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Anaplasmosis

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Diagnosis

The diagnostic criteria for confirmed human granulocytic anaplasmosis are clinical signs and laboratory findings suggestive of granulocytic anaplasmosis together with

1) detection of morulae within neutrophils (rarely eosinophils) on blood smears combined with a single positive reciprocal antibody titer to A. phagocytophilum (or a positive PCR result ),

2) a 4-fold increase or decrease in the antibody titer within 4 weeks;

3) a positive PCR test result using specific A. phagocytophilum primers

4) isolation of A. phagocytophilum from blood.

These criteria can also be applied to dogs and other species, however, isolation is not used routinely for diagnosis.

Antibody testing can be performed by IFAT (indirect immunofluorescence antibody test) or ELISA (enzyme-linked immunosorbent assay). Since the seroprevalence is high in endemic areas, a diagnosis cannot be based on a single positive titer (which may only reflect previous exposure). During acute illness, antibodies may be inapparent. A four times or higher increase in antibody titers is essential to confirm the diagnois. Paired serum specimens taken at least two to three or more weeks apart are considered to be most helpful for evaluation (Center for Disease Control, USA).

Cross reactions of antibodies do occur to some extent with other Anaplasma, Ehrlichia and Neorickettsia species.

Conventional and real-time PCR assays have been developed for detection of A. phagocytophilum DNA in peripheral blood, buffy coat, bone marrow, liquor cerebrospinalis or splenic tissue. The targets of the assays have been either the 16S rRNA gene, or the outer surface protein genes such as msp2. Assays based on the msp2 gene are usually specific for A. phagocytophilum , whereas assays based on the 16S rRNA gene may detect other Anaplasma species or even other bacteria. PCR may pick up infection when microscopy has appeared negative. In experimentally infected dogs, PCR tests on whole blood were positive for 6-8 days before and 3 days after morulae appeared on blood smears.

A diagnosis of A. platys may be made by detecting organisms within platelets on stained blood films or buffy coat smears (e.g. Giemsa or Diff-Quik). Due to cyclic parasitemia the pathogen could either be absent or present in very low numbers. Thus this method is not reliable. An IFAT for detection of serum antibodies is available (likely cross-reacts with A. phagocytophilum ) and different PCR-based assays have been developed.

   

Further information

  • Carrade DD, Foley JE, Borjesson DL, et al.: Canine granulocytic anaplasmosis: A review. J Vet Intern Med. 2009, 23, 1129–41
  • Fisher M, McGarry J: Focus on Small Animal Parasitology. 2006, Kingfisher Press Limited, London

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