Europe sees a spike in malaria cases caused by mosquitoes brought in by airplanes

According to a retrospective analysis in France and a systematic review of studies in Europe published in the journal Eurosurveillance, there has been an increase in malaria cases caused by the bites of mosquitoes imported by airplanes from regions where malaria is widespread.

Since malaria was eradicated in Western Europe in the 1970s, most cases in the EU/EEA have been reported exclusively in travelers returning from malaria-prone countries. Of the 6131 cases reported in the EU/EEA in 2022, 99% were travel-related.

Cases of locally acquired infections are reported annually in Western Europe. These include imported infections, which are transmitted by a local mosquito after a bite from an infected returned traveler whose blood contains plasmodia; induced cases associated with other transmission routes, such as healthcare-associated infection or mother-to-child transmission; and Odyssey malaria, which refers to cases caused by the bite of an infected mosquito arrived by plane, luggage or parcel from an endemic area.

The systematic review analyzed data from studies in Europe from 1969 to January 2024 from MEDLINE, Embase and OpenGrey databases. The data were supplemented by a request to EU/EEA and UK health authorities for information for 2022.

Of the 145 described cases from nine countries, 105 were classified as airport malaria, 32 as baggage malaria, and eight as both types of malaria. Most cases were reported in France, Belgium and Germany, and half of those who became ill lived or worked near or at an international airport. It turned out that malaria cases originating from airports and baggage are on the rise: in the past five years, they have been reported to account for one-third of all reported cases of malaria. And this is even despite the reduction in air travel during the COVID-19 pandemic.

The average age of people who contracted malaria was 37.9 years, with more males than females (1.5:1 ratio). In 124 cases with a known outcome, patients recovered and nine died. The patients who died were on average older, with a mean age of 57.2 years. Forty-eight of the 145 cases were epidemiologically related to at least one other case.

Similar trends were observed in a retrospective analysis of surveillance and investigation data on local malaria cases in France from 1995 to 2022. Cases were classified according to the most likely mode of transmission, using the classification developed by the European Center for Disease Prevention and Control (ECDC). Descriptive analysis was also performed to identify spatial and temporal patterns.

The researchers found a total of 117 locally acquired malaria infections reported in the European part of France. They also found that overall, the rate of locally acquired infections remained unchanged, with more cases of Odyssey malaria reported since 2011. Fifty-one of the 117 cases identified were classified as Odyssey malaria, 36 as induced, 27 as hidden (when investigation was inconclusive) and three as imported.

Among patients with locally contracted malaria, severe cases and deaths were observed more frequently than in imported cases.

To combat the risk of imported malaria, researchers in a retrospective analysis conducted in France advised strict monitoring of airplane disinsection. To improve treatment, they also recommended that clinicians consider the possibility of local malaria infection in patients with unexplained fever, even if they have no travel history.

The authors of the systematic review emphasized the need for more structured surveillance of malaria cases in Europe. They also recommended implementing preventive measures and evaluating the effectiveness and adherence of existing measures.