R. rickettsii, R. parkeri, R. prowazekii
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.
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.
Situation in Austria
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.
The standard serological test for the diagnosis of rickettsialpox is the indirect immunofluorescence assay (IFA). The examination of paired serum samples allows the detection of a significant (fourfold) increase in antibody titers. This improves the validity of the serology. The first sample should be collected during the first week of illness; the result is often negative. The second sample is taken two to four weeks later. IgM antibodies are less specific than IgG antibodies and can lead to false positive results. IgM results alone should not be used for laboratory diagnosis.
During the acute phase of illness, whole blood analysis by polymerase chain reaction (PCR) can be performed. This method is highly sensitive at the beginning of the disease; however, sensitivity may decrease after antibiotic use begins. In SENLAT, detection of rickettsiae by PCR is often successful from the Eschar smear.
DNA detection by PCR from blood, tissue samples, or Eschar smears can also be used for diagnosis.
Last updated: 09.03.2023