Mucocutaneous Leishmaniasis disease: Sand flies, these diminutive tan insects—roughly one-fourth the size of a mosquito—call warm, damp, rural, and forested areas home. In various parts of the world, they’ve gained notoriety for transmitting a parasite—a single-celled organism—that triggers the infectious disease known as leishmaniasis. These sneaky insects are most active during the night and have a knack for slipping through standard mosquito nets on tents and window screens.
Dr. Mary Kamb, a medical epidemiologist at the US Centers for Disease Control and Prevention in Atlanta, has pointed out, “Sometimes you don’t even notice that you’ve been bitten.” The CDC has identified cases of leishmaniasis in individuals who claim they haven’t traveled outside the United States, hinting at the possibility of the disease being endemic within the US.
Leishmaniasis typically presents as skin infections, characterized by small bumps that evolve into ulcerous sores several days to weeks after a sand fly bite. Although these sores are generally not painful, they tend to scar and can be disfiguring, especially when they occur on a person’s face.
Leishmaniasis can also affect internal organs, including the liver, spleen, and bone marrow. This severe form of the disease, known as visceral leishmaniasis, is not believed to be transmitted in the United States but can be contracted by traveling to tropical countries.
Most of the skin samples in the CDC study were obtained from Texas, the only US state that mandates reporting of leishmaniasis cases. A 2021 research review reported locally acquired cases in southeast Oklahoma.
About half a dozen cases of leishmaniasis skin infections are reported annually in non-travelers in the US. The World Health Organization lists the disease as endemic in the country, although awareness among the general population and healthcare professionals is limited.
Sand flies capable of carrying the parasite are found in various southern and southwestern states. As the climate warms, these insects, like other species, have been extending their range in recent years. Some biting fly species have been observed as far north as Delaware, New Jersey, Ohio, and Maryland, although it remains unclear whether sand flies in all these states transmit infections to humans.
For this study, researchers analyzed over 2,100 skin samples sent to the CDC between 2005 and 2019. These samples came from all 50 states, Puerto Rico, and the Virgin Islands. Approximately half of the samples (1,222) tested positive for leishmaniasis, with most of the positive cases linked to a history of international travel. However, 86 positive samples came from patients with no travel history.
Among those without a travel history, the most common parasite species was Leishmania mexicana. Within this species, researchers identified two distinct genotypes. One of these, known as CCC, was found in nearly 94% of non-travelers, suggesting that this particular parasite type may be endemic in the United States.
The transmission of leishmaniasis is believed to occur when sand flies, carrying the parasite after biting infected rats, pass the parasite to humans. Humans generally cannot transmit the infection to each other.
While there’s still much to learn about the spread of leishmaniasis by sand flies in the United States, taking precautions in warm rural areas is advisable. Sand flies can be repelled by bug sprays containing DEET and killed with permethrin. Spraying camping equipment and clothing can offer protection.
If you notice a new skin sore that develops a few days after a bug bite and doesn’t heal, seeking treatment is wise. Treatment for leishmaniasis typically involves a month-long course of medications, such as amphotericin B, which inhibits the parasite. Dr. Gideon Wasserberg of the University of North Carolina at Greensboro emphasizes the importance of raising awareness about this disease in the US, as many doctors remain unaware of its existence.
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