Overview on Inclusion Body Hepatitis in Broilers
Abstract
Since Inclusion Body Hepatitis (IBH) was first detected in two broiler chicken flocks in the USA in 1963, outbreaks of the disease have been reported. Historically, IBH was known to occur as a secondary pathogen, particularly in the presence of immunosuppressive agents, but it´s no longer the case. During the late 1980´s and recently, IBH and Hydropericardium Syndrome (HHS) have been widely distributed in broiler flocks in several countries and regions, such as Mexico, North America, Latin-America, Middle East, and Asia, where the significant mortality and growth retardation associated with the disease result in economic losses.
IBH/HHS outbreaks in broilers caused by various FAdV serotypes have been reported globally in recent years, with serotypes 2, 8a, 8b, 11, and 4 being the most frequently involved. These viruses can be transmitted vertically, horizontally or by contaminated vectors. Mortality peaks during IBH outbreaks, when vertically transmitted to susceptible chicks, occur at 3–5 days of age and can reach up to 10%, and on occasions more than that, especially when concomitant infections are present, and the second curve of mortality traditionally occurs at 3 – 5 weeks of age and in some cases can reach 10% to 30%, depending on the flock susceptibility and concurring factors, such as IBD, CIA, etc. In rare occasions, IBH has been reported also in layers and broiler breeders.
Recently in Mexico we performed a retrospective genetic analysis of IBH outbreaks in broiler flocks during the period 2016-2024 and found that FAdV serotype 8b counted approximately for 86% of the cases, serotype 11 for 9%, serotype 4 for 3% and serotype 8a for 2%.
Vaccination strategies have been put in place with variable results. When heavy breeders are properly vaccinated during the rearing period, mainly with inactivated vaccines, the vertical transmission to the progeny is limited, depending on the FAdV serotype(s) that is infecting the flocks, the viral strains included in the vaccines, vaccines´ formulation and vaccination programs. When vaccine strains match the wild viruses, the vaccination program is correct and the vaccine administration is properly performed, it has resulted in a very effective preventive measure.