Rocky Mountain Spotted Fever – A Tick-Borne Infectious Disease

On 7 September 1942, LIFE wrote:

"Years before the scientists arrived, people in the valley had mysteriously fallen ill, suddenly developed a fever, shown red-purple rashes and died. Farmers said the condition came from drinking melted snow water." 

However, medical detectives discovered that Rocky Mountain spotted fever (Rocky Mountain Stopped Fever - RMSF) was transmitted by a hard-bodied, blood-feeding tick.

In 1906, American pathologist Howard Ricketts made a dangerous journey to the frontier regions of western Montana to identify the source of this life-threatening disease that appeared every spring. He carried out much of his research in tents set up in the grounds of a hospital in the Bitterroot Valley. He used rabbits as experimental subjects and proved that the disease was caused by a bacterium now known by his name, Rickettsia rickettsii. Howard Ricketts also showed that the RMSF bacterium was transmitted through tick bites. 

By 1938, a laboratory in the Bitterroot Valley was producing a vaccine for RMSF, but it was not very effective or practical. Today, RMSF is treated with antibiotics such as doxycycline, tetracycline and chloramphenicol.

RMSF is currently the deadliest rickettsial disease in the United States. Early symptoms may include fever, headache and muscle pain, followed by a rash beginning at the wrists and ankles and spreading towards the trunk. The bacterium infects cells lining blood vessels throughout the body and can therefore affect many organs, damaging tissues by causing paralysis and tissue death (gangrene). 

Although early research focused on the Rocky Mountain region of the United States, the disease was actually widespread throughout the continental United States, as well as in Canada and Central and South America. 

The two most important vectors (carriers) of RMSF are the American dog tick (Dermacentor variabilis) and the Rocky Mountain wood tick (Dermacentor andersoni).

It should be remembered that today the most common tick-borne disease in the Northern Hemisphere is Lyme disease. Borrelia bacteria cause this disease, which is transmitted by Ixodes ticks.  

Historical figure mentioned in the article: Howard Taylor Ricketts (1871–1910)

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