Malaria cases from mosquito bites transported by aircraft from areas where it is common have increased, according to a retrospective analysis in France and a systematic review of studies in Europe, published in Eurosurveillance.
After the elimination of malaria in Western Europe in the 1970s, most cases in the EU/EEA have been reported among travelers returning from countries where malaria has become established. Of the 6,131 cases reported in the EU/EEA in 2022, 99% involved travel.
Locally acquired infections are reported sporadically every year in Western Europe. These include imported infections, which are transmitted by a local mosquito after biting an infected returning traveler carrying plasmodia in their blood. caused cases, which are associated with other means of transmission, such as healthcare-associated infection or mother-to-child transmission; and Ulysses malaria, which refers to cases resulting from the bite of an infected mosquito carried by aircraft, baggage or package from endemic area.
Findings of a 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. The numbers were supplemented by a call for data to EU/EEA and UK public health authorities which started in 2022.
Of the 145 cases described from nine countries, 105 were classified as airport malaria, 32 as baggage malaria, and eight as malaria of any type. Most cases were reported in France, Belgium and Germany, and half lived or worked near or at an international airport. Reports of airport and baggage malaria cases were found to be on the rise, with a third of cases reported in the past five years, even as air traffic decreased 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, by a ratio of 1.5:1. For the cases with a known outcome, 124 recovered and nine died. Patients who died were older on average, with a mean age of 57.2 years. Forty-eight of the 145 cases were epidemiologically linked to at least one other case.
Locally acquired malaria for nearly three decades in France
Similar trends were observed in a retrospective analysis of surveillance and case investigation data in France for locally acquired malaria from 1995 to 2022. Cases were classified according to the most likely mode of transmission, using a classification derived from the European Center for Disease Prevention and Control (ECDC). Descriptive analysis was also performed to identify spatial and temporal patterns of cases.
The researchers found a total of 117 locally acquired malaria cases reported in European France. They also found that locally acquired infections remained stable overall, with more Odyssean cases reported since 2011. Fifty-one of the 117 identified cases were categorized as Odyssean, 36 as induced, 27 as cryptic (where the investigation was inconclusive) and three as introduced.
Most cases involved men with a median age of 34.5 years. Half of the 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 Île-de-France region. 102 were hospitalized and seven patients died. Among patients with locally acquired malaria, severe cases and deaths were more common than among imported cases.
Public health implications
To address the risk of Ulysses malaria, retrospective analysis researchers in France recommended strict enforcement of aircraft disinfection. To improve treatment, they also recommended that doctors consider the possibility of locally acquired malaria in patients with unexplained fever early, even if there is no history of travel.
The authors of the systematic review emphasized the need for more structured surveillance of malaria cases in Europe, including a standardized case definition. They also recommended the implementation of preventive measures and the evaluation of the effectiveness and compliance of measures currently in place.
