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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

Age sero-prevalence plots for MSP-119(a) and AMA-1 (b) fitted by maximum likelihood with a two forces of infection for Same district.Black triangles represent observed data and black lines predicted values. Dotted black lines represent upper and lower 95% CI for the predicted SCR.
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pone-0006083-g005: Age sero-prevalence plots for MSP-119(a) and AMA-1 (b) fitted by maximum likelihood with a two forces of infection for Same district.Black triangles represent observed data and black lines predicted values. Dotted black lines represent upper and lower 95% CI for the predicted SCR.

Mentions: ELISA was performed on 3859 filter paper samples for MSP-119 and 3862 samples for AMA-1. Sero-positivity to both antigens increased with age and was higher in the Korogwe health facilities (MSP-119 and AMA-1 both p<0.001; Table 2). Antibody positivity rates were not significantly different between sick children and children who were well (MSP-119 12.0% vs 8.6% p = 0.1, AMA-1 17.2 vs 19.3 p = 0.8). Age sero-prevalence plots for the Same and Korogwe regions are shown in Figure 3. Visual assessment of the plots for the Same dispensaries indicated a poor fit of the model, for younger age groups, where sero-prevalence was lower than predicted. When a model, which allowed for a single change in sero-conversion rate was fitted to the combined data from the 4 Same health facilities, the best fitting model was that with the change between the two SCRs occurring approximately 15 years previously (CI 11–18) (i.e.1992) according to the MSP-119 data (Figure 4a) and 8 years previously (CI 6–14) (i.e. 1999) according to the AMA-1 data (Figure 4b). We chose a model compatible with both antigens which assumed that the SCR in Same changed 10 years previously, which had a significantly better fit than the model that assumed the SCR had remained constant (likelihood ratio test for MSP-119 Χ2 = 9.6 p = 0.002 and AMA-1 Χ2 = 45.4 p<0.0001). Sero-prevalence plots for Same assuming a change in SCR 10 years previously are shown in Figures 5a and 5b, for MSP-119 and AMA respectively. A change in SCR was observed for all 4 health facilities in Same (Table 3) but was not observed for any of those in Korogwe region (Figures 4c & 4d)(Similar analysis was conducted on pilot survey data which showed the best fitting model with a single conversion rate).


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)

Age sero-prevalence plots for MSP-119(a) and AMA-1 (b) fitted by maximum likelihood with a two forces of infection for Same district.Black triangles represent observed data and black lines predicted values. Dotted black lines represent upper and lower 95% CI for the predicted SCR.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0006083-g005: Age sero-prevalence plots for MSP-119(a) and AMA-1 (b) fitted by maximum likelihood with a two forces of infection for Same district.Black triangles represent observed data and black lines predicted values. Dotted black lines represent upper and lower 95% CI for the predicted SCR.
Mentions: ELISA was performed on 3859 filter paper samples for MSP-119 and 3862 samples for AMA-1. Sero-positivity to both antigens increased with age and was higher in the Korogwe health facilities (MSP-119 and AMA-1 both p<0.001; Table 2). Antibody positivity rates were not significantly different between sick children and children who were well (MSP-119 12.0% vs 8.6% p = 0.1, AMA-1 17.2 vs 19.3 p = 0.8). Age sero-prevalence plots for the Same and Korogwe regions are shown in Figure 3. Visual assessment of the plots for the Same dispensaries indicated a poor fit of the model, for younger age groups, where sero-prevalence was lower than predicted. When a model, which allowed for a single change in sero-conversion rate was fitted to the combined data from the 4 Same health facilities, the best fitting model was that with the change between the two SCRs occurring approximately 15 years previously (CI 11–18) (i.e.1992) according to the MSP-119 data (Figure 4a) and 8 years previously (CI 6–14) (i.e. 1999) according to the AMA-1 data (Figure 4b). We chose a model compatible with both antigens which assumed that the SCR in Same changed 10 years previously, which had a significantly better fit than the model that assumed the SCR had remained constant (likelihood ratio test for MSP-119 Χ2 = 9.6 p = 0.002 and AMA-1 Χ2 = 45.4 p<0.0001). Sero-prevalence plots for Same assuming a change in SCR 10 years previously are shown in Figures 5a and 5b, for MSP-119 and AMA respectively. A change in SCR was observed for all 4 health facilities in Same (Table 3) but was not observed for any of those in Korogwe region (Figures 4c & 4d)(Similar analysis was conducted on pilot survey data which showed the best fitting model with a single conversion rate).

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