A journey for mosquitoes and medical providers.
Odysseus and Polyphemus (1896) by Arnold Böcklin. Oil and tempera on panel, 66 cm × 150 cm (26 in × 59 in). Museum of Fine Arts, Boston, Massachusetts. Accessed through Wikimedia Commons at https://commons.wikimedia.org/wiki/File:Arnold_B%C3%B6cklin_-_Odysseus_and_Polyphemus.jpg
I recently learned of Odyssean malaria while reviewing part of the Centers for Disease Control’s 2024 Yellow Book on South Africa. Like the legendary Greek character Odysseus, who traveled far from home, Odyssean malaria is caused by mosquitoes that have traveled from their usual home (unlike Odysseus, these mosquitoes likely don’t return home). Odysseus traveled by ship and land, whereas these mosquitoes may hitch a ride in airplanes, vehicles, and other modes of travel.
Odyssean malaria refers to malaria transmitted by translocated mosquitoes and the term encompasses ‘airport malaria’, ‘baggage malaria’, ‘taxi malaria,’ and so on. A case of odyssean malaria is one in which there is no travel history, and mechanical transmission (by blood transfusion, injection or needlestick injury) is excluded. Odyssean malaria is therefore a diagnosis of exclusion, as the probability of finding the responsible vector is miniscule. Because of the unexpected nature of the infection, diagnosis is often delayed and severe and complicated malaria is common in these patients.
If you’re going for a stroll one afternoon in Tennessee and hear hooves clopping nearby, it’s likely horses, not zebras, causing the sound. This concept underscores the importance of looking for what’s common rather than unusual. Yet, the concept of Odyssean malaria is an important reminder for medical providers to also be open to the unusual, unexpected, and unsuspected.
As the authors above noted, not being open to “zebras” may delay care. In the case of malaria, delaying care can have serious consequences. Specifically for South Africa, where malaria exists in just part of the country, the authors conclude that malaria cases may be missed as a result of not suspecting malaria in non-endemic areas, but that “malaria should always be kept in mind as a cause of unexplained fever and thrombocytopenia, even in the absence of travel history.”
Another example of this is found in a 2022 article for Eurosurveillance. Here, Van Bortel et al. describe a Belgian married couple who both developed and ultimately died from malaria in Belgium in late 2020 -- an uncommon event in Belgium. The first case, the husband, was retroactively diagnosed with malaria after his wife, the second case, was diagnosed. Interestingly, the wife's blood sample was flagged by an analyzer machine due to hematology abnormalities, after which a technician identified Plasmodium falciparum (P. falciparum) trophozoites (P. falciparum is one of a variety of Plasmodium parasites that cause malaria).
The investigation revealed that the spouses had not left Belgium for over 50 years, ruling out a travel etiology. The investigation also ruled out transmission via blood or organ transfusion and via hospital admission exposure (nosocomial infection), as well as transmission from a returning infected traveler. Nearby environmental and entomological investigations did not prove a likely epidemiological cause.
However, the couple lived approximately 3 miles from two airports: an international airport in Brussels and a military airport in Melsbroek. From the period of August 1, 2020 - September 15, 2020, these two airports together received 483 flights from Africa, 166 of which were from West Africa and 20 from Cameroon. These are countries where Plasmodium falciparum is present.
As quoted earlier, Odyssean malaria is a "diagnosis of exclusion." And the process of excluding other possibilities is how investigators reached a likely hypothesis of an exotic mosquito hitching a ride on an airplane and infecting this Belgian couple with malaria, which, sadly, proved fatal for them.
Odyssean malaria is rare. But it can seriously impact a patient through delayed or incorrect care, leading to complicated infection and even death.
So how should a medical provider proceed? Where is the balance between being open to the rare and being efficient with time and attention, responsibly managing resources and not needlessly increasing expenses for a patient? A medical provider certainly should be open to the rare but cannot chase every rabbit down every hole.
In the case of malaria, Van Bortel et al. suggest increased vigilance in medical providers near airports by placing malaria on their differential diagnosis if the patient shows signs and symptoms suggestive of malaria. This makes sense, as these indicators of malaria should be weighed heavier in places where we now know malaria can exist, even if rarely, and lighter in places without airports and other possible international connections.
Generally, medical providers should remain competent for expected situations, but also be open to rare situations by taking into account local geography, population patterns and habits, and other unique variables.
This may be a challenge for medical providers as it requires, perhaps, uncomfortable questioning of one’s presuppositions, by looking for both the routine and the rare.
But disruptive change might be beneficial in this instance. Being open to the rare chance of a wild zebra galloping the rolling hills of Tennessee might just save a life.
(This article was written by a human, not A.I. Feel free to share it with others.)