Flea Infestation & Anemia in a Dog

ArticleLast Updated April 20086 min readPeer Reviewed

A 12-year-old male Labrador retriever was presented for otitis externa and a moist exudative dermatitis. 

History. In addition to the otitis externa and exudative dermatitis, the owner indicated that the dog exhibited decreased exercise tolerance but no coughing or sneezing.

Physical Examination. The dog had severe flea infestation, with marked flea excreta over some areas of the body. The mucous membranes appeared pale, multiple lymph nodes were enlarged, and the heart rate was increased. The rectal temperature was normal. 

Laboratory Findings. The dog had severe microcytic (low MCV) hypochromic (low MCHC) anemia as measured by a Cell-Dyn 3500 hematology analyzer (www.abbott.com) (Table). The presence of reticulocytosis indicated regenerative anemia. Plasma was clear and colorless when examined after centrifugation of a microhematocrit tube. Total plasma protein concentration was within the reference interval when measured by a refractometer. Slight anisocytosis, slight poikilocytosis, moderate polychromasia, and marked hypochromasia were visible on a stained blood film (Figure 1). Thrombo-cytosis was present, and some platelets were large. The differential leukocyte count revealed slight leukocytosis with neutrophilia, eosino-philia, and basophilia. Numbers of nucleated erythrocytes in blood were slightly increased.

Diagnosis: Chronic iron deficiency anemia secondary to ongoing blood loss caused by a severe flea infestation

The hypochromic appearance of most erythrocytes on the stained blood film and the presence of severe microcytic hypochromic anemia indicate that chronic iron deficiency is highly likely in this dog (Figure 1). Less common causes of microcytosis in dogs, including portosystemic shunts and anemia of inflammatory disease, generally are associated with normal MCHC and normal-appearing erythrocytes. 

Iron Deficiency Anemia. Chronic iron deficiency anemia rarely results from dietary iron deficiency in adult animals but rather is almost always the result of chronic blood loss. About two thirds of total body iron is normally contained within erythrocytes, and substantial ongoing hemorrhage can result in iron deficiency when iron loss exceeds dietary iron absorption. Consequently, anemia in iron-deficient animals generally results from a combination of hemorrhage and impaired (iron-limited) erythrocyte production. However, iron-deficient erythrocytes also exhibit decreased life spans.1 

Chronic iron deficiency anemia is common in adult dogs in areas where bloodsucking parasite infestations (especially hookworms and fleas) are severe. Iron deficiency may also result from hemorrhage associated with intestinal neoplasms, transitional cell carcinomas, gastrointestinal ulcers, thrombocytopenia, inherited hemostatic disorders, and hemorrhagic colitis.2

Course/Progression. Depending on the initial MCV and MCHC values and the magnitude of ongoing blood loss, 1 or more months are required before the MCV and MCHC decrease below reference intervals. Body iron stores must be depleted, and then the microcytic hypo-chromic cells formed must make up a high enough percentage of the total erythrocytes present to decrease the MCV and MCHC below reference intervals. 

Increased production and release of reticulocytes (and often nucleated erythrocytes) from bone marrow into blood typically occur in response to hemorrhage in dogs. As in this dog, absolute reticulocytosis is present in about half of the dogs recognized with chronic iron deficiency anemia.3 As iron depletion becomes more severe, there is insufficient iron for reticulocyte production, and the absolute reticulocyte count is no longer increased. 

Thrombocytosis (as seen in this case) is often present in animals with iron deficiency anemia. The platelet increase may in part be related to a stimulation of megakaryocytopoiesis by high erythropoietin concentration in plasma, but the mechanism has not been clearly defined.1 The neutrophilia may have been in response to the dermatitis, and the eosinophilia and basophilia may have been in response to the flea infestation, especially if a flea-bite allergic reaction occurred.

Additional Diagnostics. In this case, the serum biochemical profile was unremarkable except for a serum iron level of 8 µg/dl (reference interval, 84 to 233 µg/dl). Although serum iron can be low in patients with anemia due to inflammatory disease, the markedly low serum iron concentration associated with microcytic hypochromic anemia supports a diagnosis of iron deficiency. In addition, anemia due to inflammatory disease results in nonregenerative anemia. 

The measurement of serum ferritin concentration (low in iron deficiency and normal or high with inflammation) or stainable iron in the marrow (low or absent in iron deficiency and normal or high with inflammation) can better differentiate iron deficiency from anemia due to inflammatory disease. Slight poikilocytosis was present in this case (Figure 2). Prominent poikilocytosis (especially keratocytes and schistocytes) may be pronounced in association with severe microcytosis.<sup4 sup> 

When iron deficiency is present, it is important to search for potential sources of blood loss; upper gastrointestinal bleeding is generally not recognized by the client. Hookworm infestations are a common source of bleeding in the southeastern United States, but in this case fecal flotation results for parasite ova were negative. Additional testing (such as a fecal occult blood test and diagnostic imaging) was not done because the flea infestation was considered severe enough to account for the anemia. 

Heartworm infection is a common cause of eosinophilia and basophilia in dogs in our area. Results of a blood test for microfilaria were negative, but an antigen test for Dirofilaria immitis was not done. The eosinophilia and basophilia (Figure 3) in this case are believed to have occurred in response to the flea infestation. 

Treatment & Outcome. After a 500-ml whole-blood transfusion was given, the hematocrit increased to 24%. The animal was treated to remove the fleas and was given 3 iron dextran injections over 3 days. In the absence of gastrointestinal signs, ongoing iron supplementation is generally given orally, rather than parenterally, as selected by the clinician in this case. 


What do the microcytic hypochromic erythrocytes indicate?

What explains the eosinophilia and basophilia?

  What additional tests are indicated? 


Chronic iron deficiency resulting from ongoing blood loss caused by a severe flea infestation

Eosinophilia and basophilia may be a response to flea infestation, especially if a flea-bite allergic reaction occurs

• Fecal flotation for hookworms, fecal occult blood, serum iron and/or serum ferritin


References1. Iron metabolism and its disorders. Harvey JW. In Kaneko JJ, Harvey JW, Bruss ML (eds): Clinical Biochemistry of Domestic Animals, 6th ed-San Diego: Academic Press, in press, 2008.2. Microcytic anemias. Harvey JW. In Feldman BF, Zinkl JG, Jain NC (eds): Schalm's Veterinary Hematology-Philadelphia: Lippincott Williams & Wilkins, 2000, pp 200-204.

  1. Chronic iron deficiency anemia in dogs. Harvey JW, French TW, Meyer DJ. JAAHA 18:946-960, 1982.4. Atlas of Veterinary Hematology. Blood and Bone Marrow of Domestic Animals. Harvey JW-Philadelphia: WB Saunders, 2001.