Malaria cases resulting from bites of mosquitoes transported by aircraft from areas where is common have increased, according to both a retrospective analysis in France and a systematic review of studies in Europe, which have been published in Eurosurveillance.
After malaria was eradicated in western Europe in the 1970s, most cases in the EU/EEA have been reported among travellers returning from countries where malaria is established. Of the 6,131 cases reported in the EU/EEA in 2022, 99% were travel related.
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Locally-acquired infections are reported sporadically every year in western Europe. These include introduced infections, which are transmitted by a local mosquito after it has bitten an infected returning traveller carrying plasmodia in their blood; induced cases, which are related to other means of transmission such as a healthcare-associated infection or mother-to-child transmission; and Odyssean malaria, which refers to cases resulting from the bite of an infected mosquito transported by aircraft, luggage or parcel from an endemic area.
Systematic review of studies in Europe
The systematic review analysed studies in Europe indexed from 1969 to January 2024 in the MEDLINE, Embase and OpenGrey databases. Numbers were supplemented by a data call to EU/EEA and UK public health authorities launched in 2022.
Of the 145 cases described from nine countries, 105 were classified as airport malaria, 32 as luggage malaria, and eight as either type of malaria. Most cases were reported in France, Belgium, and Germany, and half resided or worked near or at an international airport. Case reports of airport and luggage malaria were found to be rising, with one third of cases reported over the last five years, even as air traffic declined during the COVID-19 pandemic.
People infected with malaria had a mean age of 37.9 years and were more likely to be male than female, at a ratio of 1.5:1. For the cases with a known outcome, 124 recovered and nine died. Patients that died were older on average, with a mean age of 57.2 years. Forty eight of 145 cases were epidemiologically linked to at least one other case.
Locally-acquired malaria over nearly three decades
Similar trends were observed in a retrospective analysis of surveillance and case investigation data in France on locally acquired malaria from 1995 to 2022. Cases were classified by the most likely mode of transmission, using a classification derived from the European Centre for Disease Prevention and Control (ECDC). A descriptive analysis was also conducted to identify spatial and temporal patterns of cases.
Researchers found a total of 117 locally acquired malaria cases reported in European France. They also found that locally acquired infections remained constant overall, with more Odyssean cases being reported since 2011. Fifty one of the 117 cases identified were categorised as Odyssean, 36 as induced, 27 as cryptic (where the investigation was inconclusive), and three as introduced.
Most cases were among males with a median age of 34.5 years. Half of patients were born in an country in Africa where malaria is common, and the other half were born in France. More than half of cases were reported in the region Île-de-France. 102 were admitted to hospital, and seven patients died. Among patients with locally-acquired malaria, severe cases and death was more frequent than in imported cases.
Public health implications
To tackle the risk of Odyssean malaria, researchers of the retrospective analysis in France advised the strict enforcement of disinsectisation of aircrafts. To improve treatment, they also recommended that physicians consider the possibility of locally-acquired malaria for patients with an unexplained fever early, even if there is no travel history.
Authors of the systematic review highlighted the need for more structured surveillance of malaria cases in Europe, including a standardised case definition. They also recommended the implementation of prevention measures and to assess the effectiveness and compliance for measures currently in place.
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