Endemic Spread of Cutaneous Leishmaniasis in the United States
Endemic Spread of Cutaneous Leishmaniasis in the United States
Leishmania, a parasitic microorganism, is responsible for the tropical illness known as leishmaniasis. This disease can manifest in various forms, leading to skin ulcers or, in severe cases, life-threatening liver damage. Transmission occurs through bites from sandflies carrying the parasite.
Cutaneous leishmaniasis, a tropical skin disease, is typically classified among the "neglected tropical diseases," impacting some of the world's most impoverished populations while receiving limited global attention. Caused by parasites transmitted through sand fly bites, the disease isn't fatal, but it leads to skin lesions that can result in depression and social stigmatization. "Facial scarring for life can cause a multitude of issues, including depression and stigma," notes parasitologist David Molyneux from the Liverpool School of Tropical Medicine in England.
Although endemic in the Middle East, Asia, Africa, and Latin America, the disease was not believed to be native to the United States until recently. Cases in Texas were initially attributed to travelers returning from Mexico. Over the past decade, reports emerged of cases in individuals with no travel history outside the U.S., indicating local transmission.
A team from the U.S. Centers for Disease Control and Prevention (CDC) has discovered that nontravelers in the U.S. were infected with a genetically distinct form of the parasite, confirming the endemic presence of cutaneous leishmaniasis in the United States. The researchers aim to enhance nationwide case detection by raising awareness that the disease can no longer be regarded as exclusively acquired abroad.
During a presentation at the annual meeting of the American Society of Tropical Medicine and Hygiene, the CDC researchers revealed the results of their analysis of 2,133 tissue samples collected between 2005 and 2019. The majority of positive samples were from individuals who had traveled to countries where cutaneous leishmaniasis is endemic. Still, 86 people who were infected had not traveled outside the U.S.
Genetic sequencing distinguished two distinct "strains," with one primarily found in travelers and the other in non-travelers, indicating that local sand fly populations were spreading the disease. This "American strain" has been observed in samples dating back 18 years. While most samples with the local strain were from Texas, awareness in other states is low, making it challenging to assess its prevalence elsewhere. Raising awareness may lead to broader reporting requirements, helping monitor the disease's transmission better.
Sand flies, the disease's vectors, acquire the parasite by feeding on infected animals, which serve as disease reservoirs. The study does not address potential reservoirs, but knowledge that the disease exists in Southern Plains wood rats could aid prevention efforts. Climate change may also contribute to the disease's northward expansion as sand flies thrive in warm conditions. Future research will explore the parasite's genome to understand the Texas strain's differences from the Central American strain. While this research provides significant insights, further studies will examine potential clinical distinctions.
There is growing concern that a more severe form of the disease, visceral leishmaniasis, might gain a foothold in the U.S. With no evidence of its circulation yet, the focus is on imported dogs that could be bitten by local sand flies, transmitting the parasite to humans. A risk assessment tool to improve the screening of imported dogs was discussed at the conference.
In summary, cutaneous leishmaniasis is no longer confined to tropical regions and should be recognized as a shared concern on a global scale, demanding attention and research efforts.
