Dogs are primary host of flesh-eating parasitic disease called leishmaniasis

The Centers for Disease Control and Prevention (CDC) has recently highlighted an alarming development. A tropical disease called leishmaniasis, once associated with Americans returning from overseas trips, now has a unique strain in the United States. 

Distinct genetic fingerprint 

“There have been previous indications of local transmission based on a small number of case reports, but now, for the first time, we have a distinct genetic fingerprint from a relatively large cluster, providing further evidence that leishmaniasis may be well-established in some parts of the United States,” said Dr. Mary Kamb, an expert in the Division of Parasitic Diseases and Malaria at CDC’s National Center for Emerging and Zoonotic Infections. 

“While most of these infections were in people living in Texas, sand flies that can transmit leishmaniasis are found in many parts of the country and especially in the southern United States.”

Sand flies and leishmaniasis

While sand flies are largely confined to tropical regions, they are expanding their range as temperatures rise. Climate change is predicted to expand the habitats of sand flies further north and increase the reach of leishmaniasis, which affects humans as well as other mammals like woodrats.

As the evidence of cutaneous leishmaniasis in American sandfly populations grows, there’s heightened concern about a more severe form of this disease surfacing in the country. 

Dogs are the primary host

The experts report that the Leishmania parasite could go undetected in dogs that are brought into the United States. Currently, the country lacks sufficient screening measures for this parasite.

“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,” explained Dr. Christine Petersen, director of the Center for Emerging Infectious Diseases at the University of Iowa. Petersen.

“Dogs are the primary host for this disease, and there are dogs now regularly coming into the U.S. that have lived in areas where Leishmania parasites circulate in animals and people.”

“That’s why we need a better system in the United States for guarding against the risk of introducing Leishmania infantum, one of the world’s deadliest tropical parasites, into U.S. sand fly populations.”

New parasitic strain of leishmaniasis

The findings from the CDC show that the disease, specifically the milder form known as cutaneous leishmaniasis, has evolved from a slightly different American parasitic strain. The researchers found that this strain differs from the Leishmania mexicana typically found in Mexico and Central America.

The disease manifests as skin ulcers, which may appear weeks or even months after a sandfly bite. These ulcers can leave lasting scars that, in low-income nations, often come with a societal stigma.

Dr. Kamb said that in Texas there is growing awareness of leishmaniasis as a potential diagnosis for skin lesions – in part due to a history of cases in people returning from Mexico, but also due to increasing recognition of the possibility of locally acquired cases.

The World Health Organization has estimated that nearly a million people contract cutaneous leishmaniasis annually, mainly in warmer regions like the Mediterranean, the Middle East, and Latin America.

Focus of the study

The CDC recently presented its research at the American Society of Tropical Medicine and Hygiene’s annual conference in Chicago. The study spanned cases sent to CDC labs for testing between 2005 to 2019. Out of the over 2,000 cases, 86 of the individuals had not traveled overseas before contracting the disease. 

Dr. Bridget McIlwee, while training in Texas, encountered a patient with no travel history who had contracted leishmaniasis. In a 2018 study, she discovered that a significant percentage of the cases in Texas over a decade had patients without a history of international travel in the previous 10 years. 

However, very few of these diagnosed cases were reported to health officials, emphasizing the need for a national reporting mechanism.

Visceral leishmaniasis

A major revelation from the study is the role of dogs in transmitting the disease. Visceral leishmaniasis, a more severe form, can spread within local insect populations from imported dogs. 

Also transmitted through sandfly bites, Visceral leishmaniasis is associated with a related parasite (Leishmania infantum). This disease impacts the organs and kills thousands of people each year in regions where the parasite thrives.

Study implications 

While there is no human vaccine for leishmaniasis, dog vaccines are accessible in Europe and Brazil. The aim is to strengthen screenings at ports of entry.

Dr. Vitaliano Cama is a senior advisor with CDC’s Division of Parasitic Diseases and Malaria who was closely involved with the study. 

“A number of factors might be contributing to the increasing number of cutaneous leishmaniasis cases sent to CDC for testing,” said Dr. Cama. 

“Among these is the speculation that that changes in climate conditions may lead to suitable environments for sand fly survival and reproduction, and that could enable the transmission of leishmaniasis to emerge in new areas.” 

“There are still a lot of questions about where this disease is going and why.”

The research, led by CDC scientist Marcos de Almeida, is published in the American Journal of Tropical Medicine and Hygiene. 

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