Through the work of international public health organizations and advancements in the biological and technological sciences, substantial progress has been made in our ability to prevent, control, ...locally eliminate, and in one case eradicate infectious diseases. Yet each successful control or local elimination has been met with the emergence of new pathogens, the evolution of novel strains, or different epidemiological circumstances that have limited or reversed control methods. To respond to the increasing threat of emerging infectious diseases and bioterrorism it is vital that we design and implement efficient programs that prevent and control infectious pathogen transmission. The theoretical tools of ecology and epidemiology may be the cornerstone in constructing future programs aimed at preventing and controlling infectious diseases throughout the world.
Although 80% of malaria occurs in children under five years of age, infants under six months of age are known to have low rates of infection and disease. It is not clear why this youngest age group ...is protected; possible factors include maternal antibodies, unique nutrition (breast milk), and the presence of foetal haemoglobin (HbF). This work aims to gain insight into possible mechanisms of protection, and suggest pathways for focused empirical work, by modelling a range of possible effects of foetal haemoglobin and other red blood cell (RBC) developmental changes on parasite dynamics in infants.
A set of ordinary differential equations was created to investigate the leading hypotheses about the possible protective mechanisms of HbF-containing red blood cells, in particular whether HbF suppresses parasite population growth because parasite multiplication in individual RBCs is lower, slower or absent. The model also incorporated the intrinsic changes in blood volume and haematocrit that occur with age, and the possibility of parasite affinities for HbF-containing RBCs or reticulocytes.
The model identified several sets of conditions in which the infant remained protected, or displayed a much slower growth of parasitaemia in the first few months of life, without any intervening immune response. The most protective of the hypothesized mechanisms would be the inhibition of schizont division in foetal RBCs so that fewer merozoites are produced. The model showed that a parasite preference for HbF-containing RBCs increases protective effects for the host, while a preference for reticulocytes has little effect.
The results from this simple model of haematological changes in infants and their effects on Plasmodium falciparum infection dynamics emphasize the likely importance of HbF and RBC number as an explanatory factor in paediatric malaria, and suggest a framework for organizing related empirical research.
The protozoan Plasmodium falciparum has a complex life cycle in which asexual multiplication in the vertebrate host alternates with an obligate sexual reproduction in the anopheline mosquito. Apart ...from the apparent recombination advantages conferred by sex, P. falciparum has evolved a remarkable biology and adaptive phenotypes to insure its transmission despite the dangers of sex. This review mainly focuses on the current knowledge on commitment to sexual development, gametocytogenesis and the evolutionary significance of various aspects of gametocyte biology. It goes further than pure biology to look at the strategies used to improve successful transmission. Although gametocytes are inevitable stages for transmission and provide a potential target to fight malaria, they have received less attention than the pathogenic asexual stages. There is a need for research on gametocytes, which are a fascinating stage, responsible to a large extent for the success of P. falciparum.
The relationship between malaria transmission intensity and clinical disease is important for predicting the outcome of control measures that reduce transmission. Comparisons of hospital data between ...areas of differing transmission intensity suggest that the mean age of hospitalized clinical malaria is higher under relatively lower transmission, but the total number of episodes is similar until transmission drops below a threshold, where the risks of hospitalized malaria decline. These observations have rarely been examined longitudinally in a single community where transmission declines over time. We reconstructed 16 years (1991-2006) of pediatric hospital surveillance data and infection prevalence surveys from a circumscribed geographic area on the Kenyan coast. The incidence of clinical malaria remained high, despite sustained reductions in exposure to infection. However, the age group experiencing the clinical attacks of malaria increased steadily as exposure declined and may precede changes in the number of episodes in an area with declining transmission.
Malaria is the direct cause of approximately one million deaths worldwide each year, though it is both preventable and curable. Increasing the understanding of the transmission dynamics of falciparum ...and vivax malaria and their relationship could suggest improvements for malaria control efforts. Here the weekly number of malaria cases due to Plasmodium falciparum (1994-2006) and Plasmodium vivax (1999-2006) in Perú at different spatial scales in conjunction with associated demographic, geographic and climatological data are analysed.
Malaria periodicity patterns were analysed through wavelet spectral analysis, studied patterns of persistence as a function of community size and assessed spatial heterogeneity via the Lorenz curve and the summary Gini index.
Wavelet time series analyses identified annual cycles in the incidence of both malaria species as the dominant pattern. However, significant spatial heterogeneity was observed across jungle, mountain and coastal regions with slightly higher levels of spatial heterogeneity for P. vivax than P. falciparum. While the incidence of P. falciparum has been declining in recent years across geographic regions, P. vivax incidence has remained relatively steady in jungle and mountain regions with a slight decline in coastal regions. Factors that may be contributing to this decline are discussed. The time series of both malaria species were significantly synchronized in coastal (rho = 0.9, P < 0.0001) and jungle regions (rho = 0.76, P < 0.0001) but not in mountain regions. Community size was significantly associated with malaria persistence due to both species in jungle regions, but not in coastal and mountain regions.
Overall, findings highlight the importance of highly refined spatial and temporal data on malaria incidence together with demographic and geographic information in improving the understanding of malaria persistence patterns associated with multiple malaria species in human populations, impact of interventions, detection of heterogeneity and generation of hypotheses.
Abstract Health systems reform processes have increasingly recognized the essential contribution of communities to the success of health programs and development activities in general. Here we ...examine the experience from Kilifi district in Kenya of implementing annual health sector planning guidelines that included community participation in problem identification, priority setting, and planning. We describe challenges in the implementation of national planning guidelines, how these were met, and how they influenced final plans and budgets. The broad-based community engagement envisaged in the guidelines did not take place due to the delay in roll out of the Ministry of Health-trained community health workers. Instead, community engagement was conducted through facility management committees, though in a minority of facilities, even such committees were not involved. Some overlap was found in the priorities highlighted by facility staff, committee members and national indicators, but there were also many additional issues raised by committee members and not by other groups. The engagement of the community through committees influenced target and priority setting, but the emphasis on national health indicators left many local priorities unaddressed by the final work plans. Moreover, it appears that the final impact on budgets allocated at district and facility level was limited. The experience in Kilifi highlights the feasibility of engaging the community in the health planning process, and the challenges of ensuring that this engagement feeds into consolidated plans and future implementation.
We examine the charts of 408 malaria-naïve neurosyphilis patients given malaria therapy at the South Carolina USPHS facility, with daily records encompassing at least 93% of the duration of ...infection, and focus on the 152 patients infected with the St. Elizabeth strain of Plasmodium vivax, 82 with the McLendon strain of Plasmodium falciparum, 36 with the USPHS strain of Plasmodium malariae, and 15 with the Donaldson strain of Plasmodium ovale in whom gametocytes appeared before drug, or other, intervention. In P. vivax infections, fever and parasitemia were higher after gametocytes were first detected than before; in P. malariae infections, parasitemia was higher. In P. ovale infections, fever and parasitemia were similar before and after. In P. falciparum infections, fever, parasitemia, and fever frequency were lower after gametocytes were first detected than before. Parasitemia and temperature correlated in P. vivax infections, before and after gametocytes were first detected; parasitemia and temperature at first fever were not correlated in infections with any species. Gametocyte density correlated with parasitemia in P. malariae and sporozoite-induced P. falciparum and P. vivax infections. Fevers and detected gametocytemia coincided more often than expected by chance with P. vivax and P. ovale; fever temperature and gametocyte density were not correlated in infections with any species.
Enumeration of parasites by microscopic examination of blood smears is the only method available for quantifying parasitemia in infected blood. However, the sources and scale of error inherent in ...this technique have not been systematically investigated. Here we use data collected in outpatient clinics in Peru and Thailand to elucidate important sources of variation in parasite density measurements. We show that discrepancies between readings from two independent microscopists and multiple readings from a single microscopist are inversely related to the density of the infection. We present an example of how differences in reader technique, specifically the number of white blood cells counted, can contribute to the differences between readings. We discuss the implications of this analysis for field studies and clinical trials.
... in 1462 patients with the disease admitted to the Uganda Cancer Institute from 1994 to 2004, the outcomes for only 228 (16%) could be documented.14 In 2002, the International Agency for Research ...on Cancer estimated that 5700 children were diagnosed with Burkitt's lymphoma in sub-Saharan Africa,1 although this number is probably grossly underestimated. ... governments and donors do not appreciate the burden of Burkitt's lymphoma and its high case fatality rate.
Background
Standard advice regarding vector control is to prefer interventions that reduce the lifespan of adult mosquitoes. The basis for this advice is a decades-old sensitivity analysis of ...‘vectorial capacity’, a concept relevant for most malaria transmission models and based solely on adult mosquito population dynamics. Recent advances in micro-simulation models offer an opportunity to expand the theory of vectorial capacity to include both adult and juvenile mosquito stages in the model.
Methods
In this study we revisit arguments about transmission and its sensitivity to mosquito bionomic parameters using an elasticity analysis of developed formulations of vectorial capacity.
Results
We show that reducing adult survival has effects on both adult and juvenile population size, which are significant for transmission and not accounted for in traditional formulations of vectorial capacity. The elasticity of these effects is dependent on various mosquito population parameters, which we explore. Overall, control is most sensitive to methods that affect adult mosquito mortality rates, followed by blood feeding frequency, human blood feeding habit, and lastly, to adult mosquito population density.
Conclusions
These results emphasise more strongly than ever the sensitivity of transmission to adult mosquito mortality, but also suggest the high potential of combinations of interventions including larval source management. This must be done with caution, however, as policy requires a more careful consideration of costs, operational difficulties and policy goals in relation to baseline transmission.
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