Effects of Malaria Parasite Density on Blood Cell Parameters

Changes in blood cell parameters are already a well-known feature of malarial infections. To add to this information, the objective of this study was to investigate the varying effects that different levels of parasite density have on blood cell parameters. Patients diagnosed with malaria at Phobphra Hospital, Tak Province, Thailand between January 1^st 2009 and January 1^st 2012 were recruited as subjects for data collection. Blood cell parameters of 2,024 malaria-infected patients were evaluated and statistically analyzed. Neutrophil and platelet counts were significantly higher, however, RBC count was significantly lower in patients with P. falciparum infection compared to those with P. vivax infection (p<0.0001). Leukocyte counts were also significantly higher in patients with high parasitemia compared to those with low and moderate parasitemia. In terms of differential leukocyte count, neutrophil count was significantly higher in patients with high parasitemia compared to those with low and moderate parasitemia (p<0.0001). On the other hand, both lymphocyte and monocyte counts were significantly lower in patients with high parasitemia (p<0.0001). RBC count and Hb concentration, as well as platelet count were also significantly reduced (p<0.05) and (p<0.0001), respectively. To summarize, patients infected with different malaria parasites exhibited important distinctive hematological parameters, with neutrophil and eosinophil counts being the two hematological parameters most affected. In addition, patients infected with different malarial densities also exhibited important changes in leukocyte count, platelet count and hemoglobin concentration during the infection. These findings offer the opportunity to recognize and diagnose malaria related anemia, help support the treatment thereof, as well as relieve symptoms of severe malaria in endemic regions.     

Effects of Juvenile Host Density and Food Availability on Adult Immune Response,Parasite Resistance and Virulence in a Daphnia-Parasite System

Host density can increase infection rates and reduce host fitness as increasing population density enhances the risk of becoming infected either through increased encounter rate or because host condition may decline. Conceivably, potential hosts could take high host density as a cue to up-regulate their defence systems. However, as host density usually covaries with food availability, it is difficult to examine the importance of host density in isolation. Thus, we performed two full-factorial experiments that varied juvenile densities of Daphnia magna (a freshwater crustacean) and food availability independently. We also included a simulated high-density treatment, where juvenile experimental animals were kept in filtered media that previously maintained Daphnia at high-density. Upon reaching adulthood, we exposed the Daphnia to their sterilizing bacterial parasite, Pasteuria ramosa, and examined how the juvenile treatments influenced the likelihood and severity of infection (Experiment I) and host immune investment (Experiment II). Neither juvenile density nor food treatments affected the likelihood of infection; however, well-fed hosts that were well-fed as juveniles produced more offspring prior to sterilization than their less well-fed counterparts. By contrast, parasite growth was independent of host juvenile resources or host density. Parasite-exposed hosts had a greater number of circulating haemocytes than controls (i.e., there was a cellular immune response), but the magnitude of immune response was not mediated by food availability or host density. These results suggest that density dependent effects on disease arise primarily through correlated changes in food availability: low food could limit parasitism and potentially curtail epidemics by reducing both the host’s and parasite’s reproduction as both depend on the same food.     

Assessing the Effects of Trematode Infection on Invasive Green Crabs in Eastern North America

A common signature of marine invasions worldwide is a significant loss of parasites (= parasite escape) in non-native host populations, which may confer a release from some of the harmful effects of parasitism (e.g., castration, energy extraction, immune activation, behavioral manipulation) and possibly enhance the success of non-indigenous species. In eastern North America, the notorious invader Carcinus maenas (European green crab) has escaped more than two-thirds its native parasite load. However, one of its parasites, a trematode (Microphallus similis), can be highly prevalent in the non-native region; yet little is known about its potential impacts. We employed a series of laboratory experiments to determine whether and how M. similis infection intensity influences C. maenas, focusing on physiological assays of body mass index, energy storage, and immune activation, as well as behavioral analyses of foraging, shelter utilization, and conspicuousness. We found little evidence for enduring physiological or behavioral impacts four weeks after experimental infection, with the exception of mussel handling time which positively correlated with cyst intensity. However, we did find evidence for a short-term effect of M. similis infection during early stages of infection (soon after cercarial penetration) via a significant drop in circulating immune cells, and a significant increase in the crabs’ righting response time. Considering M. similis is the only common parasite infecting C. maenas in eastern North America, our results for minimal lasting effects of the trematode on the crab’s physiology and behavior may help explain the crab’s continued prominence as a strong predator and competitor in the region.     

Effects of Season and Host Physiological State on the Diversity,Density, and Activity of the Arctic Ground Squirrel Cecal Microbiota

We examined the seasonal changes of the cecal microbiota of captive arctic ground squirrels (Urocitellus parryii) by measuring microbial diversity and composition, total bacterial density and viability, and short-chain fatty acid concentrations at four sample periods (summer, torpor, interbout arousal, and posthibernation). Abundance of Firmicutes was lower, whereas abundances of Bacteroidetes, Verrucomicrobia, and Proteobacteria were higher during torpor and interbout arousal than in summer. Bacterial densities and percentages of live bacteria were significantly higher in summer than during torpor and interbout arousal. Likewise, total short-chain fatty acid concentrations were significantly greater during summer than during torpor and interbout arousal. Concentrations of individual short-chain fatty acids varied across sample periods, with butyrate concentrations higher and acetate concentrations lower during summer than at all other sample periods. Characteristics of the gut community posthibernation were more similar to those during torpor and interbout arousal than to those during summer. However, higher abundances of the genera Bacteroides and Akkermansia occurred during posthibernation than during interbout arousal and torpor. Collectively, our results clearly demonstrate that seasonal changes in physiology associated with hibernation and activity affect the gut microbial community in the arctic ground squirrel. Importantly, similarities between the gut microbiota of arctic ground squirrels and thirteen-lined ground squirrels suggest the potential for a core microbiota during hibernation.     

Effects of Host Diet on Romanomermis culicivorax,a Mermithid Parasite of Mosquitoes

When larval mosquitoes (Aedes aegypti) infected with the mermithid nematode Romanomermis culicivorax were fed on a diet low in quantity or protein content or both, the number of postparasites which emerged from the hosts decreased and host mortality increased marginally. Parasitic development was prolonged and became asynchronous in nutritionally deprived hosts. Nematodes emerged from insects infected by more than one nematode before the remaining juveniles comprising such infections had completed parasitic development; this resulted in substantial reductions in postparasite nttmbers. Host development was retarded by low protein and/or reduced diets. Postparasites emerging from second and third instars were reduced in size and in the amount of stored nutriment compared to those recovered from hosts fed on a high protein diet ad libitum. A greater proportion of the rnermithids developed into males in hosts fed on reduced diets but not in hosts fed on low protein diets.     

Host Parasite Relations in Initiation of Infection: II. Hyperglycemia and Stress in Experimental Infection with L. Monocytogenes

The effects of applied stimuli on the initiation of experimental infection were studied on lemmings, rabbits, hamsters, and guinea pigs. Stress was simulated by injection of cortisone acetate, or by trauma, heat, or cold. L. monocytogenes was the organism used for experimental infection. The results showed that the course of the infection was influenced in favour of the invading microorganism by the stress agents used. Hyperglycemia was present in the animals that developed the infection to overt disease. This suggests that hyperglycemia may be the trigger mechanism.     

Parasite Induced Summer Mortality in the Cockle Cerastoderma edule by the Trematode Gymnophallus choledochus

In late summer 2004, a conspicuous cockle (Cerastoderma edule) mortality event was observed on a tidal flat in the northern Wadden Sea (North Sea, Germany) with many fresh valves and still living cockles lying on the sediment surface. To investigate whether trematode parasites utilizing the cockle as first or second intermediate host were involved in this mortality, buried and surfaced cockles were sampled and analyzed, and a laboratory experiment conducted. The field survey showed no statistical difference in intensity of parasites encysted in the foot of cockles. Three species of Himasthla utilizing the cockle as second intermediate host and known to impair the cockle’s burrowing ability were found in buried cockles with 148.4±111.1 metacercariae/foot and in surfaced cockles with 164.2±84.4. There was also no difference in infection levels of parasites utilizing the cockles as second intermediate host in other cockle tissues between buried and surfaced cockles. In contrast, surfaced cockles showed a ten times higher prevalence (71.0%) than buried cockles (7.4%) of the trematode Gymnophallus choledochus – a parasite utilizing the cockle as first (and second) intermediate host – filling almost the entire body cavity and eliminating gonad structures. In an aquarium experiment of 14 days, all cockles found buried on the tidal flat survived compared to only 23.3% found on the surface. This suggests G. choledochus to be a castrating agent and a serious mortality factor in adult cockle populations.     

Natural Parasite Infection Affects the Tolerance but Not the Response to a Simulated Secondary Parasite Infection

Parasites deplete the resources of their host and can consequently affect the investment in competing traits (e.g. reproduction and immune defence). The immunocompetence handicap hypothesis posits that testosterone (T) mediates trade-offs between parasite defence and reproductive investment by suppressing immune function in male vertebrates while more recently a role for glucocorticoids (e.g. cortisol (C)) in resource allocation has been suggested. These hypotheses however, have not always found support in wild animals, possibly because most studies focus on a single parasite species, whereas infections with multiple parasites are the rule in nature. We measured body mass, T- and C-levels of wild male highveld mole-rats (Cryptomys hottentotus pretoriae) naturally uninfected or infected with a cestode (Mathevotaenia sp.) right after capture. Subsequently, we injected animals subcutaneously with a lipopolysaccharide (LPS) to simulate a bacterial infection and recorded changes in body mass, food intake, haematological parameters and hormone levels. As a control, animals were injected with saline. Natural infection neither affected initial body mass nor C-levels, whereas infected males had significantly reduced T-levels. We observed significant reductions in food intake, body mass and T in response to LPS but not saline while C increased. However, this response did not vary with infection status. In contrast, final body mass and some haematological parameters were significantly lowered in infected males. Our results suggest that naturally infected males are able to compensate for resource depletion by physiological adjustments. However, this leaves them less tolerant to the challenges of a secondary infection.     

Experimental Evolution of a Trypanosome Parasite of Bumblebees and its Implications for Infection Success and Host Immune Response

Selection on basic growth properties of parasites may have many consequences for parasite traits, infection outcome, or host responses to infection. It is known that genotypes (strains) of the trypanosome parasite of bumblebees Crithidia bombi vary widely in their growth rates in their natural host, Bombus terrestris, as well as when cultured in medium. To test for changes in growth rates and their consequences, we here experimentally evolved six strains of C. bombi for fast and slow growth under controlled conditions in culture medium. Subsequently, we infected the evolved lines in live host and found that lines selected for slow growth attained higher infection intensity in the live bumblebee than those evolved for fast growth, whilst the immune response of the host was the same to both kinds of lines. These results fit the expectation that attenuation through rapid adaptation to a different environment, the culture medium, makes the parasite less successful in its next host. Selection for fast growth therefore does not necessarily lead to higher parasite success or more transmission. Hence, insect trypanosome pathogens can be attenuated by experimental evolution in the culture; this could inform important aspects of host-parasite evolution and perhaps vaccine development.     

Host Parasite Relations In Initiation of Infection: III. Hyperglycemia without Stress in Experimental Infection with L. Monocytogenes

Experimental hyperglycemia and infection with L. monocytogenes, and the effects of somatotsopic hormone and cortisone, were studied. Hamsters, obese mice, and normal mice were used. The results supported the hypothesis that an upset carbohydrate metabolism initiated by stress is the trigger mechanism that makes conditions favourable for proliferation of L. monocytogenes and probably of other glucose fermenting pathogenic agents.     

Effects of Density, Age and Host Cues on the Dispersal of Heterorhabditis megidis

Agar plate assays were used to assess the effect of density, incubation time and age of nematodes and the presence of insect hosts on the dispersal of infective juveniles (IJs) of Heterorhabditis megidis (strain NLH-E87.3). IJs dispersed faster and further at high densities than at low densities. Dispersal was also influenced by the age of the IJs. Individuals stored for a period of 1.5 and 4.5 weeks showed to be more active than those stored for 2.5 and 3.5 weeks. The presence of a host insect enhanced the dispersion of nematodes. The increasing in the incubation period showed that IJs responded positively to host cues from Galleria mellonella but poorly to cues from Otiorhynchus sulcatus larvae.     

Co-transmission of Related Malaria Parasite Lineages Shapes Within-Host Parasite Diversity

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Effects of Host Size and Parasite Burden on Sex Ratio in the Mosquito Parasite Octomyomermis muspratti

The ratio of Octomyomermis muspratti to the host mosquito at the time of exposure had little effect on the ratio of male to female parasites that resulted. However, the ratio of males to females increased as the number of parasites/host increased. Hosts with a single nematode produced fewer than 1% males in comparison with hosts with 8 parasites which produced about 40% males; hosts with 10 or more nematodes generally produced more male than female nematodes. Males of O. muspratti usually emerged before females because of the earlier death of multiply-infected mosquitoes. The size of the host at the time of invasion bad no significant influence on nematode sex ratios. Since mating is apparently necessary for reproduction in O. muspratti, the low male to female ratios that occur will be important in developing successful mass production techniques.