Leishmaniosis in Dogs (Canis) | Vetlexicon
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Leishmaniosis

ISSN 2398-2942

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Synonym(s): Leishmaniasis, CanL; Kala-azar (in its visceral form in humans

Introduction

  • Serious zoonotic protozoal infection of man and animals.
  • Cause: intracellular protozoan parasites of the genus Leishmania Leishmania infantum.
  • Transmission is predominantly by sand-fly bites Phlebotomine sandfly.
  • Signs: include alopecia, exfoliative dermatitis, nodular skin lesions, generalized lymphadenopathy, progressive weight loss, muscle atrophy, exercise intolerance, lethargy, decreased appetite, polyuria, polydipsia, ocular lesions.
  • Diagnosis: demonstration of the parasite in macrophages in lymph node or bone marrow aspirates Cytology: lymph node aspirate Bone marrow aspiration and serology or PCR Leishmania infantum: blood smear.
  • Prognosis: relapses usually occur. Print off the owner factsheet on Leishmaniosis Leishmaniosis to give to your client.

Presenting signs

Geographic incidence

  • Infection rates can reach 40% in endemic areas.
  • Infection endemic in areas between 40°N and 40°S in Africa, South America, Europe and Asia. Outside these areas, occurs in dogs that have traveled through or are imported from endemic areas.
  • Countries adjoining the Mediterranean, including Southern Europe (Spain, Portugal, France, Italy and Greece) and North Africa, Southern Russia, Central and South America.
  • Reports from the Netherlands suggest that up to 0.23% of dogs taken on vacation to the countries bordering the Mediterranean and Portugal return with leishmaniosis Pet Travel Scheme.
  • South-East USA, Asia (including India, Central Asia, China) and Africa south of the Sahara.
  • Increasing prevalence in non-traveled Foxhounds resident in previously non-endemic areas of North America and Canada. Not present in Australia.

Age predisposition

  • Dogs >1 years old.

Breed/Species predisposition

Public health considerations

  • Leishmania infantum Leishmania infantum and L. braziliensis are Human Hazard Group 3 pathogens.
  • L. tropica is a Human Hazard Group 2 pathogen.
  • Dogs and foxes form the main reservoir of infection in the Mediterranean area and in South America.
  • There appears to be no animal reservoir in India and coastal China whereas elsewhere in Asia the situation is similar to that in the Mediterranean area.
  • People are infected by the bites of infected sandflies Phlebotomine sandfly or by direct contact with infected animals.

Pathogenesis

Etiology

  • The main species infecting dogs is Leishmania infantum Leishmania infantumL. chagasi is a synonym for the same organism occurring in Central America. L. infantum has been found in dogs infected in the US.
  • Other species causing clinical disease in dogs are:
    • L. tropica causes cutaneous/mucocutaneous leishmaniosis (with cutaneous nodules and ulcers) in dogs in the Mediterranean area, Middle East and central Asia.
    • L. braziliensis causes cutaneous form in dogs in South America.
  • Dogs can be infected with other species of Leishmania but clinical disease does not occur.

Predisposing factors

General

  • Exposure to sandfly challenge.
  • High prevalence of infected animals.
  • Virulence of parasite strain.
  • Immunocompromised host.
  • Infected blood transfusions, needle contamination.

Pathophysiology

  • The parasite occurs in the amastigote form Leishmania infantum: amastigotes in the vertebrate host and in the promastigote form Leishmania infantum: promastigote in the sandfly vector and on culture.
  • The promastigotes inoculated by the sandfly vector enter macrophages where they transform into amastigotes before multiplying.
  • Infection and multiplication in cells of the monocyte/macrophage line leads to generalized lymphadenopathy and splenomegaly.
  • Immune complex formation contributes to the pathological changes.
  • Visceral leishmaniosis is a chronic wasting disease in the dog.
  • While dogs can be infected in any area where leishmaniosis occurs, they appear to act as a reservoir host principally in the Mediterranean area, Central Asia, parts of China, Sudan and South America.
  • Sandflies of the genus Phlebotomus Phlebotomine sandfly are the principal vectors in Europe; Lutzomyia species are the principal vectors in South and Central America. Sandfly species have very specific bio-climatic requirements. They are not restricted to the coastal fringes but are prevalent in rural wooded areas. In South America, sandfly species have adapted to peri-urban environments.
  • Culicoides species have been suggested as possible vectors.
  • Female sandflies feeding on an infected dog ingest amastigote Leishmania infantum: amastigotes laden macrophages → promastigotes form Leishmania infantum: promastigote in the insect's gut and migrate to the proboscis.
  • Promastigotes (flagellated forms) are inoculated into the host, enter macrophages and transform into amastigotes.
  • They multiply in and disrupt the macrophages with the released parasite infecting other cells → lymphoreticular hyperplasia with generalized lymphadenopathy and splenomegaly.
  • Visceral leishmaniosis is associated with dissemination of the amastigotes throughout the reticuloendothelial system - particularly the spleen, bone marrow, lymph nodes, liver and small intestine.
  • The parasite has been detected in all organs and tissues.
  • Infection induces a cytokine response which results in over-exuberant antibody production. Excessive immune-complex formation results in the development of lesions in the kidneys, joints, eye and blood vessel walls. Auto-antibody production may result in Coombs positive hemolytic anemia Direct Coombs' test Anemia: immune mediated hemolytic and positive antinulclear antibody testing. A moderate to severe glomerulonephritis Glomerulonephritis with massive protein loss Protein-losing enteropathy is commonly present and renal failure is often the cause of death Kidney: chronic kidney disease (CKD). Immune complex desposition in joints produces a polyarthritis. Increased gammaglobulin levels may be associated with a monoclonal or biclonal spike Serum protein electrophoresis.
  • Local proliferation of the parasite in macrophages causes granulomatous lesions in many organ systems including the skin, joints and gastrointestinal system. Granulomatous dermatits in associated with scaling, alopecia Skin: alopecia - overview , ulceration and nodule formation.
  • Co-infection particularly with other arthropod borne infections such as Ehrlichia canis Ehrlichia canis may complicate the pathogenesis.
  • Direct transmission of amastigotes through blood transfusions/needle contamination.

Timecourse

  • Incubation period: 3 months-several years.
  • Clinical signs could appear in animals imported from endemic areas after leaving quarantine.

Epidemiology

  • The sandfly vectors are most active at dawn and dusk.
  • Sandflies have a limited flight range.
  • Transmission can occur by blood transfusion.

Diagnosis

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Treatment

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Prevention

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