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

Abstract

Blood parasites of the genus Leucocytozoon (Leucocytozoidae) only inhabit birds and represent a readily distinct evolutionary branch of the haemosporidians (Haemosporida, Apicomplexa). Some species cause pathology and even severe leucocytozoonosis in avian hosts, including poultry. The diversity of Leucocytozoon pathogens is remarkable, with over 1400 genetic lineages detected, most of which, however, have not been identified to the species level. At most, approximately 45 morphologically distinct species of Leucocytozoon have been described, but only a few have associated molecular data. This is unfortunate because basic information about named and morphologically recognized Leucocytozoon species is essential for a better understanding of phylogenetically closely related leucocytozoids that are known only by DNA sequence. Despite much research on haemosporidian parasites during the past 30 years, there has not been much progress in taxonomy, vectors, patterns of transmission, pathogenicity, and other aspects of the biology of these cosmopolitan bird pathogens. This study reviewed the available basic information on avian Leucocytozoon species, with particular attention to some obstacles that prevent progress to better understanding the biology of leucocytozoids. Major gaps in current Leucocytozoon species research are discussed, and possible approaches are suggested to resolve some issues that have limited practical parasitological studies of these pathogens.

Prevalence of Leucocytozoon infection in domestic birds in Ghana

“…It is highly possible that due to the extremely low parasitemia in these naturally infected birds, we could not find any gametocytes of the parasite. Nevertheless, this observation could also be a result of the incomplete life cycle of the parasites within the host causing the detection of sporozoites DNA in the host [ 15 ] suggesting abortive infection similar to reports on Haemoproteus minutus [ 24 ]. This notwithstanding, it is also likely that gametocytes were simply undetected by microscopy due to difficulty in proper morphological identification of the gametocytes.…”

“…In monitoring the parasites that can affect poultry health, it has been established that parasites such as Leucocytozoon are of great importance. So far, about 45 morphologically distinct species of Leucocytozoon parasites [ 15 ] have been described for causing leucocytozoonosis disease in wild and domestic birds. Only a few of these species have, however, been described in poultry.…”

High Abundance of Haemoproteus Parasites in Culicoides (Diptera, Ceratopogonidae), with a Confirmation of Culicoides reconditus as a New Vector of These Avian Blood Parasites

“…and Hippoboscidae flies transmitting Haemoproteus (Haemoproteus) spp. [ 1 , 2 , 3 , 4 , 5 ]. This high parasite diversity is confirmed by the 177 species described [ 2 ], and the 2019 genetic lineages (the haplotypes of a fragment of the cytochrome b gene ( cytb ) of the parasite) reported in the MalAvi database ( , accessed on 20 November 2023) [ 6 ].…”

Molecular survey and genetic diversity of Plasmodium sp. infesting domestic poultry in northeastern Thailand

“…Infection with these bloodborne parasites affects various organs within a bird’s body, causing loss of function and affecting poultry production. Clinical symptoms in birds infected with haemosporidian parasites regularly include lethargy, loss of appetite, dizziness, diarrhoea, cyanosis, anaemia and thrombocytopaenia ( 4 , 38 ). After postmortem examination, hepatomegaly, splenomegaly, and haemorrhagic areas in internal organs are frequently noted in infected animals ( 19 , 32 , 36 ).…”