Rickettsiae are a genus of bacteria that cause a group of diseases called rickettsioses. These include Rocky Mountain spotted fever and spotted typhus. These bacteria are usually transmitted by ticks. Fleas, lice, and mites can also be vectors. Only a few species of rickettsiae are pathogens of humans.

Rickettsiae are spread worldwide

Hosts of rickettsiae include dogs and rodents. In spotted typhus (louse spotted fever), humans are the reservoir.

Ticks can pick up rickettsiae during the blood meal from an infected host, such as dogs, rodents, and the like, and transmit them to humans when bitten. In the case of typhus, transmission of the pathogens occurs through the feces of infected clothes lice.

Rocky Mountain spotted fever: sudden onset of fever, headache, nausea with vomiting, muscle pain, and rash on wrists, ankles, and forearms. The rash is seen in only about half of the cases.

Rickettsiosis caused by R. parkeri is characteristically less severe than Rocky Mountain spotted fever and is almost always accompanied by a scab at the site of the tick bite. A few days after the scab appears, the following symptoms may develop: Fever, headache, rash, muscle aches.

Mediterranean tick-bite fever is a severe disease with high fever, severe muscle and joint pain, fatigue and exhaustion. Patients with underlying diseases are at much higher risk.

In TIBOLA/SENLAT, a skin lesion develops at the tick bite site that resembles a cigarette burn and is called an eschar. The bite site is often located on the head. Enlargement of lymph nodes in the neck and throat is also found. Accompanying symptoms include fever, fatigue, and skin rashes.

In spotted typhus (lice spotted fever), there are chills, increasingly high fever, headache, pain in the limbs and clouding of consciousness if the brain is also affected. A blue- to red-spotted skin rash is typical.

Rickettioses are treated with the antibiotic doxycycline. Clinical suspicion of these diseases is sufficient to start treatment. Delays in treatment result in serious illness and even death.

A vaccine is currently not available. Essential for prevention is the avoidance of tick bites or the rapid removal of ticks from the body. Spotted typhus can be prevented by good hygienic conditions.

Diseases with a source of infection in Austria have not been documented in recent decades. This is partly due to the fact that the most common rickettsial species in Austrian ticks, Rickettsia helvetica, causes little to no disease.

About 17 percent of domestic Ixodes ricinus ticks are infected with rickettsiae(R. helvetica, R. raoultii, R. monacensis, R.slovaca).

Pathogenic rickettsiae species are distributed worldwide. Depending on the geographical location, they differ and cause different diseases in humans. Rickettsial diseases can be divided into two main groups:

• The spotted fever group, which is transmitted by ticks or mites. These include Rocky Mountain spotted fever; rickettsiosis caused by Rickettsia parkeri; Mediterranean tick-bite fever; and TIBOLA (tick-borne lymphadenopathy) and SENLAT (scalp eschar and neck lymphadenopathy after tick bite), respectively
• the typhoid group, which is mainly transmitted by lice or fleas, and which includes spotted typhoid fever (lice spotted fever)

In recent years, numerous new pathogenic rickettsiae have been discovered.

In the U.S., more than 500 cases of Rocky Mountain spotted fever caused by R. rickettsii occurred between 2002 and 2021. Rocky Mountain spotted fever has become increasingly common over the past several years in certain regions of Arizona.

Rocky Mountain spotted fever, caused by Rickettsia prowazekii, is a notifiable infectious disease. Individuals who have had spotted typhus are excluded from donating blood. Spotted typhus is observed very rarely and only outside Europe (Latin America, Africa, Afghanistan, Himlaya areas). Rickettsia persisting in the human body can lead to a generalized infection ten to 30 years after the original infection (Brill-Zinsser's disease). This is usually milder; there is no association with lice in this case.