Blood and Lymphatic Infections

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SEM of the tip of the mouthparts of a female mosquito

100 mm

SEM of the tip of the mouthparts of a female mosquito lexandre Emile John Yersin (1863-1943) is one of the most interesting though relatively unknown contributors to the conquest of infectious diseases. He was born in 1863 in the Swiss village of Lavaux, where his family lived in a gunpowder factory. His father, director of the factory and a self-taught insect expert, died unexpectedly 3 weeks before Yersin's birth. Alexandre developed an interest in science when as a young boy he discovered in an attic trunk the microscope and dissecting instruments of the father he never knew. A local public health physician befriended the family and influenced Yersin to study medicine, and at age 20 he began pre-med studies in Lausanne. Later, while a medical student in Paris, Yersin volunteered to help at the Pasteur Institute, and in his fourth year of medical training, he was hired by Emile Roux, a coworker of Pasteur. Yersin became increasingly recognized for his work at the Institute, but he was bored with research, and he did not want to practice medicine because he also felt it was wrong for physicians to make a living from sickness.

He abruptly left the Pasteur Institute and was employed as a physician on a ship sailing from Marseilles to Saigon. Most of Indochina was under French control and was largely unexplored and undeveloped. Yersin became enchanted with the land and its peoples, exploring crocodile-infested rivers in a dugout canoe and making expeditions on elephant into jungles where tigers roared. For the rest of Yersin's life, Vietnam was his home. His many contributions to the region included the introduction of improved breeds of cattle, cultivation of rubber and quinine-producing trees, and the establishment of a medical school.

Yersin also studied the diseases that affected the Vietnamese people. One of them, plague, was a horrifying recurring problem. The disease had killed millions in Europe in medieval times and had struck France as recently as 1720. This great killer came and went unpredictably, an incurable disease, its cause and transmission completely unknown.

In 1894, Yersin went to study a Hong Kong outbreak of plague because the facilities for studying the disease were better in Hong Kong than in Vietnam. Unfortunately for Yersin, Shibasaburo Kitasato, the famous colleague of Robert Koch and Emil von Behring, had arrived 3 days before he did with a large team of Japanese scientists. British authorities had given them access to patients and laboratory facilities. Since Yersin did not speak English, it was difficult for him to communicate with the authorities. Moreover, although both he and the Japanese scientists spoke fluent German, the Japanese team treated him coolly, perhaps as a reflection of the intense rivalry between

Pasteur and Koch. Yersin was reduced to setting up a laboratory in a bamboo shack. He bribed British sailors responsible for disposing of the bodies of plague victims to allow him to get samples of material from their swollen, pus-filled lymph nodes called buboes.

A week after his arrival in Hong Kong in the summer of1894, Yersin reported to the British authorities his discovery of a bacillus of characteristic appearance, invariably present in the buboes of plague victims. The bacterium could be cultivated, and it caused plaguelike disease when injected into rats. Later, he showed that the disease was transmitted from one rat to another. Yersin's plague bacillus, now known as Yersinia pestis, was used to make an antiplague vaccine, and in 1896, antiserum prepared against the organism provided the world's first cure of a patient with plague. Not long afterward, another Pasteur Institute scientist proved that the rat flea was crucial in transmission. ■ Robert Koch, pp. 4,83,464,691 ■ Shibasaburo Kitasato, p. 691

Kitasato, working with blood from the hearts of plague victims, announced shortly after his arrival in Hong Kong that he had isolated the bacterium that caused plague. Although subsequently it proved to be only a laboratory contaminant, Kitasato was named co-discoverer of the plague bacillus because of his great prestige.

—A Glimpse of History

716 Chapter 28 Blood and Lymphatic Infections

THE CIRCULATION OF BLOOD AND LYMPH FLUIDS supplies nutrients and oxygen to the body's tissue cells and carries away the cells' waste products. The circulatory system also heats and cools body tissues to maintain an optimum temperature. Infection of the system can have devastating effects because infectious agents become systemic, meaning they can be carried to all parts of the body, producing disease in one or more vital organs or causing the circulatory system itself to stop functioning. Thus, even a small scratch can cause considerable harm if it results in a pathogen entering the bloodstream. The circulation of an agent in the bloodstream is given a name ending in -emia that specifies the nature of the agent, as with bacteremia, viremia, and fungemia. In many cases, there are no symptoms associated with the circulating agent. When illness results from a circulating agent or its toxins, the condition is referred to as septicemia, or blood poisoning. When, as a result of septicemia, the blood pressure falls to such low levels that blood flow to vital organs is insufficient to maintain their functioning, the condition is called septic shock.

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