Avian blood parasites in an endangered columbid: Leucocytozoon marchouxi in the Mauritian Pink Pigeon Columba mayeri.

There is increasing evidence that pathogens can play a significant role in species decline. This study of a complete free-living species reveals a cost of blood parasitism to an endangered host, the Pink Pigeon Columba mayeri, endemic to Mauritius. We investigated the prevalence and effect of infection of the blood parasite, Leucocytozoon marchouxi, in the free-living Pink Pigeon population. Overall, L. marchouxi infection prevalence detected was 18.3%. Juveniles were more likely to be infected than older birds and there was geographical variation in infection prevalence. Survival of birds infected with L. marchouxi was lower than that of uninfected birds to 90 days post-sampling. This study suggests that while common haematozoa are well tolerated in healthy adults, these parasites may have greater pathogenic potential in susceptible juveniles. The study is unusual given its completeness of species sampling (96%) within a short time-period, the accurate host age data, and its focus on blood parasites in a threatened bird species. Species for which long-term life-history data are available for every individual serve as valuable models for dissecting the contribution of particular pathogens to species decline.

Hypothermia for the treatment of neonatal ischemic encephalopathy: is the genie out of the bottle?

Evidence suggests that hypothermia for hypoxic ischemic encephalopathy in the term neonate may decrease the risk of death or neurodevelopmental impairment. The objective of this study was to determine how hypothermia has been incorporated into practice. An anonymous survey was sent to medical directors of United States neonatal intensive care units (NICUs) in October 2005. We received completed surveys from 441 (54.5%) of 809 of NICUs. Only 6.4% of respondents used hypothermia. The most common method was total body cooling (64.3%) compared with head cooling (25%) or both (10.7%). At centers that did not offer hypothermia, 29% transferred infants to an institution that did. Centers that offered hypothermia were more likely at academic institutions (76.9%) compared with private practices (11.5%; p < 0.001). Hypothermia was more likely offered at institutions that offered extracorporeal membrane oxygenation (ECMO; 57%) than centers where ECMO was not offered (43%; p < 0.001). There has not been widespread use of hypothermia. There are a variety of protocols used. As results of further outcome studies become available, educational efforts and national practice guidelines will be essential.

Limitation of Trypanosoma brucei parasitaemia results from density-dependent parasite differentiation and parasite killing by the host immune response.

In the bloodstream of its mammalian host, the "slender" form of Trypanosoma brucei replicates extracellularly, producing a parasitaemia. At high density, the level of parasitaemia is limited at a sublethal level by differentiation to the non-replicative "stumpy" form and by the host immune response. Here, we derive continuous time equations to model the time-course, cell types and level of trypanosome parasitaemia, and compare the best fits with experimental data. The best fits that were obtained favour a model in which both density-dependent trypanosome differentiation and host immune response have a role in limiting the increase of parasites, much poorer fits being obtained when differentiation and immune response are considered independently of one another. Best fits also favour a model in which the slender-to-stumpy differentiation progresses in a manner that is essentially independent of the cell cycle. Finally, these models also make the prediction that the density-dependent trypanosome differentiation mechanism can give rise to oscillations in parasitaemia level. These oscillations are independent of the immune system and are not due to antigenic variation.

The life cycle of Trypanosoma cruzi revisited.

The basic features of the life cycle of Trypanosoma cruzi have been known for nearly a century. Various aspects of the life cycle, however, have been elucidated only recently, whilst others remain either controversial or unstudied. Here, we present a revised life cycle influenced by recent findings and specific questions that remain unresolved.

Anisomorphic cell division by African trypanosomes.

In the bloodstream of a mammalian host, African trypanosomes are pleomorphic; the shorter, non-proliferative, stumpy forms arise from longer, proliferative, slender forms with differentiation occurring via a range of morphological intermediates. In order to investigate how the onset of morphological change is co-ordinated with exit from the cell cycle we first characterized slender form cell division. Outgrowth of the new flagellum was found to occur at a linear rate, so by using outgrowth of the new flagellum as a temporal marker of the cell cycle we were able determine the order in which single copy organelles (nucleus, kinetoplast and mitochondrion) were segregated. We also found that flagellar length was an effective marker of the slender to stumpy differentiation and were, therefore, able to study both cell division and differentiation. When these differentiating cells were compared to cells undergoing proliferative cell division, they were found to be anisomorphic--showing discernible differences not only in the length of their new flagella but also in the shape and size of the cells and their nuclei.

Flagellar elongation induced by glucose limitation is preadaptive for Trypanosoma cruzi differentiation.

Trypanosomes must sense and respond to environmental change in order to progress through their life cycles. The American trypanosome, Trypanosoma cruzi, differentiates from the noninfective epimastigote form to the infective metacyclic form spontaneously in axenic culture. Here, we investigate the initial stimulus for that change and demonstrate that T. cruzi epimastigotes sense limitation of glucose in the medium and respond by undergoing significant morphological and biochemical change. As part of this change, the mean flagellar length of the population triples, which is correlated with an increased ability to maintain interactions with hydrophobic substrates, a requirement for differentiation to the next life cycle stage.

The bloodstream differentiation-division of Trypanosoma brucei studied using mitochondrial markers.

In the bloodstream of its mammalian host, the African trypanosome Trypanosoma brucei undergoes a life cycle stage differentiation from a long, slender form to a short, stumpy form. This involves three known major events: exit from a proliferative cell cycle, morphological change and mitochondrial biogenesis. Previously, models have been proposed accounting for these events (Matthews & Gull 1994a). Refinement of, and discrimination between, these models has been hindered by a lack of stage-regulated antigens useful as markers at the single-cell level. We have now evaluated a variety of cytological markers and applied them to investigate the coordination of phenotypic differentiation and cell cycle arrest. Our studies have focused on the differential expression of the mitochondrial enzyme dihydrolipoamide dehydrogenase relative to the differentiation-division of bloodstream trypanosomes. The results implicate a temporal order of events: commitment, division, phenotypic differentiation.