Frequent Plasmodium ovale Recurrence in Coastal Tanzania

Plasmodium ovale are the most common malaria parasites found throughout sub-Saharan Africa capable of causing relapse, but little is known about their patterns of carriage and recurrence.

Asymptomatic adults and children >5 years of age living in Bagamoyo, Tanzania, who screened positive for P. ovale parasitemia by real-time polymerase chain reaction were enrolled and followed for up to 6 months, with biweekly polymerase chain reaction testing for P. ovale and Plasmodium falciparum infection. Those with persistent P. ovale carriage to 4 weeks, and those later diagnosed with incident or recurrent P. ovale or P. falciparum infection, were offered treatment with artemether-lumefantrine at the next study visit.

Among 74 participants enrolled, 31 had P. falciparum co-infection at baseline, 55 were followed to 24 weeks, and 32 were treated over the course of follow-up. Most initial P. ovale parasitemias were short-lived, with only 19 of 74 (26%) persisting until the enrollment visit, a median of 4 days after screening. Just over half of participants (41/74, 55%) developed recurrent P. ovale infection a median of 10 weeks (interquartile range: 4, 12) later; 9 experienced a second P. ovale recurrence during follow-up. Risk of P. ovale recurrence did not differ by sex or between children and adults, but appeared to increase in the dry season, especially before the long rainy season. Using microsatellite genotyping, most infection pairs demonstrated heterologous recurrence.

Though apparently short-lived, detectable asymptomatic P. ovale parasitemia frequently recurs. The proportion of P. ovale recurrences attributable to relapse in this setting remains unclear.