Lack of an effect from repeated blood sucking by mosquitoes on their infectivity with the causative agent of malaria

The lack of repeated bloodsucking does not affect essentially the infection of Ae. aegypti mosquitoes with malaria agent, P. gallinaceum.     

Effect of mosquito contact with DDT and their susceptibility to the causative agent of malaria

The contact of Aedes aegypti mosquitoes with DDT one hour prior to the infectious feeding results in a slight decrease of their susceptibility to Plasmodium gallinaceum. The contact 24 hours prior to the infectious feeding does not affect the susceptibility of mosquitoes.     

The relationship of the susceptibility of mosquitoes to the causative agents of malaria to their taxonomic position and the geographical origin of the interacting organisms

The belonging of mosquitos to certain taxonomic group does not show a susceptibility to certain group of malaria parasites, but point out that this susceptibility should not be excluded off studies without preliminary checking. There is no correlation between taxonomic relations of mosquito species and their susceptibility to malaria parasites. Geographical isolation of microorganisms and insects does not guarantee an absence of susceptibility. A susceptibility is possible even in those cases, when a long coevolutionary process between organisms do not take place. Generally the susceptibility of mosquitos to exotic species or strains of Plasmodium is lower. Plasmodia are capable to adapt quickly to new vectors.     

New models of the circulation of the causative agent of malaria Plasmodium gallinaceum using malarial mosquitoes in the fauna of the USSR]

The capacity of An. sacharovi and An. pulcherrimus to be infected with P. gallinaceum and to transmit the agent to the vertebrate host, a chick, has been established. Sufficient differences have been found in the extensiveness and intensity of infection of different species of mosquitoes and in other characteristics reflecting the agent-vector relationships.     

An evolutionary view of the interactions between anopheline mosquitoes and malaria parasites

The transmission of malaria is governed by the mosquito vector's biting rate, its mortality, and the developmental period of the parasite within the mosquito. This review covers some data on the interactions among these parameters and describes possible evolutionary mechanisms underlying two aspects of the parasite's life cycle.     

The glycolipids of the causative agent of tularemia]

Up to 10 glycolipids were detected in F. tularensis with the use of thin-layer chromatographic techniques. These glycolipids were slime antigens of F. tularensis membrane. Attenuated F. tularensis strains were found to have defects in their glycolipid composition: in the vaccine strain glycolipid 8 was replaced by more polar lipid 8-a; the avirulent strain had only two glycolipids, and one of them was not typical for virulent strains. Considering that glycolipids differed from entero-bacterial Vi-antigen in their physical-chemical and biological properties, the suggestion was made that the use of the symbol "Vi" to denote the surface substances of F. tularensis should be abolished.     

The effects of subcurative doses of chloroquine on Plasmodium vinckei petteri gametocytes and on their infectivity to mosquitoes

The effects of subcurative doses of chloroquine on rodent and human Plasmodium transmission to the mosquito have been studied by several authors who showed a short-term (12 h) enhancement of gametocyte infectivity by the drug, restricted to chloroquine-resistant strains, and a long term (4-6 days) enhancement of gametocytogenesis of chloroquine-sensitive strains of Plasmodium chabaudi. We investigated both short- and long-term effects of chloroquine on Plasmodium vinckei petteri, a chloroquine-sensitive rodent Plasmodium strain. Chloroquine treatment reduced the index of gametocytogenesis to 73% (5 mg/kg) and 55% (2.5 mg/kg) of controls, on day 6 post-infection (p.i.). The reduction was statistically significant with 5 mg/kg chloroquine. However, the reduction of gametocyte numbers did not affect the transmission capabilities of the strain. Our experiments showed that doses of 1 mg/kg chloroquine had no effect on the oocyst counts, 12 h post-administration to mice. A statistically non-significant 61% reduction of oocyst numbers was observed in mosquitoes fed on mice treated with 5 mg/kg chloroquine. The effect of 5 mg/kg chloroquine administration on the infectivity of gametocytes to mosquitoes fed 1 h post-treatment was also investigated. An overall 41% reduction of oocyst numbers was observed. This immediate effect was statistically significant in 73% of the mice. These results are consistent with the hypothesis that the short-term enhancing effect of chloroquine on transmission is restricted to the drug-resistant strains of Plasmodium.     

Plastid origin of an extrachromosomal DNA molecule from Plasmodium, the causative agent of malaria.

Several species of Plasmodium have been shown to contain a circular extrachromosomal DNA molecule which is widely supposed to be mitochondrial DNA. However, it has recently been shown to have a number of features in common with chloroplast DNA. Here, a phylogenetic analysis of RNA polymerase coding sequences from the Plasmodium molecule has been carried out using distance matrix, maximum likelihood, parsimony and operator invariant methods. The analysis indicates that the molecule is in fact derived from an oxygenic photosynthetic organism and should be regarded as plastid DNA. This suggests that Plasmodium originated from a phototroph that has lost the capacity to photosynthesize.     

The intriguing relationship between screen filtration pressure, quantity of microaggregates and amount of debris in stored human blood

Screen filtration pressure (SFP), quantity of microaggregates and debris weight were measured in stored human blood. The number of aggregates correlated with the debris weight but not with SFP. No correlation was seen between the debris weight and SFP. The mechanisms behind and the functional importance of these findings are outlined.     

The interaction of the causative agent of melioidosis with the host's alveolar macrophages]

Studies were carried out on guinea pigs and albino rats, intranasally infected with P. pseudomallei C-141. The cells of bronchovesicular exudate were obtained from animals 1, 4 and 24 hours after infection. Electron microscopy was applied to study the process of interaction of the agent and alveolar macrophages. Bacteria were shown to form a capsule which permitted avoiding phagocytosis, when entering the host respiratory system. Microbes that failed to form a capsule were absorbed by macrophages and enclosed in a phagosome. Then some bacteria were destroyed by the lysosomal enzymes, the other synthesized a capsule, which protected them against the effect of phagolysosome content. There were also such microbes which escaped from a phagosome prior to fusion with lysosomes and parasitized in phagocytic cytoplasma forming a capsule there. By the end of the first 24 hours of observation the intact encapsulated microbe species were found to prevail in the host cells.     

The relationship between pH and the amount of calcium bound to glycerinated muscle fibers

Variation of pH over the range 6.2–7.4 had no effect on the Ca²⁺ titration curve of glycerinated rabbit psoas muscle fibers. Thus the effect of H⁺ on muscle contraction is not due to a simple H⁺Ca²⁺ competition for binding sites.     

The relationship between HIV-1 genome RNA dimerization, virion maturation and infectivity

The relationship between virion protein maturation and genomic RNA dimerization of human immunodeficiency virus type 1 (HIV-1) remains incompletely understood. We have constructed HIV-1 Gag cleavage site mutants to enable the steady state observation of virion maturation steps, and precisely study Gag processing, RNA dimerization, virion morphology and infectivity. Within the virion maturation process, the RNA dimer stabilization begins during the primary cleavage (p2-NC) of Pr55 Gag. However, the primary cleavage alone is not sufficient, and the ensuing cleavages are required for the completion of dimerization. From our observations, the increase of cleavage products may not put a threshold on the transition from fragile to stable dimeric RNA. Most of the RNA dimerization process did not require viral core formation, and particle morphology dynamics during viral maturation did not completely synchronize with the transition of dimeric RNA status. Although the endogenous virion RT activity was fully acquired at the initial step of maturation, the following process was necessary for viral DNA production in infected cell, suggesting the maturation of viral RNA/protein plays critical role for viral infectivity other than RT process.     

Quantitative aspects of the relationship between the sickle-cell gene and malaria

The relationship between resistance to Plasmodium falciparum infection and the frequency and distribution of the sickle-cell gene in populations exposed to endemic malaria transmission is reducible to clear and quantifiable terms. In this review, Trevor Jones examines the prediction of gene frequency changes under selective pressure, the selective advantage to the heterozygote (balanced polymorphism) that the sickle-cell gene provides to individuals in areas with malaria transmission, and the relationship between sickle-cell gene frequency and malaria, as measured by, for example, sporozoite rate and basic reproduction rate. He seeks to clarify what one can infer about malaria transmission from an analysis of the distribution and inheritance patterns of the sickle-cell gene and sickle-cell disease and under what circumstances these inferences should be made.     

The Rengen Grassland Experiment: relationship between soil and biomass chemical properties, amount of elements applied, and their uptake

The Rengen Grassland Experiment (RGE) was established in the Eifel Mountains (Germany) on a low productive Nardetum in 1941. Since then, the following fertilizer treatments have been applied with a late two-cut system: unfertilized control, Ca, CaN, CaNP, CaNPKCl and CaNPK₂SO₄. We aimed to understand how concentrations of macro (N, P, K, Ca and Mg), micro (Cu, Fe, Mn and Zn) and trace (As, Cd, Cr, Ni and Pb) elements in the plant biomass were affected by long-term fertilizer application, soil chemical properties and biomass production. In 2008, biomass samples from the first cut (early July) and the second cut (mid-October) were collected and analyzed. The simultaneous application of N, P and K decreased nitrogen concentration in the aboveground biomass, but substantially increased biomass production. Late cutting management decreased forage quality in highly productive more than in low productive plant communities. The concentrations of P and K in the plant biomass were positively related to P and K application and, therefore, to plant available P and K concentrations in the soil. The concentrations of some micro (Fe, Mn and Zn) and trace (As, Cd, Cr, Ni and Pb) elements in the plant biomass were negatively correlated with the amount of elements supplied by fertilizers and biomass production, probably because of the dilution effect. Long-term fertilizer application resulted in the accumulation of macro (P, Ca and Mg), micro (Fe and Mn) and trace (As and Cr) elements in the soil, but in many cases this accumulation was not connected with an increase in the concentrations of these elements in the plant biomass. Nutritional status, as indicated by the biomass N:P ratio, was consistent with N or P limitation as indicated by the nitrogen and phosphorus nutrition indices. Furthermore, additional K (co-)limitation was indicated by the N:K and K:P ratios in the biomass from the NP treatment. The results from the RGE indicate that there is no simple positive relationship between the applied elements and their concentrations in the plant biomass.