PLASMODIUM VIVAX BLOOD-STAGE DYNAMICS McKenzie, F. Ellis; Jeffery, Geoffrey M; Collins, William E
The Journal of parasitology,
06/2002, Letnik:
88, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We examine the dynamics of parasitemia and gametocytemia reflected in the preintervention charts of 221 malaria-naive U.S. neurosyphilis patients infected with the St. Elizabeth strain of Plasmodium ...vivax, for malariatherapy, focusing on the 109 charts for which 15 or more days of patency preceded intervention and daily records encompassed an average 98% of the duration of each infection. Our approximations of merogony cycles (via “local peaks” in parasitemia) seldom fit patterns that correspond to “textbook” tertian brood structures. Peak parasitemia was higher in trophozoite-induced infections than in sporozoite-induced ones. Relative densities of male and female gametocytes appeared to alternate, though without a discernably regular period. Successful transmission to mosquitoes did not depend on detectable gametocytemia or on absence of fever. When gametocytes were detected, transmission success depended on densities of only male gametocytes. Successful feeds occurred on average 4.7 days later in an infection than did failures. Parasitemia was lower in homologous reinfection, gametocytemia lower or absent.
New sources of funding have revitalized efforts to control malaria. An effective vaccine would be a tremendous asset in the fight against this devastating disease and increasing financial and ...scientific resources are being invested to develop one. A few candidates have been tested in Phase I and II clinical trials, and several others are poised to begin trials soon. Some studies have been promising, and others disappointing. It is difficult to compare the results of these clinical trials; even independent trials of the same vaccine give highly discrepant results. One major obstacle in evaluating malaria vaccines is the difficulty of diagnosing clinical malaria. This analysis evaluates the impact of diagnostic error, particularly that introduced by microscopy, on the outcome of efficacy trials of malaria vaccines and make recommendations for improving future trials.
We develop a simple three-state stochastic description of individual malaria infections that relates dynamics of disease and immune status to age and previous exposure, under different intensities of ...transmission. We apply the resulting individual-based community models to examine the effects of drug treatment and vaccination on the frequency and severity of disease in ensembles of children. The several broad qualitative similarities between our results and field observations include potential rebound effects following intervals of drug treatment.
From the 1920s to the 1970s, a large body of principles and evidence accumulated about the existence and character of 'strains' among the Plasmodium species responsible for human malaria. An ...extensive research literature examined the degree to which strains were autonomous, stable biological entities, distinguishable by clinical, epidemiological or other features, and how this knowledge could be used to benefit medical and public health practice. Strain theory in this era was based largely on parasite phenotypes related to clinical virulence, reactions to anti-malarial drugs, infectivity to mosquitoes, antigenic properties and host immunity, latency and relapse. Here we review the search for a definition of 'strain', suggest how the data and discussion shaped current understandings of many aspects of malaria and sketch a number of specific connections with perspectives from the past 30 years.
The rational design of interventions is critical to controlling communicable diseases, especially in urban environments. In the case of the Chagas disease vector Triatoma infestans, successful ...control is stymied by the return of the insect after the effectiveness of the insecticide wanes. Here, we adapt a genetic algorithm, originally developed for the travelling salesman problem, to improve the spatio-temporal design of insecticide campaigns against T. infestans, in a complex urban environment. We find a strategy that reduces the expected instances of vector return 34-fold compared with the current strategy of sequential insecticide application to spatially contiguous communities. The relative success of alternative control strategies depends upon the duration of the effectiveness of the insecticide, and it shows chaotic fluctuations in response to unforeseen delays in a control campaign. We use simplified models to analyse the outcomes of qualitatively different spatio-temporal strategies. Our results provide a detailed procedure to improve control efforts for an urban Chagas disease vector, as well as general guidelines for improving the design of interventions against other disease agents in complex environments.
The intensity of malaria transmission is often measured by looking at the fraction of individuals infected at a given point in time. However, malaria infections in individuals are dynamic, leading to ...uncertainty about whether a cross-sectional survey that represents a single snapshot in time is a useful representation of a temporally complex process. In this analysis, we examine the impact of parasite density fluctuations on the measurement of parasite prevalence. Our results show that parasite prevalence may be underestimated by 20% or more, depending on the sensitivity of parasite detection.
Intermittent preventive treatment (IPT) administers a full therapeutic course of an anti-malarial drug at predetermined intervals, regardless of infection or disease status. It is recommended by the ...World Health Organization (WHO) for protecting pregnant women from the adverse effects of malaria (IPTp) and shows great potential as a strategy for reducing illness from malaria during infancy (IPTi). Administered concurrently with standard immunizations, IPTi is expected to reduce the frequency of clinical disease, but to allow blood-stage infections to occur between treatments, thus allowing parasite-specific immunity to develop. While wide deployment of IPTi is being considered, it is important to assess other potential effects. Transmission conditions, drug choice and administration schedule will likely affect the possibility of post-treatment rebound in child morbidity and mortality and the increased spread of parasite drug resistance and should be considered when implementing IPTi.
We used sentinel animal enclosures to measure the rate of infestation by the Chagas disease vector, Triatoma infestans, in an urban community of Arequipa, Peru, and to evaluate the effect of ...deltamethrin-impregnated netting on that rate. Impregnated netting decreased the rate of infestation of sentinel enclosures (rate ratio, 0.23; 95% confidence interval, 0.13-0.38; P < 0.001), controlling for the density of surrounding vector populations and the distance of these to the sentinel enclosures. Most migrant insects were early-stage nymphs, which are less likely to carry the parasitic agent of Chagas disease, Trypanosoma cruzi. Spread of the vector in the city therefore likely precedes spread of the parasite. Netting was particularly effective against adult insects and late-stage nymphs; taking into account population structure, netting decreased the reproductive value of migrant populations from 443.6 to 40.5. Impregnated netting can slow the spread of T. infestans and is a potentially valuable tool in the control of Chagas disease.
Fever in Patients with Mixed-Species Malaria McKenzie, F. Ellis; Smith, David L.; O'Meara, Wendy P. ...
Clinical infectious diseases,
06/2006, Letnik:
42, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Background. Clinical symptoms of mixed-species malaria infections have been variously reported as both less severe and more severe than those of single-species infections. Methods. Oral temperatures ...were taken from and blood slides were prepared for 2308 adults who presented at outpatient malaria clinics in Tak Province (Thailand) during May–August 1998, May–July 1999, and May–June 2001 with malaria infections diagnosed by 2 expert research microscopists, each of whom was blinded to the other's reports. Results. In each year, temperatures of patients with mixed Plasmodium vivax—Plasmodium falciparum infections were higher than temperatures of patients with P. vivax or P. falciparum infections. In every mixed-species case, P. falciparum parasitemia was higher than P. vivax parasitemia, but patient temperature was not correlated with the parasitemia of either species or with the total parasitemia. Conclusions. Among adults who self-report to malaria clinics in western Thailand, patients with mixed P. vivax—P. falciparum infections have higher fevers than patients with single-species infections, a distinction that cannot be attributed to differences in parasitemia. This observation warrants more detailed investigations, spanning wider ranges of ages and transmission environments.
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