JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

October 2023

P-V11

 

Signalment (JPC #4057682): Adult Barnevelder hen, Gallus gallus, avian

 

HISTORY: Hens in a “backyard” flock developed respiratory distress following close contact with ducks overnight in a very small, poorly ventilated accommodation. The ducks and geese remain unaffected. Clinical signs included anorexia, depression, mouth breathing, nasal discharge, coughing, and gasping.

 

HISTOPATHOLOGIC DESCRIPTION: Trachea:  The tracheal mucosa is diffusely eroded and necrotic with an abundant inflammatory infiltrate composed of numerous lymphocytes and macrophages admixed with fewer plasma cells, heterophils, eosinophilic fibrillar material (fibrin), increased clear space (edema), and hemorrhage. This inflammatory infiltrate also diffusely expands the submucosa.  Within the tracheal mucosa, respiratory epithelial cells multifocally contain up to fifteen nuclei (viral syncytial cells). Syncytial cell nuclei often contain a single central, 3 um diameter, round, eosinophilic, intranuclear viral inclusion surrounded by a clear halo with peripheralized chromatin.   Overlying the mucosa is an exudate composed of eosinophilic cellular and karryorhectic debris (necrosis) admixed with hemorrhage, fibrin, previously described inflammatory cells, and sloughed viral syncytial cells (diphtheritic membrane).

MORPHOLOGIC DIAGNOSIS: Trachea: Tracheitis, fibrinous and necrotizing, acute, diffuse, severe, with epithelial viral syncytial cells and intranuclear viral inclusion bodies, Barnevelder chicken, avian.

ETIOLOGIC DIAGNOSIS: Alphaherpesviral tracheitis

 

CAUSE: Avian infectious laryngotracheitis virus (Gallid herpesvirus type 1)

 

CONDITION: Infectious Laryngotracheitis; Fowl Diphtheria

 

GENERAL DISCUSSION: 

• Infectious laryngotracheitis (ILT) is an acute, highly contagious disease of chickens characterized by respiratory distress, coughing, expectoration of bloody, mucoid exudate, and high morbidity (50-70%) and considerable mortality (10-20%).
• Causative agent is Gallid herpesvirus type 1 (GaHV-1), genus Iltovirus, subfamily alphaherpesviridae; dsDNA virus
• One of the three most important respiratory diseases of chickens along with infectious bronchitis (coronavirus) and Newcastle disease (paramyxovirus)
• Results in significant economic losses; decreased egg production, decreased rate of gain, or death
• Outbreaks range from highly pathogenic epizootic forms to mild enzootic disease
• Primarily a disease of chickens, also in pheasants, peafowls, and turkeys
• Classically affects adults but can impact any age group
• Viral inclusions are only present during days 1-5 of infection

 

PATHOGENESIS: 

• Spreads via aerosolization of respiratory secretions
• Virus enters through upper respiratory membranes, conjunctiva or may be ingested; spread is from cell to cell with no detectable viremia
• Recovered birds may become inapparent carriers and harbor virus in the upper respiratory epithelium for months, creating an endemic condition within flocks   
• The virus can become latent in the trigeminal nerve ganglion for potentially the life of the bird, with subsequent reactivation in immunocompromised animals
• Cell-mediated immunity is the key to disease resistance 
• Outbreaks of acute disease have occurred as a result of reversion to virulence of live-attenuated chicken embryo origin vaccine virus strains

 

TYPICAL CLINICAL FINDINGS:

• Severe cases have severe dyspnea with gasping sounds and coughing (birds may raise and extend their head and neck during inspiration); bloody discharge from beak and nostrils; weakness; cyanosis; loss of weight; decreased egg production; characteristic head shaking; death due to suffocation or other secondary bacterial or fungal infection
• Mild cases have conjunctivitis, swollen infraorbital and nasal sinuses, congestion of mucous membranes, and decreased egg production
• “Silent form” of ILT in broilers lacks characteristic respiratory signs; confined to conjunctiva, nasal passages, and trachea with mild catarrhal exudate 

 

TYPICAL GROSS FINDINGS:

• Severe laryngotracheitis with necrosis, hemorrhage, ulceration, and occlusive fibrinonecrotic casts in the trachea   
• Increased mucus > fibrinonecrotic exudate > tracheal and laryngeal hemorrhages (Carnaccini, Vet Pathol 2022)
• In milder forms there is sinusitis, conjunctivitis, congestion of mucous membranes, and seromucoid to bloody nasal discharge
• The lungs and air sacs are less commonly affected; rarely ulcerative esophagitis and pharyngitis occur (Carnaccini, Vet Pathol 2022)

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Intranuclear inclusion bodies (Cowdry Type A) in tracheal, laryngeal, nasal turbinate,  and conjunctival epithelial cells early in infection (1-5 days); difficult to find in more chronic cases due to desquamation of epithelium
• Multinucleated syncytial cells formed by ciliated tracheal mucosal epithelial cells (also respiratory epithelium lining parabronchi and air sacs, if affected)
• Necrosis and loss of epithelium with ulceration and attenuation of remaining cells; loss of goblet cells; formation of diphtheritic (fibrinonecrotic) membrane
• Hemorrhage may occur in cases of severe epithelial destruction and desquamation due to exposure and rupture of tracheal capillaries
• Lymphocytic, heterophilic, and histiocytic inflammation within the mucosa and submucosa
• Virulent strains may cause severe suppurative bronchopneumonia and air sacculitis  

 

ULTRASTRUCTURAL FINDINGS:

• Viral capsids with icosahedral symmetry form in the nucleus and bud through the nuclear membrane to acquire the cell-derived envelope
• Viral particles migrate through endoplasmic reticulum and form large masses within intracytoplasmic vacuoles
• Viral particles are released upon cell lysis or exocytosis of vacuolar membrane

 

ADDITIONAL DIAGNOSTIC TESTS:

• Real-time/qPCR, IFA, virus isolation on samples of larynx, trachea, and lungs
• IHC is highly effective; detected viral antigen in 8/34 chicken tissues without definitive histologic changes (Carnaccini, Vet Pathol 2022)

 

DIFFERENTIAL DIAGNOSIS:

• Newcastle Disease (Paramyxovirus) – high mortality; surface epithelium seldom lost
• Fowl Pox (Avian pox virus) - intracytoplasmic inclusion bodies (Bollinger bodies), no syncytial cells, proliferative epithelium, tracheal diphtheritic lesions
• Infectious Bronchitis (Coronavirus) - no inclusion bodies; affects lower respiratory tract; nephrotic strains may also affect kidneys
• Avian Influenza (Orthomyxovirus, Type A Influenza virus) - non-respiratory organs also involved
• Mycoplasmosis (M. gallisepticum)- severe air sacculitis; no pseudomembranes; lack of extensive epithelial necrosis
• Infectious Coryza (Avibacterium paragallinarum) - early stages with facial edema; usually involve lower respiratory tract and other organs
• Fowl Cholera (Pasteurella multocida) - high mortality; respiratory signs; diarrhea
• Trichomonas gallinae (frounce, canker) - caseous material in the trachea and esophagus; flagellates visible with Giemsa staining
• Vitamin A deficiency – hyperkeratosis; lesions primarily in the mouth and tongue

 

COMPARATIVE PATHOLOGY:

Herpesvirus in other avians (all avian herpesviruses are alphaherpesvirinae): 

• Gallid herpesvirus 1: Other affected galliformes include peafowl, pheasants and turkeys
• Gallid herpesvirus 2: Marek’s disease (CD4+ T cells) chicken, quail, pheasants, turkeys
• Psittacid herpesvirus 1: Pacheco’s disease; massive hepatic and splenic necrosis
• Amazon tracheitis virus: Proliferative tracheitis in parrots, conures, others
• Gaviid herpesvirus 1: Ulcerative tracheitis in common loons
• Columbid herpesvirus 1: Young pigeons, raptors, owls
• Passerid herpesvirus I (PaHV-l): Finch cytomegalovirus in Gouldian finches
• Herpes also isolated from penguin diphtheria and nodular proliferative facial hyperkeratosis of magnificent frigatebirds 

 

Other Herpesviral Respiratory Diseases: 

• Infectious Bovine Rhinotracheitis (Bovine herpesvirus 1, alphaherpesvirus)
• Caprine Herpesvirus (Caprine herpesvirus 1, alphaherpesvirus)
• Pseudorabies (Suid herpesvirus 1, alphaherpesvirus)
• Canine Herpesvirus (Canid herpesvirus 1, alphaherpesvirus)
• Feline Herpesvirus (Felid herpesvirus 1, alphaherpesvirus)
• Equid Herpesvirus 1 (alphaherpesvirus)
• Porcine Cytomegalovirus (Suid herpesvirus 2, betaherpesvirus)
• Rhesus cytomegalovirus (Macacine herpesvirus 3, betaherpesvirus)
• Malignant Catarrhal Fever (Alcelaphine herpesvirus 1 or Ovine herpesvirus 2, gammaherpesvirus)
• Equine Nodular Pulmonary Fibrosis (Equid herpesvirus 5, gammaherpesvirus)

 

REFERENCES:

1. Blakely J, Stoute S, Crossley B, Mete A. Retrospective analysis of infectious laryngotracheitis in backyard chicken flocks in California, 2007-2017, and determination of strain origin by partial ICP4 sequencing. J Vet Diagn Invest. 2019;31(3):350-358.
2. Carnaccini S, Palmieri C, Stoute S, Crispo M, Shivaprasad HL. Infectious laryngotracheitis of chickens: Pathologic and immunohistochemistry findings. Vet Pathol. 2022;59(1):112-119.
3. Crespo R, Franca MS, Fenton H, Shivaprasad HL. Galliformes and Colubriformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018:752-754.
4. Schmidt R, Reavill DR, Phalen DN. Pathology of Pet and Aviary Birds. 2nd ed. Ames, IA: John Wiley & Sons, Inc.; 2015.:29 
5. Sellers H, Ojkic D. Viral diseases.  In: Boulianne M, ed. Avian Disease Manual. 8th ed.  Jacksonville, FL: American Association of Avian Pathologists, Inc; 2019:56-58.
6. Stidworthy MF, Denk D. Sphenisciformes, Gaviiformes, Podicipediformes, Procellariiformes, and Pelecaniformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018:667. 

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