You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Eosinophilia is a common finding in blood samples submitted to veterinary diagnostic laboratories, but interpretation of its significance is often difficult.

Eosinophils are mainly located tissue and increased numbers in the bloodstream  may, or may not, be associated with increased numbers of eosinophils in  tissues such as the gastrointestinal tract, heart, kidney,  liver, lungs, lymph nodes, skeletal muscle, pancreas, skin, spleen and uterus. Eosinophils are one component of the immune system. They are attracted into areas of the body by histamine release from mast cells and this most often results from an allergic antibody-antigen reaction. Eosinophils have both cytotoxic and neurotoxic properties and their primary roles appear to be :

• To target helminth parasites (Many of the tissues in which eosinophils predominate in the body are also the tissues which are most likely to be in contact with parasites - eg gastrointestinal tract, skin, lungs and skeletal muscle in dogs).
• They play a protective role against dietary allergens, and in other allergic diseases
• Because of their ability to secrete cytokines and destroy cells eosinophils have an important role in inflammatory processes

Excessive tissue numbers (identifiable on biopsies) are of significance because they cause local inflammation and may cause tissue damage (eg in the lungs). Increased numbers in the circulation (over 1.25x10⁹/l in dogs ; over 1.5x10⁹/l in cats) reflect increased production and release into the circulation - mainly from the bone marrow. 

Unfortunately, many conditions can be associated with the development of an eosinophilia, including :

• Atopy
• Basal cell tumours (cats)
• Dermatitis
• Enteritis - acute and chronic
• Eosinophilic granuloma complex (cats)
• Feline asthma
• Feline infectious peritonitis (FIP)
• Flea hypersensitivity
• Food allergy
• Gastritis - acute and chronic
• Hypereosinophilic syndrome in cats (rare)
• Hypoadrenocorticism - Addisons Disease
• Lymphoma
• Mast cell tumours
• Methimazole therapy for hyperthyroidism (cats)
• Myositis (eosinophilic)
• Oestrus (normal)
• Ovarian tumours
• Panosteitis (dogs)
• Pansteatitis (cats)
• Parasitism - helminths, various sites and stages
• Pemphigus foliaceous
• Pneumonia
• Pyometra
• Snakebite
• Steroid withdrawal
• Toxoplasmosis
• Tracheobronchitis

This makes interpretation extremely difficult...especially as there is overlap between many of the diseases. For example, pneumonia may be a sequel to injury caused to the lungs by migrating helminth larvae. Eosinophilia often responds to corticosteroid therapy, nevertheless a concerted effort should be made to determine the underlying cause before treatment is started, even though many cases will remain idiopathic.

References

Diseases associated with pronounced eosinophilia : a study of 105 dogs in Sweden. Lilliehook et al. Journal of Small Animal Practice (2000) 41, 248-253

Manual of Small Animal Clinical Pathology (1998) M. Davidson (General Editor) BSAVA Publications *

Interpretation of Laboratory Results for Small Animal Clinicians (1991) B.Bush, Blackwell Scientific Publications *

Veterinary Clinical Immunology (1989) Halliwell and Gorman. Saunders  

Last updated : January 2016