Leishmania Flashcards
What are the two forms of leishmania?
Amastigote - intracellular
Promastigote - infectious
Outline the transmission
Sandfly has a blood meal from an infected animal, acquires amastigote
This transforms to a promastigote and moves to mouth apparatus where it is injected into another animal
This infects the macrophage, goes into phagolysome where is is protected from the immune system
Transfers to an amastigote - multiplies, lyses macrophages when there are lots
other than sandflies, how else can it be transmitted?
In utero dog to bitch when mating poss dog to dog blood transfusion Possibly through other athropods
What are the most commonly affected systems and why
Infects macrophages so mostly reticulo-endothelial system
LN, liver, spleen, BM,
What is the preferred immune response?
TH-1 response
Activation of macrophages, B cells, cytotoxic lymphocytes
If this occurs the animal has no clinical signs and may even be able to clear the infection
If animal has TH-2 response (mostly ABs) then they get sick
Animals can switch between the two response - an infected dog may appear healthy and get sick later
What are susceptible genetic factors
Breed - GSD, Rottie, Cocker, Boxer all higher risk
Ibizan hound protected
2 peak age ranges - 2-4 then over 7
Outline the pathogensis
❖ Specific T-cell unresponsiveness and unprotective humoral responses allow the dissemination and multiplication of L. infantum in different tissues
❖ Continuous antigenic stimulation → proliferation of B cells → excess antibody production → chronic hypergammaglobulinaemia → formation and deposit of immune complexes (IC)
❖ Glomerulonephritis, vasculitis, polyarthritis, uveitis, meningitis, Ab against RBC and PLT
❖ Glomerulonephritis is the leading cause of death: Membranous/membranoproliferative/minimal change glomerulonephritis (100%), interstitial nephritis (96%),
tubular nephropathy (78%), amyloidosis
❖ Systemic vasculitis → areas of ischemia → visceral and cutaneous necrosis and, rarely CNS involvement
❖ Paraglobulinaemia → interference with fibrin polimeration (+ uraemia) → thrombocytopathy → increased bleeding tendency (+/- nasal ulcers, +/-hypertension →
epistaxis)
❖ Cryoglobulins → ischaemic necrosis to extremities exposed to cold
WHat ocular changes may be seen?
Uveitis
Glaucoma
Conjunctivitis
Blepharitis
What are the typicl clin path changes noted
High globulin Anaemia 20% coombs or ANA +ve Low albumin Low Alb: glob ratio Proteinuria Thrombocytopaenia Leucopaenia/ leukocytosis
How can cytology/ histology be used to dx Leishmania?
❖ Cytology - (sens. 8-93%; spec. 100%) • Bone marrow • Lymph node • Spleen • Buffy coat • Cutaneous lesions • Joint fluid • Effusions • CSF Cheap and easy, BM and spleen samples best
❖ Histology of skin lesions
• + immunohistochemistry (sens. 18.2-100%)
• + direct immunofluorescence (sens. 64.3-100%)
• + in situ hybridization (sens. 50-74.5%)
How can PCR be used for direct diagnosis?
• BM/LN >spleen > skin > conjunctiva > buffy coat > blood (BM sens. 95%, spec. 100%; LN sens. 89.7%, spec. 100%)
• a positive result confirms infection but not disease
• conventional, nested, quantitative (real-time PCR)
• real-time PCR:
✓ run in closed systems and then less prone to contamination
✓ provides information about the copy number of DNA present
in the sample
✓ useful during the follow-up to monitor the efficacy of therapy
Outline serology as an indirect method of diagnosis
➢ Seroconversion generally happens 5 months (1-22 mths) after natural infection
➢ Abs titres tend to be high or increase only in dogs in which the parasite has disseminated
• Immunochromatography (rapid in-house tests):
✓ immediate results but only qualitative
✓ good specificity but variable/low sensitivity (30-70%)
✓ less likely to recognise vaccine-induced Abs
• ELISA - IFAT (OMS and OIE ref test):
✓ quantitative tests
✓ sensitivity (87.5%-100%) and specificity (100%*)
Outline the Leishmaniasis working group classification of different patients
❖ Stage A: exposed dogs
→ negative direct tests and low serologic titres against Leishmania
→ no signs or signs associated with other diseases
→ no treatment but serologically monitoring 2 to 4 months after initial seropositivity
❖ Stage B: infected dogs
→ positive direct tests and low serologic titres against Leishmania
→ no signs or signs associated with other diseases
→ treatment only if increase in antibody titre (serology every 2-4 months for at least 1 year)
→ clinical monitoring every 6-12 months for the rest of life
❖ Stage C: sick dogs (dogs with clinically evident leishmaniasis)
→ positive cytology and/or high serologic titres and > 1 clinical sign
→ anti-Leishmania treatment is recommended
❖ Stage D: severely sick dogs
→ sick + proteinuric nephropathy/CKD (IRIS 3-4), severe ophthalmic/joint diseases
→ anti-Leishmania treatment + specific therapy (+/- immunosuppressive)
❖ Stage E:
→ Ea: unresponsive to treatment
→ Eb: early relapse soon following cessation of recommended treatment(s)
Outline the tx options
❖ Meglumine antimoniate
80-100 mg/kg/24h/ 30 - 45 days based on SEP
selectively inhibits leishmanial glycolysis and fatty acids ox. Not available in UK. Has to be given S/S. Stronger than melgumine
❖ Allopurinol
5-20 mg/kg/12h
analogue of hypoxanthine → interferes with uric acid synthesis blocking xanthine-oxidase (Leishmania unable to synthesise purine)
Side effects (13% of cases): xanthinuria, renal mineralisation, urolithiasis
give with either Meglumine or miltofosine
❖ Miltefosine
2 mg/kg/24 h/po 28 days
impairment of signalling pathways and cell membrane synthesis
How effective is therapy?
❖ Dogs frequently become cured of the clinical disease
❖ In most cases the treatment does not eliminate completely the infection
❖ The possibility of re-infection always exists
❖ Evaluating and controlling other problems especially in non-responding dogs → parasites, co-infections, nutrition, neoplasia
❖ Relapses necessitating re-treatment are common
