Does your Cat Have a Weak Immune System? Hereโ€™s what you Should Know


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Your kittyโ€™s immune system defends it from bacteria, parasites, and viruses from the outside world. When this defense system becomes weaker than usual, your feline friend is more vulnerable to illnesses which can be life-threatening.Weak immune system is caused due to deficiency of phagocytes, a type of white blood cell. Phagocytes are vital to the immune system, as they swallow up any foreign particles in the blood. This process is known as phagocytosis. Cats with a low deficiency in phagocytosis are more prone to different types of health problems.


Cats with weak immune systems appear to be healthy for the first few months after birth. Once they pass the nursing stage, their bodies become more vulnerable to infections. The symptoms of a weak immune system are highlighted below:

  • Anorexia
  • Continuous illness
  • Lethargy
  • Mediocre hair coat
  • Recurring infections that donโ€™t respond to conventional medicines
  • Stunted growth

There may be symptoms from contracted infections and viruses such as feline immunodeficiency, feline leukemia, and feline parvoviruses.


The causes for the weak immune system are the following:

  • The cats are born with immunodeficiency disorder, resulting in a low number of phagocytes.
  • The cats get infected with viruses such as feline immunodeficiency virus, feline leukemia virus and feline parvovirus. These viruses attack the immune system which affects the count of phagocytes.


The veterinarian goes through the medical history of the cat and will ask the owner further details about when the symptoms began. The vet will then do the following.

  • Conduct a physical examination
  • Complete blood count (CBC)
  • Urinalysis
  • Biochemistry profile

Additional testing may be done based on the results of the previous tests.


Cats who have congenital weak immune system have no known treatment or cure. Viruses that lead to weak immune system havenโ€™t been caught early enough to effectively treat the problem. There is no effective treatment available that can cure the disease. However, supportive care is used to extend the felineโ€™s life as long as possible.The vet may resort to the following in order to treat the secondary conditions that come with the disease.

  • Antibiotics โ€“ bacterial infections
  • Antimicrobial medications โ€“ yeast/fungal infections
  • Chemotherapy


The best way to keep your feline friends healthy is to be proactive. Isolate the cats from other animals and stop them from leaving your house. Vaccinations have to be administered at the correct time and the vet will give additional vaccines to help the cats. Secondary infections are quite common in this disease, so you will have to visit the vet for medical treatment.The owners of cats who have weak immune system are requested to stay away from reproductive practices as it can be passed on to the next generation.

Feline Immunodeficiency Virus (FIV) 

Cat owners often confuse feline leukemia with feline immunodeficiency virus (or FIV, also known as feline AIDS). Like feline leukemia, FIV is caused by a virus. However, the similarities end there. The diseases differ in many ways including risk, transmission, and prognosis.

What Is FIV?

Much like human immunodeficiency virus (HIV), FIV attacks a catโ€™s immune system, reducing their ability to fight off other infections. An infected cat may be at greater risk of developing other infections because their immune system isnโ€™t as strong as that of a healthy cat. Thus, they are at greater risk of catching what are called โ€œopportunisticโ€ infectionsโ€”those resulting from their depleted immune system being unable to fight infections that a healthy cat may be able to fight off.

A catโ€™s risk of catching FIV is much lower than that of catching feline leukemia because experts do not believe that FIV is spread through routine contact with infected cats but instead through deep bite wounds such as might occur during intense territory battles among male cats. Mother cats can transmit the disease to their kittens, but in some instances the kittens are not infected by the virus.

Signs of FIV

Many of the signs of FIV look like those for feline leukemia including fever, lethargy, weight loss, swollen lymph nodes, and skin and respiratory infections. Other problems include dental or oral infections, diarrhea, eye diseases such as cloudiness in the cornea, vomiting, abscesses, poor coat or hair loss, ear mites, and ringworm, among others. Some cats show neurological problems or anemia. Viewed individually, some of these infections (like ear mites or ringworm) are normal problems affecting even healthy cats. However, a vigilant cat owner should take note when infections occur at greater frequency, duration, or in concert with other infections.

What if My Cat Has FIV?

FIV is not necessarily a death sentence. Unlike feline leukemia, many cats infected with FIV can live healthily for many years, even to a normal life span. If the cat does succumb to the disease, their death is caused by opportunistic infections or diseases rather than the virus itself.

Additionally, if you have multiple cats, the risk of transmission of FIV to other uninfected cats is low as long as they donโ€™t fight and bite. If they do, you may wish to keep them separate. Though the risk of transmission is low, the only way to truly put a risk of transmission at zero is to keep your healthy cat from contact with infected cats.

It's also recommended to keep cats with FIV inside, so they can't spread the virus to other cats in the neighborhood.

If your cat has FIV, you do need to take steps to help them live a long, comfortable life. Because the virus reduces a catโ€™s ability to fight other opportunistic infections, youโ€™ll need to keep a close eye on the state of your catโ€™s health and effectively treat opportunistic infections as they arise. That means taking them routinely for wellness visits to the veterinarian every six months. You may also speak to your veterinarian about the type of diet and supplements that may help boost your cat's immune system.

Protecting My Cat from FIV

The best way to protect your cat from catching FIV is by keeping them away from potentially infected cats. That may mean keeping your cat indoors or allowing them only supervised outdoor access. Neutering and spaying cats can often help reduce the territorial battle instincts while keeping such cats from wandering excessively (and reproducing uncontrollably). 

Because of the general low risk of transmission, following these precautions can be enough to keep your cat FIV-free; however, you may also wish to consider the FIV vaccine. Talk to your veterinarian about the pros and cons of the vaccine and whether it would be a benefit to your cat.

More on Caring for Your Cat

Feline Leukemia
Underweight Pets
Separation Anxiety in Cats

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.

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