Atypical Herpesvirus Infection Associated with Primary Respiratory Disease in Brown-throated Conures (Aratinga pertinax)
Mary L. Gray, Kenneth S. Latimer, and W. L. Steffens
Department of Pathology, College of Veterinary Medicine, The University of Georgia, Athens, Georgia 30602-7388 (USA)
Abstract. Ten of 250 conures housed in an aviary developed acute respiratory distress and abnormal vocalization. These birds died shortly after clinical signs developed. The primary histologic findings were proliferative bronchitis with mild necrosis and syncytial cells. Type A nuclear inclusion bodies were observed in bronchial epithelial and syncytial cells. Microscopic lesions in the liver included many nuclear inclusions, but very mild hepatocellular necrosis. Electron microscopy demonstrated nuclear and cytoplasmic particles with typical morphology of herpesvirus. DNA in situ hybridization demonstrated homology between this respiratory herpesvirus and Pacheco's parrot disease virus (PDV). This cluster of cases illustrates an unusual tissue tropism of herpesvirus for the lower respiratory tract similar to that observed in infectious laryngotracheitis of chickens.
Key Words: Avian, Psittacine, Brown-throated Conure, Aratinga pertinax, Herpesvirus, Pacheco's parrot disease, Respiratory tract disease
Introduction
Herpesviruses are enveloped virions that measure approximately 120 to 200 nm in diameter.1 The capsid has icosahedral symmetry. The genome consists of linear double-stranded DNA ranging from 120 to 220 kbp in length. Herpesviruses replicate in the nucleus and acquire their envelope by budding through the nuclear membrane.1 Viral subfamilies include alphaherpesvirinae, betaherpesvirinae, and gammaherpesvirinae. Members of the alphaherpesvirinae have a moderately wide host range and are associated with rapid viral replication, cytolysis, and ability to establish latent infection.1 An example of this viral family is avian herpesvirus 1 that causes infectious laryngotracheitis in chickens.
Herpesvirus infection in psittaciform birds is usually manifested as Pacheco’s parrot disease, which is characterized by massive hepatic necrosis and death.2 However, herpesvirus infections infrequently may be associated with respiratory disease and the etiologic agents have been designated Amazon tracheitis virus and Parakeet herpesvirus.2-4 This case report describes respiratory herpesvirus infection in a group of Brown-throated Conures (Aratinga pertinax).
Case Report
Ten of 250 conures housed in an aviary were acutely affected by signs of respiratory disease including dyspnea and abnormal vocalization that was described as a "barking" sound. Following a short duration of clinical signs, all 10 affected birds died within a short time period. One of the dead birds was necropsied.
Necropsy revealed no significant gross findings, and the local veterinarian submitted tissues fixed in 10% neutral-buffered formalin for histologic examination. Tissues were processed routinely, embedded in paraffin wax, sectioned at 3 µm, stained with hematoxylin and eosin, and examined. Microscopically, sections of lung had a hyperplastic bronchial epithelium that was thrown into folds. Scattered epithelial cell necrosis was present. Numerous syncytial cells within the bronchial lining and airway lumina contained type A eosinophilic nuclear inclusions (Fig. 1). Occasional syncytial cells with nuclear inclusions were observed lining the air sacs. Inclusions also were observed in hepatocytes in association with mild multifocal hepatocellular necrosis. Mild multifocal splenic necrosis also was present but nuclear inclusions were rare.
 |
| Fig. 1. Brown-throated Conure, lung, atypical herpesvirus infection, H&E stain. Syncytium with nuclear inclusions is present (center). |
Additional 2 mm3 portions of lung were processed for ultrastructural study. Tissue cubes were post fixed in osmium tetroxide, dehydrated in a series of graded alcohols, and embedded in Spurr plastic. Ultrathin sections were stained with uranyl acetate and lead citrate and examined by transmission electron microscopy. Examination of the pulmonary tissues revealed non-enveloped and enveloped viral particles typical of herpesvirus. Associated with the cytoplasmic viral particles were aggregates of tubular structures with a clear core, similar to that previously described in PDV infections (Fig. 2 & 3).4,5
 |
 |
| Fig. 2. Brown-throated Conure, lung, atypical herpesvirus infection, electron micrograph. Degenerating respiratory epithelial cell contains intranuclear cluster of herpesvirus particles. |
Fig. 3. Brown-throated Conure, lung, atypical herpesvirus infection, electron micrograph. Herpesvirus particles from a disrupted nucleus. |
DNA in situ hybridization was performed on paraffin embedded tissues using an oligonucleotide probe that detected conserved nucleic acid sequences of Pacheco's herpesvirus.6 The hybridization procedure was weakly positive, indicating that the herpesvirus causing respiratory disease was similar (but not identical) to the herpesvirus responsible for Pacheco’s parrot disease (Fig. 4).
 |
| Fig. 4. Brown-throated Conure, liver, atypical herpesvirus infection, DNA in situ hybridization (left) and H&E stain (right). Syncytia (right) with nuclear inclusions from bile duct epithelium contain herpesvirus nucleic acid (left center). |
Discussion
The major clinical signs of a short duration of respiratory distress followed by sudden death is attributable to the lesions found in the lower respiratory airways of this bird. Epithelial cell hyperplasia, syncytia, detritus, and secretions probably interfered with gas exchange within the respiratory tract resulting in hypoxia / anoxia and death.
Pacheco's parrot disease affects many species of psittacine birds and is caused by psittacid herpesvirus 1. Clinical signs, if present, are usually non-specific and include anorexia, depression, diarrhea, and ruffled feathers. Alternatively, death may occur suddenly in the absence of premonitory signs. Microscopically, Pacheco’s parrot disease is characterized by massive hepatic and splenic necrosis with formation of nuclear inclusion bodies. However, with a longer duration of clinical illness, microscopic lesions may reflect a systemic disease manifested by nuclear inclusions in a wide variety of other tissues including kidney, intestine, ovary, endocrine organs, cloaca, and lung. 5,7-9 Signs of upper respiratory disease, such as sinusitis and mild nasal discharge, occasionally may be observed. 3,4,7 Within the lung, nuclear inclusions have been observed in epithelial and syncytial cells of the larynx, trachea and bronchi. 5,9 In one report, a sulfur-crested cockatoo with primary signs of respiratory and neurologic disease had hypertrophic air sac epithelial cells that contained nuclear eosinophilic inclusions. Inclusions were lacking in hepatocytes.
Other herpesviruses of psittacine birds with a tropism for the respiratory tract have been described, but apparently are not related to PDV. These include a respiratory herpesvirus infection of parakeets5,10 and Amazon tracheitis virus.11 In the conure of this report, the microscopic lesions within the respiratory tract are similar to those described in parakeets. In contrast, Amazon tracheitis has severe hemorrhagic or fibrinonecrotic inflammation that primarily affects the upper respiratory tract 3 and is similar to changes observed in chickens with infectious laryngotracheitis of chickens.12
The disease in this conure is unusual in that it represents a sporadic outbreak herpesvirus-induced respiratory disease of low morbidity but high mortality. Although normally characterized by hepatic and splenic necrosis, unusual variants of PDV have been described.13 An unusual outbreak of erosive and necrotizing herpesvirus-induced esophagitis has been described in a group of parrots. In this report, the authors speculated that the disease may have been an unusual manifestation of Pacheco's disease, due to one of at least three serologically distinct herpesviruses that are recognized as causing Pacheco's disease in psittacines.13,15,16 This case report may be analogous in representing a variation in tissue tropism among herpesvirus strains that are recognized as PDV. Ultimately, nucleic acid sequence data will be necessary to clarify the relationships of these viral subgroups and their variable tissue tropism.
References
1. Fenner F, Bachmann PA, Gibbs EPJ, Murphy FA, Studdert MJ, White DO: Veterinary Virology. Academic Press, Inc. , San Diego, 1987, pp. 339-373.
2. Ritchie BW: Avian Viruses: Function and Control. Wingers Publishing, Inc. , Lake Worth, Florida, 1995, pp. 171-222.
3. Gerlach H: Viruses. In: Ritchie BW, Harrison GJ, Harrison LR (eds): Avian Medicine: Principles and Application. Wingers Publishing, Inc. , Lake Worth, Florida, 1994, pp. 874-885.
4. Simpson CF, Hanley JE: Pacheco's Parrot Disease of Psittacine Birds. Avian Dis 21:209-219, 1977.
5. Tsai SS, Park JH, Hirai K, Itakura C: Herpesvirus infections in psittacine birds in Japan. Avian Pathol 22:141-156, 1993.
6. Ramis A, Latimer KS, Niagro FD, Campagnoli RP, Ritchie BW, Pesti D: Diagnosis of psittacine beak and feather disease (PBFD) viral infection, avian polyomavirus infection, adenovirus infection and herpesvirus infection in psittacine tissues using DNA in situ hybridization. Avian Pathol 23:643-657, 1994.
7. Panigrahy B, Grumbles LC: Pacheco's disease in psittacine birds. Avian Dis 28:808-812, 1984.
8. Gómes-Villamandos JC,Mozos E, Sierra MA, Fernández A, Díaz F: Mortality in psittacine birds resembling Pacheco's disease in Spain. Avian Pathol 20:541-547, 1992.
9. Ramis A, Tarrés J, Fondevila D, Ferrer L: Immunocytochemical study of the pathogenesis of Pacheco's parrot disease in budgerigars. Vet Microbiol 52:49-61, 1996.
10. Helfer DH, Schmitz JA, Seefeldt SL, Lowenstine L: A new Viral Respiratory Infection in Parakeets. Avian Dis 24:781-783, 1980.
11. Winterroll G, Gylstorff I: Schwere durch Herpesvirus Verursachte Erkrankung des Respirationsappartes bei Amazonen. Berliner und Munchener Tierarztliche Wochenschrift 92:277-288, 1979.
12. Purcell DA: Histopathology of laryngotracheitis in fowl infected by an aerosol. J Comp Pathol 81:423-441, 1971.
13. Krautwald ME, Kaleta EF, Foerster S, Herbst W, Schildger B, Spenkoch-Piper H: Heterogenicity of Pacheco's disease and its causative agents. Proc Assoc Avian Vet, 1988, pp. 11-21, 1988.
14. Cheeseman MT, Riddell C: Esophagitis due to a herpesvirus associated with mortality in a psittacine aviary. Avian Dis 39:658-660, 1995.
15. Kaleta EF: Herpesvirus of birds -- a review. Avian Pathol 19:193-211, 1990.
16. Horner RF, Parker M, Abrey ANS, Kaleta, EF, Prozesky: Isolation and identification of psittacid herpes-virus 1 from imported psittacines in South Africa. J South African Vet Assoc 63:59-62, 1992. This Page Last Updated May 15, 1998 |