Introduction

Feline infectious anemia (FIA) is a common contagious condition seen most frequently in outdoor intact cats with poor parasite prevention protocols - especially in unneutered males prone to territorial fighting. Two types of mycoplasmal bacteria cause this infection, and their names have recently been reclassified based upon updated genetic sequencing. Both species can cause clinical disease and they can be co-infectious. Many infected cats show no clinical signs, although once infected they remain infected and are carriers for life.

Types of Feline Infectious Anemia

Most clinical cases of FIA are caused by Mycoplasma haemofelis, which formerly was called the “large form” of Haemobartonella felis. A closely related bacterial species, Mycoplasma haemominutum, formerly referred to as the “small form” of Haemobartonella felis, can infect cats as well but less commonly causes clinical disease. Co-infection by both species tends to cause the most severe disease in cats.

FIA can be acute, chronic or subclinical. Acute FIA usually presents with weakness, depression, collapse, rapid breathing, inappetance, fluctuating fever, pale mucous membranes and sometimes sudden death. Chronic FIA typically causes similar signs, and also weight loss and an enlarged spleen. Cats with subclinical feline infectious anemia show no outward signs of illness. Mycoplasma haemofelis is the more pathogenic of the two causative organisms and typically causes both acute and chronic anemia. Why some cats develop clinical signs of infection and others do not remains a mystery. However, any cat infected by these organisms will remain infected for life, whether or not it ever develops symptoms of the disease, and will be a carrier and source of potential infection for other cats.