Health experts are sounding the alarm on a deadly tropical disease currently spreading in the US because it used to be so rare that most doctors have never seen a single case of it. This parasitic disease called leishmaniasis was seen only in people who had traveled to tropical countries.

What is Leishmaniasis?

Leishmaniasis is a vector-borne disease caused by obligate intracellular protozoa of Leishmania. It spreads to humans through the bites of female sand flies (Phlebotomus), although it can also be transmitted through blood transfusions or by sharing contaminated needles.

The most common form of this disease is cutaneous leishmaniasis, which causes skin sores and ulcers to erupt in spots where someone is bitten. If left untreated, these can become disfiguring scars.

Cutaneous leishmaniasis has been previously detected in the Southern region of the US, particularly in Texas. Such cases, however, have been sporadic and were seen mainly in people who have returned from countries where it was endemic. These include Central Asia, the Mediterranean, the Middle East, and Central and South America.

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Deadly Tropical Disease

During the Annual Meeting of the American Society of Tropical Medicine and Hygiene (ASTMH) held in Chicago on October 19, experts reported that they detected a genetically distinct strain of a Leishmania parasite that causes cutaneous leishmaniasis. The newly discovered strain belongs to Leishmania Mexicana, which is different from stresses that cause leishmaniasis cases in the US.

Vitaliano Cama, senior adviser with the Centers for Disease Control and Prevention's Division of Parasitic Diseases and Malaria, suggests that the new strain is being spread by US sand flies. The researchers genetically sequenced over 2,000 tissue samples from patients with suspected cutaneous leishmaniasis across 50 US states between 2005 and 2019 to confirm this theory. Over 80 cases of locally caught human leishmaniasis have been reported in the US as of 2018, but it isn't easy to accurately estimate the case numbers.

Leishmaniasis is a reportable condition in Texas, which means that the diagnoses must be reported to local public health officials, but this is not the case nationally. The new study acted almost as a proxy for surveillance, allowing the researchers to get a sense of how frequently the disease occurs.

Leishmania parasites were detected in 1,222 of the more than 2,000 tissue samples. Over 1,100 samples were from people who had traveled internationally, while 86 were from nontravelers. Of the obtained samples, 164 were Leishmania mexicana, of which 32% of the cases occurred in Texas. This strain is the most common species among nontravelers, with over 60% testing positive.

The research team also detected two distinct strains of Leishmania mexicana: ACT and CCC. ACT strain appeared dramatically more prevalent in travelers, while CCC was much more common in nontravelers, especially those in Texas. These findings provide evidence that leishmaniasis may be endemic in the US.

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