Seabird surveillance for evidence of past and present infectious agent incursion into New Zealand

Australasian gannet colony at Muriwai Beach. Image - Dan Tompkins

Border biosecurity is a real and present concern for New Zealand. Many infectious agents that impact on plant, animal and human health in other parts of the world are not currently found here, yet there is the risk that such agents could be introduced, in some cases with potentially devastating consequences.

In response to this threat, much emphasis is currently placed on managing the risks of exotic agent incursion associated with human activities such as international air travel and container shipping. However, natural pathways of potential agent incursion into New Zealand also exist and should not be overlooked. In particular, many of our sea birds undergo long flights to other countries, and could bring back agents they are exposed to overseas. Some terrestrial birds also fall into this category, such as the shining cuckoo which migrates from the New Britain–Solomon Islands archipelago to New Zealand to breed.

Given that global change drivers, such as changes in land-use and climate, can alter bird dispersal and migration patterns, it is essential to understand the potential for agent incursion into New Zealand, and to be able to assess future change, which requires current baseline measures. To start to address these knowledge gaps, a team led by Dan Tompkins conducted surveys of seabirds at three locations – Muriwai Beach, Cape Kidnappers and Kaikoura Peninsula. Both Muriwai Beach and Cape Kidnappers are home to large colonies of Australasian gannets (photos), whose young cross the Tasman Sea within three months of hatching, remain in Australian waters until they are two to three years old, then return to their natal gannetries. The Kaikoura Peninsula is home to large populations of red-billed gulls (photo) and white-fronted terns. Red-billed gulls can move over 300 km after breeding and occasionally migrate across the Tasman Sea, while large numbers of white-fronted terns migrate from New Zealand to Australia (the farthest known movement of a banded bird being 2970 km from Kaikoura to South Australia).

For Dan’s study, large numbers of these seabirds were captured at these three New Zealand locations, using hand nets for red-billed gulls and white-fronted terns, and shepherd’s crooks for Australasian gannets. Blood samples were taken from individuals caught, and ticks (Carios capensis – formerly Ornithodoros capensis – and Ixodes eudyptidis) were also collected from birds captured at Kaikoura Peninsula.

The blood collected was centrifuged for serum extraction for serological testing, apart from single drops for thin blood smears and small amounts to go into buffer solutions for molecular diagnostics. Sera samples were generically screened for antibodies to flaviviruses; potential positives with sufficient sera were re-tested, and also subjected to specific tests for Murray Valley encephalitis virus and Kunjin virus (flaviviruses of incursion concern from Australia). Testing for antibodies for specific alphaviruses (Ross River virus, Barmah Forest virus and Sindbis virus; arboviral agents of incursion concern also from Australia) was carried out on some samples (including some ticks). Smears were examined microscopically for blood parasites, with follow-up DNA sequencing to identify any infectious agents observed.

Babesia sp. parasites were detected in blood smears from Australasian gannets at both Muriwai Beach and Cape Kidnappers, and from both red-billed gulls and white-fronted terns (and their ticks) at Kaikoura Peninsula. Sequencing and phylogenetic reconstruction revealed three new unique sequence variants that were similar to two bird-derived variants already known. Two of the new variants were similar to Babesia poelea known from brown boobies in the Central Pacific, and the third was similar to B. kiwiensis from the North Island brown kiwi. The Babesia sequences identified in Dan’s study showed no evidence of host specificity; hence ticks from seabirds are likely to be part of the incursion pathway by which Babesia parasites infect kiwi.

Antibodies to flavivirus were also detected in both red-billed gulls and white-fronted terns at Kaikoura Peninsula. This suggests that two flaviviruses (Saumarez Reef virus and an unidentified Hughes group arbovirus) previously isolated from birds and ticks at Kaikoura Peninsula are still present at this site. In addition, one Australasian gannet from Muriwai Beach was positive for antibodies to Ross River virus. This is most likely the result of exposure in Australian waters prior to returning to New Zealand. Mathematical models indicate that climate change will increase the capacity of mosquitoes in New Zealand to support Ross River virus outbreaks, and should birds return to New Zealand with this virus, they will provide a potential pathway for disease incursion into the country. As Ross River virus is a public health concern, causing debilitating polyarthritis in many people infected, more thorough surveillance should be carried out at Muriwai Beach to confirm its current status.

Serological testing was carried out by Cheryl Johansen’s group at The University of Western Australia, and Babesia molecular diagnostics were carried out by Peter Irwin’s group at Murdoch University, Melbourne, Australia. Funding was provided by the Foundation for Research, Science and Technology Cross Department Research Funding to Graham Mackereth (while at Biosecurity New Zealand).