Avian haemosporidian parasites of accipitriform raptors

Background The order Accipitriformes comprises the largest group of birds of prey with 260 species in four families. So far, 21 haemosporidian parasite species have been described from or reported to occur in accipitriform birds. Only five of these parasite species have been characterized molecular genetically. The first part of this study involved molecular genetic screening of accipitriform raptors from Austria and Bosnia-Herzegovina and the first chromogenic in situ hybridization approach targeting parasites in this host group. The aim of the second part of this study was to summarize the CytB sequence data of haemosporidian parasites from accipitriform raptors and to visualize the geographic and host distribution of the lineages. Methods Blood and tissue samples of 183 accipitriform raptors from Austria and Bosnia-Herzegovina were screened for Plasmodium, Haemoproteus and Leucocytozoon parasites by nested PCR, and tissue samples of 23 PCR-positive birds were subjected to chromogenic in situ hybridization using genus-specific probes targeting the parasites’ 18S rRNAs. All published CytB sequence data from accipitriform raptors were analysed, phylogenetic trees were calculated, and DNA haplotype network analyses were performed with sequences from clades featuring multiple lineages detected in this host group. Results Of the 183 raptors from Austria and Bosnia-Herzegovina screened by PCR and sequencing, 80 individuals (44%) were infected with haemosporidian parasites. Among the 39 CytB lineages detected, 18 were found for the first time in the present study. The chromogenic in situ hybridization revealed exo-erythrocytic tissue stages of Leucocytozoon parasites belonging to the Leucocytozoon toddi species group in the kidneys of 14 infected birds. The total number of CytB lineages recorded in accipitriform birds worldwide was 57 for Leucocytozoon, 25 for Plasmodium, and 21 for Haemoproteus. Conclusion The analysis of the DNA haplotype networks allowed identifying numerous distinct groups of lineages, which have not yet been linked to morphospecies, and many of them likely belong to yet undescribed parasite species. Tissue stages of Leucocytozoon parasites developing in accipitriform raptors were discovered and described. The majority of Leucocytozoon and Haemoproteus lineages are specific to this host group, but most Plasmodium lineages were found in birds of other orders. This might indicate local transmission from birds kept at the same facilities (raptor rescue centres and zoos), likely resulting in abortive infections. To clarify the taxonomic and systematic problems, combined morphological and molecular genetic analyses on a wider range of accipitriform host species are needed.

Novel RNA viruses associated with avian haemosporidian parasites

Avian haemosporidian parasites can cause malaria-like symptoms in their hosts and have been implicated in the demise of some bird species. The newly described Matryoshka RNA viruses (MaRNAV1 and MaRNAV2) infect parasites that in turn infect their vertebrate hosts. MaRNAV2 was the first RNA virus discovered associated with parasites of the genus Leucocytozoon. By analyzing metatranscriptomes from the NCBI SRA database with local sequence alignment tools, we detected two novel RNA viruses; we describe them as MaRNAV3 associated with Leucocytozoon and MaRNAV4 associated with Parahaemoproteus. These had ~40-60% amino acid identity to the RNA-dependent RNA-polymerase (RdRp) of MaRNAV1 and 2, respectively. These findings lead us to hypothesize that MaRNAV_like viruses are widespread and tightly associated with the order Haemosporida since they have been described in human Plasmodium vivax, and now two genera of avian haemosporidians.

Prevalence of Avian Haemosporidian Parasites in Village Chickens (Gallus gallus domesticus) from Kwami, Gombe State, Nigeria

This study was carried out to determine the prevalence of avian haemosporidian parasites in village chickens in Kwami, Gombe State, Nigeria using microscopy and the associated risk factors using structured questionnaires. To achieve this goal, blood samples were collected from 346 apparently healthy village chickens in Kwami of Gombe State, and a total of 45 farmers were interviewed using structured questionnaires. Microscopy revealed an overall prevalence of 20.8% (72/346) for haemosporidian parasites comprising of Plasmodium spp. with 41 (11.8%; 95% CI = 8.9 – 15.7) and Haemoproteus spp. 23 (6.6%; 95% CI = 4.5 – 9.8) as single infection and mixed infection of Plasmodium + Haemoproteus spp. having 8 (2.3%; 95% CI = 1.2 – 4.5). Prevalence of avian haemosporidian parasites was significantly higher in male (13.9%) compared to hens (6.9%), as well as in adults (14.50%) compared to growers (6.4%). The prevalence was also found to be higher in the rainy season (15.6%) compared to the dry (5.2%) seasons of the study period. Questionnaire survey on attitude and practice of the village chicken farmers in the study area has shown that village chicken are raised under the extensive management system and are reared with other village poultry species on free range. Inadequate biosecurity, poor management and husbandry systems constituted the predisposing risk factors associated with haemoparasite infections in this study. Key words: Haemosporidian parasites; Avian malaria, Microscopy, Scavenging Chickens; Kwami, Gombe State

Seasonal Dynamics and Diversity of Haemosporidians in a Natural Woodland Bird Community in Slovakia

Despite the ubiquity of disease seasonality, mechanisms behind the fluctuations in seasonal diseases are still poorly understood. Avian hemosporidiosis is increasingly used as a model for ecological and evolutionary studies on disease dynamics, but the results are complex, depending on the focus (hosts, parasites, vectors) and scale (individuals, community, populations) of the study. Here, we examine the local diversity of haemosporidian parasites and the seasonal patterns of infections, parasite richness, and diversity in a natural woodland bird community in Slovakia. In 35 avian species, we detected 111, including 19 novel, haemosporidian cytochrome b lineages. The highest numbers of lineages were detected during spring and autumn, corresponding with higher avian species richness and infection prevalence in the avian community during these periods of time. Nevertheless, the haemosporidian community in the local breeders in summer was relatively stable, Haemoproteus lineages dominated in the local avian haemosporidian community, and only few parasite lineages were abundant within each genus. While prevailing Leucocytozoon infections in spring suggest that the majority of sampled birds wintered in the Mediterranean region, Plasmodium infections in spring can be due to relapses in reproductively active short-distance migrants. Multiple haemosporidian infections, both intra- and inter-generic ones, were common in the local avian community. Infection intensity peaked during summer and tended to be higher in older birds, pointing to the role of supressed immunity in reproductively active birds.

Apparent Absence of Avian Malaria and Malaria-Like Parasites in Northern Blue-Footed Boobies Breeding On Isla Isabel

Haemosporidian parasites are common in birds, but often are not in seabirds. The absence of vectors/genetic resistance to infection have been proposed to explain this pattern. Examination of different host populations is required to confirm the absence of blood parasites in widespread host species, which could be differently exposed to blood parasites across their geographic range. Moreover, screening of blood parasites in many seabirds has been done only by visual inspection of blood smears, which can miss low-intensity infections. Screening of blood parasites of the genera Plasmodium, Haemoproteus and Leucocytozoon, combining inspection of blood smears and PCR-based detection methods, revealed that a highly philopatric colony of blue-footed boobies (Sula nebouxii) in the Tropical North Pacific is likely free of these parasites. Earlier detection of Haemoproteus parasites in frigatebirds cohabiting with boobies in our study site and blue-footed boobies breeding on the Galapagos Islands suggests that absence of blood parasites in this northern booby colony could not be attributable to the absence of vectors or genetic resistance to infection. High host specificity or fine-scale spatial heterogeneity in the abundance of insect vectors could explain our negative results, but these hypotheses remain to be tested. We emphasize the relevance of assessing the occurrence of blood parasites in different populations of widespread host species, such as blue-footed boobies.

How Does Circadian Rhythm Shape Host-Parasite Associations? A Comparative Study on Infection Patterns in Diurnal and Nocturnal Raptors

Infection patterns of parasites, including their prevalence, diversity and host specificity, can be impacted by many biological and environmental factors, but no study has focused on the circadian rhythms of vertebrate hosts, which may affect susceptibilities and encounter rates between hosts and vectors and further shape host-parasite associations. In this study, we focused on avian haemosporidians, a classical model in studies of host-parasite associations, and investigated the infection patterns in rescued raptors brought to the Beijing Raptor Rescue Center during 2007–2020. We first assessed the association between prevalence and host biotic traits; haemosporidian prevalence was higher in the nocturnal raptors than in the diurnal raptors, and the prevalence of Haemoproteus and Leucocytozoon in the nocturnal raptors was significantly higher than that in the diurnal raptors. Furthermore, we analysed the phylogenetic relationship and host-parasite network-level differences of haemosporidian parasites in diurnal and nocturnal raptors, and demonstrated that the lineages infecting the diurnal and nocturnal raptors were not clearly separated, but the nocturnal lifestyle led to a more specialized host-parasite network structure. These variations in host-parasite associations may be driven by different susceptibilities of the hosts and the diversity or abundance of vectors during the day and night. Our study provides new insight into host-parasite associations shaped by circadian rhythm and calls for more studies on the underlying mechanisms of parasite infection.

Assessment of Associations between Malaria Parasites and Avian Hosts—A Combination of Classic System and Modern Molecular Approach

Avian malaria and related haemosporidian parasites are responsible for fitness loss and mortality in susceptible bird species. This group of globally distributed parasites has long been used as a classical system for investigating host–parasite associations. The association between a parasite and its hosts can be assessed by the prevalence in the host population and infection intensity in a host individual, which, respectively, reflect the ability of the parasite to infect the host and reproduce within the host. However, the latter has long been poorly investigated due to numerous challenges, such as lack of general molecular markers and limited sensitivity of traditional methods, especially when analysing naturally infected birds. The recent development of genetic databases, together with novel molecular methodologies, has shed light on this long-standing problem. Real-time quantitative PCR has enabled more accurate quantification of avian haemosporidian parasites, and digital droplet PCR further improved experimental sensitivity and repeatability of quantification. In recent decades, parallel studies have been carried out all over the world, providing great opportunities for exploring the adaptation of haemosporidian parasites to different hosts and the variations across time and space, and further investigating the coevolutionary history between parasites and their hosts. I hereby review the most important milestones in diagnosis techniques of avian haemosporidian parasites and illustrate how they provide new insights for understanding host–parasite associations.