Abstract
A surge in fowl adenovirus (FAdV) causing inclusion body hepatitis (IBH) outbreaks has occurred in several countries in the last two decades. In Spain, a sharp increase in case numbers in broilers and broiler breeder pullets arose since 2011, which prompted the vaccination of breeders in some regions. Our retrospective study of IBH cases in Spain from 2011 to 2021 revealed that most cases were reported in broilers (92.21%) and were caused by serotypes FAdV-8b and -11, while cases in broiler breeder pullets were caused by serotypes FAdV-2, -11, and -8b. Vertical transmission was the main route of infection, although horizontal transmission likely happened in some broiler cases. Despite the inconsistent and heterogeneous use of vaccines among regions and over time, the number of cases mirrored the use of vaccines in the country. While IBH outbreaks were recorded year-long, significantly more cases occurred during the cooler and rainier months. The geographic distribution suggested a widespread incidence of IBH and revealed the importance of a highly integrated system. Our findings contribute to a better understanding of FAdV infection dynamics under field conditions and reiterate the importance of surveillance, serological monitoring of breeders, and vaccination of breeders against circulating serotypes to protect progenies.
Highlights
Inclusion body hepatitis (IBH) is an acute disease of chickens usually caused by certain strains of fowl adenovirus (FAdV) species D (FAdV-2, -3, -9, -11) and E (FAdV-6, -7, -8a, -8b) of the genus Aviadenovirus, family Adenoviridae [1]
All cases were submitted between June 2011 and May 2021 and were collected from commercial broiler and broiler breeder pullet farms in Spain
3.1.3.Distribution of IBH Cases Based on Poultry Type
Summary
Inclusion body hepatitis (IBH) is an acute disease of chickens usually caused by certain strains of fowl adenovirus (FAdV) species D (FAdV-2, -3, -9, -11) and E (FAdV-6, -7, -8a, -8b) of the genus Aviadenovirus, family Adenoviridae [1]. IBH has a worldwide distribution, affects mainly young broiler chickens up to 5 weeks of age, and is characterized by a sudden increase in mortality, which may occasionally be as high as 30% [1]. Broilers are more susceptible to IBH than layers, pointing to the importance of the genetic background [2]. In the last two decades, a growing number of IBH outbreaks due to FAdV-2, -8a, -8b, and -11 have been reported worldwide [1,6,7,8,9,10,11,12,13,14,15]. In Spain, a sharp increase in the number of IBH outbreaks in broiler and broiler breeder pullet flocks has occurred since 2011. We previously performed a molecular and pathobiological characterization of FAdV-8b and
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