Beak and feather disease virus (BFDV) prevalence, load and excretion in seven species of wild caught common Australian parrots

Abstract

Pathogens pose a major risk to wild host populations, especially in the face of ongoing biodiversity declines. Beak and feather disease virus (BFDV) can affect most if not all members of one of the largest and most threatened bird orders world-wide, the Psittaciformes. Signs of disease can be severe and mortality rates high. Its broad host range makes it a risk to threatened species in particular, because infection can occur via spill-over from abundant hosts. Despite these risks, surveillance of BFDV in locally abundant wild host species has been lacking. We used qPCR and haemagglutination assays to investigate BFDV prevalence, load and shedding in seven abundant host species in the wild in south-east Australia: Crimson Rosellas (Platycercus elegans), Eastern Rosellas (Platycercus eximius), Galahs (Eolophus roseicapillus), Sulphur-crested Cockatoos (Cacatua galerita), Blue-winged Parrots (Neophema chrysostoma), Rainbow Lorikeets (Trichoglossus moluccanus) and Red-rumped Parrots (Psephotus haematonotus). We found BFDV infection in clinically normal birds in six of the seven species sampled. We focused our analysis on the four most commonly caught species, namely Crimson Rosellas (BFDV prevalence in blood samples: 41.8%), Sulphur-crested Cockatoos (20.0%), Blue-winged Parrots (11.8%) and Galahs (8.8%). Species, but not sex, was a significant predictor for BFDV prevalence and load. 56.1% of BFDV positive individuals were excreting BFDV antigen into their feathers, indicative of active viral replication with shedding. Being BFDV positive in blood samples predicted shedding in Crimson Rosellas. Our study confirms that BFDV is endemic in our study region, and can inform targeted disease management by providing comparative data on interspecies variation in virus prevalence, load and shedding.

Fig 1. Mean BFDV prevalence (% of total individuals tested) ± 95% confidence intervals.

Shown for blood and pectoralis muscle samples, as well as cloacal swabs, separately for each focal host species and pooled across the four focal host species. Data labels represent number of birds infected out of number of birds tested.

Fig 2. Mean viral load, shown separately for each of the four focal species.

Log₁₀-transformed viral load is shown ± 95% confidence intervals. Numbers at the base of bars indicate sample size of individuals for each species.

Fig 3. BFDV antigen excretion into feathers (positive HA result), in birds which were BFDV positive as detected by qPCR, in at least one sample type (either blood or cloacal swabs, or both).

Bars show percentage of birds with antigen excretion out of all birds tested ± 95% confidence intervals, with number of birds with detectable antigen excretion out of total number of birds tested at the base of bars. Dots show average HA titre (relative amount of antigen (log₂)) in BFDV positive birds with HA activity ± 95% confidence intervals. Percentage of birds with antigen excretion, and mean antigen titres, are shown per species (panel a), and per sample type that was BFDV positive when tested with qPCR, for all four species combined (panel b) and for Crimson Rosellas only (panel c).