My Cat Has a Fever and is Lethargic: Why & How to Help

When you own a cat, they’re like a child to you. Watching them grow, play, and explore new things are some of the most rewarding moments as a pet parent. Unfortunately, this also means that an ill cat is one of the worst things you can experience.

When my cat has a fever and is lethargic, I feel awful. I hate not knowing what’s wrong with her or what I need to do to help. That’s why I’ve done some research to try and answer these questions for you, so you don’t have to go through the same thing!

There are various possible causes of fever and lethargy in cats, including infections, internal injuries, autoimmune disease, and poisoning.

In this article, I will go over each of these reasons and more, giving symptoms for each, so you know how to spot them in your feline. I also cover the best ways you can help your kitty make a quick recovery!

What Are the Signs of a Fever in Cats?

If a cat’s internal body temperature is above 103 degrees Fahrenheit, they have a fever. It is considered serious if this fever lasts more than a few days or goes beyond 106 degrees Fahrenheit. In these cases, you should always take your feline friend to see a professional as medical attention is required.

When running a fever, it is extremely common to see your cat suddenly lethargic and weak. Other signs of fever, such as your cat not eating much or becoming dehydrated, tend to vary based on the underlying condition, but lethargy is present in nearly all cases. This means it can indicate that your kitty is feverous and something is wrong.

Depending on the cause of your kitty’s fever, they may also show the following symptoms:

• Lack of appetite
• Rapid heart rate
• Dehydration
• Decreased activity
• Shivering
• Poor grooming
• Weakness
• Vomiting and/or diarrhea

Another good indicator of illness can be seen by observing your kitty’s sleeping habits. You’ll likely notice different cat sleeping positions when sick, so a sudden change in how they sleep can suggest something is wrong.

What Would Cause a Fever in Cats?

When your feline is ill, it will be exposed to a pyrogen (fever-producing substance). Depending on the underlying cause of your cat’s illness, this pyrogen will either be produced by the body (endogenous) or taken in from the outside (exogenous). In both instances, this pyrogen causes your kitty’s white blood cells (leukocytes) to release substances, such as interleukin-1 and -6.

These substances will travel to the hypothalamus (an area of the brain in control of temperature regulation) and reset your cat’s internal “thermostat.” This is what causes the physiologic responses that eventually result in a fever.

In more basic terms, a cat will often develop a fever in response to an infection or disease, much like we do when we are ill. There are tons of conditions that can have this effect, but some of the most common causes include:

• Bacterial and viral infections
• Fungal infections
• Internal injury
• Parasitic infections
• Autoimmune disease
• Poisoning or toxins
• Immune-mediated inflammatory disease
• Fever of unknown origin

Below I have given a more detailed description of what is involved with each of these conditions to help you identify the cause of your kitty’s fever.

1. Bacterial and Viral Infections

Bacterial and viral infections are some of the most common causes of fever and lethargy in cats. When a harmful bacterium or virus is picked up, it will start attacking your kitty’s body. This can affect the skin, eyes, ears, and major organs. The severity of your cat’s condition and the parts of the body affected will change depending on the infection that they have contracted.

The other symptoms your cat may display will also vary depending on the area of the body being attacked. For example, if your cat is breathing heavy and lethargic behavior is common, it may have an upper respiratory infection.

2. Fungal Infections

Next up, we have fungal infections. Although there are many species of fungi in the world, only some of them cause infection. Perhaps one of the best-known fungal infections among cats is ringworm. While this only affects a cat’s skin, other fungal infections can impact the entire body.

Much like bacterial and viral infections, the symptoms caused by a fungal infection will differ based on which fungus is causing the disease. Fever and extreme exhaustion are two symptoms that are very common among various fungal infections. You may also notice that your cat has watery eyes and sneezes a lot or that they’ve developed cysts underneath its skin.

3. Internal Injury

Cats have adapted to be very good at hiding their pain, as pain can make them seem vulnerable. Unfortunately, this can make it harder for us to realize they have an internal injury causing them harm. These kinds of injuries are most often caused by trauma, such as being hit by a car, having a bad fall, or getting into a catfight.

If you know your kitty has recently been through a traumatic event, this is likely the cause of their fever. You may also notice your cat is sleeping all day and not eating. In any case, I would highly recommend taking your kitty to the vet after a serious trauma just in case.

4. Parasitic Infections

Unfortunately, parasitic infections are a common occurrence in cats. I know I’ve had to deal with my fair share of flea infestations during my years as a cat mom! Alongside fleas, lice, and mites, several parasites can cause a more severe infection, resulting in fever. If these infections attack the eyes, you may also see your cat’s third eyelid showing.

One such infection that is extremely prevalent in cats is toxoplasmosis. This parasite is usually picked up from contaminated meat or cat feces and can be fatal in the most severe cases. The most common symptoms of this parasitic infection are a high fever, loss of appetite, and lethargy.

5. Autoimmune Disease

Autoimmune diseases occur when the body’s immune system fails to distinguish between normal and foreign cells and, therefore, starts attacking itself. This can affect just one of your feline’s body systems or many of them, but in either case, it will cause your cat to display the symptoms of a normal immune response.

Fever, lethargy, and a loss of appetite are all common in the acute stages of the disease, so don’t be shocked if your older cat is suddenly losing weight, sleeping more often, and seems very warm to the touch. You may also notice swollen joints, ulcerations, and hair loss as the disease progresses.

6. Poisoning or Toxins

When a cat ingests a poison or toxin, it is extremely dangerous. Plants, household cleaners, and other everyday items can be poisonous to your cat, and due to their size, even a tiny dose of one of these toxic substances could be fatal.

Alongside their fever, your cat may vomit or have diarrhea, have breathing difficulties, start twitching and fitting, or even fall into a coma. If you think your feline friend has ingested a poisonous or toxic substance, you must immediately take them to the vet. I cannot stress this enough: do not wait for other symptoms to develop, as this could mean it is too late for your cat to receive help.

7. Immune-Mediated Inflammatory Disease

Immune-mediated inflammatory diseases are very similar to autoimmune diseases because they result from the body’s immune system attacking itself. The main difference between the two is that, while the antibody causing an autoimmune disease can be identified, the cause of an immune-mediated inflammatory disease cannot.

Alongside their fever and lethargy, your feline may show signs of abdominal pain, weight loss, vomiting, and diarrhea. As with many of these causes, the exact combination of symptoms will vary depending on the most affected areas of the body.

8. Fever of Unknown Origin

In rare cases, your cat’s fever may continuously come back or continue despite treatment. If this happens, your feline is said to have a fever of unknown origin, although infections are most commonly the cause.

After several diagnostic tests and examinations, the exact cause of a fever of unknown origin can usually be determined. An effective treatment plan is developed so that your kitty will soon be happy and healthy. However, a specific diagnosis may never be found. Different treatments will be tested if this happens until an effective one is found.

What to Do if My Cat Has a Fever and is Lethargic?

As fever and lethargy are symptoms rather than an illness, the underlying cause must be determined before they can be treated appropriately. You will need to take your cat to the vet to do this. Depending on the severity of the fever, your vet may not even try to reduce your kitty’s temperature, as this is a normal immune response.

The most crucial part of treating any fever is to increase your cat’s hydration levels, as water is essential in speeding up the immune response. All other aspects of your feline’s treatment will change depending on their illness, but some of the most common treatments include:

• Intravenous (IV) or subcutaneous (SQ) fluids: If your cat shows signs of dehydration, it will be given some form of fluid therapy. IV and SQ fluids are commonly used as they can help to lower your feline’s body temperature and provide them with nutrients while still having a low risk of side effects.
• Antibiotics: As we’ve covered, bacterial infections often trigger fever and lethargy in cats. Antibiotics are excellent at eliminating harmful bacteria, so they are often prescribed by vets to help a cat fight off these infections. I’ve had to administer them to my cat before when she had an E. coli infection. Within a few days, the infection was gone!
• Fever-reducing medications: When prescribed by a vet, pain relief and anti-inflammatory drugs, such as nonsteroidal anti-inflammatories, can be very effective in reducing a fever. Your veterinarian will consider your cat’s size and needs when prescribing this treatment. Never try to medicate your feline yourself, as this can be fatal to cats.
• Corticosteroids: Corticosteroids are often used to treat fevers of unknown origin. This drug category is very good at fighting inflammation, which commonly causes fever in cats.
• Surgery: In the most severe cases, your cat may need surgery to remove the cause of its fever and lethargy. This usually happens with severe infections, certain parasites, and tumors. However, surgery can be very high risk, so your vet will only suggest this option if it is the best way to ensure your kitty’s recovery.

MY FINAL THOUGHTS

Does your cat seem hotter than normal? Are they more lethargic and vocal? Often, cats make weird noises when sick, become more tired, and develop a fever. The most common causes include bacterial and viral infections, parasites, poison, and internal injuries.

If your cat’s fever lasts more than a few days, its illness is probably serious and needs to be treated as such. Whenever I notice my cat has a fever and is lethargic, I take her straight to the vet. Although it is usually nothing serious, I always prefer to get her checked out as soon as possible to receive the treatment she needs.

In my case, I’ve only ever had to administer antibiotics to my kitty. However, your cat may need fever-reducing medications, corticosteroids, or surgery to feel better. Your vet knows best, so get their advice to help your furry friend regain full health.