2015 Zoetis Infectious Disease Symposium (NAVC/WVC)

2015 Zoetis Infectious Disease Symposium (NAVC/WVC)

Monday, January 19, 2015

The opinions expressed in these answers are those of the speakers and do not necessarily reflect the official label recommendations and point of view of the company or companies that manufacture and/or market and of the pharmaceutical agents, products, or services mentioned.

Infectious Disease: A "Whodunit" Approach to Diagnosis and Treatment

Jane Sykes, BVSc(Hons), DACVIM (SAIM) & Leah A. Cohn, DVM, PhD, DACVIM (SAIM)

From Dr. Cohn:

Is it more likely with ehrlichiosis to not see a fever?
Acute ehrlichiosis, including acute infection with Ehrlichia ewingii associated with polyarthropathy, is often but not always accompanied by fever. Fever does not necessarily make ehrlichiosis more likely than immune-mediated polyarthropathy, however, because that also often results in fever.

Do you ever see improvement of immune-mediated polyarthritis due to chondroprotective effects of doxycycline without an underlying tick-borne disease?
Certainly, doxycycline has anti-inflammatory effects that might help improve clinical signs of inflammatory conditions, including idiopathic immune-mediated polyarthritis. The improvement of arthropathy due to nonspecific effects of tetracyclines, however, is likely to be only partial, whereas correct treatment of polyarthropathy due to ehrlichiosis or anaplasmosis is very likely to result in a rapid and complete response without recurrence.

Is there a one-stop source to determine which infectious diseases are prevalent in your area?
No, not yet—although efforts led by Dr. Scott Weese are underway to develop such a tool. For vector-borne disease, sites such as Dogsandticks.com or http://www.capcvet.org/parasite-prevalence-maps/ provide useful information on the regional prevalence of heartworm, Lyme, ehrlichiosis, and anaplasmosis.

What test would be more reliable to screen for leptospirosis?
Screening for leptospirosis can be done in several ways. The diagnosis should be considered in every dog presented with acute kidney injury, and the suspicion should increase if there is renal/abdominal pain, fever, concurrent increases in liver enzymes, thrombocytopenia, or leukocytosis. If the dog has not yet received antibiotics, a urine polymerase chain reaction (PCR) test can be a good way to both screen and confirm infection. A negative PCR can never be used to completely rule out disease, however, and is not useful after antibiotics have begun. MAT testing, or microscopic agglutination testing, has long been the standard test. But it is absolutely crucial to remember that in an acute illness, MAT testing might be negative if there has not yet been time to form antibodies. A negative MAT test should be repeated approximately 2 weeks later in dogs that might have acute leptospirosis. Recently, an ELISA test has been marketed for leptospirosis. This ELISA is currently a “send out” test, but may soon be available in an in-clinic platform. As for the MAT test, an ELISA test can be negative during acute infection and should be repeated at a later date if leptospirosis is still a consideration.

Realizing it is rare, how do you rule out fungal or protozoan arthritis before starting steroids?
It isn’t always easy, making follow-up after steroid treatment starts extra important. First, look for clues to the odd infections on complete blood count (CBC), chemistry, and urinalysis (UA). It would be rare to have such an infection in only the joints, although reaction to these infections may result in a reactive immune-mediated arthritis. Second, perform arthrocentesis and evaluate the slide thoroughly for any evidence of pathogens. Routine bacterial culture won’t show some of the atypical pathogens, however, and is not necessarily a routine part of diagnostic investigation for polyarthropathy. Finally, do that follow-up! If drug therapy isn’t working to control suspected immune-mediated polyarthopathy (IMPA), think again…could you have missed an infectious agent? And don’t hesitate to repeat the arthrocentesis. While it isn’t how we’d hope to make a diagnosis, there are occasions where steroids make infections easier to find after steroid administration than they were before.

Should healthy dogs that are positive for Ehrlichia on the SNAP test be treated?
That depends! It depends on the wishes of the owner, the likely pathogens in the area, and the results of other testing. In the case of a positive Ehrlichia SNAP® (IDEXX) test in a healthy dog, the ideal minimum evaluation would include a CBC with smear evaluation and a urinalysis. Findings of thrombocytopenia, intracellular morulae, anemia, hyperglobulinemia, or proteinuria would likely be good reasons to treat. If all these are negative/normal, then treatment should be based on a discussion with the pet owners. Treatment with tetracyclines is usually well tolerated, but every drug carries a cost—both in potential adverse reaction and monetary. Treatment is no guarantee that the pathogen will be eliminated or disease prevented, and it certainly doesn’t prevent recurrence of infection. In areas where chronic (and more serious) E canis is the most likely pathogen, the choice to treat the healthy dog is quite reasonable with the hope that it might prevent illness. In areas where E ewingii (an acute and less serious pathogen found in much of the south-central and southeastern US) is more likely than E canis, a “watch and wait” approach may be very reasonable. Of course, it is “watch and wait,” not just wait. The owner should be educated about disease signs, and a CBC and UA should be repeated yearly. In either case—treated or not—ectoparasite control measures should be reevaluated for the pet.

Is minocycline an appropriate substitute for doxycycline for tick-borne disease?
Although there are no published studies comparing efficacy of the two drugs, there is every reason to believe that minocycline can be used as a more cost-effective alternative to doxycycline for the treatment of many tick-borne infections.

Canine Infectious Respiratory Disease Complex: Update on Novel and Emerging Pathogens

Stephan A. Carey, DVM, PhD, DACVIM (SAIM)

What methodology is available to confirm suspected canine influenza infection?
The two methods available for diagnosis of canine influenza infection are the polymerase chain reaction (PCR) and serology. PCR detects the organism or parts of the organism (the viral genome). Because viral shedding starts and stops so quickly, it is really only useful during the acute phase of infection. This can be performed on nasal and tonsillar swabs, lavage fluid, and biopsy samples.

Viral serology is effective in documenting exposure to the virus, as well as confirming an immune response to the virus. Viral titers rise shortly after exposure, and remain elevated even during the chronic phase of infection, and therefore are useful during or even shortly after the period of clinical illness.
If a dog has an unknown vaccination history and will be kenneled in 2 days, what Bordetella vaccine do you give—intranasal or parenteral?

Because no vaccine can effectively generate a protective immune response in an immunologically naïve dog in 48 hours, I would use an intranasal Bordetella bronchiseptica vaccine in a patient with that type of potential exposure. This would be primarily for the purpose of stimulating innate immune responses at the airway surface rather than for the generation of a specific immune response. Ideally, in my opinion, a naïve patient should receive a priming vaccination 2 weeks prior to exposure, while a seropositive adult dog should receive a booster vaccine 5 (parenteral) to 10 (intranasal) days prior to a potential exposure.

Would it be better to use an injectable or intranasal kennel cough vaccine in an immunocompromised animal?
This is a difficult question to answer with a blanket statement, as it would depend on the type of immune compromise and on the circumstances. For example, I would manage an adult dog with hyperadrenocorticism or receiving chemotherapy the same way that I would manage any other adult dog, which would be via annual parenteral Bordetella vaccination boosters. An orphaned puppy would probably be best managed with intranasal vaccination early in life, and parenteral vaccination later. Ultimately, I would want the most effective form of vaccination, as the risks of complicated infection are higher in a patient with immune compromise.

Is the ciliary dyskinesia that occurs with coronavirus temporary or permanent?
This depends on the degree of injury caused by the virus. The respiratory epithelium is capable of regeneration if the basement membrane remains intact, so mild disease can have a reversible impairment. In the face of severe airway injury associated with deep epithelial injury, however, this may lead to a metaplastic response associated with squamous metaplasia or mucous cell metaplasia, and a permanent loss of cilia.

Do you recommend canine flu vaccine as a requirement to board if you have a large kennel even if there is currently no outbreak in the area (Western Pennsylvania)?
This may sound as if I’m dodging the question, but I really think that any individual facility needs to consider the risks and benefits in their own situation. Michigan (where I practice) has not seen a lot of canine influenza. However, LOTS of my clients are snowbirds and spend an appreciable amount of time down in Florida, where we do see a lot of Influenza. In these cases, I think that the risk of an outbreak is relatively high, since all of the criteria are potentially present (stress, close quarters, infected and vulnerable dogs in the same environment), so I do recommend it in this area. If you’re in an area with a more closed population and not much canine influenza, it may be appropriate to take a wait and watch approach. Having seen several facilities that were shut down due to canine influenza outbreaks in the northeastern US and in the mid-Atlantic region, I tend to lean toward recommending the vaccine if you’re in close proximity to an area that has seen it.

What effect do antihistamines have on shedding and on the mucociliary apparatus?
I do not know the effects of antihistamines on viral or bacterial shedding. I do know that several of the second-generation antihistamines have anticholinergic effects, and that the drying effect that makes them so useful in hay fever also may make them detrimental in conditions in which clearance is important (chronic bronchitis, pneumonia). In general, unless there is a specific indication (e.g., documented allergic rhinitis or allergic bronchitis) and a fairly certain positive response to therapy, I don’t use antihistamines in canine respiratory disease.

Is PCR or tracheal wash a better diagnostic tool?
I think this depends on the situation. If you have an outbreak setting, for instance, where multiple dogs from the same boarding facility or veterinary hospital are acutely exhibiting upper respiratory symptoms, then running PCR on multiple dogs is an ideal test because it’s minimally invasive and a great screening test for herd health.

If you have a dog with chronic bronchitis who exhibits an exacerbation of his disease following a week of boarding, then a tracheal wash would be a better choice. Plus, you can submit the fluid from a tracheal wash for PCR analysis to look for the viral pathogens.

Do you have to booster the modified live virus (MLV) intranasal Bordetella vaccine in a puppy or in an adult as a first known vaccination?
The intranasal Bordetella bronchiseptica vaccines are labeled and effective for one year when given as a single dose, either in a puppy >4 weeks of age, or in an adult dog. So, the technical answer to that question is “no.”

However, based on the evidence in the two studies by John Ellis published in JAVMA, the combination of a priming and a booster vaccine in early life (puppies) provided better protection from Bordetella challenge than the administration of either vaccine alone. Therefore, I generally will give an intranasal as an initial vaccine at ~8 weeks of age, and boost that with a parenteral at ~12 weeks of age. 

Can you give Bordetella intranasal vaccine followed by only one subcutaneous injection or are two necessary?
To my knowledge, that study has not been done, so I don’t know with certainty that intranasal followed by a single parenteral is better than intranasal alone, but if I had to speculate, I would guess that you would get a booster effect with the first parenteral. In a recent study, John Ellis did report that there is an anamnestic effect when two parenteral Bordetella vaccines are given in series. My personal belief is that two boosts are better than one, but that one would be better than none in driving a memory response.

Would you use the oral Bordetella vaccine?
I would consider using it if there was a well-designed, comparative efficacy study that documented both the local (i.e., nasal) and systemic immunologic effects of oral vaccination, and also demonstrated superior efficacy in protection from challenge over intranasally and/or parenterally administered Bordetella vaccines. To date, those don’t exist, and I really trust the data that are published supporting intranasal and parenteral vaccines.

What is your standard empirical treatment for a coughing patient while awaiting diagnostic test results?
That’s a bit of a loaded question, as the dogs in whom I perform diagnostic testing frequently have either more severe disease or a co-morbidity that increases their risk of developing a complicated infection. If that is the case, and they present as an uncomplicated case of CIRD, then my “default” empirical treatment would be mild cough suppression alone (hydrocodone ~0.25 mg/kg PO BID), and wait for PCR or preliminary culture prior to starting antibiotics.

For empirical treatment without diagnostics, I like tetracyclines and hydrocodone.

Do you recommend closing a boarding area for a time as premise control following a kennel cough outbreak?
I don’t think that is always necessary. Large facilities that can effectively close off sections of the structure can still run, especially if their ventilation allows them to close off the ventilation in the affected area. If the facility cannot effectively contain or quarantine the affected areas, then I would recommend testing multiple dogs to identify the cause of the outbreak and proper sanitization prior to letting dogs back into the facility.   


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