Module 7: Hematogenous Infectious Disease

Module 7.2: Blood Smear Examples

Blood smear examples

Here are a few examples of common organisms found on the blood film of veterinary patients in the United States:

Table 7.1: Common organisms found on the blood film of United States veterinary patients; *picture of the organism in the text below


Species found in

Where it is found (intra/extracellular)

Magnification easiest found at

Location on blood smear

Dirofilaria immitus Canine, Feline Extracellular 10x Feathered edge
Trypanosoma sp. Canine, Bovine Extracellular 40x Monolayer
Babesia sp.* Canine, bovine RBC 40x, 100x Monolayer
Cytauxzoon felis* Feline RBC (piroplasms), monocytes (schizonts) 100x Monolayer (piroplasms), Feathered edge (schizonts)
Anaplasma phagocytophilum Canine, equine Neutrophils, eosinophils 40x Monolayer
Anaplasma marginale* Bovine RBC 40x, 100x Monolayer
Ehrlichia ewingii Canine Neutrophils, eosinophils 40x, 100x Monolayer
Ehrlichia canis Canine Monocytes, lymphocytes 40x, 100x Monolayer
Mycoplasma sp. (M. haemofelis, M. haemolamae, M. canis) Canine, feline, camelids, many others Surface of RBC’s 100x Monolayer
Histoplasma capsulatum* Canine Monocytes 40x, 100x Feathered edge, sometimes monolayer

Visual atlas

Here is a visual atlas of some of the organisms described in the table.


Large variant Babesia sp. in RBC of a canine blood smear (monolayer) at 100x
Babesia sp. in RBC of a canine blood smear (monolayer) using the 100x objective lens (oil).


Histoplasma capsulatum in a monocyte on the feathered edge at 40x
Histoplasma capsulatum yeast within a monocyte on the feathered edge using the 100x objective lens (oil).


Cytauxzoon felis in feline RBC's in the monolayer at 100x
Cytauxzoon felis piroplasms within feline RBC’s in the monolayer using a 100x objective lens (oil).


Anaplasma marginale in the RBC of a bovine blood smear (monolayer) at 100x.
Anaplasma marginale morulae within an RBC of a bovine blood smear (monolayer) using a 100x objective lens.

Knowledge check

Key Takeaways

  • Always begin by scanning the feathered edge at low power (10x objective) to identify large organisms (i.e. microfilariae, schizonts, macrophages with intracellular yeast)
  • Organisms are largely predictable and have cells they prefer to invade and replicate in
  • Small Intracellular pathogens are easiest to identify in the monolayer
  • We use cytologic stains to screen for pathogens
You have now reached the end of Module 7. If you are enrolled in CVM 6925, please go to the Canvas page and take the quiz: “Module 7: Hematogenous infectious disease quiz.” There is an assignment that accompanies the in-person laboratory for this module.


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