Yellow-eyed penguins are the most endangered penguin species in the world, with just 4,000 left in the wild. Found only in New Zealand and its outlying islands, these birds can grow up to 79cm tall and weigh 8.5kg, which is similar to a one-year-old child. They’re easily identified by the pale-yellow band of feathers that extends from their eyes and around the backs of their heads.
Their shrill calls during the mating season earned them their local name Hoiho, which means “noise shouter” in Māori. Yellow-eyed penguins are great divers and mostly catch their food – small fish, molluscs and crustaceans – from the seabed. Unlike most of their kin, yellow-eyed penguins are not very social and often nest away from other penguins.
These withdrawn breeding pairs have been in sharp decline for the last two decades, especially on islands to the north of their distribution where the population has declined by 65%. The primary cause is outbreaks of diphtheria-like infections that are particularly fatal to young chicks between one and 28 days old. The mouth and tongue of infected chicks are covered by a thick membrane, pus and ulcers that stop them from eating. The infection can spread to the entire body, resulting in sepsis.
Even when treated with a combination of antibiotics, infected birds often die. Up to 93% of yellow-eyed penguin chicks contract avian diphtheria every year in the northern population and up to 70% of them die, threatening the future of the species.
Despite the alarming situation, scientists knew very little about the cause of avian diphtheria. But in our recently published study, we identified the bacterium causing these infections, how it infects penguin chicks and how it might be treated to save the species from extinction.
A familiar foe
To identify the bacterium, my colleagues from the New Zealand Department of Conservation, University of Otago and Massey University collected swabs from the mouths of chicks in infected nests on the Otago peninsula on the east coast of New Zealand’s South Island. My colleagues and I isolated the bacteria in the laboratory and sequenced its DNA to create a family tree that showed how this bacteria is related to other species.
The results were fascinating. The strains from these penguins belong to a new species which has not been reported before, within a group of bacteria called Corynebacterium.
This group includes another species that causes diphtheria in humans. Diphtheria once killed up to 20,000 people a year in the US alone, many of them children, before a global vaccination campaign in the 1940s. Outbreaks are still reported globally which kill thousands of people every year.
Fortunately, we also found unique DNA sequences in the bacteria that helped us develop a simple test to identify the infection rapidly and more reliably than other methods. Being able to quickly detect these strains will help conservationists start early treatment of infected chicks, improving their chances of survival.
The disease-causing genes in the bacteria from yellow-eyed penguins are similar to those in the species which cause human diphtheria. This helped us understand how this bacteria attaches and invades cells in the mouth of penguins.
One of these genes produces a protein called Phospholipase D that helps the bacteria survive once inside the host. This protein can be modified to protect animals from bacterial infections. This is very exciting, as it could help us develop a vaccine for the world’s most endangered species of penguin, and possibly, save it from extinction.