116 research outputs found
A humanized mouse model for sequestration of Plasmodium falciparum sexual stages and in vivo evaluation of gametocytidal drugs
The development of new drugs to disrupt malaria transmission
requires the establishment of an in vivo model to address the
biology of Plasmodium falciparum sexual stages (gametocytes).
Herein we show that chemically immune-modulated NSG mice grafted
with human erythrocytes support complete sexual development of
P. falciparum parasites and generate high gametocytemia.
Immunohistochemistry and RT-qPCR analyses indicate an enrichment
of immature gametocytes in the bone marrow and the spleen,
suggesting a sequestration mechanism reminiscent to that
observed in humans. Upon primaquine treatment, elimination of
gametocytes from peripheral blood and from sequestration sites
was observed, providing a proof of concept that these mice can
be used for testing drugs. Therefore, this model allows the
investigation of P. falciparum sexual commitment, gametocyte
interactions with the bone marrow and spleen and provides the
missing link between current in vitro assays and Phase I trials
in humans for testing new malaria gametocytidal drugs
Dynamics of Afebrile Plasmodium falciparum Infections in Mozambican Men
Background: Afebrile Plasmodium falciparum infections usually
remain undetected and untreated in the community and could
potentially contribute to sustaining local malaria transmission
in areas aiming for malaria elimination. Methods: Thirty-two men
with afebrile P. falciparum infections detected with rapid
diagnostic test (RDTs) were followed for 28 days. Kaplan-Meier
estimates were computed to estimate probability of parasite
positivity and of reducing parasitaemia by half of its initial
level by day 28. Trends of parasite densities quantified by
microscopy and qPCR were assessed using Poisson regression
models, and the microscopy to qPCR positivity ratio was
calculated at each time point. Three survival distributions
(Gompertz, Weibull, and gamma) were used to evaluate their
strength of fit to the data and to predict the median lifetime
of infection. Results: The cumulative probability of parasite
qPCR positivity by day 28 was 81% (95% CI 60.2-91.6). Geometric
mean parasitemia at recruitment was 516.1 parasites/muL and fell
to <100 parasites/muL by day 3, reaching 56.7 parasites/muL
on day 28 (p-value<0.001). The ratio of P. falciparum
positive samples by microscopy to qPCR decreased from 0.9 to
0.52 from recruitment to day 28. The best model fit to the data
was obtained assuming a Gompertz distribution. Conclusions:
Afebrile P.falciparum infections detectable by RDT in
semi-immune adults fall and stabilize at low-density levels
during the first four days since detection, suggesting a rapid
decline of potential transmissibility in this hidden parasite
reservoir
Molecular surveillance of pfhrp2 and pfhrp3 deletions in Plasmodium falciparum isolates from Mozambique
BACKGROUND: Malaria programmes use Plasmodium falciparum
histidine-rich protein-2 (PfHRP2) based rapid diagnostic tests
(RDTs) for malaria diagnosis. The deletion of this target
antigen could potentially lead to misdiagnosis, delayed
treatment and continuation of active transmission. METHODS:
Plasmodium falciparum isolates (n = 1162) collected in Southern
Mozambique were assessed by RDTs, microscopy and/or 18SrRNA
qPCR. pfhrp2 and pfhrp3 deletions were investigated in isolates
from individuals who were negative by RDT but positive by
microscopy and/or qPCR (n = 69) using gene-specific PCRs, with
kelch13 PCR as the parasite DNA control. RESULTS: Lack of pfhrp2
PCR amplification was observed in one of the 69 isolates
subjected to molecular analysis [1.45% (95% CI 0.3-7.8%)].
CONCLUSIONS: The low prevalence of pfhrp2 deletions suggests
that RDTs will detect the vast majority of the P. falciparum
infections. Nevertheless, active surveillance for changing
deletion frequencies is required
Changing plasma cytokine, chemokine and growth factor profiles upon differing malaria transmission intensities
Background: Malaria epidemiological and immunological data suggest that parasite tolerance wanes in the absence
of continuous exposure to the parasite, potentially enhancing pathogenesis. The expansion of control interventions
and elimination campaigns raises the necessity to better understand the host factors leading to susceptibility or
tolerance that are afected by rapid changes in malaria transmission intensity (MTI). Mediators of cellular immune
responses are responsible for the symptoms and pathological alterations during disease and are expected to change
rapidly upon malaria exposure or cessation.
Methods: The plasma concentrations of 30 cytokine, chemokine and growth factors in individuals of all ages from
a malaria endemic area of southern Mozambique were compared between 2 years of diferent MTI: 2010 (lower,
n=234) and 2013 (higher, n=143). The efect of the year on the correlations between cytokines, chemokines and
growth factors and IgGs to Plasmodium falciparum (markers of exposure) was explored. The efects of age, sex, neighbourhood and parasitaemia on analyte levels and their interactions with year were also assessed.
Results: An inverse correlation of several cellular immune mediators with malarial antibodies in 2013, and a lack of
correlation or even a positive correlation in 2010 were observed. Most cytokines, chemokines and growth factors,
regardless of their immune function, had higher concentrations in 2010 compared with 2013 in P. falciparum-infected
and uninfected subjects. Age and neighbourhood showed an efect on analyte concentrations.
Conclusions: The results show a diferent regulation of the cellular immune response in 2010 vs 2013 which could
be related to a loss of immune-tolerance after a decline in MTI in 2010 and previous years, and a rapid re-establishment of tolerance as a consequence of more continuous exposure as MTI began increasing in 2012. Cellular immune
mediators warrant further investigation as possible surrogates of MTI-associated host susceptibility or tolerance
Placental Infection With Plasmodium vivax: A Histopathological and Molecular Study
Background. Evidence of the presence of Plasmodium vivax in the placenta is scarce and inconclusive. This information is relevant to understanding whether P. vivax affects placental function and how it may contribute to poor pregnancy outcomes. Methods. Histopathologic examination of placental biopsies from 80 Papua New Guinean pregnant women was combined with quantitative polymerase chain reaction (qPCR) to confirm P. vivax infection and rule out coinfection with other Plasmodium species in placental and peripheral blood. Leukocytes and monocytes/macrophages were detected in placental sections by immunohistochemistry. Results. Monoinfection by P. vivax and Plasmodium falciparum was detected by qPCR in 8 and 10 placentas, respectively. Seven of the 8 women with P. vivax placental monoinfection were negative in peripheral blood. By histology, 3 placentas with P. vivax monoinfection showed parasitized erythrocytes in the intervillous space but no hemozoin in macrophages nor increased intervillous inflammatory cells. In contrast, 7 placentas positive for P. falciparum presented parasites and hemozoin in macrophages or fibrin as well as intervillous inflammatory infiltrates. Conclusions. Plasmodium vivax can be associated with placental infection. However, placental inflammation is not observed in P. vivax monoinfections, suggesting other causes of poor delivery outcomes associated with P. vivax infectio
In-Vivo Efficacy of Chloroquine to Clear Asymptomatic Infections in Mozambican Adults: A Randomized, Placebo-controlled Trial with Implications for Elimination Strategies
Recent reports regarding the re-emergence of parasite
sensitivity to chloroquine call for a new consideration of this
drug as an interesting complementary tool in malaria elimination
efforts, given its good safety profile and long half-life. A
randomized (2:1), single-blind, placebo-controlled trial was
conducted in Manhica, Mozambique, to assess the in-vivo efficacy
of chloroquine to clear plasmodium falciparum (Pf) asymptomatic
infections. Primary study endpoint was the rate of adequate and
parasitological response (ACPR) to therapy on day 28
(PCR-corrected). Day 0 isolates were analyzed to assess the
presence of the PfCRT-76T CQ resistance marker. A total of 52
and 27 male adults were included in the CQ and Placebo group
respectively. PCR-corrected ACPR was significantly higher in the
CQ arm 89.4% (95%CI 80-98%) compared to the placebo (p <
0.001). CQ cleared 49/50 infections within the first 72 h while
placebo cleared 12/26 (LRT p < 0.001). The PfCRT-76T mutation
was present only in one out of 108 (0.9%) samples at baseline,
well below the 84% prevalence found in 1999 in the same area.
This study presents preliminary evidence of a return of
chloroquine sensitivity in Mozambican Pf isolates, and calls for
its further evaluation in community-based malaria elimination
efforts, in combination with other effective anti-malarials.
TRIAL REGISTRATION: www.clinicalTrials.gov NCT02698748
Adaptation of targeted nanocarriers to changing requirements in antimalarial drug delivery.
The adaptation of existing antimalarial nanocarriers to new Plasmodium stages, drugs, targeting molecules, or encapsulating structures is a strategy that can provide new nanotechnology-based, cost-efficient therapies against malaria. We have explored the modification of different liposome prototypes that had been developed in our group for the targeted delivery of antimalarial drugs to Plasmodium-infected red blood cells (pRBCs). These new models include: (i) immunoliposome-mediated release of new lipid-based antimalarials; (ii) liposomes targeted to pRBCs with covalently linked heparin to reduce anticoagulation risks; (iii) adaptation of heparin to pRBC targeting of chitosan nanoparticles; (iv) use of heparin for the targeting of Plasmodium stages in the mosquito vector; and (v) use of the non-anticoagulant glycosaminoglycan chondroitin 4-sulfate as a heparin surrogate for pRBC targeting. The results presented indicate that the tuning of existing nanovessels to new malaria-related targets is a valid low-cost alternative to the de novo development of targeted nanosystems
Adaptation of targeted nanocarriers to changing requirements in antimalarial drug delivery
The adaptation of existing antimalarial nanocarriers to new
Plasmodium stages, drugs, targeting molecules, or encapsulating
structures is a strategy that can provide new
nanotechnology-based, cost-efficient therapies against malaria.
We have explored the modification of different liposome
prototypes that had been developed in our group for the targeted
delivery of antimalarial drugs to Plasmodium-infected red blood
cells (pRBCs). These new models include: (i)
immunoliposome-mediated release of new lipid-based
antimalarials; (ii) liposomes targeted to pRBCs with covalently
linked heparin to reduce anticoagulation risks; (iii) adaptation
of heparin to pRBC targeting of chitosan nanoparticles; (iv) use
of heparin for the targeting of Plasmodium stages in the
mosquito vector; and (v) use of the non-anticoagulant
glycosaminoglycan chondroitin 4-sulfate as a heparin surrogate
for pRBC targeting. The results presented indicate that the
tuning of existing nanovessels to new malaria-related targets is
a valid low-cost alternative to the de novo development of
targeted nanosystems
Association of Maternal Factors and HIV Infection With Innate Cytokine Responses of Delivering Mothers and Newborns in Mozambique
Maternal factors and exposure to pathogens have an impact on infant health. For instance, HIV exposed but uninfected infants have higher morbidity and mortality than HIV unexposed infants. Innate responses are the first line of defense and orchestrate the subsequent adaptive immune response and are especially relevant in newborns. To determine the association of maternal HIV infection with maternal and newborn innate immunity we analyzed the cytokine responses upon pattern recognition receptor (PRR) stimulations in the triad of maternal peripheral and placental blood as well as in cord blood in a cohort of mother-infant pairs from southern Mozambique. A total of 48 women (35 HIV-uninfected and 13 HIV-infected) were included. Women and infant innate responses positively correlated with each other. Age, gravidity and sex of the fetus had some associations with spontaneous production of cytokines in the maternal peripheral blood. HIV-infected women not receiving antiretroviral therapy (ART) before pregnancy showed decreased IL-8 and IL-6 PRR responses in peripheral blood compared to those HIV-uninfected, and PRR hyporesponsiveness for IL-8 was also found in the corresponding infant's cord blood. HIV infection had a greater impact on placental blood responses, with significantly increased pro-inflammatory, T H 1 and T H 17 PRR responses in HIV-infected women not receiving ART before pregnancy compared to HIV-uninfected women. In conclusion, innate response of the mother and her newborn was altered by HIV infection in the women who did not receive ART before pregnancy. As these responses could be related to birth outcomes, targeted innate immune modulation could improve maternal and newborn health
Host age and expression of genes involved in red blood cell invasion in Plasmodium falciparum field isolates
Plasmodium falciparum proteins involved in erythrocyte invasion
are main targets of acquired immunity and important vaccine
candidates. We hypothesized that anti-parasite immunity acquired
upon exposure would limit invasion-related gene (IRG) expression
and affect the clinical impact of the infection. 11 IRG
transcript levels were measured in P. falciparum isolates by
RT-PCR, and IgG/IgM against invasion ligands by Luminex(R), in
50 Mozambican adults, 25 children with severe malaria (SM) and
25 with uncomplicated malaria (UM). IRG expression differences
among groups and associations between IRG expression and
clinical/immunologic parameters were assessed. IRG expression
diversity was higher in parasites infecting children than adults
(p = 0.022). eba140 and ptramp expression decreased with age (p
= 0.003 and 0.007, respectively) whereas p41 expression
increased (p = 0.022). pfrh5 reduction in expression was abrupt
early in life. Parasite density decreased with increasing pfrh5
expression (p < 0.001) and, only in children, parasite
density increased with p41 expression (p = 0.007), and decreased
with eba175 (p = 0.013). Antibody responses and IRG expression
were not associated. In conclusion, IRG expression is associated
with age and parasite density, but not with specific antibody
responses in the acute phase of infection. Our results confirm
the importance of multi-antigen vaccines development to avoid
parasite immune escape when tested in malaria-exposed
individuals
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