A disease of young chickens characterized by: sudden onset, hepatitis, and increased mortality.

1. Etiology

• Pathogen: Fowl Adenovirus, Genus Aviadenovirus (“Group I avian adenovirus”).
• Characteristics: Non-enveloped, DNA virus. It is highly resistant to chemical and physical factors.
• Serotypes: * Serotypes 2, 8b, and 11 are isolated from cases of I.B.H.
  • Serotype 4 is usually isolated from cases of Hydropericardium-Hepatitis Syndrome (H.H.S), which causes severe losses.

2. Transmission

The virus spreads via both vertical and horizontal way:

• Vertical Transmission: Typically associated with outbreaks in young chicks (1–2 weeks old).
• Horizontal Transmission: Most often responsible for the disease in older birds (3–7 weeks old).

3. Clinical Signs

• Onset: Can begin at 7 days of age.
• Symptoms: Depression and listlessness.
• Progression: Clinical signs peak within 3–5 days and usually stop by the 5th day.
• Mortality: Marked increase in mortality for 3–5 days, levels off for 3–5 days, then decreases to normal level 3–5 days.

4. Lesions

Gross Lesions

• Petechial and ecchymotic hemorrhages of leg muscles.
• Swollen, enlarged, and mottled liver.
• Petechial and ecchymotic hemorrhages under the liver capsule.
• Swollen, pale, and mottled kidneys.
• Bursa may be reduced in size.

Microscopic Lesions

• Large basophilic intranuclear inclusion bodies in hepatocytes.

5. Diagnosis

• Case history, clinical signs, and gross lesions.
• Histopathological examination.
• Detection of FAdV (Fowl Adenovirus) DNA from the liver by PCR test.
• Isolation and identification of the virus.

6. Prevention

• Vaccination: Vaccination of the breeders using an inactivated vaccine, administered at least twice during the rearing period.