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Team Sequences Fowl Adenovirus Strains Circulating in Chinese Chickens

NEW YORK (GenomeWeb) – In a study published in PLOS One last night, Chinese researchers used genome sequencing, phylogenetics, and pathogenicity testing to begin characterizing high-mortality fowl adenovirus (FAdV) strains detected recently in chickens from China.

Researchers from China Agricultural University focused on three fowl adenovirus strains suspected of contributing to particularly virulent outbreaks of diseases affecting Chinese chicken populations, particularly a liver condition known as inclusion body hepatitis (IBH) and hydropericardium syndrome (HPS), which involves the accumulation of fluid in the tissue around the heart.

Based on the apparent pathogenicity of at least two of the strains, the study's authors called for methods aimed at preventing further FAdV outbreaks in China's poultry farms, including ongoing analyses of FAdV strains to support future vaccine development efforts.

"In addition to … good management practices and strict biosecurity measures, the use of efficacious vaccines may help in prevention of FAdV infections," senior author Guo-zhong Zhang, an animal epidemiology and zoonosis researcher at China Agricultural University, and colleagues wrote.

They noted that "further genetic and pathogenic analysis of FAdVs is necessary and would provide useful information for the development of [an] efficient vaccine against IBH or HPS."

FAdV outbreaks have already impacted flocks of chicken and other fowl around the world, the team explained, leading to bird death and disease as well as economic loss. Such diseases have been on the rise in China sine around 2012, prompting interest in more detailed studies of the pathogens.

The fowl adenoviruses identified so far fall into five species designated as FAdV-A through FAdV-E, which can be further broken down into a dozen serotypes, known as FAdV-1 to FAdV-8a and FAdV-8b to FAdV-11.

For their current analysis, the researchers focused on three strains linked to outbreaks of IBH and HPS from flocks in different parts of China between 2012 and 2013.

The team did Sanger sequencing on PCR-amplified DNA from these strains — dubbed HBQ12, BJH13, and JSJ13 — before putting together genome assemblies that spanned between 43,756 and 44,081 nucleotides.

While the HBQ12 and BJH13 strains clustered together in the so-called FAdV-D species and had a FAdV-11 serotype, the JSJ13 strain fell in the C species of FAdV-4 — marking the first documented example of the FAdV-4 serotype in China, according to the study's authors.

Moreover, the latter strain was linked to far higher mortality rates than those detected in chickens infected with one of the FAdV-11 strains.

In pathogenicity experiments involving more than 100 three-week-old chickens infected with HBQ12 or JSJ13, for example, the former strain killed almost 9 percent of infected chickens within 21 days. On the other hand, the JSJ13 isolate was linked to nearly 29 percent mortality during the same time frame and tended to produce more pronounced clinical symptoms in the chickens. 

The infected chickens showed a range of symptoms, including liver lesions, necrotic tissue in the small intestine, swollen, fluid-filled heart sacs, and kidney abnormalities, the researchers reported.