Canis ISSN: 2398-2942

Ehrlichiosis

Synonym(s): Canine rickettsiosis, Canine hemorrhagic fever, Tropical canine pancytopenia (severe chronic phase, Lahore canine fever,Nairobi bleeding disease

Contributor(s): Maggie Fisher, Lisa Moore, Alex Morrow, Bryn Tennant

Introduction

  • Cause: serious tick-borne rickettsial infections of dogs acquired in parts of the tropics, sub-tropics, warm temperate regions and Finland.
  • Signs: non-specific in the acute phase, sudden onset of fever, depression, anorexia and in the chronic phase, hemorrhages including epistaxis.
  • Diagnosis: antibiotics with efficacy against rickettsia.
  • Concurrent infection with Babesia spp and Leishmania infantum common.
  • Treatment: doxycycline 10-20 mg/kg daily for 3 weeks.
  • Prognosis: good when acute phase is treated properly; guarded if proceeds to tropical canine pancytopenia; guarded if severe chronic form of canine monocytic Ehrlichiosis.
    Print off the owner factsheet on Ehrlichiosis Ehrlichiosis to give to your client.

Pathogenesis

Predisposing factors

General

  • Exotic dogs imported as adults into endemic areas from non-endemic areas.
  • Immunological status of the host.
  • Stress including malnutrition and pregnancy.
  • Virulence of the strain of the organism.
  • Size of challenge dose.
  • Dogs can remain infected for at least 2 years and possibly for life therefore iatrogenic transmission can occur.

Specific

  • Failure to treat adequately may lead to the development of the chronic form, tropical canine pancytopenia.

Pathophysiology

  • A tick-transmitted rickettsial infection in which, depending on the Ehrlichia species involved, mononuclear cells, granulocytes or platelets are parasitized.
  • Clinical signs of acute monocytic ehrlichiosis tend to be non-specific with the insidious development of the chronic form in which bone marrow suppression results in pancytopenia and a hemorrhagic crisis.
  • E. canis is an obligatory intracellular parasite multiplying inside cytoplasmic vacuoles in mononuclear phagocytic cells.
  • Hematogenous → splenomegaly, hepatomegaly and lymphadenopathy.
  • Vasculitis affecting various organs including lungs, kidneys and possibly the meninges.
  • Bone marrow depression → thrombocytopenia, anemia and leukopenia during the acute phase and may persist during the subsequent subclinical phase.
  • Platelet dysfunction also contributes to the occurrence of hemorrhages.
  • Infection appears to induce an immune-mediated thrombocytopenia and immune-mediated hemolytic anemia.
  • Severely affected animals are susceptible to secondary infections. Persistent latent infection → lymphoproliferative syndrome, with accumulation of large numbers of plasma cells in various organs including lymphopoietic tissues, kidneys and meninges, develops in some dogs several weeks after the primary clinical episode (chronic form known as Tropical Canine Pancytopenia).
  • Hemorrhages, especially epistaxis Epistaxis , and various other symptoms, depending on the organs/tissues involved, occur in affected animals.
  • E. platys causes a cyclical rickettsiemia with thrombocytopenia with diminishing severity as immunity develops, at approximately 10 day intervals.

Timecourse

  • Incubation period of monocytic canine ehrlichiosis ranges from 8-20 days.
  • The course of the illness is variable with the acute phase lasting 2-4 weeks.
  • Clinical signs of the acute phase can resolve spontaneously in 1-4 weeks.
  • Death may occur within a week of the onset of clinical signs.
  • The subclinical phase lasts for months or years before the development of the chronic phase in some infected dogs.
  • Death may occur within a few hours of the onset of clinical signs in tropical canine pancytopenia with severe hemorrhages.
  • The incubation period of cyclical canine thrombocytopenia due to E. platys ranges from 1-2 weeks.

Epidemiology

  • E. canis, the etiologic agent of canine monocytic ehrlichiosis is transmitted by Rhipicephalus sanguineus Rhipicephalus sanguineus.
  • Transtadial but not transovarial transmission occurs in infected ticks.
  • Rhipicephalus sanguineus can survive for up to 500 days as unfed adults remaining infected for at least 155 days.
  • Ticks are more abundant and acute infections more common during the warm season.
  • E. canis can be transmitted by blood transfusions.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Murphy K & Shaw S (2004) Disease risks for the travelling pet: EhrlichiosisIn Practice 26 (9), 493-497 VetMedResource.
  • Egenvall A, Lilliehook et al (2000) Detection of granulocytic Ehrlichia species DNA by PCR in persistently infected dogs. Vet Rec 146 (7), 186-190 PubMed.
  • Suksawat J et al (2000) Seroprevalence of Ehrlichia canis, Ehrlichia equi and Ehrlichia risticii in sick dogs from North Carolina and Virginia. J Vet Intern Med 14 (1), 50-5 PubMed.
  • Harrus S & Hylton B (1997) Canine Monocytic Ehrlichiosis - An Update. Comp Cont Educ Pract Vet 19 (4), 431-444 PubMed.


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