I. Etiology of Pigeon Adenovirus  

Pigeon adenovirus belongs to the Adenoviridae family. It was first detected in Belgium in 1984 and has since spread worldwide. Currently, pigeon adenovirus is classified into Type 1 (also known as classical adenovirus or PiAd-1) and Type 2 (also known as necrotic hepatitis virus or PiAd-2). The exact role of adenovirus as a primary or secondary pathogen remains incompletely understood. Adenoviruses exhibit strong resistance in natural environments, with relatively high heat tolerance, retaining activity at room temperature for up to 6 months. They can survive pH levels of 3–9, allowing them to pass through the gastrointestinal tract without being inactivated. Effective disinfectants include 0.1% formaldehyde and 0.1% povidone-iodine.

II. Epidemiology of Pigeon Adenovirus  

Adenoviruses can cause latent infections and are often detected in the intestines of healthy pigeons as non-pathogenic strains. The primary mode of transmission is direct contact with feces, though airborne transmission, human activities, and contaminated equipment can also facilitate horizontal spread. Additionally, vertical transmission is a significant route, as adenovirus can be passed through eggs. The disease can occur year-round and spreads rapidly once an outbreak begins. Mortality rates in cases of simple infection are relatively low, typically 2%–3%, but can rise significantly with co-infections involving E. coli or coccidia. Currently, Type 2 pigeon adenovirus is prevalent in China.

III. Clinical Symptoms and Pathological Changes  

Clinical symptoms of pigeon adenovirus infection are non-specific and lack characteristic lesions. The incubation period is 3–5 days, with the highest mortality occurring 3–4 days post-infection. However, some cases may persist for 2–4 weeks or longer, presenting only with diarrhea.  

- Type 1 Adenovirus Infection: Also known as "young pigeon diarrhea syndrome," it manifests as acute ingluvitis and enteritis, with crop impaction and characteristic vomiting and diarrhea. It primarily affects pigeons under one year of age, especially those 3–5 months old, with racing pigeons being more susceptible. Clinical signs include lethargy, ruffled feathers, anorexia, crouching, elevated body temperature, excessive drinking, enlarged and soft crop, vomiting, and sudden diarrhea. Feces are often pale yellow or yellowish-green and watery, sometimes white. Key pathological findings include ingluvitis, enteritis, and hepatitis. Crop contents may be undigested and rancid, while the intestines show acute catarrhal inflammation with mucosal redness, swelling, and occasional petechial or linear hemorrhages. The liver may appear pale, fragile, and enlarged.  

- Type 2 Adenovirus Infection: Can affect pigeons of any age, from 10 days to 6 years. Clinical symptoms are generally rare, and infected pigeons often die within 24–48 hours. Persistent infections can last 6–8 weeks, with sporadic new cases and mortality rates of 30%–70%, potentially reaching 100%. Some reports indicate rapid deaths in certain pigeons while others in the same loft remain unaffected. Pathological changes include hepatitis, with the liver turning pale to yellowish and enlarging, and occasional hemorrhages in the liver and skeletal muscles.

IV. Prevention and Control of Pigeon Adenovirus  

Adenoviruses often cause subclinical infections and only lead to disease when immunity is compromised by stressors. Therefore, strengthening daily management, ensuring adequate nutrition, maintaining hygiene and disinfection, conducting regular deworming, and minimizing stress can enhance resistance and reduce infection risks.  

Currently, no commercial pigeon-specific adenovirus vaccine is available in China. Based on existing knowledge, the primary role of adenovirus in disease pathogenesis remains uncertain. International studies suggest that inactivated oil-emulsion vaccines for chicken egg drop syndrome may offer some cross-protection against pigeon adenovirus.  

For Type 1 adenovirus infections:  

- Immediately withhold feed from affected pigeons.  

- For severe crop distension, flush the crop with 0.1% povidone-iodine or 0.01% potassium permanganate solution.  

- Provide electrolyte multivitamins in drinking water and administer vitamin C solution to prevent septicemia and tissue necrosis.  

- Administer metoclopramide hydrochloride to promote gastric motility and emptying. Resume feeding small amounts multiple times only after crop contents are fully digested and cleared.  

Antiviral treatments should be promptly implemented to control viremia. Industry practice has proven that Andrographis paniculata possesses antibacterial and antiviral properties, clearing heat, detoxifying, cooling blood, and reducing swelling, making it effective against adenovirus infections. For mild cases or group treatment, oral administration is suitable, while severe cases may require injections of Andrographis extract.