Malaria parasites (Plasmodium spp.) infecting introduced, native and endemic New Zealand birds

Abstract

Avian malaria is caused by intracellular mosquito-transmitted protist parasites in the order Haemosporida, genus Plasmodium. Although Plasmodium species have been diagnosed as causing death in several threatened species in New Zealand, little is known about their ecology and epidemiology. In this study, we examined the presence, microscopic characterization and sequence homology of Plasmodium spp. isolates collected from a small number of New Zealand introduced, native and endemic bird species. We identified 14 Plasmodium spp. isolates from 90 blood or tissue samples. The host range included four species of passerines (two endemic, one native, one introduced), one species of endemic pigeon and two species of endemic kiwi. The isolates were associated into at least four distinct clusters including Plasmodium (Huffia) elongatum, a subgroup of Plasmodium elongatum, Plasmodium relictum and Plasmodium (Noyvella) spp. The infected birds presented a low level of peripheral parasitemia consistent with chronic infection (11/15 blood smears examined). In addition, we report death due to overwhelming parasitemia in a blackbird, a great spotted kiwi and a hihi. These deaths were attributed to infections with either Plasmodium spp. lineage LINN1 or P. relictum lineage GRW4. To the authors' knowledge, this is the first published report of Plasmodium spp. infection in great spotted and brown kiwi, kereru and kokako. Currently, we are only able to speculate on the origin of these 14 isolates but consideration must be made as to the impact they may have on threatened endemic species, particularly due to the examples of mortality.

Fig. 1

Phylogenetic analysis and comparison of 14 Plasmodium spp. isolates from New Zealand avian species and previously published Plasmodium spp. sequences present in the GenBank and/or MalAvi database. Bayesian and neighbour-joining (NJ) phylogeny of mitochondrial cytochrome b gene from Plasmodium falciparum used as an outgroup, 20 previously published Plasmodium spp. submitted to Genbank or the MalAvi database and the 14 Plasmodium spp. New Zealand isolates (in bold font) from this study. Lineages of malaria parasites which are closely related (within a genetic distance of ≤5%) to P. (Huffia) elongatum, P. (Haemamoeba) relictum and P. (Novyella) spp. are marked by bars A, C and D to represent the different subgenera. The bar B indicates a possible subgroup of Plasmodium elongatum. Numbers above or below branch nodes indicate bootstrap support based on 1,000 replicates. Names of the lineages (when available) and Genbank accession numbers of the sequences are given after the species names of the parasites. The branch lengths are drawn proportionally to the amount of changes (scale bar is shown)

Fig. 2

Representative developmental structures observed in the erythrocytes from two bird species demonstrating distinct Plasmodium subgenus morphologies. t trophozoites, mg macrogametocyte, s intraerythrocytic schizont/meront. a, b Kokako #1 erythrocytes suggestive of P. (Haemomoeba) relictum. c, d Blackbird #3 erythrocytes infected with P. (Novyella) spp. suggestive of P. rouxi. Scale bars = 10 μm

Fig. 3

Haematoxylin-and-eosin-stained tissues from the dead blackbird (a cerebellum, b lung), great spotted kiwi (c spleen, d lung) and hihi (e spleen, f lung). Arrows indicate areas containing Plasmodium spp. schizonts. ×100 magnification. Scale bars = 20 μm