Dataset Information

Three different Plasmodium species show similar patterns of clinical tolerance of malaria infection.

ABSTRACT:

Background

In areas where malaria endemicity is high, many people harbour blood stage parasites without acute febrile illness, complicating the estimation of disease burden from infection data. For Plasmodium falciparum the density of parasitaemia that can be tolerated is low in the youngest children, but reaches a maximum in the age groups at highest risk of infection. There is little data on the age dependence of tolerance in other species of human malaria.

Methods

Parasite densities measured in 24,386 presumptive malaria cases at two local health centres in the Wosera area of Papua New Guinea were compared with the distributions of parasite densities recorded in community surveys in the same area. We then analyse the proportions of cases attributable to each of Plasmodium falciparum, P. vivax, and P. malariae as functions of parasite density and age using a latent class model. These attributable fractions are then used to compute the incidence of attributable disease.

Results

Overall 33.3%, 6.1%, and 0.1% of the presumptive cases were attributable to P. falciparum, P. vivax, and P. malariae respectively. The incidence of attributable disease and parasite density broadly follow similar age patterns. The logarithm of the incidence of acute illness is approximately proportion to the logarithm of the parasite density for all three malaria species, with little age variation in the relationship for P. vivax or P. malariae. P. falciparum shows more age variation in disease incidence at given levels of parasitaemia than the other species.

Conclusion

The similarities between Plasmodium species in the relationships between parasite density and risk of attributable disease are compatible with the hypothesis that pan-specific mechanisms may regulate tolerance to different human Plasmodia. A straightforward mathematical expression might be used to project disease burden from parasite density distributions assessed in community-based parasitological surveys.

SUBMITTER: Muller I

PROVIDER: S-EPMC2719654 | biostudies-literature | 2009 Jul

REPOSITORIES: biostudies-literature

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Publications

Three different Plasmodium species show similar patterns of clinical tolerance of malaria infection.

Müller Ivo I Genton Blaise B Rare Lawrence L Kiniboro Benson B Kastens Will W Zimmerman Peter P Kazura James J Alpers Michael M Smith Thomas A TA

Malaria journal 20090714

<h4>Background</h4>In areas where malaria endemicity is high, many people harbour blood stage parasites without acute febrile illness, complicating the estimation of disease burden from infection data. For Plasmodium falciparum the density of parasitaemia that can be tolerated is low in the youngest children, but reaches a maximum in the age groups at highest risk of infection. There is little data on the age dependence of tolerance in other species of human malaria.<h4>Methods</h4>Parasite dens ...[more]

PMID: 19602275

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Project description:The identification of epidemiological pattern of infection with Plasmodium falciparum and Plasmodium vivax in malaria-endemic area, where multiple episodes are common, is important for intervention programmes.A longitudinal cohort study based on weekly house-to-house visits was conducted between July 2008 and June 2010 in 2040 children less than 10 years of age, living nearby the Gilgel-Gibe hydroelectric power dam reservoir in order to determine factors associated with increased P. vivax and P. falciparum incidence. Two types of multivariate frailty models were applied (using time-to-first malaria episode data and time-to-recurrent malaria episode data), allowing the estimation of adjusted hazard ratios (AHR) of potential risk factors (gender, age, proximity to the dam reservoir, and season) for species-specific malaria incidence.Of 2040 children in 96 weeks of follow up, 864 children experienced at least one malaria episode: 685 due to P. falciparum in 548 children, and 385 due to P. vivax in 316 children. Plasmodium vivax and P. falciparum malaria incidence rates were 8.2 (95 % CI: 7.3-9.1) and 14.6 (95 % CI: 13.4-15.6) per 1000 children per month, respectively. According to the time-to-recurrent event models, children aged ?7 years had a lower risk of presenting P. vivax episodes (AHR = 0.6; 95 % CI: 0.4-0.9), but a higher risk of P. falciparum episodes, when compared with children under ?3 years (AHR = 1.2; 95 % CI: 1.1-1.6). In addition, P. vivax (AHR = 2.7; 95 % CI: 2.2-3.5) and P. falciparum (AHR = 16.9; 95 % CI: 14.3-20.2) episodes were respectively 2.7 and 16.9 times more frequent in the dry season than in the long rainy season.The analysis of all malaria episodes (first and recurrent episodes) in the malaria cohort suggests different species-specific patterns of malaria disease in children, with mild seasonality in the incidence of P. vivax episodes mostly observed in younger age groups, and with marked seasonality in the incidence of P. falciparum episodes mainly seen in older children.

Project description:BACKGROUND: Malaria transmission in Ethiopia is unstable and variable, caused by both Plasmodium falciparum and Plasmodium vivax. The Federal Ministry of Health (FMoH) is scaling up parasitological diagnosis of malaria at all levels of the health system; at peripheral health facilities this will be through use of rapid diagnostic tests (RDTs). The present study compared three RDT products to provide the FMoH with evidence to guide appropriate product selection. METHODS: Performance of three multi-species (pf-HRP2/pan-pLDH and pf-HRP2/aldolase) RDTs (CareStart, ParaScreen and ICT Combo) was compared with 'gold standard' microscopy at three health centres in Jimma zone, Oromia Regional State. Ease of RDT use by health extension workers was assessed at community health posts. RDT heat stability was tested in a controlled laboratory setting according to WHO procedures. RESULTS: A total of 2,383 patients with suspected malaria were enrolled between May and July 2009, 23.2% of whom were found to be infected with Plasmodium parasites by microscopy. All three RDTs were equally sensitive in detecting P. falciparum or mixed infection: 85.6% (95% confidence interval 81.2-89.4). RDT specificity was similar for detection of P. falciparum or mixed infection at around 92%. For detecting P. vivax infection, all three RDTs had similar sensitivity in the range of 82.5 to 85.0%. CareStart had higher specificity in detecting P. vivax (97.2%) than both ParaScreen and ICT Combo (p < 0.001 and p = 0.05, respectively). Health extension workers preferred CareStart and ParaScreen to ICT Combo due to the clear labelling of bands on the cassette, while the 'lab in a pack' style of CareStart was the preferred design. ParaScreen and CareStart passed all heat stability testing, while ICT Combo did not perform as well. CONCLUSIONS: CareStart appeared to be the most appropriate option for use at health posts in Ethiopia, considering the combination of quantitative performance, ease of use and heat stability. When new products become available, the choice of multi-species RDT for Ethiopia should be regularly re-evaluated, as it would be desirable to identify a test with higher sensitivity than the ones evaluated here.

Dataset Information

Three different Plasmodium species show similar patterns of clinical tolerance of malaria infection.

Background

Methods

Results

Conclusion

Publications

Three different Plasmodium species show similar patterns of clinical tolerance of malaria infection.

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