Lecture 3 - RBC Parasites and Blood Film

Hemoparasites may be associated with...

The external RBC membrane (epicellular)

Within the cytoplasm (intracellular)

Hemoparasite infection often results in...

Anemia, which may be in part or entirely due to an immune-mediated response

Hemolysis resulting in the anemia may be intravascular and/or extravascular

What are hemotropic mycoplasmas?

Gram negative bacteria with an affinity for RBCs

Epicellular parasites

Very small (0.5-1.5 micron) cocci, rod, or ring shaped structures

May be found individually or in chains

Virulence varies between organisms

When infection results in anemia, it is typically via extravascular hemolysis

Treated animals may become carriers and recurrence possible

What are challenges associated with hemotropic mycoplasmas?

Can detach from the RBC during transport ex vivo and may be in the background

Can be confused for stain precipitate and vice versa

If infection is suspected, how do we test for hemotropic mycoplasmas?

PCR testing

What is Mycoplasma haemofelis?

Can cause disease in normal animals, most pathogenic of feline forms

Concurrent retroviral infection can increase susceptibility (FIV/FeLV)

Acute hemolytic anemia, typically regenerative

Cyclic parasitemia (infected # of RBCs increases over days, then will abruptly decrease (sometimes within hours)

Survivors often remain carriers

How is Mycoplasma haemofelis transmitted?

Fleas, ticks, mosquitos

Blood (including blood transfusions)

Vertical (from queen to kitten)

What is theileriosis?

Protozoal organism that affects ruminants, including cervids

Intracellular

Often nonpathogenic in US, but can cause hemolytic anemia

Multistage lifecycle (schizonts in lymphocytes, piroplasms in RBCs)

What is Cytauxzoon felis?

Intracellular protozoa

Feline pathogen of southern, south-central, midwest, and mid-atlantic US

Bobcat is the wild reservoir

Tick vectors

How does Cytauxzoon felis appear cellularly?

Piroplasms in RBCs (basophilic, sound to signet-ring structures, 1-3 microns)

Schizonts in tissue macrophages: very large/swollen and affect blood flow and cell function in affected organs, main cause of clinical signs

What are clinical signs of Cytauxzoon felis?

Depression and lethargy

High fever

Icterus

Leukopenia and thrombocytopenia (dec WBC/platelet)

Non-regenerative anemia, mild and later developed

Often fatal for cats that become symptomatic

What is babesiosis?

Intracellular protozoan

Mainly seen in dogs and cattle

Sporozoites penetrate and multiply and RBCs (can rupture RBCs, invade other RBCs, cause intravascular hemolysis, +/- thrombocytopenia)

Large and small forms (over or under 3 micron)

What is Anaplasma marginale?

Intracellular rickettsia

In cattle, widespread

Tick vectors, mechanical transmission

Increasing parasitemia occurs until anemia develops (hemolytic crisis)

Fever and mild to severe anemia

Must be differentiated from Howell-Jolly bodies (usually not perfectly round and may be smaller than HJ bodies)

What is hemoproteus?

Protozoa seen in birds

Non-pathogenic or mild

What is hemogregarines?

Protozoa seen in reptiles

Non-pathogenic or mild

What are plasmodium?

Protozoa in birds and reptiles

What are leukocytozoon?

Protozoa in birds

Low pathogenicity for most birds

What are examples of extracellular parasite classes?

Microfilaria

Trypanosomes

Where are extracellular parasites found?

In free plasma

What is the microfilaria responsible for heartworm infection in dogs and cats?

Dirofilaria immitis

What is the monolayer on a blood smear?

Where RBC density and morphology are most accurately assessed

In a sample from a patient with a normal Hct, the RBCs are typically in a single layer and will be just close enough that about 50% will touch or slightly overlap

Central pallor in dogs most prominent here

Slightly iridescent area grossly

When is the monolayer of a blood smear harder to identify?

Anemic patients

When evaluating a blood smear, what should we look for on 10X?

Assess for platelet clumps and large organisms (microfilaria) in body

Do not evaluate for agglutination, often an artifact

Determine if central pallor and RBC density in monolayer is normal

Evaluate feathered edge for any larger organisms, cells, and cell clumps

When evaluating a blood smear, what should we look for on 40X?

Differentiate rouleaux vs agglutination

Assess for nRBCs (may falsely elevate automated WBC count)

When evaluating a blood smear, what should we look for on 100X?

Stay in the monolayer

WBC and platelet morphology/inclusions

Platelet count, morphology, and inclusions

RBC characteristics (anisocytosis, polychromasia, poikilocytosis, hemoparasites/inclusions)

What are characteristics of nRBCs?

Typically seen in response to anemia

When increased numbers are seen in non-anemic patients, bone marrow or splenic disease should be considered

Don't mistake for lymphocytes

Quantified during leukocyte differential and reported as # per 100 WBCs

Automated analyzer may count them as WBCs