Emerging infectious disease or evidence of endemicity? A multi-season study of beak and feather disease virus in wild red-crowned parakeets (Cyanoramphus novaezelandiae)

Beak and feather disease virus (BFDV) is a single-stranded DNA virus that is the etiological agent of beak and feather disease in both wild and captive parrots. Given that BFDV is globally recognized as a conservation threat for wild parrots, between 2011-2013, red-crowned parakeets (Cyanoramphus novaezelandiae, n = 229), which are endemic to New Zealand, were captured in mist nets on Tiritiri Matangi Island and Hauturu-o-Toi/Little Barrier Island (LBI), New Zealand, for disease surveillance. Blood and feathers from all birds were tested by PCR for BFDV, and full genomes were recovered and sequenced. A subset of blood samples (n = 96) were tested for antibodies to BFDV by the haemagglutination inhibition (HI) test. A further 238 feather samples were obtained from red-crowned parakeets from three sites in the Wellington region of the North Island, and these were screened for BFDV. The DNA-based prevalence of BFDV infection determined on Tiritiri Matangi Island was 1.09 % (CI 95 %, 0.1-3.9 %); on Hauturu-o-Toi/LBI, 4.4 % (95 % CI, 0.5 %-15.1 %); on Kapiti Island, 3.4 % (CI 95 %, 1.1-7.8 %); at the ZEALANDIA-Karori sanctuary, 1.6 % (95 % CI, 0-8.4 %); and on Matiu-Somes Island, 0 % (CI 95 %, 0-12.3 %). Seroprevalence for BFDV, indicating prior or current exposure, in the Tiritiri Matangi Island population, it was 2 % (CI 95 %, 0-10.1 %), and in the Hauturu-o-Toi/LBI population was 14 % (CI 95 %, 5.3-27.9 %). BFDV-positive birds showed no signs of clinical disease, with the exception of an individual bird obtained opportunistically from Shakespear Regional Park during the study period, which had classical signs of feather loss. Phylogenetic analysis of the 11 full genome sequences recovered from BFDV-positive red-crowned parakeets revealed evidence of ongoing viral flow between red-crowned parakeets and eastern rosellas (Platycercus eximius) in the Hauraki Gulf/Auckland region, with separate but closely related strains from the Wellington region of the North Island. This is the first study to report HI results for a New Zealand endemic parrot species, and the first epidemiological analysis of serial cross-sectional surveys in a BFDV-infected population of red-crowned parakeets in New Zealand. We postulate that although BFDV remains a threat to small, isolated or naïve populations of parrots globally, the low viral prevalence in this and other studies suggests that native parakeets in New Zealand may act as dead-end or spillover hosts.