Ricketts, Howard (1871–1910)

Howard Taylor Ricketts was an American pathologist and an ambitious pioneer of infectious disease who became renowned as the first to establish the identity of the infectious organism that causes Rocky Mountain spotted fever. The groundbreaking efforts of Ricketts and his research team was one of the earliest collaborations between physicians and entomologists, and the results have had an enormous impact on the often interdisciplinary field of epidemiology. His findings opened new pathways of knowledge in understanding the etiology of diseases.

Ricketts was born in Findley, Ohio. He completed his undergraduate degree in zoology at the University of Nebraska and went on to Northwestern University where he attained his medical degree. While working as a professor of pathology at the University of Chicago, he became interested in the mysterious and widely feared disease that was causing a very high fever and spots on the skin and was killing people who were spending a great deal of time outdoors. In 1906, Dr. Ricketts devoted his research on the discovery of the etiology of Rocky Mountain spotted fever. He characterized the basic epidemiologic features of the disease, including the role of tick vectors.

His definitive studies in the endemic area of Montana's Bitterroot Valley (where the disease was especially virulent) found that Rocky Mountain spotted fever was caused by a microorganism now called Rickettsia rickettsii. These unique microorganisms have both bacterial and viral characteristics and are pathogenic in humans. Ricketts demonstrated that Rocky Mountain spotted fever is not only transmitted by wood ticks but also caused by a bloodborne bipolar bacillus. Although he observed a small bacillus, Rickets was unable to culture a causal agent. His work suggested that bacterial diseases could be biologically passed from pests to people in his published findings in 1909, ‘A Micro-Organism Which Apparently Has a Specific Relationship to Rocky Mountain Spotted Fever: A Preliminary Report.’

Through a series of groundbreaking investigations, now considered landmark epidemiological achievements, Ricketts used noninfected guinea pigs as hosts for ticks carrying the disease, and afterward the guinea pigs developed the infection. He proved that a nonfilterable virus, not protozoa, was the etiologic agent for Rocky Mountain spotted fever. Ricketts was quite devoted to his research and was known to inject himself with pathogens on several occasions to measure their effect.

Four years later, he showed that typhus is caused by a similar organism carried by lice. Tragically, Dr. Ricketts died of typhus (another rickettsial disease) in Mexico in 1910 at the age of 39, shortly after completing his remarkable studies on Rocky Mountain spotted fever. His death came only a few days after he isolated the organisms he believed caused typhus. The two organisms Ricketts discovered were the first of what were later shown to be an unusual genus of virus-like bacteria—the Rickettsiae. He is now remembered as one of the great martyrs of epidemiologic research.