What are the Causes of Low WBC in Cats?

While white blood cell count is often discussed in the context of serious illnesses like cancer or immune-deficiency disorders, a low count doesn't always indicate a fatal disease. In fact, pretty much any infection or inflammation causes a drop in WBC count. The cells are attracted to damaged tissue and pathogens. A physical injury or a localized illness attracts a large number of them from the bloodstream to a specific location. As they congregate at the site, their concentration elsewhere in the body drops temporarily. This behavior is only cause for concern if the cell count does not return to normal levels after a few days.

White blood cells are produced by the bone marrow, which is a special type of tissue hidden within the hard exterior of your cat's skeletal structure. Diseases that directly affect the bone marrow decrease WBC count by damaging the tissue that produces the cells. The panleukopenia virus, also known as feline parvovirus, is one of several possible suspects in cats. The virus targets cells that reproduce rapidly, so the WBC-producing bone marrow is at high risk, according to cat rescue organization Purrs from the Heart. There is a reliable vaccine for feline parvovirus.

Viruses are among the primary enemies of your cat's immune system. Your kitty's white blood cells fight them practically every day, usually with success. Unfortunately, a few types of virus have very little to fear from your cat's internal defenses. In fact, they actually use the WBCs to reproduce and spread themselves to the rest of your cat's body. The feline immunodeficiency virus (FIV) and feline infectious peritonitis (FIP) are among the worst of these infections. They break into the cells and use the genetic material inside to make copies of themselves. Since anti-immune viruses systematically destroy WBCs, they invariably cause them to decrease in number.

While infection is often to blame for a low white blood cell count, a few other explanations are possible. Some medications, including sorticosteroids, hamper your cat's immune system by repressing cell production. Your cat's brain could also be producing chemicals that suppress her own immune system when she is experiencing stress, according to the Merck Veterinary Manual. Constant exposure to a stress-inducing environment can lead to a chronic reduction in WBC count.