The challenge of diagnosing Plasmodium ovale malaria in travellers: report of six clustered cases in french soldiers returning from West Africa

Abstract

BackgroundPlasmodium ovale is responsible for 5% of imported malaria in French travellers. The clinical and biological features of six clustered cases of P. ovale malaria in an army unit of 62 French soldiers returning from the Ivory Coast are reported.Case reportAll patients were symptomatic and developed symptoms on average 50 days after their return and 20 days after the end of chemoprophylaxis (doxycycline). Clinical features included fever (6/6), mostly tertian (4/6), aches (6/6), nausea (3/6), abdominal pain (2/6), diarrhoea (2/6), or cough (2/6). Thrombocytopaenia was lower than 100,000/mm3 in half the cases only, and the haemoglobin count was normal for all patients. The diagnosis was made after at least three thick and thin blood smear searches. Parasitaemia was always lower than 0.5%. All rapid diagnostic tests were negative for HRP2 and pLDH antigens.DiscussionPlasmodium ovale malaria is currently a problem to diagnose in travellers, notably in French soldiers returning from the Ivory Coast. Early attempts at diagnosis are difficult due to the lack of specific clinical features, the rarity of biological changes and the poor sensitivity of diagnostic tools to detect low parasitaemia. Thus, the diagnosis is commonly delayed or missed. Physicians should be aware of this diagnostic challenge to avoid relapses and provide prompt and adequate treatment with chloroquine and radical cure with primaquine.

Molecular characterization of misidentified Plasmodium ovale imported cases in Singapore

“…Such an increase would be puzzling given the constant decrease in the total number of malaria cases recorded in Singapore since 2010 [ 80 ]. This pattern does not seem to be restricted to Singapore, with similar, recent reports of P. ovale in imported malaria cases among soldiers deployed in endemic areas [ 16 , 81 ], tourists visiting endemic countries [ 82 , 83 ], and foreign workers returning from endemic regions [ 84 – 86 ]. Several hypotheses, alone or in combination, might be for formulated to explain such an increase: (1) an upsurge of studies employing molecular tools that allow sensitive and accurate detection and identification of Plasmodium species (this would not apply to the cases imported to Singapore over the last 6 years, because all were molecularly tested); (2) an increase over recent years in the number of travellers, visitors or migrant workers to P. ovale -endemic countries; and, (3) a recent increase in the prevalence of P. ovale in the endemic areas, possibly as a result of extensive campaigns directed against P. falciparum that might favour this less common species as suggested by [ 15 ] or as observed with the recent increase of P. knowlesi in Malaysia [ 87 ].…”

“…Plasmodium ovale occurs principally in West Africa and the Southwest Pacific where it can account for more than 10 % of all malaria infections. Outside these regions, its prevalence is generally quite low (<5 %, and often it is very rarely encountered), and its presence is yet to be confirmed in the Americas [ 9 – 16 ]. However, results from surveys based on sensitive molecular detection assays indicate that routine light microscopic examination of blood smears has underestimated its true prevalence [ 17 – 20 ].…”

Characterization of Plasmodium ovale curtisi and P. ovale wallikeri in Western Kenya Utilizing a Novel Species-specific Real-time PCR Assay

“…Second, the characteristic low-level parasitemia of P. ovale infection further complicates microscopic detection due to the difficulty in finding and identifying low numbers of P. ovale parasites [ 13 ]. Finally, malaria Rapid Diagnostic Tests (RDTs) show a reduced ability to detect P. ovale compared to other human malaria parasites, resulting in false negative cases [ 14 – 16 ]. However, the use of extremely sensitive molecular detection methods, such as polymerase chain reaction (PCR), have revealed a higher prevalence of P. ovale and expanded the geographical distribution of this malaria parasite compared to what was previously identified based on microscopy [ 10 , 17 – 20 ].…”

A combined strategy for screening a clustered mobile population returning from highly endemic areas for Plasmodium falciparum

“…However, none of the three diagnostic methods could find the non-P. falciparum-positive cases among the 226 individuals at their first visit in this study. This might be because of the characteristics of long-period dormant Plasmodium hiding in the hosts' livers and reviving after a period of time [12,[33][34]. It seemed that strengthened surveillance among populations should be continued for at least one year based on the known dormant period of P. vivax and P. ovale.…”