It may be accepted as demonstrated that the common diphtheria of birds is essentially distinct from the genuine diphtheria of man, and that when such diphtheria of the bird is conveyed to man as has been often alleged (Richter, Gips, Bonig, Gerhart, etc.), it is one of the forms of pseudo diphtheria that is produced, and not that which is caused by the Klebs-Löffler bacillus. Dr. V. A. Moore, who has cultivated specimens of the bacillus diphtheriæ Columbarum obtained from Germany, considers the germ as belonging to the group of the bacillus coli communis, and as not the cause of the chicken diphtheria in America. Further investigation must settle whether the bacillus diphtheriæ Columbarum is the one cause of this affection in Europe, and what is the microbian cause or causes of the disease in America.
Incubation. This is very variable. False membranes may form in twenty-four hours in some cases; in other cases they may be delayed from four to fourteen days (Colin, Babes, Puscarin, Marinescu).
Symptoms. There is dullness, prostration, sunken head, ruffled feathers, altered hoarse voice, drooping wings, wheezing breathing, difficult deglutition, sneezing, and patches of dark red congestion in the fauces covered with a thin film, at first translucent, but soon becoming dense, adherent, opaque, whitish or yellowish. As it becomes older this deposit becomes granular, wrinkled, dry and friable. It is more adherent in chickens than in pigeons and causes bleeding when detached. Necrotic changes may take place in the mucosa leading to considerable loss of tissue, and even to perforations of the soft palate, pharynx or œsophagus. It may remain circumscribed by the region of the mouth and end in an early recovery, or it may extend to the organs of the chest and abdomen, or the germs may proliferate largely in the blood and induce fatal results. On the other hand it may become subacute or even chronic, and, as already noted in the case of the parent pigeons, it may persist as an infecting disease without materially injuring the general health of a comparatively immune animal.
The affected nasal passages become filled by frothy liquid and blocked by false membranes, so that the bird is driven to breath through the open mouth. The skin around the nares, and eyelids and the cavity beneath the eye may be covered with the false membrane, by the increase of this product the bones may be driven out of place, so that the palatines press downward, the eyeball is pressed outward and the root of the beak may seem swollen. The false membranes that form on the skin or reach the surface are soft, creamy, cheesy, or dry, granular and friable.
When the eye is specially affected there are swelling of the lids, profuse lachrymation, closure of the lids by adhesion, and formation around their borders or on their inner surface and on the membrana nictitans of false membranes which press the lids outward more or less unevenly, and may be easily recognized when the lid is everted. The cornea and even the interior of the eye may suffer, leading to perforation, internal tension, and in some cases atrophy, with permanent blindness.
The tongue may suffer on the tip as in pip, or on its dorsum, from which the disease extends to the larynx, trachea and even the air sacks, which become filled with false membranes, that are coughed up, and decomposing in the mouth, add to the infection and fœtor. Dyspnœa and cyanosis of comb and wattles are marked features.
The extension may take place downward along the alimentary track, the false membranes forming on the gullet or crop and interfering with swallowing or digestion, or on the intestine and determining a fœtid, often greenish or bloody diarrhœa with indications of false membranes. Vomiting may be a marked symptom.
The skin is usually attacked secondarily around the margin of the beak, the eyelids, the nares, the ears, the comb, the wattles, the anus, but it may develop at any point where the infecting material has touched an abraded surface.
Trinchera found that in acute cases the acme was reached in fifteen days after which improvement might be looked for. A chronic form affecting the gullet might however persist indefinitely in pigeons without proving incompatible with good health.
Paralysis of the wings or limbs may remain after the healing of the local lesions.