Chickens treated with a nitric oxide inhibitor became more resistant to Plasmodium gallinaceum infection due to reduced anemia, thrombocytopenia and inflammation

The Immunological Capacity of Thrombocytes

Thrombocytes are numerous in the blood of aves (birds) and ichthyoids (fish). The origin of this cell type is a common hematopoietic stem cell giving rise to a cell that is active in blood coagulation, inflammatory functions, and the immune response in general. It has been well documented that thrombocytes can phagocytize small particles and bacteria. While phagocytosis with an associated oxidative burst has been reported for chicken thrombocytes, some questions remain as to the degradation capacity of phagosomes in ichthyoids. As innate cells, thrombocytes can be stimulated by bacterial, viral, and fungal pathogens to express altered gene expression. Furthermore, there have been observations that led researchers to state that platelets/thrombocytes are capable of serving as "professional antigen presenting cells" expressing CD40, CD80/86, MHC I, and MHC II. This indeed may be the case or, more likely at this time, provide supporting evidence that these cells aid and assist in the role of professional antigen-presenting cells to initiate adaptive immune responses.

Oxidative Stress in Malaria: Potential Benefits of Antioxidant Therapy

Malaria is an infectious disease and a serious public health problem in the world, with 3.3 billion people in endemic areas in 100 countries and about 200 million new cases each year, resulting in almost 1 million deaths in 2018. Although studies look for strategies to eradicate malaria, it is necessary to know more about its pathophysiology to understand the underlying mechanisms involved, particularly the redox balance, to guarantee success in combating this disease. In this review, we addressed the involvement of oxidative stress in malaria and the potential benefits of antioxidant supplementation as an adjuvant antimalarial therapy.

Central and peripheral effects of L-citrulline on thermal physiology and nitric oxide regeneration in broilers

The mechanism that mediates L-citrulline (L-Cit) hypothermia is poorly understood, and the involvement of nitric oxide signaling has not been fully elucidated. Therefore, this study aimed to determine L-Cit's influence on body temperature and to ascertain the central and peripheral mechanisms associated with this response. Chicks responded to intracerebroventricular (ICV) injection of L-Cit with high and low body temperatures (P < 0.05) depending on the dose tested, for both the surface and rectal temperatures. Peripheral (i.p.) L-Cit injection did not affect body temperature responses. Nitric oxide (NO) concentration and NO synthase (NOS) were influenced with varying doses of L-Cit. Hypothalamic NO was increased at 4 µg L-Cit whereas, plasma iNOS was elevated at 2µg L-Cit treatment. However, i.p. L-Cit did not change the NO content, rather it induced higher (P < 0.05) plasma tNOS and iNOS activity, and further upregulated iNOS and nNOS gene expression in the hypothalamus. In addition, ICV L-Cit potentiated a pro- versus anti-inflammatory milieu with the induction of IL-8, IL-10, and TGFβ (P < 0.05), which may be related to the changes in body temperature. Following ICV L-Cit administration, it was observed that L-Cit caused dose variable changes in the ultrastructure of hypothalamic neurons. The lowest dose was associated with a higher number of dead or degenerating neurons, whereas the highest L-Cit dose had fewer neuronal numbers with larger sizes. Therefore, this study shows that central and peripheral L-Cit administration imposes changes in body temperature, nitric oxide production, and inflammatory responses, in a dose-dependent manner.

Microbiome and biological blood marker changes in hens at different laying stages in conventional and cage free housings

With the majority of conventional cage (CC) laying facilities transitioning into cage-free (CF) systems in the near future, it is important to characterize biological markers of health in layers housed in commercial housings for sustainable production. The objectives of this study were to compare i) blood markers, that is heterophil:lymphocyte (H:L) ratios and susceptibility to avian pathogenic Escherichia coli (APEC) and ii) lung and ceca microbiome between hens at different maturity stages in commercial CC and CF farms. Laying hens at 3 maturity stages were randomly sampled (N = 20 per maturity and per farm). Blood was tested for H:L ratios and APEC killing ability using microscopy and in vitro assay, respectively. Microbiomes were assessed using 16S rRNA sequencing and QIIME2 analysis. Data show H:L ratios did not differ between maturities in both farms. Avian pathogenic Escherichia coli killing was only different in CC hens, where χ7122 level was higher (P < 0.05) in peak compared with early lay. In both farms, microbiome diversity was consistently different (P < 0.05) in both ceca and lung of early lay compared with peak and late lay. In the ceca and lung, relative abundances of the 3 predominant phyla (Bacteroidetes, Firmicutes, and Proteobacteria) did not significantly change with maturity in both farms. Potential pathogens Campylobacter and Staphylococcus reached greater (P < 0.05) abundances in CC lungs in early lay and in CF lungs in late lay, respectively. Overall, this study showed no differences in the stress marker H:L but identified some differences in resistance to APEC and microbiome composition across maturity stages in CC and CF. The lung and gut microbiomes were highly similar, with both serving as potential reservoirs for Campylobacter and Staphylococcus. Future studies on controllable environments for CF and CC are needed to develop adequate strategies for each housing and maturity stage to reduce pathogens and optimize disease-resistance.

Exogenous glucocorticoids amplify the costs of infection by reducing resistance and tolerance, but effects are mitigated by co-infection

Individual variation in parasite defences, such as resistance and tolerance, can underlie heterogeneity in fitness and could influence disease transmission dynamics. Glucocorticoid hormone concentrations often change in response to fluctuating environmental conditions and mediate changes in immune function, resource allocation and tissue repair. Thus, changes in glucocorticoid hormone concentrations might mediate individual variation in investment in resistance versus tolerance. In this study, we experimentally increased glucocorticoid concentrations in red-winged blackbirds ( Agelaius phoeniceus) that were naturally infected with haemosporidian parasites, and assessed changes in resistance and tolerance of infection. Glucocorticoid treatment increased burdens of Plasmodium, the parasite causing avian malaria, but only in the absence of co-infection with another Haemosporidian, Haemoproteus. Thus, glucocorticoids might reduce resistance to infection, but co-infection can mitigate the negative consequences of increased hormone concentrations. Glucocorticoid treatment also decreased tolerance of infection. We found no evidence that the inflammatory immune response or rate of red blood cell production underlie the effects of glucocorticoids on resistance and tolerance. Our findings suggest that exogenous glucocorticoids can increase the costs of haemosporidian infections by both increasing parasite numbers and reducing an individual's ability to cope with infection. These effects could scale up to impact populations of both host and parasite.

Experimental characterization of the complete life cycle of Haemoproteus columbae, with a description of a natural host-parasite system used to study this infection

Characterization of complete life cycles of haemoparasites requires the maintenance of suitable susceptible vertebrate hosts and vectors for long periods in captivity, in order to follow the complete parasitic cycle in definitive and intermediate hosts. Currently, there are few host-parasite models established in avian haemosporidian research, and those have been developed mainly for species of Passeriformes and their parasites. This study aimed to develop an experimental methodology to access the complete life cycle of Haemoproteus columbae (cytb lineage HAECOL1), which parasitizes the Rock Pigeon (Columba livia) and louse fly (Pseudolynchia canariensis). A colony of louse flies, which are the natural vectors of this parasite, was established. Thirty newly emerged insects were exposed to H. columbae infection and used to infect naïve Rock Pigeons. The peak of parasitaemia (acute stage) was seen between 27 and 32 days p.i. when up to 70.8% of red blood cells were infected. The crisis occurred approximately 1 week after the peak, and the long-lasting chronic parasitaemia stage followed. Exo-erythrocytic meronts were seen mainly in the lungs where extensive tissue damage was reported, but also in the kidneys and spleen. In the vector, the sporogonic cycle of H. columbae was completed between 13 and 16 days p.i., at an average temperature ranging between 12 and 15 °C. This host-parasite model is tractable for maintenance in captivity. It is recommended for use in studies aiming for detailed characterization of host-parasite relationships in areas such as physiology, pathology, immunobiology, genetics, as well as for evaluative treatments and to follow the infection in any stage of parasite development both in the vertebrate or invertebrate host.

Molecular detection and genetic diversity of avian haemosporidian parasites in Iran

Background

The mobility of birds across or between continents exposes them to numerous vectors that have the potential to transmit pathogens and spread them into new regions. A combination of rich species diversity of birds along with the small amount of molecular studies in Iran makes observing the blood parasite distribution in wild avian populations indispensable for further estimation and administration of blood parasites.

Methodology/Principal findings

In order to evaluate the infection rate and molecular context of avian blood parasites, bird samples were collected (passerine = 316 and non-passerine = 14) in eight provinces of northern Iran between June to September 2015 and 2016. All bird samples were examined for haematoprotozoan infections by morphological screening using light microscope and mtDNA cytb gene amplification. A total of 115 birds were positive for blood parasites by molecular approach (34.84% overall infection). The infection rate of Haemoproteus, Plasmodium, and Leucocytozoon were 33.03%, 1.21%, and 0.6%, respectively. Sequences analysis has detected 43 lineages in Iranian birds’ hosts. Lineages were attributed to three genera Haemoproteus (n = 37), Plasmodium (n = 4), and Leucocytozoon (n = 2), of which 23 lineages fully matched previously recorded sequences in GenBank and MalAvi data reciprocities. Five lineages of ACDUM1, ACDUM2, PARUS1, PYERY01, and SISKIN1 were detected in multiple hosts’ species from dissimilar families. In Bayesian tree, all sequences were clustered in three main monophyletic clades as Haemoproteus, Plasmodium, and Leucocytozoon genera.

Conclusions/Significance

As the first study outlining the molecular detection of hematozoa of passerines from Iran, the current study has recorded 20 new lineages for three genera of Haemoproteus, Plasmodium, and Leucocytozoon. Additional investigations into these taxa in the avifauna for the other parts of Iran may provide extra information on blood parasites, hosts relationships and distribution patterns.

Exposing migratory sparrows to Plasmodium suggests costs of resistance, not necessarily of infection itself

Migratory birds move through multiple habitats and encounter a diverse suite of parasites. This raises concern over migrants' role in transporting infectious disease between breeding and wintering grounds, and along migratory flyways. Trade-offs between flight and immune defenses could interfere with infected individuals' migratory timing and success, potentially affecting infection dynamics. However, experimental evidence that parasitic infection affects migratory preparation or timing remains scant. We hypothesized that birds encountering hematozoan parasites shortly before migration incur physical costs (reduced body condition) and behavioral costs (delayed migration), due to the infection itself and/or to the demands of mounting an immune response. We experimentally inoculated song sparrows (Melospiza melodia) with Plasmodium shortly before fall migration. We monitored infection and body composition for 2 weeks after inoculation, and used radiotelemetry to track timing of migratory departure for another 7 weeks after release. Inoculated individuals that resisted infection had lower lean mass 12 days post exposure, relative to controls and infected individuals. This suggests trade-offs between body composition and immune defenses that might reduce migration success of resistant individuals. Despite group differences in body composition prior to release, we did not detect significant differences in timing of migration departure several weeks later. Thus, malarial infection did not appear to incur detectable costs to body composition or to migratory timing, at least when exposure occurs several weeks before migration. This study is novel considering not only the costs of infection, but also the costs of resisting infection, in an experimental context.

Higher plasma corticosterone is associated with reduced costs of infection in red-winged blackbirds

Glucocorticoid hormones allow individuals to rapidly adjust their physiology and behavior to meet the challenges of a variable environment. An individual's baseline concentration of glucocorticoids can reflect shifts in life history stage and resource demands while mediating a suite of physiological and behavioral changes that include immune modulation and resource allocation. Thus, glucocorticoids could facilitate a response to parasites that is optimized for an individual's specific challenges and life history stage. We investigated the relationship between endogenous circulating glucocorticoids and measures of resistance and tolerance to Haemosporidian parasites (including those that cause avian malaria) in red-winged blackbirds (Agelaius phoeniceus). We found that higher endogenous concentrations of circulating glucocorticoids were associated with reduced costs of parasite infection, which is indicative of higher tolerance, but were unrelated to parasite burden in free ranging, breeding male birds. Post-breeding, both males and females with higher glucocorticoid concentrations had higher measures of tolerance to Haemosporidian infection. Our findings suggest a potentially adaptive role for glucocorticoids in shifting the response to parasites to align with an individual's current physiological state and the challenges they face.

Immune-relevant thrombocytes of common carp undergo parasite-induced nitric oxide-mediated apoptosis

Common carp thrombocytes account for 30-40% of peripheral blood leukocytes and are abundant in the healthy animals' spleen, the thrombopoietic organ. We show that, ex vivo, thrombocytes from healthy carp express a large number of immune-relevant genes, among which several cytokines and Toll-like receptors, clearly pointing at immune functions of carp thrombocytes. Few studies have described the role of fish thrombocytes during infection. Carp are natural host to two different but related protozoan parasites, Trypanoplasma borreli and Trypanosoma carassii, which reside in the blood and tissue fluids. We used the two parasites to undertake controlled studies on the role of fish thrombocytes during these infections. In vivo, but only during infection with T. borreli, thrombocytes were massively depleted from the blood and spleen leading to severe thrombocytopenia. Ex vivo, addition of nitric oxide induced a clear and rapid apoptosis of thrombocytes from healthy carp, supporting a role for nitric oxide-mediated control of immune-relevant thrombocytes during infection with T. borreli. The potential advantage for parasites to selectively deplete the host of thrombocytes via nitric oxide-induced apoptosis is discussed.

Plasmodium spp. and Haemoproteus spp. infection in birds of the Brazilian Atlantic Forest detected by microscopy and polymerase chain reaction

In recent years haemosporidian infection by protozoa of the genus Plasmodium and Haemoproteus, has been considered one of the most important factors related to the extinction and/or population decline of several species of birds worldwide. In Brazil, despite the large avian biodiversity, few studies have been designed to detect this infection, especially among wild birds in captivity. Thus, the objective of this study was to analyze the prevalence of Plasmodium spp. and Haemoproteus spp. infection in wild birds in captivity in the Atlantic Forest of southeastern Brazil using microscopy and the polymerase chain reaction. Blood samples of 119 different species of birds kept in captivity at IBAMA during the period of July 2011 to July 2012 were collected. The parasite density was determined based only on readings of blood smears by light microscopy. The mean prevalence of Plasmodium spp. and Haemoproteus spp. infection obtained through the microscopic examination of blood smears and PCR were similar (83.19% and 81.3%, respectively), with Caracara plancus and Saltator similis being the most parasitized. The mean parasitemia determined by the microscopic counting of evolutionary forms of Plasmodium spp. and Haemoproteus spp. was 1.51%. The results obtained from this study reinforce the importance of the handling of captive birds, especially when they will be reintroduced into the wild.