Avian Histopathology Case Submissions 1980-1996: Psittacine Viral Diseases

Raymond P. Campagnoli and Kenneth S. Latimer

Department of Pathology, College of Veterinary Medicine, The University of Georgia, Athens, Georgia 30602-7388 (USA)

Abstract: This manuscript presents data on psittacine birds that were diagnosed with viral infections by the University of Georgia College of Veterinary Medicine, Department of Pathology from 1980 to 1996.

Key Words: Psittacine, Polyomavirus, Psittacine beak and feather disease virus, Pacheco’s disease, Herpesvirus, Poxvirus, Adenovirus, Virus, Viral diagnostics

All avian histopathology cases submitted since 1980 to the UGA Department of Pathology are collated in a computer database for rapid retrieval of archived information. These case submissions include the out-of-state mail-in biopsy service and case materials submitted by the College of Veterinary Medicine Small Animal Clinic. With some exceptions, most in-state samples are sent to the Athens Diagnostic Laboratory at the College of Veterinary Medicine. These submissions are not included in this database. Also, many samples of specific interest to the Psittacine Disease Research Group at the University of Georgia were submitted as research cases. These research cases are not yet part of this database. Because the specimens included in the database are diagnosed on a fee basis, the information collated has a bias toward more expensive birds; fewer owners of less expensive birds are willing to pay for histopathology.

The database entries currently are complete through 1996 and contain 4,021 birds. Distribution of orders of birds are as follows: Psittaciformes (parrots), 2,796; Passeriformes (songbirds), 466; Anseriformes (ducks & geese), 244; Ciconiiformes (flamingos, spoonbills & egrets), 81; Columbiformes (doves & pigeons), 61; Galliformes (chickens, quail & turkeys), 56; Piciformes (toucans & woodpeckers), 51; Falconiformes (raptors), 46; Struthioniformes (ratites), 36; and Cuculiformes (turacos & cuckoos), 32.

Viruses are a major cause of morbidity and mortality in companion and aviary psittacine birds.¹ Psittacine Beak and Feather Disease (PBFD), avian polyomavirus (APV), and Pacheco's Disease (PDV) are the three most commonly diagnosed viral diseases in this database.

PBFD is caused by a virus from the Circoviridae family.¹ PBFD can be diagnosed by histopathology from hematoxylin & eosin (H&E)-stained tissue sections upon the observation of characteristic nuclear or cytoplasmic viral inclusions.² Of the 217 PBFD submissions, 19 were complete necropsy cases while the remainder were skin and/or feather biopsies. Diagnosis was made primarily by histopathology. The diagnosis often was confirmed by immunoperoxidase staining (1988-1991), polymerase chain reaction (PCR, 1989-present), or DNA in situ hybridization (1991-present); however, these techniques were used earlier in research studies.

Skin and Feather Biopsies

Skin and feather biopsies were received at UGA for PBFD evaluation beginning in 1984. In 1988 the Department of Pathology began performing immunoperoxidase staining to diagnose PBFD and the number of submissions increased significantly (Fig. 1). Some tissue diagnoses were nondiagnostic because the submitted material consisted only of mature feathers that lacked viable epithelium. In 1992 the Psittacine Disease Research Group at The University of Georgia licensed PCR testing to a commercial laboratory for the diagnosis of PBFD and avian polyomavirus infection. In 1993 the number of biopsy submissions and the apparent incidence of PBFD decreased dramatically, presumably due to the diagnostic efficacy of commercial molecular testing. The overall decline in PBFD diagnoses is probably the result of different test methodology (PCR) and sensitivity, as well as a control of the disease in the pet trade.

Fig. 1

PBFD by Species

Figure 2 presents the 216 PBFD cases by species. The psittacines are grouped by genera or groups of genera, depending upon the number of birds of various type (e.g., "cockatoos"). Cockatoos are most numerous, followed by African grey parrots, lovebirds and Eclectus parrots. The species that are not listed may say as much about the nature of PBFD as those birds with the disease. Aside from a few Amazon parrots, New World psittacine species were not diagnosed with PBFD during this time period. Also, the most surprising omission was the cockatiel. There was one cockatiel that was suspect for PBFD by histopathology and immunoperoxidase staining; however, retesting by in situ hybridization was negative.

Fig. 2

PBFD by Age

Although sometimes found in older birds, PBFD is most often found in birds up to three years of age.^1,2 As indicated by the blue bars in Figure 3, the cases agree with this finding. The right hand column of the bars in Figure 3 list adult birds where the precise age was not given. The age is given for the birds at the time of disease diagnosis; some of the birds may have had PBFD for years prior to this time.

Fig. 3

Avian Polyomavirus Infection

Of the 105 psittacine APV cases, 11 cases were feather and skin biopsies while the remaining 94 cases consisted of necropsy tissues. Histologic diagnosis, using H&E-stained tissue sections, was often confirmed by DNA in situ hybridization and/or PCR. With the exception of one cockatiel, the necropsies indicated that the birds died from systemic polyomavirus infection and were not just asymptotic carriers.

Polyomavirus Infection by Species

Figure 4 indicates the proportions of the different species with APV infection. The Australian parakeet category contained three budgerigars, one Neophema species, and one Polytelis species. Macaws were the most common species submitted for histopathology with a diagnosis of APV infection. Considering macaws’ value and susceptibility to polyomavirus infection, this observation would be expected. After macaws, cockatoos are the next most numerous group of birds with APV infection. Phalen et al.³ suggest that cockatoos and most adult psittacines are extremely resistant to disease caused by polyomavirus, unless they are co-infected with PBFD virus or are otherwise immunocompromised. Only three of the 22 cockatoos also had PBFD viral infection. Although all of the cockatoos presented here were not evaluated for the presence of PBFD by molecular testing, we regularly see cockatoos with polyomavirus infection that are test-negative for PBFD by in situ hybridization. Histopathology alone is not a perfect method to diagnose PBFD and APV infections, especially when characteristic viral inclusions are not present in H&E-stained tissue sections.⁴

Fig. 4

Polyomavirus Infection by Age

Figure 5 lists the ages of the psittacines with APV infection. The age often was not reported at submission. Young birds were diagnosed with polyomavirus infection more often than adults. Of the 105 psittacines diagnosed with APV infection, nine (8.6%) also were co-infected with PBFD virus. This included two of the four older birds. Even though older birds are infected with APV less commonly, psittacines appear to be quite susceptible at an age where they would enter the pet trade. Phalen et al.³ indicate that APV causes an "unapparent infection" in conures older than 6 weeks of age. Of the seven conures with ages given, only two were less than six weeks of age and five (62%) were eight to eleven weeks of age. Phalen et al.³ also state that macaws are no longer susceptible to APV infection and disease after 14 weeks of age. In this database, 2 of 21 macaws (9.6%) had APV infection when they were older than 14 weeks of age. One of the macaws was four months of age and the other was five months of age. Thus, both macaws exceeded Phalen’s designated age range for susceptibility to APV infection. Of the six Eclectus parrots of known age, three were three months old, one was five months old, and two were six months old. The database does not list many older birds that were received as research cases during this time period.

Fig. 5

Pacheco's Disease is caused by a herpesvirus that only affects psittacine birds.¹ All 27 of the diagnoses of Pacheco’s Disease were made from necropsy tissues. The diagnosis was based upon histopathology and sometimes confirmed by DNA in situ hybridization. Although the small number of cases limits the amount of information available, the large proportion of Amazon parrots with Pacheco’s Disease is apparent in Figure 6. Also noteworthy is the fact that most deaths occurred in adult birds when the age was known (yellow bars, Fig. 3).

Fig. 6

Although a viral etiology is still suspected in the development of cloacal papillomas, the precise etiology currently is unknown. Papillomavirus has been associated with some oral papillomas of African Grey Parrots.⁵ Papillomavirus⁶ and herpesvirus⁷ are being investigated as possible causes of cloacal papillomas.

Figure 7 presents 28 psittacine birds with cloacal papillomas. Diagnoses were based on 26 biopsy specimens and two sets of necropsy tissues. One of the two necropsies also had a bile duct carcinoma, a common occurrence in birds with cloacal papillomas.^1,5 Thirteen of the birds with papillomas were of known age. One was seven weeks old, and the rest were two to ten years old.

Fig. 7

Four cases of avian pox were reported, all in different genera of New World psittacine birds. This observation would be expected because poxvirus is most commonly found in New World psittacine birds. It also has been reported in lovebirds, budgerigars, and lories.^1,8

One case of avian adenovirus also was reported in an African grey parrot.

Acknowledgement

Ashley Ayoob for data entry.

1. Ritchie BW: Avian Viruses: Function and Control. Winger's Publishing, Inc., Lake Worth, FL, 1995.

2. Latimer KS, Rakich PM, Niagro FD, Ritchie BW, Steffens WL, Campagnoli RP, Pesti DA, Lukert PD: An Updated Review of Psittacine Beak and Feather Disease. J Assoc Avian Vet 5:211-22, 1991.

3. Phalen DN, Radabaugh, CS Dahlhausen: Avian polyomavirus: More pieces to the puzzle. Proc Annu Conf Assoc Avian Vet, 1998, pp.151-156.

4. Campagnoli RP, Latimer KS: Improved diagnosis of psittacine viral diseases with DNA in situ hybridization. International Virtual Conferences in Veterinary Medicine: Diseases of Psittacine Birds, 1998.
http://www.vet.uga.edu/IVCVM/1998/campagnoli/campagnoli.htm

5. Latimer KS, Niagro FD, Rakich PM, Campagnoli RP, Ritchie BW, McGee BW: Investigation of parrot papillomavirus in cloacal and oral papillomas of psittacine birds. Vet Clin Path 26:158-163, 1997.

6. Bonda M, Rose RC, Shivaprasad HL: Western blot immunoassay and immunohistochemistry supporting a papillomavirus as the etiology of a cloacal papilloma/adenomatous polyp in a hyacinth macaw. Proc Annu Conf Assoc Avian Vet, 1998, pp.49-54.

7. Tomaszewski E, Phalen DN, Wilson VG: Synchronicity, papillomas, and herpes disease. Proc Annu Conf Assoc Avian Vet, 1999, pp.219-221.

8. Helga Gerlach H, Ramis AJ, Enders F, Casares M, Truyen U: Avian Pox in Lories (Neopsittacus sp.): A Case Report. International Virtual Conferences in Veterinary Medicine: Diseases of Psittacine Birds, 1998.
http://www.vet.uga.edu/ivcvm/1998/gerlach2/gerlach2.htm