Limits...
Dynamics of malaria transmission and susceptibility to clinical malaria episodes following treatment of Plasmodium falciparum asymptomatic carriers: results of a cluster-randomized study of community-wide screening and treatment, and a parallel entomology study.

Tiono AB, Guelbeogo MW, Sagnon NF, Nébié I, Sirima SB, Mukhopadhyay A, Hamed K - BMC Infect. Dis. (2013)

Bottom Line: The intervention arm had lower prevalence of asymptomatic carriers of asexual parasites and lower prevalence of gametocyte carriers during campaigns 2 and 3 as compared to the control arm.This trend was not seen in those individuals aged ≥5 years.Over the year, monthly variation in mosquito density and entomological inoculation rate was comparable in both arms, with September peaks in both indices.

View Article: PubMed Central - HTML - PubMed

Affiliation: Novartis Pharmaceuticals Corporation, One Health Plaza, East Hanover, NJ 07936-1080, USA. kamal.hamed@novartis.com.

ABSTRACT

Background: In malaria-endemic countries, large proportions of individuals infected with Plasmodium falciparum are asymptomatic and constitute a reservoir of parasites for infection of newly hatched mosquitoes.

Methods: Two studies were run in parallel in Burkina Faso to evaluate the impact of systematic identification and treatment of asymptomatic carriers of P. falciparum, detected by rapid diagnostic test, on disease transmission and susceptibility to clinical malaria episodes. A clinical study assessed the incidence of symptomatic malaria episodes with a parasite density >5,000/μL after three screening and treatment campaigns ~1 month apart before the rainy season; and an entomological study determined the effect of these campaigns on malaria transmission as measured by entomological inoculation rate.

Results: The intervention arm had lower prevalence of asymptomatic carriers of asexual parasites and lower prevalence of gametocyte carriers during campaigns 2 and 3 as compared to the control arm. During the entire follow-up period, out of 13,767 at-risk subjects, 2,516 subjects (intervention arm 1,332; control arm 1,184) had symptomatic malaria. Kaplan-Meier analysis of the incidence of first symptomatic malaria episode with a parasite density >5,000/μL showed that, in the total population, the two treatment arms were similar until Week 11-12 after campaign 3, corresponding with the beginning of the malaria transmission season, after which the probability of being free of symptomatic malaria was lower in the intervention arm (logrank p < 0.0001). Similar trends were observed in infants and children <5 years and in individuals ≥5 years of age. In infants and children <5 years old who experienced symptomatic malaria episodes, the geometric mean P. falciparum density was lower in the intervention arm than the control arm. This trend was not seen in those individuals aged ≥5 years. Over the year, monthly variation in mosquito density and entomological inoculation rate was comparable in both arms, with September peaks in both indices.

Conclusion: Community screening and targeted treatment of asymptomatic carriers of P. falciparum had no effect on the dynamics of malaria transmission, but seemed to be associated with an increase in the treated community's susceptibility to symptomatic malaria episodes after the screening campaigns had finished. These results highlight the importance of further exploratory studies to better understand the dynamics of disease transmission in the context of malaria elimination.

Show MeSH

Related in: MedlinePlus

Temporal variation of Anopheles density and entomological inoculation rate (EIR) by study arm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4225764&req=5

Figure 7: Temporal variation of Anopheles density and entomological inoculation rate (EIR) by study arm.

Mentions: From January to December 2011, a total of 12,466 mosquitoes were collected across the 10 clusters (6,677 in the control arm and 5,789 in the intervention arm). The species composition collected in the two arms of the study was similar (Table 2). The frequency of the kdr gene mutation was slightly higher in the control arm (0.71; SD 0.16) than the intervention arm (0.65; SD 0.12). The intervention arm mean (SD) biting rate was 1.12 (1.20) bites per person per night, vs 1.12 (1.19) bites per person per night in the control arm. Over the year, EIR and mosquito density results were also comparable in both arms, with peaks for both observed in September (Table 3, Figure 7). Although the monthly EIR appeared to be slightly higher in the intervention arm than the control arm throughout the study period (except September, when it was slightly lower in intervention arm), the difference was not statistically significant (p = 0.7086, considering all 12 months). Similar results were also obtained considering only the months July to December (p = 0.8182).


Dynamics of malaria transmission and susceptibility to clinical malaria episodes following treatment of Plasmodium falciparum asymptomatic carriers: results of a cluster-randomized study of community-wide screening and treatment, and a parallel entomology study.

Tiono AB, Guelbeogo MW, Sagnon NF, Nébié I, Sirima SB, Mukhopadhyay A, Hamed K - BMC Infect. Dis. (2013)

Temporal variation of Anopheles density and entomological inoculation rate (EIR) by study arm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4225764&req=5

Figure 7: Temporal variation of Anopheles density and entomological inoculation rate (EIR) by study arm.
Mentions: From January to December 2011, a total of 12,466 mosquitoes were collected across the 10 clusters (6,677 in the control arm and 5,789 in the intervention arm). The species composition collected in the two arms of the study was similar (Table 2). The frequency of the kdr gene mutation was slightly higher in the control arm (0.71; SD 0.16) than the intervention arm (0.65; SD 0.12). The intervention arm mean (SD) biting rate was 1.12 (1.20) bites per person per night, vs 1.12 (1.19) bites per person per night in the control arm. Over the year, EIR and mosquito density results were also comparable in both arms, with peaks for both observed in September (Table 3, Figure 7). Although the monthly EIR appeared to be slightly higher in the intervention arm than the control arm throughout the study period (except September, when it was slightly lower in intervention arm), the difference was not statistically significant (p = 0.7086, considering all 12 months). Similar results were also obtained considering only the months July to December (p = 0.8182).

Bottom Line: The intervention arm had lower prevalence of asymptomatic carriers of asexual parasites and lower prevalence of gametocyte carriers during campaigns 2 and 3 as compared to the control arm.This trend was not seen in those individuals aged ≥5 years.Over the year, monthly variation in mosquito density and entomological inoculation rate was comparable in both arms, with September peaks in both indices.

View Article: PubMed Central - HTML - PubMed

Affiliation: Novartis Pharmaceuticals Corporation, One Health Plaza, East Hanover, NJ 07936-1080, USA. kamal.hamed@novartis.com.

ABSTRACT

Background: In malaria-endemic countries, large proportions of individuals infected with Plasmodium falciparum are asymptomatic and constitute a reservoir of parasites for infection of newly hatched mosquitoes.

Methods: Two studies were run in parallel in Burkina Faso to evaluate the impact of systematic identification and treatment of asymptomatic carriers of P. falciparum, detected by rapid diagnostic test, on disease transmission and susceptibility to clinical malaria episodes. A clinical study assessed the incidence of symptomatic malaria episodes with a parasite density >5,000/μL after three screening and treatment campaigns ~1 month apart before the rainy season; and an entomological study determined the effect of these campaigns on malaria transmission as measured by entomological inoculation rate.

Results: The intervention arm had lower prevalence of asymptomatic carriers of asexual parasites and lower prevalence of gametocyte carriers during campaigns 2 and 3 as compared to the control arm. During the entire follow-up period, out of 13,767 at-risk subjects, 2,516 subjects (intervention arm 1,332; control arm 1,184) had symptomatic malaria. Kaplan-Meier analysis of the incidence of first symptomatic malaria episode with a parasite density >5,000/μL showed that, in the total population, the two treatment arms were similar until Week 11-12 after campaign 3, corresponding with the beginning of the malaria transmission season, after which the probability of being free of symptomatic malaria was lower in the intervention arm (logrank p < 0.0001). Similar trends were observed in infants and children <5 years and in individuals ≥5 years of age. In infants and children <5 years old who experienced symptomatic malaria episodes, the geometric mean P. falciparum density was lower in the intervention arm than the control arm. This trend was not seen in those individuals aged ≥5 years. Over the year, monthly variation in mosquito density and entomological inoculation rate was comparable in both arms, with September peaks in both indices.

Conclusion: Community screening and targeted treatment of asymptomatic carriers of P. falciparum had no effect on the dynamics of malaria transmission, but seemed to be associated with an increase in the treated community's susceptibility to symptomatic malaria episodes after the screening campaigns had finished. These results highlight the importance of further exploratory studies to better understand the dynamics of disease transmission in the context of malaria elimination.

Show MeSH
Related in: MedlinePlus