The nervous centres exceptionally show meningeal congestions, and exudations, and petechiæ as has been noted of other serosæ.
Lesions of the eye may be confined to the mucosa, or they may extend to the membrane of the aqueous humor, the iris, or even the deeper structures.
Other lesions such as laminitis, bursitis, arthritis, like those attendant on abortion need no special description.
When pulmonary lesions are extensive, the bronchial mucosa is not only softened, opaque and covered with a serous, or muco-purulent discharge, but deeply congested and petechiated. When the chest is opened there is usually an effusion, pale straw, red or bloody and more abundant than in contagious pneumonia. False membranes may exist and show a blackish tint from extravasated blood. The lung fails to collapse and shows on the surface and throughout its substance petechiæ and small black infarctions. In some instances the whole lung is blood gorged, black, almost jelly like, as in acute congestion. In others these are limited infiltrations, concentrated especially in the anterior and lower parts, and almost invariably affecting both right and left lungs. The infiltration is circumscribed in area in comparison with the attendant fever and constitutional disturbance, resembling in this respect, the lesions of contagious pneumonia. It differs however in having a greater tendency to liquid infiltration of the connective tissue, and but for the lack of such tissues in the horse’s lung it would tend to approximate to the lesions of lung plague in cattle. It shows a distinct thickening of the interlobular septa, a tendency to extension to the pleura, and to issue in pleural and subpleural infiltration, and to a more copious effusion into the pleural cavity than in either fibrinous or contagious pneumonia. The lung tissue may be granular and hepatized, but far more frequently it is only splenized, the lung being the seat of a bloody infiltration, yet retaining much of its elasticity and coherence. Portions may be infarcted and black and large areas may have a pale or parboiled appearance, and gangrene is by no means uncommon.
Diagnosis. This is based largely on the suddenness of the attack, its epizoötic character, the numbers attacked in rapid succession, and over a large area as contrasted with contagious pneumonia, the sudden and extreme prostration and weakness, the swelling, watering and discoloration of the eyes, the mildness of the average case, the congestion of the upper air passages, and in the mild cases a comparative immunity of the lungs, the irritability or congestion of the gastro-intestinal mucosa, and the history of the case:—the arrival of the infected horses within a few days from an infected place, or coming through infected channels, or the attack of new arrivals in a previously infected stable, or the known advance of the disease towards the place where the patients are, will usually serve to mark the true nature of the affection.
As a help to correct diagnosis we give below some of the prominent conditions and phenomena of the three forms of lung disease known as fibrinous pneumonia, contagious pneumonia, and the pneumonia of equine influenza:
| Pneumonia: | Pneumonia: | Pneumonia: |
|---|---|---|
| Croupous Fibrinous. | Contagious, of Equine Animals. | of Equine Influenza. |
| From climatic vicissitude, exposure, etc. Attacks exposed animals only, and all at once | Slow succession of cases in the same stable, irrespective of climate or exposure | Rapid succession of cases in the same stable or locality, irrespective of climate or exposure |
| Prevails in inclement seasons, spring, autumn, (Winter) | Any season: worse in inclement season | Any season: worse in inclement season |
| Infection from close proximity, contact, stall, manger, rack, bucket, trough, etc.: Spread slow | Infection spreads widely and rapidly through the air. Spread rapid and often general | |
| Carried in manure, on harness, wagons, clothes, etc. | Carried in manure, on harness, wagons, clothes, etc. | |
| Incubation, 3–10 days | Incubation, 1–2 days | |
| Rigor may be late: after exudation has commenced | Rigor early and well marked, before exudation | Rigor not always well marked |
| Sets in slowly or with acute congestion; appetite and pulse vary with inflammation | Sets in slowly, cough, dulness, impaired appetite, pulse rapid, prostration slight | Profound nervous prostration like opium poisoning, appearing early and suddenly |
| Nasal discharge, watery or rusty, later muco-purulent | Nasal discharge, yellow | Nasal discharge, watery, may become yellow |
| Eye pink, dark red | Eye yellow, rarely swollen or watery | Eyelids bloodshot (pink eye), violet, madder hue, swollen, watery, closed |
| Temperature rises with inflammation | Temperature rises early and extremely, before exudation, 104°–107° | Temperature rises early and extremely, in some hours, 104°–107° |
| Swelling of limbs rare | Limbs swell rarely | Limbs often swell greatly |
| Rheumatoid arthritis may follow | Rheumatoid arthritis may set in; often in advanced stage | |
| Crepitation more constant around the exudation | Crepitation less constant around the exudation | Crepitation may escape recognition |
| Exudation (Hepatization) in lung, lower, posterior, anterior, or central, usually undivided area | Exudate affects lower or anterior border of lung; often in small isolated areas or around bronchia; less blood engorgement than in fibrinous pneumonia | Exudate less granular than in pneumonia; forms in or gravitates to lower part of lung. Congestion passive |
| If pleurisy effusion may be copious | Pleural effusion infrequent, or limited, though pleurisy is common | Pleural effusion frequent and abundant |
| Abscess not infrequent | Abscess rare | Abscess not infrequent |
| Pulmonary gangrene infrequent | Pulmonary gangrene and sequestra frequent | Infarctions, sequestra, and cavities not uncommon |
| Pericarditis infrequent | Pericarditis frequent | Pericarditis frequent |
| Blood, decrease of red globules; encrease of white, hæmatoblasts, fibrine formers and soda salts | Less altered than in either of the other forms. Shows cocco-bacilli in the earlier stages: streptococci later | Blood at first clots firmly, later becomes, thick, black, sizy, hæmatosis tardy. Reaction acid. |
| Coagulation firm, buffy coat | Coagulum loose, buffy coat slight | |
| Hepatic congestion, not hepatitis | Hepatic congestion excessive, hepatitis, necrotic changes | Hepatic congestion excessive, hæmorrhagic; fatty degeneration |
Prognosis. Mortality. As usually met with and under favorable conditions, equine influenza is a mild disease. In 1872 when the disease, sweeping the continent and hardly sparing an equine animal, might be assumed to have reached its maximum, the actual deaths varied from 2 per cent. in country districts to 7 per cent. in large cities. The same holds for Europe where Friedberger and Fröhner gives 4 to 5 per cent. Früs (Denmark) 1 per cent., Aureggio (Italy) 3 per cent., Siedamgrotzky 10 per cent. Much depends on conditions: In horses infected in transit on a long railroad journey it may be 100 per cent. and in fat dealer’s horses, out of condition for active work it usually reaches a high figure. If the patients are kept at work the complications and mortality run very high. The same applies to debilitated animals kept in close, foul, ill-aired stables, or reduced by exhausting or long standing diseases. The very young and the senile suffer more than animals in middle life and vigorous condition. Finally the parts invaded have a controlling effect. The milder cases affecting the upper air passages only, nearly all recover, in those showing abdominal lesions the indications are still favorable; while with double pulmonary and pleural lesions the patient is too often in a hopeless condition. Brain lesions are almost equally redoubtable.
The actual money losses, in an epizoötic of influenza, are more in the way of the loss of work and the complete stagnation of trade in all departments, than in the number of deaths. Yet even in this sense it may prove more ruinous than would a disease having a less universal sway, though far more fatal to the animals attacked.
Treatment. A disease like this, which tends to spontaneous and perfect recovery, needs mainly dietetic and hygienic care in the vast majority of cases. Rest is a prime consideration in a pure genial atmosphere. In the summer season, in the absence of rainstorms, an open air life, at pasture is the best. Shelter must be had in case of storms, and in the cold season a clean, sweet, roomy well-aired loose box, with a sunny exposure, is important. Clothing, bandages, blankets and even hoods may be required if there is any tendency to chill. Food should be laxative, cooling and of easy digestion. Bran mashes, scalded oats or barley, ensilage, roots, potatoes, apples, fresh grass or scalded hay may be suggested. Milk has been strongly advocated, from twelve to fifteen quarts a day, and linseed tea as being especially adapted to the irritable stomach and bowels. Food should be given often, in small quantities so as not to destroy the appetite.