There are a number of infectious agents that directly or indirectly result in anaemia. The anaemia may be a result of a direct effect of the organism on the erythrocyte itself or due to a secondary immune-mediated process. In some cases, the organism may affect the bone marrow resulting in a non-regenerative anaemia. A mild to moderate non-regenerative anaemia can also develop with any chronic bacterial infection, referred to as the anaemia of chronic disease. The following diseases have been associated with anaemia:

 Viruses:

 Feline leukaemia virus

 Feline immune-deficiency virus

 Feline infectious peritonitis

 Parvovirus

 Mycoplasma:

 Mycoplasma haemofelis (Haemobartonella felis)

 Haemobartonella canis

 Bacteria:

 Ehrlichiosis

 Leptospira

 Protozoa:

 Canine babesiosis

 Feline babesiosis

 Cytauxzoonosis

 Trypanosomiasis

 Leishmaniasis

 Toxoplasmosis

 Fungal:

 Histoplasmosis

 Helminths:

 Ancyclostomiasis

FELINE LEUKAEMIA VIRUS

Feline leukaemia virus infection is a worldwide disease of major significance caused by the retrovirus, feline leukaemia virus (FeLV). Anaemia is a common finding in cats infected with FeLV and has the following possible pathomechanisms:

 The infection, by predisposing the cat to other diseases, may induce anaemia of inflammatory disease.

 Pure red cell aplasia may occur by selective marrow depletion of blast-forming unit erythroids or by inhibition of differentiation blast-forming unit erythroids to colony-forming unit erythroids.

 Haemolytic anaemia may occur as a result of haemobartonellosis or secondary immune-mediated mechanisms.

 Myeloproliferative, lymphoproliferative or myelofibrosis of the bone marrow can occur with FeLV.

Thus the anaemia associated with FeLV can be of a normocytic, normochromic non-regenerative, haemolytic, or macrocytic normo-to-hypochromic non-regenerative nature.

FELINE IMMUNODEFICIENCY VIRUS

Feline immunodeficiency virus (FIV) is caused by a lentivirus (retrovirus) similar to the human immunodeficiency virus (HIV). Anaemia is not uncommon in the disease and is most likely associated with anaemia of chronic disease rather than a direct affect of the virus on the bone marrow or erythrocyte. The anaemia associated with FIV is thus usually normocytic, normochromic non-regenerative.

FELINE INFECTIOUS PERITONITIS

Feline infectious peritonitis (FIP) is a progressive, immune-mediated, debilitating, viral disease that can result in anaemia of chronic infection. Thus the anaemia is usually normocytic, normochromic non-regenerative.

PARVOVIRUS

Parvovirus infection causes acute aplastic anaemia as a result of virus proliferation in progenitor and proliferative cells within the bone marrow. There is also a possibility of bone marrow damage by secondary endotoxaemia or septicaemia. Haematological recovery is usually rapid if the animal survives the infection.

FELINE HAEMOBARTONELLOSIS (Feline infectious anaemia)

Feline infectious anaemia is a mycoplasmal infection that may be asymptomatic (Mycoplasma haemominutum) or manifested by chronic or acute forms that lead to regenerative anaemia (Mycoplasma haemofelis). Infection typically results in a regenerative anaemia that can vary from mild to severe. The anaemia is often complicated by secondary immune-mediated haemolytic anaemia. There may be concurrent infection with FeLV, FIP, FIV, feline babesiosis, and cytauxzoonosis, all of which will worsen the anaemic state.

CANINE HAEMOBARTONELLOSIS

Haemobartonella canis is an opportunistic pathogen of dogs that causes haemolytic anaemia in dogs that are splenectomised and dogs that are treated with cancer chemotherapeutics and immune suppressive drugs. The anaemia is usually mild in nature.

CANINE EHRLICHIOSIS

Canine ehrlichiosis is an acute to chronic disease characterized by infection of monocytes and lymphocytes, with the intra-cellular gram-negative bacterium, Ehrlichia canis. Infection may result in either regenerative or non-regenerative anaemia. In the acute disease, there is acute aplastic anaemia due to the destruction of progenitor and proliferative cells in the bone marrow. Because of the long erythrocyte lifespan, the anaemia is usually mild or absent. The organism can also trigger a secondary immune-mediated haemolytic anaemia. In the chronic phase of the disease, haemopoietic stem cell injury occurs, resulting in moderate to severe non-regenerative anaemia. Ehrlichiosis may be complicated by concurrent infection with babesiosis and haemobartonellosis.

LEPTOSPIROSIS

Leptospirosis is a contagious disease of varying severity, from latent to acute, caused by various species of the Leptospira spirochetes. Infection typically results in regenerative anaemia due to a haemolytic disease process.

BABESIOSIS

In the dog, it is caused by Babesia canis or B. gibsoni, whereas in the cat, the causative organism is B. felis. Infection typically results in a regenerative anaemia due primarily to erythrocyte destruction by the parasite or as a result of a secondary immune-mediated haemolytic anaemia.

CYTAUXZOONOSIS

An infrequent, usually fatal, disease of domestic cats caused by the theileria-like protozoan Cytauxzoon felis. Infection results in mild to moderate non-regenerative anaemia as a result of peracute erythrocyte destruction. Differentiation needs to be made between Cytauxzoon felis and the smaller feline parasites Babesia felis and Mycoplasma haemofelis.

CANINE TRYPANOSOMOSIS

The commonest form is due to Trypanosoma brucei, but T. congolense infections can also occur. Infection can initially result in haemolytic anaemia that has been attributed to immune-mediated mechanisms. However, in chronic infections, anaemia of chronic disease develops and is thus characterised by mild to moderate non-regenerative anaemia.

LEISHMANIASIS

Leishmaniasis is a chronic, systemic, protozoal disease that can result in anaemia as a result of direct bone marrow damage by the organism and/or anaemia of chronic disease can occur. Moderate to severe non-regenerative anaemia is usually evident.

TOXOPLASMOSIS

This is a widespread, frequently subclinical, protozoal disease of many warm-blooded animals and humans throughout the world caused by the coccidia-like protozoan Toxoplasma gondii. Infection can result in non-regenerative anaemia attributed to anaemia of chronic disease.

HISTOPLASMOSIS

Histoplasmosis is a fungal disease caused by Histoplasma capsulatum that can cause subclinical, chronic and severe systemic infections. Infection results in non-regenerative anaemia either as a result of direct bone marrow damage by the organisms or anaemia of chronic disease.

ANCYLOSTOMA

A regenerative anaemia is the principal consequence of A. caninum infection. Initially, the anaemia is normochromic and normocytic, becoming hypochromic, microcytic and non-regenerative as the condition progresses. Secondary immune-mediated haemolytic anaemia can also result from the parasitic infection.