The statement that domestic animals, especially horses, are simultaneously affected with man at the time of large influenza epidemics, and are victims of this human disease, can be traced back for some distance in the annals of epidemics. In England especially, both during the previous century as well as during all the epidemics of the present century, was this point the subject of special attention. In the last pandemics, too, attention was drawn by Finkler and others to the "highly astonishing"and "interesting" coincidence of human influenza and that of horses.
The English collective investigation of 1889-1890 laid such importance upon this point that on their inquiry forms a separate question was given to it: " Have you observed any unusual complaints among domestic animals? in what animals and with what symptoms?"
The answers were very numerous (compare Parsons' reports), and were affirmative in regard to horses, but negative regarding cats, dogs, and canaries and other domestic birds.
Although there is a considerable literature on this subject, it can really be dismissed in the following few words: Human influenza is a disease which is peculiar to the human race and, up to the present time, has not been observed in animals.
This statement applies also to the much discussed influenza of horses, an epizootic disease which is quite common and was not more prevalent at the time of the last influenza epidemic than before. Various contagious diseases of the horse are called "influenza."
1. The catarrhal influenza or "la grippe," a disease of the whole respiratory mucous membrane, occasionally ending in bronchopneumonia.
2. The "erysipelatous influenza" (erysipelas, "horse typhoid," horse scourge), characterized by a marked involvement of the digestive tract, by petechias, erysipelatous swellings, conjunctivitis ("pink eye"), grave nervous symptoms, but comparatively benign. It is alleged that this form is transmissible to dogs and to human beings.
3. The "pectoral influenza," a contagious pleuropneumonia due to a diplococcus, which differs, however, from the Diplococcus pneumoniae of man, and causes, when inoculated into mice, fatal septicemia. Of these forms it is only the first, the catarrhal, which has slight symptomatic resemblance to, but has really no connection with, human influenza, for the equine affection has frequently raged at times when the human race was entirely free from influenza.