Rickettsia rickettsii is a bacteria that causes Rocky Mountain spotted fever (RMSF).  It infects animals such as dogs and rodents and is spread to humans by ticks.  These ticks must first bite an infected animal and then bite a human.  The bacteria is transmitted after the tick has been attached to the skin of an unlucky child for 6 to 12 hours.  The tick bite is not painful and often goes unnoticed.  Rocky Mountain spotted fever causes symptoms which include a characteristic rash that often starts at the wrists or ankles, fever, headaches, and muscle aches.  Without treatment, the disease can be serious, therefore, an antibiotic such as doxycycline should be started as soon as possible.

Diseases

Rocky Mountain spotted fever

Appearance (under a microscope)

Very small, short rods that stain poorly with normal microscope stains

Habitat and Transmission

• Are carried by mammals such as dogs and rodents
• Are spread to humans by ticks who bite an infected animal and then a human
• Despite the name (i.e., Rocky Mountain...) the disease is most common on the East Coast of the United States.
• Live within the cells of the infected animal or human

Weapons and Defenses

• Are able to hide and thrive within the cells of human blood vessel walls

Weaknesses

• T-lymphocytes and natural killer cells work together to eliminate Rickettsia rickettsii infection
• Suceptible to antibiotics such as doxycycline

Photo 1 - This photograph of a child's right arm depicts the characteristic spotted rash of Rocky Mountain spotted fever. CDC. 1975. Used with permission.

Photo 2 - Under a low magnification of 23X, this scanning electron micrograph (SEM) depicted a dorsal view of an unidentified male Dermacentor sp. tick found upon a cat in the suburbs of Decatur, Georgia, which measured approximately 3.5mm from its gnathosoma (i.e., capitulum), which is where its mouthparts are located, to the distal abdominal margin. CDC/ Callie Carr/ Janice Carr. 2006. Used with permission.