The Role of Fertilized Eggs in Vertical Transmission of Avian Adenovirus

 

 

Dr. Majed Hamed Al Saegh / poultry pathologist / Australia

7/ June/ 2025

The Role of Fertilized Eggs in Vertical Transmission of Avian Adenovirus (FAdV): Implications for Control in Hatcheries in Iraq

 

Fowl adenoviruses (FAdVs) are important viral pathogens affecting the poultry industry, responsible for serious diseases such as Inclusion Body Hepatitis (IBH) and Hydropericardium Syndrome (HPS). One of the most dangerous mechanisms of spread of these viruses is vertical transmission through fertilized eggs, where the infection is passed from mother to embryo during egg formation, bypassing all traditional biosecurity measures that often focus on horizontal transmission after hatching.

Studies indicate that the virus can be incorporated into albumen, yolk, or embryonic membranes (Ojkic et al., 2008), transmitted through the oviduct, and deposited in embryonic tissues, resulting in the hatching of chicks carrying the virus without immediate symptoms. The infection may remain latent in the first few days but later reactivates under stressful or immunocompromised conditions, leading to clinical symptoms and failure of vaccination programs.

 

In Iraq, a recent study by Abdulla et al. (2024), published in the Anbar Journal of Veterinary Sciences, confirmed the presence of FAdV DNA in the livers and spleens of one-day-old chicks using PCR, clearly demonstrating transegg transmission. Results of viral isolation using fertilized egg embryos showed that the virus causes significant embryonic changes, such as hemorrhage and embryo death, after the second pass.

 

These results highlight the dangers of the absence of strict control programs in Iraqi hatcheries, where fertilized eggs from mothers that may be carriers of the virus are traded without molecular or serological testing. This contributes to the widespread spread of the infection, especially in the absence of reliable health certificates, leading to poor herd performance and the emergence of “complex” cases resistant to vaccination, due to immunosuppression (Grgić et al., 2006; Schachner et al., 2018).

Therefore, a national strategy must be developed to limit vertical transmission. This strategy includes:

• Routine PCR testing in hatcheries on liver and spleen samples from dead or sick chicks within the first days after hatching.
• Requiring hatcheries to issue a “FAdV-free” certificate for each production batch, certified by licensed veterinary laboratories.
• Screening of exporting broodstock for fertilized eggs or locally produced or imported chicks, particularly against genotypes 8b and 11 prevalent in the region.
• Conducting periodic serological tests of live broodstock to determine the true incidence of viral exposure and to decide on preventive vaccination in endemic areas.

In conclusion, fertilized eggs are a pivotal link in the viral infection chain. Given the epidemiological challenges and institutional weaknesses in Iraqi hatcheries, ignoring the vertical transmission of FAdV could exacerbate production losses and undermine national biosecurity. Therefore, establishing an integrated system for early detection, laboratory documentation, and health certification has become an urgent necessity.