Objectives Leishmaniosis is a vector-borne disease and in European countries is caused by Leishmania infantum. Cats are considered secondary reservoirs of the infection in endemic areas. The objective of this retrospective study is to describe the clinical findings, diagnosis, treatment and outcome of feline leishmaniosis (FeL) in 16 cats in Spain. Methods Medical records of cats diagnosed with leishmaniosis were retrospectively reviewed for cases that met the following inclusion criteria: identification of Leishmania organisms and/or DNA on cytological and/or histological specimens and/or a high anti- Leishmania antibody titre, compatible clinical findings and pathological abnormalities. Results Sixteen cats met the inclusion criteria, all of which were living in areas endemic for canine leishmaniosis. Systemic signs were present in 11 cases (68.8%). The most common clinical signs on presentation included cutaneous lesions in 12 cats (75%), ocular disease in six cats (37.5%) and anorexia in six cats (37.5%). A polyclonal gammopathy was noted in 12 cats (85.7%). Non-regenerative anaemia and renal abnormalities were present in six (37.5%) and five patients (31.3%), respectively. In nine cats (56.3%), immunosuppressive conditions/comorbidities were identified. The diagnosis was made in eight of the cats (50%) by cytology, but a combination of diagnostic tests was needed for definitive diagnosis in the remaining patients. Twelve cats (75%) were treated specifically for leishmaniosis. Five of the 12 cats (41.7%) did not improve with treatment. The median survival time in the group of patients treated specifically for leishmaniosis was 17 months. Median survival of patients treated with concomitant diseases was 13 months vs 41 months in those without, although this was not statistically significant ( P = 0.557). Conclusions and relevance Presentation of FeL appears to be similar to canine leishmaniosis but with some specific features: ulcerative and nodular skin lesions are the predominant cutaneous signs; cats with immunosuppressive conditions or co-existing diseases were more commonly present than typically seen in dogs (mainly feline immunodeficiency virus). A combination of diagnostic tests may be needed for definitive diagnosis.

Four dogs infected with Leishmania had proliferative lesions on the mucosae of the penis, tongue, oral cavity, prepuce, or nose. These mucosal, nodular lesions produced by parasites of the genus Leishmania have not been described previously in the dog. Leishmaniasis should be considered in the differential diagnosis of tumor-like lesions of mucous membranes.

This study demonstrates that urolithiasis and renal mineralisation can occur in dogs receiving allopurinol therapy. Dogs receiving therapy should be monitored for the development of urinary adverse effects from the beginning of treatment.

One dog with visceral leishmaniasis associated with monoclonal gammopathy is described. Most dogs with visceral leishmaniasis present with hyperproteinemia due to a polyclonal gammopathy, but the possibility of monoclonal gammopathy must be considered. Because dogs accompany their owners when they travel, the diagnosis of leishmaniasis should be considered if an animal with monoclonal gammopathy has visited an area where the disease is endemic. The observation of Leishmania in the macrophages of a bone marrow, lymph node smear, or skin biopsy specimen is diagnostic.

Visceral leishmaniasis with glomerulonephritis and nephrotic syndrome was diagnosed in a six‐year‐old dog presented with thromboembolic manifestations. A blood coagulation test indicated low levels of antithrombin III, prolonged partial thromboplastin time, hypofibrinogenaemia, an increase in fibrin degradation products and decreased plasminogenic activity. These results confirmed the diagnosis of thrombosis induced by glomerulonephritis, accompanied by secondary fibrinolysis. Bone marrow aspiration revealed an abundance of parasites of the genus Leishmania. Histopathology confirmed the presence of membranous glomerulonephritis due to Leishmania species parasites, as well as the presence of thrombosis in the aorta, iliac arteries, vena cava and femoral veni.