Serious & Contagious Cat Illnesses

Serious cat illnesses are sometimes contagious and symptoms can impact a cat's long-term physical health and well-being. They can even be fatal if not treated soon enough. To help you avoid surprises, our Park Pet vets list signs of illness. 

What are common cat illnesses?

You may have difficulty telling whether your cat is sick — and whether their symptoms need attention from a veterinarian.

Cats are unique animals and this goes doubly when they are ill, as they tend to isolate out of instinct when this occurs. So, cat parents need to be on high alert for some serious, contagious cat illnesses. 

Here are some cat illnesses and diseases many cats experience during their lifespan. 


Cats can become infected with numerous intestinal parasites, including some we commonly refer to as "worms", which can lead to many symptoms. While sometimes few to no outward signs of infection will appear, the infection may thrive undetected — while becoming a serious health issue. Common types of worms in cats include roundworms, hookworms, lungworms, and tapeworms. 

Symptoms may include:

  • Weight loss
  • Round, potbellied or bloated abdomen
  • Diarrhea
  • Anemia
  • Coughing
  • Difficulty breathing
  • Constipation

Worms Can Be Transmitted to Humans 

Worms are among the cat illnesses that can affect humans. Roundworm eggs can accumulate in large numbers in cat's feces. People, especially children who ingest these eggs can fall seriously ill and develop health issues such as encephalitis, blindness, and damage to other organs. Surgery may be required to treat blindness caused by roundworms. 

Human skin can be penetrated by hookworm larvae, and lesions may develop. People may acquire tapeworms by ingesting infected fleas, though this is rare. 

Since worms are not always visible or identifiable, you should avoid self-diagnosis. If you suspect your cat may have worms, it's important to bring him or her to a veterinarian for proper, safe diagnosis and treatment. 

Feline Leukemia Virus (FeLV)

This transmittable RNA retrovirus can severely impair a cat's immune system, putting them at risk for many other diseases and infections including lymphosarcoma, kidney disease, and anemia. One of the most commonly diagnosed causes of disease and death in domestic cats, this virus sometimes will not lead to symptoms right away. Any sick cat or new cat entering a household should be tested for FeLV.

Young cats and kittens less than one-year-old are most susceptible to the virus. Cats that are allowed outdoors can be bitten by an infected cat, kittens born to a mother who is FeLV positive, and cats that live with an infected cat are most susceptible to infection. 

While cats can be infected and not display any signs, those who do show symptoms may exhibit: 

  • Lethargy 
  • Weight loss
  • Loss of appetite 
  • Upper respiratory infections 
  • Vomiting and diarrhea
  • Seizures 
  • Respiratory distress 
  • Jaundice 
  • Chronic skin disease
  • Inflamed or pale gums 
  • Poor coat condition 

While there is a vaccine available for cats who are at risk of contracting FeLV, it is not a 100% guarantee against infection. Ask your veterinarian whether your cat should have the vaccine. The best prevention for any infectious disease is eliminating exposure, and that's true here. Have your cat routinely tested for FeLV and keep them indoors and away from cats whose FeLV status is unknown. 

When it comes to diagnosing FeLV, veterinarians can use an ELISA (enzyme-linked immunosorbent assay) test, which will detect antigens to FeLV in the bloodstream. Other tests such as IFA (indirect fluorescent antibody) or PCR (polymerase chain reaction) test may be recommended to confirm positive ELISA test results. 

Feline Calicivirus 

FCV is highly contagious and leads to oral disease and upper respiratory infections in both domestic and exotic cat species.

Symptoms are similar to an upper respiratory infection and can include:

  • Nasal congestion 
  • Discharge from the eyes and nose 
  • Conjunctivitis 
  • Sneezing 

Infected cats may shed the virus in secretions from their eyes or nose, or in their saliva. Airborne viral particles from a sneeze may spray several meters through the air. In a contaminated environment, the virus may survive for up to a week (perhaps longer in a cool, damp location).

Vulnerable cats may also become infected via environmental exposure to items contaminated with infectious secretions or by direct contact with another cat. Symptoms tend to be more severe in young kittens, though all susceptible cats may develop an infection. 

In most cases, vets will diagnose calicivirus based on clinical signs, especially if ulcers are discovered. Definitive diagnosis is sometimes necessary and may be done by collecting samples of cells for specialized testing such as viral isolation or PCR test. 


Caused by uncontrolled growth of cells, cancer can affect a wide range of organs and cells in a cat’s body. This disease first begins to develop within a cell, before attaching to tissue underneath the skin and potentially spreading to other areas.

As mentioned above, Feline Leukemia Virus (which cats can be vaccinated against) commonly contributes to cancer in cats. Other causes may include toxins in the environment. If detected during a physical exam, cancer may be able to be treated.

Symptoms include:

  • Bumps or lumps that change in shape or size
  • Unexplained discharge or bleeding
  • Difficulty urinating or defecating
  • Marked increase or decrease in appetite
  • Chronic weight loss
  • Odour from the mouth
  • Sores that do not heal

Depending on a number of factors, such as the type of cancer and its extent, the specific location, whether the tumour is detected and diagnosed in its early stages, whether an effective treatment plan is developed, and more, a number of treatments such as chemotherapy, radiation and surgery may be used.

What to Do If Your Cat is Ill

If your cat is sick and any of the symptoms above appear, it’s critical that they see a vet as soon as possible. At Park Pet Hospital in Lethbridge, we have an in-house laboratory and pharmacy and are able to handle emergencies to provide your pet with the care they need.

When your cat is ill, every minute counts. Taking them for treatment right away could decrease recovery time, reduce pain and even save a life.

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.

Is your cat displaying signs of an illness? Contact our veterinary hospital to book an exam today.

(403) 328-0028