Viral stomach bugs in dogs: vomiting and diarrhoea

Overview

Viral gastroenteritis means virus-induced gastrointestinal inflammation. "Stomach bug" is an everyday symptom-based term; diarrhoea alone does not identify the organism. Diet changes, parasites and other internal diseases can cause similar signs.

Parvoviral diarrhoea occurs particularly in inadequately vaccinated puppies. Canine enteric coronavirus can also cause vomiting and diarrhoea. Rotavirus is a possible cause of diarrhoea particularly in young puppies.

Viral infection can be symptom-free, so absence of signs does not prevent spread within a group. Vaccination status and concurrent signs in other dogs help assess an outbreak.

Causes

Faecal-to-oral transmission

Parvovirus usually spreads between dogs through virus-containing faeces. Contaminated equipment, surroundings or people can also carry it. Enteric coronavirus also usually spreads by the faecal–oral route. Rotavirus spreads through contact with faecal contamination.

Parvovirus lacks a protective lipid envelope and resists many ordinary cleaners. Coronavirus has a lipid envelope that makes it more vulnerable to environmental cleaning and disinfection. Prevention therefore requires methods suited to each virus's resistance.

Intestinal damage affects severity

Enteric coronavirus multiplies in small intestinal villi and impairs nutrient absorption. Parvovirus damages renewing intestinal cells and can break the protective barrier. It can also reduce white blood cells involved in immune defence. Together, these changes help intestinal bacteria enter the bloodstream.

Concurrent intestinal parasites or other pathogens can worsen parvovirus disease. In rare severe coronavirus infections, the virus can spread beyond the intestine to other organs. Canine enteric coronavirus differs from the respiratory coronavirus associated with kennel cough. It also differs from the virus causing human COVID-19.

Risk factors

Puppies around 6 weeks to 6 months old are most susceptible to parvovirus. Risk rises when maternal antibodies decline before adequate vaccine protection develops. An unvaccinated or incompletely vaccinated older dog can also become ill.

Symptomatic rotavirus risk is greatest in puppies under 12 weeks. Adults can also become ill in heavily contaminated surroundings or with weakened immunity. Crowding and poor hygiene promote coronavirus spread in groups. Weaning, overcrowding and malnutrition can increase parvovirus severity.

Breeds at increased parvovirus risk include Rottweilers, Dobermanns and German Shepherd Dogs.

Typical symptoms

Parvovirus signs usually start within 5–7 days of infection, ranging from 2 to 14 days. Initially, your dog may only be tired, off food or feverish. Vomiting and severe diarrhoea may develop over the following 24–48 hours.

• Stools become loose or watery and more frequent.
• Your dog vomits and eats less.
• Your dog is subdued and cannot play or exercise normally.
• Blood may appear in diarrhoea.
• Weight falls and your dog may rapidly look dehydrated.

About 25% of dogs with parvovirus do not have bloody diarrhoea. Absence of blood therefore does not exclude it. Mild coronavirus infection may cause only brief diarrhoea without a major change in general condition.

Complications and consequences

Dehydration can impair circulation

Diarrhoea causes excessive intestinal water loss and can lead to dehydration. Vomiting alongside diarrhoea accelerates this further. Dehydration disrupts electrolytes and strains the kidneys. Severe fluid loss can cause organ dysfunction and death.

Severe parvovirus can cause sepsis and shock. Young puppies may also develop dangerously low blood glucose. Intussusception is a possible complication, particularly suspected with abdominal pain.

In intussusception, one intestinal segment slides inside an adjacent one and can obstruct it. Severe parvovirus can also involve thrombosis and acute respiratory distress syndrome. Heavy intestinal protein loss can lower blood albumin.

Outlook depends on the virus and care needs

Many mild enteric coronavirus infections resolve with supportive care. However, severe infection spreading to other organs can be fatal. With appropriate supportive care, parvovirus survival is generally 70–90%. With intensive hospital care, it can exceed 90%. Most puppies surviving the first 3–4 days of illness recover completely in about 1 week.

Veterinary-managed outpatient parvovirus protocols have reported success around 80%. Recovery produces long-term, possibly lifelong immunity to parvovirus.

A new enteric coronavirus variant was found in dogs during a British gastroenteritis outbreak in 2022. Of 438 owner questionnaire responses, 170 described signs lasting 3–7 days (38.8%). These outbreak findings cannot represent the usual duration of every viral diarrhoea because each dog's cause was not confirmed.

Diagnosis at the vet

Condition and dehydration determine investigation extent

Your vet assesses whether your dog is otherwise well, dehydrated or systemically ill. Mild, rapidly resolving diarrhoea generally needs no extensive investigations. Blood tests assess fluid balance and metabolic changes in a seriously ill dog. A blood count can show parvovirus-associated white cell reduction.

Faecal samples can test for parasites mimicking viral diarrhoea. Suspected obstruction requires imaging such as X-rays. Persistent abdominal pain or vomiting may need intussusception excluded.

Virus testing follows the suspected infection

Parvovirus is sought in faeces using a rapid antigen test or PCR detecting its genetic material. Suspected patients are tested promptly so isolation can limit spread. A test may be falsely negative very early or after shedding decreases. A live parvovirus vaccine may cause a false positive within 4–10 days of vaccination.

Enteric coronavirus can be tested by faecal PCR. Respiratory coronavirus requires a different sample, such as a nasal swab. Rotavirus can be detected in faeces by PCR or antigen testing. Coronavirus detection is interpreted alongside symptoms because dogs can carry it without signs.

Faecal parvovirus shedding may fall rapidly about 10–12 days after infection. This can occur just 3–4 days after signs begin and complicate interpretation. Profuse watery diarrhoea can also dilute a sample and produce a false negative.

Treatment

Fluids and nutrition support intestinal recovery

Your vet bases treatment on the severity of dehydration, vomiting and systemic illness. There is no established targeted treatment that eliminates enteric coronavirus. Severe illness requires intravenous fluids and close monitoring. Fluid therapy replaces lost water and corrects electrolyte and metabolic disturbances.

In parvovirus patients, potassium and blood glucose need particular attention during treatment. Persistent vomiting can be treated with an antiemetic prescribed by your vet. Early feeding through the digestive tract supports recovery of the intestinal barrier in parvovirus patients. Hospitalised dogs that will not eat can receive nutrition through a feeding tube.

A suitable, easily digestible diet can be used for mild diarrhoea. A home-made rice and meat diet is not nutritionally complete for long-term feeding.

For hospitalised parvovirus patients that are not eating, the aim is to start tube feeding within 12 hours. If your dog cannot tolerate feeding through the digestive tract and has not eaten for more than 3 days, intravenous nutrition may be needed.

Antibiotics are not needed for every case of diarrhoea

Mild acute diarrhoea in an otherwise well, hydrated dog is generally not treated with antibiotics. Even blood in the stools does not automatically mean an otherwise well dog needs antibiotics. Systemic signs persisting despite adequate fluid therapy may justify antibiotic treatment. Intestinal damage and reduced neutrophils in parvovirus increase the risk of secondary bacterial infection.

Antidiarrhoeal medicines that slow intestinal movement are not recommended for parvovirus. A common human diarrhoea medicine can be harmful to dogs. Evidence is insufficient to recommend either for or against probiotics for acute diarrhoea.

Targeted parvovirus treatment is also being developed

A monoclonal antibody treatment that recognises parvovirus has been developed. Its effectiveness in typical clinical patients and the best time to give it are still being investigated.

Prevention

Parvovirus vaccination is a core vaccination for dogs. Vaccination does not protect against every virus causing vomiting and diarrhoea. Canine enteric coronavirus vaccination is currently not recommended routinely. There is no evidence that current coronavirus vaccines protect against rare severe forms of the virus.

Keep an infected dog apart from healthy dogs to interrupt transmission. Remove faeces and other visible dirt from surfaces before disinfection. Parvovirus control requires a disinfectant effective against it. Ordinary quaternary ammonium compounds do not reliably eliminate parvovirus.

Parvovirus can survive indoors at room temperature for at least 2 months. Outdoors, protected from sunlight and drying, it can survive for months or even years. An incompletely vaccinated puppy needs protection from exposure until vaccine immunity develops.

Protective clothing and gloves when caring for a parvovirus patient help prevent carrying the virus to healthy dogs. Completely disinfecting outdoor soil is often practically impossible.

Important for dog owners

Tell the practice beforehand if you suspect infectious diarrhoea or parvovirus, so your dog can be isolated from others. Bring a fresh faecal sample for testing. Record when signs began, vomiting episodes, stool appearance and your dog's appetite. Also note whether other dogs in your household or group have become ill.

Keep fresh water available at all times for an otherwise well dog that can drink. If vomiting prevents drinking, correcting dehydration may require intravenous treatment. Dogs with parvovirus usually shed the virus for 1–2 weeks. Resolution of signs alone therefore does not determine when returning to contact with other dogs is safe.

Frequently asked questions

Are stomach bugs in dogs always contagious?

Not every gastrointestinal illness is infectious: diarrhoea may result from a dietary change, foreign body or another disease. Viral diarrhoea, however, can spread to other dogs through faeces. Isolating an affected dog reduces transmission.

Can a vaccinated dog get viral diarrhoea?

Parvovirus vaccination provides important protection against severe intestinal disease. However, it does not protect against every virus causing diarrhoea. A puppy can also become ill when maternal antibody protection has declined but vaccine protection is not yet adequate.

How can you tell whether diarrhoea is parvovirus or coronavirus?

Signs alone cannot reliably distinguish the cause, as severe coronavirus disease can resemble parvovirus. Parvovirus is tested for using a faecal antigen test or PCR. Faecal PCR can test for enteric coronavirus. Results are interpreted alongside your dog's condition and exposure history.

Does a viral stomach bug need antibiotics?

An otherwise well dog with mild acute diarrhoea does not usually benefit from additional antibiotic treatment. In severe illness, antibiotics may be needed for secondary bacterial infection or sepsis. Parvovirus-related intestinal damage and reduced white blood cells increase this risk.

How long does recovery from viral diarrhoea take?

Mild enteric coronavirus infection may resolve by itself. Puppies with parvovirus that survive the first 3–4 days generally recover in about 1 week. Severe dehydration or another complication may require hospitalisation. Parvovirus shedding usually continues for 1–2 weeks.