Felis ISSN 2398-2950

Ehrlichiosis

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

Contributor(s): Stephen Barr, Maggie Fisher, Alex Morrow, Kim Willoughby

Introduction

  • Little recorded information about the disease in cats.
  • Cause: serious tick-borne rickettsial infections of dogs and cats acquired in parts of the tropics, sub-tropics, warm temperate regions and Sweden.
  • Usually tick transmitted.
  • Signs: non-specific in the acute phase, sudden onset of fever, depression and anorexia.
  • Diagnosis: antibiotics with efficacy against rickettsia.
  • Concurrent infection with other tick borne infections may occur.
  • Treatment: doxycycline 10 mg/kg daily for 3 weeks.
  • Infection with Ehrlichia spp is much more commonly recognized in dogs than cats. In the latter relatively little is known of the disease, including the identity of the Ehrlichia species involved and epidemiology.
  • This component will review what is known of infection in the cat and then infection in the dog, since details of infection in this species are better understood.

Pathogenesis

Etiology

  • E. canis causes canine monocytic ehrlichiosis, the most important type of canine ehrlichiosis.
  • E. ewingii causes canine granulocytic ehrlichiosis, a much milder disease than the acute form of canine monocytic ehrlichiosis.
  • E. platys causes canine cyclic thrombocytopenia, which is often asymptomatic.
  • Human granulocytotropic Ehrlichia species cause mild infections in dogs infected experimentally.
  • Other Ehrlichia species, including E. equi, may occasionally cause infections in dogs.

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 but possibly for life therefore iatrogenic transmission can occur.

Specific

  • Infestation with the three-host brown tick Rhipicephalus sanguineus.
  • ? Infestation with Ixodes ricinus Ixodes ricinus in parts of Northern Europe.

Pathophysiology

  • A tick-transmitted rickettsial infection in which, depending on theEhrlichiaspecies involved, mononuclear cells granulocytes are parasitized.
  • Clinical signs of acute monocytic ehrlichiosis tend to be non-specific with 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 autoimmune response including anti-platelet antibodies.
  • 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, 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 etiological agent of canine monocytic ehrlichiosis, is transmitted by Rhipicephalus sanguineus.
  • Ixodes ricinus may be responsible for the transmitting E. canis in Finland.
  • 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: Ehrlichiosis. In Practice 26 (9), 493-497 VetMedResource.
  • Trees A & Shaw S (2001) Imported diseases in small animals. In Practice 21 (9), 482-491 ResearchGate.
  • Bj√∂ersdorff A, Svendenius L, Owens J H et al (1999) Feline granulocytic ehrlichiosis -a report of a new clinical entity and characterization of the infectious agent. JSAP 40 (1), 20-24 VetMedResource.
  • Harrus S, Bark H, Waner T (1997) Canine Monocytic Ehrlichiosis - An Update. Comp Cont Educ Pract Vet 19 (4), 431-444 VetMedResource.
  • Peaves G M, Holland C J, Dutta S K et al (1997) Suspected ehrlichial infection in five cats from a household. JAVMA 210 (2), 231-234 PubMed.

Other sources of information

  • Ramsey I, Gunn-Moore D & Shaw S (2001) The hemopoietic and lymphoreticular systems. In: Manual of canine and feline infectious diseases. Eds I Ramsey and B J Tennant. Gloucester: British Small Animal Veterinary Association. pp. 65-88.


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