Eosinophilia

Eosinophilia (from the name of the dye eosin and the Greek philia — love, inclination) is a condition characterized by an increase in the number of eosinophils in the peripheral blood of more than 0.5 × 10⁹/L.

Eosinophilia can be of several types:

• Primary — associated with hematological disorders;
• Secondary — caused by various non-hematological factors, including infectious;
• Idiopathic — when the cause of eosinophil elevation is unknown.

In infectology, this laboratory marker is an indicator of tissue parasitic (helminthic) invasion.

Etiology and pathophysiology

Eosinophils are a type of leukocyte (granulocyte). They comprise several important functions for humans:

• provide protection against parasitic infections;
• participate in the development of allergic reactions;
• regulate oncohematological and autoimmune pathologies.

They are formed in the bone marrow influenced by hematopoietic growth factors (granulocyte-macrophage colony-stimulating factor, interleukin-3 and interleukin-5).

The pathogenesis of eosinophilia in various conditions is diverse and complex. Eosinophils infiltrate the tissues during helminthic invasion or allergies and exhibit properties of antigen-presenting cells.

Granules released by eosinophils significantly influence the recruitment and activation of dendritic cells, which facilitate the activation of the immune response.

Clinical significance

In clinical practice, the detection of eosinophils in a complete blood count (at levels greater than 0.5 × 10⁹/L) is a reason to search for helminthic invasion, as viruses and bacteria rarely cause an increase in the number of eosinophils.

Eosinophilia typically coincides with the larval migration phase through organs (e.g., with ascariasis, toxocariasis, or trichinosis).

Once the parasite encapsulates or dies in the tissues, or the larva leaves the organ, the eosinophil count gradually decreases to normal.