Ruas et al. Malar J (2017) 16:298 DOI 10.1186/s12936-017-1952-3 Malaria Journal RESEARCH Open Access Non‑falciparum malaria imported mainly from Africa: a review from a Portuguese hospital Rogério Ruas1,2* , André Pinto1,2, João Nuak1,2, António Sarmento1,2 and Cândida Abreu1,2 Abstract Background: Non-falciparum malaria (NFM) has been reported to be responsible for around 25% of imported malaria cases in Europe but is often neglected due to its less severe clinical course when compared to Plasmodium falciparum. Diferentiation between species is however crucial for a correct approach. The objective of this study is to report the cases of this often missed aetiology of malaria in a tertiary hospital in Portugal. Methods: Data were retrospectively analysed from patients admitted from January 2006 to August 2016 with a NFM diagnosis based on microscopy, rapid diagnostic tests (RDT) ­(BinaxNow®) and/or PCR. Epidemiologic and clinical aspects were reviewed. Results: A total of 19 NFM cases were diagnosed, corresponding to 8.4% of the total 225 cases of malaria. Seventeen (89%) were male with a median age of 41 years. All but one case were imported from sub-Saharan Africa, with 12 (63%) of the cases returned from Angola. Microscopy was positive for all patients and correctly identifed the species in 12 (63%) patients. ­BinaxNOW® was performed in all patients and it was positive in 11 cases, showing a sensitivity of 58%. PCR was performed in nine patients and was positive in eight of them, being responsible for the identifca- tion of the species in four cases. Plasmodium malariae accounted for 37% (n 7) of the cases, Plasmodium ovale for 32% (n 6) and Plasmodium vivax for 17% (n 3). In three (16%) patients, morphology= was suggestive of P. vivax or P. ovale=, but precise species identifcation was= not possible. Regarding presentation, fever was the most reported symptom, and the most frequent laboratory fnding was thrombocytopaenia. Quinine–doxycycline was prescribed in eleven patients (58%), chloroquine in six cases (32%) and artemether–lumefantrine in two (11%). All of the patients showed clinical improvement. Conclusions: NFM remains an important cause of imported malaria in patients from sub-Saharan Africa, alone or as mixed infection with P. falciparum. Access to PCR techniques facilitates diagnosis, as low sensitivity from RDTs and microscopy are to be expected. Keywords: Non-falciparum malaria, Epidemiology, Imported Background historical reasons, a close relationship with Portuguese- Malaria remains one of the most important infectious speaking African countries (Angola, Guinea-Bissau, diseases responsible for a high morbidity and mortality Mozambique) is observed and imported malaria cases burden worldwide. Nearly half of the world’s population represent a signifcant burden. lives in endemic regions [1], and in developed countries Te disease in humans is caused by several species malaria is one of the most common causes of fever in of the genus Plasmodium. Plasmodium falciparum is migrants and travellers arriving from the tropics [2], con- responsible for the majority of cases and is also associ- stituting a global public health problem. In Portugal, for ated with a more severe course of illness. As such, it is the most studied species in scientifc literature. Non-falcipa- *Correspondence: [email protected] rum malaria (NFM), i.e., Plasmodium vivax, Plasmodium 1 Infectious Diseases Department, Centro Hospitalar São João, Alameda ovale, Plasmodium malariae, and Plasmodium knowlesi, Professor Hernani Monteiro, 4200 Porto, Portugal is less well documented, although it has been reported to Full list of author information is available at the end of the article © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Ruas et al. Malar J (2017) 16:298 Page 2 of 5 be responsible for around 25% of the imported malaria tertiary hospital centre in Porto, which is the reference cases in Europe [3–5]. Plasmodium vivax is the most centre for malaria and imported diseases in the north of geographically widespread species, accounting for 6% Portugal. of estimated cases globally [1]. Outside of Africa, where infection transmission is generally low and seasonal, P. Methods vivax comprises about half of the estimated cases [1], Data were retrospectively analysed from patients admit- with around the same prevalence as Plasmodium fal- ted at São João Hospital Centre (SJHC) from January ciparum. In sub-Saharan Africa, P. vivax infections are 2006 to August 2016 with a NFM diagnosis. Parasito- uncommon because of the presence in a high propor- logical diagnosis was done either by light microscopic tion of the population of Dufy antigen-negative red observation of Giemsa-stained thin blood smear, immu- cells which cannot be invaded by this parasite [6]. Plas- nochromatographic assay for the qualitative detection modium malariae and P. ovale are relatively common in of Plasmodium antigens (BinaxNOW ®) or by molecular many parts of sub-Saharan Africa and comprise <10% techniques (in-house one step Real Time Polymerase of isolates [1]. Plasmodium knowlesi has recently been Chain Reaction (PCR) based on the 18S subunit of the identifed as the cause of human malaria in Malaysian parasite’s ribosomal DNA) which became available in Borneo, but seems so far to be limited to Southeast Asia 2013. Te diferent Plasmodium species were identifed [7]. Clinically, P. vivax and P. ovale have a similar pres- morphologically by the laboratory when possible. Demo- entation to P. falciparum, although usually less severe. graphic, clinical and epidemiological data of the patients Tese two species have dormant liver stages (hypno- were collected. Te delay before diagnosis was defned as zoites), and can induce re-activation of malaria several the time between the onset of symptoms and the day of months after the initial infection. Plasmodium malariae diagnosis. SPSS was used on data analysis. Te study was (quartan fever) can result in long-lasting infection if approved by the SJCH Ethics Committee. not well treated. Plasmodium ovale and P. malariae are also believed to be responsible for asymptomatic cases Results [8]. Diagnosis of malaria by microscopic examination of A total of 19 NFM cases were diagnosed at SJHC, cor- Giemsa-stained thick and thin blood flms is still con- responding to 8.4% of a total 225 cases of malaria sidered the gold standard, as it has good sensitivity and diagnosed in the same period. Plasmodium malariae specifcity and it allows species diferentiation and parasi- accounted for 37% (n = 7) of the cases; P. ovale occurred taemia quantifcation. However, misclassifcation of non- in 32% (n = 6), and P. vivax in 16% (n = 3). In three (16%) falciparum species is common and highly dependent on patients the diagnosis of NFM was made by microscopy laboratory experience, especially when dealing with very because of morphology suggestive of P. vivax or P. ovale, low parasite densities [9]. Rapid diagnostic tests (RDTs) but precise species identifcation was not possible. Dur- have shown great sensitivity and specifcity for P. falcipa- ing the same period there were 2 cases of mixed infection rum infection [10–13], but seem to have a limited role in with P. falciparum (one patient with P. malariae infection diagnosing non-falciparum species, probably because of and another with P. vivax/P. ovale). small quantities of antigen circulating due to low parasi- Microscopy was positive for all 21 patients. Species taemia. BinaxNOW®, a RDT available for use in Portu- identifcation was made by microscopic examination of gal, detects the histidine-rich protein 2 (HRP-2), specifc Giemsa-stained thin blood flms in 12 (63%) patients. to P. falciparum, and aldolase, a pan-malarial antigen Out of the seven cases where species identifcation was common to all Plasmodium species [14], and as such, it not possible by microscopy, PCR was diagnostic in four is inappropriate to distinguish between non-falciparum patients: three patients as P. malariae and one patient as species. Polymerase chain reaction (PCR) seems to be the P. ovale. In the three remaining patients, species identi- most accurate method of detecting Plasmodium spp. and fcation was not possible, but BinaxNOW® was positive diferentiating species [15, 16], although it is not used in for the pan-malarial antigen aldolase for two of them, routine clinical care due to elevated costs and need of while the other one had a negative RDT. BinaxNOW ® specifc techniques. was performed in all 19 patients. It was positive for the Due to current incomplete data on artemisinin combi- pan-malarial antigen in 11 (58%) patients. Te test was nation therapy (ACT) efcacy for NFM in non-endemic negative in eight (38%) cases, showing a sensitivity of settings and the need for efective elimination of hypno- 58% (95% confdence interval 33.5–79.7%). PCR was per- zoites, diferentiation between species is crucial, as well formed in nine patients and was positive in eight cases (in as understanding the epidemiology of NFM. Terefore, fve patients for P. ovale and in three for P. malariae). In the objective of this study was to describe the clinical and one patient, PCR was negative for P. falciparum, P. ovale epidemiological features of imported cases of NFM in a and P. vivax (PCR for P. malariae was not performed at Ruas et al. Malar J (2017) 16:298 Page 3 of 5 that time), although microscopic examination of thin myalgia with 63, 52 and 53%, respectively.