Rickettsial diseases of the cardiovascular and lymphatic systems

•The rickettsia bacteria are obligate intracellular parasites of eukaryotes, and are responsible for a number of diseases spread by arthropod vectors.
•Arthropods are animals with jointed appendages and include mites, ticks, and insects such as mosquitoes, fleas, and lice.
•There are several related rickettsial diseases, which differ mainly in their severity and in their arthropod vectors.
•These include Epidemic typhus, Endemic murine typhus and Spotted fevers or Rocky Mountain spotted fever.

1. Epidemic typhus. 

• Epidemic typhus is caused by Rickettsia prowazekii , a rickettsia transmitted by the body louse of the genus Pediculus.
• The organism invades the bloodstream and causes a maculopapular skin rash beginning on the body trunk and spreading to the appendages.
• The fever is extremely high, and the death rate is significant.
• Tetracycline antibiotics are effective for therapy, and elimination of lice is essential to stem the spread of the epidemic.

2. Endemic typhus.
• Endemic typhus is also called murine typhus because it occurs in mice and other rodents.
• It is transmitted by the rat flea and is caused by Rickettsia typhi , a submicroscopic rickettsia.
• The symptoms are similar to those of epidemic typhus but are much milder, and the mortality rate is much lower.

3. Rocky Mountain spotted fever.
• Rocky Mountain spotted fever is caused by the rickettsia Rickettsia rickettsii.
• This submicroscopic bacterium is transmitted by ticks of the genus Dermacentor.
• The disease is characterized by a maculopapular skin rash (a “spotted rash”) occurring on the appendages and then spreading to the trunk.
• The fever is very high, and headaches accompany the disease.
• Antibiotics such as tetracycline are effective for therapy.

•Several other rickettsiae are known to cause diseases in humans.
• One example is rickettsial pox, caused by Rickettsia akari. This organism is transmitted by mites and causes a skin rash that resembles chickenpox.
• Another disease is tsutsugamushi, also called scrub typhus. This disease is also transmitted by mites.
• It occurs in Pacific regions and is characterized by a fever and skin rash.

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Several other rickettsiae are known to cause diseases in humans.
• One example is rickettsial pox, caused by Rickettsia akari. This organism is transmitted by mites and causes a skin rash that resembles chickenpox.
• Another disease is tsutsugamushi, also called scrub typhus. This disease is also transmitted by mites.
• It occurs in Pacific regions and is characterized by a fever and skin rash. 

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Another rickettsial disease is trench fever, caused by Rochalimaea quintana. This disease is transmitted by lice and was common during World War I, when it affected soldiers in the trenches.
• Ehrlichiosis is a rickettsial disease due to Ehrlichia canis. Patients suffer headache and fever, but there is no skin rash associated with the disease.
• A similar disease is human granulocytic ehrlichiosis (HGE), which is also caused by a species of Ehrlichia. Ehrlichia species are transmitted by ticks.
• The diseases can be treated with tetracycline and other antibiotics.