Researchers have discovered the likely cause of a highly fatal respiratory disease that has caused mass deaths among endangered hoiho chicks during the past three years.

Led by University of Otago postdoctoral research fellow Janelle Wierenga and virologist Dr Jemma Geoghegan along with agencies across the country, they identified a novel gyrovirus likely to be responsible for the fatal respiratory disease affecting very young chicks.

About 25% of the chicks from the mainland died of the disease during the 2021 November to December hatching season.

One hundred and thirty-seven wild hoiho chicks were admitted to the Dunedin Wildlife Hospital. Thirty-one of those had been admitted because they started showing signs of respiratory disease within their first week of life. The majority – 27 – died within 12 to 24 hours of presentation of symptoms; one survived for five days with intensive veterinary support before succumbing, while just three were able to be successfully treated and returned to the nest.

The hoiho is considered to be one of the rarest penguins in the world and is endangered.

The research group, which includes the Dunedin Wildlife Hospital, Yellow-Eyed Penguin Trust, Department of Conservation, Ministry for Primary Industries, and both Otago and Massey universities, has also developed a PCR test to identify the presence of the virus in the

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Geoghegan said total RNA extracted from tissue sampled during post-mortems of 43 dead chicks revealed a novel and "highly abundant gyrovirus".

"We collected tissues from the chicks that died of Respiratory Distress Syndrome and used next-generation sequencing technology to try to identify any pathogens present.

"This is the same technology that Chinese scientists used to identify that a new coronavirus was causing a respiratory disease in humans, which of course, was later named SARS-CoV-2. We identified a novel gyrovirus that appears to be abundant in samples from the diseased chicks. The virus is related to other gyroviruses that cause disease in other birds, including chickens," she said.

The disease was initially identified in 2019, although historical epidemiological records show the first suspected cases as early as 2015.

It presents as lung congestion and haemorrhage, and lymphnoid depletion in the spleen and bursa.

"In 2020 and 2021, the number of chick deaths from this disease increased four and five-fold, compared to 2019, with a mortality rate of more than 90 per cent. Chicks usually succumb to the disease within the first 10 days of life," Geoghegan said.

The next step is understanding the disease and the virus so that it can be prevented and treated.

"The disease has only really been noticed in the past few years, meaning it is likely a new virus in hoiho. This means the virus would have likely jumped from another animal – perhaps another seabird – to hoiho recently. This is part of our ongoing investigation – to try and understand from where and when the virus emerged."