The early clinical presentation of Rocky Mountain spotted fever is nonspecific and may resemble a variety of other infectious and noninfectious diseases.

Most often the rash begins as small, flat, pink, nonitchy spots (macules) on the wrists, forearms, and ankles.

[15] People can develop permanent disabilities including "cognitive deficits, ataxia, hemiparesis, blindness, deafness, or amputation following gangrene".

[citation needed] A female tick can transmit R. rickettsii to her eggs in a process called transovarial transmission.

American dog ticks are widely distributed east of the Rocky Mountains and they also occur in limited areas along the Pacific Coast.

[citation needed] Other tick species have been shown to be naturally infected with R. rickettsii or serve as experimental vectors in the laboratory.

[citation needed] Rickettsia rickettsii can be transmitted to human hosts through the bite of an infected tick.

Following generation time in the cytoplasm of the host cells, the bacteria utilizes actin based motility to move through the cytosol.

The characteristic rash observed in Rocky Mountain spotted fever is the direct result of this localized replication of rickettsia in blood vessel endothelial cells.

Severely ill people may require longer periods before their fever resolves, especially if they have experienced damage to multiple organ systems.

Preventive therapy in healthy people who have had recent tick bites is not recommended and may only delay the onset of disease.

"[28] The CDC observed that "clearer language on the drug label may help avoid hesitation in prescribing life-saving doxycycline to children.

"[28] Treatment typically consists of 100 milligrams every 12 hours, or for children under 45 kg (99 lb) at 4 mg/kg of body weight per day in two divided doses.

Chloramphenicol is an alternative drug that can be used to treat Rocky Mountain spotted fever, specifically in pregnancy.

Long-term health problems following acute Rocky Mountain spotted fever infection include partial paralysis of the lower extremities, gangrene requiring amputation of fingers, toes, or arms or legs, hearing loss, loss of bowel or bladder control, movement disorders, and language disorders.

[30] There are between 500 and 2500 cases of Rocky Mountain spotted fever reported in the United States per year,[31] and in only about 20% can the tick be found.

[citation needed] Host factors associated with severe or fatal Rocky Mountain spotted fever include advanced age, male sex, African or Caribbean background, long-term excessive alcohol use and glucose-6-phosphate dehydrogenase (G6PD) deficiency.

[7] Rocky Mountain spotted fever (or "black measles" because of its characteristic rash) was recognized in the early 1800s, and in the last 10 years of the 1800s (1890–1900) it became very common, especially in the Bitterroot Valley of Montana.

Their studies found that Rocky Mountain spotted fever is caused by Rickettsia rickettsii, named in Ricketts's honor.

Ricketts died of typhus (another rickettsial disease) in Mexico in 1910, shortly after completing his studies on Rocky Mountain spotted fever.

[citation needed] Prior to 1922, Doctors McCray and McClintic both died while doing research on Rocky Mountain spotted fever, as did an aide of Noguchi Hideyo at the Rockefeller Institute.

Spencer of the Hygienic Laboratory of the U.S. Public Health Service was ordered to the region, and he led a research team at an abandoned schoolhouse through about 1924.

[38] Through a series of discoveries, the team found that a previous blood meal was necessary to make the tick deadly to its hosts, as well as other facets of the disease.

[38] On May 19, 1924, Spencer put a large dose of mashed wood ticks, from lot 2351B, and some weak carbolic acid into his arm by injection.

This vaccine worked, and for some years after it was used by people in that region to convert the illness from one with high fatality rate (albeit low incidence) to one that could be either prevented entirely (for many of them) or modified to a non-deadly form (for the rest).

[citation needed] Much of the early research was conducted at Rocky Mountain Laboratories,[39][40] a part of the National Institute of Allergy and Infectious Diseases.

The schoolhouse laboratory of 1922–1924, filled with ticks in various phases of the life cycle, is identified in retrospect as a biohazard, although the team did not fully appreciate it at first.

In the 1936 film His Brother's Wife, Robert Taylor plays a doctor who is part of a team frustrated by their inability to find RMSF in ticks collected from plants in the jungle, while infected people die all around them.

[citation needed] Rocky Mountain spotted fever is a big part of the 1947 Republic Pictures movie Driftwood, starring Walter Brennan, James Bell, Dean Jagger, Natalie Wood, and Hobart Cavanaugh.

[citation needed] In December 2013, hockey player Shane Doan was diagnosed with Rocky Mountain spotted fever, and returned to play in January 2014.