Scrub typhus is a form of typhus caused by Orientia tsutsugamushi and transmitted by chiggers, which are found in areas of heavy scrub vegetation. Symptoms include fever, headache, muscle pain, cough, and gastrointestinal symptoms.
An early attempt to create a scrub typhus vaccine occurred in Britain in 1937 (with the Wellcome Foundation infecting around 300,000 cotton rats in a classified project called "Operation Tyburn" (http://www.nal.usda.gov/awic/newsletters/v5n2/5n2princ.htm#toc5)), but the vaccine was not used.
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