The Disease


Canine Leishmaniasis

(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.
• Transmission is predominantly by sand-fly bites.
• Signs : the visceral form is more common in the dog and 90% of dogs have cutaneous or mucocutaneous involvement.
• Specific signs include chronic weight loss, lymphadenopathy, alopecia and exfoliative dermatitis, nodular skin lesions, chronic renal failure and epistaxis.
• Diagnosis : demonstration of the parasite in macrophages in lymph node or bone marrow aspirates and serology or PCR.
• Prognosis : relapses usually occur.
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Presenting signs

• Cutaneous lesions – periocular alopecia extends to nasal skin and ears. Exfoliative dermatitis, nodular dermatitis, ulcerative dermatitis generalized particularly involving extremities. Claw abnormalities.
• Progressive weight loss.
• Anemia.
• Hyperkeratosis.
• Polyarthritis.
• Lethargy.
• Polydipsia /polyuria (renal failure).
• Ulcerative and nodular dermatitis.
• Diarrhea.
• Abdominal distension.
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Acute presentation

• Epistaxis.
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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, 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 leishmaniasis.
• South-East USA, Asia (including India, Central Asia, China) and reported in Senegal, the Gambia and Sudan.
• Increasing prevalence in non-traveled Foxhounds resident in previously non-endemic areas of North America and Canada. Not present in Australia.
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Age predisposition

• Dogs>1 years old.
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Breed predisposition

  • Any dog, but the following are predisposed:
    • Dobermann Pinschers.
    • o German Shepherd Dogs.
  • Foxhounds in USA?

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Public Health considerations

• Leishmania infantum and L. braziliensis are Human Hazard Group 3 pathogens.
• L. tropicais 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 or by direct contact with infected animals.
Pathogenesis Top

Etiology

  • The main species infecting dogs is Leishmania infantum . L. chagasiis a synonym for the same organism occurring in Latin America. L. infantumhas been found in dogs infected in the US.
  • Other species causing clinical disease in dogs are:
    • L. tropica causes cutaneous/mucocutaneous leishmaniasis (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.

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Predisposing factors

General
• Exposure to sandfly challenge.
• High prevalence of infected animals.
• Virulence of parasite strain.
• Immunocompromised host.
• Infected blood transfusions, needle contamination.
Specific
• Being bitten by infected sandfly vectors.

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Pathophysiology

• The parasite occurs in the amastigote form in the vertebrate host and in the promastigote form 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 leishmaniasis is a chronic wasting disease in the dog.
• While dogs can be infected in any area where leishmaniasis 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 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 laden macrophages promastigotes form in the insect’s gut and after massive multiplication, are deposited into the skin of the next animal to be bitten.
• 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 leishmaniasis 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 and positive antinulclear antibody testing. A moderate to severe glomerulonephritis with massive protein loss is commonly present and renal failure is often the cause of death . Immune complex desposition in joints produces a polyarthritis. Increased gammaglobulin levels may be associated with a monoclonal or biclonal spike .
• 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 , ulceration and nodule formation.
• Co-infection particularly with other arthropod borne infections such as Ehrlichia canis may complicate the pathogenesis.
• Direct transmission of amastigotes through blood transfusions/needle contamination.
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Timecourse (incubation, duration)

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

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

Diagnosis

Presenting problems
• History of exposure to sandflies in an endemic area.
• Weight loss.
• Lymphadenopathy.
• Skin lesions – facial and pinnal exfoliative dermatitis .
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Client history

• Exposure to sandfly bites in an endemic area (especially the Mediterranean area).
• Progressive weight loss despite normal appetite.
• Exercise intolerance/lethargy.
• Non-pruritic dermatitis that is unresponsive to conventional treatment.
• Stiffness/lameness.
• Chronic inflammatory eye disease including conjunctivitis.
• Polydipsia/polyuria.
• Vomiting
• Diarrhea
• Decreased appetite
• Abdominal distension
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Clinical signs

  • Splenomegaly
  • Mild-moderate lymphadenopathy
  • Anemia
  • Exfoliative dermatitis, periocular alopecia and scaling
  • Ulcerative nodular dermatitis especially involving the nose, lips, eyelids, tips of the ears, tail and feet.
  • Onychogryposis
  • Muscular atrophy
  • Ocular lesions:
    • Keratitis
    • Uveitis
    • Chorioretinitis
    • Corneal edema
    • Glaucoma
  • Epistaxis
  • Polyarthritis – intermittent lameness.
  • Pneumonia
  • Neurological abnormalities

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Diagnostic investigation

    Cytopathology

    • Lymph node and bone marrow aspirates can be stained with Giemsa or May-Grunwald for examination for the presence of the intracellular or free amastigotes . Combined bone marrow and lymph node examination identifies about 90% of infected dogs.

    Histopathology

    • Demonstration of the organism in Giemsa or Leishman stained biopsies of skin lymph nodes or bone marrow. The amastigotes are oval shaped, about the size of a blood platelet (1-3 x 2-6 um), with reddish-purple nuclei at right angles to the rod shaped, dark staining kinetoplast .
    • They are found in macrophages or extracellular, especially in lymph node biopsies.

    Other

    • Culture of the organism from bone marrow or lymph node biopsies. Strains appear similar morphologically but may be differentiated by their behavior in culture (in modified Schneider’s Drosophila insect medium), their position in the sandfly, and the lesions they produce in hamsters.
    • More precise differentiation can be obtained by isoenzyme electrophoresis, reactivity with monoclonal antibodies and hybridisation with kinetoplast DNA .

    Serology

    • Detection of specific serum antibodies using an Indirect Fluorescent Antibody Test or ELISA. Cross reactivity between Leishmania species and false negatives may occur.
    • Positive IFAT result indicates exposure to the infection and not necessarily active infection.

    Polymerase chain reaction analysis (PCR)

    • Detection of genus or species Leishmania DNA in blood, lymph node and bone marrow aspirates is indicative of active infection. PCR on peripheral blood is less sensitive (60-70%) when compared to bone marrow.

    Biochemistry

    • Hypergammaglobulinemia
    • Usually polyclonal gammopathy but monoclonal or biclonal spikes may occur.
    • Hypoalbuminemia may be due to protein loss in urine.

    Urinalysis

    • Moderate to severe proteinuria.

    Hematology

    • Thrombocytopenia may occur particularly with Ehrlichia canis infection.
    • Increased or decreased leukocyte numbers.
    • Anemia – may be non-regenerative in chronic renal disease. May be regenerative if immune-mediated hemolytic anemia is present.

    Other

    • Examination of synovial fluid from affected joints shows inflammatory response – increased numbers of non-degenerate neutrophils.

    Radiography

    • Thoracic radiographs may demonstrate pneumonia in systemic cases.
    • Hepatosplenomegaly apparent on abdominal radiography.

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Confirmation of diagnosis

    Discriminatory Diagnostic features

    • History.
    • Clinical signs.
    • Cytopathology.
    • Serology.
    • PCR.

    Definitive Diagnostic features

    • Identification of the organism in tissues.
    • PCR.

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Gross autopsy findings

• Small localized cutaneous nodules.
• Enlargement of the spleen, liver and lymph nodes.
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Histopathology findings

• Granulomatous perifolliculitis and superficial and deep perivascular dermatitis.
• Large numbers of amastigotes in macrophages in the spleen, and other visceral organs.
• Glomerulonephritis and interstitial nephritis.
• Multifocal or diffuse plasmacytic infiltration of various organs/tissues including skin, kidneys, bone marrow, liver, intestines and conjunctiva and the presence of infected macrophages.
• Amyloidosis of liver and kidneys .
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Differential diagnosis

Co-infection with ehrlichiosis, hepatozoonosis and/or babesiosis may occur and further investigation of these infectious diseases is required if regenerative anemia and/or thrombocytopenia are major signs.
• Systemic lupus erythematosus .
• Immune-mediated polyarthritis , anemia , pnophthalmitis due to other causes.
• Other causes of non-pruritic exfoliative dermatitis and alopecia nutritional, endocrine, demodicosis, dermatophytosis, sebaceous adenitis .

Treatment

    Initial symptomatic treatment

    Zoonotic implications should be considered before treating.
    • Meglumine antimonate , 100 mg/kg IV or SQ q24h for up to 6 weeks.
    • Allopurinol 10-30 mg/kg/day PO for at least 6 months.
    • Sodium stibogluconate, 10-50 mg/kg IV, SQ q24h for 3-4 weeks.
    • Amphotericin B .
    • Ketoconazole .
    • Itraconozole (less toxic than ketoconazole).

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Standard treatment

• Combinations of Meglumine antimonate and allopurinol appear to give improved results in terms of clinical efficacy and incidence of clinical relapses while reducing the duration of meglumine therapy.
• One reported treatment regimen involved giving Meglumine antimonate 100mg/kg SC every 24 hours and Allopurinol 15 mg/kg PO BID for 1 month followed by Allopurinol alone for 8 months.
Side effects of the antimonials and Amphotericin B include nephrotoxicity.
Meglumine antimonate is the only drug licensed for the treatment of canine leishmaniasis in continental Europe.
• Meglumine antimonate , 100-200 mg/kg IV, SQ q24h for up to 6 weeks.
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Monitoring

• Relapses are common.
• Monitor closely at 3 monthly intervals after treatment.
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Subsequent management

    Prevention Control
    • Controlling sandflies is difficult, but there are certain steps that can be taken .
    • Insecticide sprays (especially Deltamethrin-based preparations) with residual activity can be effective .
    • Keep dogs indoors in the evenings and at night (sandflies are mainly active at night) – especially upstairs (sandflies have limited powers of flight).

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Prophylaxis

• No prophylactic drugs or vaccine available.
• Insecticide-impregnated collars can be effective.
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Group eradication

• Domestic dog reservoirs should be treated or destroyed.

Sequelae

    Prognosis
    • The prognosis for resolution of clinical signs is good in animals treated early.
    • Relapses following treatment are common.

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Expected response to treatment

• Resolution of clinical signs.

Sources

Publications(Refereed papers)
• Roze M (2005) Canine leishmaniasis. A spreading disease. Diagnosis and treatment. EJCAP 15 (1), 39-52.
• Tafuri W L et al (2004) An alternative immunohistochemical method for detecting Leishmania amastigotes in paraffin-embedded canine tissues. J Immunol Methods 292, 17-23.
• Lima W G et al (2004) Canine visceral leishmaniasis: a histopathological study of lymph nodes. Acta Trop 92 , 42-53.
• Moreno J & Alvar J (2004) Canine leishmaniasis: epidemiological risk and the experimental model. Trends Parasitol 18 , 399-405.
• Lamonthe J (2001) Activity of amphotericin B in lipid emulsion in the inital treatment of canine leishmaniasis. JSAP 42 , 170-175.
• Owens S D, Oakley D A, Marryott K et al (2001) Transmission of visceral leishmaniasis through blood transfusions from infected English Foxhounds to anemic dogs. JAVMA 219 , 1076-1083.
• Orndorff G R (2000) Canine visceral leishmaniasis in Sicily. Mil Med 165 (1), 29-32.
• Denerolle P & Bourdoiseau G (1999) Combination allopurinol and antimony treatment vs antimony alone and allopurinol alone in the treatment of canine leishmaniasis (96 cases). JVIM 13 (5), 413-415.
• Cavaliero T, Arnold P et al (1999) Clinical, serologic and parasitologic follow-up after long-term allopurinol therapy of dogs naturally infected with Leishmania infantum. JVIM 13 , 330-334.
• Bravo L, Franks L A & Brenneman K A (1993) Canine Leishmaniasis in the United States. Comp Cont Educ Pract Vet 15 , 699-708. (Comprehensive review.)
• Kontos V J (1993) Old World Canine Leishmaniasis. Comp Cont Educ Pract Vet 15 , 949-960. (Comprehensive review.)

Other sources of information

• Canine Leishmaniasis: an update. Proceedings of the International Canine Leishmaniasis Forum, Barcelona, Spain 1999. Edited by R Killick-Kendrick. Hoechst Roussel Veterinar GmbH, Wiesbaden, Germany.
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Vetstream contributor(s)

• Dr Gad Baneth DVM PhD, School of Veterinary Medicine, Hebrew University of Jerusalem, PO Box 12, Rehovot 76100, Israel.
• Dr Alex Morrow MVB BA PhD MRCVS , The Alexander Robertson Centre for Tropical Veterinary Medicine, Faculty of Veterinary Medicine, Royal (Dick) School of Veterinary Studies, Easter Bush Veterinary Centre, Near Roslin, Midlothian EH25 9RG, UK.
• Dr Lisa Moore DVM DipACVIM , Veterinary Medical Teaching Hospital, Kansas State University, 1800 Denison Avenue, Manhattan, KS 66506-5606, USA.
• Susan Shaw BVSc(Syd) MSc DipACVIM MRCVS , University of Bristol, Department of Clinical Veterinary Science, Division of Companion Animals, Langford, Bristol BS40 5DU, UK.
• Dr Bryn Tennant BVSc PhD CertVR MRCVS , Capital Diagnostics, Bush Estate, Penicuik, Midlothian EH26 0QE, UK.