Blanche was a delicate little stray cat of unknown age when her owners adopted her two years ago. She adjusted well to her new home and came in recently for a routine annual visit. She was due for rabies vaccination. Her distemper vaccination was current, but she needed feline leukemia virus vaccination, which is recommended for cats who go outside. We also decided to microchip and deworm her. Blanche tolerated our poking and prodding and went home with a clean bill of health.
A week later, her dad called. “Blanche has been acting weird ever since her visit.”
“Weird how?” I asked. It seems she had been fine for a day or so after, but then had started hiding, barely coming out to eat. “I wouldn’t expect a vaccination reaction to last so long,” I said, and suggested he bring her in.
When I extracted Blanche from her carrier, it was clear she had lost weight and was not the feisty kitty I had seen one week before. She had a fever of over 104, normal being 101-102.5. “Better run some tests,” I advised. As I drew blood, I could see immediately it was unusually thin. It looked watery, flowing too quickly into the tube.
“We’ll need a complete blood count to confirm,” I said, inverting the tube and watching the thin red fluid slosh back and forth “but I can tell just by looking at this that she is anemic. The combination of fever and anemia in an outdoor cat is suspicious for Feline Infectious Anemia (FIA).”
When I was in vet school the organism that causes FIA was called Hemobartonella felis, but in recent years the name has been changed to Mycoplasma haemofelis, to reflect the fact, discovered by gene sequencing, that it is actually a member of the Mycoplasma bacteria group. These bacteria are unusual in that they do not have cell walls but instead attach themselves to the red blood cells (RBCs) of their hosts. The organism usually gets into the cat via flea bites, then attacks the RBCs. When the cat’s immune system notices the abnormal RBC, it does what it is supposed to do. It destroys the abnormal cell. That’s fine if you’ve only got a few abnormal RBCs, but becomes a problem when large numbers of cells are infected. After a while, the body can’t keep making enough new RBCs to replace those being destroyed and kitty becomes progressively more anemic.
FIA symptoms vary widely. Some infected cats show no signs at all, while in others, FIA can be quickly fatal. Typical signs include intermittent fever, depression, weakness, poor appetite, enlarged spleen, pale gums, and jaundice. Cats who have Feline Leukemia Virus or Feline Immunodeficiency Virus are at greater risk, so I immediately tested Blanche for those co-infections, as well as for multiple tick-borne diseases. All were negative. Definitive FIA diagnosis can sometimes be made using a microscope to identify the parasites in the RBCs but the organisms only occur in the blood cyclically, so absence of visible parasites does not rule out the disease. I stained slides of Blanche’s blood but couldn’t identify any Mycoplasma haemofelis.
“She’s just on the edge of needing a blood transfusion,” I sighed. FIA is more common in young tom cats than in females, probably due to life style differences like roaming and fighting that increase the risk of exposure to infected fleas, but we knew little of Blanche’s life prior to her adoption.
“I think it’s possible she was already an asymptomatic carrier of the disease when you got her,” I continued. Maybe last week’s visit and multiple vaccinations stressed her just enough to let the illness become clinical.” Left untreated, one third of cats with FIA will die, so despite our lack of definitive diagnosis, I started Blanche on antibiotics as well as low dose prednisone which I hoped would suppress her immune system just enough to get it to stop destroying her RBCs.
Three days later, Blanche was eating a bit, had gained a little weight, and had a normal temperature. Her anemia had improved but only marginally. “Let’s give this protocol another week,” I suggested.
But a week later, I was not happy. Clinically, Blanche was acting better and had gained even more weight, but her anemia was still marked, and she was again running a low grade fever.
“Let’s change the antibiotic to doxycycline,” I advised. “It’s the best drug for FIA but it’s tricky with cats.” On rare occasions, the tablet form of doxycycline can cause serious esophageal irritation in cats, leading to irreversible strictures. The human liquid form is expensive and not a cat-friendly flavor. We opted to get doxycycline compounded into a palatable fish-flavored slurry and see how Blanche responded. Three weeks of doxycycline cures most cats of FIA, although a significant percentage remain asymptomatic carriers for life.
“We’ll recheck next week,” I said, walking them out, but I was uneasy. Most cats I have seen with FIA have responded more rapidly. I thought back to a similar case several years ago — a cat I initially thought had FIA but ultimately diagnosed with kidney cancer.
In addition to filtering the blood and excreting waste, kidneys produce a hormone that stimulates red blood cell production, hence kidney dysfunction can lead to anemia. Maybe Blanche has kidney cancer, I worried. Bone marrow disease can also cause profound anemia. Maybe Blanche has myeloproliferative disorder — essentially a form of bone marrow cancer. If the anemia does not improve dramatically soon, we will need to proceed with further testing — radiographs, perhaps referral for ultrasound and/or bone marrow aspirate. But today, I am still hopeful she will respond to doxycycline, confirming our presumptive diagnosis of FIA. Then next year, when she’s once again a happy, healthy cat due for her annual exam, I will suggest I visit her via house call, and we be extra careful not to overstress her, in case those little organisms still lurk somewhere in her system.