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Anaplasma phagocytophila (Ehrlichia equi) in horses |
Unlike E. canis and E. chaffeensis, which target
monocytes, Anaplasma phagocytophila (E. equi) TARGETS
GRANULOCYTES.
Anaplasma phagocytophila is transmitted by Ixodes
spp. tick vectors, especially Ixodes pacificus and
Ixodes scapularis.
- Note that these are the same species that transmit Lyme
disease in the U.S.
Clinical disease in horses:
- Granulocytic ehrlichiosis in horses is a seasonal disease
(late fall-to-spring), reflecting the activity of the tick vectors
at that time. The greatest number of cases have been reported
in California.
- This disease of horses characterized by:
- fever, lethargy
- stocking edema
- thrombocytopenia, leukopenia, anemia and petechiae
- possibly ataxia
- An outbreak in Connecticut in November, 1996 affected 50+
horses.
Differential diagnoses:
- equine infectious anemia virus (EIAV)
- equine arteritis virus (EAV)
- Streptococcus equi ("strangles")
(This ehrlichial infection should not be confused
with Potomac horse fever, a diarrheal disease [typhlocolitis]
caused by Neorickettsia risticii [E. risticii],
which targets monocytes.)
Diagnosis of A. phagocytophila infection in horses:
- serology
- PCR
- Morulae inclusions are transient and can't be depended upon
to make a diagnosis.
Treatment of A. phagocytophila infection in horses:
