Frequent <i>Plasmodium ovale</i> Recurrence in Coastal Tanzania

Abstract

BACKGROUND: Plasmodium ovale (Po) 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. METHODS: Asymptomatic adults and children >5 years of age living in Bagamoyo, Tanzania who screened positive for Po parasitemia by real-time PCR were enrolled and followed for up to 6 months, with biweekly PCR testing for Po and P. falciparum (Pf) infection. Those with persistent Po carriage to 4 weeks, and those later diagnosed with incident or recurrent Po or Pf infection, were offered treatment with artemether-lumefantrine at the next study visit. RESULTS: Among 74 participants enrolled, 31 had Pf co-infection at baseline, 55 were followed to 24 weeks, and 32 were treated over the course of follow-up. Most initial Po parasitemias were short-lived, with only 19 out 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 Po infection a median of ten weeks [IQR: 4w, 12w] later; nine experienced a second Po recurrence during follow-up. Risk of Po recurrence did not differ by sex or between children and adults, but appeared to increase in the dry season, especially prior to the long rainy season. Using microsatellite genotyping, most infection pairs demonstrated heterologous recurrence. DISCUSSION: Though apparently short-lived, detectable asymptomatic P. ovale parasitemia frequently recurs. The proportion of Po recurrences attributable to relapse in this setting remains unclear.