Epidemiology of fowl adenovirus (FAdV) infections in South Korean chickens during 2013–2019 following introduction of FAdV-4 vaccines

Abstract

Fowl adenoviruses (FAdV) are important infectious pathogens responsible for causing substantial economic losses to the poultry industry worldwide. One hundred and forty-six FAdV strains were continuously collected and analysed from 2013 to 2019 to understand the epidemiological change and nature of the virus in South Korea from two different standpoints, before and after the release of multiple commercial FAdV-4 vaccines. Phylogenetic analysis of the hexon loop-1 gene sequences showed that 92 strains belonged to FAdV-C (63%), 35 strains to FAdV-E (24%), 18 strains to FAdV-D (12.3%), and one strain to FAdV-A (0.7%), respectively. We provide evidence that the dominant FAdV serotype has recently changed from FAdV-4 to FAdV-8b, as reflected in the proportion of each serotype in field cases in 2019 (18.5% and 77.8%, respectively). The newly emerged FAdV-8b cluster was significantly noticeable compared to the old FAdV clusters, indicating that the development of a vaccine for FAdV-8b may be necessary. Overall, this new insight into FAdV prevalence provides a foundation for strategic control and the development of efficient vaccines against FAdV cases in chickens in South Korea. RESEARCH HIGHLIGHTS. The dominant FAdV serotype in South Korea shifted from FAdV-4 to FAdV-8b in 2013-2019. . A new cluster of FAdV-8b has emerged in South Korea, indicating the development of new vaccines.

Historical Investigation of Fowl Adenovirus Outbreaks in South Korea from 2007 to 2021: A Comprehensive Review

“…The results demonstrated that the mono-serotype FAdV-4 vaccine could provide broad cross-protection against all five serotypes of FAdVs used in this study, not only in vaccinated chickens but also in their progenies with confirmed maternally derived antibodies. The coordinated efforts by the research and industry sectors to control FAdV-4 outbreaks through vaccination programs were fortunately fruitful at some level, as cases involving this serotype started to decline rapidly in 2017 [45].…”

“…There has been an increase in reports of HHS and IBH outbreaks from various regions in the last ten years, such as in Europe [41][42][43][44], Asia [45][46][47][48][49], Oceania [30], North America [50], South America [51,52], and Africa [53,54], indicating even geographical spread of FAdVs. As in most Asian countries, FAdV-induced outbreaks in poultry have been observed in South Korea for many years, and, to date, these outbreaks persist.…”

“…From 2007 to 2021, a total of 387 clinical cases of FAdVs were officially documented, with an average of 25.8 cases per year, involving 6 serotypes during the 15-year period in South Korea (Table 1). The cases were evenly spread across all eight provinces, and documented mortalities of infected flocks ranged from 0.01% to 55% between 2007 and 2010 [55] but sharply declined after that period to 0.5-4% due to heightened biosecurity and implementation of vaccination programs [45,56,57]. The purpose of this comprehensive review is to provide an overview of the history and status of FAdV outbreaks in South Korea and to update the epidemiological situation that was observed in recent years.…”

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

“…Although heterologous protection in FAdV-causing IBH is still under debate [1,6], previous experimental studies suggest that FAdV-4 inactivated vaccines could provide broad cross-protection against various serotypes of FAdV, not only in vaccinated breeders but also in their progenies [3,26], in line with our findings. However, the crossprotective efficacy of FAdV-4 vaccines in the field has yielded conflicting results; while a field study in China suggests that FAdV-4 inactivated vaccine successfully controlled FAdV-11 [27], its application in South Korea caused an increase of FAdV-11 cases [28], and no cross-protection against FAdV-8b was observed in either country [27,28]. Thus, the complete absence of FAdV-11 in breeders in 2012-2013 provides a strong field evidence for cross-protection by the inactivated vaccine containing FAdV-4.…”

Fowl adenovirus strains 1/A and 11/D isolated from birds with reovirus infection

“…Avian adenovirus (6/E, 7/E and 8/E) have been reported to cause IBH in Australia and New Zealand. Saudi Arabia investigated type/species 2/D and 6/E, and newly shifted from 4/C to 8b/E strains indicated in South Korea [ 37 ] and other parts of the world [ 12 , 16 ]. Additionally, researchers from India have reported the presence of avian adenoviruses such as 2/D, 5/B, 6/E, 7/E and 12/D in addition to type/species 4/C and 8/E [ 38 ].…”