VetBact

Phylum	Class	Order	Family	Genus	Species/Subspecies

Species/Subspecies:

Neorickettsia risticii

Etymology:

Gemus name: the new rickettsia.
Species epithet: named after Miodrag Ristic.

Significance:

The disease is common in some regions of the United States, Canada and South America. Has also been detected in France and Italy, but never in Sweden. However, it may occur in horses imported from the United States.
[Of minor importance]

Old Species Name(s):

Ehrlichia risticii

Taxonomy:

Phylum	Class	Order	Family	Genus
Proteobacteria	Alphaproteobacteria	Rickettsiales	Anaplasmataceae	Neorickettsia

Type Strain:

Illinois = HRC-IL = ATCC VR-98.

Macromorphology (smell):

Cannot be cultured on cell free substrates (for instance agar plates)

Micromorphology:

Small (0.8 x 1.5 µm) nonmotile coccoid rods

Gram +/Gram -:

G-, is normally not gram stained. Lymph node aspirate can be stained by Giemsa or Machiavello-staining, which gives blue and red bacteria, respectively.

Metabolism:

Aerobic

Catalase/Oxidase:

Fermentation of carbohydrates:

Is not used for identification of Neorickettsia spp. Furthermore, many intracellular bacteria lack enzymes for carbohydrate metabolism because of evolutionary gene reduction.

Spec. Char.:

Hosts:

Horse, (cattle, mouse, dog and cat)

Vector:

Liver fluke (Fasciola gigantica)

Reservoir:

Insects infected by the liver fluke

Disease (Swedish):

Monocytär "ehrlichios" hos häst.

Disease (English):

Potomac horse fever or equine monocytic ehrlichiosis or equine scours.

Clinical Picture: