This disease has become increasingly prevalent in the last ten years after a period of only slight prevalence for about twenty-five years. I have shown that epidemics of diphtheria occur during a succession of years of protracted drought. Diphtheria is more common in girls than boys, possibly owing to their more affectionate habits; and occurs chiefly under ten years of age, the fifth year of life being that of greatest prevalence. Unlike the acute infections hitherto considered, the bacillus causing diphtheria has been identified and cultivated in the laboratory (called the Klebs-Loeffler bacillus or diphtheria bacillus). Direct infection from patient to patient is probably more common than indirect infection by clothes, etc., though the latter occurs. The infection may hang persistently about a house and its belongings, in the absence of complete purification. When diphtheria is prevalent slighter sore throats occur, sometimes before true diphtheria is detected. This led to the theory that under conditions of overcrowding, especially in schools, there occurred in the micro-organisms causing these sore-throats “the progressive development of the property of infectiveness.” Possibly these were slight non-typical attacks of diphtheria. Such attacks occur also during epidemics of diphtheria, and unless specimens (“throat swabs”) from these sore-throats are examined bacteriologically, are likely to spread diphtheria by attendance at school, etc. Aggregation in schools seems to intensify the contagium of diphtheria. The practices of kissing, of transferring sweetmeats from mouth to mouth, of cleaning slates with saliva, are common means of spreading it. Effluvia from foul drains and sewers have been commonly held to cause diphtheria. If they aid in producing it, it is rather by lowering the vitality and causing ordinary sore throat. Sore throats and catarrhs make the subjects of them much more prone to diphtheria (see also page [117]). Damp houses have been stated to favour the development of diphtheria. Probably they do so in the same way as effluvia from drains. It is likely that the diphtheria bacillus has a saprophytic stage of existence in the soil, as indicated by its excessive prevalence in dry warm years. Besides direct infection from patient to patient and indirect infection by fomites (i.e. in clothing, etc.), milk occasionally causes epidemics of diphtheria. The infection has been usually caused by the handling of the milk by an infectious person. In certain outbreaks no human contamination of the milk could be discovered; and it has been surmised that an analogous disease in the cow may cause diphtheria in man. This is still a moot point. Fowls, cats, and other animals are the occasional victims of diphtheria, and may convey it to man.
The duration of infection in diphtheria is usually less than six weeks; but it may be much more protracted. In some instances long after all naked-eye evidences of diphtheria has disappeared, bacteriological examination may still show the presence of the diphtheria bacillus for two or three months; in rare cases even longer. The protection afforded by one attack of diphtheria against a second is slight and only temporary. The means of prevention are isolation and disinfection as for other infectious diseases. Two additional means are available (a) bacteriological diagnosis; (b) prophylactic injection of antitoxic serum. Many sore throats without membrane on the throat are due to the diphtheria bacillus. Even if membrane be present there may be doubt as to whether the case is true diphtheria. Hence the importance of bacteriological examination.
The patient’s throat is swabbed with cotton-wool which has been rolled around a metal probe and sterilised. The wool is then smeared over sterilised and solified blood serum in a test tube. It is then incubated over night at a temperature of 37° C. Next morning the minute growth that has occurred on the surface of the blood serum is spread on a microscopic cover-glass, appropriately stained, and examined microscopically. If diphtheria bacilli are present, they can be recognised by their form and arrangement. The same means enable us to ascertain when a patient has recovered, whether he is fit to be released from isolation.
Antitoxic serum has been found to be a valuable prophylactic and curative agent.
The serum is obtained as follows: Sterilised broth is inoculated with virulent diphtheria bacilli, and grown at 37° C. for a week or more. The broth is then filtered through a Pasteur filter. The filtrate contains toxine free from bacilli. Some of this toxine is injected under the skin of a horse. A few days later the dose is repeated, gradually increasing amounts being injected until injection of further quantities of the toxine is found experimentally not to increase the antitoxic value of the horse’s blood serum. Next the horse is bled. Its serum is found to have acquired the power of protecting a guinea-pig against doses of the toxine of diphtheria which would otherwise be fatal. Ten times the quantity of the horse’s serum which will protect a guinea-pig (of 250 grammes weight) against ten times the minimum fatal dose of the toxine is called an antitoxic unit.
The treatment of diphtheria in man by the antitoxic serum thus obtained has proved to be remarkably successful. Furthermore, if a susceptible person who has been exposed to the infection of diphtheria, is injected with a small dose of antitoxic serum, he becomes temporarily immune, and does not fall a victim to diphtheria. This is a most important point especially for young children, who may already be incubating a disease which but for this prophylactic injection might occur and prove fatal.
TYPHUS FEVER.
This disease was formerly known as spotted or jail-fever, and for many ages has been the scourge of prisons and armies, and all collections of people living in overcrowded and insanitary districts. The history of typhus is the history of human misery. It is essentially associated with filth, overcrowding, and destitution; but when once established by these conditions, it can be carried by infection to others who live amidst healthy surroundings. It generally occurs in winter, when overcrowding is greatest. With free ventilation, the disease cannot be carried more than a few feet. It can be transmitted by clothing. The micro-organism causing it has not been discovered. With the clearance of the rookeries of our great towns, it is rapidly decreasing, and appears likely to become extinct. The means of prevention, in addition to the abatement of nuisances, including overcrowding, are isolation and disinfection (pages 319 and 325).
RELAPSING FEVER.
This disease was formerly common in this country, but except in some parts of Ireland has entirely died out. It is caused by a micro-organism (Spirillum Obermeieri) which can be detected in the blood. Inoculation of this will produce the disease in man or in monkeys.