The study, which has potential applications in the development of protective strategies for bird species threatened by outbreaks of infectious diseases, focuses on the analysis of immune response in populations of the Coryʼs shearwater (Calonectris diomedea) to Newcastle disease, a viral disease that can be deleterious for chickens and for which vaccines are available. The results are compared to data for populations of black-legged kittiwake (Rissa tridactyla) and quail (Coturnix coturnix).
Maternal antibodies: from mothers to chicks
As Dr. González-Solís explains, “This is the first study of maternal immunoglobulin transfer in bird species with long life spans. Immunoglobulins are transferred via the yolk and help to protect the chicks against pathogens that affect the population. This process is very similar to the transfer of antibodies through the placenta during gestation in mammals”.
The team of experts compared the immune responses of chicks from vaccinated female birds and unvaccinated controls and were surprised by the average half-life of the antibodies in Coryʼs shearwater chicks from vaccinated females. In quails and black-legged kittiwakes the half-life is five days, but in the shearwater chicks the observed half-life of the immunoglobulins is 25 days. “This means that even 40 days later the antibodies still provide immune protection and improve survival rates in the event of infectious outbreaks,” explains Dr. González-Solís, although he adds that, for now, the team has not established “the mechanism that enables this extraordinary persistence of the antibodies for so many days.”
A strategy for survival
The Coryʼs shearwater and albatross are extreme examples of the trade-off between quality and quantity in reproductive strategies: Coryʼs shearwaters have very long life spans, do not reach sexual maturity until they are seven and have very low rates of reproduction, investing a great deal of time in caring for their young. Since chicks are reared on oceanic islands, far from the mainland, they are not exposed to predators, although, as Dr. González-Solís points out: “An outbreak of infection in a seabird colony could have devastating consequences.”
“Without the selection pressure of predation, rearing times can be longer and chicks can develop a more robust immune system. In this evolutionary scenario, maternal antibody transfer must be more effective and show greater durability to protect chicks during the growth stage, and this theory has been born out by our research.” The results indicate that, in the event of an infectious outbreak, the population could be protected by vaccinating only the mothers, a strategy that would save chicks the strain of forcing an immune response.
Albatrosses: also under threat
Like other colonial birds, albatrosses are also highly vulnerable to epidemics. The researchers behind the recent study used demographic modelling to analyse the effects of vaccination on albatross species threatened by potential outbreaks of infection: the Amsterdam albatross (Diomedea amsterdamensis) and the yellow-nosed albatross (Thalassarche chlororhynchos). In these long-living species, which also care for their young for an extended period, avian cholera - an infectious disease caused by the pathogenic bacteria Pasteurella multocida, which provokes infections of the respiratory and skeletal systems - has been suggested to be responsible for mortalities during the rearing period. According to the authors, in the event of a viral epidemic, vaccination of adult females could be a key factor in stabilizing the population and safeguarding the demographic recovery of the colony in its natural habitat.
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