‘Airport malaria’ is rare, but can be deadly when doctors don’t expect it

Doctors outside malaria zones often don’t think to test for it, while symptoms, rapid tests and drug resistance can all complicate diagnosis and treatment.

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A few days after landing at Frankfurt Airport, several people who had never left Germany developed a fever. None had travelled anywhere near a malaria zone – but the mosquitoes that infected them had.

That’s the theory behind a small but serious cluster of malaria cases now linked to the airport – three of them fatal. It is known as “airport malaria”: mosquitoes carrying the malaria parasite arrive on aircraft – in luggage or cargo – from countries where malaria is common. They then escape at the airport and bite people nearby.

Airport malaria is extremely rare and the risk to the wider public is still very low. But the cases point to a real problem anywhere malaria isn’t normally seen: doctors have to be extra vigilant to identify it. And even once they do, diagnosing and treating it rapidly isn’t always straightforward.

Malaria is caused by parasites that pass into the body when an infected Anopheles mosquito bites someone. Several species of Plasmodium parasite can infect humans, but Plasmodium falciparum is the most dangerous. It multiplies rapidly in the blood and can quickly lead to severe, life-threatening illness.

Malaria-carrying mosquitoes can hitch a ride on a plane.
Patrik Dietrich/Shutterstock

Early symptoms, such as fever, chills, headaches and tiredness, can easily be mistaken for flu or a stomach bug. In malaria-free countries, the usual clue for doctors that something more serious is at play is a recent trip abroad. A person who mentions a holiday in west Africa, say, is likely to get tested for malaria, but a baggage handler or someone living near the airport may be overlooked.

Without that clue, doctors have to catch the diagnosis on symptoms alone, and even with a travel history to help them, they often don’t. A study from China found that more than a quarter of imported malaria cases (where a person is infected abroad) were not correctly diagnosed at the first visit. Delays in diagnosis are one of the main reasons patients have worse outcomes.

Testing and treatment problems

Rapid tests in hospitals work like a home COVID test and give results in minutes. Where malaria is common they usually pick up most cases, but they can miss an infection.

Many of these tests look for a particular protein made by the parasite, and some parasites no longer make this protein. The World Health Organization (WHO) has found such parasites in more than 40 countries, although nothing suggests they were involved in the Frankfurt case. Even so, a negative rapid test should not rule out malaria if a doctor has good reasons to suspect it.

Once malaria is suspected from symptoms and travel history, the standard test is to look at a blood sample under a microscope. A technician can spot the parasite and see how many red blood cells it has infected, which shows how ill the patient is.

But reading these slides takes practice, and a hospital that rarely sees malaria may not have anyone experienced on shift. Early in an infection there may be few parasites in the blood, so the test sometimes has to be repeated.

Doctors need to treat severe falciparum malaria fast because it can quickly damage the brain, kidneys and lungs if left untreated. The WHO recommends artesunate given by injection, followed by a full course of tablets. The drug works quickly, but not all hospitals will have it in stock.

Another complicating factor is that malaria parasites in parts of Asia have developed resistance to artemisinin drugs – of which artesunate is one – and resistance is now appearing in parts of Africa. Usually, this means the parasites take longer to clear from the blood rather than the treatment failing completely.

There is no evidence that drug resistance played a part in the Frankfurt deaths. But mosquitoes arriving on planes could carry parasites from any region with direct or connecting flights to Frankfurt, including places where resistance is spreading.

Genetic tests on the parasites can show whether the patients were infected by the same mosquito. The same tests can also flag signs of drug resistance or of parasites that rapid tests may not detect. But genetics alone can’t explain how the mosquito got there.

Investigators are also looking at flight routes, workplaces, the dates each person fell ill and the mosquitoes caught in traps around the airport. Trap samples have been sent to a laboratory in Belgium, but the results have not yet been released.
Khalid Beshir previously received funding from Wellcome ISSF, WHO, Malaria Consortium and EDCTP.

Tags: Academic Journalism, The Conversation, The Conversation Academic News