Role of reticulocytes on gametocytogenesis in chickens infected with Leucocytozoon caulleryi

Pathology and molecular characterization of Leucocytozoon caulleryi from backyard chickens in Khon Kaen Province, Thailand

Aim:

The aim of this study was to characterize Leucocytozoon caulleryi from backyard chickens in Khon Kaen Province, Thailand.

Materials and Methods:

Tissue samples were collected from backyard chickens suspected to have leucocytozoonosis and subjected to histopathology examination. The BLAST Tool at NCBI GenBank (Basic Local Alignment Research Tools) (http://www.ncbi.nlm.nih.gov/BLAST) was used to identify the nucleotide sequence of the partial cytochrome c oxidase subunit I (cox I) gene. A Phylogenetic tree for analysis of L. caulleryi was constructed by using MEGA 7.0 software (https://www.megasoftware.net/).

Results:

The necropsy results revealed the subcutaneous hemorrhages of pectoral muscles, multifocal hemorrhages of the thymus and pectoral muscles, hemorrhage of the proventriculus and peritoneal cavity, and megaloschizonts of the pancreas and intestine, including subcapsular hemorrhages of the liver. Microscopic examination revealed numerous megaloschizonts of Leucocytozoon spp. in the pectoral muscles, intestine, pancreas, and thymus. Molecular analysis of the partial cox I gene showed that the causal agent was closely related to L. caulleryi reported in Japan.

Conclusion:

From these results, L. caulleryi was determined to be the causal agent of leucocytozoonosis and was closely associated with L. caulleryi reported in Japan.

Phenotypic plasticity in reproductive effort: malaria parasites respond to resource availability

The trade-off between survival and reproduction is fundamental in the life history of all sexually reproducing organisms. This includes malaria parasites, which rely on asexually replicating stages for within-host survival and on sexually reproducing stages (gametocytes) for between-host transmission. The proportion of asexual stages that form gametocytes (reproductive effort) varies during infections-i.e. is phenotypically plastic-in response to changes in a number of within-host factors, including anaemia. However, how the density and age structure of red blood cell (RBC) resources shape plasticity in reproductive effort and impacts upon parasite fitness is controversial. Here, we examine how and why the rodent malaria parasite Plasmodium chabaudi alters its reproductive effort in response to experimental perturbations of the density and age structure of RBCs. We show that all four of the genotypes studied increase reproductive effort when the proportion of RBCs that are immature is elevated during host anaemia, and that the responses of the genotypes differ. We propose that anaemia (counterintuitively) generates a resource-rich environment in which parasites can afford to allocate more energy to reproduction (i.e. transmission) and that anaemia also exposes genetic variation to selection. From an applied perspective, adaptive plasticity in parasite reproductive effort could explain the maintenance of genetic variation for virulence and why anaemia is often observed as a risk factor for transmission in human infections.

Host cell preference and variable transmission strategies in malaria parasites

Malaria and other haemosporin parasites must undergo a round of sexual reproduction in their insect vector in order to produce stages that can be transmitted to vertebrate hosts. Consequently, it is crucial that parasites produce the sex ratio (proportion of male sexual stages) that will maximize the number of fertilizations and thus, transmission to new vertebrate hosts. There is some evidence to show that, consistent with evolutionary theory, the sex ratios of malaria parasites are negatively correlated to their inbreeding rate. However, recent theory has shown that when fertilization success is compromised, parasites should respond by increasing their investment in sexual stages or by producing a less female biased sex ratio than predicted by their inbreeding rate alone. Here, we show that two species of rodent malaria, Plasmodium chabaudi and Plasmodium vinckei petteri , adopt different strategies in response to host anaemia, a factor thought to compromise transmission success: P. chabaudi increases investment in sexual stages, whereas P. vinckei produces a less female biased sex ratio. We suggest that these different transmission strategies may be due to marked species differences in host cell preference.