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Relation between Plasmodium falciparum asymptomatic infection and malaria attacks in a cohort of Senegalese children.

Le Port A, Cot M, Etard JF, Gaye O, Migot-Nabias F, Garcia A - Malar. J. (2008)

Bottom Line: At the beginning of the transmission season, 27.8% (147/529) of the children were asymptomatic carriers (ACs) and 5.4% (8/147) of MMA occurred among these, versus 1% (4/382) among non-carriers (RR = 5.32; IC = [1.56-18.15], p = 0.008).At the end of the transmission season, the frequency of asymptomatic carriers was similar to that observed at the beginning of the season (31.9%, p = 0.15), but no MMA was detected during this period.A significant association between P. falciparum asymptomatic carriage and the occurrence of MMA at the beginning of the transmission season was demonstrated, with a five-fold increase in the risk of developing a MMA in ACs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institut de Recherche pour le Développement (IRD), Unité de Recherche 010: Santé de la mère et de l'enfant en milieu tropical, Laboratoire de Parasitologie, Faculté de Pharmacie, 4 avenue de l'Observatoire, 75006 Paris, France. agnes.leport@ird.fr

ABSTRACT

Background: It is important to establish whether or not the presence of malaria parasites in peripheral blood of asymptomatic individuals is a predictor of future clinical mild malaria attacks (MMA). The aim of this study was to determine how an asymptomatic positive thick blood smear could be related to the occurrence of a MMA during the nine following days.

Methods: The study was conducted in a cohort of 569 Senegalese children, who were investigated for Plasmodium falciparum asymptomatic carriage at two different times of the transmission season, the beginning (September) and the end (November). The occurrence of MMA was investigated in asymptomatic carriers and non-carriers, every three days for nine consecutive days. Survival analysis was performed and risk estimates were calculated by Cox proportional hazards model.

Results: At the beginning of the transmission season, 27.8% (147/529) of the children were asymptomatic carriers (ACs) and 5.4% (8/147) of MMA occurred among these, versus 1% (4/382) among non-carriers (RR = 5.32; IC = [1.56-18.15], p = 0.008). At the end of the transmission season, the frequency of asymptomatic carriers was similar to that observed at the beginning of the season (31.9%, p = 0.15), but no MMA was detected during this period.

Conclusion: A significant association between P. falciparum asymptomatic carriage and the occurrence of MMA at the beginning of the transmission season was demonstrated, with a five-fold increase in the risk of developing a MMA in ACs. In the context of a possible distribution of IPTc in the future, drug strategies may have dramatic consequences due to the existence of ACs (both long term and short term), as they seem to play an important role in the individual protection to malaria, in the most exposed age groups.

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Related in: MedlinePlus

Clinical malaria occurrences over time at the end of the malaria transmission season, Niakhar, 2002. § n: number of patients per day. # PI: Plasmodial Index (= ACs frequency).
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Figure 3: Clinical malaria occurrences over time at the end of the malaria transmission season, Niakhar, 2002. § n: number of patients per day. # PI: Plasmodial Index (= ACs frequency).

Mentions: 527 children out of 566 were present at the end of the malaria transmission season (Figure 3). Three children presented a MMA on the day of enrolment and were excluded. The remaining 524 children did not differ from those included in the first study period for age, sex ratio, village of residence and frequency of positiveness for the search of chloroquine metabolites in the urine. The mean parasite density at enrolment was 5,597.6 parasites/μl (SD = 13,941.1) and was not different from the beginning of the transmission season (p = 0.14). The frequency of Plasmodium falciparum ACs was similar at enrolment between the two periods (27.8% at the beginning vs. 31.9% at the end of the transmission season, p = 0.15). The parasite density was homogenous during the 10 days of enrolment (p = 0.13), but not the plasmodial index (p = 0.005), even if there was no particular trend of increase. The same pattern of results concerning the association of AC and measured covariates as observed in September, was observed at this period. No MMA occurred during the nine following days.


Relation between Plasmodium falciparum asymptomatic infection and malaria attacks in a cohort of Senegalese children.

Le Port A, Cot M, Etard JF, Gaye O, Migot-Nabias F, Garcia A - Malar. J. (2008)

Clinical malaria occurrences over time at the end of the malaria transmission season, Niakhar, 2002. § n: number of patients per day. # PI: Plasmodial Index (= ACs frequency).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2567330&req=5

Figure 3: Clinical malaria occurrences over time at the end of the malaria transmission season, Niakhar, 2002. § n: number of patients per day. # PI: Plasmodial Index (= ACs frequency).
Mentions: 527 children out of 566 were present at the end of the malaria transmission season (Figure 3). Three children presented a MMA on the day of enrolment and were excluded. The remaining 524 children did not differ from those included in the first study period for age, sex ratio, village of residence and frequency of positiveness for the search of chloroquine metabolites in the urine. The mean parasite density at enrolment was 5,597.6 parasites/μl (SD = 13,941.1) and was not different from the beginning of the transmission season (p = 0.14). The frequency of Plasmodium falciparum ACs was similar at enrolment between the two periods (27.8% at the beginning vs. 31.9% at the end of the transmission season, p = 0.15). The parasite density was homogenous during the 10 days of enrolment (p = 0.13), but not the plasmodial index (p = 0.005), even if there was no particular trend of increase. The same pattern of results concerning the association of AC and measured covariates as observed in September, was observed at this period. No MMA occurred during the nine following days.

Bottom Line: At the beginning of the transmission season, 27.8% (147/529) of the children were asymptomatic carriers (ACs) and 5.4% (8/147) of MMA occurred among these, versus 1% (4/382) among non-carriers (RR = 5.32; IC = [1.56-18.15], p = 0.008).At the end of the transmission season, the frequency of asymptomatic carriers was similar to that observed at the beginning of the season (31.9%, p = 0.15), but no MMA was detected during this period.A significant association between P. falciparum asymptomatic carriage and the occurrence of MMA at the beginning of the transmission season was demonstrated, with a five-fold increase in the risk of developing a MMA in ACs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institut de Recherche pour le Développement (IRD), Unité de Recherche 010: Santé de la mère et de l'enfant en milieu tropical, Laboratoire de Parasitologie, Faculté de Pharmacie, 4 avenue de l'Observatoire, 75006 Paris, France. agnes.leport@ird.fr

ABSTRACT

Background: It is important to establish whether or not the presence of malaria parasites in peripheral blood of asymptomatic individuals is a predictor of future clinical mild malaria attacks (MMA). The aim of this study was to determine how an asymptomatic positive thick blood smear could be related to the occurrence of a MMA during the nine following days.

Methods: The study was conducted in a cohort of 569 Senegalese children, who were investigated for Plasmodium falciparum asymptomatic carriage at two different times of the transmission season, the beginning (September) and the end (November). The occurrence of MMA was investigated in asymptomatic carriers and non-carriers, every three days for nine consecutive days. Survival analysis was performed and risk estimates were calculated by Cox proportional hazards model.

Results: At the beginning of the transmission season, 27.8% (147/529) of the children were asymptomatic carriers (ACs) and 5.4% (8/147) of MMA occurred among these, versus 1% (4/382) among non-carriers (RR = 5.32; IC = [1.56-18.15], p = 0.008). At the end of the transmission season, the frequency of asymptomatic carriers was similar to that observed at the beginning of the season (31.9%, p = 0.15), but no MMA was detected during this period.

Conclusion: A significant association between P. falciparum asymptomatic carriage and the occurrence of MMA at the beginning of the transmission season was demonstrated, with a five-fold increase in the risk of developing a MMA in ACs. In the context of a possible distribution of IPTc in the future, drug strategies may have dramatic consequences due to the existence of ACs (both long term and short term), as they seem to play an important role in the individual protection to malaria, in the most exposed age groups.

Show MeSH
Related in: MedlinePlus