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Rapid assessment of malaria transmission using age-specific sero-conversion rates.

Stewart L, Gosling R, Griffin J, Gesase S, Campo J, Hashim R, Masika P, Mosha J, Bousema T, Shekalaghe S, Cook J, Corran P, Ghani A, Riley EM, Drakeley C - PLoS ONE (2009)

Bottom Line: A pilot study, conducted near Moshi, found SCRs for AMA-1 were highly comparable between samples collected from individuals in a conventional cross-sectional survey and those collected from attendees at a local health facility.Both malaria parasite prevalence and sero-positivity were higher in Korogwe than in Same.MSP-1(19) and AMA-1 SCR rates for Korogwe villages ranged from 0.03 to 0.06 and 0.07 to 0.21 respectively.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK.

ABSTRACT

Background: Malaria transmission intensity is a crucial determinant of malarial disease burden and its measurement can help to define health priorities. Rapid, local estimates of transmission are required to focus resources better but current entomological and parasitological methods for estimating transmission intensity are limited in this respect. An alternative is determination of antimalarial antibody age-specific sero-prevalence to estimate sero-conversion rates (SCR), which have been shown to correlate with transmission intensity. This study evaluated SCR generated from samples collected from health facility attendees as a tool for a rapid assessment of malaria transmission intensity.

Methodology and principal findings: The study was conducted in north east Tanzania. Antibodies to Plasmodium falciparum merozoite antigens MSP-1(19) and AMA-1 were measured by indirect ELISA. Age-specific antibody prevalence was analysed using a catalytic conversion model based on maximum likelihood to generate SCR. A pilot study, conducted near Moshi, found SCRs for AMA-1 were highly comparable between samples collected from individuals in a conventional cross-sectional survey and those collected from attendees at a local health facility. For the main study, 3885 individuals attending village health facilities in Korogwe and Same districts were recruited. Both malaria parasite prevalence and sero-positivity were higher in Korogwe than in Same. MSP-1(19) and AMA-1 SCR rates for Korogwe villages ranged from 0.03 to 0.06 and 0.07 to 0.21 respectively. In Same district there was evidence of a recent reduction in transmission, with SCR among those born since 1998 [MSP-1(19) 0.002 to 0.008 and AMA-1 0.005 to 0.014 ] being 5 to 10 fold lower than among individuals born prior to 1998 [MSP-1(19) 0.02 to 0.04 and AMA-1 0.04 to 0.13]. Current health facility specific estimates of SCR showed good correlations with malaria incidence rates in infants in a contemporaneous clinical trial (MSP-1(19) r(2) = 0.78, p<0.01 & AMA-1 r(2) = 0.91, p<0.001).

Conclusions: SCRs generated from age-specific anti-malarial antibody prevalence data collected via health facility surveys were robust and credible. Analysis of SCR allowed detection of a recent drop in malaria transmission in line with recent data from other areas in the region. This health facility-based approach represents a potential tool for rapid assessment of recent trends in malaria transmission intensity, generating valuable data for local and national malaria control programs to target, monitor and evaluate their control strategies.

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Related in: MedlinePlus

Map showing the study area: Squares mark major towns, circles mark villages with study dispensaries.
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pone-0006083-g001: Map showing the study area: Squares mark major towns, circles mark villages with study dispensaries.

Mentions: Samples were collected from subjects recruited at the Msitu wa Tembo health facility in lower Moshi (Figure 1) in a 3 week period in February 2007. This is a low malaria transmission area on the slopes of mount Kilimanjaro with an EIR of ∼3 ib/p/yr [28] where we have previously conducted a cross-sectional malaria prevalence surveys. Eligible participants were any attendee at the health facility for any reason (i.e. family members or guardians accompanying patients as well as patients themselves) who consented to take part. There were no age or gender restrictions. Study details were explained to all potential adult and guardians of child participants. Subsequently, signed or fingerprinted informed consent was obtained for adults and guardians of child participants prior to enrolment. A copy of the consent form was offered to all subjects. Staff at the health facility were informed of the study during a group sensitization session at both the Outpatient Department (OPD) and Maternal and Child Health (MCH) sections of the clinic. Study information sheets in Kiswahili were posted at the clinic.


Rapid assessment of malaria transmission using age-specific sero-conversion rates.

Stewart L, Gosling R, Griffin J, Gesase S, Campo J, Hashim R, Masika P, Mosha J, Bousema T, Shekalaghe S, Cook J, Corran P, Ghani A, Riley EM, Drakeley C - PLoS ONE (2009)

Map showing the study area: Squares mark major towns, circles mark villages with study dispensaries.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2698122&req=5

pone-0006083-g001: Map showing the study area: Squares mark major towns, circles mark villages with study dispensaries.
Mentions: Samples were collected from subjects recruited at the Msitu wa Tembo health facility in lower Moshi (Figure 1) in a 3 week period in February 2007. This is a low malaria transmission area on the slopes of mount Kilimanjaro with an EIR of ∼3 ib/p/yr [28] where we have previously conducted a cross-sectional malaria prevalence surveys. Eligible participants were any attendee at the health facility for any reason (i.e. family members or guardians accompanying patients as well as patients themselves) who consented to take part. There were no age or gender restrictions. Study details were explained to all potential adult and guardians of child participants. Subsequently, signed or fingerprinted informed consent was obtained for adults and guardians of child participants prior to enrolment. A copy of the consent form was offered to all subjects. Staff at the health facility were informed of the study during a group sensitization session at both the Outpatient Department (OPD) and Maternal and Child Health (MCH) sections of the clinic. Study information sheets in Kiswahili were posted at the clinic.

Bottom Line: A pilot study, conducted near Moshi, found SCRs for AMA-1 were highly comparable between samples collected from individuals in a conventional cross-sectional survey and those collected from attendees at a local health facility.Both malaria parasite prevalence and sero-positivity were higher in Korogwe than in Same.MSP-1(19) and AMA-1 SCR rates for Korogwe villages ranged from 0.03 to 0.06 and 0.07 to 0.21 respectively.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK.

ABSTRACT

Background: Malaria transmission intensity is a crucial determinant of malarial disease burden and its measurement can help to define health priorities. Rapid, local estimates of transmission are required to focus resources better but current entomological and parasitological methods for estimating transmission intensity are limited in this respect. An alternative is determination of antimalarial antibody age-specific sero-prevalence to estimate sero-conversion rates (SCR), which have been shown to correlate with transmission intensity. This study evaluated SCR generated from samples collected from health facility attendees as a tool for a rapid assessment of malaria transmission intensity.

Methodology and principal findings: The study was conducted in north east Tanzania. Antibodies to Plasmodium falciparum merozoite antigens MSP-1(19) and AMA-1 were measured by indirect ELISA. Age-specific antibody prevalence was analysed using a catalytic conversion model based on maximum likelihood to generate SCR. A pilot study, conducted near Moshi, found SCRs for AMA-1 were highly comparable between samples collected from individuals in a conventional cross-sectional survey and those collected from attendees at a local health facility. For the main study, 3885 individuals attending village health facilities in Korogwe and Same districts were recruited. Both malaria parasite prevalence and sero-positivity were higher in Korogwe than in Same. MSP-1(19) and AMA-1 SCR rates for Korogwe villages ranged from 0.03 to 0.06 and 0.07 to 0.21 respectively. In Same district there was evidence of a recent reduction in transmission, with SCR among those born since 1998 [MSP-1(19) 0.002 to 0.008 and AMA-1 0.005 to 0.014 ] being 5 to 10 fold lower than among individuals born prior to 1998 [MSP-1(19) 0.02 to 0.04 and AMA-1 0.04 to 0.13]. Current health facility specific estimates of SCR showed good correlations with malaria incidence rates in infants in a contemporaneous clinical trial (MSP-1(19) r(2) = 0.78, p<0.01 & AMA-1 r(2) = 0.91, p<0.001).

Conclusions: SCRs generated from age-specific anti-malarial antibody prevalence data collected via health facility surveys were robust and credible. Analysis of SCR allowed detection of a recent drop in malaria transmission in line with recent data from other areas in the region. This health facility-based approach represents a potential tool for rapid assessment of recent trends in malaria transmission intensity, generating valuable data for local and national malaria control programs to target, monitor and evaluate their control strategies.

Show MeSH
Related in: MedlinePlus