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Neorickettsia helminthoeca is a bacterium in the Neorickettsia genus that causes Salmon poisoning disease.

Introduction
Heterophils are the most abundant granulocyte in most avian species and occur alongside lymphocytes, monocytes, eosinophils and basophils in avian blood. These cells are also found in some reptile and mammalian species.

Development
Heterophils have a similar development to other granulocytes; this process is called granulopoiesis.

Appearance
The cytoplasm of normal heterophils appears colourless and contains eosinophilic granules (dark orange to brown-red) with Romanowsky stains. The cytoplasmic granules are elongated (rod or spiculated shape) but they may appear oval to round in some species.

The granules frequently have a distinct central body that appears to be refractile. The granules may be affected by the staining process and appear atypical.

The nucleus of mature heterophils is lobed (usually two to three) with coarse, clumped chromatin that stains purple. The nucleus is often partially hidden by the cytoplasmic granules.

Function
Heterophils are functionally equivalent to neutrophils. They actively participate in inflammatory lesions and are phagocytic.

The cytoplasmic granules of heterophils contain lysozyme and proteins needed for bactericidal activity, although chicken heterophils lack peroxidase activity.