K9 Ehrlichiosis Flashcards by Ella Pittman

Overview

Tick transmitted, intracytoplasmic 
Intracytoplasmic stage --> morula 
Species divided into 3 genera based on 16S rRNA sequences 
Used to be based on cell type infect 
--some infect multiple cell types

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Ehrlichia canis

World-wide
Vertebrate hosts: canids but also cats
–similar syndromes but not well characterized
Endemic in German Shepards from Vietnam

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E. Canis epizootiology - vector

Rhipicephalus sanguineus = brown dog tick

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E. Canis epizootiology

Geographic range depends on tick
Ticks infected when feed on dogs during first 5-10d of acute IFX
–chronically infected dogs NOT source of IFX
Transtadial IFX occurs
No transovarial –> tick not true reservoir

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E. Canis - when/how infectious?

Adult ticks live 570d
Infectious for 5mo 
--Overwinter in ticks 
Both M and F infectious 
Concurrent IFX occur: Babesia, Hepatozaoon, RBC mycoplasmas

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E. Canis Pathogenesis

Incubation 8-20d
Development of 3 phases of dz:
--acute (most cases)
--subclinical 
--chronic (few reach true chronic stage)

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E canis Acute Phase (2-4wks)

Invade mononuclear cells --> division 
VASCULITIS (endothelial damage) in multiple organs 
--Spleen, LN, liver --> organomegaly 
Parasite enters sub-endothelial tissues 
Varying degrees of IFM 
THROMBOCYTOPENIA mainly from vasculitis
--exacerbated by anti-platelet AB
Most dogs survive to enter subclin phase

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E canis Subclinical Phase (mo-yrs)

ANTIGENIC PERSISTENCE
Thrombocytopenia, leukopenia +/- CS
AB Titers rise 7-21d
HYPERGLOBULINEMIA begins to develop
Phase can last 6-9 wks –> even into years
Most will eliminate organism during this phase

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E canis Chronic Phase - Mo

Develops in dogs that don't eliminate organism 
Severity of clinical dz based on:
--Strain
--Age 
--Breed 
--Presence of other dz

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CS of E canis Chronic Phase

PANCYTOPENIA
–thrombocytopenia
–Erythroid hypoplasia w/ plasma cell cytosine
Dogs remain immune to re-IFX if retain organism –> successful tx will allow re-IFX
Death DT hemorrhage, secondary IFX

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CS E canis - systemic illness

Fever, depression +/- bleeding
Less common:
–Splenomegaly
–Lymphadenopathy

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CS E canis - acute dz

May find ticks!

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CS E canis - Ocular

Uveitis
Chorioetinitis
Retinal Hemorrhages
Papillodema

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Other CS of E canis

Neuromuscular 
--Meningitis, sz, stupor, ataxia 
Polyarthritis 
--E. Ewingii, N. Risticii 
Chronic Stage 
--Severe WL 
--Dz as a consequence of pancytopenia

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Dx E canis - CBC

Suspect based on hx, PE and LD 
Non regen anemia 
Thrombocytopenia 
Leukopenia 
Granular lymphocytosis 
Pancytopenia in chronic disease 
Morula --> BM or buffy coat

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Dx E canis Chemistry Panel

Hyperproteinemia 
--HYPERGLOBULINEMIA (usually multiclonal vs multiple myelomas which are monoclonal)
--Hypoalbuminemia 
Increased ALT
CSF = increased protein/lymphocytes

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Dx E canis - serology

IFA: pos test usually 1:80 or greater
Most labs measure IgG
–most positive by 1wk PI
Paired titers as a single titer can reflect past IFX
Titer progressively decreases over 6-9mo after tx

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Challenges with E canis IFA

Highly sensitive, poor specificity
Cross-reactivity w/ other E. Spp ie E chaffeensis, E ewingii
–not a problem ion the Northeast or California
No cross-reaction w/ A. Phagocytophilum
Very little cross reactivity w/ RMSF or A platys

E canis dx - Canine Snap 3 and 4Dx Test

8min in house test
Positive titers: equivalent IFA titer of >1:500
Sensitivity of 95%, Specificity of 100%
Detects AB against E. Chaffeensis not E. Ewingii

Challenges with Snap Test

Predictive value depends on sensitive and specificity but also prevalence
–Low prevalence areas = high false positive rates
Screening test so should confirm with IFA
Western blotting may be used to differentiate mixed IFX

E. Canis dx PCR

More reliable than finding morulae
Usually positive by day 7 PI (CS by d9 PI) in experimental settings
Less reliable in natural IFXs
Real time PCR methods - may be more sensitive

E canis ABX tx

In acute stage, rapid improvement
NOT ENROFLOX
Tetra, oxytet, doxy, minocycline, chloramphenicol, amicarbalide

E canis Tx

May need to hospital E canis cases –> stabilize
Short term-prednisone in acute dz
–Vasculities
–Limit IFM, immune-mediated platelet and tissue destruction
Chronic cases
–Androgens or granulocyte colony stimulating factor to stim BM
Monitor serum globulin levels or IFA
–Should decrease over time

E canis prevent

1) prophylactic ABX

2) strict tick control

E canis prevent: prophylactic ABX

Tetracycline long term Repository oxytet successful Doxy

E canis prevent: strict tick control

Dips/sprays - dichlorvos, chlorfenvinphos, dioxathion, propoxur, carbaryl Flea/tick collars - reduce reinfestation, reliability unproven Selamectin topically (Revolution) monthly too slow in kill Combo of imidacloprid, permethrin = effective

Anaplasma phagocytophilum

``` Vectors (same as Lyme Dz) --Ixodes scapularies --Ixodes pacificus Incubation period --> 1-3weeks Reservoir hosts = wide variety of small mammals, birds ```

Anaplasma Pathogenesis

``` After IFX, enters PMNs and multiplies Not known how causes dz 10d post IFX --> strong immunity usually controls IFX Acute dz only (if at all) --NO CHRONIC DZ ```

Anaplasma CS

Middle aged dogs, presenting in spring, summer or early fall MILD fever, lethargy, anorexia Generalized pain /stiffness - *jt pain rare* THROMBOCYTOPENIA BUT NO BLEEDING Dogs with Anaplasma and lyme dz show more severe signs

Anaplasma Dx

- -MORULA IN PMNs (40% can be infected) - -~80% of cases have mild THROMBOCYTOPENIA, lymphopenia, eosinopenia - -More cases picked up on 4dx - -Standard test = IFA --> + by 5d PI - -Need paired sample 3weeks apart - 4 fold titer increase - -PCR not good

Anaplasma K9 4dx - what to do with results?

Cross rxn w/ A platys, slight with E canis --none with Lyme, RMSF + Souteast = A platys + west/Northeast = A phagocytophilum

What if both E canis and Anaplasma are positive on the 4Dx?

Dual IFX Anaplasma IFX w/ cross reaction w/ E canis --likely to be an acute active infection and not convalescence Unlikely to have E canis alone because virtually no cross reactivity between E canis antigen and anaplasma serum

4Dx: if have E canis alone

Only going to react with positive to E canis

4Dx: if have acute Anaplasma only

Could get reaction to both Anaplasma and E canis

4Dx: if have convalescent Anaplasma

Probably only going to get reaction to Anaplasma

Positive for Anaplasma - tx or don't tx? Symptomatic

If symptomatic - w/ typical CBC changes --Tx w/ doxy for 4 weeks Remember: case likely to have a slightly positive E canis spot on the 4Dx

Positive for Anaplasma - tx or don't tx? Asymptomatic

Perform CBC - thrombocytopenia, eosinopenia --Tx or ignore - repeat CBC in 3wks --If E canis slightly positive (even close to acute IFX for Anaplasma), might want to treat If no CBC changes, recovered from IFX --> don't treat or run paired IFA Look for other diseases

Anaplasma IFA

Seroconversion occurs 2-5d AFTER modulate appear in the blood (5-9d PI) --IFA becomes positive 7-14d PI Need paired samples (3 weeks apart to show 4 fold increase) because 40% of morula and positive dogs will be seronegative CR mild for E canis, other for anaplasma

Anaplasma Treatment - yes

Most cases do not need tx --most dogs get 3-4 week course of doxy anyway Anaplasma = sensitive to enrofloxacin ***unlike Ehrlichia***

Infectious cyclic thrombocytopenia - Etiology

Anaplasma platys - infects platelets Transmitted by ticks High incidence of combined IFX w/ E canis and A platys A platys occurs mainly in SE (Florida)

ICT: pathogenesis

IP 1-2wks During initial IFX, get large # of platelets infected Leads to drop in platelet count - parasite very difficult to find Then platelet #s rise, cycle repeated Cycles of high parasitemeia followed by thrombocytopenia recur Q1-2 weeks

ICT Clinical Features

Dogs rarely become ill Even with low platelet counts, don't usually show signs - hemorrhage Get severe signs if co-infected w/ E canis or Babesia

ICT Dx

Morula in platelets IFX - + just after first parasitemia Remember 4Dx snap test picks up A platys

ICT Tx

As per E canis BUT can use enrofloxacin (Baytril) if need be