A 20-year longitudinal study of Plasmodium ovale and Plasmodium malariae prevalence and morbidity in a West African population

Abstract

Background: Plasmodium ovale and Plasmodium malariae have long been reported to be widely distributed in tropical Africa and in other major malaria-endemic areas of the world. However, little is known about the burden caused by these two malaria species.

Methods and findings: We did a longitudinal study of the inhabitants of Dielmo village, Senegal, between June, 1990, and December, 2010. We monitored the inhabitants for fever during this period and performed quarterly measurements of parasitemia. We analyzed parasitological and clinical data in a random-effect logistic regression model to investigate the relationship between the level of parasitemia and the risk of fever and to establish diagnostic criteria for P. ovale and P. malariae clinical attacks. The prevalence of P. ovale and P. malariae infections in asymptomatic individuals were high during the first years of the project but decreased after 2004 and almost disappeared in 2010 in relation to changes in malaria control policies. The average incidence densities of P. ovale and P. malariae clinical attacks were 0.053 and 0.093 attacks per person per year in children <15 years and 0.024 and 0.009 attacks per person per year in adults ≥ 15 years, respectively. These two malaria species represented together 5.9% of the malaria burden.

Conclusions: P. ovale and P. malariae were a common cause of morbidity in Dielmo villagers until the recent dramatic decrease of malaria that followed the introduction of new malaria control policies. P. ovale and P. malariae may constitute an important cause of morbidity in many areas of tropical Africa.

Figure 1. P. falciparum, P. malariae and P. ovale prevalence from 1990 to 2010 in Dielmo villagers (all age groups).

Figure 2. P. ovale prevalence by year and age group from 1990 to 2010.

Figure 3. P. malariae prevalence by year and age group from 1990 to 2010.

Figure 4. The mean P. ovale parasitemia (arithmetic mean of parasites per µl of blood) in asymptomatic control and fever case observations by age group, Dielmo 1990–2010.

Figure 5. Random-effect logistic regression model derived threshold level of parasitemia for attributing fever episodes to P. ovale by age, Dielmo, 1990–2004.

Figure 6. The mean P. malariae parasitemia (arithmetic mean of parasites per µl of blood) in asymptomatic control and fever case observations by age group, Dielmo 1990–2010.

Figure 7. Random-effect logistic regression model derived threshold level of parasitemia for attributing fever episodes to P. malariae by age and period, Dielmo, 1990–2010.

Figure 8. Trends in yearly incidence density of P. ovale clinical attacks. Dielmo, 1990–2010.

Figure 9. Mean yearly incidence density of P. ovale clinical attacks by age group.

Dielmo, 1990–2010.

Figure 10. Trends in yearly incidence density of P. malariae clinical attacks.

Dielmo, 1990–2010.

Figure 11. Mean yearly incidence density of P. malariae clinical attacks by age group.

Dielmo, 1990–2010.