Equid Blog : Horse Health & Diseases : University of Guelph : Ontario Veterinary College : Equine Infectious Diseases

equIDblog has now been active for one year, and look how far it’s come! Just this week we surpassed 75 000 unique hits since our launch. We now regularly have over 700 unique hits on the site per day during the week, and the numbers are still growing. It's great that we're able to provide a reliable source of information about equine infectious diseases to such a wide and diverse audience.

Everyone involved in equIDblog would like to take this opportunity to thank all the visitors who come to our site, and especially those who keep coming back for more! Please continue to help us spread the word about equine infectious disease control so everyone can do their part to help protect our equine companions, on a local, national and even global scale!  Questions, comments and suggestions are always welcome!  -Scott & Maureen

(Image credit: Tatiana Sapaterio)

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At the recent symposium of the American College of Veterinary Surgeons, there was an interesting abstract presented about liposome technology.  Liposomes are basically teeny-tiny "bubbles" made up of the same basic components as cell membranes.  They are sometimes call nanoparticles because they are so small, but they are still much bigger than even large molecules, which gives them some interesting biological abilities.  When liposomes are injected into the bloodstream, they go all over the body, but they tend to accumulate where there is tissue inflammation, because blood vessels become "leaky" in inflamed tissue, allowing these nanoparticles to escape the bloodstream.  What's great about liposomes is you can put different things inside them (such as drugs), and they help deliver their contents to inflamed sites in greater concentration and over a longer period of time, while reducing the exposure of the other body tissues to whatever they're carrying.  This can ultimately help improve the efficacy and safety of the drugs they carry.  Liposomes also tend to accumulate in tumors, so they are sometimes used to deliver anti-neoplastic chemotherapy drugs to these sites.

Liposomes have actually been around for a long time.  They were first described by Dr. Alec Bangham in 1961, and since then have become valuable tools in biology, biochemistry and medicine.  The technology still has its share of problems that need to be worked out.  Some people may have acute adverse reactions when liposomes are injected intravenously.  Sometimes the body's immune system will "attack" the liposomes, taking them out of circulation prematurely.  Much work is still being done to find better ways to help liposomes target particular tissues.

In terms of treating infectious diseases, liposomes can be used to deliver antibiotics to infected tissues.  Because of the targeted delivery system, the toxic/side effects of drugs on the rest of the body can be reduced while still achieving the same (or higher) concentrations of drug at the site of infection.  An example of this is the drug Abelcet (Enzon Pharmaceuticals), which is a liposomal preparation of the very toxic antifungal drug amphotericin B.  Abelcet has been licensed for use in the US and Europe since 1995.

The abstract presented at the ACVS (C. Underwood et al.) described the use of liposomes containing a radioactive marker (99-m Technetium) in horses.  They injected 10 healthy horses with a dose of liposomes, monitored them for adverse effects (of which there were none detected), and then used the radioactive marker to determine where the liposomes accumulate in a horse under normal conditions.  Their ultimate objective is to determine if liposomes can be used to better deliver antimicrobials to areas of infected bone (osteomyelitis), which are typically very difficult to treat.  Liposome technology still has a long way to go before it's being used widely in horses, but this was an important first look at how liposomes can possibly be applied to equine medicine in the future.

Image credit: Kosi Gramatikoff (1999)

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As a vet, I've been bitten by a wide range of animal species. When people talk about animal bites, they usually think about dogs and cats. Horses can (and do) bite as well. Most horse bites are probably playful nips that hurt a little yet don't cause major problems, but some bites can cause serious injuries and infections can result.

A recent paper in the Journal of Agromedicine (Langley and Morris 2009), with the rather unwieldy title of "That Horse Bit Me: Zoonotic Infections of Equines to Consider after Exposure Through the Bite or the Oral/Nasal Secretions". Bites apparently account for 3-4.5% of the approximately 100 000 annual emergency room visits in the US that are associated with horses. The authors of the paper review infections associated with bites and contact with organisms in the mouth and nose of horses.

A large number of bacteria have been associated with horse bite infections in people, including Actinobacillus, Streptococcus, Psuedomonas and Staphylococcus species. Some viruses can theoretically be transmitted by bites, but there's little evidence that this actually happens.

Although viruses are not of as much of a concern overall, rabies needs to be considered in every bite from a mammal. We pay a lot of attention to rabies with dogs, cats and wildlife, but it often gets ignored with horses. While I'm not aware of any reports of rabies transmission from horses to humans by a bite, it could happen.  Fortunately, rabies is rare in horses so the likelihood of exposure from this species is very low. However signs of rabies aren't always obvious initially, and rabies in horses may mimic other diseases. Sometimes, rabies looks like colic, and human exposure through bites or other contact is possible when handling, evaluating and treating affected horses.

Unlike with dogs and cats, there are no clearly defined protocols for dealing with bites from horses. Any dog or cat that bites a person is supposed to be quarantined for 10 days. The reason for this is if the animal is rabid and the disease is advanced enough for the animal to be capable of spreading rabies virus, it would invariably develop signs of rabies and die within this time period. We don't have similar guidelines for horses. I suspect the 10 day observation period would be adequate but we don't have good data. The paper states that in Kentucky, a 14 day observation period has been used by the state Department of Public Health.

At the conclusion of the paper, the authors make a few important general recommendations for reducing the risk of disease transmission from bites and oral or nasal secretions of horses:

• Use good general hygiene, especially hand hygiene, after any contact with horses.
• Use gloves and gown or lab coat when examining horses in a veterinary clinic or hospital. (This might be overkill for all horses. We don't require gloves for every horse contact, just contact with mucous membranes (e.g. mouth, nose), wounds, incision sites and other high-risk areas. I think bare hands are fine for general contact as long as there is good attention to handwashing after.)
• Consider mask and goggles if the horse is coughing or sneezing.
• Develop standard operating procedures for handling sick horses.
• Use isolation when needed.

I'd add a few more points:

• Avoid bites. Pay attention to what you are doing around horses to reduce the risk of being bitten. Do not encourage playful behaviours (e.g. nipping) that could lead to bites.
• If you are bitten and it breaks the skin, clean the site thoroughly with soap and water. If there is significant trauma, or if the bite is over a joint, hand, foot, or a prosthetic device, you should see a doctor immediately because antibiotics are most likely indicated. If you have a weakened immune system, you should be evaluated by a doctor after any bite.
• Avoid contact with the horse's mouth or nose if you have skin lesions. Cuts and scrapes can allow bacteria to enter your body and cause infections. If you have a cut on your hand, make sure it is covered with a glove or waterproof dressing if you are going to have contact with the horse's mouth or something that came from its mouth (e.g. a bit).

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A recent post about mandatory vaccination in show horses sparked a discussion about concerns regarding adverse reactions to vaccines. Dr. Carolyn Cooper of the Canadian Food Inspection Agency posted the following comment.

"There is mandatory reporting of adverse vaccine reactions in Canada by the vaccine manufacturers to the Veterinary Biologics Section (VBS) of the Canadian Food Inspection Agency. VBS monitors the type and frequency of reports in order to identify any potential issues with the safety and efficacy of licensed products. In order to increase the usefulness of mandatory adverse reaction reporting, veterinarians should report all suspected adverse reactions to the vaccine's manufacturer. Any comments regarding the licensing of veterinary vaccines in Canada, or adverse reaction reporting in Canada, can be directed to VBS at http://www.inspection.gc.ca/english/anima/vetbio/conpere.shtml "

This is a very important reminder for veterinarians and horse owners. While there is mandatory reporting, adverse reactions to drugs and vaccines are rarely reported by veterinarians. There's nothing underhanded about the lack of reporting, it's mainly that people don't think about it when it happens. Without good data, however, we are left to debate the true risks of vaccines and drugs with only incomplete information. Drugs and vaccines can be marketed for animals with rather minimal safety data. Even with large studies, safety issues can be missed until the drug/vaccine is mass marketed, as has been shown with some high-profile human drugs. If regulatory agencies don't get the data (i.e. if the reactions aren't reported to them), then they can't adequately monitor safety concerns. If your horse has an adverse reaction to a pharmaceutical product, you should make sure this is reported. It doesn't take your vet much time and shouldn't take any effort on your part.

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Toxicology tests have confirmed suspicions that selenium overdose was the cause of the sudden death of 21 polo ponies in Florida. The pre-event supplement the horses received was suspected early in the investigation, and the compounding pharmacy that provided it confirmed that the selenium level turned out to be too high.  They would not say whether this was due to a pharmacy error, or if the wrong amount of selenium was specified on the original veterinary order.

While this is hopefully an extremely rare event, it raises questions about what we give horses and why. The amount of money that is spent on supplements for horses is astounding. It's questionable whether most (or any) are needed, even for the highest level performance horse - yet a large percentage of horses, including "backyard" pleasure horses, are regularly treated with a variety of unproven supplements. I'm not saying that all supplements don't work, but for most of them there's just no evidence that they do work. There are also issues with quality control, as has been clearly shown with probiotics and glucosamine supplements.

Using supplements is very clearly a "buyer beware" situation. Most supplements have not been shown to be effective. Most are likely safe, but toxic reactions to some compounds (especially some herbs), contaminants and mixing errors can occur. Supplements are also a concern in terms of positive drug tests if their contents are not very clear, if they contain small amounts of contaminants, or if the contents have similar properties to tested drugs.

Am I saying stop using supplements? No. What I'm saying is think before you buy. Don't fall for flashy sales pitches and testimonials. Don't use a supplement because "everyone else is using it." Remember the general rule: above all, do no harm.

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The latest edition of Equine Disease Quarterly, a newsletter produced by the Gluck Equine Research Center, has a couple of interesting articles. Coincidentally, one involves African horse sickness (AHS), a disease foreign to North America that I've mentioned in the past week. The article is about the potential threat of AHS being introduced into the US, and  gives a relatively brief but excellent overview of the disease and why there is concern. The authors discuss a hypothetical outbreak scenario in the US, which is certainly not beyond the realm of possibility - many of the required pieces to the puzzle are already in place when in comes to the potential for this virus to spread in the US:

• The US has a large and often concentrated pool of susceptible horses. Very few horses have any immunity against the AHS virus.
• Many areas of the country have weather conditions that are suitable for survival of the insect vectors (Culicoides midges) that might be introduced carrying the virus.
• A different midge species, Culicoides sonorensis, is widespread in the US (except for the northeastern part of the country) and has been shown experimentally to be a highly capable vector for the AHS virus.

So what is needed for an outbreak to occur?

First, the virus needs to enter the country. This could occur by 1) inadvertent introduction of an infected midge (e.g. a "hitchhiker" on a plane would be one way for this to happen) or 2) introduction of an infected reservoir host. The reservoir host for this virus is zebras - fortunately  few zebras get imported into the US because of successful captive breeding programs, so this is probably less likely than the first. The other possibility, which certainly can't be ignored, is 3) intentional introduction of the virus: bioterrorism.

For an outbreak to maintain itself, a large population of reservoir hosts is needed. In Africa, the virus resides in zebras. Midges get infected by feeding on infected zebras, then infect horses by biting them. The lack of a large zebra population in North America could be the difference between a minor introduction and a major outbreak, unless there is another species that can act as a reservoir host in North America. This is one of the crucial unknown factors in the equation, but we shouldn't count on the lack of zebras as our main line of defense against this devastating disease.

The April 2009 edition of Equine Disease Quarterly can be downloaded here.

Image from: http://www.vet.uga.edu/vpp/fad/horse/vector.htm

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In a recent post on our sister site, Worms & Germs Blog, I commented on an article by Toronto Star columnist Linda Diebel. The article prompted me to write about a topic I've wanted to address for a while -  needlestick injuries. In the column, Ms. Diebel discusses her cat with idiopathic cystitis (a bladder disorder) and the need to treat it at home periodically with subcutaneous fluids (injections of fluid under the skin) and injectable medications. These are relatively easy procedures that most pet owners can manage with a little training, and it can be instrumental to improving the quality and length of life of some animals. However, safe and appropriate needle handling and needlestick injuries are rarely discussed.

The same holds true for horses. Some horse owners often (too often, in some situations) inject their horses with drugs or vaccines. Needle handling, needlestick injuries and avoiding contact with blood are (generally) very poorly managed by the veterinary profession and by horse owners. Needlestick injuries are incredibly common in the veterinary field, yet there is often little effort taken to reduce the risk of such injuries occuring. In contrast, there is a great deal of effort expended to prevent needlesticks in human medicine, largely because of concerns about transmission of viruses such as HIV and hepatitis B.  Fortunately, (currently) there are no common pathogens in horses that are transmitted by contact with blood and that are a significant concern in people. However, new diseases are emerging all the time, and there's no way to guarantee that the next big infectious disease in horses won't  be a bloodborne virus that can be transmitted to people by blood or dirty needles. It's not very likely, but you don't want to be the first person to get it if it does happen!

When it comes to injecting horses with medications, vaccines or anything else, some very basic precautions can greatly reduce the risk of injuries. The most important are:

• Know how to handle needles. You should be properly instructed on how to handle needles and treat your horse by your veterinarian.
• Make sure your horse is properly restrained. If the horse is not under control, you may get injured by the horse or accidentally inject yourself.
• Never recap a needle. This is a very common cause of injury!  When trying to recap, it's easy to miss the cap and stick yourself.  Instead of recapping the needle, after use dispose of it immediately in an approved sharps container. These containers are puncture-proof and are designed to help prevent anyone from getting the needles back out (either by accident or intentionally).  You can get a sharps container from your veterinarian or a medical supply store. Once the container is 3/4 full, put the cap on it (once on the cap cannot be removed) and take it to your veterinarian for disposal. There may be a small fee for disposal, but it shouldn't be too expensive.
• Never leave an upcapped needle lying around anywhere for any period of time.
• Never put a needle in your pocket.  Pretty obvious why.
• Never put needles in your regular garbage.  People collecting and handling your garbage could get stuck by the needles.

Even though needlestick injuries associated with animals are incredibly common, fortunately they don't usually cause problems (although they still hurt, of course!). However, various types of infectious, allergic and other reactions can occur, and serious consequences, while rare, can develop. This may be a greater concern with horses than dogs and cats, because larger volumes of drugs are used (so more could get injected into you), and because the larger needles used can cause more damage. More information on needlestick injuries in veterinary medicine can be found in a commentary published recently in the Canadian Veterinary Journal.

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Unlike dogs, which commonly have urinary tract disease, urinary tract infections (UTIs) are very uncommon in horses, but they can occur.

• Foals less than a month old are at risk of developing upper urinary tract infections (affecting the kidneys themselves) secondary to bloodstream infections (septicemia).
• Critically ill foals that are given broad spectrum antibiotics to treat serious bacterial infections can (rarely) develop fungal infection of the lower urinary tract (affecting the urethra and bladder) caused by Candida sp. These infections can also “ascend” the urinary tract, eventually traveling from the bladder up the ureters to the kidneys as well.
• UTIs in adults are very uncommon, but when they occur they usually affect the lower urinary tract. Mares are slightly more likely to develop UTIs than geldings and stallions because they have a much shorter urethra, so it’s easier for bacteria to reach the bladder (they don’t have as far to go!).

Upper UTIs are very serious because the kidneys themselves are affected (nephritis), which can ultimately lead to kidney failure. Animals with this kind of infection are typically very sick, depressed, and can have a fever. In general, lower UTIs are not as serious, but they do make it very uncomfortable for the animal to urinate (the same is true for people!). However, lower UTIs that result in or are the result of stones in the urinary tract can be life threatening if one of the stones becomes lodged in the urethra, preventing the horse from urinating altogether (this is similar to the situation with “blocked cats,” which occurs relatively commonly). Most of these infections are caused by the same common types of bacteria – E. coli, Proteus mirabilis, Klebsiella sp., Staphylococcus sp., Enterobacter sp., Corynebacterium sp., Pseudomonas aeruginosa – but sometimes fungi can be involved (such as Candida sp.) and there are also some parasites which rarely can affect the urinary tract of horses.

The important thing to remember, though, is that these infections are uncommon in general, and they are very rare in otherwise healthy horses. So if a horse has signs of a UTI (e.g. difficulty urinating, unusual behaviour when urinating, frequenting “squirting” without emptying the bladder completely, scalded skin from urine dribbling, blood in urine), there is often something else wrong. An important predisposing factor is bladder paralysis, when a horse loses control of the muscles in the bladder wall that make the bladder contract. When the bladder can’t contract, it never empties, and the urine just sits there, allowing bacteria to grow and sometimes even allowing infection to travel up to the kidneys (i.e. ascending infection). Bladder paralysis can result from diseases or certain toxins affecting the central nervous system (e.g. equine herpesvirus type 1 (EHV-1), Sorghum spp. toxicosis). In horses, it is often difficult to determine if stones (uroliths) are the cause of a UTI or the result of the UTI.

As in any other animal, the best way to definitively diagnose a UTI is to culture bacteria from a urine sample that has been collected as aseptically as possible (usually by passing a catheter, as in the photo above). It’s important to collect a urine sample for culture before starting any antibiotic treatment. If you suspect your horse may have a UTI, it should be examined by your veterinarian as soon as possible.

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I find it amazing that mammals can regulate their body temperature they way they do, despite drastic changes in the temperature of their environment. It was -30 degrees celcius  this morning (welcome to Ontario in February!) as I was waiting with my daughters for the school bus, and despite the feeling that my ears were going to freeze and fall off, I'm sure my core body temperature was about the same as it was when I left the house. Body temperature regulation is a key function in mammals that is controlled by the central nervous system.  The body expends a lot of energy and great effort to keep its temperature within quite a narrow range.

Increased body temperature (i.e. fever) is often a key indicator of disease, and usually, but certainly not always, infection.  Other things that can cause increased body temperature include exercise (particularly during hot weather), some toxins, and sometimes cancer. Fever is a natural response to infection that can actually help the body fight infection.  Unfortunately, fever can also have adverse effects on the body, particularly if it is prolonged or extreme.   Different sources use slightly different ranges for the "normal" body temperature of a horse, but 37.5-38.5C (99.5 to 101.4F)  is commonly used. Slight elevations can be present in healthy horses, so a true fever is usually considered a temperature above 38.9C (102F) .

Taking a horse's temperature is a standard part of any physical examination. A high temperature usually triggers concern about infection, and leads to further investigation. A few things need to be considered when taking and interpreting a horse's temperature.

• An accurate reading is critical. The thermometer used must be in good working order. New, digital thermometers are cheap and accurate, and usually the best option.
• If there is air in the rectum, the horse's temperature may read falsely low. This is most problematic if someone has performed a rectal exam shortly before taking the animal's temperature.  This is one reason that the temperature is taken early in an examination.
• There are some horses that normally have a temperature outside the range that is considered "normal" for the majority of other horses. Knowing your individual horse's normal temperature when it's healthy can help interpret temperature changes when your horse is sick.
• Body temperature normally varies throughout the day. This diurnal variation usually follows a regular pattern - usually higher during the day and lower at night.  The temperature of an individual horse can vary by as much as 1C (1.8 F) over a 24-hour period. This needs to be considered when interpreting temperature changes in a sick horse.
• A normal body temperature does not rule out infection, especially in young foals. Temperature is just one of many important factors used to identify illness.
• If you are going to take your horse's temperature, make sure you know how to do it safely. Don't get kicked in the process. Make sure you are always in a safe position. Although it may seem counter-intuitive, the closer you stand to a horse, the harder it is for the horse to kick you hard.  Don't rely on your horse's normal good temperament, especially if it's sick.  Animals that are sick or in pain may turn on even their closest companions.
• Don't let go of the thermometer... ever.

On a final, admittedly picky note, when students tell me a horse "has a temperature", I usually respond "So does a dead horse.  Everything has a temperature.  Does it have a fever?" Does that make me an anal academic (pardon the pun)?

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New animal health products are released on a daily basis. A great deal of time, effort and money is usually spent to market these products - sometimes more than was put into developing them. As a consumer, it's important to think before you buy, especially with new products.  Take a moment to consider whether a product is right for your animal, and whether the product's intended use and claims are  reasonable. The biggest problems tend to occur with "alternative" or non-traditional products, which encompass a huge range of products that are aggressively marketed, with little to no research or testing to back them up.  Here are some specific points to think about:

• Ask for research proving that the product works. "Data on file", anecdotes and other non-scientific sources are not adequate. Demand published research in peer-reviewed scientific journals. That means that the research has been independently scrutinized. Published data are not a guarantee that something will work, because some journals are not very strong and may publish weak research, but the lack published research altogether may indicate that research was not done, was not done right, or showed no benefit to using the product. Regardless of the type of product, there is no reason why proper research cannot be done to prove it is beneficial if it actually works.
• When looking at promotional literature, read it with a bit of skepticism. Think about whether or not what they say makes sense. A good general rule that I have is something that claims to cure all that ails you, probably cures nothing.
• If promotional materials do talk about research, check if they did a proper statistical analysis to really show that the product is better than the alternative. Showing a difference in numbers between two groups really mean nothing without proper analysis. For example, you could flip a coin 10 times and get 6 heads and 4 tails. Someone else may flip the coin 10 times and get 5 head and 5 tails. Clearly there's a difference in the numbers, but does it mean there's a difference in the ability of the two people to toss a head or a tail? Absolutely not.
• Don't get taken in by endorsements from "big names". More often than not, they're being paid for the promotion.
• Consult your veterinarian about new products. Be aware, however, that bad science is often marketed to vets as well and your veterinarian needs to be equally diligent.

At the end of the day, it's still "buyer beware". However, thinking about these basic points may help weed-out some particularly poor products. Additionally, and more importantly, increasing demands by consumers to see solid supportive research may be the only way to get companies to actually invest in testing and research to make sure their products work.

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This is one of my favourite radiographs. It's from a foal that was referred to the Ontario Veterinary College because of diarrhea. While we were taking the history, we learned that someone had tried to take the foal's temperature before it was referred, but the thermometer got "lost". They assumed that the thermometer had been dropped in the stall.  A radiograph was taken when the foal got to the hospital, and as you can probably see, there was a glass/mercury thermometer right in the middle of the foal's abdomen. (The really white part is the mercury in the tipof the thermometer. You can see the rest of the thermometer as a more faint white line running diagonally from the bottom left to the top right). They had apparently inserted the thermometer into the foal's rectum and left it unattended. The thermometer then migrated in the into the foal, working it's way in through over one metre of intestine (but it did, thankfully, stay within the intestine and the thermometer did not break). We ended up having to surgically remove the thermometer.

Beyond the novelty factor of the radiograph, this case highlights a couple of important points:

• Never leave a thermometer unattended while taking a horse's temperature. Digital thermometers that are available these days don't take long at all to get a reading, so just hang on to them.
• Don't use old glass/mercury thermometers. They can (and do) break.  This releases liquid mercury (which can be very toxic), and the broken glass can also cause problems. Digital thermometers are cheap, accurate and easy to find, so there's no excuse not to use them.

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This post originally appeared (in modified form) on www.wormsandgermsblog.com on January 1, 2009.

An important step in diagnosing infectious diseases and determining the optimum approach to treatment and management is rapid and accurate diagnostic testing. Many different testing methods are used, particularly bacterial culture (at least for bacterial diseases). Molecular testing has revolutionized the field of microbiology, and is making inroads into the field of diagnostic testing. Polymerase chain reaction (PCR) testing is a very powerful tool that can be used to detect DNA or RNA from specific microorganisms.  This technique can be very useful, but it can also be easily misused or misinterpreted.

The potential PROS of molecular diagnostic testing include:

• Rapid turnaround time: Testing can take as little as a few hours versus a few days for other tests like bacterial culture.
• Sensitivity: Organisms that are difficult or impossible to grow in a lab can be detected, and they can often be detected at lower levels than with other diagnostic methods.

The potential CONS of molecular diagnostic testing include:

• Sample contamination: This is a common concern with highly sensitive molecular tests - even a minute amount of contamination in the sample can cause a false positive result.
• Test inhibition: Samples from complex biological sites (e.g. stool) can contain substances that interfere with the many complex molecular reactions upon which the tests rely. Without good (and proven) methods to prepare the sample, this can result in a false negative result.
• Biologically irrelevant results: Some bacteria that cause disease are also commonly found as part of the normal microflora in healthy animals - simply finding it does not tell you that it is necessarily relevant to the problem. For example, Clostridium difficile can be found in the intestine of normal, healthy horses, but the diagnosis of C. difficile diarrhea requires detection of the bacterial toxins in stool samples, not just the bacterium itself.  A molecular test that simply identifies the presence of C. difficile, even if it identifies strains that possess the genes to produce toxins, tells you nothing about whether the bacterium was actually producing toxins in the animal.
• Lack of validation: This is a common problem with many (if not most) molecular tests. Some companies, especially those that just run molecular tests, offer a huge array of completely unvalidated and sometimes illogical tests.  It is also important to remember that tests must be validated for each species in which they are used - a test that works well in people will not necessarily work on a sample from a horse or a dog.

Molecular testing can be useful in some situations. If you are unsure, here are some things to ask the lab:

• Do they have a validated test that provides relevant results?  If they don't have good data (ideally published data) that their test is useful, accurate and reproducible, I'd avoid it.
• Do they have a quality control program, which includes running positive and negative control samples with each test batch?

Finally, as with any test that we use in veterinary (or human) medicine, it's important to evaluate all  results in the context of what is happening with the animal - treat the patient, not the test result.

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