Hematologic and Immunologic Diseases

Chapter 5 Hematologic and Immunologic Diseases

Immune-mediated and hematologic disorders are commonly seen in veterinary practice. Although these diseases may be interrelated in some cases, this chapter discusses the most important diseases as individual entities. The technician is referred to a veterinary hematology text for review of the sequence of erythropoiesis and the function of the immune system; the introduction to this text also should be referenced. Knowledge of hematology and the functions of the immune system will assist the student in understanding these diseases.


Erythrocyte disorders are frequently diagnosed in the dog and cat and may be associated with decreased production, increased destruction, or inappropriate loss of red blood cells (hemorrhage). Included in this category of disorders are anemias, hemorrhage, and neoplasia.

Anemia is one of the most common laboratory findings encountered in veterinary medicine and is usually secondary to a primary disorder elsewhere in the body. The major causes of anemia are varied and include hemorrhage, hemolysis, blood parasites, iron deficiencies, immune-mediated disease, and toxins.

A systematic diagnostic approach to anemia is necessary and should include a good history, physical examination, and a complete blood count, including blood films. Treatment should be aimed at correcting the primary disorder and supporting the patient. Therefore it is important to establish whether the anemia is regenerative or nonregenerative. This can be done by evaluating the reticulocyte count. Regenerative anemias are usually the result of hemorrhage or hemolysis, whereas nonregenerative cases may involve the bone marrow.

Blood-Borne Parasites

Several commonly seen blood parasitic diseases produce anemia through hemolysis. Mycoplasma hemofelis is a common cause of anemia in cats. The parasite attaches to the erythrocyte membrane, causing increased destruction of the cells. Animals that have nonspecific signs of weight loss, anorexia, fever, hepatomegaly, and splenomegaly should have blood films examined for the presence of this microorganism. Some of these animals may be icteric on examination.

Babesia canis and Babesia gibsoni both produce hemolytic disease in the dog (Fig. 5-1). The brown dog tick Rhipicephalus sanguineus transmits these parasites. The presence of this intracellular parasite results in hemolysis of the infected red blood cells. Diagnosis is accomplished by finding the intracellular organism on blood films or by serology testing. Symptoms exhibited in the dog include hemoglobinuria, dehydration, fever, anorexia, and depression. Treatment involves tetracycline administration (for M. hemofelis) and supportive care.

Cytauxzoon felis is a protozoal organism from the southern United States (Florida to Texas and Oklahoma) that is responsible for a fatal disease in cats. The intracellular form of the disease produces an anemia, whereas the extracellular form proliferates within the macrophages lining the vascular system, resulting in blood stasis and vascular occlusion. Cats die within days of the development of clinical signs.

Immune-Mediated Hemolytic Anemia

Although the specific cause of IMHA is unknown, the accelerated red blood cell destruction occurs because of the presence of antibodies that attach to the red blood cell membrane. These cells are then removed by the immune system, resulting in anemia. The antibodies may bind directly to the cell membrane or may attach to a microorganism or drug that has previously been bound to the membrane receptor sites. Adherence of these antibodies activates the complement system, causing agglutination and destruction of the red blood cell.

IMHA is found most commonly in dogs 2 to 8 years of age. A breed predisposition exists in poodles, Old English sheepdogs, Irish setters, and cocker spaniels. The disease is four times more prevalent in female than male dogs.

Clinical syndromes seen with IMHA include immune-mediated extravascular hemolysis, intravascular hemolysis, and cryopathic IMHA.

Immune-Mediated Thrombocytopenia

As in IMHA, IMTP occurs when platelets become coated with antibodies or complement-antibody complexes. Destruction may occur in the spleen, bone marrow, or liver. The inciting cause is usually unknown, but some drugs such as sulfonamide, chlorothiazide, arsenicals, digitoxin, and quinidine have been associated with the development of IMTP. The disease typically appears in dogs 5 to 6 years of age; female dogs are twice as likely to be affected as male dogs.

As platelet numbers decline to less than 30,000 thrombocytes/mm3 blood, bleeding problems develop. Animals are usually presented for bleeding, most commonly epistaxis. Petechial hemorrhages may appear on mucous membranes, earflaps, and other mucocutaneous surfaces. Bloody stool or blood in vomitus is seen occasionally.


Ehrlichia canis was first recognized in the United States in 1963. The disease gained prominence because of the large losses among military working dogs stationed in Vietnam. The disease is seen primarily in tropical and subtropical environments throughout the world.

This rickettsial disease is spread by the tick vector Rhipicephalus sanguineus, the brown dog tick, and is most commonly diagnosed in dogs living in the southeastern and southwestern United States, which are areas with large tick populations. Infection occurs when the organism is transmitted via the tick saliva during a blood meal. It may also be transmitted by blood transfusion from an infected to a noninfected animal. After infection, the organism multiplies within mononuclear cells, both circulating and fixed (liver, spleen, and lymph nodes). The infected circulating cells can infect other organs. Infection results in vascular endothelial damage, platelet consumption, and erythrocyte destruction. Suppression of the bone marrow also occurs, resulting in aplastic anemia.

Dogs unable to mount an adequate immune response become chronically infected.

Aug 31, 2016 | Posted by in GENERAL | Comments Off on Hematologic and Immunologic Diseases

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