Rickettsial refers to diseases, infections or characteristics associated with bacteria in the genus Rickettsia and related genera.
Overview and Features
Rickettsial diseases are caused by small, obligate intracellular Gram‑negative bacteria that depend on arthropod vectors for transmission. Members of the genus Rickettsia invade endothelial cells lining blood vessels, leading to vasculitis, increased vascular permeability and a systemic inflammatory response. Because they lack complete metabolic pathways, rickettsiae obtain ATP and other metabolites from the host cell. The adjective “rickettsial” encompasses the clinical syndromes and pathologic features associated with these infections. Symptoms typically include fever, headache, myalgia and a characteristic rash that reflects vascular injury. Laboratory diagnosis often relies on serologic testing or nucleic acid amplification, as culture requires specialized biosafety measures. Rickettsial infections respond well to tetracycline antibiotics, and treatment should not await laboratory confirmation.
Common Rickettsial Diseases
The spotted fever group comprises diseases such as Rocky Mountain spotted fever, Mediterranean spotted fever and Queensland tick typhus, all transmitted by hard ticks. The typhus group includes epidemic typhus, caused by Rickettsia prowazekii and transmitted by body lice, and endemic typhus due to Rickettsia typhi, transmitted by fleas. Rickettsialpox, caused by Rickettsia akari and spread by mites, presents with an eschar and vesicular rash. Scrub typhus, now assigned to the genus Orientia, is still referred to as a rickettsial disease and is transmitted by chiggers. These infections are widely distributed across temperate and tropical regions and often occur in association with poverty, overcrowding or exposure to ticks and mites.
Rickettsial diseases illustrate the complex interactions among bacteria, arthropod vectors and mammalian hosts. Prompt recognition and treatment reduce morbidity and mortality associated with these infections.
Related Terms: Rickettsia, Rickettsia rickettsii, Typhus, Spotted fever, Rickettsialpox