Rocky Mountain spotted fever is still another infectious disease caused by rickettsia carried by ticks.
These rickettsia damage blood vessels, causing blotchy skin (the "spots" in RMSF) and even hemorrhage.
RMSF can mimic other tick diseases. Definitive diagnosis usually depends on antibody titers.
Rocky Mountain spotted fever (RMSF) is another tick-borne disease that affects small mammals, dogs, and humans. The infectious organism is called Rickettsia rickettsii. This rickettsia is most often transmitted by the American dog tick (Dermacentor variabilis) or the Rocky Mountain wood tick (D. andersoni), and less commonly, by the lone star tick (Amblyomma americanum).
Rocky Mountain spotted fever can be transmitted to humans during the removal of an engorged tick from a pet. If the tick's midgut and excrement get into a person's eye or abraded skin, infection is possible. Clinical signs early in the disease process consist of high fever (up to 105° F), loss of appetite, swollen lymph nodes, and sore joints. The severity of disease depends on the magnitude of infection, which can vary.
The rickettsial organisms enter the endothelial (inner cell) lining of small blood vessels and reproduce. Damage to this inner lining of blood vessels, along with a loss of platelets, can lead to the development of petechiae (minute reddish/purplish spots in the skin or mucous membranes containing blood) and ecchymoses, (blotches in the skin and mucous membranes due to the escape of blood from ruptured blood vessels). A disorder called disseminated intravascular coagulation (DIC) can develop in extreme cases, which leads to epistaxis (bloody nose) and uncontrollable hemorrhage. Rocky Mountain spotted fever can mimic other diseases such as Lyme disease and ehrlichiosis due to the development of lameness and fever.
Despite its name, most of the cases of Rocky Mountain spotted fever occur east of the Mississippi River. Diagnosis is made by demonstrating a four-fold increase in antibody titers in conjunction with the above clinical signs. In the western United States, a single titer of 1:128 or above suggests recent infection. In the eastern United States, a single titer of more than 1:512 is required to signify active disease. Regional strain differences among R. rickettsii organisms are responsible for these differing titer cut-offs.
Treatment with tetracycline antibiotics is usually very effective. Additional supportive treatment with intravenous fluids and blood transfusions may be necessary. Immunity appears to be lifelon