Dogs with Diarrhea - Campylobactor vs. Parvovirus

June 2011

There is a lot of information floating around out there about campylobacter and parvo. I would like to help clarify matters a bit by detailing some known facts about both. Well informed owners are by all means the best ones!

Let’s start by looking at campylobacter jejuni. It is a hardy, gram negative, motile, slender curved bacteria that is an important intestinal pathogen of many species including both dogs and people. Clinical signs of infection vary from none at all to profuse bloody diarrhea, vomiting and fever. These bacteria cause erosion of the small and large intestinal lining resulting in diarrhea lasting from 5 to 15 days. Animals most likely to become ill are those with an immature or weakened immune system such as the very young. In fact, many perfectly normal adult dogs and cats (as much as 40%) have been shown to shed campylobacter in their feces without showing any signs of illness at all. It is often speculated that illness due to campylobacter most often occurs when associated with another pathogen such as giardia, parvo virus, or intestinal worms such as hookworms or whipworms.

Diagnosis of campylobacter infection can be definitively made only by bacterial culture. This type of culture requires isolation from fresh feces using a special enteric medium for sample collection and often takes roughly 5 days to get an answer. A presumptive diagnosis can be made by simple observation of a slide under a microscope. Although this method is much faster, it is very speculative at best since fecal samples contain many mobile bacteria that are a normal part of the fecal flora and can easily be mistaken for campylobacter.

Treatment of campylobacter enteritis consists of antibiotics and supportive care based on the severity of the clinical signs. The antibiotic of choice is erythromycin. Second choice antibiotics are flouroquinolones (Baytril, Zeniquin, Orbax), and tetracyclines such as doxycycline. Which antibiotic is used depends on the case. Although erythromycin is the drug of choice, it also comes with a high incidence of causing vomiting and diarrhea. This is obviously not what ones wants to then treat a patient with that already has vomiting and diarrhea. Flouroquinolones, on the other hand, are contraindicated in young puppies because they can cause cartilage deformities to developing joints, but are a great choice for dogs over about 5 months age. Third choice antibiotics that have rather questionable efficacy may include ampicillin and cephalexins. Almost all drug formularies site the dosing for cephalexins in general to be between 15 and 30 mg per kg (or about 7 to 15 mg per pound). Use of higher doses would be strictly off label. Further treatment for campylobacter would be based on the severity of the case would also include intravenous fluid support with a balanced electrolyte solution and glucose. Medications to control vomiting may also be needed as well as pain control.

Spread of campylobacter jejuni is fecal-oral. In other words anything that has been contaminated with feces and is then taken in orally will transfer the bacteria. We know our canine companions love to eat and chew on many objects that are less than perfectly clean which is where they pick up the bacteria. It can remain viable in contaminated soil, etc for up to 1 month.

Now let’s have a look at parvo. This disease is not caused by bacteria at all, but rather a virus (parvo virus type 2) that is specific to dogs only. It is an acute, highly contagious intestinal pathogen of dogs worldwide. Clinical signs include decreased appetite, depression, fever, vomiting and diarrhea. Adult pets may have only very mild signs of infection while young pups with an as yet under developed immune system are most likely to be extremely ill even to the point of fatality. The virus causes a severe sloughing of the entire small intestinal lining.

Diagnosis can be made through a specific test (ELISA snap) since the parvo virus is far to small to be identified with a normal microscope. This snap test has a known sensitivity of 95% and specificity of 99.7%. The sensitivity means that the test will identify the parvo virus in 95% of cases but result in a false negative or miss the virus in 5% of cases. In that remaining 5% of cases, further tests such as PCR have been needed to correctly identify the virus. The specificity means that 99.7% of the time the parvo virus was correctly identified. In the other 0.3% of the time the test was a false positive and incorrectly identified the parvo virus as being present. All in all these are pretty good statistics. It is quite unlikely that campylobacter cases would be misdiagnosed as parvo (only 0.3% of the time at most).

What then, about these “weak positives” on the parvo snap test? Yes, this can happen and most often does happen when a puppy is tested within 1 to 2 weeks after being given a vaccination. Our current vaccines are all highly effective modified live vaccines meaning that puppies are inoculated with an inactive version of the virus. This inactive virus then replicates within the pup and stimulates the immune system, but does not cause the debilitating disease. The inactive virus is of course similar enough to the pathogenic strain to cause a cross reaction both with the pet’s immune system (what we want) and with the test. The result then is a weak positive parvo test. That is not to say, however, that a pup newly vaccinated for parvo could not become infected with campylobacter at the same time.

Treatment for parvo is entirely based on the severity of the clinical signs. It is after all a virus and there is no treatment that will directly kill the virus itself. We must simply provide support to the patient and control symptoms while we wait for the virus to run it’s course. That means intravenous fluid support with electrolytes and glucose, medications to control vomiting and pain as well as antibiotic support. Why do we need antibiotics when we are treating a viral infection? The answer is that we need to control secondary bacterial infections. Remember that the parvo virus causes a severe sloughing of the intestinal lining. The protective barrier of the intestine is now gone and the body is open to infection by the bacterial that normally reside in the intestinal tract. Broad spectrum antibiotics are indicated for treatment of parvo to prevent a secondary septic infection. The most common antibiotics used include ampicillin, cephalexins, and flouroquinolones (depending on the age of the pup as discussed above). The aggressiveness of the treatment depends entirely on the degree of illness that the patient presents. A dog that has only very mild diarrhea may do perfectly well treated at home with oral antibiotics alone. On the other hand, a puppy with profuse vomiting and diarrhea resulting in severe dehydration needs much more aggressive therapy including hospitalization, intravenous fluids, injectable antibiotics, etc. in order to save his/her life.

Like campylobacter, spread of parvo virus is also by the fecal-oral route. During illness and for several weeks after, dogs will shed over 1 billion viral particles per gram of feces!! The virus can then remain infectious for many months in the environment.

If the signs of parvo sound very much like campylobacter, you are right they are very similar in the clinical presentation and other than testing there would be no way to tell the difference. In addition many other enteric virus’, bacteria, parasites (giardia, hookworms, whipworms), etc cause the same vomiting and diarrhea signs. In fact, there are at least 500 known causes of diarrhea in dogs including diseases such as Addison’s disease, PLE and PLN that are not caused by a pathogen at all. Thus, reliable definitive testing rather than presumptive speculation is an important part of understanding which disease or diseases we are dealing with and, therefore, deciding on an appropriate treatment.

Finally, treatment also depends on and must be appropriately modified to fit the individual case. All patients should not and need not be treated exactly the same. Severe cases warrant hospitalization where as mild cases may not. Also there are often multiple causes at the same time all of which should be addressed. For instance it would not be unusual for a puppy with parvo to also have another problem such as campylobacter or hookworms that can exacerbate the clinical signs of the parvo. A successful outcome requires correct identification and treatment of all problems.