Feline Infectious Anaemia

Previously known as: Haemobartonellosis

Caused by: Mycoplasma haemofelis , previously known as Haemobartonella felis

Introduction

Feline Infectious Anaemia, caused by Mycoplasma haemofelis (Mhf), is a regenerative anaemia of cats. The disease occurs worldwide and should be considered as a differential diagnosis for any cat presenting with anaemia.

Aetiology

Mhf is one of a group of organisms known as haemotropic mycoplasmas which infect several other domestic animal species. The causative organism was previously called Haemobartonella felis and thus the disease was known as haemobartonellosis. Polymerase chain reaction (PCR) assays allowing DNA analysis resulted in the reclassification of the organism in 2001. Two other haemotropic mycoplasmas (“Candidatus M. haemominutum” and “Candidatus M. turicensis”) have been identified in cats but appear to be less pathogenic¹.

The mode of transmission of Mhf is poorly understood.

Signalment

The major group at risk for Mhf infection are male cats who spend time outdoors. In many areas of the world an association has been shown between Mhf and retroviral infections¹.

Clinical signs

The peracute disease is associated with severe anaemia and immunosuppression, and can be rapidly fatal.

Fever, anaemia, depression, weakness and jaundice occur in the acute form. In the chronic form animals present with anaemia, lethargy and weight loss.

Cyclic fever may also occur during the transient period of parasitaemia.

Recovery can occur with a regenerative bone marrow response, however severe anaemia may occur in the presence of feline leukaemia virus (FeLV).

Diagnosis

The best diagnostic test is a PCR, which is very sensitive and enables differentiation of the different species.

The organism can also be diagnosed on blood smears. The organism can be intermittently seen microscopically on the surface of red blood cells on Giemsa-stained blood smears. The organism stains blue and can look like rings or rods.

Erythrophagocytosis may be evident and parasitised erythrocytes will become spherical.

The organism must be differentiated from Howell-Jolly bodies and other parasites. Due to the cyclic parasitaemia the organism causes, negative blood smears will not rule out the disease.

Additionally Immunofluorescence of blood smears can demonstrate the organism.

Haematology will show a decreased packed cell volume and a low red blood cell count. The anaemia is usually regenerative. FeLV infection is associated with macrocytosis.

Treatment

Infected cats should be treated with doxycycline for 3 weeks twice daily. Enrofloxacin is also a good treatment choice especially in refractory cases when combined with doxycycline.

A blood transfusion may also be required in cases of severe anaemia.

As blood sucking endoparasites, such as Fleas, are thought to spread disease the animal should also receive flea treatment.

Prednisolone is also advised to treat the immune mediated mechanisms and to prevent further erythrophagocytosis.

Prognosis

Varied prognosis depending on the severity of the anaemia at presentation. If not treated 1/3 of affected animals will die. Antibiotics do not clear the infection so many cats become carriers of the organism however relapses are uncommon.

References

Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2)W.B. Saunders Company

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial