Vaccination with FAdV-8a induces protection against inclusion body hepatitis caused by homologous and heterologous strains

Abstract

Fowl aviadenoviruses (FAdV) are important avian pathogens, responsible for several poultry diseases prevalent worldwide, including inclusion body hepatitis (IBH). FAdV intraspecies cross-protection has been clearly demonstrated, but there is little evidence that any interspecies cross-protection exists. The present study aimed to assess the inter-and intraspecies protection between three FAdV field isolates (FAdV-8a, FAdV-8b, FAdV-11) identified in association with severe IBH outbreaks. Inocula prepared using inactivated plaque-purified virus with adjuvant Montanide™ ISA 71VG, were injected intramuscularly into 3-week-old SPF chickens. At 6-weeks of age, the birds were challenged with 10 6 TCID 50 of homologous or heterologous virus intraperitoneally, and full post mortem examination performed at 4 days post-challenge. Various tissues were examined for gross and histological lesions and assessed for the presence of virus by PCR-HRM. All homologous-type vaccine/ challenge groups exhibited protection against IBH lesions with no virus detected in the tissues. Unvaccinated groups challenged with virus showed evidence of FAdV-induced lesions; however, FAdV-8a demonstrated lower pathogenicity compared with FAdV-8b and FAdV-11. In the heterologous-type vaccine/challenge groups, FAdV-8a vaccine was shown to protect against challenge with both FAdV-8b and FAdV-11. FAdV-8a and 8b belong to species E and were therefore anticipated to cross-protect. However, FAdV-11 belongs to species D and therefore cross-protection by FAdV-8a was an uncharacteristic and unique finding of this study. Further research is required to disseminate the molecular basis for the interspecies cross-protection between FAdV-8a and FAdV-11. Nonetheless, the FAdV-8a isolate was shown to have substantial potential as a vaccine candidate in countries where FAdV-8a, 8b or 11 are prevalent.

Fowl adenovirus (FAdV) fiber-based vaccine against inclusion body hepatitis (IBH) provides type-specific protection guided by humoral immunity and regulation of B and T cell response

“…On the other hand, experimental data on immunization against IBH collectively indicate a certain extent of heterotypic protection, albeit these studies remain ambiguous about coverage across the species boundary due to the use of bivalent FAdV-D/FAdV-E vaccines [17][18][19]. Cross protection amongst different IBH-causing serotypes was also reported using FAdV-C and FAdV-E strains as inactivated vaccines [20][21][22]. However, all these studies are based on whole virus as vaccine antigen, with protection likely resulting from a synergy of all antigenic components, an effect that does not apply for subunit vaccines.…”

Detection, Quantification and Molecular Characterization of Fowl Adenoviruses Circulating in Ecuadorian Chicken Flocks during 2019–2021

“…In our country, vaccination against FAdV is used with inactivated vaccines of genotype FAdV-8a/E2 [ 10 ] and is intended for the vaccination of broiler chickens and breeders for the prevention of IBH and HHS, but the protection capacity that this vaccine generates in animals has not been studied or determined. However, studies carried out with FAdV-8a/E2 or FAdV-8b/E3 viral strains as candidates for possible vaccines indicate that the strain could be effective in protecting against infections with homologous strains and with some heterologous strains, specifically against strains of the FAdV-8a/D2, FAdV-8b/E3, and FAdV-11/D3 genotypes [ 1 , 12 , 44 , 45 ]. These findings could suggest that vaccination in Ecuador should protect against infections with genotypes FAdV-8a/E2 and FAdV-11/D3, and could possibly generate protection against genotypes FAdV-2/D2 and FadV-6/E1, since they are included in species D and E of FadV.…”

Molecular Analysis of Hexon and Fiber Genes of Fowl Aviadenoviruses Isolated From Field Cases of Inclusion Body Hepatitis

“…Birds still susceptible to heterologous FAdVs infections regardless of the pre-existing immunity against other FAdVs species, and likely represents the molecular basis for the newly stated natural recombination of FAdVs (Schachner et al, 2019). The cross protection between different FAdVs species was reported between FAdV-C and FAdV-E strains as inactivated vaccines (Steer et al, 2019).…”