Rickettsia rickettsii

Rickettsia rickettsii is a gram-negative, obligate intracellular bacteria that causes Rocky Mountain spotted fever. This bacterium is the most pathogenic of the Rickettsia genus and is found in North, Central, and South America. It is transmitted to humans and other mammals through the bite of an infected tick.

Taxonomy

Rickettsia rickettsii is a member of the genus Rickettsia, which belongs to the larger family of Rickettsiaceae. The Rickettsiaceae family is a part of the order Rickettsiales, within the class Alphaproteobacteria. The genus Rickettsia is divided into four groups: spotted fever, typhus, ancestral, and transitional. Rickettsia rickettsii falls into the spotted fever group.

Morphology

Rickettsia rickettsii is a small, rod-shaped bacterium, typically measuring 0.3 to 0.5 μm wide and 0.8 to 2.0 μm long. It is Gram-negative, meaning it does not retain the violet stain used in the Gram stain procedure. Instead, it takes up the red counterstain. The bacterium is also aerobic, requiring oxygen for growth.

Pathogenesis

Rickettsia rickettsii is the causative agent of Rocky Mountain spotted fever, one of the most severe and well-known rickettsial diseases. The bacterium is transmitted to humans through the bite of an infected tick. Once inside the host, the bacteria invade the endothelial cells lining the blood vessels, causing vasculitis and leading to symptoms such as fever, headache, and rash.

Diagnosis and Treatment

Diagnosis of Rickettsia rickettsii infection is often based on clinical signs and symptoms, as well as patient history of tick exposure. Laboratory testing can confirm the diagnosis. Treatment typically involves the antibiotic doxycycline, which is most effective when started early in the course of the disease.

Prevention

Prevention of Rickettsia rickettsii infection primarily involves avoiding tick bites through the use of repellents, wearing protective clothing, and performing regular tick checks after being in tick-infested areas.