# Viral and Bacterial Diarrhea in Cats: Causes and Treatment Diarrhea in cats has many possible causes, and infectious ones top the list. A cat diarrhea bacterial infection often comes from eating contaminated food or water, while viruses like feline enteric coronavirus and panleukopenia are also frequent culprits. Most cases are short-lived with supportive care, but some need testing and targeted treatment. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Most short bouts of diarrhea in cats are self-limiting and improve with hydration and nutrition support, so routine antibiotics are not recommended for uncomplicated cases [1]. - Bacterial causes include Campylobacter species, which cats can pick up from undercooked poultry, raw meat, or contaminated water [2]. - Viral causes include feline enteric coronavirus, which is highly contagious among cats in close contact but usually not fatal [3]. - COVID-19 is not a recognized common cause of diarrhea in cats, and there is no evidence that it is a major concern for feline gut disease. - Red flags like blood in stool, repeated vomiting, lethargy, or a kitten with diarrhea mean you should call your veterinarian promptly. ## What Is Infectious Diarrhea in Cats? Diarrhea means your cat passes loose or watery stool more often than usual. When the cause is a virus, bacterium, or other infectious organism, vets call it infectious diarrhea. The large intestine helps maintain fluid and electrolyte balance, absorbs nutrients, and stores feces, so when it is damaged by illness or infection, diarrhea often results [3]. Infectious diarrhea can be short-term (acute) or long-lasting (chronic). Acute cases often follow a diet change, stress, or exposure to a new environment. Chronic diarrhea is a common clinical sign in cats and can stem from many underlying conditions, which makes accurate diagnosis important for effective treatment [4]. ## Signs Owners Notice The most obvious sign is stool that is softer, looser, or more frequent than normal. You may also see: - Straining to defecate or going outside the litter box - Mucus or blood in the stool - Weight loss or poor appetite, especially with long-term infection [5] - Vomiting, lethargy, or hiding - Dehydration, which you can check by gently lifting the skin on the back of the neck Cats with long-term infection may show weight loss, poor appetite, straining to defecate, and diarrhea, and any of these signs may be continuous or come and go [5]. If your cat has diarrhea along with worms, the picture can look similar, so see [Cat Diarrhea with Worms: Causes and Treatment Options](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-diarrhea-worms-causes-treatment). ## Causes and Risk Factors ### Bacterial Causes Campylobacter infection is a bacterial disease caused by various Campylobacter species. These organisms can be found in carrier cats that show no signs as well as in ill cats, and cats recently obtained from shelters can be sources of human infection [2]. Exposure to feces of infected animals and food- or waterborne transmission appear to be the most common routes. One suspected source for pets and people is eating undercooked poultry and other raw meat or dairy products, and wild birds may also contaminate water [2]. Other bacteria can play a role too. Gram-negative bacterial overgrowth is widely presumed to be a key cause of feline diarrhea, and gut bacteria from diarrheic cats can impair intestinal barrier integrity and trigger colon inflammation in research models [6]. This does not mean every cat with diarrhea needs antibiotics, but it does mean bacteria matter in many cases. ### Viral Causes Feline enteric coronavirus is highly contagious, especially among cats in close contact, and it is closely related to the virus that causes feline infectious peritonitis. Infection causes inflammation of the small intestine but is not usually fatal [3]. Feline panleukopenia virus causes severe enteric and systemic disease in cats, with particular importance in shelters where susceptible kittens, high population turnover, and contamination increase infection pressure [7]. Feline astrovirus is recognized as a cause of feline gastroenteritis, though a study of cats in Japan found it at low prevalence and often co-detected with other enteric viruses in asymptomatic cats [8]. This tells us that finding a virus in stool does not always mean it is the cause of the diarrhea. ### Other Infectious Causes Protozoa can also cause diarrhea. Amebiasis is caused by the amoeba Entamoeba histolytica and produces inflammation of the large intestine with persistent diarrhea. Cats become infected by eating food or water contaminated with feces containing infective cysts [5]. Coccidiosis is an invasion and destruction of intestinal tissues by protozoa, and while infections are very common, signs are much less common [5]. ### Risk Factors - Living in or coming from a shelter or multi-cat home [2][7] - Eating raw or undercooked meat, poultry, or dairy [2] - Contact with infected feces or contaminated water [2] - Being a kitten or having an incomplete vaccination history [7] - Stress, diet changes, or a disrupted gut microbiome [9] ## How Veterinarians Diagnose It Your vet starts with a history and physical exam. They will ask about diet, litter box habits, vaccination status, and possible exposure to other cats. From there, testing depends on how sick your cat is and how long the diarrhea has lasted. Common tests include: - Fecal exam to look for parasites, protozoa, and bacterial clues [5] - Fecal culture or PCR testing for specific bacteria like Campylobacter [2] - Blood work to check hydration, electrolytes, and organ function - Viral testing when panleukopenia or coronavirus is suspected [7] Diagnostic testing should be tailored to each case, focusing on ruling out systemic illness or infectious causes [1]. In many uncomplicated cases, extensive testing is not needed right away. | Test | What It Looks For | When It Is Used | |---|---|---| | Fecal float or smear | Parasites, protozoa, some bacteria | First-line for most diarrhea | | Fecal PCR or culture | Campylobacter and other bacteria | Suspected bacterial infection [2] | | Blood chemistry | Dehydration, electrolyte loss, organ health | Sick or dehydrated cats | | Viral PCR | Panleukopenia, coronavirus | Kittens, shelter cats, severe cases [7] | ## Treatment Options Treatment depends on the cause, the severity, and your cat's overall health. Most cases of acute diarrhea in dogs and cats are self-limiting and primarily managed with supportive care, including hydration and nutrition [1]. ### Supportive Care Fluids are often the first step, especially if your cat is dehydrated. Your vet may give fluids under the skin or into a vein. Nutrition matters too. Recent evidence advocates against routine antibiotic use in uncomplicated acute diarrhea to prevent antimicrobial resistance and microbiome disruption, with targeted therapy reserved for systemic or bacterial infections [1]. Antiemetics may be used if your cat is vomiting [1]. ### Antibiotics and Targeted Therapy When a bacterial infection is confirmed or strongly suspected, your vet may prescribe antibiotics. Antibiotics may also be prescribed to treat amebiasis [5]. The choice of drug and the dose are calculated by your veterinarian based on your cat's weight and health, so never use leftover antibiotics from another pet or a human prescription. ### Antivirals for Viral Disease Feline infectious peritonitis used to be regarded as fatal, but effective antiviral therapies, particularly nucleoside analogues such as oral GS-441524, have changed the outlook. FIP is now a treatable and frequently curable disease, with treatment success rates often exceeding 90% for GS-441524 [10]. This is a specialized treatment your vet will manage. ### Nutritional Management Nutritional management is indispensable for the long-term treatment of chronic diarrhea [4]. Your vet may recommend a highly digestible diet, a novel protein diet, or a fiber-modified diet depending on whether the diarrhea is small bowel or large bowel in origin. For home care basics between visits, see [Cat Diarrhea Home Treatment](/knowledge/veterinary-medicine/symptom-guides/cat-diarrhea-home-treatment). ## Recovery, Outlook, and Long-Term Management Most cats with uncomplicated acute diarrhea recover within a few days with supportive care [1]. Cats with bacterial infections that are properly treated usually improve quickly. Viral infections like feline enteric coronavirus cause small intestine inflammation but are not usually fatal [3]. Chronic diarrhea is a different story. It can be classified as small or large bowel diarrhea based on clinical signs, and the mechanisms involved are complex, including osmotic and secretory diarrhea, impaired intestinal barrier function, and dysregulated intestinal motility [4]. Long-term management often combines diet, monitoring, and periodic vet visits. Cats with long-term amebiasis may show weight loss, poor appetite, straining to defecate, and diarrhea that comes and goes [5]. If your cat has chronic diarrhea, your vet may want to recheck stool samples and adjust the diet over time. For a broader look at causes and home care, see [Cat Diarrhea: Causes, Home Care, and When to Worry](/knowledge/veterinary-medicine/online-vet-and-care-costs/cat-diarrhea-causes-home-care). ## Prevention You cannot prevent every case, but you can lower the risk. - Cook meat and poultry thoroughly and avoid raw meat or dairy treats [2] - Keep your cat away from wild bird areas and standing water that may be contaminated [2] - Scoop the litter box daily and wash your hands after handling stool [2] - Keep vaccinations current, especially for kittens and shelter cats [7] - Introduce diet changes slowly to avoid disrupting the gut microbiome [9] - Isolate a new cat from others until your vet confirms it is healthy [2] If you have a kitten with diarrhea, the risks are higher. See [Kitten Diarrhea: Causes, Safe Home Care, and Emergency Signs](/knowledge/veterinary-medicine/digestive-and-urinary-care/kitten-diarrhea-causes-and-care) for age-specific guidance. ## Limitations and When to Contact a Veterinarian This article gives general information. Your individual cat needs a veterinarian who can examine it, run tests if needed, and set a treatment plan. Contact your vet the same day if your cat: - Has blood in the stool or black, tarry stool - Is vomiting repeatedly or cannot keep water down - Seems lethargic, weak, or is hiding more than usual - Has diarrhea lasting more than 24 to 48 hours - Is a kitten, senior, or has a chronic illness Go to an emergency clinic now if your cat: - Is unresponsive, collapsing, or having trouble breathing - Has severe abdominal pain or a swollen, painful belly - Is showing signs of severe dehydration, such as tacky gums or skin that stays tented - Has uncontrolled vomiting and diarrhea together For routine concerns, such as a single soft stool in an otherwise bright cat, call your vet's office for advice. They can tell you whether to monitor at home or bring your cat in. ## Frequently Asked Questions ### Can COVID-19 cause diarrhea in my cat? COVID-19 is not a recognized common cause of diarrhea in cats. The coronaviruses that matter most in feline medicine are feline enteric coronavirus and the virus that causes feline infectious peritonitis [3]. If your cat has diarrhea and you have concerns about any infection, your veterinarian can advise you. ### How do I know if my cat's diarrhea is bacterial or viral? You usually cannot tell from looking at the stool. Your vet may need a fecal test, culture, or PCR to identify bacteria like Campylobacter [2]. Many cases are managed without identifying the exact organism because most acute diarrhea is self-limiting [1]. ### Should my cat get antibiotics for diarrhea? Not automatically. Routine antibiotic use is not recommended for uncomplicated acute diarrhea because it can promote resistance and disrupt the gut microbiome [1]. Antibiotics are reserved for confirmed or strongly suspected bacterial infections, and your vet sets the dose based on your cat's weight and health. ### Is my cat's diarrhea contagious to me or other pets? Some causes are contagious. Campylobacter can spread from cats to people, especially cats recently obtained from shelters [2]. Feline enteric coronavirus is highly contagious among cats in close contact [3]. Wash your hands after handling stool and keep sick cats separated from others. ### How long does infectious diarrhea last in cats? Most uncomplicated acute cases improve within a few days with supportive care [1]. Chronic diarrhea can last weeks to months and often needs a diagnostic workup and long-term nutritional management [4]. If diarrhea lasts more than 24 to 48 hours or your cat seems sick, call your vet. ## Related Articles - [Cat Diarrhea Treatment](/knowledge/veterinary-medicine/symptom-guides/cat-diarrhea-treatment) - [Cat Diarrhea with Worms: Causes and Treatment Options](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-diarrhea-worms-causes-treatment) - [Cat Diarrhea: Causes, Home Care, and When to Worry](/knowledge/veterinary-medicine/online-vet-and-care-costs/cat-diarrhea-causes-home-care) - [Cat Diarrhea Home Treatment](/knowledge/veterinary-medicine/symptom-guides/cat-diarrhea-home-treatment) - [Kitten Diarrhea: Causes, Safe Home Care, and Emergency Signs](/knowledge/veterinary-medicine/digestive-and-urinary-care/kitten-diarrhea-causes-and-care) - [What to Do If Your Cat's Medication Is Causing Diarrhea](/knowledge/veterinary-medicine/pet-medication-guide/cat-medication-diarrhea-what-to-do) - [Colitis in Cats: Causes, Symptoms, and Treatment](/knowledge/veterinary-medicine/digestive-and-urinary-care/colitis-in-cats-treatment) - [Long-Term Diarrhea in Cats: Causes and Next Steps](/knowledge/veterinary-medicine/digestive-and-urinary-care/long-term-diarrhea-in-cats) - [Why Does My Cat Keep Getting Diarrhea? Causes and Next Steps](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-recurring-diarrhea-causes) - [Viral Enteric Infections](/knowledge/viruses/avian-viruses/viral-enteric-infections) ## References 1. [From Diagnosis to Resolution: A Practical Guide to Acute Diarrhea in Veterinary Patients](https://pubmed.ncbi.nlm.nih.gov/41763984/). The Veterinary clinics of North America. Small animal practice, 2026. 2. [Disorders Caused by Bacteria of the Digestive System in Cats - Cat Owners](https://www.merckvetmanual.com/cat-owners/digestive-disorders-of-cats/disorders-caused-by-bacteria-of-the-digestive-system-in-cats). Merck Veterinary Manual. 3. [Disorders of the Stomach and Intestines in Cats - Cat Owners](https://www.merckvetmanual.com/cat-owners/digestive-disorders-of-cats/disorders-of-the-stomach-and-intestines-in-cats). Merck Veterinary Manual. 4. [Feline chronic diarrhea: causes and nutritional management](https://pubmed.ncbi.nlm.nih.gov/42502773/). Veterinary and animal science, 2026. 5. [Disorders Caused by Protozoa of the Digestive System in Cats - Cat Owners](https://www.merckvetmanual.com/cat-owners/digestive-disorders-of-cats/disorders-caused-by-protozoa-of-the-digestive-system-in-cats). Merck Veterinary Manual. 6. [Gram-Negative Bacterial Overgrowth Predominated by: Potential Association with Intestinal Barrier Impairment and Inflammatory Diarrhea in Cats](https://pubmed.ncbi.nlm.nih.gov/42798011/). Veterinary sciences, 2026. 7. [Gut Microbiome Disruption in Shelter Cats with Feline Panleukopenia: Virome Co-Detection and Enteric Dysbiosis](https://pubmed.ncbi.nlm.nih.gov/42450634/). Biology, 2026. 8. [Low prevalence and frequent co-detection of feline astrovirus with feline enteric coronavirus and feline bocaparvovirus in asymptomatic cats in Japan](https://pubmed.ncbi.nlm.nih.gov/42168424/). Archives of virology, 2026. 9. [Identification of Gut Microbiome and Metabolites Associated with Acute Diarrhea in Cats](https://pubmed.ncbi.nlm.nih.gov/37428087/). Microbiology spectrum, 2023. 10. [Update on Treatment of Feline Infectious Peritonitis: European Advisory Board on Cat Diseases (ABCD) Guidelines](https://pubmed.ncbi.nlm.nih.gov/42043241/). Viruses, 2026. ## Further Reading - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information) - [American Veterinary Medical Association: Pet Care](https://www.avma.org/resources-tools/pet-owners/petcare)