Leishmania in dogs is a parasitic disease caused by protozoan parasites of the genus Leishmania, primarily Leishmania infantum. The condition affects various organs and systems, leading to a wide range of clinical signs. Dogs are considered the main reservoir host for this parasite.
How Dogs Contract Leishmania
Dogs primarily contract Leishmania through the bite of infected female phlebotomine sand flies. These tiny insects, active from dusk to dawn, act as vectors, transmitting the parasite from an infected host to a susceptible dog.
The sand fly becomes infected when it feeds on the blood of an infected mammal, ingesting the parasite in its amastigote form. Inside the sand fly, the parasites transform into flagellated promastigotes and multiply, migrating to the fly’s mouthparts. When an infected sand fly bites a dog, it injects these promastigotes into the dog’s skin, initiating the infection. While sand fly transmission is the primary route, direct dog-to-dog transmission through blood contamination, venereal contact, or transplacental transmission has also been reported, though it is less common.
Leishmania is widespread globally, particularly in tropical, subtropical, and Mediterranean regions, including Southern and Eastern Europe, South America, and Central and Southwest Asia. Environmental factors like temperature and moisture play a role, as sand flies thrive in warmer, humid conditions and often reside near animal shelters or in crevices like dry stone walls. The disease is expanding into new areas, including parts of the Northern Hemisphere, possibly due to climate change and the movement of infected dogs.
Recognizing Leishmania Symptoms
Leishmania in dogs presents with a wide array of clinical signs, making early recognition challenging. Symptoms can vary greatly depending on the severity of the infection and which organs are affected. Some dogs may remain asymptomatic for months or even years after infection.
Common skin manifestations, affecting 80-90% of symptomatic dogs, include exfoliative dermatitis, characterized by dry, flaky skin, often with hair loss (alopecia), particularly around the eyes and muzzle, sometimes forming a “butterfly sign.” Ulcerative lesions can also develop, especially over bony prominences like the carpal and tarsal regions. Hardening and thickening of the muzzle and footpads, known as hyperkeratosis, along with hard lumps or nodules on the skin, are also observed.
Beyond skin issues, dogs may exhibit other general signs of illness, such as weight loss, muscle atrophy, and lethargy. Enlarged lymph nodes (lymphadenopathy) are a frequent finding, along with an enlarged spleen (splenomegaly) and liver (hepatomegaly). Ocular signs can include blepharitis (inflammation of the eyelids), conjunctivitis, and keratoconjunctivitis, which might involve dry eyes.
Unusual nail overgrowth and abnormal curvature, termed onychogryphosis, occurs in some cases. Other potential symptoms include nosebleeds (epistaxis), increased thirst and urination (polyuria/polydipsia), chronic diarrhea, and lameness due to joint, muscle, or bone lesions. In advanced stages, Leishmania can lead to severe systemic involvement, most notably kidney problems, which can be life-threatening if left untreated.
Diagnosing and Treating Leishmania
Diagnosing Leishmania in dogs involves clinical suspicion, especially in endemic areas, and laboratory testing to confirm the presence of the parasite or antibodies against it. Serological tests are commonly used to detect antibodies in the blood, with methods like Indirect Immunofluorescence Antibody Test (IFAT) and Enzyme-Linked Immunosorbent Assay (ELISA) being widely employed. High antibody titers indicate active disease, while lower titers may suggest exposure or an early stage of infection.
Molecular techniques such as Polymerase Chain Reaction (PCR) are sensitive for detecting Leishmania DNA in various tissues. Samples for PCR can be taken from lymph nodes, bone marrow, spleen, skin lesions, or blood, with bone marrow and lymph nodes often yielding more accurate results due to higher parasite loads. Cytology or biopsy of affected tissues, such as lymph nodes or bone marrow, can also directly identify the amastigote form of the parasite within macrophages. This direct visualization provides a definitive diagnosis.
Treatment for canine Leishmania is typically a long-term management strategy rather than a complete cure, as the parasite often remains in the dog’s body even after symptoms improve. The primary goal of treatment is to alleviate clinical signs, improve the dog’s quality of life, and reduce the parasite load to minimize transmission risk. Common drug therapies often involve a combination of medications.
Meglumine antimoniate, administered subcutaneously, is a frequently used antimonial drug, often combined with allopurinol. Allopurinol, given orally, helps inhibit parasite replication and is usually continued for an extended period, often 6-12 months or longer, after the initial course of other medications. Miltefosine, an oral medication, is another effective option that can be used in combination with allopurinol. While both meglumine antimoniate and miltefosine combined with allopurinol can significantly improve clinical signs and reduce parasitic load, studies suggest meglumine antimoniate may lead to more stable long-term outcomes.
Regular monitoring is important during and after treatment, involving physical examinations, complete blood counts, biochemical profiles, urinalysis, and serological tests every 3-6 months. This allows veterinarians to assess treatment efficacy, detect potential side effects like kidney issues or xanthine urolithiasis from allopurinol, and identify any disease relapses. Relapses can occur when treatment is discontinued, requiring ongoing management.
Preventing Leishmania Infection
Preventing Leishmania infection in dogs focuses on minimizing exposure to infected sand flies, particularly in endemic regions.
Topical Insecticides
One strategy involves using topical insecticides with repellent activity against sand flies. These products include spot-on formulations containing permethrin or other synthetic pyrethroids, which can offer protection for 3-4 weeks. For dogs traveling to endemic areas, these spot-ons should be applied at least two days before exposure.
Insecticidal Collars
Deltamethrin-impregnated collars are an effective preventive measure, providing protection against sand fly bites for up to 6-12 months. Flumethrin-containing collars also offer proven repellent efficacy for up to 8 months. Apply these collars at least 1-2 weeks before potential exposure to allow the active ingredients to spread. These insecticidal collars and spot-ons work by repelling sand flies and, in some cases, killing them upon contact, reducing transmission risk.
Limiting Exposure
Limiting a dog’s exposure to sand flies during their peak activity hours is also beneficial. Sand flies are most active from dusk to dawn, so keeping dogs indoors during these times can reduce the risk of bites. Using fine-mesh screens on windows and doors can also create a physical barrier to prevent sand flies from entering living spaces. In areas with sand fly activity, these measures should be maintained throughout the period of potential exposure.
Vaccination
Vaccination is a component of a comprehensive prevention strategy, especially for dogs living in or traveling to endemic areas. While current vaccines may not entirely prevent infection, they are designed to reduce the risk of developing clinical disease and can help lower the parasitic load in infected animals, potentially limiting transmission to other dogs and humans. A multimodal approach combining topical insecticides with vaccination is considered effective to protect dogs against both infection and the development of severe disease.