The outcome of experimentally induced inclusion body hepatitis (IBH) by fowl aviadenoviruses (FAdVs) is crucially influenced by the genetic background of the host

Matos et al. Vet Res (2016) 47:69 DOI 10.1186/s13567-016-0350-0 Open Access RESEARCH ARTICLE The outcome of experimentally induced inclusion body hepatitis (IBH) by fowl aviadenoviruses (FAdVs) is crucially influenced by the genetic background of the host Miguel Matos1*, Beatrice Grafl1, Dieter Liebhart1 and Michael Hess1,2 Abstract In the present study, inclusion body hepatitis (IBH) was experimentally induced by oral inoculation of two groups of specific pathogen-free (SPF) broilers and two groups of SPF layers at day-old with either a fowl aviadenovirus (FAdV)-D or a FAdV-E strain. A substantial variation in the degree of susceptibility was observed with mortalities of 100 and 96% in the FAdV-E and D infected SPF broiler groups, respectively, whereas in the groups of infected SPF layers mortalities of only 20 and 8% were noticed. Significant changes in clinical chemistry analytes of all infected birds together with histopathological lesions indicated impairment of liver and pancreas integrity and functions. Furthermore, significantly lower blood glucose concentrations were recorded at peak of infection in both inoculated SPF broiler groups, in comparison to the control group, corresponding to a hypoglycaemic status. High viral loads were determined in liver and pancreas of SPF broilers already at 4 days post-infection (dpi), in comparison to SPF layers, indicating a somewhat faster viral replication in the target organs. Overall, highest values were noticed in the pancreas of SPF broilers independent of the virus used for infection. The actual study provides new insights into the pathogenesis of IBH, a disease evolving to a metabolic disorder, to which SPF broilers were highly susceptible. Hence, this is the first study to report a significant higher susceptibility of SPF broiler chickens to experimentally induced IBH in direct comparison to SPF layers. Introduction Fowl aviadenoviruses (FAdVs) belong to the genus Aviadenovirus within the family Adenoviridae, being further divided into five species designated FAdV-A to E [1]. Throughout the years, many reports established a causality between strains from species FAdV-A, FAdV-C and FAdV-D together with FAdV-E with specific diseases in chickens, such as adenoviral gizzard erosion (AGE), hydropericardium hepatitis syndrome (HHS) and inclusion body hepatitis (IBH), respectively [2]. In the last 10 years IBH outbreaks have been reported in different geographic regions emphasizing the wide *Correspondence: 1 Clinic for Poultry and Fish Medicine, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna, Veterinaerplatz 1, 1210 Vienna, Austria Full list of author information is available at the end of the article distribution of FAdVs throughout the world [3–8]. In the field, IBH has been reported essentially from commercial broiler flocks (meat-producing chickens), being responsible for serious economic losses due to increased mortality combined with reduced performance within flocks [2]. However, experimental in vivo studies were predominantly conducted in specific pathogen-free (SPF) white leghorn layers (egg-producing chickens), which are the experimental model for infection studies. In a recent study we were able to demonstrate the influence of virulent FAdV-D and E field strains on different enzyme systems and metabolite concentrations in the plasma of orally inoculated day-old SPF layer chickens due to the infection of liver and pancreas as target organs [9]. Consequently, it can be hypothesized that hosts with different metabolic activities vary in their susceptibilities towards infection. Therefore, the aim of the present study © 2016 The Author(s). This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Matos et al. Vet Res (2016) 47:69 was to characterize and compare the susceptibility of SPF broiler and SPF layer chickens to experimentally induced IBH by FAdV-D and E field strains. Materials and methods Viruses The FAdV strains used in the present study—08/18 926 and 13/18 153—were isolated from liver samples of broilers during recent IBH outbreaks in Europe and they were genotyped as belonging to species FAdV-D and E, respectively [4, 8]. The viruses were plaque purified three times and propagated in primary chicken embryo liver (CEL) cell cultures as described elsewhere [10]. The titers were determined according to the method of end point titration [11] and a titer of 107 median tissue culture infective dose (TCID50) per mL was used to infect the birds. A polymerase chain reaction (PCR) and a reverse transcription-PCR were performed to confirm the absence of contaminations by chicken anaemia virus and avian reovirus, respectively. The strains’ pathogenicity was characterized in vivo by inoculating SPF white leghorn chickens at dayold [9]. Animal trial Embryonated SPF broiler eggs (Animal Health Service, Deventer, The Netherlands) and SPF layer eggs (VALO, Lohmann Tierzucht GmbH, Cuxhaven, Germany) were incubated at our facilities. After hatch, the chicks were individually tagged subcutaneously (Swiftack, Heartland Animal Health Inc., Fair Play, USA) and divided in six groups: three groups of 27 SPF broiler chicks (groups B0–2) and three groups of 20 SPF layer chicks (groups L0–2). The groups were housed separately in isolator units (Montair Andersen bv, HM 1500, Sevenum, Netherlands) under negative pressure, where feed and water were available ad libitum throughout the animal experiment. At first day of life, the body weight of all birds was measured and birds from groups L1 and B1, and from groups L2 and B2 were orally inoculated with 0.5 mL of the 13/18 153 and the 08/18 926 strains, respectively, while birds from groups L0 and B0 were left uninoculated (Table 1). All birds were daily monitored and an individual score was given based on clinical signs: 0—active with no adverse clinical signs; 1—slightly weak with dropped wings; 2—depressed with swollen crops; 3—weak, apathetic, with ruffled feathers and reluctant to move; 4—apathetic, unable to move or stand, breathing intensely with eyes closed. Euthanasia was applied to birds clinically rated with the highest score. The body weight of all birds was measured at 4, 7, 10, 14 and 21 days post-infection (dpi). Furthermore, at 4 dpi four randomly selected birds of each group were blood sampled, euthanized and necropsied (Table 1). The same procedure was performed at 7, 10, 14 and 21 dpi in groups (...truncated)