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Feline Infectious Anemia
Introduction
Feline infectious anemia (FIA) is a disorder caused by a tiny red blood cell parasite, Mycoplasma haemofelis (and, less frequently, by Mycoplasma haemominutum).
How Feline Infectious Anemia Affects Cats
Infected animals develop a progressive and usually cyclic decrease in the number of healthy circulating red blood cells, which leads to weakness, inappetance, lethargy, depression, splenomegaly, weight loss, pallor, often a fluctuating fever and sometimes sudden death.
Causes & Prevention
Causes of Feline Infectious Anemia
FIA is caused by Mycoplasma haemofelis and, less commonly, by Mycoplasma haemominutum. These are parasitic bacterial microorganisms that attach to the surface membranes of red blood cells, initiating an immune response in the cat as if the affected blood cells were foreign intruders. Naïve cats can become infected through bites by fleas and ticks that have fed on blood from infected cats. Infection is also transmitted through bite wounds, most commonly incurred during territorial squabbles between intact tom cats. Kittens with infected mothers often are infected either transplacentally, through the milk or from ingesting maternal blood somehow during the birth process. Transfusion with infected whole blood or blood products can confer infection as well.
Preventing Feline Infectious Anemia
Cats kept exclusively indoors are much less likely to develop FIA, because they are not exposed to cat fights and uncontrolled feral cat populations. Routine flea and tick control is especially important if cats are allowed to go outdoors or if indoor cats are in contact with other pets with outdoor access (dogs, cats, others). Neutering and spaying can reduce roaming tendencies and decrease the chances of territorial cat fights.
Special Notes
Finding the causative organism microscopically on a blood smear is diagnostic of FIA. However, these organisms are difficult to detect given the cyclic nature of the disease, and serial blood samples may be recommended. Blood work in infected cats will reflect a regenerative anemia. A polymerase chain reaction (PCR) test has been developed to identify the particular causative organisms, but these may not yet be commercially or widely available.
The more pathogenic strain of this organism can cause fatality in up to 30% of untreated cats, making prompt treatment essential. Cats with concurrent viral infections are usually more severely affected, and co-infection unfortunately is rather common in cats with FIA.
Antibiotics, steroid therapy and perhaps intravenous fluids and whole-blood transfusions may be required. Therapy never completely clears the parasite, although relapse is uncommon.
Symptoms & Signs
Feline infectious anemia (FIA) is an infection by a bacterial blood parasite that latches onto the surface of feline red blood cells, triggering an auto-immune response which results in reduced numbers of healthy circulating red blood cells. Cats infected by this microorganism may be asymptomatic or may develop a number of acute and chronic signs of anemia ranging from mild to very severe. These signs often are vague and nonspecific, reflecting the existence rather than the cause of the anemia.
Symptoms of Feline Infectious Anemia
Red blood cells, also called erythrocytes, contain a molecule called hemoglobin that is responsible for transporting oxygen throughout the body. A decrease in the amount of red blood cells causes an insufficient amount of oxygen delivery to the brain and other vital tissues. Once a cat is infected, it typically takes about 10 days for clinical signs to develop, if they develop at all. Cycles of parasitemia (detectable levels of parasites in the blood) then occur, lasting 1 to 2 days with an average of 6 days between episodes. The level of parasites in the blood can vary markedly within a matter of hours. Adult cats, especially males, are reportedly more frequently affected, as are free-roaming unvaccinated animals and FeLV-positive cats.
In acute cases, affected animals suddenly become weak, lethargic, depressed, anorexic and pale. They may or may not have a fluctuating fever and bouts of vomiting. Their mucus membranes tend to turn blue-ish, and their heart and respiratory rates become elevated. In extreme cases, FIA can cause sudden death. Cats with chronic clinical disease have similar symptoms, but their signs linger and eventually are accompanied by weight loss, poor body condition, an enlarged spleen and chronic fatigue.
Cats infected with feline leukemia virus have a greater risk of developing severe disease when they also become infected with the microorganism that causes feline infectious anemia. Currently, there is no direct evidence that the strength of a cat's immune system plays a significant role in whether or not the symptoms of FIA are mild or severe.
Treatment Options
Feline infectious anemia (FIA) is caused by a bacterial blood parasite and is best treated with antibiotics, immunosuppressant drugs and aggressive supportive care. In severe cases, whole-blood transfusions may be necessary.
Treating Feline Infectious Anemia
The therapeutic goals for cats with infectious anemia are to resolve the clinical signs and restore red blood cell volume. In acute cases, affected cats may need hospitalization so that intravenous fluid replacement, blood transfusion and nutritional support are readily available. Doxycycline/tetracyclines are the current drugs of choice to clear the infective bacteria from the bloodstream. They should be given for a minimum of 21 days. Doxycycline tends to be better tolerated in cats, although it can contribute to esophageal inflammation and strictures in cats. Fluoroquinolone antibiotics are reportedly effective in cats as well, but they can cause blindness in cats if given at high doses. Antibiotic therapy will not actually "cure" feline infectious anemia. However, it can dramatically reduce the number of blood-borne bacteria to the point where the cat is no longer clinically affected.
Because the infectious microorganisms trigger the cat's immune system to destroy "marked" red blood cells, immunosuppressive doses of glucocorticoids are often given for a few days. Prednisone, prednisalone and dexamethasone are among the drugs a veterinarian may consider in these cases. Of course, concurrent diseases that might be exacerbated by steroid administration should be ruled out before steroids are given. When feline infectious anemia becomes life-threatening, whole-blood transfusion may be necessary.
Most cats with feline infectious anemia have a good to excellent prognosis, as long as they receive aggressive supportive care and appropriate antibiotic treatment. Cats that have underlying disease, such as feline leukemia virus or feline immunodeficiency virus infection, have a more guarded prognosis and are more prone to recurrent bouts of anemia. Once infected, whether clinically or subclinically, all cats become "carriers" for life and may become symptomatic during periods of excitement, stress or immunosuppression from whatever cause. Cats with chronic infection but without clinical signs do not require treatment, as no treatment has been identified to completely clear the carrier state.
