Mallein must be used under precautions like tuberculin. It must be obtained freshly prepared from a reputable maker. If preserved for months its force may be largely lost. The animal to be tested should be in his customary environment, and not just arrived from a railroad journey nor other cause of excitement. He must not be fevered as any rise of temperature is then equivocal, and a fall of temperature, which sometimes occurs in the febrile system under mallein, is no sure evidence of glanders. Reaction sometimes fails in advanced cases of glanders, but in such a case other symptoms are usually diagnostic so that mallein is superfluous and should not be misleading. The greatest care should be taken to prevent infection from the syringe, nozzle, skin, hands, etc., as other infections may give rise to local swelling and hyperthermia (see tuberculin test). If a first test leaves the matter in doubt, the animal should be secluded and tested again in a month (some prefer 3 months).
Pathological Anatomy. The colonization of the bacillus mallei in a tissue usually determines a concentration and multiplication of leucocytes, so as to form rounded nests of small lymphoid cells in a scanty fibrous network. These may be miliary or by aggregation they form masses the size of a pea or larger, which bear a close resemblance to the neoplasms of tuberculosis. As in tubercle the central cells of the group, degenerate, forming a granular fatty debris, and constituting an ulcer or abscess. In certain cases with a proliferation of fibrous tissue a cicatricial material is developed. Another characteristic lesion is the occurrence of hyperplasia in the walls of the lymph vessels so as to constitute firm tender cords, and the infiltration of the adjacent lymphatic plexus.
In the nasal mucosa the bacilli form prolific colonies at different points of the membrane and submucosa with the active production of lymphoid cells, followed by granular fatty degeneration and ulceration. Hence may be found different lesions representing the different stages. First there may be miliary deposits with clear contents and standing out like grains of sand. Then there are the larger pea-like nodules with congested vessels and minute hæmorrhages, but made up largely of the nests of lymphoid cells. These may bear on the surface a distinct blood extravasation, or the epithelium may be raised from the corium layer by a liquid exudation. The more advanced nodules show the centre light colored, grayish or yellowish with a distinct granular degeneration of the cells. Later still the degeneration involves the superficial layers and epithelium and an open ulcer is formed with a strong tendency to extend in depth and width. The formation and degeneration of numerous foci of cell proliferation gives the ulcer a very uneven outline. The continuous growth of fresh centres of proliferation may cause marked elevations between the ulcers, constituting extended patches, or the entire nasal mucosa may be thickened as the result of the morbid deposit. The cicatrices resulting from the apparent healing of deep or extensive ulcers or from a fibroid, transformation of the neoplasm consist of condensed connective tissue with small scattered nests of lymphoid cells and bacilli. In chronic cases the bacilli are very scanty.
The mucosa of the Eustachian pouches and tubes, the larynx, trachea and bronchia often present lesions similar to those of the pituitary membrane.
The lungs are usually marked in chronic cases by circumscribed lobular pneumonia, interlobular and peribronchial inflammations and miliary or larger areas of degeneration resembling tubercles. These may begin as a minute congestion and ecchymosis, which later shows in the centre a translucent or gray mass of lymphoid cells, with a surrounding area of congestion. Later still this central mass becomes yellowish and caseated from granular and fatty degeneration and this gradually extends so as to involve the whole area of the nodule. The peripheral portion may condense into a fibroid envelope, but usually this is less smooth and evenly rounded than in the case of an inspissated abscess or bladder-worm. The bacilli are found in the affected tissue but not always abundantly.
In cutaneous glanders the lesions may begin in the papillary layer by active congestion and infiltration and proliferation of lymphoid cells which cause an eruption of rounded papules like small peas that degenerate and soften and form superficial ulcers. When the derma is mainly involved the inflamed area becomes the seat of larger hard nodules which are at first deeply congested, with capillary thrombi, minute extravasations and rapid cell proliferation; later on section they show numerous caseated centres with a dense fibroid framework and surrounded by an area of active congestion and capillary hæmorrhage; later still the caseation and softening has caused rupture of the investing epithelium and the discharge from the ulcerous cavity of a yellowish, glairy, grumous liquid (open farcy buds). Sometimes the nodule undergoes fibroid induration and fails to ulcerate, becoming the counterpart of the cicatrices in the nose. When the infective inflammation extends to the subcutaneous connective tissue, diffuse engorgements and extensive swellings occur from the general infiltration of the abundant lymph plexuses. Lymphoid cells accumulate in the perivascular sheaths and lymph plexuses, the walls of the lymphatic trunks running out of these swellings become swollen and indurated and at intervals, mostly on the seat of the valves there is the proliferation of small round cells to form farcy buds. In chronic cases the fibroid thickening involves the skin, subcutaneous connective tissue and walls of the lymph vessels binding the whole into one dense resistant mass, more or less studded with corded lymphatics, firm nodules, and ulcerous sores.
The lymphatic glands in the line of circulation from the infected centres are constantly involved. Hypertrophy, congestion, serous infiltration, and rapid cell proliferation are present and a section will usually show caseated or caseopurulent centres confined by the outer dense fibrous envelope. Exceptionally, these necrosed contents will escape through an ulcerous opening, forming a deep cavity which is slow and difficult to heal. In the vicinity of these glands and in the loose intermuscular connective tissue abscesses of the size of an egg or an orange or larger are sometimes met with.
Nodules and ulcers are found on the pharyngeal and intestinal mucosa, similar to those of the larynx.
The spleen, and less frequently the liver, may be the seat of caseating nodules exactly comparable to those of the lungs. Glanders of the kidney is rare.
Nodules have been seen on the ventricular endocardium and one case of nodules of the choroid plexus (Boschetti).