False layer syndrome in Canada due to DMV/1639

False layer syndrome due to the Delmarva 1639 (DMV/1639) variant of the infectious bronchitis virus (IBV) is leading to huge economic losses in the Canadian egg industry.

Hens with false layer syndrome can look healthy, but if they’re infected with DMV/1639, egg production can be adversely affected since the virus affects the oviducts, Mohamed Hassan, a PhD student at the University of Calgary, told Poultry Health Today.

Egg production can be reduced significantly, while producers may also see poor quality eggs, he said.

Hassan and colleagues infected specific-pathogen-free chickens in peak lay with a Canadian strain of DMV/1639 to understand the lesions caused by the pathogen, particularly in the reproductive tract.

Compared to uninfected controls, egg production in the infected hens dropped from 90% to 40% starting 5 days post-infection.

Upon necropsy at 10 days post-infection, the investigators found regressed ovaries and atrophied oviducts, as well as missing epithelium, edema and protein deposition in the uterus, Hassan reported.

ELISA testing of reproductive tract washes to measure the local and systemic immune response demonstrated a significant level of antibodies as well as higher cytokine production.

These findings indicate the immune response to the virus was working but did not prevent reproductive tract damage, Hassan said, though he planned to replicate the experiment with a larger number of birds to investigate the implications further.

The Animal Health Lab at the University of Guelph genotyped 600 samples of IBV between 2015 and 2018.

In 2015, DMV/1639 represented only about 1% of all IBV strains found in Canada. In 2016, the prevalence of DMV/1639 had grown to just under 25% of the IBV strains in the country.

By 2017 and 2018, DMV/1639 had escalated dramatically, representing around 45% of all IBV strains in Canada and was far more prevalent than any other IBV strain.