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that "Simond...... has given a great deal of attention to this subject (and) came to the conclusion that Indian rat fleas bite man and that rat fleas spread plague from one rat to another and also to the human species."* However, Hunter himself was not convinced of this theory and subscribed to the view that cockroaches picked up the bacillus and transferred the disease to food stuffs. Others shared his scepticism.
Finally, studies undertaken in 1905-06 by the Indian Plague Commission in Bombay conclusively established that fleas were the principal agents of transmission. Of the 1500 species of fleas about 100 can transmit plague; the most widely disseminated is Xenopsylla cheopis which is equally at home on rats or homo sapiens. At one feeding on a rat, the blood of which contains 100 million organisms per millilitre, a flea will ingest about 5000 organisms which then multiply in the flea's digestive tract. Later, its proventriculus becomes plugged by gelatinous masses of bacilli and, as a result, the valvular action becomes impaired. Because of this obstruction, blood cannot be sucked into the stomach. The esophagus becomes distended and the elastic recoil of the walls of both pharynx and gullet when the flea stops sucking may drive back into the bite wound highly infective blood. An infected flea may regurgitate as many as 10,000 to 24,000 organisms at one biting. Many species of fleas, however, may become infected without incurring blockages and these may never become pestiferous unless they have fed on severely infected rodents.
Once a rat has become infected and subsequently dies the fleas carried thereon migrate to another host when the corpse loses its body heat. When the rat population has become decimated the fleas transfer their attention to human beings. This sequence of events thus explains the commonly observed phenomenon that plague in rats precedes plague among the inhabitants of infected premises.
Even though the discovery of how plague was transferred from rats to man enabled more effective preventive measures to be taken to eradicate the disease in Hong Kong, it continued to afflict the colony until as late as 1929 when two cases were recorded. Virulent
*W. Hunter, A Research into Epidemic and Epizootic Plague, Hong Kong, 1904, p. 32.
THE GREAT PLAGUE OF HONG KONG
69
that "Simond...... has given a great deal of attention to this subject (and) came to the conclusion that Indian rat fleas bite man and that rat fleas spread plague from one rat to another and also to the human species."* However, Hunter himself was not convinced of this theory and subscribed to the view that cockroaches picked up the bacillus and transferred the disease to food stuffs. Others shared his scepticism.
Finally, studies undertaken in 1905-06 by the Indian Plague Commission in Bombay conclusively established that fleas were the principal agents of transmission. Of the 1500 species of fleas about 100 can transmit plague; the most widely disseminated is Xenopsylla cheopis which is equally at home on rats or homo sapiens. At one feeding on a rat, the blood of which contains 100 million organisms per milliletre, a flea will ingest about 5000 or- ganisms which then multiply in the flea's digestive tract. Later, its proventriculus becomes plugged by gelantinous masses of bacilli and, as a result, the valvular action becomes impaired. Because of this obtruction, blood cannot be sucked into the stomach. The esophagus becomes distended and the elastic recoil of the walls of both pharynx and gullet when the flea stops sucking may drive back into the bite wound highly infective blood. An infected flea may regurgitate as many as 10,000 to 24,000 organisms at one biting. Many species of fleas, however, may become infected without incur- ring blockages and these may never become pestiferous unless they have fed on severely infected rodents.
Once a rat has become infected and subsequently dies the fleas carried thereon migrate to another host when the corpse loses its body heat. When the rat population has become decimated the fleas transfer their attention to human beings. This sequence of events thus explains the commonly observed phenomenon that plague in rats precedes plague among the inhabitants of infected premises.
Even though the discovery of how plague was transferred from rats to man enabled more effective preventive measures to be taken to eradicate the disease in Hong Kong, it continued to afflict the colony until as late as 1929 when two cases were recorded. Virulent
*W. Hunter, A Research into Epidemic and Epizootic Plague, Hong Kong, 1904, p. 32.
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