JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
November 2021
D-V13
Signalment (JPC #1712658): Adult cockatoo
HISTORY: One of several psittacine birds in a pet shop that died after exhibiting acute, profuse, green, watery diarrhea.
HISTOPATHOLOGIC DESCRIPTION: Liver: Affecting 90% of the liver are multifocal to coalescing, random foci of hepatocellular necrosis characterized by disruption and loss of hepatic architecture with replacement by abundant eosinophilic cellular and karyorrhectic debris, few heterophils, and individualized hepatocytes with hypereosinophilic cytoplasm and nuclear pyknosis, karyolysis or karyorrhexis. The few remaining hepatocytes are swollen with pale, vacuolated cytoplasm (degeneration). Approximately 90% of the viable hepatocytes contain round, 4-8 um diameter, eosinophilic intranuclear viral inclusion bodies that marginate the chromatin and completely fill the nucleus or are surrounded by a clear halo. Randomly, there are few multinucleate hepatocytes that contain 8-10 karryorhectic or karryolytic nuclei (viral syncytia). Multifocally, there are periportal aggregates of low numbers of lymphocytes and fewer heterophils.
MORPHOLOGIC DIAGNOSIS: Liver: Hepatocellular necrosis and degeneration, acute, diffuse, severe, with eosinophilic intranuclear viral inclusion bodies and viral syncytia, Cockatoo (Cacatua galerita), avian.
ETIOLOGIC DIAGNOSIS: Alphaherpesviral hepatitis
CAUSE: Psittacid herpesvirus 1 (PsHV-1)
CONDITION: Pacheco's disease
SYNONYMS: Herpesvirus of psittacine birds, Amazon parrot herpesvirus, Pacheco's parrot disease virus
GENERAL DISCUSSION:
- Herpesviruses are large (120-200nm), enveloped, and contain a single linear molecule of dsDNA in an icosahedral capsid
- PsHV-1 is an alphaherpesvirus that causes an acute, systemic disease with high mortality in psittacine birds and has four distinct genotypes and several serotypes
- PsHV-1 genotypes 1, 2, and 3 cause mucosal papillomas of the oral, cloacal and upper digestive mucosae, termed internal papillomatosis of parrots (IPP)
- PsHV-1 genotype 3 can cause biliary and pancreatic duct carcinomas (see D-N09)
- Occurs in individual birds, or as outbreak
- There is pronounced species variation in mortality rate; cockatoos and Amazon parrots are highly susceptible and often die suddenly
- Conures, specifically Nanday and Patagonian, are often implicated as carriers; however, any bird that recovers should be considered a carrier due to latency
- Causes massive hepatic necrosis and splenic necrosis; pancreas, crop and intestine second most likely locations for lesions; less commonly affects kidney, endocrine organs, and cloaca; unlikely to affect respiratory system
PATHOGENESIS:
- Not well defined, but believed to be similar to that of other herpesviruses
- Virus shed in feces of asymptomatic carriers and clinically ill birds
- Inhalation and ingestion of viral particles
- Viremia leads to parenchymal necrosis in liver, spleen, and other organs
- Incubation period and clinical course are shorter (2-6 days) in smaller species than in larger parrots (5 days to 5 weeks or more)
TYPICAL CLINICAL FINDINGS:
- Spontaneous death
- Nonspecific - weakness, lethargy, anorexia, ruffled plumage, and diarrhea
- Less common - sinusitis, nasal discharge, convulsions or tremors of the head, neck, wings, and/or legs
- Dyspnea, polyuria, and uremia from secondary infection of lung or kidney
TYPICAL GROSS FINDINGS:
- May be none
- Liver normal in size or enlarged/friable (subacute cases)
- Yellow-gray mottling ± hemorrhage in liver
- Scattered foci of necrosis in the liver and spleen ± splenomegaly
- Petechiae on serous membranes
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Liver – multifocal to coalescing random areas of acute necrosis with minimal inflammation (consistent finding)
- Eosinophilic to lightly basophilic intranuclear inclusion bodies, rarely syncytial cells
- Splenic and pancreatic necrosis ± intranuclear inclusion bodies
- Intestine – mucosal necrosis
- Crop – multifocal ballooning degeneration of the basal cell layer leading to erosions, ulcers and rare vesicles
- Thymus – lymphoid depletion, syncytial cells
- Ovary – syncytial cells with intranuclear inclusions (Abdul-Aziz, Avian Histopathology, 2016)
ULTRASTRUCTURAL FINDINGS:
- Dense core 120-200 nm icosahedral virions that acquire an envelope by budding through the nuclear membrane
ADDITIONAL DIAGNOSTIC TESTS:
- Virus isolation, polymerase chain reaction (PCR)
- Cytology: impression smears of liver may contain hepatocytes with viral inclusions
DIFFERENTIAL DIAGNOSIS:
For hepatic necrosis:
- Psittacosis (Chlamydopia psittaci; D-B12): Random areas of lymphoplasmacytic and/or histiocytic hepatitis often with necrosis and intrahistiocytic organisms
- Lead poisoning (especially in single, pet birds; U-T02): Necrosis with occasional acid fast eosinophilic intranuclear inclusions (more numerous in renal tubular epithelium)
- Avian polyomavirus (Budgerigar fledgling disease; U-V08, I-V03): Necrosis; glassy intranuclear inclusions
- Avian adenovirus 1 (Inclusion body hepatitis; D-V20): Diffuse hepatocellular degeneration, multifocal necrosis with eosinophilic to amphophilic INIB’s; inflammatory infiltrates
Other psittacid alphaherpesviruses:
- Psittacid herpesvirus 2 has been isolated from 3 African grey parrots (isolated from papillomas in 2 and the cloaca of the 3rd one that was apparently healthy); significance is unknown
COMPARATIVE PATHOLOGY:
Alphaherpesviruses that cause similar signs and lesions in other captive birds:
- Anatid herpesvirus 1 (D-V10): Duck virus enteritis
- Crane herpesvirus (CrHV)
- Columbid herpesvirus 1: Pigeons
- Falconid herpesvirus 1: Falcons
- Ciconiid alphaherpesvirus 1: Fatal infection recently identified in captive juvenile white stork (Ciconia ciconia) (Mack, J Vet Diagn Invest. 2020)
Abortigenic alphaherpesviruses causing fetal/newborn hepatic necrosis:
- Equid herpesvirus 1: Equine herpes viral abortion, myeloencephalitis, rhinopneumonitis
- Bovine herpesvirus 1: Infectious bovine rhinotracheitis
- Caprine herpesvirus 1: Vulvovaginitis or balanoposthitis
- Canid herpesvirus 1: Hemorrhagic disease of pups
- Felid herpesvirus 1: Feline viral rhinotracheitis
- Suid herpesvirus 1: Pseudorabies/Aujeszky’s Disease
Other significant alpha herpesviruses:
- Gallid herpesvirus 1: Avian infectious laryngotracheitis
- Gallid herpesvirus 2: Marek's disease
- Psittacid herpesvirus 1: Pacheco’s disease
- Psittacid herpesvirus 3: Respiratory disease in parrots
- Bovine herpesvirus 2: Bovine mammillitis/pseudo-lumpy skin disease
- Bovine herpesvirus 5: Bovine herpes encephalitis
- Equid herpesvirus 3: Equine coital exanthema
- Equid herpesvirus 4: Equine rhinotracheitis
- Macacine herpesvirus 1: B virus of macaques; lethal in humans
- Macacine herpesvirus 9: Simian varicella virus
- Saimiriine herpesvirus 1: Herpes tamarinus/Herpes T of squirrel monkeys; lethal in owl monkeys
- Human herpesvirus 1 & 2: Herpes simplex; lethal in owl monkeys
REFERENCES:
- Abdul-Aziz T, Fletcher O, Barnes H. Avian Histopathology. 4th ed. Jacksonville, FL: American Association of Avian Pathologiests, Inc; 2016: 589.
- Brown DL, Van Wettere AJ, Cullen JM. Hepatobiliary system and exocrine pancreas. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:441.
- Gabor M, Gabor LJ, Peacock L, Srivastava M, Rosenwax A, Phalen D. Psittacine herpesvirus 3 infection in the eclectus parrot (Eclectus roratus) in Australia. Vet Pathol. 2013; 50(6): 1053-7.
- Mack ZE, Bonar CJ, Garner MM, Connolly MJ, Childress AL, Wellehan JFX, Jr. A novel herpesvirus in a white stork associated with splenic and hepatic necrosis. J Vet Diagn Invest. 2020;32: 471-475.
- Schmidt RE, Reavill DR, Phalen DN. Pathology of Pet and Aviary Birds. 2nd Philadelphia, PA: John Wiley & Sons, Inc.; 2015:29-30, 96-98; 183.
- Tomaszewski EK, Wigle W, Phalen DN. Tissue distribution of psittacid herpesviruses in latently infected parrots, repeated sampling of latently infected parrots and prevalence of latency in parrots submitted for necropsy. J Vet Diagn Invest 2006; 18: 536-544.
