Symptoms. These vary greatly with the animal and its environment. Other things being equal it may develop more suddenly and violently in the obese Shorthorn, Angus, Hereford, Ayrshire or Dutch, and less so in the spare Brittany or Jersey. In very hot weather the attack is very sudden and severe. A chill from exposure, an attack of bronchitis or pneumonia, the excitement attendant on parturition, on travelling by rail or driving may precipitate and aggravate the seizure. Under some such conditions there may be sudden and extreme hyperthermia, rapid pulse, oppressed breathing, percussion and auscultation evidence of extensive pulmonary consolidation and death in two or three days, while the body is still plump and fat.
Individual susceptibility appears to have influence, the same stable presenting simultaneously cases of acute and fatal type and others that are slow, and insidiously progressive. In newly invaded countries and in bovine families that have not been exposed to the infection for many generations the tendency is to a higher proportion of severe and fatal cases, while in herds native to districts that have been continuously or frequently exposed, mild cases tend to predominate. The more susceptible strains of blood have been killed out, and the surviving strains show a greater power of resistance.
Apart from the predisposing environment the tendency of lung plague is to set in slowly, insidiously, and for a time almost without outward symptom. For a week, fortnight, month or more there may be a slight cough heard only at rare intervals and neither painful nor specially troublesome. Though sometimes hard, it is more commonly small, weak, short and husky, noticed only when the animal rises, drinks cold water, goes out to the cold air, or eats dusty or fibrous fodder, and is usually attended by arching of the back, extension of the head, opening of the mouth and protrusion of the tongue. For weeks there may be no indication of constitutional disorder, appetite, rumination, milking, and other functions appearing to be normal. Driving the animal may unduly accelerate the breathing, and a careful auscultation may detect an unusually loud blowing sound behind the middle of the shoulder, a mucous râle, or a wheeze. In some cases the disease never advances farther, the trouble subsides and the subject is thereafter immune. Cases of this kind occurring as the first in a herd, explain some instances of what are claimed to be specially prolonged incubations.
In the great majority of cases further symptoms appear, hyperthermia sets in, varying in different animals from 103° to 108° F., the animal becomes dull, depressed, loses in appetite, rumination and milking, omits pandiculation on rising, shows stiffness of the hind limbs, sometimes knuckles forward at the fetlocks, wanders apart from the herd, is found lying apart, shows extra thirst, bloats slightly, and shows some constipation. Pulse and breathing are accelerated, auscultation signs are more marked, and on percussion, areas of flatness may indicate lobular consolidation, usually more extended than in ordinary pneumonia with the same grade of constitutional disturbance. The muzzle becomes hot and dry, the roots of the ears and horns hot, and the hair stands erect along the dorsal aspect or in patches over the body. Pinching of the dorsal spines, sternum or intercostal spaces, may cause marked wincing and a deep groan. The eye is dull, lacking in prominence and clearness, and the lids are often partially closed. At this stage improvement sometimes ensues and after inappetence and suppression of milk for one or two days, the patient may take to feeding and milking as before, and apparently recover, though with a large pulmonary sequestrum.
In the continuous and violent cases all the symptoms are aggravated. Fever may run to its extreme height, there is complete anorexia and suspension of rumination, pulse and breathing are rapid, the victim no longer lies down but stands with feet apart, arms and elbows turned out, head extended nearly on a line with the neck, mouth open, tip of the tongue projecting, and each expiration accompanied by a moan, so loud that it may be heard at a distance (often 50 yards). The breath is heavy, feverish, mawkish. The flanks heave violently, the nostrils are widely dilated and discharge muco-purulent, often bloody liquid, strings of fœtid saliva drivel from the open mouth, there may be tympany or even colic, the eyes are sunken, and the conjunctiva and nasal and buccal mucosæ are of a dull brownish and yellowish red. Emaciation advances at a rapid rate, and the constipation may be superseded by a profuse, fœtid diarrhœa which wears out the animal. The skin is dry, scurfy, withered, pale, and clings firmly to the bones, and the interior of the vulva may show the pallor of anæmia. The spine, sternum and intercostals are more than ever tender, and pressure on the tender areas may detect a lack of movement of the lung which is felt on the healthy parts.
On percussion very extensive areas of consolidation are revealed by the dulness and flatness. If pleuritic effusion exists the resulting flatness is extreme below and up to a given horizontal level, the line of which may, however, be elevated at points by consolidation of the lung at such parts. Auscultation may reveal almost any of the abnormal sounds of pneumonia or pleurisy. Absence of respiratory murmur over large areas, with blowing, heart or abdominal sounds in unwonted situations (where the murmur is absent), and abnormally loud murmur where the lungs are still pervious; crepitation around the margins of the consolidated portions; the creaking sound of stretched false membranes, scarcely distinguishable from crepitation; mucous râles; wheezing sounds of various pitches; exceptionally splashing sounds, and if the animal has just risen, the metallic tinkling sound. In other cases the pleural friction sound is prominent.
Abortions are common in pregnant animals.
Course. This varies greatly. In our northern states in winter, many would seem to recover after a few days illness; in summer, many died in a few days with excessive exudate, dyspnœa, and prostration. Others died early from tympany of the rumen. In others still, profuse, fœtid, colliquative scouring led to an early death. In extreme cases there would be a loss of one-third or one-half the weight in a single week. In the less rapidly fatal cases all the symptoms became aggravated, the emaciation progressed, and a liquid pultaceous condition of the bowels continued for two, three, four, or even six weeks, the animal finally dying in a state of marasmus. In such cases the shrunken, pallid skin and mucosæ bespoke an extreme degree of anæmia.
Recoveries may take place from comparatively advanced stages, but they are liable to be slow and imperfect, the animal remaining unthrifty for a length of time. In some of the more favorable cases, when the recovery is less interrupted or retarded, fattening may take place rapidly, so that it would appear as if the loss of a portion of lung, and the lessened consumption of hydrocarbonaceous matter contributed to the deposition of fat.
In some cases the active morbid processes subside, but are not quite arrested and the malady assumes a chronic form, the exudates become organized, causing a sclerotic or fibroid condition of the lung and especially of the interlobular tissue, which compresses and carnifies the lung tissue, or leads to necrotic changes and the formation of sequestra, or again to liquefaction and the formation of vomicæ. Here the proliferation of the germ may go on, though little new tissue is invaded, and the animal may remain infecting for a long period. The patient remains thin, and weak, is easily blown under exercise, has a small, accelerated pulse, little power of digestion or assimilation, shows frequent tympanies, and may have profuse diuresis or diarrhœa. The cough is frequent, often paroxysmal, easily roused, loose, mucous, painful and may be attended by muco-purulent discharge. Such animals are liable to die in the end in marasmus.