Hidden Plasmodium diversity revealed in southeastern Asian passerines using next-generation amplicon sequencing

Monitoring haemosporidian (Genus <i>Plasmodium</i>) infections in passerine birds is essential for understanding the intricate dynamics of avian malaria and its implications for ecology and evolution of avian populations. In this study, we investigated the prevalence and diversity of malaria infections caused by <i>Plasmodium</i> species in three passerine species in Cat-Tien National Park, Vietnam. Using next-generation amplicon sequencing (NGS) of haemosporidian cytochrome <i>b</i> gene, we identified two known and ten novel <i>Plasmodium</i> lineages. Our genetic analysis revealed a high rate of <i>Plasmodium</i> infections in the little spiderhunter (<i>Arachnothera longirostra</i>; Nectariniidae), the white-rumped shama (<i>Copsychus malabaricus</i>; Muscicapidae) and the blue-winged pitta (<i>Pitta moluccensis</i>; Pittidae). Species delimitation methods identified five distinct operational taxonomic units (OTUs), consistently across the majority of the used methods. Each of the passerine species was infected with a specific subset of the total <i>Plasmodium</i> diversity. Phylogenetic analysis showed that sympatric <i>Plasmodium</i> OTUs are not closely related and possess overlapping host preferences. Our findings may reflect differences in habitat use, such as the vertical strata occupied by different bird species, which contribute to varying exposure levels to suitable vectors, thereby influencing infection rates and parasite diversity. Our findings corroborate the view that avian malaria parasites are not uniformly opportunistic; rather, their distribution is filtered by host identity and ecology. Understanding these dynamics is crucial for avian conservation and broader ecological studies, as avian malaria serves as a model for studying parasite-vector-host co-evolution and the impact of environmental changes on disease dynamics.