wildlife and zoo assay data sheet

Rickettsia

Test code: B0056 - Ultrasensitive screen for Rickettsia species by real time polymerase chain reaction. This assay detects but does not differentiate most common Rickettsia species, including the organisms that cause Rocky Mountain spotted fever, typhus, and most other common rickettsial diseases.

Rickettsiae are small, gram-negative, aerobic, coccobacillus bacteria. They are obligate intracellular organisms. The genus belongs to the family Rickettsiaceae of the order Rickettsiales and consists of many species associated with human disease. Pathogenic Rickettsiae can be divided into three major groups based on clinical characteristics of disease: spotted fever group, typhus group and scrub typhus group.

Spotted fever group
The type species of this group is Rickettsia rickettsii which causes Rocky Mountain spotted fever (RMSF). Rickettsia rickettsii is found in the Americas and is transmitted to humans through the bite of infected ticks. The bacterium infects human vascular endothelial cells, producing an inflammatory response.

Other members of this group can also be pathogenic, such as R. conorii (Mediterranean spotted fever), R. mongolotimonae (Lymphangitis-associated rickettsiosis) and R. slovaca (boutonneuse fever and similar illnesses), R. akari (rickettsial pox), R. japonica (Japanese spotted fever), R. sibirica (North Asian tick typhus), R. africae (African tick bite fever), R. helvetica (perimyocarditis), R. australis (Queensland tick typhus) and R. honei (Flinders Island spotted fever).

Typhus Group
Rickettsia prowazekii is a well-known member of this group and causes epidemic or louse-borne typhus. It infects human vascular endothelial cells, producing widespread vasculitis. In contrast to RMSF, louse-borne typhus tends to occur in the winter. Infection is usually transmitted from person to person by the body louse and therefore tends to manifest under conditions of crowding and poor hygiene. The southern flying squirrel is the animal reservoir in the United States, but what vector is involved in transmission from the flying squirrel to humans is unknown. The disease has a worldwide distribution.

Other Rickettsiae in the typhus group include R. typhi and R. felis. Murine typhus is caused by transmission of R. typhi from rats, cats and opossums to humans via a flea vector. Murine typhus is found worldwide and is endemic in areas including Texas and southern California. R. felis has also been detected in cat fleas and opossums.

Scrub Typhus Group
Orientia (Rickettsia) tsutsugamushi is a well-known member of this group and causes scrub typhus. This organism was originally called Rickettsia tsutsugamushi, and was subsequently given its own genus designation because it is phylogenetically distinct from the other Rickettsiae. It is transmitted to humans by the bite of trombiculid mites (chiggers), which are the vector and host. Scrub typhus occurs throughout much of Asia and Australia.

Current diagnosis of Rickettsia infection may be via blood smear microscopy, serological detection or Polymerase Chain Reaction. However, blood smear microscopy is insensitive and serological detection may be of limited value since some people infected with the bacteria may not seroconvert. Also, current commercially available kits only target a few species of Rickettsia. Molecular detection by PCR is therefore a more useful tool for rapid and sensitive diagnosis of acute infection by most common Rickettsia species.

Utilities:

• Help confirm the disease causing agent
• Shorten the time required to confirm a clinical diagnosis of Rickettsia infection
• Help ensure that animal facilities and populations are free of Rickettsia
• Early prevention of the spread of Rickettsia in animal facilities and populations
• Minimize human exposure to Rickettsia

References
Unsworth, N., Graves, S., Nguyen, C., Kemp, G., Graham, J. and Stenos, J.  (2008) Markers of exposure to spotted fever rickettsiae in patients with chronic illness, including fatigue, in two Australian populations. QJM 101: 269-274.

Specimen requirement: 0.5 ml whole blood in EDTA (purple top) or ACD (yellow top) tube, or 0.5 ml plasma or serum, or 0.2 ml synovial fluid, or 0.2 ml cerebrospinal fluid, or 0.2 ml tissue, or tick.

For specimen types other than those listed here, please call to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology: Qualitative real time PCR

Normal range: Nondetected