Plasmodium Yoelii Nigeriensis Research Articles

Plasmodium yoelii nigeriensis: the effect of high and low intensity of infection upon the egg production and bloodmeal size of Anopheles stephensi during three gonotrophic cycles.

Anopheles stephensi mosquitoes showed a reduction in fecundity over 3 successive gonotrophic cycles, after becoming infected with Plasmodium yoelii nigeriensis. This effect could be observed at high oocyst burdens (> 75) or at low oocyst burdens (mean of 4.36). Mean bloodmeal size of the infected mosquitoes was significantly reduced only when feeding upon a mouse with a high gametocytaemia and the conversion of the bloodmeal into eggs by the infected mosquitoes was disrupted. Patterns of infected mosquito mortality, over the 3 gonotrophic cycles, varied with severity of infection. Although in 1 case increased mortality and decreased bloodmeal size may have affected fecundity, this could not have accounted for all of the observed fecundity reduction. We propose that other, unknown parasite related factors, are involved.

Antimalarial Effects of C18 Fatty Acids on Plasmodium falciparum in Culture and on Plasmodium vinckei petteri and Plasmodium yoelii nigeriensis in Vivo

Following the demonstration of the antimalarial effect of the long chain saturated alcohol n-hentriacontanoi ((CH2)29CH2OH), isolated from the Bolivian endemic solanaceous plant Cuatresia sp., we have tested the effect of the C18 fatty acids oleic, elaidic, linoleic, and linoleic on malaria parasites. These fatty acids inhibited the parasitemic development in mice infected with Plasmodiurn vinckei petteri or with Plasmodium yoelii nigeriensis in a 4-day suppressive test. To gain a deeper discernment of the antimalarial mode of action, the effects of these compounds were evaluated on Plasmodiun falciparum growth in culture. Whereas n-hentriacontanol did not show any inhibition of this parasite, on the contrary, the C18 acids displayed a considerable inhibitory activity at ≤ 200 μg/ml both in intact infected cells and in free parasites. In order to understand the mechanism of their antimalarial action, several tests were performed. No hemolysis of infected cells could be observed up to 500 μg/ml. No effect on the lipid peroxidation, ATP levels, transport through the parasite-induced permeabiIity pathways, or on the phagocytosis of the infected cells could be observed. The cytotoxic effect of the fatty acids was very rapid: full inhibition of nucleic acids and protein syntheses was observed in less than 30 min. This inhibition was not relieved by the addition of deferrioxamine or FeCl3, indicating that fatty acids (FA) do not act by facilitating the transport of iron. Inhibition was relieved in neither the presence of erotic acid or its methyl ester, indicating that FA do not act at the mitochondrial level of pyrimidine synthesis. Inhibition was not relieved when cells were incubated in high potassium medium, implying that FA did not act by depleting the parasite of this physiologically important cation. Vitamin E had no protective effect and no evidence for Lipid peroxidation could be obtained, suggesting that the inhibitory effect of FA was not due to lipid peroxidation. These results suggest that octadecenoic acids may have a specific target(s) inside the parasite. Further investigations are warranted since soybean lipid emulsions used for parenteral nutrition show similar inhibition of parasite propagation in vivo and in culture.

Malaria‐induced reduction of fecundity during the first gonotrophic cycle of Anopheles Stephensi mosquitoes

Anopheles stephensi mosquitoes which had fed upon mice infected with Plasmodium yoelii nigeriensis malaria parasites produced significantly fewer eggs than mosquitoes fed on an uninfected mouse. Fecundity reduction was more pronounced when the bloodmeal contained malaria gametocytes and the mosquitoes developed oocysts. Egg production and haematin excretion were correlated for uninfected bloodfed mosquitoes; the presence of P.y.nigeriensis in the blood affected this relationship. Reduced fecundity was associated with a significant reduction of bloodmeal size (measured by haematin excretion) in mosquitoes which ingested gametocytaemic blood. The bloodmeal size in mosquitoes fed on parasitaemic blood without gametocytes was not significantly reduced. The use of haematin assays for determination of bloodmeal size in mosquitoes is discussed.

A-15 マラリア原虫が宿主の生態に及ぼす影響 : 5. 唾腺内スポロゾイトの消長と感染性について

A-15 マラリア原虫が宿主の生態に及ぼす影響 : 5. 唾腺内スポロゾイトの消長と感染性について

Plasmodium yoelii nigeriensis: biological mechanisms of resistance to chloroquine.

The sensitivity to chloroquine according to the degree of synchronicity of Plasmodium yoelii nigeriensis, which is considered to be the most resistant of the rodent malaria strains, was studied. The infection was synchronised by means of a Percoll-glucose gradient which separates rings and young trophozoites from other stages. The mid-term trophozoite, when it predominated in the blood at the time of treatment, was shown to be as sensitive to chloroquine as Plasmodium vinckei petteri. According to previous results indicating that part of the population of merozoites is latent and penetrates around midnight, the inoculations were timed in order to obtain a lower or higher degree of synchronisation. The infection appeared to be better synchronised if rings and young trophozoites, were inoculated at 06:00 hrs rather than at 15:00 hrs and consequently the efficacy of chloroquine was higher in the former than in the latter.

Neuropathological studies on Plasmodium yoelii nigeriensis-induced malaria in mice

Malaria infection in mice was produced by intraperitoneal inoculation of 10(6) erythrocytes parasitized with Plasmodium yoelii nigeriensis, a virulent strain of murine malaria. About one week after infection parasitaemia ranged between 60 and 80%, and 100% mortality was observed. Infected animals were killed 6 days after infection to allow the examination of brain tissue. Electron microscopical observations revealed marked damage to cerebral vascular vessel walls with separation of muscular layers, media and adventitia. The endothelial cell layer was discontinuous in places. Activated fibroblast cells producing collagen fibres were seen around the necrotic region of cerebral vasculature. Some parasitized erythrocytes were also seen attached to the endothelial cell lining. Cerebral oedema was prominent around the blood vessels.

Synchronization ofPlasmodium yoelii nigeriensis andP. y. killicki infection in the mouse by means of Percoll-glucose gradient stage fractionation: Determination of the duration of the schizogonic cycle

The youngest (rings and young trophozoites) erythrocytic stages of Plasmodium yoelii nigeriensis and P. yoelii killicki, two rodent malaria subspecies developing very asynchronously in the blood, were separated from the other stages using a discontinuous Percoll-glucose gradient. They were inoculated into mice and the subsequent infection remained synchronous for two generations. The duration of the asexual cycle was found to be 18 h.

Schizogony of Plasmodium yoelii nigeriensis. Role of latent merozoites

Several procedures were employed to try to specify the schizogonic cycle of Plasmodium yoelii nigeriensis. The Percoll-glucose gradient technique for concentrating the very young stages (rings and young trophozoites), allowing a very precise follow up of the development of the parasitaemia during the first schizogonic cycles. A method for studying the prepatencies, providing an approximation of the number of merozoites inoculated. A comparison between the numbers of merozoites present in the blood, after--firstly simple dilutions in saline, revealing the total number of merozoites,--secondly dilutions in saline after a passage of a few hours in the organism of a mouse, revealing the number of latent merozoites. It was shown that the infection, during the first two cycles, varies according to the time of inoculation. In all cases the increase of the parasitaemia occurred mainly from 00:01 to 06:00. This increase of parasitaemia in mice inoculated with the Percoll concentrated parasites was significantly high during the first cycle in mice inoculated at 06:00 and 09:00 and during the second cycle in those inoculated at 12:00, 15:00 and 18:00. However, differences were rapidly compensated and parasitaemias became comparable at the 3rd or 4th cycle when they ceased to be dependent on the time of inoculation.

Aberrations in cerebral vascular functions due to Plasmodium yoelii nigeriensis infection in mice

Plasmodium yoelii nigeriensis infection in mice caused an increase in uptake of 125I-labeled bovine serum albumin, 51Cr-labeled erythrocytes and Evans blue dye from peripheral circulation into the brain. Isolated cerebral microvessels which were characterized in terms of their morphology under scanning electron microscope and enhancement of the specific activities of biochemical markers, viz. alkaline phosphatase, γ-glutamyl transpeptidase, and monoamine oxidase, showed significant decrease in these activities due to P. yoelii nigeriensis infection. On the other hand, relatively minor (statistically insignificant) changes occurred in the first two enzyme specific activities in the cerebral cortex and monoamine oxidase registered an increase in this tissue due to infection. Histological examination of the cerebral tissue of infected animals by light and electron microscopy showed broken blood vessel walls and leakage of erythrocytes into extravascular space, some of which contained intraerythrocytic malarial parasite in a state of cell division.

ネズミマラリア Plasmodium yoelii nigeriensis に感染した Anopheles stephensi の吸血行動の変動

Using a cage-test method, reduction and restoration of behavioral activity of Plasmodium-infected Anopheles stephensi was demonstrated. Reduction in the ability to pass through a net barrier and the rate of blood-feeding during the period oocysts are present was notable. However, net passage and bait-feeding activities in sporozoite-infected mosquitoes following disappearance of the oocyst were entirely restored.

The effects of Nosema algerae on the development of Plasmodium yoelii nigeriensis in Anopheles stephensi.

Experimental simultaneous infections of Anopheles stephensi (Diptera: Culicidae) with Nosema algerae (Microsporida: Nosematidae) and Plasmodium yoelii nigeriensis under standardized laboratory conditions showed partial suppression of the malaria parasite. At 9 days after an infective bloodmeal, the oocysts in the midgut were counted; 12.1%-66.6% of the double-infected mosquitoes exhibited no oocysts, whereas only 4.5%-12% of the control group showed no oocysts. The mean reduction in oocyst numbers under the influence of Nosema was 84.68%. At 14 days after infection with Plasmodium, the amount of sporozoites was examined; their mean reduction in eight experiments was 70%.

Status of hepatic heme and heme oxygenase during Plasmodium yoelii nigeriensis infection in mice

Plasmodium yoelii nigeriensis infection in albino mice caused a significant increase in hepatic heme level, the increase being concomitant with a rise in parasitemia. This elevated heme was found to be associated with all the subcellular fractions except the cytosol, where its content remained unaltered. Activity of heme oxygenase, the key enzyme responsible for catabolism of heme, also increased progressively with rise in parasitemia. Treatment of normal mice with cobalt chloride [60 mg (kg body wt) −1; subcutaneously] brought about a 150% increase in the level of heme oxygenase; similar treatment of infected mice at low parasitemia could induce the enzyme activity while at high parasitemia the enzymic activity remained unaltered as compared to untreated infected mice. In spite of an increased level of heme oxygenase in the cobalt-treated mice, the level of heme did not show any noticeable change. Oral administration of chloroquine [64 mg (kg body wt) −1 × 4 days] brought about a 56% reduction in the level of heme oxygenase of normal animals but there was no change in infected animals when compared with the corresponding untreated infected mice. However, the amount of chloroquine present in livers of normal and infected animals was not significantly different.

室内試験でみられた Plasmodium yoelii nigeriensis に感染された Anopheles stephensi の吸血源接近の行動

室内試験でみられた Plasmodium yoelii nigeriensis に感染された Anopheles stephensi の吸血源接近の行動

Penetration of the mosquito midgut wall by the ookinetes ofPlasmodium yoelii nigeriensis

The penetration route of ookinetes of Plasmodium yoelii nigeriensis in the midgut of a mosquito, Anopheles omorii, was investigated by electron microscopy. Within 15-18 h after an infective blood meal, ookinetes could be seen in the midgut lumen, in the process of entering the midgut wall, or lodged between the basement membrane and the basal lamina. The morphology of the ookinetes and their transformation into early oocysts were found to be similar to those previously reported. Ookinetes penetrated the midgut wall by the intercellular route; however, the intracellular occurrence of the parasite was also observed. Vacuoles appeared around the penetrating ookinetes during the penetration process, but no change in the electron density of the rhoptry-microneme complex was noted.

Possible Involvement of Platelets in <i>Plasmodium yoelii nigeriensi</i><i>s</i> Malaria Infection in Mice

The possible involvement of platelets in the pathogenesis of malaria was examined by monitoring the changes in platelet function (bleeding time [BT] and thrombin time [TT]) concomitantly with changes in packed cell volume (PCV) and erythrocyte infection rate (EIR) in Plasmodium yoelii nigeriensis infection in mice. In untreated plasmodium-infected mice, there was a progressive reduction (day 1-7) in BT from 120.0 +/- 12.6 s to 77.5 +/- 5.9 s (p less than 0.005), a reduction in TT from 26.8 +/- 1.2 s to 17.8 +/- 1.2 s (p less than 0.005), an increase in EIR from 0 to 64.6 +/- 6.3% and a reduction in PCV from 44.9 +/- 1.9% to 21.5 +/- 3.9% (p less than 0.001). Mortality on day 9 was 100%. Antiplatelet serum treatment of plasmodium-infected mice protected against malaria and there was a blunting of the malaria-induced changes in platelet function, EIR and PCV. The values obtained in these rats were significantly higher than those of the untreated malarious mice. The respective values obtained on day 1 were comparable to those of control mice. Data obtained on day 7 were: BT, 106.4 +/- 7.4 s (p less than 0.05), TT, 22.7 +/- 1.1 s (p less than 0.05), EIR, 45.7 +/- 3.2% (p less than 0.01) and PCV, 39.5 +/- 2.0% (p less than 0.01). Mortality on day 9 of infection was 60%. The protection by antiserum was not due to its thrombocytopenic response as busulphan-induced thrombocytopenia did not have the same effect. These results suggest that platelets play an important role in malaria infection as well as in the attendant coagulopathic complications.

マラリア病原体のオーシスト保有の数が宿主である蚊の行動に及ぼす影響

マラリア病原体のオーシスト保有の数が宿主である蚊の行動に及ぼす影響

The Effects of Host Diet on Plasmodium yoelii nigeriensis

A comparative study carried out on infected mice to investigate the effect of host diet on Plasmodium yoelii nigeriensis showed that concentrations of blood protein, hemoglobin, and erythrocytes began to decrease in infected mice on day 2 after inoculation and reached the lowest levels on day 8. The greatest decrease was among mice fed on protein-rich mouse cubes, whereas the least decrease was among mice fed on cassava meal. Inflammation of the spleens and livers of infected mice also was noticed. Leucocyte numbers and parasitemia in infected mice reached their peaks on day 8. Again, the greatest prevalence of these abnormalities was apparent among mice whose diet contained the highest amount of protein in comparison to the other diets used in this study. The abnormalities decreased proportionately among the other groups of infected mice, corresponding to the protein content of their various diets. Mice fed on cassava meal, with the lowest content of protein, had the fewest abnormalities. Elevated body temperature, characteristic of severe malaria, and extensive liver damage were highest among mice with the greatest amount of protein in their diet. In view of these observations, it was surmised that during malaria, host diets high in protein heighten the severity of this disease.

Plasmodium yoelii nigeriensis circumsporozoite gene structure and its implications for the evolution of the repeat regions

The circumsporozoite (CS) gene encodes the most immunogenic component of the plasmodial sporozoites. The immunodominant epitope-encoding domain of the CS gene shows sequences that are repeated in tandem. A detailed analysis of the CS repeats of certain closely related malaria parasites (strains of Plasmodium cynomolgi, Plasmodium knowlesi, and Plasmodium vivax) showed that they evolve rapidly yet are well conserved within the gene. We were interested in studying whether the CS repeats of Plasmodia more distantly related to these species evolve in a similar manner. To this end, we isolated and characterized the Plasmodium yoelii nigeriensis CS gene. A comparative analysis of its sequence with that Plasmodium yoelii yoelii shows that both have three sets of repeats, termed PR, R1, and R2. The R1 and basically also the R2 sequences show the features observed in most CS repeats, i.e., they evolve rapidly and are nearly perfectly tandemly repeated. In contrast, the PR repeats are not internally conserved nor divergent in sequence. The implications of these findings for the evolution of the CS repeats are discussed.

Role of DNA-binding antibodies in kidney pathology associated with murine malaria infections

We performed a series of studies to examine the sequential development of nephritis during murine malaria infections and to define the role of DNA-binding antibodies in the associated pathology. Serum levels of these antibodies were assessed throughout acute and chronic malaria infections. Increased levels of double-stranded DNA- and single-stranded DNA-binding antibodies were initially detected in mice infected with Plasmodium vinckei or Plasmodium yoelii nigeriensis during the middle stages of infection, and these levels were maintained until death. Infection with the more chronic organism Plasmodium berghei clone RC also resulted in increased single-stranded DNA-binding antibody titers, which fluctuated as the infection progressed. All three species caused kidney damage and dysfunction, as assessed by changes in morphology, blood urea nitrogen, and excreted albumin; this damage correlated with the extent of parasitemia and was observed before the levels of DNA-binding antibodies were detectably elevated in the serum. However, the results of immunohistochemical studies demonstrated that DNA-binding monoclonal antibodies bound ex vivo to glomeruli within kidneys prepared from mice at late stages of infection, after the initial damage had been incurred. Our findings suggest how DNA-binding antibodies could contribute to the kidney pathology associated with both malaria and certain autoimmune diseases, such as systemic lupus erythematosus.

The effects of chloroquine on the infectivity of chloroquine-sensitve and -resisant populations of Plasmodium yoelii nigeriensis to mosquitoes

Subtherapeutic doses of chloroquine have been reported to enhance infectivity of drug-resistant Plasmodium species to their vectors. In this investigation, Plasmodium yoelii nigeriensis N67 strain showed enhanced infectivity to mosquitoes when stimulated by chloroquine. Both sensitive and resistant clones were derived from the N67 strain by dilution, showing that this strain is polymorphic for the resistant trait. A resistant subline was derived by selection under drug pressure from a chloroquine-sensitive clone, but neither the sensitive nor the resistant clones or sublines showed enhancement of infectivity in the presence of chloroquine. This suggests that the enhancement of infectivity shown by the N67 strain is a response to chloroquine stimulation shown only by certain of the genotypes within it, and that this response to chloroquine is not a trait causally connected with the genes coding for chloroquine resistance.