Also called black fever, feline leishmaniasis (FeL) is a zoonotic disease caused by an intracellular protozoan parasite of Leishmania. There are two types of leishmaniasis, skin (cutaneous) and visceral. Cutaneous leishmaniasis is most common in cats. Visceral leishmaniasis can affect the liver, kidneys, spleen, eyes and bone marrow.
The disease is of particular significance because it is zoonotic, which means it can be spread from an infected animal to humans. It is less common in cats than it is in dogs, it is thought they have a natural resistance to the parasite.
Five species of Leishmaniasis have been identified in cats:
- Leishmania mexicana
- Leishmania venezuelensis
- Leishmania braziliensis
- Leishmania amazonensis
- Leishmania infantum
The first case of leishmania in cats was in 1912 in Algeria. Global distribution is Mexico, Central America, South America, southern Europe, some parts of Asia, Middle East and Africa. The only known Leishmania in Australia is L. australiensis which was isolated from a skin lesion of a group of captive red kangaroos in the Northern Territory. It has not been associated with human or domestic animal infection. It is believed that day-biting midges are responsible for transmission of L. australiensis.
The parasite is named after Lieutenant General Sir William Boog Leishman, a Scottish pathologist who discovered Leishmania donovani the causative agent of kala azar, an alternate term for visceral leishmaniasis.
Leishmaniasis is associated with poverty, poor housing and sanitary conditions, malnutrition and a weakened immune system in people. In symptomatic cats, it is often seen in those who are immunocompromised.
The parasite is transmitted to the cat when a female phlebotomine sandfly infected with flagellated extracellular promastigote forms of the parasite feeds on the blood of a host. The sandfly is most active during the summer months at dusk and dawn.
Once inside the cat, the promastigotes are consumed by macrophages (a type of white blood cell that engulfs pathogens) where they transform into amastigotes (protozoa without visible flagella or cillia) which multiply in the infected cells.
Cats can serve as reservoirs to the parasite, they do not exhibit symptoms, but carry the parasite which can be transmitted to other animals when the sand fly ingests blood containing the parasite from the affected cat.
The incubation period of leishmaniasis can range from two weeks to several years and can vary depending on the type (skin vs visceral). Most infected cats develop cutaneous leishmaniasis.
- Skin or mucocutaneous lesions (ulcers, crusting, nodular dermatitis, exfoliative), the nose, ears, and distal limbs are most commonly affected
- Enlarged lymph nodes
- Hyperkeratosis (excessive scaling and thickening of the skin along with loss of pigmentation)
- Symmetrical areas of hair loss (alopecia)
The most commonly affected organs include the kidneys, liver, and spleen. Common symptoms include:
- Loss of appetite
- Weight loss
- Enlarged spleen
- Exercise intolerance
- Increased thirst and urination due to kidney disease
- Ocular (eye) lesions
- Chronic gingivostomatitis
- Mucocutaneous ulcerative or nodular lesions
- Lameness due to lesions on bones, joints or muscles
- Abnormal nail growth
The veterinarian will perform a complete physical examination of the cat and obtain a medical history from you, including onset of symptoms and any recent travel your cat has undertaken. Diagnostic tests will be necessary to confirm the diagnosis. This can include the following:
Baseline tests: Biochemical profile, complete blood count and urinalysis. May reveal low red blood cells (anemia) and low platelets (thrombocytopenia), hyperproteinemia (increased protein in the bloodstream), hyperglobulinemia (high concentration of globulins) and hypoalbuminemia (low blood albumin levels) and an increase in liver enzymes.
Serology: Tests on blood serum to detect specific antibodies to the parasite. ELISA (enzyme-linked immunosorbent assay) is the most common method.
Polymerase chain reaction: This test magnifies a segment of DNA to create millions of copies to identify the pathogen from a sample (eye, skin, blood or other tissue).
Cytology: A smear taken from lesions which are evaluated under a microscope by a veterinary pathologist to detect amastigotes.
Histopathology: Detection of amastigotes in a tissue sample from the lymph nodes, spleen, skin, liver and bone marrow.
The most common drug used to treat leishmaniasis in cats is Allopurinol. This medication interrupts the protein synthesis of Leishmania. This is not a cure but can keep the parasites in remission. However, the cat will still be infected. Other drugs which may be used include Sodium stibogluconate, Meglumine antimoniate, Fluconazole, and Itraconazole.
Surgical removal of skin nodules or pinnectomy (surgical removal of the ear flap) where indicated.
Cats who are severely affected have a poor prognosis and euthanasia is usually the only option.
Keep cats indoors, especially during dusk and dawn and screen windows and doors to reduce the chances of sand flies entering the home.