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(ii.) The presence of plague bacilli in bubonic cases before the formation
of the bubo; and
(iii.) The presence of plague bacilli in the blood of patients convalescing
from this disease.
Avenues of Infection in Plague.
1
Dr. HUNTER's investigations lead him to the conclusion that it is chiefly through the alimentary canal that the bacillus enters the body, this raises the important question of the possibility of food infection.
In the Annual Report of the Medical Department for 1898 I drew attention to the fact that outbreaks of what was known as rinderpest in cattle had preceded the epidemics of 1894, 1896 and 1998.
In the earlier months of 1898 the neighbouring provinces of Kwantung and Kwangsi were overrun with this disease which killed off large numbers of cattle. Dr. MACDONALD of Wenchow wrote me in that year "that preceding the outbreak of plague in that town there was an epidemic of rinderpest in the native cattle."
Again in 1896 an epidemic occurred amongst the pigs imported to the Colony from Hoihow. Dr. WILM and myself examined several of the pigs and the symp- toms and post-mortem appearances found were similar to those met with in cattle which had died of rinderpest. In the light of recent researches these diseases must have been of the nature of hæmorrhagic septicamia. A similar epidemic occurred amongst pigs in and around Canton preceding the outbreak of plague there in 1898.
In 1899 Cheung Chau, a small island sixteen miles from Hongkong, was attacked with plague and an epidemic of a similar nature prevailed amongst the pigs on this island prior to the outbreak in man, and distinct evidence was obtained that pigs which had died of this disease had been used as food. Suggestive as these facts were of the possibility of infected food spreading the disease it was impossible for us with our then limited staff to follow up these investigations.
On the arrival of Professor SIMPSON in 1902 I told him of these outbreaks and particularly of the one at Cheung Chau and suggested how important it would be to carry out experiments in regard to the susceptibility of animals to plague infection.
The results of these experiments are given in Professor SIMPSON's Report on the Causes and Continuance of Plague in Hongkong published in 1903. They proved that pigs, calves, sheep, monkeys, fowls, &c., are more or less susceptible to plague of a fatal nature; that they take the infection by feeding as well as by inoculation and that the type of plague induced by feeding is usually septicemic.
Dr. HUNTER, as his report shows, has further investigated the possibilty of the infection being communicated by way of food.
He has shown that the plague bacillus grows exceedingly well in media, prepared with rice. He has found plague bacilli in the cheapest and most inferior quality of rice; rats fed with this rice contracted the disease, guinea pigs fed with it gave similar results, so that there can be no doubt that infected rice may spread the disease. This quality is used as food by the poorer class of Chinese.
The spread of plague infection by insects is an interesting chapter, this occurs indirectly by infecting food and household utensils.
Occurrence of Disease in Animals,
This report shows conclusively the important part played by rats, that are suffering from plague, in conveying the infection to man. The presence of chronic rat plague is dealt with very fully and it is this chronic rat plague which Dr. HUNTER thinks bridges over the intervals between successive epidemics. Again other animals such as cats, fowls, calves, sheep and pigs, &c., are susceptible to plague infection and may become elements of danger.