My Cat Has a Fever and is Lethargic : Symptoms, Causes, Diagnosis & Treatment

Having a sick cat is always worrisome. You notice your furry friend is more tired than usual and feels warm to the touch. Upon taking your cat’s temperature, you confirm your suspicions – your cat has a fever. Fevers often go hand-in-hand with lethargy in cats. If your cat has a fever and is lethargic, it likely means something is wrong. But what causes these symptoms, and what should you do about it? This comprehensive guide will cover the common causes of fever and lethargy in cats, symptoms to look out for, when to see the vet, how it’s diagnosed and treated, and how to care for your sick kitty at home. Read on for tips from vets and cat health experts for helping your feline friend feel better fast.

What’s Considered a Fever in Cats?

Before getting into what causes fever and lethargy in cats, let’s cover the basics of fevers in felines. A normal temperature for cats ranges between 100.5°F to 102.5°F. Unlike humans, cats have a naturally higher body temperature.

A fever in cats is defined as a body temperature above 103°F. Fevers are the body’s way of fighting off an infection or illness. Mild fevers under 103.5°F aren’t always a major concern. But higher fevers, especially those over 104°F, can be dangerous if left untreated.

Cats also can’t sweat like humans. So they rely on panting and licking to help cool themselves down. When they’re sick, these cooling mechanisms fall short, allowing body temperature to spike. That’s why it’s crucial to help lower a high fever in a cat promptly.

What Causes Fever and Lethargy in Cats?

There are many possible causes of fevers and lethargy in cats. Here are the most common illnesses and infections that induce these symptoms:

Upper Respiratory Infections

Upper respiratory infections (URIs) are extremely common in cats. The main pathogens behind URIs are the feline herpesvirus and calicivirus. Symptoms include sneezing, congestion, runny nose and eyes, ulcers in the mouth, fever, and lethargy. Young kittens, shelter cats, and multi-cat households are most at risk. URIs are usually mild but can become serious if untreated.


Panleukopenia, also known as feline distemper, is a severe viral disease. It’s caused by the feline parvovirus and spreads through contact with infected feces and bodily fluids. Symptoms appear within a week of exposure and include fever, lethargy, vomiting, diarrhea, and dehydration. The disease can be fatal, especially in unvaccinated kittens. Vaccination is key to preventing panleukopenia.

Feline Leukemia Virus (FeLV)

FeLV weakens the immune system and predisposes cats to secondary infections. Common symptoms are fever, lethargy, weight loss, poor coat condition, swollen lymph nodes, diarrhea, and more. It does not often cause cancer directly but increases cancer risk. There is no cure, but supportive care and veterinary monitoring help manage the disease. Vaccination, testing, and preventing exposure are crucial.

Feline Immunodeficiency Virus (FIV)

FIV is very similar to FeLV, except it progresses more slowly. It compromises the immune system, leaving cats prone to fever, lethargy, weight loss, gum disease, skin problems, and other secondary illnesses. There is no vaccine or cure, but infected cats can live relatively normal lives with good care. Early detection through testing allows for careful monitoring and preventative care.

Urinary Tract Infections (UTIs)

UTIs are common in cats, especially females. Bacteria enter the urinary tract and multiply, causing symptoms like fever, lethargy, straining to urinate, blood in urine, and urinating outside the litter box. UTIs should be treated quickly with antibiotics prescribed by a vet to prevent the infection spreading to the kidneys. Increase water intake and address other risk factors like concentrated urine.

Dental Infections

Bacteria accumulated under the gums or in rotten teeth often spreads to the rest of the body, causing illness. Abscesses around the mouth are also common. Dental infections manifest as oral pain, fever, lethargy, swollen lymph nodes, and loss of appetite. Seek prompt veterinary dental care for diagnosis and treatment. Prevent dental disease through regular teeth brushing and professional cleanings.


Wounds or bacterial invasions anywhere on the body can lead to abscesses, which are pockets of pus and inflammation. Common locations are skin, mouth, face, feet, and body cavities. Symptoms depend on the location but often include fever, lethargy, limping, swelling, and pain. Abscesses should be treated with wound care, antibiotics, and sometimes drainage. Identifying the source helps prevent recurrence.


Feline cancers like lymphoma often cause nonspecific symptoms like fever, lethargy, weight loss, and poor appetite – making diagnosis tricky. Senior cats are most at risk. Seek diagnostic testing if symptoms persist, like bloodwork, imaging, biopsies, and bone marrow aspirates. Cancer treatment typically involves chemotherapy, surgery, radiation, and supportive medical care. Prognosis varies by case.

Inflammatory Bowel Disease (IBD)

IBD involves chronic gastrointestinal inflammation. It interferes with proper digestion and absorption of nutrients. Symptoms commonly include recurrent vomiting, diarrhea, low appetite, weight loss, and lethargy. Diagnosis typically requires intestinal biopsies. IBD is managed through anti-inflammatory medications, dietary modification, and supplements. Controlling flare-ups is key to quality of life.

Recognizing Symptoms of Fever and Lethargy

Aside from the high body temperature, what other signs indicate your cat may have a fever? Here are the common symptoms that accompany fever and lethargy in cats:

  • Warm and dry nose – A healthy cat’s nose feels moist and cool. A dry, warm nose points to a fever or dehydration.
  • Warm ears – Feel your cat’s ears with your hand. Warm, hot ears indicate a fever.
  • Loss of appetite – Sick cats often refuse food and water, leading to dehydration.
  • Hiding and sleeping more – Cats instinctively retreat and sleep when ill to conserve energy for healing.
  • Fast breathing or panting – This helps dissipate body heat from fever. Watch for over 20 breaths per minute at rest.
  • Drooling – Some fevers cause nausea and drooling.
  • Irritation when touched – Sick cats often react when pet due to pain and discomfort.
  • Poor grooming habits – Ill cats neglect grooming, leaving their coats unkempt.
  • Pale or reddened gums – Check your cat’s gums for abnormal color indicating illness.
  • Squinting eyes – Some infections cause eye discomfort and light sensitivity.
  • Dehydration – Lethargy, dry gums, and skin tenting indicate dehydration.

Keep a close eye on all these potential symptoms of fever and illness in your cat. Seek prompt medical attention when you notice multiple symptoms or a fever over 103°F.

When to Take a Cat with Fever and Lethargy to the Vet

It’s always a good idea to call your vet for advice anytime your cat seems ill. But here are some clear signs it’s time to book an urgent veterinary appointment:

  • Fever over 103°F – Fevers this high can be dangerous if left untreated. Seek same or next day vet care.
  • Fever lasting over 2 days – Fevers persisting more than 48 hours likely require medical treatment.
  • Lethargy lasting over 2 days – Lethargy and inactivity this long points to a serious health problem.
  • Difficulty breathing – Labored breathing, wheezing, or open-mouth breathing indicates respiratory distress.
  • Poor appetite beyond 1 day – A cat who refuses food for more than 24 hours risks liver damage from not eating.
  • Severe dehydration – Dry gums, weakness, and collapsing indicate an emergency.
  • Uncontrollable fever – A fever that doesn’t respond to home cooling measures calls for prompt vet intervention.
  • Seizures or convulsions – Sudden seizures or twitching warrant emergency vet treatment.
  • Extreme pain or crying – Cats in severe pain or who vocalize need immediate help.

Trust your instincts. You know your cat best. Any significant changes from their usual energetic, happy self signal it’s time to seek veterinary care right away.

How Vets Diagnose Fever and Lethargy in Cats

Veterinarians use a combination of a full physical exam, diagnostic testing, and observation of symptoms to diagnose the cause of a fever and lethargy. Here are some steps vets commonly take:

  • Complete medical history – Your vet will ask about your cat’s health, symptoms, vaccine status, environment, and recent activities. This provides important clues.
  • Thorough physical exam – Your vet will check temperature, pulse, breathing rate, weight, ears, eyes, mouth, skin, coats, limbs, and abdomen while feeling for lumps and swelling.
  • Blood and urine tests – These screen for issues like infections, kidney problems, diabetes, cancer, FIV, FeLV, blood cell abnormalities, and more.
  • Fecal exam – Stool samples check for intestinal parasites and bacterial infections.
  • Chest x-rays and ultrasound – Imaging of chest and abdomen helps identify respiratory infections, masses, fluid, and organ issues.
  • Biopsies – Skin, lymph node, mass, or intestinal biopsies may be taken for pathological analysis.
  • Bacterial cultures – Testing isolates infectious organisms in wounds, urine, or blood to identify the best antibiotic treatment.
  • Specialist referral – For tricky cases, vets may recommend seeing a specialist like an internal medicine expert, oncologist, dentist, or ophthalmologist.

With fever and lethargy, vets typically move quickly to run diagnostics and start treatment right away. Leaving a high fever untreated for too long can have serious consequences. Notify your vet about any worsening symptoms after diagnosis as well. Ongoing observation and care are key.

How Are Fever and Lethargy Treated in Cats?

Treatment varies based on the specific illness causing the fever and lethargy. But some general treatment approaches include:


Dehydration is a major risk with fever, vomiting, and inappetence. Vets often administer IV or subcutaneous fluids to rehydrate sick cats and provide electrolyte balance. Oral fluids and supplements are recommended for at-home care.


Depending on test results, vets may prescribe:

  • Antibiotics – For treating bacterial infections.
  • Antivirals – For some viral diseases.
  • Anti-inflammatories – To reduce fever and pain. Only use pet-safe versions.
  • Immunosuppressants – For immune disorders or cancers.
  • Antiemetics – To control vomiting.
  • Speciality medications – Such as chemotherapy drugs for cancer treatment.

Follow all medication instructions carefully. Track for improvements as well as side effects. Report concerns to your vet promptly.

Supportive Medical Care

Vets utilize various supportive therapies to help chronically ill cats, such as:

  • Oxygen therapy – For respiratory distress.
  • Tube feeding – For cats unwilling or unable to eat.
  • Pain management – Important for cats to heal, eat, and rest.
  • Blood or plasma transfusions – To treat blood cell deficits or clotting issues.
  • Vitamins and supplements – Such as B-vitamins, iron, omega-3s.
  • At-home nursing care – For severely ill cats, including subcutaneous fluids, feeding tube usage, medication administration, and wound management. Vets teach owners how to provide quality home care.


For conditions like cancer, abscesses, or traumatic injuries, surgery is often necessary, combined with other treatments. Common surgeries include:

  • Tumor removal
  • Abscess drainage
  • Biopsies
  • Tooth extractions
  • Foreign body removal
  • Debridement of necrotic tissue

Strictly follow all post-op instructions to support healing. Limit activity and prevent complications. Discuss pain management with your vet.

Caring for a Cat with Fever and Lethargy at Home

While your cat is recovering from fever and illness, here are some tips for providing care at home:

  • Offer tempting foods. Make food smell enticing by warming it up or adding broths or tuna juice. Try hand feeding. Avoid dairy.
  • Keep water available. Provide fresh, clean water in multiple bowls around the home. Add some low-sodium chicken or vegetable broth for flavor.
  • Hydrate with syringes or droppers. Gently squirt small amounts of water or oral hydration fluids into your cat’s mouth to maintain hydration.
  • Wipe with cool cloths. Gently wipe your cat’s ears, paws, and coat with a cool, damp cloth to help lower body temperature. Avoid cold baths.
  • Limit activity. Make sure your cat rests. Restrict games, jumps, stairs, or anything too strenuous until fully recovered.
  • Provide comfortable bedding. Help your cat feel secure. Wash bedding frequently to avoid reinfection.
  • Give medication properly. Follow vet instructions carefully. Pill pockets or mixing meds in food can help.
  • Keep up hygiene. Gently brush and clean soiled fur. Clean litter frequently. Sanitize food and water bowls between uses.
  • Isolate sick cats. House contagious cats separately from other pets to avoid disease spread.
  • Destress the environment. Reduce noise, visitors, and disturbances to encourage rest. Provide favorite toys.
  • Follow up with the vet. Complete any prescribed monitoring, lab work, or imaging to ensure your cat is improving.

With attentive home care and cooperation from your cat, most fevers and infections can be overcome within a week or two. But call your vet promptly if symptoms worsen or if fever persists beyond 48 hours. Your cat may need further medical intervention or hospitalization. Stay vigilant until your furry friend is back to full health.

When to Seek Emergency Vet Care

In severe cases of fever and lethargy, cats may need emergency or critical care. Rush to an emergency vet clinic right away if you notice any of these extremely concerning symptoms:

  • Difficulty breathing, panting heavily
  • Gums or tongue turning blue
  • Seizures or twitching
  • Loss of consciousness
  • Continuous crying or shrieking
  • Less than 2 urinations in 24 hours
  • Vomiting or diarrhea containing blood
  • Sudden collapse or inability to stand
  • Signs of severe dehydration

These all indicate a life-threatening problem requiring immediate treatment to prevent grave consequences. It’s better to be safe than sorry. Don’t hesitate to seek emergency vet care even outside regular hours if your cat’s condition appears dire.

Preventing Future Fevers and Illness in Cats

While occasional fevers and infections are inevitable, you can take steps to lower your cat’s risk of illness in the future:

  • Vaccinate annually – Core vaccines like panleukopenia and rabies are vital. Discuss other recommended vaccines with your vet.
  • Deworm and use flea control – Parasites weaken the immune system. Treat monthly.
  • Feed quality nutrition – Choose a balanced cat food tailored to your cat’s age and health status.
  • Promote dental health – Brush teeth and get annual dental cleanings. Watch for mouth pain, drooling, or tooth loss.
  • Reduce stress – Limit changes, travel, visitors, and introductions. Make sure litter boxes, food, water bowls, beds, perches, and play areas are amply provided in quiet locations.
  • Limit exposure to contagions – Keep your cat indoors. Avoid contact with stray or unvaccinated cats. House ill cats separately.
  • Spay/neuter your cat – Intact cats are more prone to abscesses and infections like pyometra.
  • Get regular vet checkups – Wellness visits allow early detection and treatment of health problems. Discuss any changes in your cat’s health promptly.

While you can’t prevent all fevers in your cat, excellent nutrition, low stress, proper preventative care, and veterinary guidance helps support your cat’s immune defenses long-term. With attentive care at home and visits with their vet, your beloved feline companion is sure to stay happy and healthy for many years to come.