JPC SYSTEMIC PATHOLOGY
Signalment (JPC # 2277382): Two-year-old male boxer
HISTORY: This dog was underweight and had hyperkeratosis of the planum nasale, ulceration of the oral mucocutaneous junction, and erythematous and edematous lesions on the feet.
HISTOPATHOLOGIC DESCRIPTION: Slide A: Diffusely infiltrating the dermis, extending to and elevating the mildly hyperkeratotic epidermis, surrounding and separating collagen bundles and adnexa, and multifocally extending deeply into the subcutis, are numerous protozoa-laden macrophages and plasma cells, fewer lymphocytes and eosinophils, and occasional multinucleated giant cells (Langhans type). Intrahistiocytic protozoal amastigotes are 2-3 um in diameter with clear cytoplasm and a single 1 um diameter basophilic nucleus. The superficial dermis is multifocally mildly expanded by edema and fibrin, and dermal collagen is multifocally smudged. There is moderate fibrosis within the deep dermis and subcutis. There is multifocal minimal orthokeratotic hyperkeratosis. Myocytes in the panniculus carnosus are often atrophied.
Slide B: Haired skin and subcutis (Giemsa): Within macrophages there are numerous 2-3 um diameter, deeply-purple amastigotes with clear cytoplasm and a 1 um diameter nucleus with a smaller adjacent, often perpendicular kinetoplast.
MORPHOLOGIC DIAGNOSIS: Haired skin and subcutis, site not specified: Dermatitis and panniculitis, granulomatous and plasmacytic, multifocal to coalescing, marked, with numerous intrahistiocytic amastigotes, boxer, canine.
ETIOLOGY: Leishmania sp.
ETIOLOGIC DIAGNOSIS: Cutaneous leishmaniasis
- Zoonotic disease with cutaneous and systemic manifestations caused by obligate intracellular diphasic protozoa
- Class: Kinetoplasta; Family: Trypanosomatidae
- L. infantum (L. chagasi) is the most common; also L. donovani, L. braziliensis
- Endemic in Mediterranean countries, parts of Africa, India, and Central and South America as well as Texas, Oklahoma, Michigan and Ohio
- Dogs are natural hosts and the primary domestic reservoir for human infection
- Three forms of the disease: Cutaneous, mucocutaneous, and visceral; dogs usually only have cutaneous and visceral manifestations (mimics histoplasmosis)
- Dogs with facial lesions due to leishmaniasis have a higher parasite load in the parotid lymph node when compared to dogs without facial lesions
- Leishmaniasis is often associated with other dermatoses such as opportunistic infections (bacterial, demodicosis), autoimmune disease or neoplasia; infection with Leishmania may induce immune dysfunction
- Leishmania amastigotes have been found within neoplastic cells of a fibrosarcoma, a T-cell lymphoma, a vaginal canine transmissible venereal tumor and an adrenocortical adenoma
- Other concomitant infections (possibly due to immunosuppression): Ehrlichia, Babesia, Anaplasma, Hepatozoon, Trypanosoma, Dirofilaria, Demodex, Sarcoptes, Spirocerca
- Also reports of concurrent autoimmune diseases (pemphigus foliaceus, SLE) and endocrinopathies (hypothyroidism)
PATHOGENESIS AND LIFE CYCLE:
- Flagellated leptomonad (promastigote) form proliferates via binary fission in the midgut of the female sandfly > regurgitation during sandfly feeding transfers promastigotes to the host skin > promastigotes are phagocytized by macrophages > multiply as non-flagellated amastigotes (leishmanial form) within phagolysosomes that separate them from host cell defense mechanisms > macrophages rupture (a mechanical consequence of proliferation) > freed amastigotes penetrate additional host cells and disseminate primarily through hemolymphatic system> sandfly takes a blood meal from infected host > ingests mononuclear cells containing amastigotes> transform into flagellated promastigotes
- Clinical signs may develop 3-months to 7-years after infection
- The outcome of infection is determined by the host immune response, genetic background and concurrent disease:
- Predominant cell-mediated immune response: Usually asymptomatic – resistance to infections (parasites cleared from the body by cell-mediated immune mechanisms) is TH1 dependent (IL-2, IFN-gamma, TNF-alpha)
- Alopecic form has fewer organisms & is associated with TH1 response
- Predominant humoral response: Usually symptomatic – susceptible to infection: TH2 (IL-4)
- B-cell activation> IgG predominates> inefficient killing with higher parasitic burden; +/- antigen:antibody complexes
- Nodular form has numerous macrophages containing large numbers of organisms and is associated with TH2 response
- Protective immunity is most likely mediated by TNF-a, IL-2 and IFN-y secreted by activated T cells to upregulate the anti-leischmanial activity of macrophages through nitric oxide production that is responsible for the parasite killing by apoptosis
- Infected macrophages are also lysed by CD8+ cytotoxic T cells in a histocompatibility complex-restricted process that can be suppressed in symptomatic dogs with a high parasitic load
- Type III hypersensitivity with immune complex deposition has historically been accepted as the primary mechanism of glomerulonephritis (and polyarthritis, vasculitis, uveitis), but there is new evidence that migration of CD4+ T-cells and increased expression of adhesion molecules such as ICAM-1 and P-selectin are also involved
- In cold weather, cryoglobulins may be generated, which precipitate in the blood vessels of the extremities; results in ischemic necrosis
- Clinical signs are due to generation of granulomatous inflammation (e.g. nodular dermatitis), autoantibodies (e.g. immune-mediated thrombocytopenia), antihistone antibodies (e.g. glomerulonephritis) and/or circulating immune complexes (e.g. arthritis)
- L. donovani requires actively transporting proton efflux pumps (LDH1A and LDHIB) to survive the acidic environment of macrophage phagolysosomal vacuoles and to maintain an electrogenic hydrogen gradient for nutrient uptake
- Bite of a female sandfly (Phlebotomous , Lutzomia sp.)
- Mechanical vectors (Rhipicephalus)
- Blood transfusions
- Vertical, in utero transmission
- Veneral transmission from infected males to healthy bitches is documented
TYPICAL CLINICAL FINDINGS:
- Non-painful, nonpruritic, generalized, dry exfoliative dermatitis with alopecia, recurrent oculonasal discharge, nasal crusting , epistaxis
- Systemic signs: Fever, lethargy, cachexia, poor body condition, rough haircoat, diarrhea, lymphadenomegaly, splenomegaly
- Most common laboratory finding is hyperproteinemia with hypergammaglobulinemia and hypoalbuminemia; also proteinuria, azotemia, elevated ALP and ALT, mild nonregenerative anemia, lymphopenia
- Urinary clusterin (a glycoprotein biomarker) has been shown to increase in dogs with renal damage due to Leishmania infection
- Skin lesions occur in over 80% of dogs with visceral involvement
- Skin lesions usually generalized instead of local
- Predisposed to generalized demodicosis due to cell-mediated immunodeficiency
TYPICAL GROSS FINDINGS:
- Alopecia, ulcers, nodules or pustules
- Exfoliative dermatitis with silvery-white, asbestos-like scales
- Most severe on muzzle, periorbital (“periocular lunettes”), and aural regions (where sandflies feed); nodular mucosal leishmaniasis is also reported
- Oncychogryphosis (hypertrophy and increased curvature of the claws) with mild to severe lichenoid and interface mononuclear dermatitis
- Generalized lymphadenopathy, hepatosplenomegaly
- Liver and spleen are enlarged and dark brown; liver contains numerous granulomas
- Kidneys usually normal contour but darker than normal
TYPICAL MICROSCOPIC FINDINGS:
- Amastigote stage found in macrophages (and occasionally other leukocytes, endothelial cells, fibroblasts or neoplastic cells): Round to oval, 2-4um in diameter with a rod-shaped kinetoplast (giant mitochondria) that is anectdotally reported to be oriented perpendicular to the nucleus
- Orthokeratotic hyperkeratosis and follicular keratosis, nodular to diffuse, superficial and deep pyogranulomatous to granulomatous to plasmacytic dermatitis
- Inflammatory pattern may be perivascular, perifollicular or interstitial composed of large, foamy macrophages with numerous organisms and few lymphocytes or large numbers of lymphocytes and plasma cells (due to effective CMI response)
- Ulcerative dermatitis with epidermal hyperplasia and neutrophil exocytosis at the border of the lesion; diffuse dermatitis with macrophages, lymphocytes, neutrophils and eosinophils in variable proportions
- Widespread plasmacytic, lymphocytic, or histiocytic inflammation, most severe in spleen, liver, lymph nodes
- Mesangioproliferative or membranoproliferative glomerulonephritis and interstitial nephritis are the most common renal manifestations of visceral leishmaniasis
- A recent study found that cardiac lesions, such as lymphoplasmacytic or granulomatous myocarditis (especially in the right atrium), myocardial necrosis and increased interstitial collagen, are prevalent in dogs with leishmaniasis (even if there are no clinical signs of cardiac disease)
- Mononuclear myositis, myonecrosis, fibrosis
- Ocular inflammation/organisms: Conjunctiva, limbus, ciliary body, iris, cornea, sclera
- Rare reports of meningoencephalitis, vasculitis, myelitis in the CNS
- Often within parasitophorous vacuole, amastigote is ovoid with a double membrane-bound nucleus
- Kinetoplast (mitochondrial complex) is often perpendicular to the nucleus
ADDITIONAL DIAGNOSTIC TESTS:
- Lymph node or bone marrow smears; biopsy; immunohistochemistry
- Amastigote load seems to increase in the preferential feeding sites of sandflies; biopsies of the skin of the muzzle may have highest parasite yield
- Giemsa: Stains cytoplasm blue, nucleus red, and kinetoplast purple
- Anti-Leishmania antibodies on serology (IFA, ELISA)
- Sarcoptic and demodectic mange, seborrhea, pemphigus foliaceus, SLE, bacterial infection, superficial necrolytic dermatitis, Zn-responsive dermatitis, neoplasia
- Trypanosoma cruzi (tissue phase/amastigote form): Anecdotally, kinetoplast tends to be oriented parallel to the nucleus
- Histoplasma capsulatum: 2-5um, intracellular, narrow-based budding; predominantly histiocytic inflammation
- Toxoplasma gondii: 2-6um tachyzoites; necrosis
- Neospora caninum: 4-7um tachyzoites
- Cryptococcus neoformans: 2-20um, mucicarmine-positive capsule
- Blastomyces dermatitidis: 10-20um, broad-based budding
- Sporothrix schenckii: 4-10um, oval to cigar shaped yeast
- Visceral leishmaniasis (caused by infantum, typically found in the Mediterranean) detected in foxhounds from a hunt club in New York in 1999; L. infantum antibody has since been detected in 69 kennels in North America
- It is not known why foxhounds seem more susceptible; other breeds in the area (as well as wild canids) did not seem to be infected
- No cases of transmission to humans have been documented from infected foxhounds
- Wild rodents: Reservoir host for cutaneous / mucocutaneous forms in humans
- Wild canids (foxes and jackals): Main reservoirs for visceral form in humans
- Cats, horses, mules, donkeys, and opossums: Susceptible but, considered accidental hosts – rare, lesions similar to those in dog; crusted, ulcerated nodules on the pinna, head and neck; granulomatous, lymphoplasmacytic dermatitis
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