Dataset Information

Comparison of surveillance methods applied to a situation of low malaria prevalence at rural sites in The Gambia and Guinea Bissau.

ABSTRACT:

Background

Health record-based observations from several parts of Africa indicate a major decline in malaria, but up-to-date information on parasite prevalence in West-Africa is sparse. This study aims to provide parasite prevalence data from three sites in the Gambia and Guinea Bissau, respectively, and compares the usefulness of PCR, rapid diagnostic tests (RDT), serology and slide-microscopy for surveillance.

Methods

Cross-sectional surveys in 12 villages at three rural sites were carried out in the Gambia and Guinea Bissau in January/February 2008, shortly following the annual transmission season.

Results

A surprisingly low microscopically detectable parasite prevalence was detected in the Gambia (Farafenni: 10.9%, CI95%: 8.7-13.1%; Basse: 9.0%, CI95%: 7.2-10.8%), and Guinea Bissau (Caio: 4%, CI95%: 2.6-5.4%), with low parasite densities (geometric mean: 104 parasites/microl, CI95%: 76-143/microl). In comparison, PCR detected a more than three times higher proportion of parasite carriers, indicating its usefulness to sensitively identify foci where malaria declines, whereas the RDT had very low sensitivity. Estimates of force of infection using age sero-conversion rates were equivalent to an EIR of approximately 1 infectious bite/person/year, significantly less than previous estimates. The sero-prevalence profiles suggest a gradual decline of malaria transmission, confirming their usefulness in providing information on longer term trends of transmission. A greater variability in parasite prevalence among villages within a site than between sites was observed with all methods. The fact that serology equally captured the inter-village variability, indicates that the observed heterogeneity represents a stable pattern.

Conclusion

PCR and serology may be used as complementary tools to survey malaria in areas of declining malaria prevalence such as the Gambia and Guinea Bissau.

SUBMITTER: Satoguina J

PROVIDER: S-EPMC2791766 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Comparison of surveillance methods applied to a situation of low malaria prevalence at rural sites in The Gambia and Guinea Bissau.

Satoguina Judith J Walther Brigitte B Drakeley Christopher C Nwakanma Davis D Oriero Eniyou C EC Correa Simon S Corran Patrick P Conway David J DJ Walther Michael M

Malaria journal 20091202

<h4>Background</h4>Health record-based observations from several parts of Africa indicate a major decline in malaria, but up-to-date information on parasite prevalence in West-Africa is sparse. This study aims to provide parasite prevalence data from three sites in the Gambia and Guinea Bissau, respectively, and compares the usefulness of PCR, rapid diagnostic tests (RDT), serology and slide-microscopy for surveillance.<h4>Methods</h4>Cross-sectional surveys in 12 villages at three rural sites w ...[more]

PMID: 19954532

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Project description:BackgroundLarge-scale surveillance of molecular markers of anti-malarial drug resistance is an attractive method of resistance monitoring, to complement therapeutic efficacy studies in settings where the latter are logistically challenging.MethodsBetween 2014 and 2017, this study sampled malaria rapid diagnostic tests (RDTs), used in routine clinical care, from two health centres in Bissau, Guinea-Bissau. In order to obtain epidemiological insights, RDTs were collected together with patient data on age and sex. A subset of positive RDTs from one of the two sites (n?=?2184) were tested for Plasmodium DNA content. Those testing positive for Plasmodium DNA by PCR (n?=?1390) were used for library preparation, custom designed dual indexing and next generation Miseq targeted sequencing of Plasmodium falciparum genes pfcrt, pfmdr1, pfdhfr, pfdhps and pfk13.ResultsThe study found a high frequency of the pfmdr1 codon 86N at 88-97%, a significant decrease of the pfcrt wildtype CVMNK haplotype and elevated levels of the pfdhfr/pfdhps quadruple mutant ranging from 33 to 51% between 2014 and 2017. No polymorphisms indicating artemisinin tolerance were discovered. The demographic data indicate a large proportion of young adults (66%, interquartile range 11-28 years) presenting with P. falciparum infections. While a total of 5532 gene fragments were successfully analysed on a single Illumina Miseq flow cell, PCR-positivity from the library preparation varied considerably from 13 to 87% for different amplicons. Furthermore, pre-screening of samples for Plasmodium DNA content proved necessary prior to library preparation.ConclusionsThis study serves as a proof of concept for using leftover clinical material (used RDTs) for large-scale molecular surveillance, encompassing the inherent complications regarding to methodology and analysis when doing so. Factors such as RDT storage prior to DNA extraction and parasitaemia of the infection are likely to have an effect on whether or not parasite DNA can be successfully analysed, and are considered part of the reason the data yield is suboptimal. However, given the necessity of molecular surveillance of anti-malarial resistance in settings where poor infrastructure, poor economy, lack of educated staff and even surges of political instability remain major obstacles to performing clinical studies, obtaining the necessary data from used RDTs, despite suboptimal output, becomes a feasible, affordable and hence a justifiable method.

Project description:PurposeBandim Health Project (BHP) monitors health and survival of women and children in a nationally representative rural Health and Demographic Surveillance System (HDSS) in Guinea-Bissau. The HDSS was set up in 1989-1990 to collect data on health interventions and child mortality.ParticipantsThe HDSS covers 182 randomly selected clusters across the whole country. The cohort is open, and women and children enter the cohort, when they move into the selected clusters, and leave the cohort, when they move out or die, or when children reach 5 years of age. Data are collected through biannual or more frequent household visits. At all village visits, information on pregnancies, vital status, vaccination status, arm circumference, use of bed nets and other basic information is collected for women and children. Today, more than 25 000 women and 23 000 children below the age of 5 years are under surveillance.Findings to dateResearch from the BHP has given rise to the hypothesis that vaccines, in addition to their targeted effects, have important non-specific effects altering the susceptibility to other infections. Initially, it was observed that mortality among children vaccinated with the live BCG or measles vaccines was much lower than the mortality among unvaccinated children, a difference, which could not be explained by prevention of tuberculosis and measles infections. In contrast, mortality tended to be higher for children who had received the non-live Diphtheria-Tetanus-Pertussis vaccine compared with children who had not received this vaccine. Since the effect differed for the different vaccines, no bias explained the contrasting findings.Future plansNew health interventions are introduced with little assessment of real-life effects. Through the HDSS, we can describe both the implementation of interventions (eg, the vaccination programme) and their effects. Furthermore, the intensive follow-up allows the implementation of randomised trials testing potential better vaccination programmes.

Dataset Information

Comparison of surveillance methods applied to a situation of low malaria prevalence at rural sites in The Gambia and Guinea Bissau.

Background

Methods

Results

Conclusion

Publications

Comparison of surveillance methods applied to a situation of low malaria prevalence at rural sites in The Gambia and Guinea Bissau.

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