Vet 101: Subclinical Infections

Answer: I am so glad that your cat is feeling better. It sounds like she might have had a subclinical respiratory and/or dental infection for a long time. I have treated many cats that came to me with long-term subclinical infections in the upper or lower respiratory tracts or, even more commonly, in the mouth.

When discharge from the nose is clear and watery, the cause is often a viral infection. Inflammation caused by the infection in turn causes overproduction of tears or watery secretions. Sometimes, though, allergy, bacterial infection, or pain is an underlying cause.

The only cure for this situation is to extract the affected teeth and treat with antibiotics. Treating with antibiotics alone can temporarily “cure” symptoms, but until the underlying problem is dealt with, the infection will always come back. Even worse, if treatment continues and the underlying problem is not addressed, the infection is likely to become resistant to antibiotics. Helping the cat at that point is incredibly difficult.

I am often amazed at the incredible changes I see after doing dentistry work on elderly cats. They seem years younger within days. They can sleep soundly and not spend all of their energy dealing with pain and fighting infection.

I firmly believe that dentistry in older patients extends their lives as well as markedly improving their quality of life. Depending on the situation, dentistry can also end the need for long-term antibiotic administration that may be harmful and lead to serious antibiotic resistance.Another consideration is the role of dental infection in kidney disease. Periodontal (i.e., dental) disease is often associated with loss of kidney function and is thought to be one of the important causes of chronic kidney disease in cats. Treating dental infection—or better yet, preventing it through routine dental care—is thus a key step in avoiding kidney disease.

Perhaps surprisingly, most cats have feline calicivirus (FCV) in their mouths. Many of the vaccines used to prevent upper respiratory viral infections are live virus vaccines that contain calicivirus. The strain of virus used in the vaccine does not cause disease, but it can stay in the cat’s system and will then be detected in any test for calicivirus. The test can’t tell the difference between the vaccine virus and the disease-causing virus.

The presence of calicivirus does not mean that it is the cause of any disease. Cats with a condition called gingivostomatitis that also have the virus might have inflammation that is harder to control, but the presence of the virus does not mean that treatment will be ineffective.

Because Riba has an ulcer in her mouth, she could have an active calicivirus infection. However, such infections generally resolve within a week to 10 days. Unless Riba has a current, active infection, healing should not be affected by the presence of the virus.

Vaccination usually prevents infection, however, and ulcers can just as easily be caused by bacterial infection in the mouth, particularly tooth root abscesses. So, if Riba is current on her vaccinations, she may not have active caliciviral infection.

The remarkable response Riba had to antibiotic therapy indicates that her problem is much more likely to be bacterial infection (antibiotics have no effect on viruses such as FCV). The response of the nasal and eye symptoms to the antibiotic also supports dental infection as the cause.

Convenia (cefovecin sodium), the cephalosporin-class antibiotic given to Riba, is a long-acting injectable antibiotic approved for use in cats and dogs and introduced in the United States in 2008. The antibiotic controls infection for a maximum of two weeks, but it stays in the system for well over a month. Once you put the drug in, you have no way to get it out. I view it as a drug of last resort. Anecdotally, it has been shown to have considerable risk. I have heard numerous reports from colleagues about cases of immune-mediated hemolytic anemia resulting in the death of cats that had been given Convenia. The connection cannot be confirmed because the drug was given to cats that were sick. This makes cause and effect difficult to prove.

I personally have treated two cats that subsequently died from complications that were consistent with known adverse responses to cephalosporin antibiotics, and other practitioners I know have seen similar adverse events. I have also seen several cases in which cats that received multiple injections of the drug later developed severe antibiotic-resistant infections (one of these was a methicillin-resistant Staphylococcus).

When bacteria are exposed to an antibiotic that is effective for only a short period but is present at low levels for a long time, the bacteria have a chance to develop resistance. During the time when not enough antibiotic is present to kill, the bacteria that are not affected by the antibiotic are able to outgrow the bacteria that are affected. The resistant population eventually takes over, and a resistant infection results.

Because of the risks of adverse reactions and resistance, I use this antibiotic only as a last resort. And I let clients know that using the drug has serious risks. Any drug can cause adverse reactions, and if the drug stays in the patient for an extended period of time, the risk of death increases substantially. Whether repeated doses increases the risk of adverse events is uncertain.

In Riba’s case, Convenia might have been the best option, but I hope you were advised of the risks and benefits beforehand so that you could make an informed decision. It sounds as if your veterinarian does not reach for Convenia as a first line antibiotic and I, for one, appreciate that. Cats can be difficult to convince that oral medications are the best option for them and I sometimes even have to send home daily injections for those that absolutely refuse to take oral medications or that have drug resistant infections.

I firmly believe that when you are deciding whether to have a surgical procedure such as dentistry (this applies to decisions about your healthcare as much as it does to that of your cats), the most important consideration is the risk vs. benefit equation. What are the risks and what are the benefits?

From your description, it sounds like Riba is in good general health with no kidney disease or heart disease, so anesthesia should be relatively safe.

Ah, but what about dental disease? Didn’t I say earlier that it is associated with loss of kidney function? If the dental disease is well advanced, a presurgical check of kidney function is warranted, but hopefully most people will consider treating dental disease long before it reaches an advanced stage. (If kidney function is found to be impaired, the risk of anesthesia may still be outweighed by the benefits and making sure that the patient is well hydrated before surgery and choosing drugs that don’t have to be metabolized by the kidneys minimizes the risks.)

For cats that will have extractions, I use a sustained-release pain medication that controls pain for three days. That way no medication needs to be given by mouth after a dental extraction—unless the cat needs antibiotics, in which case I sometimes prescribe powdered antibiotics that can be mixed into canned food.

If Riba is in reasonably good health with no heart disease or major organ dysfunction, she would probably benefit greatly from having the dentistry done. I encourage you to talk again with your veterinarian and work out the risk-benefit equation that is specific to Riba. With proper anesthesia, fluid support during the procedure, and pre- and postoperative pain control, she should feel much better afterward.

Letrisa Miller, MS, DVM