Part 132

Catarrhal affections have often prevailed among the domestic animals when influenza has been epidemic. Horses, dogs, and cats are subject to these disorders; neat cattle, goats, and sheep have been less commonly affected; chickens and pheasants have suffered, and it is stated by some of the older writers that birds, and particularly the sparrow, have deserted localities in which influenza was prevailing, and that migratory birds have taken flight earlier than usual.

These epizoötics have sometimes preceded the appearance of influenza among men by a period of some weeks or days; in other instances they have appeared at the same time; and in a widespread outbreak among horses in the United States in 1872, in which the symptoms and morbid anatomy, accurately observed, were undoubtedly those of influenza, the disease did not affect man except to a very limited extent. A want of fulness of description, and the inaccuracy of diagnosis too common in the consideration of the general diseases of the lower animals, leave the precise nature of most of the epizoötics described by the earlier writers doubtful.

An extensive influenza of moderate intensity prevailed as an epizoötic, chiefly affecting horses, during the latter part of the summer and the autumn of 1880 in Canada and the United States east of the Mississippi River. Dogs were also affected, but less generally, and human beings to a still slighter extent. In several localities where this invasion was observed by the writer the horses were first affected, the dogs next, and after the lapse of some weeks, as the animals were recovering, the disease became epidemic; but those persons who took care of horses and were much in contact with them neither suffered earlier nor more severely than others not so exposed.

ETIOLOGY.--1. Predisposing Influences.--There are no {860} well-established facts pointing to the existence of individual peculiarities that can be regarded as predisposing influences. When the disease appears a large proportion of the population is attacked without distinction of age, sex, social condition, or occupation. Previous illness, whether acute or chronic, local or constitutional, affords no protection. Aged and infirm persons and those of nervous temperament are peculiarly liable to attack, but the robust possess no immunity. All races and dwellers in every climate are the victims of influenza. In a community invaded by the disease females are apt to be the first attacked, adult males next, and children last. It has been observed that in some epidemics children are but little liable to contract the disease.

An attack confers no exemption from the disease in another epidemic, and independently of relapses, which are not infrequent, persons have been known to experience a second attack during the prevalence of the same epidemic.

Persons dwelling in overcrowded and ill-ventilated habitations and in low, damp and unhealthy situations have, in certain epidemics, especially suffered, and the increase of deaths by influenza is proportionately much greater in districts in which there is ordinarily a high mortality than in healthier places.

Influenza appears at all seasons of the year and affects the inhabitants of every latitude. It has no connection with known atmospheric conditions. Many of the earlier writers sought to establish a relation between low temperatures and sudden variations of temperature and influenza, and by reason of the confusion among the people between these diseases and common "colds" there has always existed an opinion that such a relation obtains. There is, however, no evidence to sustain this view; neither low temperature nor abrupt changes give rise to the affection. It has prevailed in hot and dry seasons, in the West Indies, on the coast of Java, in India, in Egypt, at the Cape of Good Hope, on the Riviera in summer.

The condition of the air as regards moisture, or dryness, does not influence the spread of the disease. It has occurred at sea, on low sea-coasts, and in the dryest climates, as, for example, in Upper Egypt.

Its spread is not much influenced by local winds. It does not travel with the same velocity, and even sometimes advances against them. In several well-authenticated instances a dense and foul fog has preceded and attended the local outbreak of epidemics. The much greater number of epidemics that have occurred altogether without such manifestations make it in a high degree probable that this has been a coincidence. Ozone in large quantities artificially produced may give rise to the symptoms of ordinary catarrh, but it is not a cause of influenza. The disease is not in any way connected with the condition of the soil, elevation, volcanic eruption, or any other local cause. The history of every epidemic may be adduced in proof of this statement.

Before taking up the consideration of the exciting causes of influenza, it is important to review the known facts concerning the march of epidemics and the spread of the disease in affected localities. It has prevailed with greater or less frequency in almost every region of the globe. Epidemics recur at irregular periods. It was at one time supposed that the course of the disease was cyclical, with a return at intervals of about one hundred years. This view was long ago proved to be unfounded. About every {861} twenty-five or thirty-five years great epidemics have swept over vast areas of the globe, and influenza may be said to be, at such times, pandemic. Less-widely extended epidemics have taken place with greater or less frequency in the intervals between the great outbreaks. But it is not possible to establish anything like a regular periodicity in the returns of the disease.

It has been supposed in some instances to prevail within restricted localities, as, for example, in a single city. Such local epidemics are without doubt due to local causes, and are of the nature of simple ordinary catarrhal fever, rather than true influenza.

The epidemics have extended over great areas, usually in a direction from the east or north-east toward the west and south. At other times they take the opposite course, and in some years they have appeared to radiate in various directions from several centres. It is in consequence of these facts that two views have arisen concerning the origin of the affection. The first of these is, that each epidemic starts out from some single unknown source, and spreads thence from point to point, invading more distant localities successfully as it advances, until at length it dies out in regions remote from the starting-point. This opinion is in accord with the popular belief. Thus, the Italians have called it the German disease; the Germans, the Russian pest; the Russians, the Chinese catarrh. The geographical relation of these nations indicates the usual track of the great epidemics, as shown in the foregoing historical sketch. The other opinion is, that it arises not from some single particular place, but that it may start anywhere, and that widespread epidemics are due to the successive outbreaks of the disease at many distinct points of origin.

The evidence that the great epidemics of influenza are due to some general and pandemic influence is conclusive. The point of origin of the great epidemics has not yet been indicated with precision, and must remain beyond conjecture until further facts bearing upon the question of their source are brought to light. When it has prevailed over a large portion of the earth's surface its progress from place to place has usually been rapid. In this respect, however, the epidemics show a great diversity. It sometimes travels exceedingly slowly. It is said to have overrun Europe in six weeks, and it has again taken six months to do so. It sometimes attacks places widely remote from each other within short intervals of time, and it has appeared at the same time in different quarters of the globe. It does not follow the great lines of travel and commercial intercourse.

When influenza enters a city it continues to prevail, as a rule, from four weeks to two months, but exceptionally it remains a longer time; for example, the epidemic of 1831 was prevalent in Paris for the greater part of the year. It in all instances finally disappears, and sporadic cases do not occur in the intervals between the epidemics.

In rare instances the epidemics are heralded by scattered cases. But as a rule this disease attacks simultaneously great numbers of the inhabitants of affected districts, so that, when the epidemic is severe, the sick are in a short time to be counted by thousands and business is paralyzed as by a blow. Epidemics rapidly reach their height, and subside almost as suddenly as they began. In a large city the disease frequently, perhaps always, makes its appearance nearly at the same time in several {862} different localities, affecting certain streets and quarters solely or more generally than others for a time, and spreading thus from several centres through the entire community. Large towns and cities are generally affected earlier than the villages around them, and the latter, though closely adjacent, sometimes escape for weeks. The crews of ships upon the high seas, not sailing from an infected port, are said to have suffered from the seizure, and epidemics have many times crossed the Atlantic from the Old World to the New, and more than once in the opposite direction.

2. The Exciting Cause.--Large as has been the place in medical literature occupied by the histories of epidemics of influenza, the nature of the "epidemic influence" which gives rise to the disease is still unknown.

The question of the contagiousness of influenza is one of grave interest, and has been the subject of much controversy. The great rapidity of the spread of epidemics, the vast area they overrun, the fact that they do not follow the lines of human intercourse, the suddenness with which great numbers of the inhabitants of an invaded district or city are seized, the fact that the most complete seclusion from intercourse with affected persons, or even the shutting up of houses, affords in most instances no protection whatever,--all go to show that the disease spreads, in the main, independently of direct contact. This opinion has been almost universally entertained. There is evidence, however, to show that the disease is to some extent contagious; and so convincing have the facts bearing upon this point appeared to some that they have believed it to be propagated entirely by human intercourse. Haygarth declares, as the result of his observations during the epidemics of 1775 and 1782, that the influenza spreads "by the contagion of patients in the distemper;" and Falconer, writing of the epidemic of 1803, says, "I have no doubt that it is contagious in the strictest sense of the word." Watson regards the instances in which the complaint has first broken out in those particular houses of a town at which travellers have arrived from infected places as too numerous to be attributed to mere chance. Very often those dwelling near the invalids are attacked next in the order of time, and when the disease affects a household all do not usually manifest the symptoms at the same time, but one member after another is stricken down with it.

In a few rare cases the isolation or seclusion of a community has appeared to give protection, as in cloisters, prisons, garrisons, and the like; at all events, there are instances on record where segregated communities of this kind have escaped attack.

The following observation, conducted under unusual circumstances, establishes the fact that influenza may be brought from an infected city in such a way as to give rise to a localized outbreak in a remote community. Drs. Guitéras and White narrate that, influenza prevailing in Europe, and particularly in Paris and London, an American gentleman in bad health contracted the disease in London, improved, suffered a relapse {863} shortly afterward in Paris, and died there at the end of December, 1879. His body was embalmed and sent home. Following the exposure of the remains of this person to the view of his family in Philadelphia there was an outbreak of influenza with characteristic symptoms, which affected, in the first place, members of that family; afterward, friends living in close intercourse with them; next, the medical attendant of some of them; and finally, the housekeeper and a patient or two of one of the physicians who wrote the paper, the whole number affected in Philadelphia being eighteen at the time of the publication of the account. Subsequently two or three other cases were developed, but the disease did not extend beyond the immediate circle of those in direct communication with the invalids.

It was at one time thought that influenza developed at once, without a period of incubation, persons in perfect health being struck down with it as by lightning-stroke. It is, however, now known that a period of incubation, varying from a few hours to several days, and usually without subjective symptoms, exists. Many instances are recorded in which persons coming into an infected city have remained well for one, two, or three days, but have eventually shared the sufferings of those into whose midst they have come. There are cases also in which the period of incubation could not have been less than two or three weeks.

There is no sufficient evidence of a causal relation between influenza and any other epidemic disease. The statement that other prevalent diseases abate in frequency and intensity upon its outbreak is not sustained by well-observed facts. Graves holds that those suffering with acute diseases are less liable during the febrile stage, but that they are attacked as convalescence sets in.

The facts in reference to the spread of epidemics of influenza and the course of the disease in infected localities are comprehensible upon no other theory than that of a specific infecting principle as its exciting cause. What this principle may be is not yet known; where it originates is equally unknown; and our knowledge of the influences that from time to time call it into activity and send it forth in definite directions over the earth is no less negative.

So general a disease can only be disseminated by the most general medium, the atmosphere, and its exciting cause must be capable of reproducing itself in that medium, otherwise it would be lost by dispersion in traversing distances measured by the boundaries of continents and oceans. The rapid diffusion of influenza, sweeping over continents in a few weeks at one time, its slow migration, creeping about a city and its environs for months, at another, are to be most easily explained upon the theory of a living miasm capable of being transmitted by the air, and possessing at the same time an independent existence. Such an entity would find certain localities more favorable to its growth, reproduction, and prolonged existence than others. From this point of view influenza is a miasmatic disease. The infecting principle of this disease is also, to a slight extent, capable of being reproduced in or about the human body and transmitted by personal intercourse, as well as conveyed from place to place by the persons or clothing of those affected or those travelling from localities in which the disease prevails. We are thus led to the conclusion that it is also contagious, though feebly so.

{864} CLINICAL HISTORY.--Influenza, in individual cases, presents the greatest variation as regards intensity, from the most trifling indisposition to an illness of the gravest kind, terminating in death. These variations are dependent upon--1st, the previous health of the individual, his age, and the power of resisting depressing influences which he possesses; 2d, the energy and the amount of the specific cause of the disease to which he has been exposed--in other words, the dose of the fever-producing poison; and 3d, the character of the prevailing epidemic.

It is important to observe that cases of very great severity are occasionally encountered during the prevalence of mild epidemics. In every epidemic, on the contrary, a considerable part of the community suffers from influenza in the mildest, or what has been called the rudimentary, form. This is characterized by general malaise, an easily oncoming weariness upon bodily and mental effort, a disinclination for business, some inability to fix the attention, and slight mental confusion; to these nervous disturbances are added catarrhal symptoms, as coryza, sore throat, a tickling cough, and the like; but the indisposition is subfebrile--it does not amount to a fully-developed fever. Other cases present the symptoms of an ordinary attack of acute coryza, laryngitis, bronchitis, pharyngitis, with unusual constitutional disturbance, distressing headache, and pains in the back and limbs. The fever in this class of cases does not range high, yet the patients are ill enough to betake themselves to bed.

In severe cases the onset is usually abrupt. The attack begins with shivering or a chill, or with fits of chilliness alternating with heat. Fever is rapidly established. It is usually moderate; sometimes it reaches a high grade. It shows a tendency to morning remissions. Sensations of chilliness occur; they are called forth by slight changes in the external temperature. They are often followed by flushes of heat, and are, in many cases, attended by annoying sweats. The febrile outbreak is sometimes preceded by intense frontal headache, with pain in the orbits and at the root of the nose. In other cases these pains quickly follow the chill. Sneezing, redness of the eyes and edges of the nostrils, a more or less abundant thin discharge from the nose, and lachrymation, now occur. In some instances there is bleeding from the nose. The throat becomes sore; there is a tickling sensation in the upper air-passages; a dry cough sets in, attended by more or less hoarseness and shortness of breath. The cough is paroxysmal, hard, distressing. It sometimes causes vomiting, like that which occurs in the paroxysms of whooping cough. Chest-pains, stitches in the side, frequent sneezing, loss of the sense of smell and of taste, attend the development of the general catarrhal manifestations.

The fever is attended by great depression, pains in the limbs, loss of appetite, thirst, constipation, and diminished secretion of urine. The pulse is full, but, as a rule, only moderately increased in frequency. There is in many cases slight, or even decided, blueness of the lips and finger-tips. The patient is distressed by restlessness and want of sleep. At the end of four or five days the febrile symptoms decline, at times gradually, oftener rapidly, with copious sweats or spontaneous flux from the bowels. The fever continues, however, when severe complications have taken place, ten or twelve days. The defervescence is marked by {865} an increased flow of sedimentary urine and considerable amelioration of the subjective symptoms. The catarrhal symptoms outlast the fever two or three days, but cough and expectoration may not disappear for some time.

With these symptoms are associated the evidences of functional disturbance of the nervous system. There is remarkable nervous depression; loss of strength and lowness of spirits are combined with mental weakness, or even stupor and delirium. In some cases slight convulsions take place. Cutaneous hyperæsthesia occasionally occurs, and areas of burning pain in the skin are to be met with. Neuralgia, muscle-pain, and aching referred to the bones are very common and often severe.