9 Science and Pract. of Med., Phila., 1868.
Various circumstances render it probable that measles is most readily propagated during the stage of efflorescence; but that it is also highly infectious during the prodromal period is now universally acknowledged.
According to Niemeyer, the probability of infection during the prodromal stage is supported by the wonderful spread of measles through schools; for, while the strictest surveillance is established over children with any suspicious eruptions, and those known to have had the disease are not allowed to return till long past the stage of desquamation, no heed is paid to those exhibiting the premonitory cough and coryza. There is no reason for believing that measles can be propagated during the period of incubation; on the other hand, there is no satisfactory argument for the denial of its infectiousness in the desquamative stage. Although Panum is inclined to doubt its contagiousness at this time—and his observations are worthy of the greatest confidence—other good authorities differ from him materially, and extend the stage of personal infection to a period of from three weeks (Squire) to forty days (Hillairet).
Reasoning from analogy, we would naturally expect that the period of incubation in measles suffered a certain amount of variation; the result of numerous observations confirms this expectation. It is manifestly a difficult matter in densely populated communities to establish with accuracy the date of a given infection, but from a study of more or less carefully noted cases it will be found that the period of incubation may vary from three to thirty days. For the vast majority of cases the average time between the reception of the measles poison and the appearance of the characteristic eruption will be about from thirteen to fourteen days. Panum, under exceptionally favorable surroundings, found it more frequently fourteen than thirteen days. Therefore, deducting the three or four days occupied by the invasion stage, we shall find that the real incubation period is from nine to ten days from the date of exposure. Mayr's two cases of inoculation with nasal mucus showed no departure from this rule, but in the inoculations made by Katona with blood the prodromic symptoms made their appearance in seven days, the cutaneous lesions developing two, and at the most three, days afterward.
Minor epidemics of measles are said to occur every three to five years, more extensive and severe ones every seven or eight years. In the centres of population measles may be said to be endemic; in isolated regions the visitations of the disease may be widely separated. Measles is a less severe disease in warm than in cold climates, and, as a rule, we also find the affection more common and more intense in the fall, winter, and spring than in the summer months.10 Epidemics of measles are usually short, and it is thought that there is a definite relation between the severity of their onset and their duration, this being in general short in proportion as the given epidemic was at first severe (Mayr). Intestinal complications are more frequent in summer, and involvements of the respiratory organs more common in winter. The varying aspects of different epidemics—sthenic, asthenic, etc.—depend on changes in the weather, season of the year, the presence of complications, and other agencies not very clearly understood. Epidemics of whooping cough may precede, accompany, or follow in the wake of measles, and it has therefore been suggested that it stands in some peculiarly close connection with the latter; but, aside from this often-observed coincidence, we are not justified in our present state of knowledge in assuming any definite relation of cause and effect between the two diseases.
10 Aitken (op. cit., p. 295) declares that the mortality returns from England and Wales show that the influence of season is most trifling. Occasionally it has been found that the deaths in summer exceeded those in winter, but we believe that the statement made above is, in the main, correct. For instance, Parson's figures for Berlin for the years 1863-67, inclusive, are: spring, 11.9 per cent.; summer, 13.3; autumn, 33.4; winter, 41.4. Voit's statistics in an average of thirty years at the Children's Clinic at Würzburg establish the same general principles (Thomas).
There would seem to be neither geographical nor racial bar to the propagation of measles, for it has been observed in all countries and among all peoples. As in the case of other zymotic diseases, a tolerance is established for measles in countries where the disease is more or less constantly prevalent; but where the affection becomes epidemic for the first time, or reappears after many years, it rages with terrific violence. This fact was particularly exemplified in the epidemic in the Faroe Islands, and more especially in the recent (1877) visitation of the Fiji Islands, where one-fourth of the population succumbed in a comparatively short time.
It is quite probable, as asserted by Mayr, that children affected with scrofulous complaints, as well as those who are the subjects of diseases of the respiratory organs—pertussis, bronchitis, or tuberculosis—are eminently susceptible of measles; but his statement that sufferers from epilepsy, chorea, and paralysis exhibit an unusual power of resistance cannot be accepted without reservation. Acute diseases often appear to delay the outbreak of measles, so that the latter does not appear till convalescence from the former (Thomas). The development of vaccinia is occasionally interfered with by an attack of rubeola; on the other hand, the two diseases may be seen running their courses together.11 The emphatic statement made by Hebra, that measles is never seen to occupy a patient simultaneously with another acute exanthem, has not been confirmed by other observers. My own experience furnishes several examples. Measles may also occur during the course of other acute or chronic maladies. From a study of the literature of measles complicating pregnancy and parturition Underhill12 finds it to be quite uncommon, due probably to the fact that most adults are insusceptible of further attacks; but when it does occur in pregnancy he regards it as a very serious and frequently fatal complication. Underhill believes measles to be most fatal when it supervenes soon after delivery, while those who are confined during the course of the malady stand a better chance of recovering from it. That puerperal women are not always unfavorably affected by measles is well shown in two remarkable cases reported by Nelson13 of St. Louis and Chantier14 of Geneva, in which the mothers were safely delivered, though suffering from measles contracted at the end of their pregnancies.
11 Hardaway, Essentials of Vaccination, p. 60.
12 Obstet. Jour. Great Britain and Ireland, July, 1880.