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Rhodococcus equi-associated necrotizing lymphadenitis in a llama
J. Comp. Path. 1995 Vol. 113, 85-88
SHORT PAPER
Rhodococcus equi-Associated Necrotizing Lymphadenitis in a Llama C. B. H o n g and J. M. D o n a h u e Livestock Disease Diagnostic Center, University of Kentucky, 1429 Newtown Pike, Lexington, KT 40511, USA Summary A case of Rhodococcus equi-associated necrotizing lymphadenitis in a 2-yearold male llama is described. Caseous necrosis, resembling macroscopically that seen in ovine caseous lymphadenitis, was observed diffusely in the tracheobronchial and mediastinal lymph nodes, and in an extensive lesion in the lungs. Necrosis was present to a lesser extent in the spleen and hepatic and gastric lymph nodes. Numerous bacteria-laden macrophages were present around the necrotic areas. The findings suggest that, as in cattle and pigs, the primary targets of R. equi infection in the llama are the lymphoid organs. 9 1995 Academic Press Limited
Rhodococcus equi is a Gram-positive, pleomorphic, facultative intracellular bacterium that is primarily a pathogen for equidae. It causes a fatal pneumonia with lymphadenitis in the regional lymph nodes and, on some occasions, enterocolitis in foals (McKenzie and Donald, 1979; Yager, 1987). O n rare occasions, R. equi causes a tuberculosis-like cervical lymphadenitis in pigs and cattle that may pose problems in the diagnosis of tuberculosis (Barton and Hughes, 1980; Hillidge, 1986). In camels, a Corynebacteriumsp. has been isolated from a case of metritis and C. pseudotuberculosis from caseous lymphadenitis cases (McGrane and Higgins, 1985; Thedford and Johnson, 1989). This report describes a case of necrotizing lymphadenitis, splenitis and pneumonia associated with R. equi in a llama. A 2-year-old male llama was referred to a veterinary hospital with weakness, loss of body weight, and anorexia of about 2 weeks' duration. Haematological examination revealed severe anaemia with a P C V of 15% and leucopenia with a total leucocyte count of 1 6 0 0 / m m a. A clinical diagnosis was not made, but immune deficiency complex and possible pleural effusion were suspected. The animal was sent back to the farm but died one day later. At necropsy, the animal was seen to be emaciated and the principal lesions were in the tracheobronchial lymph nodes, mediastinal lymph nodes, spleen and lungs. The tracheobronchial nodes were strikingly enlarged, up to a diameter of 11 cm. The cut surface revealed an encapsulated necrotic mass (Fig. 1), which was cheesy, dry and friable, resembling the lesions of caseous lymphadenitis in sheep. The mediastinal lymph nodes were also markedly enlarged and formed an elongated, cylindrical mass, which was about 30 cm 0021 9975/95/050085 + 0 4 $12.00/0
9 1995 Academic Press Limited
86
Fig. 1.
C . B . Hong and J. M. Donahue
Coronary section of the llama lung. The tracheobronchial lymph nodes (arrows) were markedly enlarged and necrotic.
long and 5 cm in diameter, beginning near the base of the heart and extending almost to the diaphragm. The appearance of the cut surface of the mediastinal nodes was similar to that of the tracheobronchial lymph nodes. The lymph nodes of the mesenteric, hepatic, gastric, distal cervical, prescapular, popliteal, and submandibular areas were slightly to moderately enlarged and dark red. The spleen was moderately enlarged and its cut surface contained many miliary white spots. In the lung, there was a large area of consolidation, approximately 15 cm in diameter, at the medial aspect of the left diaphragmatic lobe. The consolidated area was in contact with the enlarged mediastinal mass. The cut surface of the consolidated area had the same texture as that seen in the tracheobronchial nodes. The llama had a whipworm infestation and showed several raised haemorrhagic areas in the mucosa of the colon. Histologically, the major lesions were necrogranulomatous; they occurred diffusely in the tracheobronchia! and mediastinal lymph nodes, multifocally in the hepatic and gastric lymph nodes and in the spleen, and focally in the lungs. The normal architecture of the tracheobronchial and mediastinal lymph nodes was totally effaced. In sections stained with haematoxylin and eosin (HE) the central area showed diffuse caseous necrosis characterized by complete cytolysis and the presence of karyolytic debris and calcified globules. The peripheral areas showed necrosis bordered by layers of macrophages (Fig. 2). The macrophages were large and had abundant cytoplasm packed with small Gram-positive rods. These bacteria were easily seen in HE-stained sections. In some sections, thrombi were seen in the necrotic areas. In the spleen and hepatic and gastric lymph nodes there was moderate depletion of lymphocytes with many necrotic areas or foci, which were
Rhodococcus equi L y m p h a d e n i t i s
in a Llama
87
Fig. 2.
Tracheobronchial lymph node. Note the large area of necrosis (n) surrounded by a zone of macrophages (m). HE. x 105.
Fig. 3.
Lung section, showing bacteria-laden macrophages (arrows). Brown and Brenn modification of Gram stain, x 1050.
surrounded by bacteria-laden macrophages. Necrosis was not observed in the mesenteric, submandibular, prescapular, popliteal or distal cervical lymph nodes, but in these sites there were various degrees of depletion oflymphocytes. The pulmonary lesion was histologically similar to those seen in the tracheobronchial lymph nodes, namely large areas of necrosis surrounded by macrophages packed with bacteria (Fig. 3). In addition, a few bronchioles contained a mixture of macrophages and fungal hyphae suggestive of Aspergillus
88
C.B. Hong andJ. M. Donahue
spp. Some alveoli away from the necrotic areas also contained macrophages. Other microscopical lesions in this llama were mycotic colitis, characterized by deep ulceration, with fungal hyphae in or adjacent to the blood vessels. The Peyer's patches were necrotic and contained fungal hyphae that resembled those seen in the bronchioles. In addition, cross sections of nematodes were present in the mucosa and their ova were present in the lumen of the colon. The lungs, liver, spleen, intestine and tracheobronchial, mediastinal and mesenteric lymph nodes were cultured for aerobic bacteria on tryptic soy agar containing equine blood 5 % and on eosin methylene blue agar. After incubation for 48 h at 36~ numerous large, non-haemolytic, mucoid colonies grew on blood agar inoculated with lung, liver, spleen and lymph nodes. This Grampositive coccoid bacterium, which was catalase- and urease-positive and nonreactive in carbohydrates, enhanced the haemolysis of the [3-haemolysin of Staphylococcus aureus and was identified as R. equi. Escherichia coli in moderate numbers was also isolated from lung, liver, intestine and mesenteric lymph node. The primary site of infection in this llama was the tracheobronchial and mediastinal lymph nodes. The macroscopical appearance resembled that of caseous lymphadenitis in sheep. However, microscopical lesions in the llama differed from those of sheep in that there were large numbers of bacteria in the macrophages, and multinucleated giant cells were absent. The lesions in the llama also differed from those of foals infected with R. equi. In foals, the primary lesion is in the lungs, whereas in the llama it was in the thoracic lymph nodes. However, the presence of a large number of bacteria in the macrophages is a typical feature of R. equi infection in all species. Acknowledgments The authors thank Dr D. H. McGehee for submission of the animal. This manuscript is publication number 94-4-76 of Kentucky Agricultural Experiment Station and College of Agriculture, University of Kentucky, USA. References
Barton, M. D. and Hughes, K. L. (1980). Corynebacterium equi: a review. Veterinary Bulletin, 50, 65-80. Hillidge, C.J. (1986). Review of Corynebacterium (Rhodococcus) equi lung abscesses in foals: pathogenesis, diagnosis and treatment. VeterinaryRecord, 119, 261-264. McGrane,J.J. and Higgins, A.J. (1985). The camel in health and disease. 6. Infectious diseases of the camel: viruses, bacteria, and fungi. British VeterinaryJournal, 141, 529-547. McKenzie, R. A. and Donald, B. A. (1979). Lymphadenitis in cattle associated with Corynebacterium equi: a problem in bovine tuberculosis diagnosis. Journal of Comparative Pathology, 89, 31-38. Thedford, T. R. and Johnson, L. W. (1989). Infectious diseases of new-world camelids (NWC). Veterinary Clinics of North America: Food Animal Practice Llama Medicine, 5, 145-157. Yager, J. A. (1987). The pathogenesis of Rhodococcus equi pneumonia in foals. Veterinary Microbiology, 14, 225-232.
Received,January 27 th, 19951 Accepted, April 12th, 1995 J
SHORT PAPER
Rhodococcus equi-Associated Necrotizing Lymphadenitis in a Llama C. B. H o n g and J. M. D o n a h u e Livestock Disease Diagnostic Center, University of Kentucky, 1429 Newtown Pike, Lexington, KT 40511, USA Summary A case of Rhodococcus equi-associated necrotizing lymphadenitis in a 2-yearold male llama is described. Caseous necrosis, resembling macroscopically that seen in ovine caseous lymphadenitis, was observed diffusely in the tracheobronchial and mediastinal lymph nodes, and in an extensive lesion in the lungs. Necrosis was present to a lesser extent in the spleen and hepatic and gastric lymph nodes. Numerous bacteria-laden macrophages were present around the necrotic areas. The findings suggest that, as in cattle and pigs, the primary targets of R. equi infection in the llama are the lymphoid organs. 9 1995 Academic Press Limited
Rhodococcus equi is a Gram-positive, pleomorphic, facultative intracellular bacterium that is primarily a pathogen for equidae. It causes a fatal pneumonia with lymphadenitis in the regional lymph nodes and, on some occasions, enterocolitis in foals (McKenzie and Donald, 1979; Yager, 1987). O n rare occasions, R. equi causes a tuberculosis-like cervical lymphadenitis in pigs and cattle that may pose problems in the diagnosis of tuberculosis (Barton and Hughes, 1980; Hillidge, 1986). In camels, a Corynebacteriumsp. has been isolated from a case of metritis and C. pseudotuberculosis from caseous lymphadenitis cases (McGrane and Higgins, 1985; Thedford and Johnson, 1989). This report describes a case of necrotizing lymphadenitis, splenitis and pneumonia associated with R. equi in a llama. A 2-year-old male llama was referred to a veterinary hospital with weakness, loss of body weight, and anorexia of about 2 weeks' duration. Haematological examination revealed severe anaemia with a P C V of 15% and leucopenia with a total leucocyte count of 1 6 0 0 / m m a. A clinical diagnosis was not made, but immune deficiency complex and possible pleural effusion were suspected. The animal was sent back to the farm but died one day later. At necropsy, the animal was seen to be emaciated and the principal lesions were in the tracheobronchial lymph nodes, mediastinal lymph nodes, spleen and lungs. The tracheobronchial nodes were strikingly enlarged, up to a diameter of 11 cm. The cut surface revealed an encapsulated necrotic mass (Fig. 1), which was cheesy, dry and friable, resembling the lesions of caseous lymphadenitis in sheep. The mediastinal lymph nodes were also markedly enlarged and formed an elongated, cylindrical mass, which was about 30 cm 0021 9975/95/050085 + 0 4 $12.00/0
9 1995 Academic Press Limited
86
Fig. 1.
C . B . Hong and J. M. Donahue
Coronary section of the llama lung. The tracheobronchial lymph nodes (arrows) were markedly enlarged and necrotic.
long and 5 cm in diameter, beginning near the base of the heart and extending almost to the diaphragm. The appearance of the cut surface of the mediastinal nodes was similar to that of the tracheobronchial lymph nodes. The lymph nodes of the mesenteric, hepatic, gastric, distal cervical, prescapular, popliteal, and submandibular areas were slightly to moderately enlarged and dark red. The spleen was moderately enlarged and its cut surface contained many miliary white spots. In the lung, there was a large area of consolidation, approximately 15 cm in diameter, at the medial aspect of the left diaphragmatic lobe. The consolidated area was in contact with the enlarged mediastinal mass. The cut surface of the consolidated area had the same texture as that seen in the tracheobronchial nodes. The llama had a whipworm infestation and showed several raised haemorrhagic areas in the mucosa of the colon. Histologically, the major lesions were necrogranulomatous; they occurred diffusely in the tracheobronchia! and mediastinal lymph nodes, multifocally in the hepatic and gastric lymph nodes and in the spleen, and focally in the lungs. The normal architecture of the tracheobronchial and mediastinal lymph nodes was totally effaced. In sections stained with haematoxylin and eosin (HE) the central area showed diffuse caseous necrosis characterized by complete cytolysis and the presence of karyolytic debris and calcified globules. The peripheral areas showed necrosis bordered by layers of macrophages (Fig. 2). The macrophages were large and had abundant cytoplasm packed with small Gram-positive rods. These bacteria were easily seen in HE-stained sections. In some sections, thrombi were seen in the necrotic areas. In the spleen and hepatic and gastric lymph nodes there was moderate depletion of lymphocytes with many necrotic areas or foci, which were
Rhodococcus equi L y m p h a d e n i t i s
in a Llama
87
Fig. 2.
Tracheobronchial lymph node. Note the large area of necrosis (n) surrounded by a zone of macrophages (m). HE. x 105.
Fig. 3.
Lung section, showing bacteria-laden macrophages (arrows). Brown and Brenn modification of Gram stain, x 1050.
surrounded by bacteria-laden macrophages. Necrosis was not observed in the mesenteric, submandibular, prescapular, popliteal or distal cervical lymph nodes, but in these sites there were various degrees of depletion oflymphocytes. The pulmonary lesion was histologically similar to those seen in the tracheobronchial lymph nodes, namely large areas of necrosis surrounded by macrophages packed with bacteria (Fig. 3). In addition, a few bronchioles contained a mixture of macrophages and fungal hyphae suggestive of Aspergillus
88
C.B. Hong andJ. M. Donahue
spp. Some alveoli away from the necrotic areas also contained macrophages. Other microscopical lesions in this llama were mycotic colitis, characterized by deep ulceration, with fungal hyphae in or adjacent to the blood vessels. The Peyer's patches were necrotic and contained fungal hyphae that resembled those seen in the bronchioles. In addition, cross sections of nematodes were present in the mucosa and their ova were present in the lumen of the colon. The lungs, liver, spleen, intestine and tracheobronchial, mediastinal and mesenteric lymph nodes were cultured for aerobic bacteria on tryptic soy agar containing equine blood 5 % and on eosin methylene blue agar. After incubation for 48 h at 36~ numerous large, non-haemolytic, mucoid colonies grew on blood agar inoculated with lung, liver, spleen and lymph nodes. This Grampositive coccoid bacterium, which was catalase- and urease-positive and nonreactive in carbohydrates, enhanced the haemolysis of the [3-haemolysin of Staphylococcus aureus and was identified as R. equi. Escherichia coli in moderate numbers was also isolated from lung, liver, intestine and mesenteric lymph node. The primary site of infection in this llama was the tracheobronchial and mediastinal lymph nodes. The macroscopical appearance resembled that of caseous lymphadenitis in sheep. However, microscopical lesions in the llama differed from those of sheep in that there were large numbers of bacteria in the macrophages, and multinucleated giant cells were absent. The lesions in the llama also differed from those of foals infected with R. equi. In foals, the primary lesion is in the lungs, whereas in the llama it was in the thoracic lymph nodes. However, the presence of a large number of bacteria in the macrophages is a typical feature of R. equi infection in all species. Acknowledgments The authors thank Dr D. H. McGehee for submission of the animal. This manuscript is publication number 94-4-76 of Kentucky Agricultural Experiment Station and College of Agriculture, University of Kentucky, USA. References
Barton, M. D. and Hughes, K. L. (1980). Corynebacterium equi: a review. Veterinary Bulletin, 50, 65-80. Hillidge, C.J. (1986). Review of Corynebacterium (Rhodococcus) equi lung abscesses in foals: pathogenesis, diagnosis and treatment. VeterinaryRecord, 119, 261-264. McGrane,J.J. and Higgins, A.J. (1985). The camel in health and disease. 6. Infectious diseases of the camel: viruses, bacteria, and fungi. British VeterinaryJournal, 141, 529-547. McKenzie, R. A. and Donald, B. A. (1979). Lymphadenitis in cattle associated with Corynebacterium equi: a problem in bovine tuberculosis diagnosis. Journal of Comparative Pathology, 89, 31-38. Thedford, T. R. and Johnson, L. W. (1989). Infectious diseases of new-world camelids (NWC). Veterinary Clinics of North America: Food Animal Practice Llama Medicine, 5, 145-157. Yager, J. A. (1987). The pathogenesis of Rhodococcus equi pneumonia in foals. Veterinary Microbiology, 14, 225-232.
Received,January 27 th, 19951 Accepted, April 12th, 1995 J