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

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.

Figure 1

Mean clinical score, cumulative mortality and mean body weight difference. A Infected birds belonging to groups L1, B1, L2 and B2 were individually scored based on the following clinical signs: 0—active with no 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. An average of each group’s clinical score was calculated at each time point. All clinical signs were observed between 4 and 9 dpi. No clinical signs were observed in the control birds. B Mortality rates (%), recorded in groups L1, B1, L2, B2, L0 and B0 throughout the animal experiment. Mortality curves with different lowercase letters are significantly different (P < 0.05). C Mean differences in body weight (%) of infected birds belonging to groups L1, B1, L2 and B2 in comparison to the respective control group (L0 or B0), at 1, 4, 7, 10, 14 and 21 dpi. Values of groups B1 and B2 at 7 dpi correspond to pooled birds that were euthanized and sampled between 5 and 7 dpi due to poor condition. Asterisks indicate statistical significant difference (P < 0.05). From 7 dpi onwards there were no SPF broilers alive in groups B1 and B2.

Figure 2

Blood glucose concentration. Means and standard deviations of blood glucose concentration values (mg/dL) of SPF layer and SPF broiler chickens from groups L1, B1, L2, B2, L0 and B0 at 4, 7, 10, 14 and 21 dpi. Values of groups B1 and B2 at 7 dpi correspond to pooled birds that were euthanized and sampled between 5 and 7 dpi due to poor condition. From 7 dpi onwards there were no SPF broilers alive in groups B1 and B2. All dead and killed birds at each investigated time point of each group (Table 1) were included. Asterisks indicate statistical significant difference when compared to the respective control group (L0 or B0) (P < 0.05).

Figure 3

Viral load in liver and pancreas. Means and standard deviations of the viral genome copies per reaction (log₁₀) in (A) liver and (B) pancreas of orally inoculated SPF layer and SPF broiler chickens from groups L1, B1, L2 and B2 at 4, 7 and 10 dpi quantified by real-time PCR. Values of groups B1 and B2 at 7 dpi correspond to pooled birds that were euthanized and sampled between 5 and 7 dpi due to poor condition. All dead and killed birds at each investigated time point from each group (Table 1) were included. Negative results are indicated with §. There were no SPF broilers alive at 10 dpi (¥). Mean values with different lowercase letters at each time point are significantly different (P < 0.05).