Dogs have been hogging the spotlight lately in this column, so this week I want to focus on a uniquely feline set of problems: Feline Leukemia Virus (FELV) and Feline Immunodeficiency Virus (FIV).

These two terrible viruses have a prevalence in the normal cat population of about 2-3%, a number that may not seem very high until it is your cat that has the problem. Both viruses are in the retrovirus family which is the same family that HIV, the causative agent for AIDS, is in. Never fear, these viruses only infect cats and cannot be transmitted to any other species.

Although the viruses are two distinct entities, they behave very similarly clinically, so we tend to talk about both of them together. Both viruses are secreted in the saliva, so a major mode of transmission is through bite wounds. Grooming contact, or contact with an infected cat’s urine or feces are other potential routes of infection. Pregnant mothers can pass the virus along to their offspring in utero or from nursing. This route is more likely with FELV than FIV.

Both viruses cause immune suppression, and FELV tends to promote cancer development. Cats who are infected with either virus may have very normal lives for many years and then suddenly start developing unusual and often catastrophic problems. When I see a three year old cat with a tumor in its chest or with life threatening anemia the next diagnostic test I run is for FELV and FIV. Cats with FIV sometimes have a long history of chronic health problems like recurrent respiratory infections, severe mouth infections, or unrelenting diarrhea. These cats may live for many years, but they tend to require quite a bit of medical intervention to keep opportunistic infections from overwhelming them. Essentially 100% of FELV or FIV cats will eventually succumb to the disease. Cats that are very ill at the time of diagnosis often do not have a good prognosis for recovery.

As with HIV and AIDS in people, there is no way to directly attack and eliminate the virus. Our current options include managing the secondary problems that the virus allows to occur and some mildly helpful medications that may help suppress the spread of the virus. Fourtunately unlike HIV there are effective vaccines available that can reliably protect a cat from both FELV and FIV. The FIV vaccine is a fairly recent development and may be more difficult to obtain because it is not in wide use yet.

Diagnosis has become much more straightforward with reliable tests for the viruses. As with any test there can be false positives and false negatives, however, so before you euthanize a clinically normal cat who tested positive for FIV on routine screening it would be a good idea to run a second, different confirmation test. Cats that have been vaccinated for FIV will test positive on the screening test even though they do not have the disease.

For owners who chose to manage a FELV or FIV positive cat while their quality of life is still good there are a few things to keep in mind. Both of these viruses are contagious, so infected cats must never be allowed outside to potentially infect other cats in the neighborhood. I am not interested in increasing my patient influx in that manner and neither are your neighbors. Any other cats in the household should be vaccinated against FELV and/or FIV, and even so they still run a small risk of getting infected themselves. The medical management of these cases can get quite involved and quite expensive sometimes.

New cats and kittens should be screened for both viruses before being added to the household. You can discuss the pros and cons of vaccinating against these viruses with your veterinarian. The vaccines will do nothing to help a cat who is already infected. Indoor only cats have a tremendously reduced risk of ever being infected (as well as an equally reduced risk of being hit by a car or eaten by a fox). It is good to know that we have effective resources available to protect our feline overlords from the dangers of FELV and FIV.