Anemia is mostly a manifestation of an underlying disease process rather than being a primary disease and it is one of the most frequent and difficult to be solved nosological problems in every day veterinary clinical practice. It is characterized by decreased packed cell volume (hematocrit) and/or decreased hemoglobin concentration. Clinical picture of anemia results from reduced oxygen delivery to tissues, which is insufficient to cover metabolic requirements.
Infectious agents are among the most frequent causes of anemia in cats including:
1. Hemoparasites, Haemobartonella, Cytauxzoon and Babesia spp and less often Ehrlichia and Leishmania species.
2. Viruses and mainly FeLV and FIV and
3. A variety of inflammatory diseases.
Hemoparasites cause regenerative anemia and consequently reversible, either of acute or chronic type. To the contrary both anemia due to viruses and to inflammatory state (Anemia of Inflammatory Disease-AID) are chronic and of the hypoplastic or aplastic form.
ANEMIA CAUSED BY HAEMOPARASITES
Haemobartonellosis is the most frequent cause of anemia in cats either as primary or secondary opportunistic disease. The prevalence of the disease is higher in male and outdoor roaming cats.
Anemia is caused by Haemobartonella felis a rickettsial microorganism with epicellular location on the surface of erythrocytes. On blood smears stained with Giemsa, Haemobartonella felis is detected as a basophilic with rods, cocci and rigs microorganism of a 0.5µm diameter.
It is mainly transmitted by blood sucking arthropods and potentially by cat-bite wounds, iatrogenically by blood transfusion and from female cats to kittens either intrauterally or by the milk during lactation. The clinical picture is the one of hemolytic anemia with acute, subacute or chronic form. However, icterus is only occasionally observed even in acute cases as the hemolysis is extravascular (erythrocytes rupture is followed by erythrophagocytosis in spleen and liver).
Detection of the microorganisms on blood smears is not always possible even in acute cases. Experimental data showed an episodic presence of the microorganism in blood smears.
Cats that recover the acute phase remain carriers and from one hand they can transmit the disease and from the other they develop recurrent episodes of parasitemia and relapses, which are potentiated by immune suppression (FeLV, FIV, others).
Doxycycline appears to be the treatment of choice. Quinolones and chloramphenicol are also effective.
Babesiosis or Piroplasmosis is a widely known hemolytic type anemia of infectious etiology in many animal species.
Feline babesiosis has been documented in South Africa and South America while sporadic cases have also been reported in North America and in the Mediterranean area. Different strains of Babesia from different geographical areas have been reported to infect cats and other feline species.
An acute or subacute disease occurs with fever while the presence of icterus is inconstant. The anemia is of intensive regenerative type. Babesia spp. can be only occasionally demonstrated as pisiform bodies in red blood cells using Giemsa strains on thin blood smears but parasitemia is variable.
Primaquine is the treatment of choice.
Feline cytauxzoonosis is a generally fatal disease of domestic cats, caused by the protozoon Cytauxzoon felis. It is transmitted by ticks and mainly by the Dermacentor variabilis. It is frequent in South Africa where it has been mainly studied, while sporadic cases from North America have also been reported.
Hemolytic anemia, whenever observed, is due to the direct parasitosis of erythrocytes by the merozoites during the erythrocyte phase. To the contrary, the severity of the disease and finally death is caused by the attack of macrophages of many tissues (spleen, liver, lymph nodes and blood marrow) by schizonts. Consequently, the initial regenerative hemolytic anemia is transformed to hypoplastic or aplastic anemia.
There is no effective specific treatment.
Regarding the anemia caused by Ehrlichia and Leishmania, although the number of cases studied is relatively small (Ehrlichia in South Africa and Leishmania in South Italy), it seems that both cause an hypoplastic or aplastic type similar to those caused by the same hemoparasites to dogs.
b. ANEMIC CAT AND FELV/FIV INFECTIONS
Many pathological agents such as bacteria and viruses could cause, among other disturbances, anemia to cats.
FeLV/FIV infections are of great interest as pale mucous membranes are a common reason of asking veterinary consultation. Often, though anemia is a finding of minor importance for the evolution of these diseases.
Viruses cause anemia by several mechanisms. Among these, the suppression of bone marrow (hypoplasia or aplasia) in different levels is one of the most important, so that normocytic and normochromic anemia is observed. A lot of the FeLV/FIV positive cats are also present hemolytic anemia, subacute or chronic due to secondary infections (e.g., Haemobartonella) as well as immune-mediated hemolysis.
Most of the available bibliographic data concern anemia in FeLV positive cats, while anemia in FIV cats is less studied and it is usually referred as anemia caused by an unknown mechanism.
c. ANEMIA OF INFLAMMATORY DISEASE
Many animals suffering from chronic inflammatory diseases present anemia which was previously characterized as anemia of idiopathic etiology. Nowadays, this anemia is described by the term Anemia of Inflammatory Disease (AID) and it is characterized by a non-regenerative, normochromic and normocytic type, which is usually of a mild to moderate in severity.
More recent studies demonstrated that three factors are involved in its pathogenesis: Shortened survival erythrocytes, decreased iron availability and decreased bone marrow response to anemia.
Regarding the clinical picture of animals affected by AID, anemia can be overseen covered by other more dominant findings of the primary disease. The list of these diseases is constantly elongated and could include every infection (bacterial, viral, parasitic and mycotic), neoplasms and immune-mediated diseases.
Diagnosis is based on laboratory findings, mostly hypoferremia, normal of increased ferritin concentration in serum and the decrease in TIBC (Total Iron Binding Capacity) in dogs with normocytic and normochromic anemia.
DIFFERENTIAL DIAGNOSIS OF ANEMIA OF INFECTIOUS ETIOLOGY
Apart from the cases where the causative agent is easily identified in blood smears, the laboratory support is required, in order to be investigated the following: a) the type of anemia by the determination of MCV, MCHV, total proteins, presence of polychromatophilic rubricytes and reticulocytes b) Biochemical parameters such mainly total, direct and indirect bilirubin as well as specific serological tests.