Reappearance Of Parasitemia Research Articles

RNAscope in situ hybridization reveals microvascular sequestration of Plasmodium relictum pSGS1 blood stages but absence of exo-erythrocytic dormant stages during latent infection of Serinus canaria

BackgroundBirds chronically infected with avian malaria parasites often show relapses of parasitaemia after latent stages marked by absence of parasites in the peripheral circulation. These relapses are assumed to result from the activation of dormant exo-erythrocytic stages produced during secondary (post-erythrocytic) merogony of avian Plasmodium spp. Yet, there is no morphological proof of persistent or dormant tissue stages in the avian host during latent infections. This study investigated persistence of Plasmodium relictum pSGS1 in birds with latent infections during winter, with the goal to detect presumed persisting tissue stages using a highly sensitive RNAscope® in situ hybridization technology.MethodsFourteen domestic canaries were infected with P. relictum pSGS1 by blood-inoculation in spring, and blood films examined during the first 4 months post infection, and during winter and spring of the following year. After parasitaemia was no longer detectable, half of the birds were dissected, and tissue samples investigated for persisting tissue stages using RNAscope ISH and histology. The remaining birds were blood-checked and dissected after re-appearance of parasitaemia, and their tissues equally examined.ResultsSystematic examination of tissues showed no exo-erythrocytic stages in birds exhibiting latent infections by blood-film microscopy, indicating absence of dormant tissue stages in P. relictum pSGS1-infected canaries. Instead, RNAscope ISH revealed rare P. relictum blood stages in capillaries of various tissues and organs, demonstrating persistence of the parasites in the microvasculature. Birds examined after re-appearance of parasitemia showed higher numbers of P. relictum blood stages in both capillaries and larger blood vessels, indicating replication during early spring and re-appearance in the peripheral circulation.ConclusionsThe findings suggest that persistence of P. relictum pSGS1 during latent infection is mediated by continuous low-level erythrocytic merogony and possibly tissue sequestration of infected blood cells. Re-appearance of parasitaemia in spring seems to result from increased erythrocytic merogony, therefore representing recrudescence and not relapse in blood-inoculated canaries. Further, the study highlights strengths and limitations of the RNAscope ISH technology for the detection of rare parasite stages in tissues, providing directions for future research on persistence and tissue sequestration of avian malaria and related haemosporidian parasites.

Persistence of mRNA indicative of Plasmodium falciparum ring-stage parasites 42\xa0days after artemisinin and non-artemisinin combination therapy in naturally infected Malians

BackgroundMalaria control in sub-Saharan Africa relies upon prompt case management with artemisinin-based combination therapy (ACT). Ring-stage parasite mRNA, measured by sbp1 quantitative reverse-transcriptase PCR (qRT-PCR), was previously reported to persist after ACT treatment and hypothesized to reflect temporary arrest of the growth of ring-stage parasites (dormancy) following exposure to artemisinins. Here, the persistence of ring-stage parasitaemia following ACT and non-ACT treatment was examined.MethodsSamples were used from naturally infected Malian gametocyte carriers who received dihydroartemisinin–piperaquine (DP) or sulfadoxine–pyrimethamine (SP–AQ) with or without gametocytocidal drugs. Gametocytes and ring-stage parasites were quantified by qRT-PCR during 42 days of follow-up.ResultsAt baseline, 89% (64/73) of participants had measurable ring-stage parasite mRNA. Following treatment, the proportion of ring-stage parasite-positive individuals and estimated densities declined for all four treatment groups. Ring-stage parasite prevalence and density was generally lower in arms that received DP compared to SP–AQ. This finding was most apparent days 1, 2, and 42 of follow-up (p < 0.01). Gametocytocidal drugs did not influence ring-stage parasite persistence. Ring-stage parasite density estimates on days 14 and 28 after initiation of treatment were higher among individuals who subsequently experienced recurrent parasitaemia compared to those who remained free of parasites until day 42 after initiation of treatment (pday 14 = 0.011 and pday 28 = 0.068). No association of ring-stage persistence with gametocyte carriage was observed.ConclusionsThe current findings of lower ring-stage persistence after ACT without an effect of gametocytocidal partner drugs affirms the use of sbp1 as ring-stage marker. Lower persistence of ring-stage mRNA after ACT treatment suggests the marker may not reflect dormant parasites whilst it was predictive of re-appearance of parasitaemia.

Sentinel study on the efficacy of three artemisinin–based antimalarial combination therapies in Kaduna, Northwest – Nigeria

Background. Resistance still remains the major obstacle in the fight against malaria and reports from Southeast Asia on resistance to ACTs are disturbing. The study was a clinical and parasitological evaluation of artemether-lumefantrine (AL), artesunate-mefloquine (AM) and dihydroartemisininpiperaquine (DP) for treatment of uncomplicated falciparum malaria in Kaduna State, North -Western Nigeria conducted in 2011.Materials and Methods. Patients aged 6 months to 60 years who were confirmed malaria falciparum positive were randomly placed in one of three treatment groups and administered with either AL, AM or DP standard doses. Patients were followed-up for either 28 or 42 days. Fever, parasite clearance times and therapeutic efficacy of study drugs were determined.Results. A total of 324 patients were enrolled for the study. Study drugs had excellent fever and parasite clearance times of 1.44 and 1.41 days respectively. A total of 28 (9.2%) patients had re-appearance of parasitaemia. PCRUncorrected success rates were 96.3% and 90.6% after 28 and 42 days follow-up respectively. Artemetherlumefantrine, AM and DP had 91.1%, 86.2%, 94.9% individual success rates respectively. Ninety per cent of failures were seen in patients 5 to 14 years.Conclusion. The study reported the therapeutic efficacy of three commonly used ACTs in Nigeria for the year 2011 and showed it to be effective in the treatment of uncomplicated malaria, however continuous monitoring of the ACTs is required.Keywords: Uncomplicated malaria, treatment, efficacy study, artemisinin combination therapy, Plasmodium falciparum, resistance, artemether – lumefantrine, artesunate – amodiaquine, dihydroartemisinin – piperaquine

Distribution of mefloquine in the blood of Thai patients with acute uncomplicated falciparum malaria following administration of therapeutic doses of artesunate

The study objectives to investigate the distribution of the antimalarial drug mefloquine (MQ) in cellular and fluid blood compartments when given at therapeutic dosage with artesunate and to investigate an eventual association with the occurrence of treatment-related adverse events in Thai patients with acute uncomplicated falciparum malaria. MQ distribution following administration of standard therapeutic doses (1,250mg MQ in split dose) with artesunate to 20 Thai patients with acute uncomplicated falciparum malaria was assessed in whole blood, serum, plasma, red blood cells (RBC), white blood cells (WBC), and platelets using high -performance liquid chromatography. All patients responded to treatment without reappearance of parasitemia during the 42-day follow-up period. There was no significant gender difference in MQ levels. The chronological change in MQ levels in all blood components, including ratios of plasma to serum, whole blood, RBC, platelets or WBC were similar and parallel in both genders. MQ concentrations at 14 and 168h, in descending order, in both male and female patients were as follow: WBC > platelets > plasma > serum > whole blood > RBC. Gender-specific whole blood, serum, and RBC concentrations were similar at all time points, with median ratios of plasma:whole blood, plasma:serum, and plasma:RBC of 0.84:1.21, 1.09:1.64, and 1.59:3.79, respectively. Plasma vs whole blood and plasma vs RBC MQ concentrations showed a highly significant correlation, with r = 0.923 and 0.867, respectively. No association between occurrence of treatment-related adverse events and MQ concentrations in various blood components/fluids was observed in either gender. Based on these observations, gender-specific therapeutic MQ dose adjustment is obviously not required.

Efficacy and safety of a new pediatric artesunate-mefloquine drug formulation for the treatment of uncomplicated falciparum malaria in Gabon

Pediatric drug formulations of artemisinin combination therapies are urgently needed for improving the treatment of children suffering from uncomplicated malaria. The aim of this clinical trial was to evaluate the efficacy, safety and tolerability of a novel pediatric fixed-dose granule formulation of artesunate-mefloquine and a new co-blister tablet formulation. A total of 71 children aged 1-13 years suffering from uncomplicated falciparum malaria were stratified into two groups according to weight: 10-20 kg, pediatric group (n = 41); 20-40 kg, tablet group (n = 30). All the children were treated once daily for three days: the pediatric group received the novel granule formulation, the tablet group received the co-blister tablets. The PCR-corrected cure rate on day 28 was evaluated. There was no reappearance of parasitemia during the follow-up period and the day-28 cure rate was therefore 100% in per-protocol analysis. In intention-to-treat analysis the cure rates were 95% in the pediatric group and 97% in the tablet group. The most frequent adverse events were vomiting (17%), abdominal pain (11%) and headache (17%). This study confirms the excellent efficacy and favorable safety and tolerability profile of a novel pediatric artesunate-mefloquine formulation for treatment in African children.

Relapses ofPlasmodium vivaxInfection Usually Result from Activation of Heterologous Hypnozoites

Relapses originating from hypnozoites are characteristic of Plasmodium vivax infections. Thus, reappearance of parasitemia after treatment can result from relapse, recrudescence, or reinfection. It has been assumed that parasites causing relapse would be a subset of the parasites that caused the primary infection. Paired samples were collected before initiation of antimalarial treatment and at recurrence of parasitemia from 149 patients with vivax malaria in Thailand (n=36), where reinfection could be excluded, and during field studies in Myanmar (n=75) and India (n=38). Combined genetic data from 2 genotyping approaches showed that novel P. vivax populations were present in the majority of patients with recurrent infection (107 [72%] of 149 patients overall [78% of patients in Thailand, 75% of patients in Myanmar {Burma}, and 63% of patients in India]). In 61% of the Thai and Burmese patients and in 55% of the Indian patients, the recurrent infections contained none of the parasite genotypes that caused the acute infection. The P. vivax populations emerging from hypnozoites commonly differ from the populations that caused the acute episode. Activation of heterologous hypnozoite populations is the most common cause of first relapse in patients with vivax malaria.

Stage-dependent role of nitric oxide in control of Trypanosoma cruzi infection.

Trypanosoma cruzi, the causative agent of Chagas' disease, is known to be susceptible to nitric oxide (NO)-dependent killing by gamma interferon-activated macrophages. Mice deficient for inducible nitric oxide synthase (iNOS) are highly susceptible to T. cruzi, and inhibition of iNOS from the beginning of infection was reported to lead to an increase in trypomastigotes in the blood and to high mortality. In the present study, we investigated whether NO production is essential for the control of T. cruzi in all phases of the infection. BALB/c mice were treated at different time intervals after T. cruzi infection with an iNOS inhibitor, aminoguanidine or L-N6-(1-iminoethyl)-lysine (L-NIL). Treatment initiated with the beginning of the infection resulted in 100% mortality by day 16 postinfection (p.i.). If treatment was started later during the acute phase at the peak of parasitemia (day 20 p.i.), all the mice survived. Parasitemia was cleared and tissue amastigotes became undetectable in these mice even in the presence of the iNOS inhibitor L-NIL. Inhibition of iNOS in the chronic phase of the infection, i.e., from day 60 to day 120 p.i., with L-NIL did not result in a reappearance of parasitemia. These data suggest that while NO is essential for T. cruzi control in the early phase of acute infection, it is dispensable in the late acute and chronic phase, revealing a fundamental difference in control mechanisms compared to those in infections by other members of the order Kinetoplastida, e.g., Leishmania major.

Clinical response and susceptibility in vitro of Plasmodium vivax to the standard regimen of chloroquine in Thailand

The clinical effectiveness of the standard regimen of chloroquine (CQ) (a total dose of 1500 mg, given over 48 h at 0, 6, 24 and 48 h) for the treatment of Plasmodium vivax malaria in Thailand was investigated in 57 patients in an endemic area of Thailand (Chantaburi Province, eastern Thailand). For radical treatment, an additional course of a tissue schizontocidal agent, primaquine, was given following the complete course of CQ. With this regimen, satisfactory whole blood concentration-time profiles of CQ and its major metabolite desethylchloroquine (DECQ) were achieved. Mean whole blood levels of CQ and DECQ always much exceeded the reported therapeutic level of CQ (90 ng/mL) during the first 7 d of treatment. All patients responded well to the treatment; in most cases, complete and rapid clearance of parasitaemia was observed within the first 48 h. No reappearance of the parasitaemia was detected in peripheral blood films of any patient within 14 d of the evaluation period. In 6 patients, however, reappearance of P. vivax parasitaemia was observed after 30 d; 2 of them had not completed the course of primaquine. There was no difference in whole blood concentrations of CQ and DECQ, admission parasitaemia, susceptibility of the isolates to chloroquine in vitro, and parasite clearance time between patients with or without reappearance of parasitaemia. A prominent trend of deteriorating sensitivity of the parasite to the drug was, however, suggested.

Plasmodium yoelii in Mice: Antigen Reactivity of CD4- and CD8-Bearing T Cells

Mice infected with Plasmodium yoelii (265 BY, a nonlethal strain) after recovering from parasitemia become resistant to reinfection. In the present study, we have attempted to define the role of T cell subsets in primary vs secondary P. yoelii infection. We have evaluated the in vivo effects of selective depletion of each subset of T cells on the course of infection and also investigated the in vitro expansion of each subset in response to homologous antigen. Depletion of CD4- or CD8-bearing T cells did not result in reappearance of parasitemia in animals cured from primary infection. However, 25% of reinfected animals treated with anti-CD4 mAb, but not with anti-CD8 mAb, displayed a low level (2 to 3%) of parasitemia late in the secondary infection. The splenocyte response to P. yoelii antigen or to T-cell mitogens was impaired during patent infection, even in the 25% of CD4-depleted animals with low parasitemia. A markedly high lymphocyte reactivity to antigen was observed in mice recovered from primary infection, and this was enhanced in animals exposed to a challenge infection. In the case of animals cured from primary infection, a marked decrease in antigen-induced in vitro lymphocyte proliferation occurred in CD8-depleted but not in CD4-depleted animals when total splenic cell populations were assayed. Although less dramatic, a significant diminution in antigen reactivity was observed also with T-rich populations in CD8-depleted animals. In contrast, there was no such decrease in CD4-depleted mice. Treatment of resistant animals which were challenged with a second infection, with anti-CD4 or anti-CD8 mAbs, resulted in a significant decrease in the proliferative response to antigen by both T-rich and total cell populations. In the secondary infection, the T-rich cell populations from CD8-depleted mice responded better to P. yoelii antigen than the total cell populations, indicating an inhibitory role on the expansion of CD4 + T cells of B cells or their product(s) which were removed during T cell enrichment. The results of our study suggest that CD8-bearing T cells were more reactive in the primary infection. In the secondary infection, although both CD8 + and CD4 + T cells were antigen reactive, the latter T cell subset appeared to play a superior role in controlling the parasitemia.