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*9 W19 Spirochetes Treponema pallidum, the etiologic agent of syphilis, can theoretically be transmitted through fresh blood components. Today, posttransfusion syphilis is of only historical interest for two reasons. The first of these is the result of the use of stored, refrigerated bank blood rather than fresh blood. The second is the routine required testing of all donor blood with a serologic test for syphilis before it can be released from the blood bank. Treponema pallidum is a spirochete measuring 5 - 20 microns in length. The agent is quickly destroyed by heating, drying, soap and water or changes in pH. Many studies have documented that T. pallidum does not survive in stored human blood. As early as 1941, it was shown that human citrated blood stored at 4C contained no viable spiro- chetes after 48 hours. Theoretically, syphilis could be transmitted by fresh blood from donors with active primary syphilis, since a serologic test for syphilis would be negative during the incubation period, despite the presence of spirochetes in the blood. Therefore, it is commonly believed that the use of refrigerated blood, rather than the routine serologic testing, is responsible for the virtual absence of reported cases of posttransfusion syphilis. Theoretically at least, platelets that are stored for a short period of time at room temperature are the component with the highest potential for transmitting syphilis. Parasites Of the parasitic infections transmitted by blood, malaria is the most common. Human malaria is caused by four species of Plasmodium: P. falciparum, P. vivax, P. ovale and P. mala- riae. In general, people are infected when the asexual sporozoites are injected into lymphatics or blood vessels during the bite of a carrier mosquito. Malaria usually results in a self-limited infection including fever, anemia, hypersplenism and edema. P. falciparum causes the most severe form of malaria, which not infrequently results in death. The life cycle of all the species of Plasmodium para- sites has two phases: a sexual cycle (sporogony) that takes place in the intestinal tract of the mosquito and an asexual cycle (schizogony) that occurs in the human host. When a person is bitten by an infected mosquito, the injected sporozoites enter the liver. There they begin to multiply in what is known as the exoerythrocyte cycle. About 10 days later, small forms known as merozoites break out of the liver cells and are released into the circulation. There BIOSAFETY - INFAGT - 0491 - PAGE 6