Mosquitoes carrying Plasmodium parasite—imported via air travel, parcels and luggage—cause Odyssean malaria in Europe

Malaria cases resulting from bites of mosquitoes transported by aircraft from areas where it 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 travelers returning from countries where malaria is established. Of the 6,131 cases reported in the EU/EEA in 2022, 99% were travel-related.

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 traveler carrying plasmodia in their blood; induced cases, which are related to other means of transmission, such as a health care-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.

Findings of systematic review of studies in Europe

The systematic review analyzed 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 in France

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 categorized 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 a country in Africa where malaria is common, and the other half were born in France. More than half of the cases were reported in the region Île-de-France. In total, 102 patients were admitted to hospital, and seven patients died. Among patients with locally-acquired malaria, severe cases and death were more frequent than in imported cases.

Public health implications

To tackle the risk of Odyssean malaria, the researchers of the retrospective analysis in France advised the strict enforcement of disinsectization of aircraft. 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.

The authors of the systematic review highlighted the need for more structured surveillance of malaria cases in Europe, including a standardized case definition. They also recommended the implementation of prevention measures and to assess the effectiveness and compliance with measures currently in place.

Provided by
European Centre for Disease Prevention and Control (ECDC)