A Parasitic Infection Spreading in the U.S. and Its Potential Dangers

A disfiguring parasitic infection, known as leishmaniasis, commonly found in the tropics, has now found a home in Texas and Oklahoma and is spreading in the U.S. Transmitted by tiny sand flies, the parasite, Leishmania mexicana, has also been detected in Maryland, Delaware, New Jersey, and Ohio.

According to a recent report from the Centers for Disease Control and Prevention, researchers discovered the presence of leishmania in 1,222 out of 2,100 skin samples examined. Alarmingly, 86 patients had no travel history, indicating that they acquired the infection within the U.S.

Different strains of leishmania cause varying types of disease. The L mexicana strain found in Texas and Oklahoma causes the mildest form, cutaneous leishmaniasis, which primarily affects the skin and usually requires no treatment. On the other hand, L brasiliensis causes mucocutaneous leishmaniasis, a more severe form encountered in Peru, which has traditionally been treated with an antimonial antibiotic called Pentostam, known for its side effects.

The most severe form of leishmaniasis occurs in the Middle East, Asia, and northern Africa. L donovani species causes kala-azar, a systemic disease that infects multiple organs in the body and can often be fatal.

Special genetic studies conducted in Texas have identified two distinct genotypes of L mexicana. One particular type, labeled as "CCC," was found in 94% of the non-travelers, suggesting the possible presence of the parasite in the region for an extended period.

Leishmaniasis spreads through the bites of sand flies. While wood rats are the normal hosts of sand flies in the U.S., there is debate about whether other wildlife species like armadillos or opossums could also serve as reservoir hosts. Additionally, dogs act as the main reservoir for the more severe visceral form of leishmaniasis. It is of concern that some dogs being imported into the U.S. from Southeast Asia as rescues may pose a potential risk for transmission.

Given the challenges of diagnosing leishmaniasis, it is crucial for physicians to be aware of the infection and consider it in their differential diagnosis, especially when patients present with skin lesions. The microscopic size of the parasites and the need for a specialized stain to identify them make diagnosis difficult. Uniform reporting requirements to the CDC are currently lacking, hindering efforts to track the frequency and spread of the infection. The potential impact of climate change and insecticide resistance on the spread of leishmaniasis also warrants careful monitoring.

As the U.S. faces the threat of this disfiguring parasitic infection, it is essential for healthcare professionals to take comprehensive exposure and travel histories from patients, maintain a high index of suspicion, and recognize that leishmaniasis can occur even in individuals without a history of international travel.