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Interpreting Research (and Making It Work for You): Is Lysine a Good Investment for Shelters Wanting to Prevent URI in Cats?

The ASPCA’s Dr. Margaret Slater shares a few principles to help you sort through new research.


In the sheltering world, people have to make decisions all the time. Do we vaccinate on intake? Do we use this cleaner or that one? How can we better inform our decisions using science—and without making anyone’s head explode? I’m going to talk about a few principles that can help you sort through all the different information coming at you and make some more informed decisions for the animals in your care.

First the bad news. There isn’t a ton of good research on many of the key shelter questions everyone wants answers to. And when there is, it isn’t always put together in a readily digestible form. Peer-reviewed publications aren’t always great (or even good) studies. Experts aren’t always objective in their assessment of the problem and solution. So, some careful thought about what we really do and don’t know is good.

Now for the good news. There are some well-accepted guidelines for what type of study makes for the strongest evidence and therefore, the best decision support. These types of studies are increasing in frequency. And increasingly the people doing the research will clearly articulate strengths and limitations of the data. There is a British university that collects them all (see especially the Best Bets and Systematic reviews—only a few things that are likely of keen interest to shelters so far, but stay tuned). 

I recently found a systematic review article that purported to address the question featured in this blog’s title—Is lysine a good investment for shelters wanting to prevent upper respiratory disease in cats? Systematic reviews are the best options for decision making. They are a structured and transparent method of synthesizing information on a specific topic or question. The question to be addressed (Does lysine prevent illness due to FHV-1?) should be clearly stated up front. Ideally, more than one person should review and assess the included articles. Systematic reviews for treatment or prevention (interventions) should focus on clinical trials with controls. And the review should talk about bias. There are many reasons that a study can be biased (have systematic errors in it). 

There are also guidelines as to what should be in a systematic review if you want to know more. I’m going to briefly touch on these guidelines and what should be included in the systematic review of lysine. (If you want the bottom line from the systematic review about lysine, just skip to the next paragraph.) When we are interested in prevention or treatment, the best study type is a clinical trial. That means there are at least two groups, one of which is getting the new or experimental treatment or prevention (lysine and supportive care) and one of which is getting the next best thing (in the case of FHV-1, just supportive care). Ideally, cats are randomly assigned to one of the groups. This makes it impossible for the researcher to unconsciously put favored cats, or cats who are more likely to get lysine, in one group or the other. And ideally, whoever determines if the cat is sick and which virus the cat has doesn’t know if the cat got lysine or not (blinding). 

Note that not all URI is due to FHV-1. In many shelters, no one knows which cats have FHV-1 and which have that and/or some other pathogen, which complicates the decision to try lysine since the URI may not even be due to FHV-1. 

According to the systematic review, there have been 3 nice clinical trials (one blinded and random, one blinded and one neither, as best I can tell). Two were actually done in shelters, which really strengthens the utility of the results. The other was in a colony housing situation in a research facility. Lysine didn’t prevent disease from FHV-1 compared to the control groups in any of these studies. In fact, in two of the studies the cats on lysine had slightly worse clinical illness than the control cats. So, not very promising on the quality of evidence and data that lysine prevents URI.

Ok, now on to thinking about causation, lysine and FHV-1. Shelters actually deal with the concept of causation a lot. Does this virus cause this disease in cats? Does vaccinating at intake cause cats to be less likely to get sick? Does this diet cause cats to eat better? Yet, the concept of X causing Y is complex and requires some subjectivity to prove. Usually it takes a critical mass of data and experts in the field to decide that yes, for example, smoking does in fact cause lung cancer in people. There are some general criteria that can help support a decision that X causes Y. (Remember vaccine-associated sarcomas in cats? We are now pretty sure that injections do cause this type of cancer in cats now, but we weren’t 20 years ago.) 

Some criteria that are useful to consider when deciding on causation are: the time sequence (X happens before Y); strong statistical associations; a dose–response relationship (more of X causes more of Y); plausibility of the relationship between X and Y given our current knowledge; consistency with other evidence; type of study design, and consideration of the extent to which the results could be “caused” by other factors. In reality, only the time sequence is required: the prevention must come before the disease. So cats must be free of FHV-1/URI before they are started on lysine and should be diagnosed with FHV-1 less often if they receive lysine. In this case, there are a few clinical trials, without statistical significance and without any data to support less severe or less frequent disease in cats receiving lysine (time sequence, statistical association, type of study design). The systematic review actually brings in some data from human medicine (where the idea to treat with lysine came from) and from laboratory research in cells, none of which support lysine as being effective at preventing or treating FHV-1 infection (plausibility, consistency). 

So, based on the evidence from the clinical trials, it doesn’t seem very likely to me that lysine prevents or treats infection with FHV-1 in shelter cats. And it doesn’t seem to be helpful at decreasing the frequency of URI when the underlying disease agent(s) are unknown. I’d really love to see shelters put their resources and time into programs aimed at getting cats adopted more quickly and therefore out of the shelter sooner (like fee-waived adoptions) and decreasing stress in cats, which does really help cats stay healthier!

So, decision time. Are you going to go with the research and not spend time and money on lysine and instead on programs that have been shown to cause cats to stay healthier and get into homes faster?


The ASPCA's Dr. Margaret Slater, DVM, PhD, Senior Director, Veterinary Epidemiology, focuses much of her work on free-roaming cats. Prior to joining the ASPCA in 2008, Dr. Slater taught epidemiology at Texas A & M's College of Veterinary Medicine and Biomedical Sciences, and today her emphasis is on research, including assessing fee-waived cat programs and the impact of spay/neuter on shelter intake.


Related Links

Webinar: Stress Reduction & Enrichment for Shelter Cats
Hiding Places Mean Happier, More Adoptable Cats
Fee-Waived Cat Adoptions


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