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Pathology of the Avian Respiratory System1
Pathology of the Avian Respiratory System1 OSCAR J. FLETCHER Poultry Disease Research Center, Department of Avian Medicine, College of Veterinary Medicine, The University of Georgia, Athens, Georgia 30602 (Received for publication December 1, 1979)
1980 Poultry Science 59:2666-2679
INTRODUCTION Illustration of the changes that follow introduction of an irritant into the avian respiratory system is the basic purpose of this presentation. Some of the more significant interactions between irritants and the normal defense mechanisms of the respiratory system are discussed with the goal of aiding our understanding of the effects of disease on respiratory function. Specific diseases are used to provide examples of basic responses to injury. Many irritants and infectious agents cause the development of similar lesions; therefore, specific disease diagnosis requires an evaluation of many factors including history, clinical signs, gross lesions, results of serologic tests, and isolation and identification of specific organisms. This paper emphasizes lesion recognition rather than specific disease diagnosis. Irritants and infectious agents that produce the range of lesions illustrated and discussed include: ammonia (Oyetunde et al, 1978); vitamin A deficiency (Bang and Bang, 1969b, Jungherr, 1943); laryngotracheitis (LT) (Bang and Bang, 1967; Purcell, 1971); Newcastle disease (ND) (Bang et al, 1974, 1975; Cheville et al, 1972; Jungherr and Minard, 1944, Jungherr et al, 1946); infectious bronchitis
1 Supported by grants from the Georgia Department of Agriculture. Manuscript Number 1693 from the Veterinary Medical Experiment Station. 2 Instrument Shop, General Research Services Physics, University of Georgia, Athens, GA 30602.
(IB) (Davelaar and Kouwenhoven, 1976; Hofstad, 1945; Purcell and McFerran, 1972, Pohl, 1974; Winterfield et al, 1972); influenza (Narayan et al, 1972); adenovirus disease (Cheville and Sato, 1977; Gallina et al, 1973, Kawamura et al, 1966); pox (Giddens et al, 1971; Kawamura et al, 1966), Hemophilus (Adler and Page, 1962); mycoplasma (Abu-Zahr and Butler, 1976; Barber, 1962; Fletcher et al, 1976; Grimes and Rosenfeld, 1972, Jordan, 1975; Jungherr, 1949, Kerr and Olson, 1967; Tajima et al, 1979); E. coli (Oyetunde et al, 1978); and Cryptospoidia (Hoerr et al, 1979). Articles dealing with avian histopathology in general, or providing comparisons of several respiratory diseases, are available (Gouffaux et al, 1977; Jungherr and Luginbuhl, 1952; Jungherr, 1963; Mayor, 1968). MATERIALS AND METHODS
The lesions illustrated were observed in tissues obtained from birds submitted for diagnosis of spontaneous disease and from birds obtained from research projects at the Poultry Disease Research Center, College of Veterinary Medicine, the University of Georgia. Tissues were fixed in 10% neutral buffered formalin, routinely processed, and stained with H & E. Selected tissues were embedded in glycol methacrylate and sectioned with glass knives (Fletcher, 1975). Air sacs were obtained using a ring stabilization procedure developed by D. W. Trampel. In this procedure a pair of aluminum rings2 was used for each air sac collected. One of the
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ABSTRACT Basic reactions of the avian respiratory system to injury include catarrhal inflammation, deciliation, necrosis, metaplasia, hyperplasia, congestion, edema, fibrin, exudation, cellular infiltrations, and lymphoid follicle formation. Specific diseases provide examples for illustration of these responses. The effects of such changes on basic defense mechanisms of the respiratory system are discussed. (Key words: respiratory system, avian pathology, histopathology, airsacculitis, inflammation)
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TABLE 1. Basic histopathologic lesions of the avian respiratory system I. Epithelium A. Increase in number of goblet cells B. Loss of cilia (deciliation) C. Metaplasia D. Hyperplasia E. Necrosis II. Lamina propria A. Congestion B. Edema C. Hemorrhage D. Infiltration of inflammatory cells 1. Heterophils 2. Lymphocytes 3. Plasma Cells 4. Macrophages 5. Lymphofollicular reaction E. Fibrosis F. Necrosis G. Hypertrophy of mucous glands
RESULTS AND DISCUSSION The basic histopathologic responses of the avian respiratory system to injury are summarized in Table 1. In general, the patterns of lesion development are similar in the middle nasal chamber, trachea, and primary and secondary bronchi of the lung. The nares and anterior nasal chamber are not regarded as sites of significant diagnostic lesions. Keratin and cellular debris may accumulate in the anterior chamber (Fig. 1). Atrophy of the olfactory mucosa lining the antorbitol portion of the nasal cavity may result from exposure to ammonia. This lesion has been observed in rats, but has not, to the author's knowledge, been described in birds. Common clinical signs of respiratory disease include discharge of exudate from the nares, conjunctivitis and swelling of the infraorbital sinuses due to accumulation of exudate (Fig. 2). The Harderian gland, located behind the eye and within the orbit, is a major source of antibody (Ewert et al., 1977, 1979; Firth, 1977) (Fig. 3). This locally produced antibody which bathes the cells lining the nasal cavity, trachea, and bronchi constitutes, along with the mucociliary system (Bang and Bang, 1959, 1969a; Bang, 1961; Cheville, 1976), a major defense mechanism of the respiratory system.
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Conjunctival and intranasal infection with IB causes increases in the number of plasma cells and lymphoid follicles in the Harderian gland of chickens (Davelaar and Kouwenhoven, 1976). Some diseases, not regarded as primary diseases of the respiratory system, have secondary adverse effects on this system due to the primary damage to the immune system. Infectious bursal disease is perhaps the best known example (Giambrone et al, 1977, Lukert gJ d., 1979). Inflammatory processes involving the nasal cavity frequently extend into the sinuses. Nodular and diffuse infiltrations of lymphocytes and plasma cells associated with mycoplasma and Hemophilus infections are common (Fig. 4). Squamous metaplasia is the replacement of ciliated respiratory epithelial cells by squamous epithelial cells. The lesion is diagnostic for vitamin A deficiency (Jungherr, 1943) when present at the mucocutaneous junction in the middle nasal cavity (Fig. 5). Squamous metaplasia may occur as a result of any chronic inflammatory process and is found in the trachea or major bronchi as well as the nasal cavity (Fig. 6). Loss of cilia and mucous glands in the areas of metaplasia hinders the formation and operation of the mucociliary defense system. The respiratory system becomes more susceptible to infections with other agents because of the decreased trapping and removal of foreign material. Lesions produced by a
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two rings (3 mm in diameter) was placed against the lining epithelial surface; the other (2 mm diameter) was placed against the mesothelial surface. The rings, with air sac between them, were clamped by a sponge-holding forcep. The tissue around the rings was cut, the rings removed, the sponge-holding forcep replaced by a binder clip, 3 and the entire apparatus placed in 10% neutral buffered formalin for fixation of the air sac. Following dehydration in a graded series of ethanol, the rings with air sac fixed between them were placed in a 7 ml polystyrene weighing boat and covered with glycol methacrylate. After polymerization a block of plastic containing the flat air sac was removed, placed in a tissue embedding mold, and reembedded in glycol methacrylate. The air sacs were sectioned with glass knives and stained with H & E.
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FLETCHER change, are seen in most respiratory diseases (Fig. 10). These changes are usually adjacent to areas of desquamation or necrosis. Degenerative changes leading to necrosis of epithelial cells provide a stimulus for the multiplication of basal cells with the resulting lesion of hyperplasia (Fig. 11). The pathogenesis of IB provides an excellent illustration of the progression of epithelial lesions from deciliation and desquamation to hyperplasia and metaplasia (Hofstad, 1945; Purcell and McFerran, 1972). The association of a protozoan parasite, Cryptosporidium (Hoerr et al, 1979), with epithelial cells provides an example of hyperplasia (Figs. 12, 13). In some cases hyperplasia results in an epithelium containing many cell layers and being three to four times normal thickness (Fig. 14). Such lesions are not specific for any particular disease but are indications of a chronic process. One exception is the disease of pox (Jungherr, 1963; Kawamura et al, 1966, Mayor, 1968). The wet form of pox is characterized by foci of caseous necrosis in the oral cavity and trachea. Necrotic plugs may obstruct the trachea and cause death by asphyxiation (Fig. 15). The presence of large inclusion bodies in the cytoplasm of the hyperplastic epithelial cells is diagnostic for pox (Figs. 16, 17). Certain diseases are characterized by extensive epithelial cell necrosis with hemorrhage and exudate accumulation (Fig. 18). The initial lesions are so severe that death occurs before hyperplastic or metaplastic lesions have an opportunity to develop. Examination of any exudate in the trachea is important in these cases. All or nearly all of the epithelial cells may die and desquamate. Large inclusion bodies in the nuclei of the desquamated cells are diagnostic for LT (Fig. 19). Inclusions may be found in any remaining epithelial cells.
FIG. 1. Accumulation of keratin debris is in the anterior nasal cavity of this chicken experimentally infected with Hemophilus gallinarum. FIG. 2. Conjunctivitis, as present in this turkey poult, is a common clinical sign of respiratory disease. FIG. 3. The Harderian gland is characterized by an accumulation of lymphocytes and plasma cells in the connective tissue. FIG. 4. Nodular aggregations and diffuse lymphoid cell infiltration is in the infraorbital sinus of a chicken experimentally infected with H. gallinarum. FIG. 5. The mucocutaneous junction at the origin of the respiratory epithelium of the middle nasal chamber is the site of squamous metaplasia in birds with vitamin A deficiency. FIG. 6. This high power magnification of tracheal mucosa illustrates a zone of squamous metaplasia (on the left) at its junction with more normal columnar respiratory epithelial cells (on the right). FIG. 7. Catarrhal inflammation is characterized by an increase in the number and size (hypertrophy of mucous glands. FIG. 8. Excess mucus is filling the trachea of this quail.
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single irritant or pathogen are usually less severe than those produced by exposing the respiratory system to several irritants in sequence or in combination. The effects of ammonia on increasing the severity of lesions due to E. colt provide an excellent example of this concept (Oyetunde et al, 1978). Respiratory diseases under field conditions tend to be more severe than those produced experimentally (Gouffaux et al, 1977; Hofstad, 1945; Jungherr and Luginbuhl, 1952; Jungherr, 1963; Kawamura et al, 1966; Mayor, 1968). Increases in the number of goblet cells and the number and size of mucous glands are associated with excess mucus production (Fig. 7). This process is called catarrhal inflammation and is present, at least in the initial stages, in nearly all cases of respiratory disease. Catarrhal rhinitis, tracheitis, or bronchitis may be the only lesion observed if the irritant is mild or present for a short time. The presence of catarrhal inflammation is an indication of the mucociliary defense response to dilute and remove the irritant. Excess mucus may be seen as a nasal discharge or may be observed in the air passages during postmortem examination (Fig. 8). Histologic diagnosis of catarrhal inflammation requires knowledge of the number and location of mucous glands normally found in the respiratory mucosa. Loss of cilia or deciliation is a common lesion often associated with catarrhal inflammation (Fig. 9). Finding cilia by histologic examination does not necessarily mean that normal ciliary movement was present. Cessation of cilial movement is the early indicator of cytotoxicity in tracheal explant organ culture systems (Abu-Zahr and Butler, 1976). Epithelial cells in various stages of degeneration, including swelling and vacuolar or hydropic
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FLETCHER often repaired by regeneration prior to submission of the chicken for diagnosis. In some cases hyperplasia of epithelial cells constitutes the predominant lesion in IB (Gouffaux et al, 1977). These variations in histologic lesions encountered further emphasize the lack of specificity of the lesions for IB. Mycoplasma infections produce lymphoid cell infiltration with increased numbers of lymphoid follicles, the lymphofollicular reaction (Barber, 1962; Jordan, 1975; Jungherr, 1949) (Fig. 4). The presence of an increased number of lymphoid follicles in the lamina propria should be regarded as only suggestive of mycoplasma infection, as this lesion is typical of chronic inflammation induced by a wide variety of agents in birds. Mycoplasma are associated intimately with surface epithelial cells (Tajima et al., 1979) and stimulate epithelial cell proliferation leading to hyperplasia. Mixed infections of IB and mycoplasma are suggested by the presence of epithelial cell hyperplasia and diffuse lymphoid cell infiltration of the lamina propria (Gouffaux et al., 1977). Neoplasms are relatively uncommon lesions of the respiratory system, particularly if only primary tumors are considered. Primary fibrosarcoma of the trachea cause marked distortion of epithelium and eventually cause near total obliteration of the tracheal lumen. Erythroblastosis, myeloblastosis, and myelocytomatosis may cause signs of respiratory distress due to anemia, and in many of these cases neoplastic tumor cells fill the capillaries of die lung, further contributing to gas exchange difficulties. Histologic sections of lung frequently contain variable numbers of erythrocytes in bronchi (Figs. 26, 27). Their presence is an
FIG. 9. Deciliation, squamous mataphasia, and mucous gland hypertrophy and hyperplasia are illustrated. This lesion is characteristic of chronic, catarrhal tracheitis and is not disease specific. FIG. 10. Focal necrosis (right side) and vacuolar (hydropic) degeneration of epithelial cells are present. Note the relative absence of lymphoid cells in the lamina propria. FIG. 11. Hyperplasia of tracheal epithelial cells is accompanied by deciliation, accumulation of exudate on the surface of epithelial cells, and by congestion of blood vessels in the lamina propria. Trachea from a chicken suspected of having ND. FIG. 12. Epithelial cell hyperplasia is marked in the trachea of a chicken with cryptosporidiosis. FIG. 13. Higher magnification of Fig. 12 illustrates the intimate association of trophozoites of Cryptosporidium sp. with respiratory epithelial cells. Note absence of cilia. FIG. 14. Tracheal mucosa is greatly (Ca. 10 X) increased in thickness due to epithelial cell hyperplasia. Cilia are absent. This lesion is characteristic of chronic tracheitis and may follow ND infection. FIG. 15. Multiple foci of caseous necrosis in the oral cavity and trachea are features of fowl pox ("wet" pox). Note the plug of caseous necrotic material plugging the trachea. FIG. 16. Tracheal mucosa from a chicken with pox exhibits hyperplasia, pustule formation, and intracytoplasmic inclusion in bodies in epithelial cells.
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Multinucleated, giant cell syncytia are characteristic features (Purcell, 1971) of LT. Intranuclear inclusions have been reported in respiratory disease caused by adenovirus infection of chickens (Gallina et al., 1973). Experimental infection of chickens with two strains of adenovirus failed to produce respiratory lesions, although typical adenoviral lesions were in other organs (Grimes et al, 1978). Examination of tissues obtained from turkeys experiencing a respiratory disease revealed intranuclear inclusions in a large number of respiratory epithelial cells including those in the lung (Cheville and Sato, 1977). Changes in epithelial cells are usually accompanied by congestion of blood vessels and by cellular infiltration of the lamina propria. Nodular deposits and diffuse lymphoid cell infiltration are common findings in the avian respiratory tract (Fig. 20). Lymphoid nodules are associated frequently with primary and secondary bronchi (Fig. 21); nodular deposits may be in the lung parenchyma in the absence of any respiratory disease (Fig. 22). These cells, regarded as normal constituents of the immune system, form the bronchial-associated lymphoid tissue (BALT). The antibody and cell-mediated responses as vital constituents of the defenses of the respiratory system were mentioned earlier. A decision as to whether lymphoid tissue is normal or increased in amount requires careful judgement and some experience with birds raised under field conditions. In some diseases, IB being a classic example, diffuse infiltration of lymphocytes and plasma cells occurs in the lamina propria (Hofstad, 1945; Purcell and McFerran, 1972), and often constitutes the major lesion seen in IB (Figs. 23, 24, 25). The epithelial cell damage is
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The presence of multiple or confluent nodules scattered throughout the lung indicates granulomatous pneumonia (Fig. 33). Histologic examination reveals central areas of caseous necrosis surrounded by multinucleated giant cells, lymphocytes and plasma cells, and finally by a layer of fibrous connective tissue. Granulomas in various stages of formation are usually encountered. Special stains may reveal the presence of fungi if a mycotic pneumonia is present or the presence of acid-fast organisms in the case of tuberculosis. (Fig. 34). Miscellaneous lesions found in the lung include: deposits of refractile debris in macrophages, melanosis, Leucocytozoon in parasitized
erythrocytes (Fig. 3 5), fat emboli in blood vessels (Brunner and Meinl, 1976), and thrombosis of branches of the pulmonary artery (Fig. 36). The relatively high incidence of airsacculitis in birds is predictable based on current knowledge of air flow patterns. Impairment of the defense mechanisms leaves the air sacs vulnerable to irritants and pathogens present in the inhaled air. Airsacculitis may also result from extension of inflammatory processes from the lung or from penetration of the air sac wall by processes involving the peritoneum or visceral organs. Structurally, the air sacs are lined by simple squamous epithelium with clumps of ciliated epithelial cells interspersed (Fig. 37a). A scant amount of connective tissue containing few blood vessels separate the lining epithelium from the mesothelial cells (Fig. 37b). Ciliated epithelial lining cells are more frequent at and near the origin of the air sacs from the lung. Normal histology at the light microscope (Cover, 1953; Fletcher et al, 1976, Lucas and Denington, 196 la,b) and electron microscope levels (Carlson and Beggs, 1973) is reported. Air sacs are subject to the same basic lesions as described for the nasal cavity, trachea, and major bronchi, with the exception that catarrhal inflammation is not a feature as goblet cells and mucous glands are not present, although metaplastic changes in air sac epithelium may result in goblet cells and mucus formation (Fletcher et al, 1976) (Fig. 38). The reactivity of the air sacs in a variety of disease conditions is discussed and illustrated in several publications (Grimes and Rosenfeld, 1972; Jungherr and Luginbuhl, 1952, Kerr and
FIG. 17. Numerous large, granular, intracytoplasmic inclusions in the epithelial cells of the trachea of a chicken are diagnostic for pox. Note the hydropic (vascuolar) degeneration and absence of cilia. FIG. 18. Hemorrhagic tracheitis is characteristic of LT in chickens. Note the accumulation of blood, mucus, and debris in the anterior portion of the trachea. FIG. 19. Examination of the exudate in the trachea of a chicken with LT reveals the presence of large intranuclear inclusions and syncytial cells. FIG. 20. Nodular aggregates of lymphoid cells are present normally in the lamina propria of the respiratory system. Note the absence of cilia on the cells covering this nodule in the trachea of a chicken. FIG. 21 Nodular deposits of lymphoid tissue are commonly associated with primary and secondary bronchi. This nodule is in the wall of a secondary bronchus and is regarded as a normal component of the bronchial associated lymphoid tissue (BALT). FIG. 22. A nodular deposit of lymphoid cells is adjacent to an arteriole in the lung parenchyma. This was considered a normal bursa-dependent lymphoid follicle. FIG. 23. A diffuse infiltration of lymphoid cells in the lamina propria of this chicken trachea. The epithelial surface appears normal. FIG. 24. Diffuse infiltration of lymphocytes and reticular cells has increased the thickness of the tracheal mucosa in this chicken suspected of having bronchitis (IB).
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artifact caused by the method of killing and subsequent processing of lung tissues. Filling of the respiratory lobule (tertiary bronchus, atria, and air capillaries) with fibrin, heterophils, macrophages, and cell debris is characteristic of Pasturella pneumonia (Figs. 28, 29, 30). Hypertrophy and hyperplasia of pneumocytes lining the tertiary bronchioles, atria, and air capillaries occurs if the irritant persists, or if the bird survives for a sufficient time. The resulting glandular type histologic pattern is called adenomatosis and is a characteristic of interstitial pneumonia (Figs. 31, 32). The ND is associated with interstitial pneumonia that may follow an earlier necrotizing lesion. Hypertrophy of smooth muscle and fibrosis, with presence of increased numbers of alveolar macrophages, are additional features of interstitial pneumonia. The absence of lung lesions in IB was considered a useful differentiating feature with ND until the discovery of several strains of IB virus capable of causing interstitial pneumonia (Winterfield et al, 1972).
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Olson, 1967; Lucas and Denington, 1961b). Airsacculitis is characterized grossly by cloudiness, increased thickness, and exudate accumulation (Fig. 39). The anatomy of the air sacs makes this an ideal location to study the inflammatory response of birds. Congestion, edema, fibrin deposition, heterophil and monocytic cell infiltration, macrophages, lymphocytes, plasma cells, fibroblasts, and lymphoid follicle formation are expected constituents regardless of the irritant. These inflammatory changes are
revealed under near ideal conditions in ring stabilized air sacs embedded in plastic and sectioned with glass knives (Figs. 40, 41, 42, 43). Mycotic infection of air sacs may result in the formation of massive growth of mycelial elements with numerous fruiting bodies present (Fig. 44a,b). Exudate is removed by macrophages and exudate on the air sac epithelial surface may become surrounded by proliferating epithelial cells (Figs. 45, 46, 47, 48).
FIG. 33. One large and two smaller granulomas have replaced lung parenchyma in this case of granulomatous pneumonia. FIG. 34. Mycelia typical of Aspergillus sp. in a lung granuloma are revealed by this PAS strain. FIG. 35. An erythrocyte parasitized by Leucocytozoon smitbi is in the center of this photomicrograph. FIG. 36. A thrombus is in a branch of a pulmonary artery. FIG. 37. Normal air sac has a patch of ciliated respiratory epithelial cells. Normal air sac with a simple squamous epithelial lining and scanty amount of connective tissue is shown in a plastic embedded section. FIG. 38. Hyperplasia of air sac epithelium and mucus production is in an air sac from a chicken experimentally infected with Mycoplasma synoviae. Plasma cells, macrophages and fibroblasts are in the edematous connective tissue. FIG. 39. Gross features of air sacculitis include cloudiness and increased thickness. FIG. 40. Focal necrosis of epithelium, exudate accumulation, and cell infiltration of the connective tissue are early lesions in MG induced air sacculitis. FIG. 4 1 . Hyperplasia of air sac. epithelial cells follows initial necrosis and exudate accumulation in MG infected chickens. FIG. 42. A small lymphoid nodule is in the connective tissue of this MG infected air sac. Note greatly increased thickness of air sac wall. FIG. 43. A large lymphoid nodule contributes to the increased thickness of this MG infected air sac. FIG. 44a. A massive growth of mycelial elements of Aspergillus sp. fills this air sac. b) A higher magnification reveals the presence of conicial heads (fruiting bodies) of Aspergillus sp. FIG. 45. Exudate lies on the surface of the squamous epithelial cells. FIG. 46. Heterophils and macrophages are intimately associated with epithelial cells in Mycoplasma infections of the air sac. FIG. 47. Macrophages, lymphocytes, plasma cells, and blood vessels are in this exudate. The surface is covered with squamous epithelial cells. FIG. 48. A more advanced stage in removal of exudate from the air sac shows large numbers of macrophages enclosed by air sac epithelial cells.
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FIG. 25. Chronic tracheitis in the chicken is characterized by diffuse reticular cell and lymphocyte infiltration, by decreased height of epithelial cells, and by loss of cilia. Tissue was from a chicken suspected of having IB. FIG. 26. Normal lung shows the junction of a secondary bronchus with a tertiary bronchus (parabronchus). A few erythrocytes are in the lumen of the parabronchus. FIG. 27. The parabronchus, atria, and air and blood capillaries are normal in this chicken lung. The erythrocytes in the air passages are considered artifacts due to the methods of killing the bird and processing the lung. FIG. 28. Fibrin and heterophils are the major components of the exudate filling the respiratory lobule of this chicken with fowl cholera. FIG. 29. A higher magnification of the parabronchus and atria illustrate fibrinous pneumonia. FIG. 30. A large accumulation of inflammatory cells, primarily heterophils, and necrosis are features of bacterial and some viral-induced pneumonias. FIG. 31. Hypertrophy of respiratory epithelial cells lining the parabronchus and atria is a feature of interstitial pneumonia. Fibrin and cellular debris fill the air passages. FIG. 32. A glandular pattern is created in chronic pneumonia by hypertrophy of epithelial cells. This lesion is often present in ND, but is not limited to ND infection.
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24:269-275. Ewert, D. L., C S. Eidson,,and D. L. Daw, 1977. Factors influencing the appearance of antibody in tracheal washes and serum of young chickens after exposure to Newcastle Disease virus. Infect. and Immun. 18:138-145. Firth, G. A., 1977. The normal lymphatic system of the domestic fowl. Vet. Bull. 47:167-179. Fletcher, O. J., 1975. Plastic embedding of avian tissues for diagnostic histopathology. Avian Dis. 19:201-208. Fletcher, O. J., D. P. Anderson, and S. H. Kleven, 1976. Histology of air sac lesions induced in chickens by contact exposure to Mycoplasma synoviae. Vet. Pathol. 13:303-314. Gallina, A. M„ R. W. Winterfield, and A. M. Fadly, 1973. Adenovirus infection and disease. 11. Histopathology of natural and experimental disease. Avian Dis. 17:343—353. Giambrone, J. J., C. S. Eidson, and S. H. Kleven, 1977. Effect of infectious bursal disease on the response of chickens to mycoplasma synoviae, Newcastle Disease virus, and infectious bronchitis virus. Amer. J. Vet. Res. 38:251-253. Giddens, W. E., Jr., L. J. Swango, J. D. Henderson, Jr., R. A. Lewis, S. D. Farner, A. Carlos, and W. C. Dolowy, 1971. Canary pox in sparrows and canaries(fringillidae) and in weavers(plociidae). Vet. Pathol. 8:260-280. Gouffaux, M., H. Vinderogel, G. Meulemans, A. Dewaele, and P. Halen, 1977. Elements du diagnostic histopathologique differential des principals affections respiratoires de la poule. Avian Pathol. 6:61-76. Grimes, T. M., O. J. Fletcher, and J. F. Munnell, 1978. Comparative study of experimental inclusion body hepatitis of chickens caused by two serotypes of avian adenovirus. Vet. Pathol. 15: 249-263 Grimes, T. M., and L. E. Rosenfeld, 1972. Experimental respiratory disease and airsacculitis in fowls caused by Mycoplasma gallisepticum. Australian Vet. J. 48:113-116. Hoerr, F. J., M. Ranck, Jr., and T. F. Hastings, 1979. Respiratory cryptosporidiosis in turkeys. J. Amer. Vet. Med. Ass. 175:623. Hofstad, M. S., 1945. A study of infectious bronchitis in chickens. 1. The pathology of infectious bronchitis. Cornell Vet. 3 5 : 2 2 - 3 1 . Jordan, F.T.W., 1975. Avian mycoplasma and pathogenicity-a review. Avian Pathol. 4:165—174. Jungherr, E. L., 1943. Nasal histopathology and liver storage in the subtotal vitamin A deficiency of chickens. Pages 5—3 5 in Agr. Exp. Sta. Bull. #250 Univ. Connecticut, Storrs, CT. Jungherr, E. L., 1949. The pathology of experimental sinusitis of turkeys. Amer. J. Vet, Res. 10: 372-383. Jungherr, E. L., 1963. Histopathology in the diagnosis of poultry diseases. Brit. Vet. J. 119:93-98. Jungherr, E. L., and R. E. Luginbuhl, 1952. Air sac infection in poultry. Pages 275—283 in Proc. 56th Annu. Mtg. US Livestock Sanitary Ass. Louisville, KY Jungherr, E. L., and E. L. Minard, 1944. The pathology of experimental avian pneumoencephalitis. Amer. J. Vet. Res. 5:125-134.
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Abu-Zahr, M. N., and M. Butler, 1976. Growth, cytopathogenicity, and morphology of Mycoplasma gallisepticum and M. gallinarum in tracheal explants. J. Comp. Pathol. 86:455-463. Adler, H. E., and L. A. Page, 1962. Haemophilus infections in chickens. 11. The pathology of the respiratory tract. Avian Dis. 6:1—6. Bang, B. G., 1961. The surface pattern of the nasal mucosa and its relation to mucous flow—A study of chicken and herring gull nasal mucosae. J. Morphol. 109:57-72. Bang, B. G., and F. B. Bang, 1959. A comparative study of the vertebrate nasal chamber in relation to upper respiratory infection. Bull. Johns Hopkins Hosp. 104:107-149. Bang, B. G., and F. B. Bang, 1967. Laryngotracheitis virus in chickens. J. Exp. Med. 125:409-428. Bang, B. G., and F. B. Bang, 1969a. Experimentally induced changes in nasal mucous secretory systems and their effect on virus infection in chickens. J. Exp. Med. 130:105-120. Bang, B. G., and F. B. Bang, 1969b. Replacement of virus-destroyed epithelium by keratinized squamous cells in vitamin A-deprived chickens. Proc. Soc. Exp. Biol. Med. 32:50-54. Bang, F. B., B. G. Bang, and M. Foard, 1975. Acute newcastle viral infection of the upper respiratory tract of the chicken. Amer. J. Pathol. 78: 417-426. Bang, F. B., M. Foard, and B. G. Bang, 1974. Acute newcastle viral infection of the upper respiratory tract of the chicken. Amer. J. Pathol. 76: 333-348. Barber, C. W„ 1962. The lymphofollicular nodules in turkey tissues associated with mycoplasma gallisepticum infection. Avian Dis. 6:289—296. Brunner, P., and M. Meinl, 1976. Fettembolische verschlusse in den blutgefassen der vogellung. Vet. Pathol. 13:17-26. Carlson, H. C , and E. C. Beggs, 1973. Ultrastructure of the abdominal air sac of the fowl. Res. Vet. Sci. 14:148-150. Cheville, N. F., 1976. Pages 323-353 in Cell pathology. Iowa State University Press, Ames, IA. Cheville, N. and S. Sato, 1977. Pathology of adenoviral infection in turkeys (Meleagris gallopavo) with respiratory disease and colisepticemia. Vet. Pathol. 14:567-581. Cheville, N. F., H. Stone, J. Riley, and A. E. Ritchie, 1972. Pathogenesis of virulent Newcastle Disease in chickens. J. Amer. Vet. Med. Ass. 161: 169-179. Cover, M. S., 1953. Gross and microscopic anatomy of the respiratory system of the turkey. 111. The air sacs. Amer. J. Vet. Res. 14:239-245. Davelaar, F. G., and B. Kouwenhoven, 1976. Changes in the Harderian gland of the chicken following conjunctival and intranasal infection with infectious bronchitis virus in one-and twenty-day old chickens. Avian Pathol. 5:39—50. Ewert, D. L., B. O. Barger, and C. S. Eidson, 1979. Local antibody response in chickens: Analysis of antibody synthesis to Newcastle Disease virus by solid-phase radioimmunoassay and immunofluorescence with class specific antibody for chicken immunoglobulin. Infect, and Immun.
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Narayan, O., J. Thorsen, T. J. Hulland, G. Anbeli, and P. G. Joseph, 1972. Pathogenesis of lethal influenza virus infection in turkeys. I. Extra-neural phase of infection. J. Comp. Pathol 82:129-137. Oyetunde, O.O.F., R. G. Thomson, and H. C. Carlson, 1978. Aerosol exposure of ammonia, dust, and Escherichia coli in broiler chickens. Canadian Vet. J. 19:187-193. Pohl, R., 1974. The histopathogenesis of the nephrosis-nephritis syndrome. Avian Pathol. 3:1 — 13. Purcell, D. A., 1971. Histopathology of infectious laryngotracheitis in fowl infected by an aerosol. J. Comp. Pathol. 81:421-431. Purcell, D. A., and J. B. McFerran, 1972. The histopathology of infectious bronchitis in the domestic fowl. Res. Vet. Sci. 13:116-122. Tajima, M., T. Nunoya, and T. Yagihashi, 1979. An ultrastructural study on the interaction of Mycoplasma gallisepticum with the chicken tracheal epithelium. Amer. J. Vet. Res. 40: 1009-1014. Winterfield, R. W., A. M. Fadly, and A. A. Bickford, 1972. The immune response to infectious bronchitis virus determined by respiratory signs, virus infection, and histopathological lesions. Avian Dis. 16:260-269.
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Jungherr, E. L., E. E. Tyzzer, C. A. Brandley, and H. E. Moses, 1946. The comparative pathology of fowl plague and Newcastle disease. Amer. J. Vet. Res. 7:250-288. Kawamura, H., T. Horiuchi, S. Shoya, and F. Shimizu, 1966. Mixed infection with avian adenovirus and fowl pox virus. Nat. Inst. Animal Hlth. Quart. 6:216-222. Kerr, K. M., and N. O. Olson, 1967. Pathology in chickens experimentally inoculated or contactinfected with Mycoplasma gallisepticum. Avian Dis. 11:559-578. Lucas, A. M., and E. M. Denington, 1961a. Pages 32—38 in Air sacs—Their distribution and microscopic structure. Agr. Res. Serv. US Dept. Agr. ARS 45-2. Lucas, A. M., and E. M. Denington, 1961b. A brief report on anatomy, histology, and reactivity of air sacs in the fowL Avian Dis. 5:460—461. Lukert, P. D., R. K. Page, and D. C. Johnson, 1979. Serologic and growth characteristics of a turkey infectious bursal disease virus. J. Amer. Vet. Med. Ass. 175:618. Mayor, D. Y., 1968. Histopathological aids to the diagnosis of certain poultry disease. Vet. Bull. 38:273-285.
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1980 Poultry Science 59:2666-2679
INTRODUCTION Illustration of the changes that follow introduction of an irritant into the avian respiratory system is the basic purpose of this presentation. Some of the more significant interactions between irritants and the normal defense mechanisms of the respiratory system are discussed with the goal of aiding our understanding of the effects of disease on respiratory function. Specific diseases are used to provide examples of basic responses to injury. Many irritants and infectious agents cause the development of similar lesions; therefore, specific disease diagnosis requires an evaluation of many factors including history, clinical signs, gross lesions, results of serologic tests, and isolation and identification of specific organisms. This paper emphasizes lesion recognition rather than specific disease diagnosis. Irritants and infectious agents that produce the range of lesions illustrated and discussed include: ammonia (Oyetunde et al, 1978); vitamin A deficiency (Bang and Bang, 1969b, Jungherr, 1943); laryngotracheitis (LT) (Bang and Bang, 1967; Purcell, 1971); Newcastle disease (ND) (Bang et al, 1974, 1975; Cheville et al, 1972; Jungherr and Minard, 1944, Jungherr et al, 1946); infectious bronchitis
1 Supported by grants from the Georgia Department of Agriculture. Manuscript Number 1693 from the Veterinary Medical Experiment Station. 2 Instrument Shop, General Research Services Physics, University of Georgia, Athens, GA 30602.
(IB) (Davelaar and Kouwenhoven, 1976; Hofstad, 1945; Purcell and McFerran, 1972, Pohl, 1974; Winterfield et al, 1972); influenza (Narayan et al, 1972); adenovirus disease (Cheville and Sato, 1977; Gallina et al, 1973, Kawamura et al, 1966); pox (Giddens et al, 1971; Kawamura et al, 1966), Hemophilus (Adler and Page, 1962); mycoplasma (Abu-Zahr and Butler, 1976; Barber, 1962; Fletcher et al, 1976; Grimes and Rosenfeld, 1972, Jordan, 1975; Jungherr, 1949, Kerr and Olson, 1967; Tajima et al, 1979); E. coli (Oyetunde et al, 1978); and Cryptospoidia (Hoerr et al, 1979). Articles dealing with avian histopathology in general, or providing comparisons of several respiratory diseases, are available (Gouffaux et al, 1977; Jungherr and Luginbuhl, 1952; Jungherr, 1963; Mayor, 1968). MATERIALS AND METHODS
The lesions illustrated were observed in tissues obtained from birds submitted for diagnosis of spontaneous disease and from birds obtained from research projects at the Poultry Disease Research Center, College of Veterinary Medicine, the University of Georgia. Tissues were fixed in 10% neutral buffered formalin, routinely processed, and stained with H & E. Selected tissues were embedded in glycol methacrylate and sectioned with glass knives (Fletcher, 1975). Air sacs were obtained using a ring stabilization procedure developed by D. W. Trampel. In this procedure a pair of aluminum rings2 was used for each air sac collected. One of the
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ABSTRACT Basic reactions of the avian respiratory system to injury include catarrhal inflammation, deciliation, necrosis, metaplasia, hyperplasia, congestion, edema, fibrin, exudation, cellular infiltrations, and lymphoid follicle formation. Specific diseases provide examples for illustration of these responses. The effects of such changes on basic defense mechanisms of the respiratory system are discussed. (Key words: respiratory system, avian pathology, histopathology, airsacculitis, inflammation)
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TABLE 1. Basic histopathologic lesions of the avian respiratory system I. Epithelium A. Increase in number of goblet cells B. Loss of cilia (deciliation) C. Metaplasia D. Hyperplasia E. Necrosis II. Lamina propria A. Congestion B. Edema C. Hemorrhage D. Infiltration of inflammatory cells 1. Heterophils 2. Lymphocytes 3. Plasma Cells 4. Macrophages 5. Lymphofollicular reaction E. Fibrosis F. Necrosis G. Hypertrophy of mucous glands
RESULTS AND DISCUSSION The basic histopathologic responses of the avian respiratory system to injury are summarized in Table 1. In general, the patterns of lesion development are similar in the middle nasal chamber, trachea, and primary and secondary bronchi of the lung. The nares and anterior nasal chamber are not regarded as sites of significant diagnostic lesions. Keratin and cellular debris may accumulate in the anterior chamber (Fig. 1). Atrophy of the olfactory mucosa lining the antorbitol portion of the nasal cavity may result from exposure to ammonia. This lesion has been observed in rats, but has not, to the author's knowledge, been described in birds. Common clinical signs of respiratory disease include discharge of exudate from the nares, conjunctivitis and swelling of the infraorbital sinuses due to accumulation of exudate (Fig. 2). The Harderian gland, located behind the eye and within the orbit, is a major source of antibody (Ewert et al., 1977, 1979; Firth, 1977) (Fig. 3). This locally produced antibody which bathes the cells lining the nasal cavity, trachea, and bronchi constitutes, along with the mucociliary system (Bang and Bang, 1959, 1969a; Bang, 1961; Cheville, 1976), a major defense mechanism of the respiratory system.
3
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Idl Manufacturing and Sales Corp., Carlstadt,
Conjunctival and intranasal infection with IB causes increases in the number of plasma cells and lymphoid follicles in the Harderian gland of chickens (Davelaar and Kouwenhoven, 1976). Some diseases, not regarded as primary diseases of the respiratory system, have secondary adverse effects on this system due to the primary damage to the immune system. Infectious bursal disease is perhaps the best known example (Giambrone et al, 1977, Lukert gJ d., 1979). Inflammatory processes involving the nasal cavity frequently extend into the sinuses. Nodular and diffuse infiltrations of lymphocytes and plasma cells associated with mycoplasma and Hemophilus infections are common (Fig. 4). Squamous metaplasia is the replacement of ciliated respiratory epithelial cells by squamous epithelial cells. The lesion is diagnostic for vitamin A deficiency (Jungherr, 1943) when present at the mucocutaneous junction in the middle nasal cavity (Fig. 5). Squamous metaplasia may occur as a result of any chronic inflammatory process and is found in the trachea or major bronchi as well as the nasal cavity (Fig. 6). Loss of cilia and mucous glands in the areas of metaplasia hinders the formation and operation of the mucociliary defense system. The respiratory system becomes more susceptible to infections with other agents because of the decreased trapping and removal of foreign material. Lesions produced by a
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two rings (3 mm in diameter) was placed against the lining epithelial surface; the other (2 mm diameter) was placed against the mesothelial surface. The rings, with air sac between them, were clamped by a sponge-holding forcep. The tissue around the rings was cut, the rings removed, the sponge-holding forcep replaced by a binder clip, 3 and the entire apparatus placed in 10% neutral buffered formalin for fixation of the air sac. Following dehydration in a graded series of ethanol, the rings with air sac fixed between them were placed in a 7 ml polystyrene weighing boat and covered with glycol methacrylate. After polymerization a block of plastic containing the flat air sac was removed, placed in a tissue embedding mold, and reembedded in glycol methacrylate. The air sacs were sectioned with glass knives and stained with H & E.
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FLETCHER change, are seen in most respiratory diseases (Fig. 10). These changes are usually adjacent to areas of desquamation or necrosis. Degenerative changes leading to necrosis of epithelial cells provide a stimulus for the multiplication of basal cells with the resulting lesion of hyperplasia (Fig. 11). The pathogenesis of IB provides an excellent illustration of the progression of epithelial lesions from deciliation and desquamation to hyperplasia and metaplasia (Hofstad, 1945; Purcell and McFerran, 1972). The association of a protozoan parasite, Cryptosporidium (Hoerr et al, 1979), with epithelial cells provides an example of hyperplasia (Figs. 12, 13). In some cases hyperplasia results in an epithelium containing many cell layers and being three to four times normal thickness (Fig. 14). Such lesions are not specific for any particular disease but are indications of a chronic process. One exception is the disease of pox (Jungherr, 1963; Kawamura et al, 1966, Mayor, 1968). The wet form of pox is characterized by foci of caseous necrosis in the oral cavity and trachea. Necrotic plugs may obstruct the trachea and cause death by asphyxiation (Fig. 15). The presence of large inclusion bodies in the cytoplasm of the hyperplastic epithelial cells is diagnostic for pox (Figs. 16, 17). Certain diseases are characterized by extensive epithelial cell necrosis with hemorrhage and exudate accumulation (Fig. 18). The initial lesions are so severe that death occurs before hyperplastic or metaplastic lesions have an opportunity to develop. Examination of any exudate in the trachea is important in these cases. All or nearly all of the epithelial cells may die and desquamate. Large inclusion bodies in the nuclei of the desquamated cells are diagnostic for LT (Fig. 19). Inclusions may be found in any remaining epithelial cells.
FIG. 1. Accumulation of keratin debris is in the anterior nasal cavity of this chicken experimentally infected with Hemophilus gallinarum. FIG. 2. Conjunctivitis, as present in this turkey poult, is a common clinical sign of respiratory disease. FIG. 3. The Harderian gland is characterized by an accumulation of lymphocytes and plasma cells in the connective tissue. FIG. 4. Nodular aggregations and diffuse lymphoid cell infiltration is in the infraorbital sinus of a chicken experimentally infected with H. gallinarum. FIG. 5. The mucocutaneous junction at the origin of the respiratory epithelium of the middle nasal chamber is the site of squamous metaplasia in birds with vitamin A deficiency. FIG. 6. This high power magnification of tracheal mucosa illustrates a zone of squamous metaplasia (on the left) at its junction with more normal columnar respiratory epithelial cells (on the right). FIG. 7. Catarrhal inflammation is characterized by an increase in the number and size (hypertrophy of mucous glands. FIG. 8. Excess mucus is filling the trachea of this quail.
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single irritant or pathogen are usually less severe than those produced by exposing the respiratory system to several irritants in sequence or in combination. The effects of ammonia on increasing the severity of lesions due to E. colt provide an excellent example of this concept (Oyetunde et al, 1978). Respiratory diseases under field conditions tend to be more severe than those produced experimentally (Gouffaux et al, 1977; Hofstad, 1945; Jungherr and Luginbuhl, 1952; Jungherr, 1963; Kawamura et al, 1966; Mayor, 1968). Increases in the number of goblet cells and the number and size of mucous glands are associated with excess mucus production (Fig. 7). This process is called catarrhal inflammation and is present, at least in the initial stages, in nearly all cases of respiratory disease. Catarrhal rhinitis, tracheitis, or bronchitis may be the only lesion observed if the irritant is mild or present for a short time. The presence of catarrhal inflammation is an indication of the mucociliary defense response to dilute and remove the irritant. Excess mucus may be seen as a nasal discharge or may be observed in the air passages during postmortem examination (Fig. 8). Histologic diagnosis of catarrhal inflammation requires knowledge of the number and location of mucous glands normally found in the respiratory mucosa. Loss of cilia or deciliation is a common lesion often associated with catarrhal inflammation (Fig. 9). Finding cilia by histologic examination does not necessarily mean that normal ciliary movement was present. Cessation of cilial movement is the early indicator of cytotoxicity in tracheal explant organ culture systems (Abu-Zahr and Butler, 1976). Epithelial cells in various stages of degeneration, including swelling and vacuolar or hydropic
2669 SYMPOSIUM: RESPIRATION IN BIRDS
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FLETCHER often repaired by regeneration prior to submission of the chicken for diagnosis. In some cases hyperplasia of epithelial cells constitutes the predominant lesion in IB (Gouffaux et al, 1977). These variations in histologic lesions encountered further emphasize the lack of specificity of the lesions for IB. Mycoplasma infections produce lymphoid cell infiltration with increased numbers of lymphoid follicles, the lymphofollicular reaction (Barber, 1962; Jordan, 1975; Jungherr, 1949) (Fig. 4). The presence of an increased number of lymphoid follicles in the lamina propria should be regarded as only suggestive of mycoplasma infection, as this lesion is typical of chronic inflammation induced by a wide variety of agents in birds. Mycoplasma are associated intimately with surface epithelial cells (Tajima et al., 1979) and stimulate epithelial cell proliferation leading to hyperplasia. Mixed infections of IB and mycoplasma are suggested by the presence of epithelial cell hyperplasia and diffuse lymphoid cell infiltration of the lamina propria (Gouffaux et al., 1977). Neoplasms are relatively uncommon lesions of the respiratory system, particularly if only primary tumors are considered. Primary fibrosarcoma of the trachea cause marked distortion of epithelium and eventually cause near total obliteration of the tracheal lumen. Erythroblastosis, myeloblastosis, and myelocytomatosis may cause signs of respiratory distress due to anemia, and in many of these cases neoplastic tumor cells fill the capillaries of die lung, further contributing to gas exchange difficulties. Histologic sections of lung frequently contain variable numbers of erythrocytes in bronchi (Figs. 26, 27). Their presence is an
FIG. 9. Deciliation, squamous mataphasia, and mucous gland hypertrophy and hyperplasia are illustrated. This lesion is characteristic of chronic, catarrhal tracheitis and is not disease specific. FIG. 10. Focal necrosis (right side) and vacuolar (hydropic) degeneration of epithelial cells are present. Note the relative absence of lymphoid cells in the lamina propria. FIG. 11. Hyperplasia of tracheal epithelial cells is accompanied by deciliation, accumulation of exudate on the surface of epithelial cells, and by congestion of blood vessels in the lamina propria. Trachea from a chicken suspected of having ND. FIG. 12. Epithelial cell hyperplasia is marked in the trachea of a chicken with cryptosporidiosis. FIG. 13. Higher magnification of Fig. 12 illustrates the intimate association of trophozoites of Cryptosporidium sp. with respiratory epithelial cells. Note absence of cilia. FIG. 14. Tracheal mucosa is greatly (Ca. 10 X) increased in thickness due to epithelial cell hyperplasia. Cilia are absent. This lesion is characteristic of chronic tracheitis and may follow ND infection. FIG. 15. Multiple foci of caseous necrosis in the oral cavity and trachea are features of fowl pox ("wet" pox). Note the plug of caseous necrotic material plugging the trachea. FIG. 16. Tracheal mucosa from a chicken with pox exhibits hyperplasia, pustule formation, and intracytoplasmic inclusion in bodies in epithelial cells.
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Multinucleated, giant cell syncytia are characteristic features (Purcell, 1971) of LT. Intranuclear inclusions have been reported in respiratory disease caused by adenovirus infection of chickens (Gallina et al., 1973). Experimental infection of chickens with two strains of adenovirus failed to produce respiratory lesions, although typical adenoviral lesions were in other organs (Grimes et al, 1978). Examination of tissues obtained from turkeys experiencing a respiratory disease revealed intranuclear inclusions in a large number of respiratory epithelial cells including those in the lung (Cheville and Sato, 1977). Changes in epithelial cells are usually accompanied by congestion of blood vessels and by cellular infiltration of the lamina propria. Nodular deposits and diffuse lymphoid cell infiltration are common findings in the avian respiratory tract (Fig. 20). Lymphoid nodules are associated frequently with primary and secondary bronchi (Fig. 21); nodular deposits may be in the lung parenchyma in the absence of any respiratory disease (Fig. 22). These cells, regarded as normal constituents of the immune system, form the bronchial-associated lymphoid tissue (BALT). The antibody and cell-mediated responses as vital constituents of the defenses of the respiratory system were mentioned earlier. A decision as to whether lymphoid tissue is normal or increased in amount requires careful judgement and some experience with birds raised under field conditions. In some diseases, IB being a classic example, diffuse infiltration of lymphocytes and plasma cells occurs in the lamina propria (Hofstad, 1945; Purcell and McFerran, 1972), and often constitutes the major lesion seen in IB (Figs. 23, 24, 25). The epithelial cell damage is
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2671 SYMPOSIUM: RESPIRATION IN BIRDS
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FLETCHER
The presence of multiple or confluent nodules scattered throughout the lung indicates granulomatous pneumonia (Fig. 33). Histologic examination reveals central areas of caseous necrosis surrounded by multinucleated giant cells, lymphocytes and plasma cells, and finally by a layer of fibrous connective tissue. Granulomas in various stages of formation are usually encountered. Special stains may reveal the presence of fungi if a mycotic pneumonia is present or the presence of acid-fast organisms in the case of tuberculosis. (Fig. 34). Miscellaneous lesions found in the lung include: deposits of refractile debris in macrophages, melanosis, Leucocytozoon in parasitized
erythrocytes (Fig. 3 5), fat emboli in blood vessels (Brunner and Meinl, 1976), and thrombosis of branches of the pulmonary artery (Fig. 36). The relatively high incidence of airsacculitis in birds is predictable based on current knowledge of air flow patterns. Impairment of the defense mechanisms leaves the air sacs vulnerable to irritants and pathogens present in the inhaled air. Airsacculitis may also result from extension of inflammatory processes from the lung or from penetration of the air sac wall by processes involving the peritoneum or visceral organs. Structurally, the air sacs are lined by simple squamous epithelium with clumps of ciliated epithelial cells interspersed (Fig. 37a). A scant amount of connective tissue containing few blood vessels separate the lining epithelium from the mesothelial cells (Fig. 37b). Ciliated epithelial lining cells are more frequent at and near the origin of the air sacs from the lung. Normal histology at the light microscope (Cover, 1953; Fletcher et al, 1976, Lucas and Denington, 196 la,b) and electron microscope levels (Carlson and Beggs, 1973) is reported. Air sacs are subject to the same basic lesions as described for the nasal cavity, trachea, and major bronchi, with the exception that catarrhal inflammation is not a feature as goblet cells and mucous glands are not present, although metaplastic changes in air sac epithelium may result in goblet cells and mucus formation (Fletcher et al, 1976) (Fig. 38). The reactivity of the air sacs in a variety of disease conditions is discussed and illustrated in several publications (Grimes and Rosenfeld, 1972; Jungherr and Luginbuhl, 1952, Kerr and
FIG. 17. Numerous large, granular, intracytoplasmic inclusions in the epithelial cells of the trachea of a chicken are diagnostic for pox. Note the hydropic (vascuolar) degeneration and absence of cilia. FIG. 18. Hemorrhagic tracheitis is characteristic of LT in chickens. Note the accumulation of blood, mucus, and debris in the anterior portion of the trachea. FIG. 19. Examination of the exudate in the trachea of a chicken with LT reveals the presence of large intranuclear inclusions and syncytial cells. FIG. 20. Nodular aggregates of lymphoid cells are present normally in the lamina propria of the respiratory system. Note the absence of cilia on the cells covering this nodule in the trachea of a chicken. FIG. 21 Nodular deposits of lymphoid tissue are commonly associated with primary and secondary bronchi. This nodule is in the wall of a secondary bronchus and is regarded as a normal component of the bronchial associated lymphoid tissue (BALT). FIG. 22. A nodular deposit of lymphoid cells is adjacent to an arteriole in the lung parenchyma. This was considered a normal bursa-dependent lymphoid follicle. FIG. 23. A diffuse infiltration of lymphoid cells in the lamina propria of this chicken trachea. The epithelial surface appears normal. FIG. 24. Diffuse infiltration of lymphocytes and reticular cells has increased the thickness of the tracheal mucosa in this chicken suspected of having bronchitis (IB).
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artifact caused by the method of killing and subsequent processing of lung tissues. Filling of the respiratory lobule (tertiary bronchus, atria, and air capillaries) with fibrin, heterophils, macrophages, and cell debris is characteristic of Pasturella pneumonia (Figs. 28, 29, 30). Hypertrophy and hyperplasia of pneumocytes lining the tertiary bronchioles, atria, and air capillaries occurs if the irritant persists, or if the bird survives for a sufficient time. The resulting glandular type histologic pattern is called adenomatosis and is a characteristic of interstitial pneumonia (Figs. 31, 32). The ND is associated with interstitial pneumonia that may follow an earlier necrotizing lesion. Hypertrophy of smooth muscle and fibrosis, with presence of increased numbers of alveolar macrophages, are additional features of interstitial pneumonia. The absence of lung lesions in IB was considered a useful differentiating feature with ND until the discovery of several strains of IB virus capable of causing interstitial pneumonia (Winterfield et al, 1972).
SYMPOSIUM: RESPIRATION IN BIRDS
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Olson, 1967; Lucas and Denington, 1961b). Airsacculitis is characterized grossly by cloudiness, increased thickness, and exudate accumulation (Fig. 39). The anatomy of the air sacs makes this an ideal location to study the inflammatory response of birds. Congestion, edema, fibrin deposition, heterophil and monocytic cell infiltration, macrophages, lymphocytes, plasma cells, fibroblasts, and lymphoid follicle formation are expected constituents regardless of the irritant. These inflammatory changes are
revealed under near ideal conditions in ring stabilized air sacs embedded in plastic and sectioned with glass knives (Figs. 40, 41, 42, 43). Mycotic infection of air sacs may result in the formation of massive growth of mycelial elements with numerous fruiting bodies present (Fig. 44a,b). Exudate is removed by macrophages and exudate on the air sac epithelial surface may become surrounded by proliferating epithelial cells (Figs. 45, 46, 47, 48).
FIG. 33. One large and two smaller granulomas have replaced lung parenchyma in this case of granulomatous pneumonia. FIG. 34. Mycelia typical of Aspergillus sp. in a lung granuloma are revealed by this PAS strain. FIG. 35. An erythrocyte parasitized by Leucocytozoon smitbi is in the center of this photomicrograph. FIG. 36. A thrombus is in a branch of a pulmonary artery. FIG. 37. Normal air sac has a patch of ciliated respiratory epithelial cells. Normal air sac with a simple squamous epithelial lining and scanty amount of connective tissue is shown in a plastic embedded section. FIG. 38. Hyperplasia of air sac epithelium and mucus production is in an air sac from a chicken experimentally infected with Mycoplasma synoviae. Plasma cells, macrophages and fibroblasts are in the edematous connective tissue. FIG. 39. Gross features of air sacculitis include cloudiness and increased thickness. FIG. 40. Focal necrosis of epithelium, exudate accumulation, and cell infiltration of the connective tissue are early lesions in MG induced air sacculitis. FIG. 4 1 . Hyperplasia of air sac. epithelial cells follows initial necrosis and exudate accumulation in MG infected chickens. FIG. 42. A small lymphoid nodule is in the connective tissue of this MG infected air sac. Note greatly increased thickness of air sac wall. FIG. 43. A large lymphoid nodule contributes to the increased thickness of this MG infected air sac. FIG. 44a. A massive growth of mycelial elements of Aspergillus sp. fills this air sac. b) A higher magnification reveals the presence of conicial heads (fruiting bodies) of Aspergillus sp. FIG. 45. Exudate lies on the surface of the squamous epithelial cells. FIG. 46. Heterophils and macrophages are intimately associated with epithelial cells in Mycoplasma infections of the air sac. FIG. 47. Macrophages, lymphocytes, plasma cells, and blood vessels are in this exudate. The surface is covered with squamous epithelial cells. FIG. 48. A more advanced stage in removal of exudate from the air sac shows large numbers of macrophages enclosed by air sac epithelial cells.
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FIG. 25. Chronic tracheitis in the chicken is characterized by diffuse reticular cell and lymphocyte infiltration, by decreased height of epithelial cells, and by loss of cilia. Tissue was from a chicken suspected of having IB. FIG. 26. Normal lung shows the junction of a secondary bronchus with a tertiary bronchus (parabronchus). A few erythrocytes are in the lumen of the parabronchus. FIG. 27. The parabronchus, atria, and air and blood capillaries are normal in this chicken lung. The erythrocytes in the air passages are considered artifacts due to the methods of killing the bird and processing the lung. FIG. 28. Fibrin and heterophils are the major components of the exudate filling the respiratory lobule of this chicken with fowl cholera. FIG. 29. A higher magnification of the parabronchus and atria illustrate fibrinous pneumonia. FIG. 30. A large accumulation of inflammatory cells, primarily heterophils, and necrosis are features of bacterial and some viral-induced pneumonias. FIG. 31. Hypertrophy of respiratory epithelial cells lining the parabronchus and atria is a feature of interstitial pneumonia. Fibrin and cellular debris fill the air passages. FIG. 32. A glandular pattern is created in chronic pneumonia by hypertrophy of epithelial cells. This lesion is often present in ND, but is not limited to ND infection.
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