Letter to the Editor, JAVMA, Published in JAVMA January 1, 2007

 I read with great interest the new AAFP feline vaccine recommendations (JAVMA, 229[9]).  I agreed with some of the conclusions and recommendations and disagreed with others, as is probably true of the Panel members themselves.  One of the aspects with which I disagree is the recommendations regarding use of FIV vaccine.  Please consider these facts:

1. FeLV and FIV transmission occurs due to bite wounds because both viruses are salivary-borne.  Bite wounds probably account for the vast majority of new infections of both viruses.

2. Cats with unsupervised outdoor exposure compose the vast majority of newly infected cases because they are the most likely to be bitten by infected cats. 

3. Once an established infection occurs with either virus, the cat is infected for life.

4. Some age immunity develops to the FeLV.  This does not happen to the FIV.  Thus, adult cats are more likely to become infected with FIV than FeLV.

5. Both viruses can have adverse effects on the immune system.  The resulting immunosuppression can lead to overwhelming, fatal infections with disease agents that may normally be only mildly to moderately pathogenic.

6. This Panel is recommending FeLV vaccine for “cats permitted outdoors.”

7. This Panel is recommending FIV vaccine for “outdoor cats that fight.”

I do not understand the double standard presented in #6 and #7.  Fighting can be a proactive or a passive event.  Many cats that become infected with the FeLV and FIV are not the aggressors; rather, they are the victims of fighting.  Therefore, how can one predict if an outdoor cat will be one that will sustain a fight wound?  A single bite from an infected cat can be sufficient for transmission.  Furthermore, waiting to see if the cat is an “outdoor cat that fights” means that exposure and infection could occur before the decision to vaccinate is made.  This is like closing the barn door after the horse gets out.

My recommendation for FeLV and FIV vaccines continues to be the same for both antigens:  1) cats that go outdoors unsupervised and 2) cats living in a household with the respective virus.

Gary D. Norsworthy, DVM

Diplomate, ABVP (Feline)

Alamo Feline Health Center

16201 San Pedro Avenue

San Antonio, TX 78232

His Reply

Dr. Richards responds:

Thank you for your interest in the American Association of Feline Practitioners Feline Vaccine Advisory Panel Report. The 12 panelists expressed diverse viewpoints (understandably and desirably so, given that they were chosen because of their varied experiences and expertise), and the discussions were sometimes quite lively. Nonetheless, after extensive debate, the panelists created a consensus document and they unanimously supported the recommendations it contains. Your comment that “bite wounds probably account for most of the new infections” and “cats with unsupervised outdoor exposure represent most new cases because they are the most likely to be bitten by infected cats” is true for FIV. However, although FeLV can be transmitted by this route, it is more likely to be transmitted via prolonged intimate contact, mutual grooming, sharing of food and water utensils, in utero exposure, and in some cases, through milk. Thus, the population of cats at risk of FIV infection is not identical to that of FeLV, partly because the transmission routes of the two viruses are not identical.

As you’ve noted here, the report lists examples of cats that the panel believes should be considered for FeLV or FIV vaccination. Specifically, FeLV vaccines are noncore vaccines recommended for cats at risk of exposure; FIV vaccines should also be considered noncore “…with use restricted to cats at high risk of infection (eg, outdoor cats that fight) and cats no infected with FIV living with FIV-infected cats.” The panelists’ differing comments (FeLV vaccination “recommended” for certain cats, with FIV vaccination ”restricted” to certain cats) would be a double standard only if the epidemiology and routes of transmission were identical for both viruses and if the consequences of vaccination were also identical. But they are not. Since the early 1900s, a number of investigators have documented the performance of FeLV vaccines in both laboratory and field challenge studies. While publication cited give reason for hope, there is still little known about how available FIV vaccine will perform in real-world cats.

Another difference of considerable importance to the panelists is that FIV vaccination induces positive test results in vaccinates, whereas FeLV vaccination does not. After taking into consideration the relative of information on FIV vaccine performance in the field, along with the loss of ability to identify infected cats, the panelists concluded that the population of cats that might benefit from FIV vaccination is likely much smaller than the population that would benefit from the FeLV vaccination. In conclusion, the epidemiology and likely transmission routes of these viruses, and the vaccines themselves, are substantially different. In the report, general advice on vaccine usage for a particular disease was followed by examples of situation. However, these are for guidance only, and in any vaccination procedure, we would expect veterinarians to use their knowledge to assess the risks and benefits of a particular vaccine for an individual cat in relation to the likelihood of exposure and its specific circumstances.

James R. Richards, DVM

Chair, 2006 American Association

Of Feline Practitioners

Feline Vaccine Advisory Panel

Director, Cornell Feline Health Center

College of veterinary medicine                        

Cornell University

Ithaca, NY      

1. Jarrett O, Hosie MJ. Feline Leukaemia Virus infection. In: Chandler EA, Gaskell CJ, Gaskell RM, eds. Feline medicine and therapeutics. Oxford, England: Blackwell Publishing Ltd, 2004; 597-605.  

2. Sparkes AH. Feline Leukemia virus: a review of immunity and vaccination. J Small Anim Pract 1997; 38:187-194.

3. Levy JK, Crawford PC, Slater MR. Effect of vaccination against feline immunodeficiency virus on results of serologic testing in cats. J Am Vet Med Assoc 2004; 225:1558-1561.

My Response to His Response  (was not published due to JAVMA protocol)

Dear Dr. Richards,

Thank you for taking your time to respond to my concerns about the use of FIV vaccine as prescribed by the 2006 AAFP Guidelines.  Your comments have generated thoughts that I would like to share with you. 

Although the main means of transmission of FeLV is cited as being social contact between infected and uninfected cats, this general observation must consider the population of cats surveyed.  Although the general rule may apply to U.S. cats as a whole, it does not apply to my patient population.  I own a 3 doctor feline practice that has very few clients who are breeders, cat hoarders, or cat rescuers.  In the last 4 years I have made a diagnosis of FeLV infection 24 times (vs. 78 new FIV infections).  In only 6 of those was the transmission most likely due to social contact instead of bite wounds.

The testing issue continues to be a stumbling block for many.  Although there is currently not a commercially available antigen-type test for FIV, the Lucy Whittier Molecular and Diagnostic Core Facility at UC Davis (530-752-7991) offers FIV-specific PCR testing to practitioners at no charge.  In a challenge trial,¹ this lab’s results were found to be 90% accurate, even though the samples included some strains of FIV not found in the US.  The test result is positive in the presence of an FIV infection and negative in the presence of vaccine or maternal antibodies.

The Panel’s concern about efficacy is interesting.  You state that FeLV vaccine was proven efficacious by independent challenge studies in the early 1990s.  However, Norden’s Leukocell vaccine was introduced in 1985.  I do not recall the AAFP recommending that we delay the use of FeLV vaccine (or any other vaccine) until independent challenge studies are performed.  Are the challenge studies required by the USDA for licensing a vaccine meaningless?  If you feel they are, you should consider 2 papers^2,3 published in peer-reviewed journals that show good immunity using Fel-O-Vax FIV (Fort Dodge Animal Health).  The only paper⁴ that appears to question its efficacy actually questions our means of performing meaningful challenge studies rather than the efficacy of the vaccine.  (See the last two paragraphs of the paper.)

In spite of the above issues, the core issue remains:  Biting is the main means of FIV transmission; cats that are bitten by FIV-infected cats are likely to become infected.  It does not matter whether the bitten cat is the aggressor or the passive victim; a single bite wound is often sufficient to transmit the virus.  By the AAFP’s new recommendations one should wait until the cat has a history of cat fights before recommending FIV protection.  This is like recommending the use of seatbelts only to those who have a prior history of automobile accidents. 

Gary D. Norsworthy, DVM, DABVP

Alamo Feline Health Center

San Antonio, Texas

1. Crawford PC Slater MR, Levy JK. Accuracy of polymerase chain reaction assays for diagnosis of feline immunodeficiency virus infection in cats. J Amer Vet Med Assoc. 2005;226(9):1503-1509.

2. Pu R, Coleman J, Coisman J, et. al.  Dual-subtype FIV vaccine (Fel-O-Vax FIV) protection against a heterologous subtype B FIV isolate.  Journal of Feline Medicine and Surgery. 2005;7:65-70.

3. Kusuhara H, Hohdatsu T, Okumura M, et. al.  Dual-subtype vaccine (Fel-O-Vax FIV) protects cats against contact challenge with heterologous subtype B FIV infected cats.  Veterinary Microbiology.  2005;108:155-165.

4. Dunham SP, Bruce J, MacKay S, Golder M, Jarrett O, Neil JC.  Limited efficacy of an inactivated feline immunodeficiency virus vaccine. Vet Rec. 2006;158:561-562.