A 10-Year Retrospective Study of Inclusion Body Hepatitis in Meat-Type Chickens in Spain (2011-2021)

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.

Keywords: Spain; broiler breeder pullets; broilers; epidemiology; fowl adenovirus; inclusion body hepatitis; phylogenetic analysis.

Figure 1

Distribution of sequenced FAdVs and FAdV serotypes by poultry type between 2011 and 2021 in Spain. Percentage of sequenced FAdV positive cases and FAdV serotypes in broilers (yellow) and broiler breeder pullets (green, referred to as Breeders).

Figure 2

Distribution of IBH cases in broilers between 2011 and 2021 in Spain. (a) Number of positive IBH cases in broilers (black line, number of cases per year indicated, (right) y axis) and percentage of FAdV serotypes per year (color-coded bars, (left) y axis). The percentage of positive cases out of the suspected IBH cases submitted per year and overall is shown as a table below. (b) Overall percentage of FAdV serotypes in positive IBH cases in broilers. Different letters designate statistical significance in Fisher’s exact test (p ≤ 0.05).

Figure 3

Distribution of IBH cases in broiler breeder pullets between 2011 and 2021 in Spain. (a) Number of positive IBH cases in broiler breeder pullets (black line, number of cases per year indicated, (right) y axis) and percentage of FAdV serotypes per year (color-coded bars, (left) y axis). The percentage of positive cases out of the suspected IBH cases submitted per year and overall is shown as a table below. (b) Overall percentage of FAdV serotypes in positive IBH cases in broilers. Different letters designate statistical significance in Fisher’s exact test (p ≤ 0.05).

Figure 4

Intra-annual seasonality of IBH cases in meat-type chickens in Spain. Distribution of FAdV serotypes and number of positive IBH cases per quadrimester. Only whole years were considered (i.e., 2011 and 2021 were not included). Statistical significance was declared at p ≤ 0.05. The p values are represented as: * (p ≤ 0.05); and *** (p < 0.001).

Figure 5

Geographic distribution of IBH cases and FAdV serotypes in meat-type chickens between 2011 and 2021 in Spain. The colors correspond to the percentage of FAdV-positive sequenced samples from each region. The pie charts indicate the percentage of FAdV serotypes in each region. The black circles indicate the number of meat-type poultry farms in each region according to the 2019 census [18].

Figure 6

Distribution of FAdV serotypes based on age in meat-type chickens between 2011 and 2021 in Spain. (a) Mean age of IBH-positive broilers and broiler breeder pullets based on FAdV serotype. Statistical significance was declared at p ≤ 0.05. (b) Percentage of FAdV serotypes per age group in broilers. (c) Percentage of FAdV serotypes per age group in broiler breeder pullets. Different letters designate statistical significance in Fisher’s exact test (p ≤ 0.05).