Primary viral replication occurs in the ciliated epithelial cells of the upper respiratory tract (nasal turbinates, trachea). Destruction of cilia compromises the mucociliary elevator, permitting inhaled secondary bacteria to invade the subcutaneous tissues of the head and infraorbital sinuses.

Field outbreaks display characteristic clinical signs and necropsy findings:

• Sneezing & Coughing: Initial mild respiratory signs (rales, nasal discharge) appear 3–5 days post-infection.
• Facial & Periocular Edema: Marked swelling of the periorbital tissues, wattles, and intermandibular space, often causing temporary blindness.
• Neurological Signs (Torticollis): Severe infection extending into cranial air spaces and middle ear structures leads to twisted neck, opisthotonos, and loss of balance.
• Post-Mortem Necropsy: Yellow subcutaneous gelatinous-to-caseous exudate covering the skull, periorbital tissues, and neck. Sinusitis and airsacculitis are prominent. Audit lesions in our Pathology Reference Manual.

SHS must be differentiated from other facial swelling diseases:

• Infectious Coryza (Avibacterium): Features foul-smelling nasal discharge and purulent conjunctivitis.
• Mycoplasma Gallisepticum (MG): Causes severe foam in eye corners and chronic sinus swelling.
• Fowl Cholera (Pasteurella multocida): Acute septicemia with dark swollen wattles.

Poor air quality (ammonia >20 ppm, high airborne dust) severely damages respiratory mucosa, accelerating SHS outbreaks. Check ventilation rates with our Ventilation Fan Calculator.

Management relies on treating secondary bacterial invaders and preventing viral introduction:

• Antibiotic Therapy: Water-soluble antimicrobial therapy (Oxytetracycline, Enrofloxacin, or Doxycycline) targeting secondary E. coli to reduce head edema and mortality.
• aMPV Vaccination: Live attenuated aMPV vaccines administered via coarse spray in rearing pullets/broilers, followed by inactivated oil-emulsion boosters in breeders. Schedule with our Flock Vaccination Scheduler.