A “potentially disfiguring” skin disease that once used to be found almost exclusively among international travelers returning to the United States has now been identified among Americans with no travel history, according to a study by the U.S. Centers for Disease Control and Prevention (CDC).
Leishmaniasis is a parasitic disease spread through the bite of sand flies. In the United States, the disease used to be detected among travelers from the tropics, subtropics, and southern Europe. But a recent study by scientists at the CDC has found infections among Americans who have not left the country, according to an Oct. 19 press release by the American Society of Tropical Medicine and Hygiene (ASTMH).
Leishmaniasis is caused by an infection from the Leishmania parasites. The CDC found that the Leishmania parasites causing infections among Americans with no travel history were distinct from “imported” cases.
The study, presented at an annual meeting of the ASTMH on Oct. 19, was the result of a “curious rise” of cutaneous leishmaniasis infections in America over the past decade.
Cutaneous leishmaniasis is the most common form of the disease and causes skin lesions that can persist for months and even years.
In the CDC study, while most of the cases involved individuals who traveled to countries where leishmaniasis is common, 86 patients had zero travel history.
An analysis of tissue samples from these 86 cases showed that the Leishmania strain infecting them had a “slightly different genetic fingerprint.”
This suggested that these infections were caused by an American variant, found to be spread by local sand fly populations.
Most of the infections of nontravelers were found among people living in Texas, said Mary Kamb from the division of parasitic diseases and malaria at the CDC’s National Center for Emerging and Zoonotic Infections.
Fatal Version of Infection
The rising number of cutaneous leishmaniasis cases in the United States is fueling concern that the fatal version of the infection, visceral leishmaniasis, could also gain a foothold among sand flies, mainly through imported dogs carrying the pathogen.Visceral leishmaniasis is the most fatal form of the infection. If left untreated, it leads to death in more than 95 percent of the infected cases, according to the World Health Organization.
Visceral leishmaniasis can affect internal organs and kills between 20,000 and 30,000 people worldwide annually.
There are no drugs to prevent the disease. Though some medications can be used to treat infections among humans, these drugs can result in serious side effects. There are vaccines for dogs, which are available in Brazil and Europe.
At the ASTMH annual meeting, another study was presented which covered the risks of visceral leishmaniasis spreading in the United States via imported dogs.
“Domestic dog imports from abroad, for breeding or via dog rescue organizations, have jumped sharply, to the point that about a million dogs enter the U.S. every year—most without receiving proper screening for infectious diseases,” said Christine Petersen, director of the Center for Emerging Infectious Diseases at the University of Iowa and co-author of the study.
Many of the dogs coming into the United States have lived in areas where Leishmania parasites are known to circulate among people and animals, she stated.
Ms. Petersen noted that infected dogs can be treated to cut down the number of parasites they carry. However, most of these dogs will relapse. As such, there will be a requirement for regular screening and treatment for infected dogs.
The Infection
According to the CDC, even though people infected with cutaneous leishmaniasis can develop lesions within weeks or months, they usually appear several years later. The lesions can evolve into ulcerative lesions and become painful if the ulcers become infected with bacteria or if the lesions take form near a joint.The skin sores usually heal on their own. However, this may take months or years. Plus, the sores leave ugly scars. A key danger is that some types of parasites may cause lesions inside the nose, mouth, or throat.
Manifestations of visceral leishmaniasis include fever, weight loss, swelling of the liver and the spleen beyond their normal size, and pancytopenia, a condition in which a person has low levels of red blood cells, white blood cells, and platelets.
In some parts of the world, infected humans are necessary to maintain transmission of the disease. In some regions, infected people are not necessary as the parasite can continually be transmitted through animal hosts.
As no drugs and vaccines exist to prevent infection, the CDC advises travelers to focus on protecting themselves from sand fly bites. “Personal protective measures include minimizing nocturnal outdoor activities, wearing protective clothing, and applying insect repellent to exposed skin.”
“Both forms of leishmaniasis cause tremendous suffering around the world and the fact that they now pose risks in the United States shows why we need to work together as a global community to fight infectious diseases wherever they exist,” said ASTMH President Daniel Bausch.
