Influenza

by Warren T. Vaughan

Abbott concluded that during the great horse epidemic of 1872 which bore a strong resemblance to influenza the disease was not unusually prevalent among men except in a few limited localities; while other infectious diseases, such as measles, small pox, scarlet fever and cholera infantum were unusually prevalent in that year.

Soper writes that, “Economically, influenza is the most important disease of horses in temperate climates. The mortality among remounts has been many times greater from influenza than from all other diseases put together. It is estimated that over 25,000 horses purchased by the British Government in America and Canada, during two years of the war, died in those countries while awaiting shipment to Europe. In a circular issued January 12, 1918, by the Surgeon General of the United States Army to the veterinarians of remount depots, it was stated that the losses from influenza among American army horses amounted to over $100,000 a week. The disease spoken of as influenza in the horse has many other names. It is commonly called pink-eye, shipping fever, stable pneumonia and bronchitis. By some influenza is not believed to be a single disease, but a group of diseases. By others it is considered to be a definite entity, varying in its symptom complex at different times and with various horses. Infectious laryngitis and infectious pharyngitis seem to be independent diseases. Two forms of influenza are generally distinguished: catarrhal and pectoral.”

Even after the last pandemic of influenza the question has again arisen as to the identity of the disease among animals. Orticoni and his co-workers observe that there was an extensive epizootic among horses at the time of the 1918 epidemic in the area which they had under observation. There have been other similar reports. The popular press, during the height of the 1918 spread, reported that there was a highly fatal influenza infesting the monkeys of South Africa and that the baboons were dying in scores, their dead bodies being found on the roadsides and in the vicinity of homesteads. Another report tells of the influenza decimating the big game in Canada, and yet another tells of the havoc wrought among the buffalos and other animals in the United States National Parks. These reports have not been corroborated by scientific observations.

Soper has analyzed the subject of so-called influenza among horses. He finds that the disease is quite generally distributed, that it has many points of close similarity to the influenza of man, but that it is a distinct and separate disease. The two diseases are not identical and neither can be transmuted into the other.

“Briefly, the symptoms, as stated in a recent publication of the United States Department of Agriculture, are sudden onset; fever in some cases preceded by chill; great physical prostration and depression of nervous force; sometimes injected mucous membranes, especially those of the eye, and loss of appetite. In uncomplicated cases the fever abates after about a week and there is a general restoration to health. Pneumonia is one of the frequent complications and is always serious. The death rate varies between two and seven per cent. The most usual form is the catarrhal type. The attack may last only two or three days; in other cases the course may extend to two weeks, in which event it takes the animal a long time to get well. Horses which have passed through this form of disease may be considered to have recovered two weeks after the disappearance of the fever.

“The diagnosis of influenza depends as much upon its epidemiological aspects as upon the symptoms. Law bases it on the suddenness of the attack, its epizootic character, the numbers attacked in rapid succession and over a large area as compared with ordinary contagious pneumonia, the sudden and extreme prostration, the mildness of the average case, the congestion of the upper air passages, the watering and discoloration of the eyes, and the history of the case. Points of interest in the history are the arrival of the infected horses within a few days from an infected place, or coming through such a place, or the attacking of new arrivals in a previously infected stable, or the known advance of the disease toward the place where the patients are located.”

Soper found that the progress of the epidemic of 1872–73 among the horses in this country was as generalized, but much slower than the progress of the recent pandemic among human beings, the rapidity of progress corresponding with the rapidity of the transport of the horses at that time. Just as we have found in the case of influenza so also at that time the spread only followed lines of communication and actual contact between horses.

It is highly interesting that attempts to transfer the disease from horse to horse experimentally met with the same degree of failure that was experienced in similar attempts to transfer influenza experimentally from man to man. In fact Lieut. Col. Watkins Pitchford of the British Army Veterinary Corps in a report in July, 1917, stated that it was impossible to produce infection experimentally. Nose bags were kept upon horses with profuse nasal discharges and high temperature, and these nose bags were then used to contain the food of other horses without infection taking place.

There are several other points of resemblance between horse influenza and human influenza. The mortality from influenza among horses is under ordinary circumstances between two and seven per cent., and is highest in horses worn out by fatigue after a long railroad journey, among fat horses out of condition, and among horses which have been driven after they were sick. The death rate in the simple catarrhal form of influenza rarely exceeds one-half of one per cent., while in the pectoral form it is never less than four or five per cent., and may reach 16 per cent. The only measure of prevention which has been found wholly satisfactory is strict isolation. Usually influenza occurs in horses who have newly arrived in a stable from elsewhere. Practically all the newly arrived horses and country horses are almost alone susceptible. Soper, who has studied the records, such as they are, in the army veterinary corps, and also the records from the Bureau of Animal Industry, concludes that they show nothing to indicate that any general epizootic of influenza occurred among horses during the year 1918 corresponding to, or connectable with the pandemic of influenza among human beings. There was influenza among the horses, but he does not think it was extensive enough to be allied with influenza among human beings. He concludes that there are two types of influenza among horses, first a mild form which nearly all horses get when transferred to a contaminated stable, after which there develops immunity, and the second type, a true epizootic which may sweep the entire country, attacking practically every horse. A most suggestive result of his study lies in the fact that predisposing influences play a most important part in the production of serious influenza among horses.

Aside from noting a certain similarity between the epizootic of so-called influenza in horses and influenza as we know it in man, we cannot acquire much additional information concerning influenza itself from a consideration of this subject. The important conclusion is that in several of the most important epidemiologic features the two diseases are similar and that the study of human influenza may be furthered by critical studies of influenza in horses. We shall attempt to demonstrate that influenza in a similar manner is not unlike other epidemic diseases.