Rickettsiaceae

Rickettsiaceae is a family of gram-negative, obligate intracellular bacteria within the order Rickettsiales and the class Alphaproteobacteria. Members infect eukaryotic cells of vertebrate hosts and are transmitted primarily by arthropod vectors such as ticks, fleas, lice, and mites. They reproduce only inside host cells and often reside in cytoplasmic vacuoles before releasing daughter cells.

The family comprises several genera, with Rickettsia and Orientia being the most well known. Representative species include Rickettsia rickettsii (Rocky Mountain spotted fever), Rickettsia prowazekii (epidemic typhus), Rickettsia typhi (murine typhus), and Orientia tsutsugamushi (scrub typhus). Taxonomic placement has varied, but these genera are commonly described as belonging to Rickettsiaceae in many classifications.

Biology and ecology: Rickettsiaceae organisms are small, pleomorphic coccobacilli that rely on the host cell for replication and survival. They typically target endothelial cells, leukocytes, or other cell types, depending on the species, and can cause systemic illness through vascular injury and inflammation. Transmission to humans occurs via arthropod bites or, in some cases, contact with contaminated vectors.

Clinical features and disease: Infections usually present with fever, headache, myalgia, and a characteristic rash in many cases. Severity ranges from mild illness to life-threatening complications such as organ dysfunction, particularly in delayed or untreated cases.

Diagnosis and treatment: Diagnosis relies on serology (often indirect immunofluorescence) and molecular methods (PCR) from blood or tissue. Culture is limited to specialized laboratories. First-line treatment is doxycycline for most rickettsial infections; alternatives are considered when doxycycline is unsuitable.

Prevention: Prevention focuses on avoidance of vectors, protective clothing, repellents, and vector-control measures.