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What causes RMSF?


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Collecting Ticks

Although it was known that RMSF was caused when the Rickettsia rickettsii bacteria infected a Dermacentor andersoni tick that then bit a human, more questions remained. Was the bacteria spread by other species of ticks? And exactly how did the ticks get infected? To find out where the ticks were picking up the infection and to answer a number of other questions, ticks had to be collected in the wild.

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Man dressed in white with pants tucked in boots waves large white flag over meadow grass in high mountains.

A staff member of the Canyon Creek Schoolhouse Laboratory—possibly Dr. Ralph Parker, C.M. Salisbury, or George Cowan—dragged a white flannel flag over brush and grass to gather ticks in the Bitterroot Valley, Montana. He wore a white jump suit over his regular clothes, tucking his pant legs into the top of his high, laced boots. When they returned from such outings, the men would check each other closely in case a tick had attached itself to one of them.

Image: Office of NIH History and Stetten Museum, 1522

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In 1923, a mountain goat (perhaps this mountain goat kid) taken by George Cowan had over 1,000 ticks engorged ticks on it. It was with these ticks that Dr. Roscoe Spencer came up with his idea for an RMSF vaccine.

Image: Montana Memory, 264

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