ISSN 2398-2942      

Anaplasma phagocytophilum

icanis
Contributor(s):

Leah Cohn

Severine Tasker

Synonym(s): Canine granulocytic anaplasmosis, the HGE (human granulocytic ehrlichia agent in humans


Introduction

Classification

Taxonomy

  • Phylum: Proteobacteria.
  • Order: Rickettsiales.
  • Family: Anaplasmataceae.
  • Genus: Anaplasma.
  • Species: phagocytophilum.
  • Many A. phagocytophilum strains exist; seem to group according to geographical origin in phylogenetic studies performed - these variants may vary in pathogenicity too (eg human disease due to A. phagocytophilum worse in USA compared to Europe).

Etymology

  • Formerly known as Ehrlichia equi and Ehrlichia phagocytophila.
  • Gk. an-, without; plasma-, anything formed or molded; phagein-, to eat up, devour; phylum-, friend, loving. Literally: a thing (a bacterium) without form, attractive to phagocytes.

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Clinical Effects

Epidemiology

Habitat

  • Wildlife such as rodents, and other small mammals act as the reservoir hosts, with transmission to domestic animals and man as a result of tick bites.
  • Wild ruminants such as deer may also act as reservoirs for selected strains.

Lifecycle

  • Alternate infection of two distinct hosts, ticks and mammals.
  • A. phagocytophilum resides in the salivary glands of tick. The bacteria persists through the nymphal molts but is not passed on transovarially.

Transmission

  • Transmitted by bites from Ixodes spp tick vectors, especially:
    • Ixodes pacificus Ixodes pacificus on western coast of United States (same spp that transmit Lymes disease in North America Borreliosis ).
    • Ixodes scapularis Ixodes scapularis in the north-eastern and southern coastal regions of the United States (same spp that transmit Lymes disease in North America).
    • Ixodes ricinus Ixodes ricinus throughout Europe (same spp that transmits Lymes disease and the flavivirus that causes tick borne encephalitis (TBE) in Europe) and eastern Russia.
    • Ixodes persulcatus across sections of Russia and northern Asia.
  • It has been suggested that the infection can be introduced into disease-free areas by migrating birds.
  • Time of tick bite transmission; ticks need at least 24 h feeding to transmit - usually occurs with 24-48 h of feeding.

Risk factors for canine infection

  • Lack of tick control Tick control.
  • Older dogs more likely to be infected (more cumulative exposure?).
  • No sex predisposition.
  • No breed predisposition although golden retrievers were overrepresented in one study.

Pathological effects

  • The seroprevalence of anaplasmosis is related to organism prevalence in the tick populations, animal density, and the variants of A. phagocytophilum found within the geographic area.
  • Exact mechanism of disease induction not known.
  • Preferentially infects myeloid cells, predominantly neutrophils
  • See cytokine myelosuppression, auto-antibody formation (eg versus platelets), infection of bone marrow hematopoietic cell precursors.
  • Acute infection most likely to be associated with clinical signs; chronic disease in dogs, as seen with Ehrlichia canis Ehrlichia canis , has not been reported with A. phagocytophilum.
  • Usually mild self-limiting disease in dogs.
  • Co-infections with Borrelia burgdorferi Borrelia burgdorferi may be responsible for more severe clinical signs in some cases.
  • Clinical signs reported almost exclusively with acute infection:
    • Pyrexia most frequently reported.
    • Lethargy.
    • Depression.
    • Anorexia.
    • Musculoskeletal pain; stiffness, lameness, weakness, swollen joints.
    • Occasionally see lymphadenopathy Lymphadenopathy , splenomegaly, hepatomegaly Abdominal organomegaly.
    • Gastrointestinal and respiratory signs rarely seen.
    • CNS signs rare.
    • Bleeding signs are rare compared withE. canisinfection even though see thrombocytopenia Thrombocytopenia.
  • Clinical pathology changes:

Control

Control via animal

  • Minimize exposure to tick bites by use of topical tick repellents (eg permethrin Permethrin or flumethrin).
  • Carefully examine for and remove ticks on return from infected areas - daily tick check by owners although note that this needs to be done promptly to prevent transmission of infection as this can occur after only 24 h of tick feeding.
  • Use tick remover for complete removal of ticks.

Antibiotics

  • Tetracyclines Tetracycline , including doxycycline (10 mg/kg/day PO) Doxycycline , are very effective at treating the infection: signs of infection (fever) usually resolve within 24-48 h of starting treatment.
  • 4 weeks of treatment has been recommended by some, although shorter courses of 2-3 weeks are generally adequate.
  • Chloramphenicol Chloramphenicol has also been used (in very young animals if tetracyclines are to be avoided).
  • Acute infection relatively easy to treat; chronic infection does not appear to be a feature of this disease.

Vaccination

  • No vaccine is currently available against A. phagocytophilium.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Chomel B (2011) Tick-borne infections in dogs - an emerging infectious threat. Vet Parasitol 179 (4), 294-301 PubMed.
  • Scorpio D G, Dumler J S, Barat N C et al (2011) Comparative Strain Analysis of Anaplasma phagocytophilum Infection and Clinical Outcomes in a Canine Model of Granulocytic Anaplasmosis. Vector-Borne Zoonotic Dis 11 (3), 223-229 PubMed.
  • Smith F D, Ballantyne R, Morgan E R et al (2011) Prevalence, distribution and risk associated with tick infestation of dogs in Great Britain. Med Vet Entomol​ 25 (4), 377-384 PubMed.
  • Carrade D D, Foley J E, Borjesson D L et al (2009) Canine Granulocytic Anaplasmosis: A Review. JVIM 23 (6), 1129-1141 PubMed.
  • Stuen S (2007) Anaplasma Phagocytophilum - the most widespread tick-borne infection in animals in Europe. Vet Res Commun 31 (Suppl 1), 79-84 PubMed.

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