Description and Molecular Characterization of Two Species of Avian Blood Parasites, with Remarks on Circadian Rhythms of Avian Haematozoa Infections

SIMPLE SUMMARY: The diversity of avian blood parasites is remarkable, and they are often found in co-infections, which is a challenge for wildlife parasitology research. Co-infections not only make parasite morphological and molecular identification difficult, but also might influence the infection dynamics and disease manifestation. This study investigated blood parasites infections in a Eurasian blackbird (Turdus merula) and a Song thrush (Turdus philomelos). A new Lankesterella species was found and described. The molecular characterization of this parasites as well as Splendidofilaria mavis, an avian filarioid nematode, was developed. As several blood infections were present in co-infection, we used this opportunity to investigate the daily changes in the parasite intensity seen in the blood of these birds. A peak of the Plasmodium matutinum parasitemia was seen during the daytime. Leucocytozoon spp. showed some parasitemia peaks close to the evening and night. Trypanosoma spp. and S. mavis parasitemia increased during the night. Data about daily variation of Haemoproteus, Lankesterella, and S. mavis parasites were obtained for the first time. No pattern in parasitemia dynamics was identified in Haemoproteus and Lankesterella infections. ABSTRACT: Avian blood parasites are remarkably diverse and frequently occur in co-infections, which predominate in wildlife. This makes wildlife pathogen research challenging, particularly if they belong to closely related groups, resulting in diagnostic problems and poor knowledge about such infections as well as the patterns of their co-occurrence and interactions. This is particularly true due to the periodicity (circadian rhythms) of parasitemia, which means that different parasitemia and parasite stages might be found throughout the day. We analysed blood samples from a Eurasian blackbird (Turdus merula) and a Song thrush (Turdus philomelos). This study aimed to describe a new avian Lankesterella species and molecularly characterize and redescribe Splendidofilaria mavis, a common avian filarioid nematode. Additionally, it was possible to investigate the circadian rhythms of the avian blood parasites belonging to Plasmodium, Haemoproteus, Leucocytozoon, and Trypanosoma, which occurred in co-infection in the same avian host individuals. Different circadian rhythms were seen in different parasites, with Plasmodium sp. peaks occurring at midday, Leucocytozoon spp. peaks mainly during the evening and night, and Trypanosoma spp. and microfilariae peaks at midnight. No periodicity was seen in Haemoproteus and Lankesterella species infections. The time of parasitemia peaks most likely coincides with the time of vectors’ activity, and this should be beneficial for transmission. Knowledge about the circadian rhythms is needed for better understanding patterns in host-parasite interactions and disease transmission.