JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
August 2021
D-B12

 

SIGNALMENT (JPC #1946537):  Tissue from a 4-year-old yellow-naped Amazon parrot

HISTORY: The bird became progressively docile, passive, and depressed.

MICROSCOPIC DESCRIPTION:  Liver:  Multifocally there are random, irregularly round, variably sized (up to 1 mm diameter) areas of lytic necrosis characterized by loss of hepatic architecture with replacement by eosinophilic cellular and karyorrhectic debris admixed with heterophils and hemorrhage, fibrin, and edema and surrounded by multinucleated giant cells (foreign body and Langhan’s type), epithelioid macrophages, and fewer lymphocytes and plasma cells.  Multifocally, there are also random foci of coagulative necrosis characterized by retention of architecture with loss of differential staining. Multifocally, few random hepatocytes and Kupffer cells contain intracytoplasmic, amphophilic to gray, indistinct, granular, coccoid bacteria.  Hepatocytes surrounding areas of necrosis often are swollen with vacuolated cytoplasm (degeneration) and are dissociated from hepatic cords.  Diffusely, sinusoids are moderately expanded by macrophages, heterophils, and lymphocytes.  Multifocally hepatocytes are mildly vacuolated and contain small aggregates of brown, granular pigment (bile, hemosiderin, and/or lipofuscin).  There is a mild increase in bile duct profiles; bile ducts are multifocally mildly ectatic and lined by hyperplastic epithelium characterized by piling up, mild anisokaryosis, and increased mitotic activity (regeneration).  Portal areas are expanded by increased clear space (edema) and contain dilated lymphatic vessels.

 

MORPHOLOGIC DIAGNOSIS: Liver: Hepatitis, necrotizing, heterophilic, and granulomatous, multifocal to coalescing, moderate, with mild bile duct hyperplasia and intracellular bacteria, yellow-naped Amazon parrot (Ochrocephala auropalliate), avian.

ETIOLOGY:  Chlamydia psittaci

 

ETIOLOGIC DIAGNOSIS:  Chlamydial hepatitis

 

CONDITION:  Avian chlamydiosis (birds); psittacosis (humans)

 

GENERAL:

• Gram negative obligate intracellular bacteria
• Synonyms: Parrot Fever, Ornithosis (non-psittacines)
• The family Chlamydiaceae contains a single genus: Chlamydia, which includes 11 species (*=have been isolated from birds)
  • C. muridarum (mouse, hamster)
  • C. suis (swine)
  • C. trachomatis (humans)
  • C. abortus* (ruminant)
  • C. caviae (Guinea pig)
  • C. felis (feline)
  • C. pecorum (ruminants, swine, koalas)
  • C. pneumoniae (human, marsupial, and amphibious origin)
  • C. psittaci* (avian serovar)
  • C. avium*
  • C. gallinacean*
• C. psittaci has 8 fairly host specific serovars: 6 in birds and 2 in mammals
  • Serovars A and F – Psittaciformes (especially cockatiels & budgerigars)
  • Serovar B – Columbiformes (pigeons, doves), galliformes (broiler chickens) *low virulence
  • Serovar C – Anseriformes (ducks, geese, swans)
  • Serovar D – Galliformes (turkeys, broiler chickens) *high virulence
  • Serovar E – Columbiformes and Galliformes (pigeons, turkeys)

• Zoonotic and reportable - take precautions during necropsy; dead birds should be immersed in disinfectant due to highly infectious nasal/fecal secretions
• Unique morphology and biphasic life cycle with four morphologically distinct forms
• Elementary body (EB): infectious form that enters the cell
• Reticulate body (RB): intracellular, metabolically active, replicating form that synthesizes DNA, RNA, and protein, and divides by binary fission
• Intermediate body (IB): morphologic characteristic between EB and RB
• Persistent aberrant body (PAB): non-replicating bodies emerge during times of stress (i.e. antibiotics), revert to RB when stressor removed, associated with long-term infection
• Organisms have tropism for coated pits on epithelial cells of the respiratory tract

 

PATHOGENESIS:

• Inhalation or ingestion of contaminated feather dust or feces > multiply in lung, air sacs and pericardial sac within 4 hours > bacteremia within 48 hours > portals of exit (cloaca & nasal turbinates)
• Reproductive cycle: EBs attach to host cell membrane at coated pit > internalization into host cell via invagination of the host cell membrane > inhibition of phagosome - lysosome fusion > differentiation into RB > replication by binary fission > reorganization, through IBs, into new EBs > release from host cell (cell lysis or exocytosis)
• Depend on eukaryotic cells for energy (therefore obligate intracellular)
  • Mitochondria are often found in juxtaposition to the psittaci inclusion
  • RBs may parasitize mitochondrial ATP via a chlamydial ATP-ADP translocase

 

TYPICAL CLINICAL FINDINGS: (in birds)

• Diarrhea and excretion of green to yellow-green urates
• Severely affected birds may become anorectic and produce sparse, dark green droppings, followed by emaciation, dehydration, and death
• Recurrent episodes of illness culminating in chronic debilitation
• Subclinical infections common, especially in cockatiels (Schmidt 201.)

 

TYPICAL GROSS FINDINGS:

• Hepatomegaly and splenomegaly +/- necrotic foci; spleen may be congested or pale (due to increased histiocytes and plasma cells)
• Fibrinous air sacculitis, pericarditis and peritonitis
• Systemic disease: subcutaneous hemorrhage, meningitis, conjunctivitis, pancreatitis, orchitis, epididymitis, enterocolitis with diffuse mucosal necrosis
• Associated with atherosclerosis in psittacines

 

TYPICAL MICROSCOPIC FINDINGS:

• Liver
  • Acute: Multifocal coagulation/lytic necrosis
  • Chronic: Granulomas, portal fibrosis, bile duct hyperplasia
  • Kupffer cell hyperplasia
  • Bacteria within hepatocytes and/or macrophages
• Spleen: Multifocal necrosis, histiocytosis, lymphoid depletion, plasmacytosis,
• Air sacs: Fibrinous exudate with heterophils and macrophages, some containing bacteria
• Inclusion body-like microcolonies may be seen in affected cells of many organs, particularly in serosal membranes; may be better visualized through impression smear of fresh tissues

 

ULTRASTRUCTURE:

• Elementary body (EB): Spherical, 0.2-0.3 um body composed of a highly electron dense nucleoid at the periphery, clearly separated from the electron dense cytoplasm
• Reticulate body (RB): 0.5-2.0 um, binary fission characterized by “hour-glass” profiles
• Intermediate body (IB): 0.3-1.0 um diameter bodies with a central electron dense core, radially arranged nucleoid fibers surrounding the core and tightly packed cytoplasmic granules at the periphery
• Persistent aberrant body (PAB): small inhomogeneous reticulate bodies
• Inside the host cell, organisms are present within endosomes

 

ADDITIONAL DIAGNOSTIC TESTS:

• Nucleic acid amplification tests (real time PCR, DNA microarray-based detection, DNA sequencing) preferred method; PCR of host-specific serovar may help pinpoint source of infection
• Isolation of the organism from tissue, feces, or swabs still most common test, but some serovars difficult to grow and hazardous to laboratory personnel (BSL3)
• Special stains (cytology or histology): Giemsa (dark purple), Gimenez, modified Gimenez (PVK stain) red, Warthin-Starry, or Macchiovello; Gram stain of little value because the chlamydial cell wall lacks peptidoglycan
• Visible on phase contrast and dark-field illumination microscopy
• EM, immunofluorescence, ELISA, immunohistochemistry, strain-specific monoclonal antibodies available
• Serology limited use due to high prevalence in certain populations and long term persistence

 

DIFFERENTIAL DIAGNOSIS:

• Hepatic necrosis in psittacine birds:
  • Pacheco’s disease (alphaherpesvirus): Intranuclear hepatocellular inclusions
  • Polyomavirus (Budgerigar Fledging Disease): Glassy intranuclear inclusions
  • Salmonellosis (Salmonella ) and colibacillosis (E. coli): Hepatocellular necrosis with necrogranulomas
  • Reoviral hepatitis: Hepatocellular necrosis without inclusion bodies
  • Lead toxicosis: Eosinophilic, acid-fast, intranuclear inclusions
  • Mycobacteriosis (MAIC): Acid-fast, intracellular bacilli
• In poultry, similar signs and lesions may be caused by the following diseases:
  • Fowl cholera (Pasteurella multocida)
  • Mycoplasmosis: gallisepticum (chronic respiratory disease/infectious sinusitis of turkeys); M. meleagridis (air sacculitis)
  • Colibacillosis ( coli)
  • Salmonellosis - Typhimurium (paratyphoid); S. Pullorum (Pullorum disease); S. Gallinarum (fowl typhoid)
  • Adenovirus: Hemorrhagic enteritis of turkeys

 

COMPARATIVE PATHOLOGY:

• Humans: Zoonotic disease; influenza-like symptoms; pneumonia
• Ruminants: abortus: sporadic bovine encephalomyelitis, pneumonia, polyarthritis of calves, conjunctivitis, and sporadic abortions, including ovine enzootic abortion (necrotizing placentitis in ewe, hepatic necrosis in fetus)
  • Has been reported to cause bronchopneumonia in experimentally challenged calves
• Cats: C. felis: persistent conjunctivitis; one case of fatal C. psittaci infection in kitten
• Guinea pigs: C. caviae: Guinea Pig Inclusion Conjunctivitis (GPIC); can also cause rhinitis and genital tract infections
• Dogs: Keratoconjunctivitis, bronchopneumonia, and reproductive problems (limited number of case reports)
• Horses: psittaci identified in cases of abortion, premature death of foals in Australia, one case in Switzerland (Bauman 2020)
• Chlamydia pecorum: causes enteritis in calves <10 days old (see N-B05 for encephalitis manifestations of sporadic bovine encephalomyelitis)
  • Intestinal tract is the natural habitat and may be the portal of entry for systemic infections resulting in hepatitis, arthritis, encephalitis, and pneumonia
  • Enteritis in calves – even “asymptomatic” animals have a 48% reduction in growth rate; these animals had conjunctival hyperemia, increased serum globulin, and decreased plasma albumin and insulin-like growth factor-1 suggesting that these asymptomatic infections may be the reason why in some calves feed-additive antibiotics aid in growth promotion
  • Pathogenesis: ingestion > adsorbs to brush border of enterocytes at the tips of intestinal villi (these cells are in G1 which is what Chlamydia requires for multiplication) > enters the cell via pinocytosis > multiplication in the supranuclear region > host cell degenerates > released into gut lumen and lamina propria > infects endothelial cells of lacteals, Goblet cells, enterochromaffin cells, and macrophages > systemic spread
  • Gross lesions are most common in the terminal ileum; mucosal edema, congestion, petechiae, +/- ulceration
  • Histologically, chlamydial inclusions are demonstrated within host cell cytoplasm using: Giemsa, Jimenez, Macchiavello or immunoperoxidase staining; crypts may be dilated with inflammatory exudate; lymphoid follicles in Peyer’s patches are necrotic
• Chlamydia suis: associated with conjunctivitis, rhinitis, pneumonia, enteritis, reproductive disorders, and asymptomatic infections in swine
  • Recognized in the intestinal mucosa of normal and clinically ill swine
  • Gnotobiotic pigs experimentally inoculated with suis had moderate diarrhea, anorexia, weakness, and body weight loss.
  • Microscopically, there was necrosis and exfoliation of enterocytes on the apical half of villi leading to villous atrophy in the distal jejunum and ileum; there was also mild lymphangitis and perilymphangitis
  • Chlamydial organisms replicated within small intestinal villus enterocytes, large intestinal enterocytes, lamina propria, submucosa, and mesenteric lymph nodes

 

REFERENCES:

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