This page: Almost all 'official' information about FIV is based on scientific studies and papers; sadly, many are not as valid as they need to be - we explain why.

How reliable is the research into FIV?

Almost all 'official' information about FIV is based on scientific studies and papers; sadly, many are not as valid as they need to be.

When FIV was first identified, scientists were hopeful it would become a model for research into the human HIV form. However, they soon realised that, although similar, FIV was not equivalent to HIV and was therefore not going to be the useful tool they had hoped it would be.

Clearly there is little money-making potential in feline health compared to human health issues, so we don't expect too much useful scientific research to emerge in the foreseeable future.


Although FIV has almost certainly been around for a very long time, it was only "discovered" and identified in 1986. The early studies that were carried out have become, in our view, over-relied-upon. Sample numbers were fairly small, and seemingly very little account was given to the natural variations in cats general make up and constitution, and none to early-life variations in diet, care etc, which we believe can have a major influence on how any individual cat reacts to health issues later in life.

The best we can hope for is to gather the hands-on experience of the many who own and care for cats with the FIV virus. This will not convince the scientists, however, and as many vets rely on the scientists for their information, this is probably why so many vets are lacking in their understanding of the practicalities of dealing with the virus. It is the basic difference between the theory and the practice.

What there is, is what there is!

Vets do have to rely upon what studies are available however, so it is important to understand the limitations. There are a number of basic issues to consider with the research that relates to FIV:

-  Sample size
-  Laboratory vs natural infection
-  Unjustified conclusions

Sample size (number of cats involved in a study)
Experience gained from many years of survey work, on innumerable subjects, shows that the number participating have a huge affect on the validity of the results.

Whatever the survey (or study) there will always be a range of factors that influence the responses/reactions, and the best way of averaging out those influences so they become insignificant in the results, is to increase the number of participants. For instance, in a typical survey of people's opinions, or health, there may be influencing factors of age, background, education, wealth, and many more, all of which could have an effect on how the participants respond. So it is vital that a broad cross section of people are selected, and the greater the number the better. Most surveys would take 1,000 participants as an absolute minimum, and ten times that number would be considered more reliably representative.

However, when it comes to studies on FIV cats, the vast majority involve numbers well below a hundred, sometimes no more than a handful.

The differences between individual cats can be large, depending on their genetics, their mother's health at birth, particularly their early life experiences (nutrition, care etc), not to mention basic age, gender and personality differences. Because of many differences in the subjects, there would need to be a correspondingly high number of subjects in any study in order for it to be truly representative of the general cat population. Consequently, there is a fundamental weakness in most studies relating to FIV.

Laboratory vs natural infection

Many of the studies into FIV have taken uninfected cats and introduced the virus by injection in the laboratory.

Quite apart from any moral issues, there are potential practical problems with this approach:

-  The strain of virus used may be particularly vigorous, or generally not representative of the field strain most cats may encounter in real-life.

-  The amount of virus injected may be far more than would be received via a bite in the normal method of transmission.

Clearly many studies have a restricted amount of time allocated for the research, and so the temptation to give 'strong' strain, and a high volume, in order to receive quick results, cannot be ignored.

The progression of the virus with naturally infected cats is slow, which also allows the body to react in its most natural way, which would form the basis for the early development of the virus in the body and thus influence the longer term reactions. Laboratory infected cats, however, may not have the time for slow natural reactions as they can be inundated with unnaturally large amount of highly potent virus right from the start. This will probably influence the later progression and reactions due to the virus, which in turn would affect the results, and potentially invalidate the conclusions.

It should be noted that initial studies into FIP (Feline Infectious Peritonitis) which used laboratory infected cats have since been majorly overturned by later research that only studied naturally infected cats. Admittedly FIP is a very different virus to FIV, but the difference in results between artificial and natural infection is worrying, particularly if it should also relate to FIV studies.

Unjustified conclusions

Scientific studies need to come to some conclusion in order to get published and form part of the scientist's body of work. There seems to be a tendency in many studies to identify a specific change or occurrence that may be observed in a number of cats that have FIV, however tenuous, and then assume what is observed is either caused by the FIV, or associated with it.  If something emerges more in the FIV cats than in non-FIV cats, there is the obvious temptation to assume FIV to be the cause, whereas there could be many other influences that have affected the cats. So, without a very large sample size, any conclusions would be questionable.

Many scientific studies throw up results that conflict with other studies.  This seem to surprise the scientists, who seem unable to see the obvious differences between individual cats before any laboratory infection comes into play.

What is particularly worrying, is that many of the 'official' organisations use the scientific papers, seemingly with little extra analysis, in order to form their positions and advice: organisations such as ICC (International Cat Care); The Cat Group; ABCD (European Advisory Board on Cat Diseases); Cats Protection; RSPCA. Most produce literature about FIV which quotes as reference many of the papers that we feel are not as solid as they might be, and consequently give 'professional' advice that we believe does not reflect accurately the realities of the situation.

One prime example where we believe the conclusions, and therefore their advice, is ill-founded, is regarding the point about casual transmission of FIV between cats in a mixed household - FIV positive cats living with uninfected cats. They quote one particular study, (reported in The Veterinary Record in 2000) and draw the conclusion, albeit in differing degrees, that casual transmission is quite likely in a mixed household without fighting.  They go on to advise against mixed households, and even suggest segregating existing feline companions when one tests positive for FIV,  with their view based mainly on this one study. This policy then makes it much harder for rescue groups that follow this advice to find suitable homes for FIV cats.  We have studied the paper, and give our assessment of its validity (see here).

Scientifically-minded people will maintain that FIV is a problem because scientific tests can show that the virus is having an effect on certain cells of the immune system, and therefore, they claim, is having a measurable effect on the cat.

They will point to many of the studies that have been carried out as evidence, often with little analysis of the validity of these studies.

Their viewpoint is, of course, scientifically valid. However, in our view, it misses the point completely that, unless the measurable progress of the virus actually affects the health of the cats outside of the laboratory studies, it is an academic point that has little relevance in practice. It is FIV in practice that we and other FIV-owners are concerned about.

See the section on our 1000 FIV cats project for a report on the recorded health experience of hundreds of FIV cats from their owners. This is practical experience as opposed to academic theory.


Most organisations that produce literature on FIV are made up of a combination of vets and scientists, who review all the published scientific papers, draw their conclusions and offer their advice based on them, with little of their own hands-on, practical experience of cats with the virus over the long term.

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