Peak Parasitemia Research Articles

Interleukin-3-deficient mice have increased resistance to blood-stage malaria (MPF1P.764)

Abstract The contribution of interleukin-3 (IL-3), a hematopoietic growth factor and immunoregulatory cytokine, to resistance to blood-stage malaria was investigated by infecting IL-3 deficient (knockout [KO]) mice with Plasmodium berghei NK65. Male IL-3 KO mice, but not female mice, were more resistant to infection than wild-type (WT) mice, evidenced by lower peak parasitemia and prolonged survival. Both male and female IL-3 KO mice had increased splenomegaly and were more anemic than corresponding WT mice. Anemia was compensated for by an increase in bone marrow and splenic erythropoiesis in IL-3 KO mice, as evidenced by higher levels of erythroid progenitors. Plasma levels of gamma interferon (IFN-γ) and CXCL9 (Monokine Induced by IFN-γ; [MIG]) were found to be significantly reduced in IL-3 KO mice during early stages of infection whereas G-CSF levels were significantly greater than in WT counterparts. Overall, our results indicate that IL-3 plays a critical role in suppressing protective immunity to P. berghei NK65 infection and that it is involved in inhibiting the development of splenomegaly, anemia, and erythropoiesis. IL-3 also influences IFN-γ, CXCL9, and G-CSF production in response to infection. The abnormal responses seen in infected IL-3 KO mice may be due to the lack of IL-3 during development, to the lack of IL-3 in the infected mature mice, or to both.

BAFF and BAFF receptor levels correlate with B cell subset activation and redistribution in controlled human malaria infection.

Characteristic features of Plasmodium falciparum malaria are polyclonal B cell activation and an altered composition of the blood B cell compartment, including expansion of CD21(-)CD27(-) atypical memory B cells. BAFF is a key cytokine in B cell homeostasis, but its potential contribution to the modulation of the blood B cell pool during malaria remains elusive. In the controlled human malaria model (CHMI) in malaria-naive Dutch volunteers, we therefore examined the dynamics of BAFF induction and B cell subset activation and composition, to investigate whether these changes are linked to malaria-induced immune activation and, in particular, induction of BAFF. Alterations in B cell composition after CHMI closely resembled those observed in endemic areas. We further found distinct kinetics of proliferation for individual B cell subsets across all developmental stages. Proliferation peaked either immediately after blood-stage infection or at convalescence, and for most subsets was directly associated with the peak parasitemia. Concomitantly, plasma BAFF levels during CHMI were increased and correlated with membrane-expressed BAFF on monocytes and dendritic cells, as well as blood-stage parasitemia and parasite-induced IFN-γ. Correlating with increased plasma BAFF and IFN-γ levels, IgD(-)CD38(low)CD21(-)CD27(-) atypical B cells showed the strongest proliferative response of all memory B cell subsets. This provides unique evidence for a link between malaria-induced immune activation and temporary expansion of this B cell subset. Finally, baseline BAFF-R levels before CHMI were predictive of subsequent changes in proportions of individual B cell subsets. These findings suggest an important role of BAFF in facilitating B cell subset proliferation and redistribution as a consequence of malaria-induced immune activation.

Evaluation of antioxidant status and oxidative stress in sheep experimentally infected with Anaplasma ovis

Summary Anaplasma ovis infections can cause severe anemia in the acute phase of the disease. In order to investigate the alterations of erythrocyte protective antioxidant mechanisms associated with anemia in sheep experimentally infected with A. ovis, 100 ml heparinized blood was collected from splenectomised sheep that showed 6% A. ovis parasitemia. Inoculums of 20 ml blood were administered intravenously to five male sheep without any blood parasite. Parasitological and haematological changes and the activities of erythrocyte superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) were studied in experimentally infected animals on the 0-38 post infection days. Parasitemia increased significantly with the progress of infection and reached its maximum level on day 15 of the experiment. From this point to day 38, there was a gradual decline in parasitemia. A significant decrease in PCV, RBC and Hb concentration was evident coincidentally with peak parasitaemia in the infected sheep. On post infection day 15, the activities of all enzymes increased, the changes being significant for SOD activity. There was a significant positive correlation among parasitemia and the activities of erythrocyte SOD (r = 0.644, P<0.0005) and CAT (r = 0.424, P<0.05). Glutathione peroxidase activity declined significantly between post infection days 23-38. From the present study, it can be concluded that oxidative stress has an important role in anemia induced by anaplasmosis in sheep. It seems that SOD is a useful indicator of oxidative stress caused by A. ovis infection, due to its constant increasing means in the course of the disease.

English

Study on sensitivity to diminazene aceturate 3.5 mg/kg and isometamidium chloride 0.5 mg/kg in tenzebu calves experimentally infected with two field isolates of Trypanosoma congolense (ET/07/Konso 59 and ET/07/Konso 114) was undertaken in Konso district, Southern Ethiopia. Calves were monitored for clinical and parasitological parameters during three months. At day 15 post-infection, corresponding to peak parasitaemia, they were treated with Diminasan® 3.5 mg/kg body weight via deep intramuscular route. Out of ten calves, only two remained parasitologically negative for 12 and 15 days after treatment with Diminasan®. Once relapse/breakthrough infection was detected in two calves, parasitemia persisted until they get second treatment with Veridium® 0.5 mg/kg body weight. However, linear regression analysis of the effects of persistent trypanosomal infections on mean packed cell volume (PCV) and loss of body condition in relation to the initial recordings in the relapsed calves was not statistically significant. Results of the trypanocidal drug sensitivity study revealed the presence of T. congolense populations exhibiting resistance to diminazene aceturate. It is strongly recommended that legislations be devised and implemented to ensure that only quality and effective trypanocidal drugs should get access to the market. Key words: Trypanosoma congolense, trypanocidal drugs, sensitivity test, Southern Ethiopia, calves.

Immune-Mediated Competition in Rodent Malaria Is Most Likely Caused by Induced Changes in Innate Immune Clearance of Merozoites

Malarial infections are often genetically diverse, leading to competitive interactions between parasites. A quantitative understanding of the competition between strains is essential to understand a wide range of issues, including the evolution of virulence and drug resistance. In this study, we use dynamical-model based Bayesian inference to investigate the cause of competitive suppression of an avirulent clone of Plasmodium chabaudi (AS) by a virulent clone (AJ) in immuno-deficient and competent mice. We test whether competitive suppression is caused by clone-specific differences in one or more of the following processes: adaptive immune clearance of merozoites and parasitised red blood cells (RBCs), background loss of merozoites and parasitised RBCs, RBC age preference, RBC infection rate, burst size, and within-RBC interference. These processes were parameterised in dynamical mathematical models and fitted to experimental data. We found that just one parameter , the ratio of background loss rate of merozoites to invasion rate of mature RBCs, needed to be clone-specific to predict the data. Interestingly, was found to be the same for both clones in single-clone infections, but different between the clones in mixed infections. The size of this difference was largest in immuno-competent mice and smallest in immuno-deficient mice. This explains why competitive suppression was alleviated in immuno-deficient mice. We found that competitive suppression acts early in infection, even before the day of peak parasitaemia. These results lead us to argue that the innate immune response clearing merozoites is the most likely, but not necessarily the only, mediator of competitive interactions between virulent and avirulent clones. Moreover, in mixed infections we predict there to be an interaction between the clones and the innate immune response which induces changes in the strength of its clearance of merozoites. What this interaction is unknown, but future refinement of the model, challenged with other datasets, may lead to its discovery.

Co-infection restrainsLitomosoides sigmodontisfilarial load and plasmodialP. yoeliibut notP. chabaudiparasitaemia in mice

Infection with multiple parasite species is clearly the norm rather than the exception, in animals as well as in humans. Filarial nematodes and Plasmodium spp. are important parasites in human public health and they are often co-endemic. Interactions between these parasites are complex. The mechanisms underlying the modulation of both the course of malaria and the outcome of filarial infection are poorly understood. Despite increasing activity in recent years, studies comparing co- and mono-infections are very much in their infancy and results are contradictory at first sight. In this study we performed controlled and simultaneous co-infections of BALB/c mice with Litomosoides sigmodontis filaria and with Plasmodium spp. (Plasmodium yoelii 17 XNL or Plasmodium chabaudi 864VD). An analysis of pathological lesions in the kidneys and lungs and a parasitological study were conducted at different times of infection. Whatever the plasmodial species, the filarial recovery rate was strongly decreased. The peak of parasitaemia in the plasmodial infection was decreased in the course of P. yoelii infection but not in that of P. chabaudi. Regarding pathological lesions, L. sigmodontis can reverse lesions in the kidneys due to the presence of both Plasmodium species but does not modify the course of pulmonary lesions. The filarial infection induces granulomas in the lungs.

Prevalence and Severity of Malaria Parasitemia among Children Requiring Emergency Blood Transfusion in a Tertiary Hospital in Imo State, Nigeria.

Background:Malaria is one of the most serious and complex health problems in Sub Saharan Africa. Anemia in Children with malaria may require blood transfusion and has been be associated with high mortality rates.Aim:The aim of this study is to evaluate the prevalence, pattern, and severity of malaria parasitemia among children 6 months to 14 years old, requiring blood transfusion.Subjects and Methods:This is a cross-sectional study carried out at the children emergency unit of the Imo state University Teaching Hospital South East Nigeria. Data were analyzed using SPSS version 21, Chicago Il, USAResults:A total of 409 children were recruited into the study. The overall rate of malaria parasitemia was 83.1% (340/409) lower in males 81.6% (228/276) than in females 86.3% (112/133). The peak of parasitemia is similar in both sexes (5-9 years). Most of the children had medium levels of parasitemia, which decreased with increasing age. The proportion of children transfused also decreased with increasing age. At medium and high levels of parasitemia; in children below 5 years, 92.8% (132/142) were transfused while in 5 years and above only 79.6% (39/49) of the children were transfused. At medium level parasitemia the proportion of children transfused was significantly higher than those not transfused (P < 0.001).Conclusion:Most children 6 months to 14 years with medium level of parasitemia may require blood transfusion. Targeted measures toward primary prevention of malaria in children should be intensified as this will not only reduce morbidity and mortality of malaria, but will reduce the economic burden of the disease in Semi-rural and rural dwellers in Sub Saharan Africa.

Evaluation of In vivo Antitrypanosomal Activity of Aqueous and Methanol Leaf Extracts of Clutia abyssinica (Euphorbiaceae) against Trypanosoma congolense Field Isolate

Aqueous and methanol leaf extracts of C. abyssinica were investigated for their in vivo activity against Trypanosoma congolence, the main causative agent of African animal trypanosomosis in Sub-Saharan Africa and Ethiopia. The in vivo antitrypanosomal efficacy of the aqueous and methanol extracts was evaluated in Swiss albino mice infected with T. congolense field isolate. The leaf extracts were administered 12 days post-infection at peak parasitaemia level of ~108 trypanosomes/ml at doses of 100, 200 and 400 mg/kg by intraperitoneal injection once daily for 7 days. Parasitaemia, packed cell volume (PCV), mean survival time and change in body weight were used as indices for monitoring the efficacy of the extracts by comparing with the positive control: 28 mg/kg dose of diminazene aceturate and negative control: 2% tween 80 treated groups. The extracts had a lethal dose greater than 2000 mg/kg and there were no evidences of acute toxicity at the doses tested. Highly significant (p<0.001) reduction in pre-treatment parasitaemia by 3.91% (7.38 ± 0.18), increase in PCV by 1.12% (48.66 ± 0.20), body weight improvement by 1.36% (22.34 ± 0.27) and mean survival time of 39.20 ± 0.37 days was observed in the group treated by 400 mg/kg methanol leaf extract of C. abyssinica. In general, the results obtained suggest ethno-pharmacological usefulness of the plant and necessitate further studies to be carried on isolated active substances from the plant.

Interleukin-3-deficient mice have increased resistance to blood-stage malaria.

The contribution of interleukin-3 (IL-3), a hematopoietic growth factor and immunoregulatory cytokine, to resistance to blood-stage malaria was investigated by infecting IL-3-deficient (knockout [KO]) mice with Plasmodium berghei NK65. Male IL-3 KO mice, but not female mice, were more resistant to infection than wild-type (WT) mice, as evidenced by lower peak parasitemia and prolonged survival. Both male and female IL-3 KO mice had increased splenomegaly and were more anemic than corresponding WT mice. Anemia was compensated for by an increase in bone marrow and splenic erythropoiesis in IL-3 KO mice, as evidenced by higher levels of erythroid progenitors. Plasma levels of gamma interferon (IFN-γ) and CXCL9 (monokine induced by IFN-γ [MIG]) were found to be significantly reduced in IL-3 KO mice during early stages of infection. In contrast, granulocyte colony-stimulating factor (G-CSF) levels were significantly higher, and the percentage of peripheral blood neutrophils lower, in infected IL-3 KO mice than in WT counterparts. Overall, our results indicate that IL-3 plays a critical role in suppressing protective immunity to P. berghei NK65 infection and that it is involved in inhibiting the development of splenomegaly, anemia, and erythropoiesis. IL-3 also influences IFN-γ, CXCL9, and G-CSF production in response to infection. The abnormal responses seen in infected IL-3 KO mice may be due to the lack of IL-3 during development, to the lack of IL-3 in the infected mature mice, or to both.

Mosquito transmission, growth phenotypes and the virulence of malaria parasites

BackgroundA series of elegant experiments was recently published which demonstrated that transmission of malaria parasites through mosquitoes elicited an attenuated growth phenotype, whereby infections grew more slowly and reached peak parasitaemia at least five-fold lower than parasites which had not been mosquito transmitted. To assess the implications of these results it is essential to understand whether the attenuated infection phenotype is a general phenomenon across parasites genotypes and conditions.MethodsUsing previously published data, the impact of mosquito transmission on parasite growth rates and virulence of six Plasmodium chabaudi lines was analysed.ResultsThe effect of mosquito transmission varied among strains, but did not lead to pronounced or consistent reductions in parasite growth rate.ConclusionsMosquito-induced attenuated growth phenotype is sensitive to experimental conditions.

Moderate physical exercise reduces parasitaemia and protects colonic myenteric neurons in mice infected with Trypanosoma cruzi

This study evaluated the influence of moderate physical exercise on the myenteric neurons in the colonic intestinal wall of mice that had been infected with Trypanosoma cruzi. Parasitology and immunological aspects of the mice were considered. Forty-day-old male Swiss mice were divided into four groups: Trained Infected (TI), Sedentary Infected (SI), Trained Control (TC), and Sedentary Control (SC). The TC and TI were subjected to a moderate physical exercise program on a treadmill for 8 weeks. Three days after finishing exercise, the TI and SI groups were inoculated with 1,300 blood trypomastigotes of the Y strain-T. cruzi. After 75 days of infection results were obtained. Kruskal-Wallis or Analyze of variance (Tukey post hoc test) at 5% level of significance was performed. Moderate physical exercise reduced both the parasite peak (day 8 of infection) and total parasitemia compared with the sedentary groups (P < 0.05). This activity also contributed to neuronal survival (P < 0.05). Exercise caused neuronal hypertrophy (P < 0.05) and an increase in the total thickness of the intestinal wall (P < 0.05). The TI group exhibited an increase in the number of intraepithelial lymphocytes (P > 0.05). In trained animals, the number of goblet cells was reduced compared with sedentary animals (P < 0.05). Physical exercise prevented the formation of inflammatory foci in the TI group (P < 0.05) and increased the synthesis of TNF-α (P < 0.05) and TGF-β (P > 0.05). The present results demonstrated the benefits of moderate physical exercise, and reaffirmed the possibility of that it may contribute to improving clinical treatment in Chagas' disease patients.

NLRP3 Controls Trypanosoma cruzi Infection through a Caspase-1-Dependent IL-1R-Independent NO Production

Trypanosoma cruzi (T. cruzi) is an intracellular protozoan parasite and the etiological agent of Chagas disease, a chronic infectious illness that affects millions of people worldwide. Although the role of TLR and Nod1 in the control of T. cruzi infection is well-established, the involvement of inflammasomes remains to be elucidated. Herein, we demonstrate for the first time that T. cruzi infection induces IL-1β production in an NLRP3- and caspase-1-dependent manner. Cathepsin B appears to be required for NLRP3 activation in response to infection with T. cruzi, as pharmacological inhibition of cathepsin B abrogates IL-1β secretion. NLRP3−/− and caspase1−/− mice exhibited high numbers of T. cruzi parasites, with a magnitude of peak parasitemia comparable to MyD88−/− and iNOS−/− mice (which are susceptible models for T. cruzi infection), indicating the involvement of NLRP3 inflammasome in the control of the acute phase of T. cruzi infection. Although the inflammatory cytokines IL-6 and IFN-γ were found in spleen cells from NLRP3−/− and caspase1−/− mice infected with T. cruzi, these mice exhibited severe defects in nitric oxide (NO) production and an impairment in macrophage-mediated parasite killing. Interestingly, neutralization of IL-1β and IL-18, and IL-1R genetic deficiency demonstrate that these cytokines have a minor effect on NO secretion and the capacity of macrophages to control T. cruzi infection. In contrast, inhibition of caspase-1 with z-YVAD-fmk abrogated NO production by WT and MyD88−/− macrophages and rendered them as susceptible to T. cruzi infection as NLRP3−/− and caspase-1−/− macrophages. Taken together, our results demonstrate a role for the NLRP3 inflammasome in the control of T. cruzi infection and identify NLRP3-mediated, caspase-1-dependent and IL-1R-independent NO production as a novel effector mechanism for these innate receptors.

Toll-Like Receptor 7 Mediates Early Innate Immune Responses to Malaria

Innate immune recognition of malaria parasites is the critical first step in the development of the host response. At present, Toll-like receptor 9 (TLR9) is thought to play a central role in sensing malaria infection. However, we and others have observed that Tlr9(-/-) mice, in contrast to mice deficient in the downstream adaptor, Myeloid differentiation primary response gene 88 (MYD88), exhibit few deficiencies in immune function during early infection with the malaria parasite Plasmodium chabaudi, implying that another MYD88-dependent receptor also contributes to the antimalarial response. Here we use candidate-based screening to identify TLR7 as a key sensor of early P. chabaudi infection. We show that TLR7 mediates a rapid systemic response to infection through induction of cytokines such as type I interferons (IFN-I), interleukin 12, and gamma interferon. TLR7 is also required for induction of IFN-I by other species and strains of Plasmodium, including an etiological agent of human disease, P. falciparum, suggesting that malaria parasites harbor a common pathogen-associated molecular pattern (PAMP) recognized by TLR7. In contrast to the nonredundant requirement for TLR7 in early immune activation, sensing through both TLR7 and TLR9 was required for proinflammatory cytokine production and immune cell activation during the peak of parasitemia. Our findings indicate that TLR7 plays a central role in early immune activation during malaria infection, whereas TLR7 and TLR9 contribute combinatorially to immune responses as infection progresses.

Density-Dependent Blood Stage Plasmodium falciparum Suppresses Malaria Super-Infection in a Malaria Holoendemic Population

Recent studies of Plasmodium berghei malaria in mice show that high blood-stage parasitemia levels inhibit the development of subsequent liver-stage infections. Whether a similar inhibitory effect on liver-stage Plasmodium falciparum by blood-stage infection occurs in humans is unknown. We have analyzed data from a treatment-time-to-infection cohort of children < 10 years of age residing in a malaria holoendemic area of Kenya where people experience a new blood-stage infection approximately every 2 weeks. We hypothesized that if high parasitemia blocked the liver stage, then high levels of parasitemia should be followed by a "skipped" peak of parasitemia. Statistical analysis of "natural infection" field data and stochastic simulation of infection dynamics show that the data are consistent with high P. falciparum parasitemia inhibiting liver-stage parasite development in humans.

Genome-wide screening identifies Plasmodium chabaudi-induced modifications of DNA methylation status of Tlr1 and Tlr6 gene promoters in liver, but not spleen, of female C57BL/6 mice

Epigenetic reprogramming of host genes via DNA methylation is increasingly recognized as critical for the outcome of diverse infectious diseases, but information for malaria is not yet available. Here, we investigate the effect of blood-stage malaria of Plasmodium chabaudi on the DNA methylation status of host gene promoters on a genome-wide scale using methylated DNA immunoprecipitation and Nimblegen microarrays containing 2,000 bp oligonucleotide features that were split into -1,500 to -500 bp Ups promoters and -500 to +500 bp Cor promoters, relative to the transcription site, for evaluation of differential DNA methylation. Gene expression was analyzed by Agilent and Affymetrix microarray technology. Challenging of female C57BL/6 mice with 10(6) P. chabaudi-infected erythrocytes resulted in a self-healing outcome of infections with peak parasitemia on day 8 p.i. These infections induced organ-specific modifications of DNA methylation of gene promoters. Among the 17,354 features on Nimblegen arrays, only seven gene promoters were identified to be hypermethylated in the spleen, whereas the liver exhibited 109 hyper- and 67 hypomethylated promoters at peak parasitemia in comparison with non-infected mice. Among the identified genes with differentially methylated Cor-promoters, only the 7 genes Pigr, Ncf1, Klkb1, Emr1, Ndufb11, and Tlr6 in the liver and Apol6 in the spleen were detected to have significantly changed their expression. Remarkably, the Cor promoter of the toll-like receptor Tlr6 became hypomethylated and Tlr6 expression increased by 3.4-fold during infection. Concomitantly, the Ups promoter of the Tlr1 was hypermethylated, but Tlr1 expression also increased by 11.3-fold. TLR6 and TLR1 are known as auxillary receptors to form heterodimers with TLR2 in plasma membranes of macrophages, which recognize different pathogen-associated molecular patterns (PAMPs), as, e.g., intact 3-acyl and sn-2-lyso-acyl glycosylphosphatidylinositols of P. falciparum, respectively. Our data suggest therefore that malaria-induced epigenetic fine-tuning of Tlr6 and Tlr1 through DNA methylation of their gene promoters in the liver is critically important for initial recognition of PAMPs and, thus, for the final self-healing outcome of blood-stage infections with P. chabaudi malaria.

Molecular and biological characterization of Trypanosoma cruzi strains isolated from children from Jequitinhonha Valley, State of Minas Gerais, Brazil

The biological diversity of Trypanosoma cruzi strains plays an important role in the clinical and epidemiological features of Chagas disease. Eight T. cruzi strains isolated from children living in a Chagas disease vector-controlled area of Jequitinhonha Valley, State of Minas Gerais, Brazil, were genetically and biologically characterized. The characterizations demonstrated that all of the strains belonged to T. cruzi II, and showed high infectivity and a variable mean maximum peak of parasitemia. Six strains displayed low parasitemia, and two displayed moderate parasitemia. Later peaks of parasitemia and a predominance of intermediate and large trypomastigotes in all T. cruzi strains were observed. The mean pre-patent period was relatively short (4.2 ± 0.25 to 13.7 ± 3.08 days), whereas the patent period ranged from 3.3 ± 1.08 to 34.5 ± 3.52 days. Mortality was observed only in animals infected with strain 806 (62.5%). Histopathological analysis of the heart showed that strains 501 and 806 caused inflammation, but fibrosis was observed only in animals infected with strain 806. The results indicate the presence of an association between the biological behavior in mice and the genetic characteristics of the parasites. The study also confirmed general data from Brazil where T. cruzi II lineage is the most prevalent in the domiciliary cycle and generally has low virulence, with some strains capable of inducing inflammatory processes and fibrosis.

1H NMR metabonomics indicates continued metabolic changes and sexual dimorphism post-parasite clearance in self-limiting murine malaria model.

Malaria, a mosquito-borne disease caused by Plasmodium spp. is considered to be a global threat, specifically for the developing countries. In human subjects considerable information exists regarding post-malarial physiology. However, most murine malarial models are lethal, and most studies deal with acute phases occurring as disease progresses. Much less is known regarding physiological status post-parasite clearance. We have assessed the physiological changes at the organ levels using 1H NMR based metabonomics in a non lethal self-clearing murine malarial model of P. chabaudi parasites and Balb/C, far beyond the parasite clearance point. The results showed distinct metabolic states between uninfected and infected mice at the peak parasitemia, as well as three weeks post-parasite clearance. Our data also suggests that the response at the peak infection as well as recovery exhibited distinct sexual dimorphism. Specifically, we observed accumulation of acetylcholine in the brain metabolic profile of both the sexes. This might have important implication in understanding the pathophysiology of the post malarial neurological syndromes. In addition, the female liver showed high levels of glucose, dimethylglycine, methylacetoacetate and histidine after three weeks post-parasite clearance, while the males showed accumulation of branched chain amino acids, lysine, glutamine and bile acids.

A Study on Course of Infection and Haematological Changes in falciparum-Infected in Comparison with Artemisinin(s)-Treated Mice

To find out the efficacy and effect of artemisinin derivatives on haematological indices, C57BL/6J mice were challenged with Plasmodium falciparum and treated with therapeutic doses of AS, AE, and AL. Course of infection was studied in the infected and treated groups up to day 42. Peak level of parasitaemia (38%) was observed on day 11 in infected group. Haematological indices indicated significant (P < 0.05) decrease in RBC, WBC, haemoglobin, packed cell volume, mean cell volume, and platelet counts in infected mice. But all the parameters were restored to normal values, and significant (P < 0.05) changes were observed in all drug-treated groups. Insignificant changes were observed for MCHC (P > 0.05) in all drug-treated groups. Percent of peak parasitaemia was much reduced in AL- (3.2% on day 3) treated group in comparison with AE- (2.4% on day 4) and AS- (4% on day 2) treated groups. Parasites were completely cleared on day 6 in AS group, day 5 in AE group, and day 4 in AL group. Hence, our results strongly support that combination therapy has high efficacy rates than monotherapy. No adverse effects were observed on haematological parameters when animals were treated with therapeutic dosages.

New Targets for Drug Discovery against Malaria

A mathematical model which predicts the intraerythrocytic stages of Plasmodium falciparum infection was developed using data from malaria-infected mice. Variables selected accounted for levels of healthy red blood cells, merozoite (Plasmodium asexual phase) infected red blood cells, gametocyte (Plasmodium sexual phase) infected red blood cells and a phenomenological variable which accounts for the mean activity of the immune system of the host. The model built was able to reproduce the behavior of three different scenarios of malaria. It predicts the later dynamics of malaria-infected humans well after the first peak of parasitemia, the qualitative response of malaria-infected monkeys to vaccination and the changes observed in malaria-infected mice when they are treated with antimalarial drugs. The mathematical model was used to identify new targets to be focused on drug design. Optimization methodologies were applied to identify five targets for minimizing the parasite load; four of the targets thus identified have never before been taken into account in drug design. The potential targets include: 1) increasing the death rate of the gametocytes, 2) decreasing the invasion rate of the red blood cells by the merozoites, 3) increasing the transformation of merozoites into gametocytes, 4) decreasing the activation of the immune system by the gametocytes, and finally 5) a combination of the previous target with decreasing the recycling rate of the red blood cells. The first target is already used in current therapies, whereas the remainders are proposals for potential new targets. Furthermore, the combined target (the simultaneous decrease of the activation of IS by gRBC and the decrease of the influence of IS on the recycling of hRBC) is interesting, since this combination does not affect the parasite directly. Thus, it is not expected to generate selective pressure on the parasites, which means that it would not produce resistance in Plasmodium.

Effects of Trypanosoma brucei infection and diminazene aceturate therapy on testicular morphology and function of Nigerian local dogs

The effects of Trypanosoma brucei infection on testicular morphology and function and the changes associated with treatment of infected dogs with diminazene aceturate were studied using fifteen Nigerian adult male dogs. The dogs were randomly assigned into three groups A, B and C consisting of five dogs each. Groups A and B were infected with 1×106 trypanosomes and group C was the uninfected control. Following infection, parasitaemia levels were monitored daily whereas the rectal temperature, body weight, packed cell volume, scrotal circumference and serum testosterone levels were monitored weekly. At parasitaemia peak, dogs in group A were orchidectomised while dogs in group B were treated with 7.0mg/kg body weight of diminazene aceturate (DA). Dogs in groups B and C were later orchidectomised on day 73 of the experiment. The harvested testes and epididymides were weighed and the epididymal sperm reserves of all the dogs determined. Also the sperm quality (mass activity, sperm motility and sperm morphology) were determined. The testes were sectioned after processing and studied histomorphologically. Acute trypanosomosis was observed following infection. The low serum testosterone levels observed from day 14 post infection (pi) gradually improved following treatment. Testicular weight, epididymal weight and sperm quality were significantly low (p<0.05) in the infected dogs when compared to the control group but gradually improved following treatment. Histomorphological studies revealed testicular degeneration characterized by depopulation of seminiferous tubules and depletion of spermatogenic cells in dogs of group A whereas the tissue sections of the testes of dogs in group B were similar to those of the control group. It was therefore concluded that infection of dogs with T. brucei adversely affected testicular morphology and function. Treatment with diminazene aceturate reversed the reproductive abnormalities caused by the parasite.