Leishmaniasis
Pathogen
Leishmania infantum -protozoa
Vector
Sandflies (Phlebotomus-genus)
Geographical distribution
The distribution of Leishmania infantum mirrors that of Phlebotomus sandflies, and they are found indigenously in countries such as Portugal, Spain, southern France, Italy and Romania. The sandflies that act as vectors are most active during twilight and live very locally in the area where they hatch. In northern Europe, including Finland, leishmaniasis has been observed in imported dogs, with isolated cases reported where Leishmania has been transmitted between dogs without a vector.
Transmission
Leishmania parasites multiply in the white blood cells (macrophages) of dogs by binary fission. Afterward, the host cells burst, allowing the Leishmania parasites to infect new white blood cells. Sandflies ingest these forms, known as amastigotes, into their digestive tract during a blood meal. Once inside the sandfly's digestive system, the amastigotes are released from the macrophages, undergo a series of transformations, replicate, and develop into flagellated extracellular promastigotes. These infectious forms are transmitted to dogs (or cats or other mammals) via the saliva of the female sandfly during its next feeding. The development of Leishmania within the vector (the sandfly) is temperature-dependent, taking 7–14 days when the temperature exceeds 18°C. Leishmania infantum can also be transmitted through bodily fluids during bites, directly from mother to offspring, or from an infected male to a healthy female during mating.
Symptoms
The clinical presentation of leishmaniasis is divided into three forms: cutaneous (skin-related), mucocutaneous (mucous membrane-related), and visceral (affecting internal organs). In dogs, both the cutaneous and visceral forms are commonly observed. The dog’s immune system level prior to infection significantly influences whether the disease develops, remains subclinical (latent), or progresses to a clinical, symptomatic disease. Breed and genetic background have also been shown to impact susceptibility to infection. Immunosuppressive medications or concurrent illnesses can trigger the clinical symptoms of latent leishmaniasis. Symptoms typically appear 3–7 months after infection, and the prevalence of leishmaniasis is highest in dogs under 3 years and over 8 years of age.
Clinical symptoms of leishmaniasis are highly variable. The most common findings are skin lesions, various eye diseases, and locally or generally enlarged lymph nodes. More than half of dogs with clinical symptoms exhibit skin changes, such as scaling and hair loss, either across the entire body or localized to the head, ears, and limbs. Other skin-related symptoms may include localized or multi-localized skin infections.
The most common clinical symptoms of the visceral form are weight loss, reduced exercise tolerance, and increased drinking and urination. Some dogs lose weight despite having a good appetite. Nosebleeds may also be associated with leishmaniasis. A sudden worsening of the disease is often linked to chronic kidney inflammation, and chronic kidney failure is considered the most common cause of death in dogs with leishmaniasis.
Prevention
Protecting pets from sandflies is most effective by avoiding outdoor activities during twilight hours and using sandfly-repellent products (e.g., Scalibor and Seresto collars, Vectra 3D, and Bayvantic spot-on solutions). Vaccines are available against Leishmania, but they are not accessible in Finland. The vaccine does not prevent infection but alleviates the symptoms of the disease. The first dose can be given at 6 months of age (a primary series of 1–3 doses depending on the vaccine), followed by annual boosters. When traveling to leishmania-endemic areas for an extended period, vaccinating the dog at a local veterinarian is advisable. A blood test is usually conducted before vaccination to confirm that the dog is not already infected with Leishmania.
There are no vaccines available for cats, so protection relies solely on using sandfly-repellent products. Note that among the products mentioned above, only Seresto is safe for use on cats.
Lähteet:
ESCCAP 2019 (European Scientific Counsel Companion Animal Parasites). Guideline 05 Control of Vector-Borne Diseases in Dogs and Cats, Third Edition.
Karkamo V, Kaistinen A, Näreaho A, Dillard K, Vainio-Siukola K, Vidgrén G, Tuoresmäki N, Anttila M. The first autochthonous non-vector-borne transmission of canine leishmaniosis in the Nordic countries. Acta Veterinaria Scandinavia 2014, 56:84
Saari S, Näreaho A, Nikander S. Canine parasites and parasitic diseases. 1.p. eBook, London, United Kingdom 2019
Solano-Gallego L, Miró G, Koutinas A, Cardoso L, Grazia Pennisi M, Ferrer L, Bourdeau P, Oliva G, Baneth G. LeishVet quidelines for the practical management of canine leishmaniosis. Parasites & Vectors 2011, 4:86
Sykes J, Greene C. Infectious diseases of the dog and cat. 4.p. Elsevier Sounders, St. Louis, Missouri, Yhdysvallat 2011