Non-imported malaria in Italy: paradigmatic approaches and public health implications following an unusual cluster of cases in 2017

Abstract

Background: The European region achieved interruption of malaria transmission during the 1970s. Since then, malaria control programs were replaced by surveillance systems in order to prevent possible re-emergence of this disease. Sporadic cases of non-imported malaria were recorded in several European countries in the past decade and locally transmitted outbreaks of Plasmodium vivax, most probably supported by Anopheles sacharovi, have been repeatedly reported from Greece since 2009. The possibility of locally-transmitted malaria has been extensively studied in Italy where the former malaria vector An. labranchiae survived the control campaign which led to malaria elimination. In this study, we present paradigmatic cases that occurred during a 2017 unusual cluster, which caused strong concern in public opinion and were carefully investigated after the implementation of the updated malaria surveillance system.

Methods: For suspected locally-transmitted malaria cases, alerts to Ministry of Health (MoH) and the National Institute of Health (ISS) were mandated by the Local Health Services (LHS). Epidemiological investigations on the transmission modes and the identification of possible infection's source were carried out by LHS, MoH and ISS. Entomological investigations were implemented locally for all suspected locally-transmitted cases that occurred in periods suitable to anopheline activity. Molecular diagnosis by nested-PCR for the five human Plasmodium species was performed to support microscopic diagnosis. In addition, genotyping of P. falciparum isolate was carried out to investigate putative sources of infection and transmission modalities.

Results: In 2017, a cluster of seven non-imported cases was recorded from August through October. Among them, P. ovale curtisi was responsible of one case whereas six cases were caused by P. falciparum. Two cases were proved to be nosocomial while the other five were recorded as cryptic at the end of epidemiological investigations.

Conclusions: The epidemiological evidence shows that the locally acquired events are sporadic, often remain unresolved and classified as cryptic ones despite investigative efforts. The "cluster" of seven non-imported cases that occurred in 2017 in different regions of Italy therefore represents a conscious alert that should lead us to maintain a constant level of surveillance in a former malaria endemic country.

Keywords: Anopheles labranchiae; Cryptic case; Genotyping; Hospital-acquired infection; Malaria vector; Non-imported malaria; Plasmodium falciparum; Plasmodium ovale spp..

Fig. 1

Geographical distribution of non-imported malaria cases occurred in 2017 in Italy (grey regions), and associated findings from entomological investigations targeting Anopheles vectors species (The map shown in Fig. 1 is an original drawing created by the authors and has not been taken from other sources)

Fig. 2

Capillary electrophoresis image showing PCR amplified products of Plasmodium falciparum DNA isolated from two malaria cases hospitalized in Florence. (1) Putative induced case; (2) imported case; (C) no DNA; (M) DNA marker. All five polymorphic markers analyzed showed complete size concordance between the two isolates

Fig. 3

PCR amplification of plasmodial DNA isolated from the non-imported case from Pesaro, targeting sequences discriminating between Plasmodium ovale curtisi and P. ovale wallikeri. Two pairs of primers were used: first one pair (rOVA1WC-rOVA2WC) is used to amplify both subspecies, and second one pair (rOVA1v-rOVA2v) is specific for P. ovale wallikeri diagnosis (Fuehrer et al., 2012). (M) DNA marker; a Amplification results using rOVA1WC+ rOVA2WC primers; (1–2) patient sample replicates; (3) P. ovale curtisi control DNA; (4) P. ovale wallikeri control DNA; (5) negative control (no DNA); b Amplification results using rOVA1v + rOVA2v primers; (6-7) patient sample replicates; (8) P. ovale curtisi control DNA; (9) P. ovale wallikeri control DNA; (10) negative control (no DNA)