Leishmaniasis: Dogs on the Front Lines

Leishmaniasis is a serious chronic parasitic disease—one that is still not well understood—that affects humans as well as an increasing number of animal species. Dogs are particularly susceptible to this disease, which is primarily transmitted through sandfly bites. Here’s a look at this zoonosis caused by Leishmania infantum, which is spreading throughout Europe, particularly in France.   Transmitted by sandflies—biting insects similar to mosquitoes—leishmaniasis is a chronic parasitic infectious disease that persists for life in its host. While it remains rare in cats, it is affecting an increasing number of species, including canids—both wild (such as foxes) and domestic (such as dogs)—certain rodents, and humans. Leishmaniasis is classified by the World Health Organization as a “neglected disease that primarily affects people in tropical and subtropical regions, particularly those without access to adequate housing and sanitation.” In these areas, dogs serve as reservoirs for the protozoan responsible for the disease and play a role in the transmission cycle of this zoonotic disease. However, as the range of the insect vector expands due to warming, the Leishmania infantum parasite is spreading as well. Today, numerous cases are being reported in dogs across Europe, and France is no exception.  

Leishmaniasis, a serious and chronic disease in dogs

In an infected dog, leishmaniasis develops only if its immune response—both cellular and humoral—is inadequate. Certain dog breeds, thanks to specific immune characteristics, will show some resistance to the parasite (a Th1-type reaction in the Ibizan Hound, for example), whereas other breeds, on the contrary, will exhibit an ineffective or insufficiently protective immune response (a Th2-type response in the Boxer). Consequently, the clinical presentation of the disease in dogs is highly variable, with systemic, cutaneous-mucosal, ocular, and other signs. The skin lesions typically described are often ulcerative (dermatitis, alopecia, squamosis), but the dog’s general condition is also affected, with progressive weight loss, nosebleeds, excessive nail growth, and sometimes fever. Leishmania parasites infect the dog’s macrophages (in the skin, spleen, liver, or bone marrow) and thereby cause visceral involvement and immunopathological dysfunction. All organs and tissues containing macrophages can therefore be irreversibly affected (liver, spleen, lymph nodes, etc.). Depending on the course of the disease, the dog’s general condition may deteriorate rapidly. Death is inevitable sooner or later. Although some advances in treatment have emerged over the past decade, canine leishmaniasis remains a serious disease. No current treatment can completely eradicate all the parasites multiplying in the body, and most existing treatments provide only temporary relief. Recently, researchers have observed an increase in drug resistance to leishmaniasis treatments and treatment failures. To date, leishmaniasis therefore remains an incurable disease. Although certain drugs can reduce symptoms, the condition is chronic and relapses are common. When it comes to this disease, prevention is therefore better than cure.  

A Vaccine Against Leishmaniasis—But Not Just That

A vaccine against canine leishmaniasis was introduced in late 2011, followed by a second one in 2018. It is a recombinant vaccine, produced through genetic engineering (not tested in cats). A fragment of Leishmania (the Q protein) is injected and is recognized by the animal’s immune system. This protein is called “recombinant” because it is produced in a laboratory using special viruses to which a Leishmania infantum gene has been added so that they can produce large quantities of this Q protein. This same technology is used for many vaccines, including human flu vaccines and the COVID-19 vaccine produced by Sanofi, which targets the coronavirus’s spike protein. However, the vaccine does not provide 100% protection. Studies have shown that it is 72% effective and reduces the risk of developing leishmaniasis by a factor of ten. It is therefore advisable to follow additional preventive measures to reduce the risk of infection from vectors. The use of topical insecticides and avoiding walks at dusk are particularly recommended in certain areas and during periods when sandflies are active. While transmission between dogs remains possible, canine leishmaniasis is primarily transmitted through the bite of the vector insect. As with mosquitoes, only the female is active and bites in the evening and at night, thereby transmitting the disease. According to a study by Lancaster University, dogs infected with the Leishmania parasite may even alter their scent to make themselves more attractive to the parasites’ vectors, specifically female sandflies, with the aim of increasing the rate of bites and the likelihood of infection by the protozoan. The parasite is therefore capable of modulating its hosts’ scent to facilitate its natural transmission, which highlights the importance of dogs in maintaining the infection within canine—and thus human—populations. For while humans represent an ecological dead end for the parasite, domestic dogs serve as a reservoir for the infection. It is therefore particularly important to understand the dynamics of infection in canids to gain a more accurate picture of the disease’s epidemiology, in order to best adapt control and diagnostic strategies.  

The parasite’s range is expanding

Today, leishmaniasis is endemic in 102 countries, ranging from tropical to temperate regions. More than 350 million people worldwide are estimated to be at risk of the disease, with the incidence increasing by approximately 300,000 new cases per year. In total, 95% of severe cases of human leishmaniasis occur in 10 countries : Brazil, China, Ethiopia, India, Iraq, Kenya, Nepal, Somalia, South Sudan, and Sudan. In France, only about 20 cases are reported annually, but this does not exclude Europe from the zone of endemicity. Southern France and other regions of the Mediterranean basin (Italy, Spain, Portugal, and Greece) are particularly at risk of infection, which potentially threatens the 2.5 million European dogs and the 1 million French dogs living in these areas. While human cases remain rare in France, dogs bear a heavier burden from this disease. Of the one million dogs in areas of endemicity, 40,000 will develop the disease. The main French hotspots—located in Provence-Alpes-Côte d’Azur, Languedoc-Roussillon, Midi-Pyrénées, and Corsica—are on red alert from March through October, the peak activity period for sandflies. In these high-risk areas, approximately 2.5% of dogs develop clinical leishmaniasis, and these figures could rise in the coming years. Researchers are particularly concerned about the spread of the disease across the country. Climate change—characterized by high temperatures, heavy rainfall, and high humidity—is allowing sandflies to expand their range and increase in number. As a result, the infection is spreading rapidly to other departments, particularly in the Northwest, the Southwest, and along the Rhône Valley. In 2000, 17 departments were affected. By 2011, that number had risen to 21, and the number of new outbreaks increased by another 9% between 2011 and 2017. Means of transportation (cars, trains, planes) also facilitate the movement of sandflies and infected dogs over long distances, allowing Leishmania parasites to establish themselves in new habitats conducive to their development. Furthermore, scientists have shown that sandflies are not the only vectors of the parasite: ticks can also transmit leishmaniasis .   Around the world, both human and veterinary doctors are concerned about this expansion of the disease—both in terms of geographic reach and the range of vectors—especially in the current context of changing climate conditions. They emphasize the importance of prevention to protect against this zoonosis, which is serious and often fatal in dogs.   For more informationhttps ://vetitude.fr/leishmaniasis-canine-EFSA-la-caracterisation-de-la-maladie-et-prevention/ https://vetitude.fr/leishmaniose-canine-des-progres-en-termes-de-diagnostic-et-de-gestion-de-la-maladie-sur-le-terrain/ https://vetitude.fr/leishmaniose-canine-infection-non-vectorielle-chiens-uk/