A Four-Year Survey of Hemoparasites from Nocturnal Raptors (Strigiformes) Confirms a Relation between Leucocytozoon and Low Hematocrit and Body Condition Scores of Parasitized Birds

Abstract

Most hemoparasites hosted by wild birds appear to be harmless, but most of the blood parasite studies in avian wildlife are mainly focused on passerines or migratory species. This study aimed to assess the occurrence of blood parasites in nocturnal raptors (Strigiformes order) and their effect on hematological parameters. A total of 134 blood samples were collected during a four-year period for hematological analysis and hemoparasite detection and quantification by microscopical examination of the samples. Overall, the occurrence of hemoparasites was 35.1%, with Leucocytozoon being the most frequently detected (32.1%), followed by Haemoproteus (11.2%), Trypanosoma and Plasmodium (2.2% each). Among the different bird species, the Eurasian eagle-owl (Bubo bubo) showed the highest blood parasite positivity (94.7%). In barn owls, the positive birds displayed a lower hematocrit measurement and body condition score than the non-parasitized ones (p = 0.007 and p = 0.005, respectively), especially those parasitized by Leucocytozoon. Moreover, the analysis of the magnitude of this association revealed that the presence of hemoparasites is five times more frequent in barn owls with a 2/5 body condition score. Despite the host–parasite coevolution in Strigiformes, our results show a correlation between the presence of hemoparasites and some health parameters, including blood parameters.

Insights into the Biology of Leucocytozoon Species (Haemosporida, Leucocytozoidae): Why Is There Slow Research Progress on Agents of Leucocytozoonosis?

“…Low chronic parasitemia often appears benign in wild birds that are observed in captivity, but the consequences of severe primary sporozoite-induced infections remain insufficiently understood in wildlife [ 3 , 4 , 217 ]. Some long-term field observations and case reports suggest that leucocytozoids might be important health problems [ 4 , 351 , 352 ]. Unfortunately, the pathogenicity of only a few parasite species has been studied in detail.…”

Host Cells of Leucocytozoon (Haemosporida, Leucocytozoidae) Gametocytes, with Remarks on the Phylogenetic Importance of This Character

“…TURMER01 induce inflammatory reaction and necroses in infected organs [ 10 ]. Blood sample analysis shows that Leucocytozoon infections (unknown lineage) in barn owls ( Tyto alba ) can increase the total leukocyte count and the heterophil:lymphocyte ratio (H:L) [ 58 ], which is a known indicator of immune response to stress and illness in birds [ 59 ], as well as low haematocrit [ 58 ]. Contrary to that, Leucocytozoon infection (unknown lineage) in the American crows ( Corvus brachyrhynchos ) showed a slight increase in haematocrit levels, but this was not statistically significant [ 60 ].…”