Listeriosis is a sporadic bacterial infection that is found worldwide, infecting a wide range of animals including felines, canines, and humans. When ingested or inhaled, the Listeria organism tends to cause latent infection, abortion, and septicemia. In other cases, the bacterium travels to the spinal column, causing symptoms of depression, facial nerve paralysis, and circling. It may take anywhere from as little as two days to as long as two months for a cat to show clinical signs of the infection.

Listeria is a foodborne bacteria found in animals, water, and soil. Listeriosis occurs when a host is affected by the bacterium Listeria monocytogenes. Listeria is commonly found in raw cat foods, canned foods, and dairy products, as well as poultry and beef. Foods can become contaminated with the bacteria if exposed to the bacterium or were not washed, pasteurized or cooked properly. Listeria can also infect humans, dogs, and grazing livestock, but occurrences of cat to human transmission is considered rare to nonexistent. Felines infected with Listeria have variable symptoms from a mild flu-like response to a neurological reaction, though some cats may not present any evident symptoms of infection at all. Felines likely to present clinical signs are old, very young, or those with compromised immune systems, but healthy felines are less likely to fall ill. 

Symptoms of listeriosis in cats depend on the individual’s response to the bacterium. Not all cats who contract the Listeria bacteria will develop listeriosis, as healthy, non-pregnant felines are rarely affected. However, other felines exposed to Listeria will develop mild gastrointestinal symptoms or symptoms related to the brain. The following symptoms may present in a feline affected with Listeria: 

Listeria is a saprophyte organism that thrives in plant-soil based environments, however, bodies of water can also become contaminated due to erosion. The bacterium is easily ingested by grazing animals as they consume plant material and defecate in the same environment, passing the bacterium on to other ruminants. Cattle are a common transit vector of the Listeria bacterium due to the fact that both meat and milk products are commonly used in cat food products. Common sources of Listeria in a cat’s environment can include: 

The diagnosis of listeriosis in cats will begin with a complete physical exam, a review of your feline’s medical record and a consultation with you about clinical signs at home. The doctor will likely ask you about your cat’s current diet, specifically, if she is fed a raw diet or meat or dairy. The veterinarian may request a blood smear test, which may reveal the presence of the Listeria monocytogenes organism under a microscope. However, if the feline is displaying evidence of neurological symptoms the veterinarian may be required to obtain cerebrospinal fluid for observation. The doctor may also ask for a urinary and fecal sample, as the bacterium is sometimes shed in the feline’s waste. 

The treatment of listeriosis in cats depends on the severity of the present symptoms and the individual feline. A feline that presents mild, flu-like symptoms may be prescribed a broad-spectrum antibiotic paired with medication to relieve gastrointestinal upset. In many cases, cats that are brought into the veterinary clinic present severe clinical signs of Listeria and likely require hospitalization. Early, aggressive antibiotic treatment is often the norm for Listeriosis patients. Common antibiotics administered include trimethoprim-sulfamethoxazole, amoxicillin, penicillin or ampicillin.

The prognosis of listeriosis in cats depends greatly on the overall health of the feline, age, and evident symptoms. Felines with compromised immune systems, disease or other unstable health conditions are less likely to make a full recovery. Likewise, if the feline is an infant or elderly, the prognosis is rather grave. The overall prognosis for listeriosis in cats depends on early and aggressive therapeutic treatment by a veterinary professional. If a feline shows signs of neurological abnormalities or illness, such as encephalitis, the outcome may be fatal despite aggressive treatment.