Cory's shearwater is able to provide immune protection to its offspring up to six years after being vaccinated

Long-lived seabird species

Cory's shearwater (Calonectris borealis) is a seabird that breeds annually in remote islets and islands. Characterized by long life expectancy, the species reaches sexual maturity after six years and its reproductive rate is very low (one chick per year). "With these characteristics, the consequences of an infection outbreak on a colony of seabirds may be devastating; it may be a threat to the restoration and viability of the affected population," says Jacob González Solís.

The scientific team has studied seabirds' immune response to a vaccine against Newcastle disease virus. The researcher Raül Ramos, first author of the article, explains that "the study simulates a viral infection with a vaccine and examines the species' immune system in order to know how to act in case of real infection."

Immune response in chicks and females

The study was conducted in a Cory's shearwater colony in the island of Gran Canaria (Canary Islands) from 2008 to 2013. Authors evaluated the persistence of immunoglobulins or antibodies in mothers through time. The research has extended the results of a previous study developed by the same research team in 2011 which was focused on immunoglobulin persistence during chick growth.

To be exact, in 2008, researchers developed the first vaccination campaign in thirty females. Then, in 2010, they repeated it in a limited number of females to observe if a second exposure to the pathogen generated a quicker and more persistent response.

Chicks are protected six years after the vaccination

Results show that mothers are still able to transfer immunoglobulins to chicks six years after a vaccination, protecting their offspring against the pathogens that might infect the population. "Immunoglobulins are of female origin and maternal antibodies are transferred only when the egg yolk is formed," points out Raül Ramos. "In the case of chicks, the average lifetime of immunoglobulins is twenty-five days."

Besides extraordinary antibody persistence in vaccinated females, the study evidences a direct correlation between the amount of antibodies that the mother has when hatching and the amount received by the shearwater chick. In other words, the chick that is born during the year when the mother is vaccinated receives a great amount of antibodies. However, the chick of a female that was vaccinated years ago receives fewer antibodies and they are lost quicker during growth.

"Immunoglobulin levels in females are significant up to six years after the vaccination -- highlights Ramos -- , whether it is a double vaccination or not. Therefore, it would not be necessary to vaccinate again females to improve offspring's survival against infection outbreaks." According to experts, this mechanism of high antibody persistence in blood may be an evolutionary strategy to avoid reinfection in seabird colonies that always breed in the same colonies and are recurrently exposed to the same pathogens.

Endangered bird populations over the world

The study developed by the UB research group that studies immune response in Corey's shearwater populations is a key research to establish demographical models that facilitate the survival of world's seabirds against possible infection outbreaks. This happens, for instance, to the Amsterdam albatross (Diomedea amsterdamensis), a species that inhabits the islands of the Indian Ocean and is threatened by the avian cholera, an infectious disease caused by the bacteria Pasteurella multocida.

"Prevention is a key factor for these species, which are not generally exposed to predators. They are seabirds that breed in dense colonies, so a pathogen can easily spread if one individual gets infected. In the future, the experimental protocol will be used to study other seabird species of the order Procellariiformes (storm petrel, albatross, etc.) to observe if there is a similar pattern and compare it with species of other taxonomic orders, such as seagulls, cormorants or penguins," explain UB authors.