thin murein layer and an outer membrane.

Murein is a strong polymer, which is found in the cell walls of prokaryotes. Lipopolysaccharides can be found on its outer membrane.

Rickettsiae thrive in environments with a high concentration of potassium and low concentration of glucose. Cell membrane transport systems are used to acquire energy and amino acids from the host. This is one of many ways this microbe exploits its host. Its inability to maintain concentrations of essential nutrients like ATP, make R. typhi relatively non-motile. This non-motility allows for accumulation of the microbe in the host cell, which causes the cell to lyse. Rickettsia has also its own metabolism, and is able to produce its own energy and proteins.

They are usually small, with dimensions 0.3-0.5 x 0.8-2.0 um. They are obligate intracellular parasites. Rickettsias enter the cell with the help of phagocytosis, destroy it, escape and replicate in other cells. The rickettsiae have very small genomes of about 1.0-1.5 million bases. Rickettsias do not form flagella or spores. Rickettsias are usually destroyed in temperatures higher than 56 degrees or any disinfectant. R. typhi contains rickettsial outer membrane protein B (OmpB).

Rickettsiae must be grown in the laboratory by co-cultivation with eucaryotic cells. They require the osmolarity and nutritional environment supplied by an intracellular habitat. This explains their intracellular growth, and the inability to survive, grow and replicate on their own.

The genus Rickettsia includes many species associated with human disease. The rickettsiae that are pathogens of humans are subdivided into three major groups based on clinical characteristics of disease:

  • spotted fever group
  • typhus group
  • scrub typhus group.

This genus alone is responsible for a number of highly virulent diseases including Rocky Mountain spotted fever, epidemic typhus, Brill-Zinsser disease, scrub typhus, and others.

The rickettsial agents of scrub typhus have a single taxonomic name: Orientia tsutsugamushi.

Rickettsia prowazekii is the cause of epidemic or louse-borne typhus. . R. prowazekii infects human vascular endothelial cells, producing widespread vasculitis. In contrast to RMSF, louse-borne typhus tends to occur in the winter. Infection usually is transmitted from person to person by the body louse and, therefore, tends to manifest under conditions of crowding and poor hygiene. This disease is distributed worldwide.

Other rickettsiae in the typhus group include R. typhi and R. felis.

Rickettsia typhi is transmitted primarily by the rat flea, Xenopsylla cheopis. Mites and lice are also potential vectors.

Although R. felis is phylogenetically more closely related to the spotted fever group of rickettsiae than the typhus group, it shares antigens with R. typhi and produces a murine typhus-like illness. Rickettsia felis has been detected in cat fleas and opossums.

The genus Rickettsia was named after Howard Taylor Ricketts (1871–1910), who studied Rocky Mountain spotted fever.

What is Typhus?

Typhus is caused by one of two types of bacteria: Rickettsia typhi or Rickettsia prowazekii. It is a bacterial disease, usually non-lethal. Death occurs in less than 2% of infected people, who were not treated. Murine typhus caused by Rickettsia typhi is much milder than epidemic typhus, caused by Rickettsia prowazekii. This infection is usually seen in areas where hygiene is poor and the temperature is cold. It is more often during summer and fall. Humans get infected from rats, fleas, cats, opossums, raccoons, and skunks.

The infection can lead to multisystem organ failure and might be spread in every organ, including the brain, liver, lungs, heart and kidneys. The incubation period is 1-2 weeks, usually 10 days. After the incubation period, signs and symptoms occur, and depending from the type of Rickettsia infected they might be mild to severe.

Typhus signs and symptoms

Typhus signs and symptoms are milder in murine typhus, while the situation is more serious in epidemic typhus. Signs and symptoms usually include: headache, very high fever which may last more than two weeks, dry caught, nausea, vomiting, abdominal pain, diarrhea, constipation, dull rash that begins in the abdomen or chests and spreads to other parts of the body, joint pain, muscular pain, etc.

Signs and symptoms of endemic typhus are always more severe and they may include: caught, high fever, chills, nausea, vomiting, abdominal pain, diarrhea, constipation, dehydration, headache, confusion, delirium, joint and muscle pain, low blood pressure, stupor and even coma. Death cases are more common with endemic typhus caused by Rickettsia prowazekii, then with murine typhus, caused by Rickettsia typhi.

How is Typhus diagnosed?

Typhus is diagnosed with blood analysis. A complete blood count CBC may show anemia, low white blood cells and low platelets. Other blood tests may also reveal lower potassium levels, lower sodium levels, low albumin levels, high levels of liver enzymes and high levels of typhus antibodies.

How is Typhus treated?

Treatment of typhus consists of antibiotics like Tetracycline and Doxycycline. In less common cases, Chloramphenicol is used. A more aggressive therapy is usually needed for epidemic typhus as it is a more severe form of the disease. Oxygen therapy and even intravenous fluids might be needed.

Patients who receive quick treatment usually fully recover. Patients over the age of 60 have greater chance for complications and lethal ending. Usually only in 2% of the cases death will occur. This is more related to murine typhus, while without treatment, in epidemic typhus death may occur in 10-60% of the infected persons, especially in persons with depressed immune system.