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Diarrhea is very common in puppies. Some of it is due to the things they eat and chew on (ref), but some of it is due to organisms that take up residence in their intestines. The most serious is the parvo virus. You can read about parvo here.
One of the viruses that is often implicated when puppies and younger dogs develop diarrhea is coronavirus. When it acts alone, diarrhea – if symptoms occur at all – lasts only a few days. The pup might be uncomfortable for a time. It might pass soft stools and occasionally some true diarrhea that messes up the house. When diarrhea occurs, it rarely if ever contains blood. Your pup's appetite might drop off for a few days. When symptoms are more severe, it is usually because the dog was co-infected with other intestinal pathogens (or even parvovirus) at the same time.
The coronavirus of dogs is a distant relative of the coronavirus of cats - the nasty one that sometimes mutates into FIP.
Canine coronavirus is highly contagious. When diarrhea occurs, it generally begins 1-4 days after exposure to the stool of a carrier dog. Few of the dogs most likely to spread coronavirus show any signs of illness – recovered dogs are thought to be able to continue shedding the virus for up to 6 months (ref)
Your dog is most likely to catch coronavirus at locations where lots of dogs congregate. Doggy daycare centers, dog parks, grooming establishments, mass vaccination clinics and animal shelters. The more crowded the animals, the poorer the sanitation, the more likely it is that cross infection will occur. It is particularly common in puppy mill puppies and pups supplied by large commercial dog-breeding operations (more than 3 breeding dams). The coronavirus can infect dogs of any age. But most dogs will have already been exposed and immune by the time they are one year old. The virus causes inflammation of the upper intestines (enteritis). The inflamed intestines, moving more rapidly to expel their contents, produce the diarrhea. Something I will mention frequently as I go along is that coronavirus of dogs rarely if ever acts alone. It produces enteritis and diarrhea as one player among many players that have taken up residence in your dog – all at the same time. (ref)
A fatty (phospholipid) protective envelope surrounds coronavirus. Unlike non-enveloped parvovirus, coronavirus are quite easy to kill with bleach, ammonia and peroxide; as well as with detergents that dissolve their fatty protective coating.
Yes there is quite a bit of confusion.
I mentioned that it is rare for dog feces from a disease-contaminated source to contain only one pathogen. When your sniffing dog's nose comes in contact with poop, it is going to be exposed to quite a few different pathogens all at the same time. A lot of early studies assumed that if a dog developed diarrhea when no parasites could be seen in the stool and tests came back negative for parvo but positive for coronavirus, then coronavirus must be the cause of the problem. But now that more sophisticated tests have been developed, we know that a multitude of different potentially disease causing organism – usually working together – are found in the bodies of coronavirus-positive dogs with diarrhea. In 2019, it is still impossible to know how much each one of those other organisms contributes to a diarrhea problem. (ref1, ref2)
To compound matters, new viral pathogens, capable of causing diarrhea in young dogs, are being discovered every year. They often co-infect the same dog infected with coronavirus. The older studies that attributed a sick dog’s symptoms to coronavirus did not check for these recently discovered pathogens. The most recent I know of are the Astroviruses. Read a 2017 study that detected astrovirus in dogs that were coinfected with coronavirus here.
The AVMA put out an advisory in 2008 regarding a “new” coronavirus that had the ability to cause severe respiratory (lung) infections in dogs. That coronavirus (CRCoV) is a different virus from the intestinal coronavirus of dogs (CCoV). That newly discovered coronavirus appears to be a much closer relative to the coronaviruses that cause respiratory infections in humans (SARS & MERS ) and others that causes respiratory problems in pigs and cows than it does to the coronavirus associated with diarrhea in young dogs. (ref) That CCoV and CRCoV are not the same virus is something not everyone grasps yet. (ref)
I mentioned the diarrhea in young dogs and puppies. As opposed to the diarrhea caused by dietary indiscretions (eating trash) or that of intestinal hookworms or giardia, the diarrhea associated with coronavirus generally contains little mucus. Blood is rarely seen in coronavirus diarrhea. Some associate coronavirus diarrhea with a fetid odor or orange tint, but that is not something to be relied upon.
Older dogs often overcome the virus (seroconvert) without experiencing diarrhea. We know they were exposed because antibodies against the coronavirus appear in their blood. Vets call those subclinical cases.
Some dogs also vomit early in the infection.
Many experience 1-3 days of diminished appetite and lethargy.
A few run fevers.
The chief danger of diarrhea is dehydration. You can read more about the signs of dehydration that you might observe in my parvovirus article here.
We know that coronavirus, as a group, have a reputation for mutation to more pathogenic forms owing to their ability to recombine in the body with other strains of coronavirus they encounter. They also have a high rate of spontaneous mutations. (ref) Some have proposed that that is the case with canine enteric coronavirus as well.
The possibility that canine coronavirus has or had mutated to a more dangerous (more pathogenic) form rests on a report of what occurred at a pet shop in Bari, Italy in 2005. Three min pins and one cocker spaniel, 1.5 –1.8 month old, developed fever, lethargy, vomiting, bloody diarrhea and neurological signs. They died 2 days later. Three to four days after, two more pinschers and a Pekinese of the same general ages also died. (ref) A variant of corona virus was detected in these dogs (CCoV type II) and tests for common alternative causes of diarrhea (parvo, distemper, adenovirus and bacteria) were negative. The authors announced that they had discovered a highly pathogenic form of canine coronavirus. (ref)They gave it the name, Pantropic Canine Coronavirus. (ref) However, to the best of my knowledge, no attempts were ever made to reproduce the disease using the isolated virus.
Subsequently Cornell University published another review of this particular corona virus strain. But they mention no cases as having occurred in North America nor did they make attempts to reproduce the disease. (ref) They did suggest that perhaps the canine coronavirus combined with the coronavirus of cats and/or swine to produce a more pathogenic mutant. That theory had been presented earlier. (ref)
Whether this mutant canine coronavirus represents a greater threat to your dog than traditional canine enteric coronavirus remains to be proven. Perhaps it is, perhaps it was just an innocent bystander to some other disease organism present in the dogs at the same time. None of these studies checked for the presence of astrovirus. Astrovirus are known to accompany coronavirus in diarrhea outbreaks in beagles. (ref1, ref2) There are just too many potentially harmful organisms present in the intestines of dogs with diarrhea to check for the known ones. Many remain unknown.
It is impossible to positively attribute a disease to one organism unless you give only that organism to a research animal and produce the disease. That has been known since 1884. (ref) To my knowledge, that was never done.
University and large commercial veterinary diagnostic laboratories can check your dog’s stool for coronavirus. They can also run blood antibody tests that tell them if your dog was ever exposed to the virus. However, those tests are rarely run on samples from individual pet dogs. They are usually reserved for scientific studies on the virus itself or, perhaps, an animal shelter facing an unacceptable number of diarrhea cases. (ref)
There is no specific treatment for dogs with coronavirus infections. TLC and supportive care are usually all that are required. In typical mild cases, the diarrhea resolves in a few days without medications being dispensed. Many vets would suggest oral fluids (electrolytes) and a bland diet given in small amounts throughout the day. Others might suggest withholding food for 24 hours.
Should the diarrhea be severe, primary treatment would be to correct dehydration and electrolyte imbalances. The rest would be selected from the same treatments suggested for parvovirus infections. You can read about those medications in detail here.
There are currently two that I know of: Boehringer Ingelheim’s Recombitek Corona MLV a weakened (attenuated) live virus product and Zoetis’s Vanguard CV a killed (inactivated) product. Both companies, plus Merck, incorporate coronavirus in their “8-way” carpet bombing formulas marketed to protect against everything. None are believed to provide complete protection against coronavirus. (rptref + product inserts).
The American Animal Hospital Association, AAHA no longer recommends coronavirus-containing vaccines (ref), based on their opinion that the disease is usually mild or subclinical and that it generally occurs in dogs 6 weeks of age or younger (too young to vaccinate).
The central pharmacy at the Vet School, University of California, Davis no longer stocks coronavirus-containing vaccines. Their rational is: "It is not possible to reproduce disease with coronavirus unless the dog is immunosuppressed with steroids. Antibodies do not correlate with resistance to infection and the length of time these vaccines might make a dog resistant to coronavirus is unknown." (ref)
Nevertheless, some boarding kennels and other commercial establishments might still insist that your dog receive a coronavirus-containing vaccination before they provide service.