In many cases, it is possible to identify the animal species by looking at the peripheral blood under the microscope as there are often selected species-specific features. For example, guinea pigs are characterised by the presence of heterophils and Foa-Kurloff cells.
Peripheral blood, guinea pig, 100x
Heterophils are the counterpart of neutrophils and are seen in selected small mammals, birds, amphibs and reptiles. They are characterised by round to rice shaped brick red granules seen in variable numbers within the cytoplasm.
Foa-Kurloff cells are another leukocyte type that is unique to guinea pigs. They are specialized mononuclear cells that contain an intracytoplasmic inclusion body of mucopolysaccharide, which appear variably pink and granular. Although Foa-Kurloff cells can be present in the blood of both males and females, they are most commonly observed in blood smears from pregnant guinea pigs. These cells may be more prominent during pregnancy because they shift from the lungs and spleen to the thymus and placenta under oestrogen stimulation. Foa-Kurloff cells possibly function as natural killer cells.