The diagnostics and treatment of tropical diseases

by E. R. Stitt

As regards pneumonic plague the origin of such epidemics is probably from pneumonia occurring secondarily in cases of bubonic plague. Provided the conditions are favorable, particularly as to moisture in the air of the room, the infection spreads directly from man to man as a result of the droplets of heavily infected sputum being sprayed into the air in the act of coughing on the part of the patient. It is an instance of Flügge’s droplet method of infection.

In the recent epidemic of pneumonic plague in North China, it was at first thought that the hunting of the tarabagan for its valuable skin, which led some of the Chinese to even capture tarabagans, possibly sick with plague, was the origin of the epidemic. This view is no longer held and we now know that the outbreak was independent of any disease in rats, tarabagans or other animals. Strong has shown that the bacillus which was isolated from these cases of pneumonic plague was identical with that isolated from cases of bubonic plague; its virulence was no greater and animals infected cutaneously or subcutaneously died of bubonic plague. Experiments by Teague and Barber, with emulsions of plague bacilli, showed that with a room temperature of 32°C. plague bacilli were quickly destroyed when the air was comparatively dry. In such an atmosphere, saturated with moisture, the viability would be greatly prolonged. In the plague wards in Manchuria the extreme cold which prevailed, together with the saturation of the atmosphere of the unventilated rooms by the moisture of the breath of the patients, made conditions most favorable for the viability of the plague bacillus. They note that in the plains of India, although about 3% of bubonic cases assume a pneumonic type, yet epidemics of plague pneumonia do not occur; this is probably due to the fact that the higher temperatures and open rooms make evaporation occur 30 times more rapidly there than was the case in the plague wards in the bitter cold weather of the Manchurian winter. The possibility of carriers of plague bacilli in those who might go on to convalescence need not be considered, as practically all cases of plague pneumonia die. Other material from the patient than sputum does not seem to be a source of danger in the spread of plague, so that there is no need for the disinfection of urine and feces. There has recently been an outbreak of septicaemic plague in Ceylon in which there was an absence of plague in the rats. The infection was possibly transferred directly through bedbugs or human fleas. As a matter of experience the transference of plague from place to place generally occurs from infected rats or infected fleas which have been transported by ships. A case of bubonic plague in a ward with other patients would not be a source of danger provided there was freedom from fleas and a lack of development of secondary pneumonias. It is very doubtful as to infection ever taking place by way of the alimentary canal, although there is some evidence that rarely the tonsil may be primarily involved. Monkeys are very susceptible to plague and the possibility of an epizootic among them should be thought of during plague epidemics.

Pathology

It is rare that one finds the primary vesicle marking the site of entrance of the plague material. Thus in 13 cases where plague was contracted by direct cutaneous inoculation of those performing autopsies on plague victims only two showed evidences of local reaction as shown by the formation of a primary vesicle.

The chief points noted in a plague autopsy are: (1) The marked involvement of the lymphatic system as shown by intense congestion and haemorrhagic oedema of the lymphatic glands. Not only are the glands tributary to the site of inoculation involved, thus forming the primary bubo, but there is secondarily more or less inflammatory change in all the lymphatic glands of the body. There is also a marked periglandular oedema, with haemorrhagic extravasations of the connective tissue surrounding the primary bubo, this mass being made up of a group of glands matted together by this periglandular exudate.

(2) The destructive effect of a toxic product of the plague bacillus, which may be designated an endotheliolysin, upon the endothelial cell lining of blood vessels as well as lymphatic ones. This causes the extensive blood extravasations so characteristic of plague as shown by petechial spots, not only of the skin but of the serous and mucous membranes as well.

There is a general congestion of all organs of the body.

The meninges of the brain are deeply congested and there may be haemorrhagic extravasations in the brain substance itself. Crowell has reported two cases of plague meningitis in which plague bacilli were found in the ventricular pus. The spleen is generally markedly congested and enlarged to 2 or 3 times its normal size.

There may be haemorrhagic extravasations throughout the spleen pulp. The bacilli are chiefly scattered throughout the venous sinuses.