Animal anatomy, histology, pathological anatomy

BIRD POX

Bird pox (Variola avium) is a contagious disease characterized by exanthema (rash) of the skin and diphtheritic inflammation of the mucous membranes of the oral, nasal cavities, larynx and eyes. Chickens, turkeys, guinea fowl, pigeons, pheasants, canaries, starlings, peacocks, and sometimes waterfowl (geese, ducks) are susceptible. Etiology. The causative agent is a DNA-containing double-stranded virus from the group of smallpox viruses of the Poxviridae family. It is specific for each bird species. Pathogenesis. The virus has epitheliotropic properties. Infection occurs aerogenously, through the skin and mucous membranes. Mechanical carriers can be arthropods (insects, ticks). Viruses multiply in the cytoplasm of epithelial cells with the development of exanthema: a gray pityriasis-like plaque, reddish-gray elevations (papules) with focal hyperemia, hyperplasia and hypertrophy of the epithelial cells of the educational layer the size of a millet grain to the size of a forest grain are formed on the skin nut when they merge. In the enlarged cells of the papules, sudanophilic inclusion bodies are found. As intracellular and extracellular edema develops, epithelial cell necrosis and serous exudate leak into the depths and onto the surface of the pockmarks, they dry out, acquire a dark brown color, hyperkeratosis and cracks are noted in them, giving the pockmarks the appearance of mulberries. Unlike mammal pox, in bird pox there is no pustule stage and no umbilical depression is formed. After necrosis of the pockmarks, demarcation inflammation occurs with cellular infiltration, and then their rejection and healing of the damaged tissues under the scab. From the primary infectious foci, the virus repeatedly enters the blood with the development of viremia. As a result, internal organs, skin and mucous membranes are widely affected. With extensive lesions and complications, healing of skin defects occurs with the formation of scar tissue. With diphtheritic damage to the mucous membranes of the upper respiratory tract and oropharynx, hyperplasia and hypertrophy also occur, and then degeneration and necrosis of the epidermis, thickening it several times, necrosis
impregnated with exudate (without fibrin or with fibrin) with the formation of diphtheritic (false or true) fibrinous films, demarcation inflammation with serous cellular infiltration with the presence of leukocytes, lymphocytes and macrophages. Complete healing under the scab is observed with superficial defects of the mucous membrane, and with deep defects, scarring occurs. Pathomorphological changes. The disease occurs in skin (smallpox), diphtheritic and mixed forms. In the cutaneous form of smallpox, red-gray nodules or warty formations covered with a brown-brown scab are found on the scalp (Fig. 20.19), especially on the crest, earrings and beard, at the base of the beak, on the cheeks, in area of ​​the corners of the mouth and eyelids. The pockmarks first have a red-gray color and a dense consistency (the stage of papule formation), and then they acquire a dark brown color. Inside three of them, hypertrophy is noted; they contain a gray-yellow mass of necrotic tissue. With a benign course, recovery of the sick bird is possible, but the pox process can spread to the feathered areas of the skin in the head, neck, abdomen and thighs, limbs, lower surface of the wings, and around the cloaca. This chronic course of the disease can be accompanied by the development of blindness in birds in one or both eyes, exhaustion and death. Histological examination reveals hyperplasia of the basal layer of the epidermis, the presence in the epithelial cells of sudanophilic Bollinger inclusion bodies of round or oval shape, sometimes occupying the entire cell, the development of hydropic degeneration of the cells of the spinous layer, serous infiltration, intracellular and intercellular edema the papillary layer of the skin and epidermis with the presence of leukocytes, lymphocytes and macrophages, but the plasma membrane of the epithelial cells is preserved, therefore bubbles (vesicles) in birds, unlike mammals, are not formed (Fig. 20.20). In the diphtheritic form of smallpox, the mucous membranes of the oral and nasal cavities, the tongue and eyes, the infraorbital fossa, along the palatine fissure, in the pharynx, the circumference of the larynx and even the trachea are affected. First, a small rash appears on the mucous membranes in the form of yellowish-white spots, which, expanding, form layers (films) in the form of a cheesy mass. The larynx is most often affected. At the same time, the birds stick out their necks and breathe with their beaks open. When the nasopharynx is affected, the lacrimal canal and infraorbital fossa are involved in the process. When the eyes are affected, keratoconjunctivitis develops with cheesy deposits on the cornea. An accumulation of virions is found in keratinocytes (Fig. 20.21). Fibrinous deposits (films) form on the hard palate and in the infraorbital sinuses, affecting both eyes (owl's head). The gastrointestinal tract is rarely affected. In the goiter and intestines, lesions may be accompanied by the formation of a curdled mass. This course of smallpox ends in death with signs of asphyxia. In the mixed form, smallpox exanthema simultaneously develops in chickens on the skin and mucous membranes. At the same time, general changes are more pronounced. Liver, kidneys and heart muscle with signs of protein-fatty degeneration, intestines in a state of catarrh, lungs - asphyxia. The tracheal form of smallpox in laying hens when kept in cages and the atypical form in young laying hens in winter are also known, which is manifested by a decrease in egg production, hepatosis and fibrinous deposits in the upper part of the trachea. Diagnosis is based on epidemiological, clinical and morphological data, virological and serological studies, as well as bioassays on chicken embryos and chicks and the results of histological studies with the detection of Bollinger inclusion bodies when impregnated with silver (B M. Apatenko, 1978). Fluorescence microscopy and immunofluorescence research (according to Koons) in a direct or indirect version are of important diagnostic value. Differential diagnosis. It is necessary to exclude hypovitaminosis A with characteristic metaplasia of the glandular epithelium of the mucous membranes into stratified squamous epithelium, infectious laryngotracheitis, in which fibrinous inflammation and intranuclear inclusions are found only in the trachea, infectious bronchitis of chickens, respiratory mycoplasmosis with fibrinous lesions of the air sacs and lungs and mycotic diseases (aspergillosis, candidomycosis) with the detection of spores and mycelium of fungi.