Already ravaged by years of violent conflict and terrorism, the people of Syria are now also battling against an outbreak of leishmaniasis, a parasitic disease that has taken hold across large swaths of the war-torn country. Making this desperate situation even worse, conservative media outlets like Breitbart News have pounced upon the opportunity to stir up xenophobic panic by erroneously suggesting that Syrian refugees are bringing the disease to the United States.
“EXCLUSIVE — SYRIAN REFUGEES BRINGING FLESH-EATING DISEASE INTO U.S.?‘, Breitbart declared in an article published last week. The author, Aaron Klein, went on to describe Syrian refugees as potential “carriers” of leishmaniasis who could slip into the country undetected, bringing the disease with them and spreading it to others on American soil.
“The blood tests [for refugees entering the U.S.] do not currently look for leishmaniasis,” Klein wrote. “[P]atients can be infected with the parasitic disease without showing symptoms for weeks, months, or even years, and an asymptomatic patient most likely doesn’t know that he or she is a carrier.”
“This means the health screening process for refugees could miss the disease entirely,” the article warns.
Within a day, the right-wing mediasphere picked up Breitbart’s story and ran with it, crafting their own panicked headlines warning of a disease that they had never heard about until this week. Dropping the question mark from the original title, the Patriot Update published an article with a patently false headline declaring, ‘BREAKING: TERRIFYING NEW DISEASE ROCKS THE NATION AS SYRIAN ‘REFUGEES’ ENTER AMERICA.‘ Meanwhile, the Conservative Tribune took the fear-mongering to the next level, running an article titled ‘ALERT: Syrian Refugees Caught Carrying New Disease, and It’s Far More Terrifying Than Ebola or AIDS‘.
Sounds pretty scary, right? And it could be scary, if we were talking about a contagious disease. But we’re not.
Leishmaniasis is not contagious and does not spread from person-to-person. It is sandflies, not people, that transmit the disease. The reason that we don’t test people for the disease during the screening process for refugees and immigrants is that people do not spread the disease directly to other people.
That’s not the only egregious mistake Klein made in his shameful attempt to stoke fears about a public health problem that he clearly isn’t qualified to opine on. He also overlooked the fact that leishmaniasis in the Eastern Hemisphere (“Old World leishmaniasis”) is transmitted by an entirely different group of sandfly species carrying completely different species of Leishmania parasites than leishmaniasis in the Western Hemisphere (“New World leishmaniasis”), rendering comparisons between Syria and the United States completely invalid. We’ll get to that in a moment, but first let’s take a step back and go over some of the key clinical and epidemiological characteristics of leishmaniasis — a step that Klein apparently skipped right over.
What is leishmaniasis?
Leishmaniasis is among the world’s oldest known infectious diseases, thought to date at least as far back as 650 BC, when the first records of the disease emerged near the Tigris/Euphrates basin. In the Western Hemisphere, accounts of leishmaniasis began appearing in pre-Incan pottery from Ecuador and Peru around the first century AD. Today, leishmaniasis is endemic in 88 tropical/subtropical countries on four continents and causes more than 1.3 million new infections annually, primarily in the developing world.
The term leishmaniasis actually describes three distinct clinical manifestations of the disease–cutaneous, mucocutaneous, and visceral–that are caused by certain species of Leishmania parasites and transmitted to humans through the bite of infected sandflies. To date, scientists have identified more than 20 Leishmania species that can cause human disease, along with at least 90 species of phlebotomine sandflies that are capable of transmitting the parasitic infection.
The most common manifestation of the disease, cutaneous leishmaniasis, is also the form seen in the ongoing Syrian outbreak, which dates back at least five years — coinciding with the start of the civil war and the subsequent collapse of the country’s health care infrastructure. However, leishmaniasis has been endemic in Syria and many other Middle Eastern countries for centuries, with a notable uptick in annual cases since the 1980’s.
As the name suggests, cutaneous leishmaniasis primarily affects the skin, causing sores that typically start out as papules or nodules and eventually turn into ulcerative lesions. Most cases of cutaneous leishmaniasis in the Middle East are self-limiting (meaning they will heal on their own, regardless of treatment, without becoming a disseminated infection), though treatment can reduce discomfort and scarring. In contrast, the visceral form of leishmaniasis, which affects the internal organs, is a much more serious disease that can be fatal without treatment. The third clinical manifestation of leishmaniasis is the mucocutaneous, or mucosal form, which occurs when skin lesions invade and damage the mucous membranes (such as inside the nose, mouth, and throat), often causing extensive scarring and disfigurement of the nasal septum, lips, and palate.
According to the latest estimates from the World Health Organization, about 90 percent of cutaneous leishmaniasis cases occur in Afghanistan, Algeria, Brazil, Iran, Peru, Saudi Arabia and Syria, while almost all (more than 90 percent) cases of visceral leishmaniasis cases are found in Bangladesh, Brazil, India, Nepal and Sudan. Mucocutaneous leishmaniasis, on the other hand, is limited to the Western Hemisphere, with 90 percent of cases occurring in just three countries: Bolivia, Brazil and Peru.
Pathogens, vectors, and the geography of disease
It is important to note here that the New World forms of leishmaniasis (those found in the Western Hemisphere, primarily in South and Central America) and Old World forms of leishmaniasis (those found in the Eastern Hemisphere) are caused by different species of leishmania, which in turn are carried by different types of phlebotomine sandflies.
According to the Centers for Disease Control and Prevention, the predominant pathogenic species of Leishmania in the Eastern Hemisphere are L. tropica, L. major, and L. aethiopica, as well as L. infantum and L. donovani. In contrast, the pathogenic species of Leishmania in the Western Hemisphere belong to either the L. mexicana species complex or the subgenus Viannia (also referred to as the L. (V.) braziliensis species complex).
All species of Leishmania are transmitted by small, blood-sucking sandflies from the subfamily Phlebotominae, but just like the disease itself, the vector also has geographical boundaries. Notably, the phlebotomine sandflies that spread leishmaniasis can only survive in warm climates, which explains why they are found in abundance throughout the tropics and subtropics but not in colder regions like the United States and northern Europe.
Additionally, different species of sandflies are responsible for spreading leishmaniasis in the Eastern Hemisphere versus the Western Hemisphere. In the Eastern Hemisphere, Leishmania parasites are transmitted to humans by certain species of “Old World” sandflies, which belong to the genus Phlebotomus and are found in the Mediterranean, Southern Europe, Africa, the Middle East, Central Asia, and South Asia. In the Western Hemisphere, “New World” sandflies belonging to the genus Lutzomyia are the vector for leishmaniasis.
The geographical distribution of each species of Leishmania and Phlebotominae affects the type of disease that occurs in different regions, as well as its clinical manifestation and severity. As explained in a 2010 review of the research on leishmaniasis, “Although [leishmaniasis cases] in the Old and New Worlds share similar characteristics, the ultimate manifestations and severity are quite different, with more severe forms associated with mucosal lesions observed in the New World.”
How Breitbart totally missed the mark
Now that we’ve reviewed some of the key facts about leishmaniasis, let’s go back and take a look at the three major points that Breitbart got wrong in their “exclusive” story about the supposed disease threat posed by Syrian refugees.
Mistake #1: Falsely equating a disease carrier with a disease vector
The whole point of the Breitbart article is to convince you, the reader, that you should be scared that Syrian refugees will spread leishmaniasis in the United States. When Klein writes that “an asymptomatic patient most likely doesn’t know that he or she is a carrier” and then warns that “the health screening process for refugees could miss the disease entirely,” he is quite obviously implying that Syrian refugees coming to America could bring the disease with them and infect others upon arrival.
While it’s true that an asymptomatic person could unknowingly harbor an infection for months or even years, it’s not true that this poses a risk of human-to-human transmission. Just like Lyme disease and malaria, leishmaniasis is classified as an infectious but non-contagious disease — meaning that it does not spread directly from human-to-human (with rare exceptions of congenital transmission of visceral leishmaniasis from mother to child upon birth, or during blood transfusions). A human infected with leishmanisis cannot transmit that infection to another person because sandflies–not humans–are the disease vector.
Anthroponotic leishmaniasis (where sandflies feed on an infected human, pick up the parasite, and then infect the next human it bites) is possible with certain species of Leishmania and Phlebotomines, but this has only been documented within households and cramped, crowded living conditions, which is one of the reasons leishmaniasis is considered a disease of poverty. Sandflies are notoriously weak fliers; they tend to hop more than they actually fly, and they can’t travel more than a few meters at a time. As a result, most sandflies never disperse more than a few hundred meters from their breeding site.
And as discussed previously, the sandflies that spread the species of Leishmania affecting Syrian refugees are not found in the Western Hemisphere. Without sandflies to spread the disease, a person infected with leishmaniasis poses no risk to public health.
Mistake #2: Conflating disease prevalence with disease transmission
In his attempt to portray Syrian refugees as a threat to public health in America, Klein pointed to research showing an increase in leishmaniasis prevalence in Lebanon and Turkey coinciding with the migration patterns of Syrian refugees as “evidence” of the disease risk they carry.
“As Syrians leave their homeland, they sometimes carry their germs with them,” Klein wrote. “There have been dramatic increases in the number of cases of cutaneous leishmaniasis in southeastern Turkey. In Turkey, 69% of cutaneous leishmaniasis patients are Syrians living in tent cities.”
Klein then cited a study claiming that Lebanon “had no cases of cutaneous leishmaniasis prior to 2008” but had experienced a spike in the prevalence of the disease as Syrian refugees moved into the area. “After the arrival of refugees, 1,033 cases were confirmed by 2012,” Klein wrote, noting that 96.6% of those cases were among Syrian refugees.
To begin with, the claim that leishmaniasis did not exist in Lebanon until 2008 is unequivocally and demonstrably false. A quick literature search on my part turned up numerous articles documenting the presence of leishmaniasis in Lebanon for more than two decades. While it is true that the prevalence of leishmaniasis in Lebanon and Turkey has increased with the influx of refugees from Syria, Klein’s interpretation of this pattern is based on a fundamental misunderstanding of disease epidemiology. Namely, he has conflated an increase in the prevalence of the disease in a specific location with an increase in disease transmission among its population.
The following hypothetical scenario demonstrates the error in Klein’s logic: Imagine that budget cuts in the U.S. left us with just two cancer treatment centers in the entire country — one in California and the other in New York. Suddenly, these two states would be faced with an influx of cancer patients coming from around the nation, resulting in a massive surge in the number of cancer cases (the prevalence) in New York and California. But does this mean that the risk of developing cancer in New York and California is suddenly higher than in the rest of the country? Are cancer patients who travel there “bringing” a higher risk of cancer along with them? Of course not. If we completely ignored the context of these figures, however, it would appear that the increase in cancer patients living in those two states was actually an increase in the risk of the disease itself.
That is exactly what Klein has done in his article. Instead of explaining that the spike in leishmaniasis prevalence in Turkey and Lebanon is directly linked to the uptick in the number of already-infected people entering these countries, he portrays it as the result of an increase in transmission among the existing population. This is illustrated by Klein’s misinterpretation of the findings from a study that he cited in his own article.
“In 2012, the CDC documented that ‘migration patterns of refugees with cutaneous leishmanias is were identified in Lebanon,'” Klein wrote. In the same sentence, he noted that the CDC had “produc[ed] a helpful illustration showing the disease’s movement…” But that’s not what the illustration shows. As the CDC stated, they have documented movement of refugees with the disease — an entirely different phenomenon than documenting movement of the spread of disease itself. This goes back to the first fact that Klein ignored: that people are notthe vectors of leishmaniasis. Contrary to what Klein claims, refugees with leishmaniasis don’t “carry their germs with them” — in fact, they can’t, since they were never contagious in the first place.
Mistake #3: Failing to distinguish Old World leishmaniasis from New World leishmaniasis
This is one of the most fundamental mistakes that Klein made, and it began when he inappropriately extrapolated information from an article published by Breitbart Jerusalem and applied it to the United States. As discussed previously, the species of Leishmania and the type of sandflies that spread it are completely different in the Western Hemisphere than in the Eastern Hemisphere.
Yet when Klein described the transmission of leishmaniasis, he wrote that “it is spread almost entirely by sandflies, including those present in the U.S.” I guess he just forgot to mention that leishmaniasis in Syria is caused by a parasite that is limited to the Eastern Hemisphere and spread by sandflies that are not found anywhere in the Western Hemisphere. And in case you were wondering, Old World sandflies are not capable of traveling long distances, nor would they survive if they reached America.
Nowhere in the Breitbart article does Klein even mention that there is a difference between the types of leishmaniasis found in the Eastern Hemisphere versus the Western Hemisphere aniasis found in the Eastern Hemisphere versus the Western Hemisphere (or the “Old World” vs. “New World” forms). This is one of the most defining features of the disease, yet even after consulting with two “experts” in the field, Klein apparently never learned this basic fact. Either that, or he learned about it but simply failed to make note of this fundamental distinction in his article because it would undermine its entire premise.
So to answer Breitbart‘s burning question — NO, SYRIAN REFUGEES ARE NOT BRINGING FLESH-EATING DISEASE INTO U.S. Nor will they be. But you know what could allow (New World) leishmaniasis to start spreading in America? Climate change. Just don’t expect to hear that from Breitbart or any other “news” organizations that prioritizes xenophobic panic over scientific fact.