The latest invasion was discovered in the vicinity of Niles, Mich., in October, 1914, after it had evidently been under way since August of the same year. This is the most serious and extensive outbreak ever known in this country. The disease extended to 22 States and the District of Columbia, at places ranging from the Atlantic to the Pacific coasts. The work of eradication was not completed for more than a year. The affected States were Connecticut, Delaware, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland, Massachusetts, Michigan, Minnesota, Montana, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Virginia, Washington, West Virginia, and Wisconsin. Illinois had the largest infected area and the largest number of animals affected. The Union Stock Yards at Chicago became infected and were a source of dissemination of the contagion north, east, south, and west. These and other yards found infected were closed temporarily and disinfected.
The first Federal quarantine was issued October 19, 1914. A campaign to check the spread of the disease and to stamp it out was immediately begun by the United States Department of Agriculture in cooperation with the State authorities. Quarantines against the movement of animals and certain materials from the infected areas were declared, shipments were traced, rumors investigated, and thorough inspections made in an effort to discover all infected stock. As measures of eradication, diseased herds were slaughtered and buried and the premises disinfected. The owners of live stock and other property destroyed on account of the disease were reimbursed to the extent of the appraised value, half of which is paid by the Federal Government and half by the State. There were slaughtered 172,720 animals (76,575 cattle, 86,492 swine, 9,511 sheep, 133 goats, and 9 deer), in 3,482 herds. The total appraised value of these animals was more than $5,800,000. The expense to the Federal Government of eradicating this outbreak was about $4,540,000.
Symptoms.—In three to six days, or even longer, after the exposure of the animal to the infection the disease makes its appearance. It is usually first indicated by the animal suffering from a chill, quickly followed by an invasion of fever, which may cause the temperature to rise as high as 106° F. These symptoms are not always present, or may be in so slight a form as to escape notice. Following this in one or two days it will be noticed that small vesicles or blisters about the size of hempseeds or peas are making their appearance upon the mucous membranes of the mouth at the border and upper surface of the tongue near the tip, the inside of the cheeks, on the gums and the inner surface of the lips, or on the margin of the dental pad. These little blisters contain a yellowish, watery fluid and gradually become more extensive as the disease advances. Soon after the eruptions have appeared in the mouth of the animal considerable swelling, redness, and tenderness will be noticed about the feet, at the coronet, and between the digits of each foot. A day or two later eruptions similar to those within the mouth make their appearance upon these swollen regions of the foot, and at this stage it is usual to find that like lesions have made their appearance upon the perineum of the victim. In the case of milk cows the udder, and more particularly the teats, show the same vesicular eruption, but the latter as the result of milking soon become covered with reddened spots deprived of the superficial layer of skin and may develop deep, obstinate fissures.
As soon as the disease has become well established the patient evinces pain when attempting to eat; in fact, the appetite is often so seriously affected that all feed is refused, and the animal uneasily opens and shuts its mouth with a characteristic smacking sound, while strings of cohesive, ropy saliva hang suspended from the lips. With the advance of the disease the vesicles widen and extend until they may reach a diameter ranging from that of a dime to that of a silver dollar. These rupture soon after their appearance, sometimes on the first day, more rarely on the second or third day. After they have ruptured, the grayish-white membrane forming the blister may remain attached for a day or more, or disappear speedily and leave deeply reddened, sensitive spots or erosions, both within the mouth and upon the coronet and between the claws of the feet. Similar erosions, which quickly form scabs, as a rule, may be noticed in cases in which the teats of milk cows have become affected, and instances are reported in which sloughing of the tegument immediately around the lesions upon the udder has occurred. Owing to the tough, fibrous nature of the bovine skin, it is exceedingly rare for sloughing to occur upon any part of the body other than those mentioned.
The attack upon the feet of an animal is frequently manifested in all four feet at once, but one or more of the feet may entirely escape and remain unaffected throughout the course of the disease. The ulceration of the interdigital tissue may extend to the ligaments of the fetlock or produce disease of the joint or bone. As the feet become sensitive and sore the animal persistently lies down, and it has been found that bedsores develop with amazing rapidity in all such cases and wholly baffle all attempts at treatment until after the patient has regained its feet.
The disease may attack some of the internal organs before it appears upon any of the external tissues. These cases are very liable to prove quickly fatal. The animal dies from paralysis of the heart, due to the formation of poisonous principles within the system; it may suffocate by reason of the action of these same poisons upon the tissues of the lungs, or it may choke to death as a result of paralysis of the throat.
In cases of serious affection of the udder the erosions will often be found within the passages of the teats, resulting in a "caked" udder, and the same toxic poisoning which is the cause of death in the apoplectiform types just mentioned may arise from this source. In any event the milk from such cases is dangerous for use, causing fatal diarrhea in sucking calves or young pigs and serious illness in human consumers. The milk obtained from cows suffering with foot-and-mouth disease is not readily converted into either butter or cheese, but remains thick, slimy, and inert in spite of churning and attempts at curdling. Pregnant animals may abort. In pigs, sheep, and goats the lesions in the foot are most common, but both forms may be observed or only the mouth lesions.
When the disease has become fully established it will be found that the duration of the attack will vary greatly with different animals. From 10 to 20 days are usually required for the recovery of the normal appetite and spirits in mild outbreaks, while the return to a full flow of milk, in the case of milk cows, seldom occurs before the arrival of the following season.
In the malignant type of the disease it requires from three months to a year for an animal to recover. The mortality, as already stated, is usually low. The disease is more fatal in young animals that have been fed on infected milk, and produces death in from 60 to 80 per cent of these cases as a result of gastroenteritis. In the 1914 outbreak numerous new centers of infection started among hogs and calves which were fed on unpasteurized, infected milk from creameries.