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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 antibody responses to P. falciparum parasite antigens MSP-119 (fig 2a) and AMA-1 (figure 2b) from the pilot study (Msitu wa Tembo).Open circles (and confidence limits) represent observed age group specific sero-prevalence points for the cross sectional survey. The dotted line represents a maximum likelihood fit using these data. The full triangles and unbroken line represent observed sero-prevalence points and fitted line for the health facility surveys.
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pone-0006083-g002: Age sero-prevalence plots for antibody responses to P. falciparum parasite antigens MSP-119 (fig 2a) and AMA-1 (figure 2b) from the pilot study (Msitu wa Tembo).Open circles (and confidence limits) represent observed age group specific sero-prevalence points for the cross sectional survey. The dotted line represents a maximum likelihood fit using these data. The full triangles and unbroken line represent observed sero-prevalence points and fitted line for the health facility surveys.

Mentions: For the pilot study, samples were collected from 341 individuals attending the health facility in Msitu wa Tembo over a 4 week period. Compared with the previous cross-sectional survey, the proportion of individuals under the age of 1 year was higher than expected (12.9% vs 4.5%, p<0.001) presumably as a result of infant attendance at the MCH clinic for routine vaccination (Table 1). Parasite positivity (as determined by RDT) was also higher in those recruited at the clinic compared with those recruited in the cross-sectional surveys (4.7% vs. 2.3%, p<0.001). Overall, sero-prevalence for MSP-119 was significantly lower at the health facility than in the cross-sectional survey (29.1% vs. 40.5%, p = 0.005) but antibody sero-prevalence was similar for AMA-1 (46.9% vs. 47.9%, p = 0.8). No significant differences in anti-AMA-1 antibody titres were seen between subjects recruited at the health facility and and those recruited in the community. Among children aged under 1 year and children aged 2–5 years, mean MSP-119 antibody titres were significantly higher among children recruited at the health facility than among children recruited in the community. However, in adults, anti-MSP-119 titres were higher among those recruited in the community than among those recruited at the health facility (Table 1). In the community surveys, mean antibody titres were significantly higher in RDT positive than in RDT negative individuals for both antigens (MSP-119: 216 vs 72 p<0.001; AMA-1: 161 vs 74 P<0.005). Antibody titres were also higher in RDT positives than RDT negatives in the health facility survey but not significantly so (MSP-1 titres 63 vs 49 p = 0.6; AMA-1 116 vs 65 P = 0.08). Age sero-prevalence plots for each antigen are shown in Figure 2. Estimated SCR values obtained from the statistical model, assuming no change in transmission intensity, for health facility and cross-sectional surveys were not significantly different for AMA-1 [ 0.63 (95% CI 0.52–0.76) and 0.61 (95% CI 0.56–0.65) respectively; p = 0.4] but the health facility estimate for MSP-119 0.24 (95% CI 0.19–0.29)] was significantly lower than the cross sectional estimate 0.42 (95% CI0.39–0.45; p = 0.012).


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 antibody responses to P. falciparum parasite antigens MSP-119 (fig 2a) and AMA-1 (figure 2b) from the pilot study (Msitu wa Tembo).Open circles (and confidence limits) represent observed age group specific sero-prevalence points for the cross sectional survey. The dotted line represents a maximum likelihood fit using these data. The full triangles and unbroken line represent observed sero-prevalence points and fitted line for the health facility surveys.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2698122&req=5

pone-0006083-g002: Age sero-prevalence plots for antibody responses to P. falciparum parasite antigens MSP-119 (fig 2a) and AMA-1 (figure 2b) from the pilot study (Msitu wa Tembo).Open circles (and confidence limits) represent observed age group specific sero-prevalence points for the cross sectional survey. The dotted line represents a maximum likelihood fit using these data. The full triangles and unbroken line represent observed sero-prevalence points and fitted line for the health facility surveys.
Mentions: For the pilot study, samples were collected from 341 individuals attending the health facility in Msitu wa Tembo over a 4 week period. Compared with the previous cross-sectional survey, the proportion of individuals under the age of 1 year was higher than expected (12.9% vs 4.5%, p<0.001) presumably as a result of infant attendance at the MCH clinic for routine vaccination (Table 1). Parasite positivity (as determined by RDT) was also higher in those recruited at the clinic compared with those recruited in the cross-sectional surveys (4.7% vs. 2.3%, p<0.001). Overall, sero-prevalence for MSP-119 was significantly lower at the health facility than in the cross-sectional survey (29.1% vs. 40.5%, p = 0.005) but antibody sero-prevalence was similar for AMA-1 (46.9% vs. 47.9%, p = 0.8). No significant differences in anti-AMA-1 antibody titres were seen between subjects recruited at the health facility and and those recruited in the community. Among children aged under 1 year and children aged 2–5 years, mean MSP-119 antibody titres were significantly higher among children recruited at the health facility than among children recruited in the community. However, in adults, anti-MSP-119 titres were higher among those recruited in the community than among those recruited at the health facility (Table 1). In the community surveys, mean antibody titres were significantly higher in RDT positive than in RDT negative individuals for both antigens (MSP-119: 216 vs 72 p<0.001; AMA-1: 161 vs 74 P<0.005). Antibody titres were also higher in RDT positives than RDT negatives in the health facility survey but not significantly so (MSP-1 titres 63 vs 49 p = 0.6; AMA-1 116 vs 65 P = 0.08). Age sero-prevalence plots for each antigen are shown in Figure 2. Estimated SCR values obtained from the statistical model, assuming no change in transmission intensity, for health facility and cross-sectional surveys were not significantly different for AMA-1 [ 0.63 (95% CI 0.52–0.76) and 0.61 (95% CI 0.56–0.65) respectively; p = 0.4] but the health facility estimate for MSP-119 0.24 (95% CI 0.19–0.29)] was significantly lower than the cross sectional estimate 0.42 (95% CI0.39–0.45; p = 0.012).

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