Skin Infections

A dividing Staphylococcus epidermidis cell

A dividing Staphylococcus epidermidis cell

^ J oward T. Ricketts was born in Ohio in 1871. He studied medicine in Chicago, and then specialized * in pathology, the study of the nature of disease and its causes. In 1902, he was appointed to the faculty of the University of Chicago, where his research interests turned to an often fatal and little understood disease characterized by a dramatic rash, Rocky Mountain spotted fever. The disease could be transmitted to laboratory animals by injecting them with blood from an infected person, and Ricketts noticed that people and laboratory animals with the disease had tiny bacilli in their blood. Ricketts was sure that these tiny bacteria were the cause of the disease, but he was never able to cultivate them on laboratory media. Based on observations of victims with the disease, Ricketts and others suspected that Rocky Mountain spotted fever was contracted from tick bites, and Ricketts went on to prove that certain species of ticks could transmit the disease from one animal to another. The infected ticks remained healthy but capable of transmitting the disease for long periods oftime, and oftentimes the offspring of infected ticks were also infected. Ricketts was able to explain this by showing that the eggs of infected ticks often contained large numbers of the tiny bacilli, an example of transovar-ial, meaning via the eggs, passage of an infectious agent. Frustrated by his inability to cultivate the bacilli for further studies, Ricketts declined to give them a scientific name and went off to Mexico to study a very similar disease, louse-borne typhus (Rocky Mountain spotted fever is also known as tick-borne typhus). Unfortunately, Ricketts contracted the disease and died at the age of 39. Five years later a European scientist, Stanislaus Prowazek, studying the same disease in Serbia and Turkey, met the same fate at almost the same age. The martyrdom of the two young scientists struggling to understand infectious diseases is memorialized in the name of the louse-borne agent, Rickettsia prowazekii. Both the genus and species names of the Rocky Mountain spotted fever agent, Rickettsia rickettsii, recognize Howard Ricketts. We now know that these bacteria are obligate intracellular parasites, which explains why they could not be cultivated on ordinary laboratory media. Antibiotics, which could have saved these men, had not yet been discovered.

—A Glimpse of History

A MAJOR PART OF THE BODY'S CONTACT WITH THE outside world occurs at the surface of the skin. As long as skin is intact, this tough, flexible outer covering is remarkably resistant to infection. Because of its exposed state, however, it is fre quently subject to cuts, punctures, burns, chemical injury, hypersensitivity reactions, and insect or tick bites. These skin injuries provide a way for pathogens to enter and infect the skin and underlying tissues. Skin infections also occur when microorganisms or viruses are carried to the skin by the bloodstream after entering the body from another site, such as the respiratory or gastrointestinal systems.

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