Rabid Horse In Texas
A rabid horse has been identified in Bandera County, Texas - this is the first case of rabies in a Texas horse in almost 40 years. The horse started acting strangely, erratically and at times violently. Rabies was eventually diagnosed (diagnosis involves testing the brain after the horse dies or is euthanized) and the owners are undergoing post-exposure treatment.
Rabies is a rare disease in horses, but there is always a risk of exposure in regions where rabies is present in wildlife. The fact that equine rabies is rare is a good thing, but it can also breed complacency and lead to decreased vaccination rates.
Decreasing vaccination is a bad thing. Vaccination is cheap insurance for a very serious disease. Rabies is invariably fatal in horses. It's also a risk to anyone around the horse. Transmission of rabies from horses to people is theoretically possible through bites or other contacts that result in introduction of saliva into wounds, cuts or possibly the mouth, nose or eyes. I'm not aware of any documented cases of equine-to-human transmission of rabies, but given the severity of rabies, we need to be careful. Additionally, rabid horses have killed people because they can be unpredictable and aggressive. Based on all these factors, it's important that we not become complacent about rabies in horses, and a key component of rabies control is vaccination. However, vaccination is not the only aspect of rabies control. Using various management practices to reduce the risk of wildlife exposure and controlling rabies in wildlife in the area are other important measures, but individual horse owners can have the greatest impact on their horses' health by ensuring they are properly vaccinated against rabies.
If you own a horse, make sure it's vaccinated against rabies unless you live in a rabies-free region. More information about rabies in horses is available on the equIDblog Resources page.
Image source: www.bbc.co.uk
. Stop focusing on the wrong things
It's common for people to wipe injection sites in horses with alcohol before inserting the needle. It's so ingrained into some peoples' minds that they may complain if their veterinarian doesn't use an alcohol wipe before injecting. But what does that little swab really do, and is it needed?
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Often, when someone calls and asks about management of strangles, one of the first questions is 
I assume that people wouldn't voluntarily and regularly walk around barefoot on dog feces (or feces of any type), yet it's perplexing that some people regularly clean out horse stalls in bare feet (I've seen it done!). While horse manure may not be as inherently gross as dog poop, it's still feces, and like all feces contains a huge population of various bacteria, some of which can be harmful. The risks of barefoot mucking may also extend to bare feet inside boots, although I don't think sock-averse people need to panic.
A three-year-old Standardbred gelding was presented to the hospital for evaluation and treatment of diarrhea (colitis). The previous week the horse had developed a mild hind-limb lameness which seemed to come and go, and it was decided to treat the horse with antibiotics “just in case” it had something to do with an infection. The horse was treated with ceftiofur (an antibiotic, often sold under the brand name Excenel or Naxcel) for five days. On the fifth day, the gelding developed moderate to severe diarrhea. The next morning the horse also had a fever. He was treated with anti-inflammatories and quickly referred to the hospital for intensive care.
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As foaling season approaches, it's a good idea for people to review proper umbilical care. The umbilicus is an important route of infection in foals, and can be associated with problems including local umbilical abscesses, large abdominal abscesses extending to the liver, and overwhelming body-wide infection (sepsis). The reason the umbilicus is such a critical structure is that it contains three major blood vessels (two arteries and one large vein) and the urachus (which connects the umbilical cord to the foal's bladder) . When the umbilicus ruptures shortly after birth, these structures are exposed to the bacteria-laden environment of the outside world and can be a route of entry for local and deep infections. Care of the umbilicus during the initial high-risk period is a key part of raising a healthy foal.
An eight-year-old Quarter Horse gelding was presented for examination due to chronic weight loss over several months. Lately he’d also been lying down frequently and exhibiting increased breathing effort, so he was treated for what was suspected to be mild signs of colic, but failed to improve. He’d also collapsed once during mild exercise.
The UK's 
Rotavirus is an important cause of diarrhea in young horses. (It's also a major cause of diarrhea in infants, but a .jpg)
Following on the heels of a few outbreaks of piroplasmosis in the US over the past year is 
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Equine Piroplasmosis Disease Investigation Continues
A five-year-old Quarter Horse mare was found down in the field in the mid-afternoon. The horse was seen moving around the field normally less than eight hours earlier. She was found near a fence, but there were no external signs of trauma on the mare's body. Some green feed material was present at the nostrils. With encouragement the mare was able to stand, but she was very unsteady and uncoordinated, particularly in the hind limbs. Upon examination by the veterinarian in the field, it was also noted that the horse could not open her mouth normally (lockjaw - which is often a sign of .jpg)
The ongoing large 
For a country that is "piroplasmosis-free," the US sure has a lot of piroplasmosis. The Texas Animal Health Commission has reported that this bloodborne disease, caused by Theileria equi, has been confirmed on a ranch in south Texas. The farm is quarantined and testing is under way to determine the scope of the problem. They are presumably also looking at ticks in the area to see if the types of ticks that are able to transmit the infection are present, and trying to figure out where the infection came from.
Equine sarcoids are skin tumours that affect horses, donkeys, mules and zebras. They are the most common type of tumour found in horses, and account for 35-90% of all equine skin tumours. Sarcoids are generally not life-threatening – unlike some other tumours, they do not metastasize (i.e. spread to other organs or tissues). However, they can be locally aggressive growths, meaning they may invade deep into the tissues immediately surrounding the primary tumour. They are also very difficult to treat, and therefore can affect a horse’s welfare or quality of life, depending on the size and location of the sarcoid. There is some evidence of a genetic predisposition to sarcoids in some horses as well. Involvement of bovine papillomavirus in the development of sarcoids was first suggested by Olson and Cook in 1951, who were able to reproduce sarcoid-like lesions in horses by inoculating them with tissue from bovine warts. Since then, researchers have used PCR to show that the vast majority of sarcoids contain BPV DNA, whereas normal horses and non-sarcoid skin tumours do not. Although BPV DNA has been found in healthy horses living in close contact with sarcoid-bearing animals, there is currently no evidence that BPV or sarcoids are transmissible horse-to-horse.
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At the ongoing 
The recent 
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During a strangles outbreak, people often ask how (and when) they can say their farm is "strangles-free." They usually don't like the answer. Declaring a facility to be free of strangles, a highly contagious disease caused by the bacterium Streptococcus equi, is not cheap, easy or quick. It is, however, important.
An Australian horse group, the .jpg)
In the wake of the 
Unfortunately, Dr. Alister Rodgers, who had been hospitalized with Hendra virus infection acquired from a sick horse, .jpg)
Horses sometimes need to be treated with antibiotics. That's an unavoidable fact. Some horses that are treated with antibiotics develop diarrhea, which can be fatal. That's another unavoidable fact. While those two situations can't be avoided, the risks can be decreased.
What's the link between chickens, Campylobacter, anti-ulcer drugs and horses? Well, nothing direct but .jpg)
I received the following question the other day: "I have a friend who had chemo embolization on tumor on liver in late June. She is in hospital now, and an abscess was discovered on liver. Pathology results said "equine strep". Her brother visited immediately after procedure, and he works with horse full time."
A veterinarian, 
To steal a line from Winston Churchill, equine protozoal myeloencephalitis (EPM) is a riddle, wrapped in a mystery, inside an enigma. It's a frustrating disease from many standpoints, and myths abound. 
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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 
Last year, there was a large equine influenza outbreak at the Crawford County Fair in Pennsylvania. In response to that, 
Hendra virus, a virus that can kill horses and people, has resurfaced in Queensland, Australia. This bat-borne disease has caused 
Dr. Bob Wright of the 
Earlier this summer, the 
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If you get bitten by a mosquito carrying West Nile virus, one of three main things could happen. The best case scenario, which happens in about 
Many peoples' idea of a parasite control program is to give their horse a dewormer and assume everything's taken care of. Many aspects of appropriate, logical and prudent anti-parasite programs are ignored with such an approach, which can lead to problems.
There is apparently still no evidence regarding the location of .jpg)
International events like the 
It was only a matter of time, but eastern equine encephalitis (EEE) has been found in more US states this year. EEE is an seasonally important disease in some areas, including Louisiana. More cases in more states, and perhaps even some regions of Canada, are likely over the course of the summer and fall.
Not long after the 
The 
Clostridial myonecrosis (also called clostridial myositis or gas gangrene) is a very serious infection caused by growth of Clostridium bacteria in muscle. Clostridia are anaerobic spore-forming bacteria, meaning they only grow in environments without oxygen and they can stay dormant in the form of very tough (e.g. difficult to kill) spores. Clostridal spores can be found in healthy muscle. Presumably they enter the bloodstream periodically from the intestinal tract, but aren't able to grow because of the presence of oxygen in healthy muscle. They lie dormant, waiting for the right conditions to start growing - which in most horses never occurs. Clostridial spores can also be introduced into muscle during injections (e.g. vaccines, medications), surgery or trauma..jpg)
Two horses from different farms in the 
The 
No, not dental plaque like you get on your teeth - in this case we’re talking about aural plaques, which are a type of skin lesion that some horses develop on the inside surface of their ears. These plaques are usually depigmented, meaning the skin cells of which they are made do not have the same pigment in them as the cells of the surrounding skin, making the lesions appear pale grey or off-white. Other than being considered unsightly in some cases, aural plaques usually don’t cause problems for the horse – they’re not itchy, sensitive or painful. They can occur in any horse, no matter the age, breed or sex. Occasionally some horses may develop similar plaques on the udder or around the anus or vulva (under the tail). The diagnosis of an aural plaque is typically made based on the horse’s clinical signs alone (i.e. a raised, depigmented skin lesion inside the ear that is not associated with any inflammation or discomfort).
Papillomaviruses (PVs) are small DNA-based viruses that are recognized causes of disease in many animal species and humans. More than 100 different human papillomavirus types (HPV) have been identified, which can cause a range of problems from annoying (but benign) warts to malignant cervical cancer. The ability of papillomaviruses to cause cancer was first recognized in animals, specifically with cottontail rabbit papillomavirus (CRPV), bovine papillomavirus (BPV) and canine oral papillomavirus (COPV). In general, PV infection causes benign disease in the vast majority of individuals, but the viruses have the potential to cause malignant disease in a small proportion of the mammals they infect as well.
Rhodococcus equi is a very well recognized pathogen in horses – it is a common cause of pneumonia in foals between the ages of 1-6 months, and infection is also sometimes associated with 
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Rhodococcus equi is a common pathogen in foals between the ages of 1 and 6 months of age that is most infamous for its ability to cause pneumonia. Classic R. equi infection results in the formation of large abscesses throughout the lungs of young foals (see picture left), which can be especially difficult to treat because the bacteria are able to hide from the body’s immune system by living within white blood cells. However, this organism’s bag of tricks doesn’t end with lung abscesses – it can also travel to other parts of the body and cause all sorts of trouble. These kinds of infections may occur with or without the classic lung infection, and are referred to as extrapulmonary disorders (EPDs).
I'm sure there are few people that haven't heard about the current worldwide flu epidemic (although you’d pretty much have to have not listened to or watched the news nor read a newspaper nor been on the internet for the last week to have missed it!). It's been called “swine flu” until the last few days, but that terminology is gradually disappearing and being replaced with the virus’s more formal name, H1N1 influenza A. It's been covered extensively in the press and we have numerous posts about it on our sister site, 
Diarrhea is a relatively common problem in foals. It can range from very mild to fatal, and sick foals can get worse (i.e. "crash") very fast. Outbreaks of diarrhea in foals can also occur. So while most cases of foal diarrhea are mild, the implications of this condition for both the foal and the farm can be huge.
Here's a recap of West Nile virus activity in Canada in 2008.
April’s "bug of the month" is Streptococcus equi subspecies equi, the cause of equine strangles, specifically strain 4047. This is the first strangles strain to have its entire genome (i.e. all of its DNA, including every gene) sequenced. The March 2009 issue of the open-access journal 
Among their conclusions (with my comments in italics) are:.jpg)
The age range of affected horses was from "born in hospital" to 31 years old. Many different breeds were affected: Any horse of any age is susceptible to MRSA.
The latest edition of 
Coincidentally, just after writing my post on the concerns about 
Climate change is a pressing topic these days. There are many potential ramifications of climate change, including shifts in disease patterns. The climate affects the populations of insects that can transmit infections. This can result in expanding ranges of certain diseases, or movement of diseases into totally new regions..jpg)
Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging problem in horses. Owners often ask if they should have their horses tested to see if they are MRSA carriers. There's no simple answer that applies to all farms, but basic points that need to be considered include:
In equine hospitals, intravenous (IV) catheters are often placed in the large jugular vein in the neck of horses to make it easier for everyone (the horse included) to give the animal fluids and/or medication. However. any time the body's normal barriers (e.g. the skin) are broken (e.g. by placing a catheter through the skin into a vein), there is an increased risk of infection. Catheter site complications can range from mild inflammation of the skin around the catheter, to serious infection causing thrombosis (blockage) of the vein and abscesses.
The other day, I wrote about a few 
Infectious disease surveillance is an important part of the infection control program. 
West Nile vaccines are labeled to provide protection for 12 months. Before they can be marketed with such a label, these vaccines have to be tested to prove that they still offer some protection for the animal for at least that long. For some vaccines, like rabies, protection likely lasts much longer than the label claim, but until recently no one’s bothered to study most vaccines beyond one year. I have no doubt that the protective immunity does decrease with time – the protective effects of vaccine are likely highest (as Scott said) about 30 days post vaccination, and lowest at the end of the 12 months. But there is no evidence that the immunity drops off so fast that after 4-6 months the vaccine would require a booster to be adequately, if not maximally, effective. There are vaccines, like herpesvirus and influenza, for which we recommend boosters for horses semi-annually, but this is for animals that are at ongoing high-risk for exposure to these diseases, which are very common. Six months after mid-April is mid-October, and in this part of the world there are very few mosquitoes still flying around at that point.
As spring approaches (slowly... at least here in Ontario!), people once again start thinking about vaccination programs for their horses. A question that comes up every year is when is the best time to vaccinate against mosquito-borne diseases? Depending on your region, the pathogens of concern may include West Nile virus (WNV), as well as Eastern/Western or Venezuelan equine encephalitis virus (EEE, WEE and VEE, respectively). Often people get the generic response of "30 days before mosquito season," which isn't always very helpful.
Horses have a very different intestinal tract than people (and dogs and cats). A horse's intestinal tract is much likely to develop problems from antibiotic use, particularly antibiotic-associated diarrhea or colitis, which can be fatal. The root of the problem in these cases is disruption of the normal bacterial populations that live in the intestine (the microbial "flora"), which can allow harmful bacteria to multiply and spread. This can occur with antibiotics given by any route (even by injection), but using oral antibiotics can result in higher drug levels in the intestinal tract, which creates a greater chance of causing problems. The likelihood of a horse developing complications from any antibiotic is probably a combination of what bacteria the antibiotic kills and how much makes it to the intestinal tract..jpg)
I usually hesitate to write posts about strangles cases or outbreaks. I don't want to give the impression that these are unusual events, because strangles is not a rare disease, in terms of either single cases or outbreaks. When I post about an outbreak, it's usually because there's something particularly interesting about the outbreak or the report about it. Such is the case with 
Lawsonia intracellularis is an important cause of disease in weanling foals, causing a disease called proliferative enteropathy. Antibiotics, mainly erythromycin,are usually used as part of the treatment for this condition. However, little is known about the true antibiotic susceptibility of this bacterium. The problem is that Lawsonia does not grow in culture plates in a lab like most other bacteria with which we deal - it can only grow in cells, which makes it very difficult to test for antibiotic resistance. Antibiotic therapy for this disease is therefore chosen based on basic knowledge about the bacterium and anecdotal information about how animals respond to treatment. Obviously, this is not the ideal situation.
"A two-day horse show is different than an eight-day fair exhibition.'" Two days is lots of time to transmit infectious diseases.
Unlike dogs, which commonly have urinary tract disease, urinary tract infections (UTIs) are very uncommon in horses, but they can occur.
Infectious diseases are a major problem in young foals. Diseases, including diarrhea, pneumonia, meningitis, umbilical infections and joint infections can range from mild to rapidly fatal. Even in foals that survive the initial infection, these conditions can sometimes result in permanent problems. A study published in a recent edition of the 
An abscess is an accumulation of pus. Pus is basically dead bacteria, partly broken-down cellular debris, and white blood cells. Sometimes there can be a thick capsule of tough, fibrous tissue surrounding an abscess, particularly if it has been there for a long time (see picture left). Most abscesses occur as the result of a local infection that the body was able to contain (at least partly), but could not eliminate altogether, and that didn't "drain" naturally to an open space (e.g. outside the body). Over time, some abscesses may continue to grow and become quite large, which can cause many different problems depending on where the abscess is. "Sterile" abscesses can also occur, but are much less common - these lesions are not associated with a bacterial infection, but may occur following a severe trauma or in association with certain tumours..jpg)
As part of the 2008 Conference of the .jpg)
Equine piroplasmosis is a blood-borne disease that is caused by the parasites Babesia equi and Babesia caballi. Infected horses may develop mild disease characterized by weakness and loss of appetite. In more serious cases, horses may develop fever, anemia, jaundice (yellow gums and eyes), a swollen belly and respiratory problems. Other signs that are sometimes present include neurological abnormalities, red urine (secondary to destruction of red blood cells) and death. In contrast, many infected horses may no signs of illness whatsoever. Horses that recover may carry the parasite for a long period of time, and these horses can be a source of infection for other horses if there are ticks in the area capable of transmitting the parasite (not all species of ticks can transmit the disease). This can lead to the need for long quarantines. Horses that become persistent carriers of piroplasmosis need to be quarantined for life, euthanized or sent to a country where the disease is endemic.
Horses that most often become infected and sick from A. equuli are foals. This bacterium can cause a wide range of infections in these young animals, including septicemia (bloodstream infection), meningitis, pneumonia, omphalophlebitis (umbilical infection) and septic arthritis (joint infection). Foals can get infected from contact with other horses or even their own mares because the bacterium is so common. However, it typically only becomes a problem in foals that do not receive 
Diarrhea is a potentially life-threatening condition in horses. It's also frustrating from a diagnostic standpoint because, even with the most complete/comprehensive testing, a cause is only identified in a minority of cases. This is true for other species too, including people, and is a reflection of the complex nature of the intestinal tract and the numerous possible causes of intestinal disease. Diagnostic testing obviously costs money, so if it gives us an answer less than half the time anyway, it begs the question - why bother? Well, here are some points to consider:
I don't know whether Truro Raceway (in Nova Scotia, Canada) has bad luck, bad infection control or is just really open about any problems. Following an outbreak of strangles in December (
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Mastitis (inflammation of the udder) is a relatively uncommon problem in mares. Some of the likely reasons that mares develop mastitis much less commonly than other animals (such as cows) is that they have comparatively small teats, and the udder, even when engorged, remains well tucked up between the hind legs. This decreases the risk that the teats will be traumatized or soiled compared to the large, low-hanging teats of a cow. Also, frequent nursing by foals (normally several times an hour) keeps the udder relatively empty and helps prevent build up of bacteria in and around the teat. The fact that people don’t frequently touch a mare’s teats and udder also helps prevent contamination with bacteria from our hands or from other sources that may be transmitted indirectly on dirty hands.
While it's a little early in the foaling season, it never hurts to think about vaccination plans for foals. Vaccination is an important part of the disease prevention program - but it's only one part... general 
Equine dysautonomia, or "grass sickness", is a very important disease in some areas of the world, particularly the United Kingdom and some parts of South America (where it's called mal seco). The cause of the disease is still unclear, but there is increasing evidence implicating the bacterium Clostridium botulinum, which produces the toxin that causes 
Salmonellosis is an important problem in horses. Infection with Salmonella can cause disease ranging from fever and/or mild diarrhea, to severe diarrhea (see picture right), bloodstream infection and death. Horses can also carry Salmonella in their intestinal tract without any signs of illness at all! Testing of horses with diarrhea for Salmonella is commonly performed, but diagnosing Salmonella infection is not as straighforward as you may think:
Streptococcus zooepidemicus (technically Streptococcus equi subspecies zooepidemicus), commonly called Strep zoo, is an important bacterium in equine medicine. It is one of the most common bacteria isolated from infections in horses. Like other streptococci, S. zooepidemicus is a Gram positive coccus, meaning that it stains purple with Gram stain and has a ball shape (coccus). Streptococci tend to stick together in chains (see picture right) which are often described as "string of pearls."
I just got back from the 
There's something ironic about traveling to a conference to speak about infectious diseases and coming down with food poisoning. As I lay in bed in Orlando in a relatively non-functional state Friday, I had lots of time to contemplate the good and bad points of vomiting. As much as it is unpleasant, the ability to vomit is useful, and it is something horses lack. As one of the many anatomical quirks that horses possess, horses are essentially unable to vomit, regardless of what in happening farther down the intestinal tract. This is serious problem, because unlike people who can relieve the pressure of a distended stomach by vomiting, the only thing a horse's stomach can do is get bigger and bigger until it finally bursts. Stomach rupture is fatal and kills numerous horses every year - it causes massive infection in the abdomen (peritonitis) due to the spillage of the bacteria-laden intestinal contents.
The investigation of the 
Until the outbreak investigation in the USA is complete and the disease is contained, use extreme caution or simply refrain from importing breeding animals, semen, embryos etc. from the USA.
Transportation, particularly over long distances, is likely the single most important predisposing factor for pleuropneumonia (aka "shipping fever") in horses. Pleuropneumonia is a very serious condition in horses that occurs when an infection in the lungs (pneumonia, typically bacterial pneumonia) spreads to the outer surface of the lungs (the pleura) and contaminates the space between the lungs and the chest wall (the pleural cavity). The inflammation of the pleura (which is also very painful) usually results in accumulation of infected fluid around the lungs (photo right: drainage of pleural fluid in a horse using a chest tube). The disease can be difficult to treat, and affected horses can end up with a lot of scarred lung and adhesions between their lungs and chest wall, as well as lung abscesses and other problems.
Potomac Horse Fever (PHF), a disease named for the 
I was reading a fact sheet on foal care today that was available online. It was one of those sources that gives a mixture of good, mediocre and bad information. One thing that I didn't like was a reference to tetanus antitoxin administration being a common practice in newborn foals. That might have been the case a couple of decades ago, but it is certainly not recommended now.
In December 2008, an outbreak of contagious equine metritis (CEM) was reported in Kentucky. The index case was a healthy stallion that underwent routine testing for exportation of semen and the causative agent, Taylorella equigenitalis, was isolated by cutlure on December 15. By the end of the month, three more stallions on the same farm were also identified as infected. At the moment, it is estimated that there are 28 horses in Kentucky and another 156 horses outside Kentucky that have been exposed. Another 250 horses are being traced across 27 states. The last outbreak of CEM in the USA was in 1979 in Missouri, although a few sporadic cases have been identified in the country in the last three decades. It is a reportable disease in both the USA and Canada, and there are strict import (and export) regulations for horses entering the USA and Canada from CEM-positive countries.
One example of this is Streptococcus equi (aka Strep equi), the cause of the highly infectious disease strangles, and its close relative Streptococcus zooepidemicus (aka Strep zoo). Streptococcus zooepidemicus is commonly found in the respiratory tracts of healthy horses and can cause secondary infections, but it is not highly transmissible like Strep equi. Technically, however, both of these organisms are actually Streptococcus equi. The S. equi that causes strangles is Streptococcus equi subspecies equi, while the other one is Streptococcus equi subspecies zooepidemicus. Usually, people just refer to them as S. equi and S. zooepidemicus for simplicity's sake, and in most situations, that's enough for people to understand what they're dealing with. However, sometimes there can be confusion if a diagnostic laboratory reports the full name of the organism and someone doesn't notice the "zooepidemicus" at the end, and panic ensues about a non-existent strangles case/outbreak until someone reads the report properly. The take-home message here is read all diagnostic test results carefully and if in doubt, call for clarification.
The outbreak occurred at a racetrack in Zagreb. Not surprisingly, an H3N8 strain was responsible. Investigation of the cases determined that vaccine status had no influence on disease - both vaccinated and unvaccinated horses became equally sick. The vaccine used in Croatia at that time contained three influenza strains, including two different H3N8 strains, but the strains that were used were from 1963 and 1979. When they compared the strain that caused the outbreak and the vaccine strains, there were multiple genetic differences, which is not surprising given influenza's capacity to evolve over time. There were far fewer differences with the more recent strains used in vaccines in most other countries.
An outbreak of salmonellosis has killed at least 22 horses in Kjalarnes, Iceland.jpg)
I commonly get asked about giving probiotics to horses, and what I recommend. While probiotics are often simply described as "good bacteria", a better definition is "live microorganisms that, when ingested in certain amounts, cause a positive health effect beyond that of their nutritional value." This definition makes it clear that there must be live microorganisms, they must be given at a certain dose and they must cause a beneficial effect. Unfortunately, while there are many, many probiotics available for use in horses, and lots of money spent on the marketing of such products, there has been basically no real research done on any commercial equine probiotic. That makes it difficult to make good recommendations. Studies have also shown that commercial probiotics often don't even contain what they say they do. So, what do I say when I'm asked? I say it probably won't hurt to give an adult horse a probiotic (one study in young foals showed that a probiotic actually caused diarrhea), but there is no guarantee that it will help either. One thing that I do recommend is always to read the label closely.
The picture (left) is of the intestinal tract of a six-month-old foal with severe diarrhea that threw a blood clot to one of the major blood vessels suppling the large intestine, killing that section of the gut (the dark purple/black intestine in the picture), and the foal. Laminitis (founder) is also a common complication.
The latest version of the DEFRA/AHT/BEVA Equine Quarterly Disease Report has been released. This is a joint venture of three British organizations, and often contains some interesting infectious disease information. This edition contains brief information about diagnoses of selected diseases such as 
This post originally appeared on the 
That's all good news. In the bigger picture, though, was anything learned, and were any measures taken to reduce the risk of this happening again? A lot of this comes back to the debate about 
EPM was first identified in horses in the 1970s, but it took more than twenty years before the causative agent, the protozoal species Sarcocystis neurona, was identified. Shortly thereafter, the definitive host of S. neurona was identified as the opossum (specifically the Virgina opossum (Didelphis virginiana) in North America). In the opossum, the parasite lives and reproduces in the animal’s intestine without causing much damage, and oocysts are passed in the feces. Horses, on the other hand, are aberrant or “dead end” hosts – if they ingest the parasite from the opossum feces, they cannot spread it to other animals of any species. However, in a horse, the parasite can leave the intestine and migrate through the animal’s tissues, ultimately reaches the brain and/or spinal cord. Damage to the nervous system caused by migration of the parasite. Although EPM has been identified in horses outside of the Americas, the vast majority of these cases are horses that were imported from or at one point traveled to the New World.
EPM commonly gets blamed for a lot of minor abnormalities in horses (mostly gait abnormalities), often without being properly diagnosed. Part of the problem is that exposure to the parasite in the New World is very common (>50% of horses in many areas), but definitive diagnosis of disease due to EPM can be very difficult. The classic sign of EPM is pronounced asymmetrical muscle wasting (note the profound muscle wasting of the left gluteal muscle in the picture) in different parts of the body. There are very few other diseases that result in this kind of condition, so a fairly confident diagnosis can be made in these cases. Horses with more subtle or less classic signs are more problematic.
Lawsonia intracellularis is a bacterium that causes an intestinal disease called proliferative enteropathy in young horses. One of the reasons we still don't know a lot about this disease is that this bacterium can't be grown in a lab. One of the areas in which researchers are working to find more information is from where horses that become sick initially get Lawsonia... Is it from healthy horses that are carriers? Does it circulate in the horse population, or is there an outside source? Does it come from pigs (pigs can also be affected by disease due to Lawsonia infection)? Do other animal species such as wildlife carry it?
Equine infectious anemia (EIA) (aka "swamp fever") is a very important disease in horses, and can also affect donkeys and mules. This is the disease for which horses are given a Coggins test, which is required every six months for horses attending most shows and competitions, and for horses traveling internationally. EIA is caused by a retrovirus, more specifically a 
On December 9, the Infectious Diseases session was held at the 2008 .jpg)
Influenza vaccination is an important preventive strategy in people, and much effort is made to vaccinate as many people as possible with effective vaccines. Every year, the 
The 
One horse owner stated "If I had known it was out there, I would have done things differently." While I understand where she's coming from, it's important for all horse owners to remember than exposure to infectious diseases is an ever-present risk. Streptococcus equi, and various other infectious agents, are widespread in the horse population, and there is never a "no-risk" situation. For that reason, we should be taking practical measures to reduce the risk of disease transmission at all times, not just when we know there is an infectious disease in the area.
The December 2008 newsletter from the University of Guelph's 
One (of many) unique anatomical aspects of horses is their guttural pouches. These pouches open into the throat area and are essentially large openings in what is the equivalent of a horse's 
The fungal infection can weaken the wall of the artery, ultimately causing it to rupture. This results in massive blood loss (which comes out of the horse's nose) and it is a potentially life-threatening event.
I'm trying not to sound like a broken record when it comes to antibiotics, but it's a very important topic so you'll see many posts on the subject. When you consider that antibiotic-associated diarrhea is a potentially life-threatening problem in horses, and that antibiotic-resistant bacteria are becoming more common in general, it should be obvious that we need to limit the use antibiotics to when they are actually needed, and potentially effective. Horses with respiratory disease are commonly treated with antibiotics. However, as discussed in a previous post (
Stomach ulcers are common in horses (especially race horses), and anti-ulcer medications are widely used. The most common of these drugs is omeprazole (sold under the brand name 
Sporotrichosis is a fungal infection of the skin and superficial lymph vessels caused by Spororthrix schenckii. This organism is often found on decaying plant material, although it can also infest living plants like sphagnum moss and rose bushes. Sporotrichosis is an uncommon condition in horses, but it occurs all over the world. It is most common in tropical and subtropical regions and is rare in northern climates.
One, several, or many firm round nodules may be found. Typically they are not itchy or painful to the horse, but as they get bigger the nodules burst and ooze a pus-like discharge. When the infection tracks up a lymphatic, the nodules may occur in a row along the vessel, appearing like "beads on a necklace". The lesions may heal and recur numerous times over months or years. These clinical signs are very suggestive of sporotrichosis, but bacterial lymphangitis should also be considered. Sometimes the yeast organisms can be seen in the discharge using a microscope, but the definitive diagnosis is made by culturing the fungus. The treatment of choice is a form of iodine that can be given orally, although more conventional antifungal drugs may also be effective (but also much more expensive). The prognosis for recovery is good.
A few years ago, I investigated an equine herpesvirus (EHV) outbreak associated with a yearling sale. We found a lot of sick horses, both from the sale and horses that were infected when purchased horses were brought home. A lot of actively racing horses got sick and missed races, which cost people even more money. Part of the investigation was asking people what percentage of horses from sales they expected to get sick right after the sale. The average answer was 80%, and many people said 100%. When you think about it, it's absolutely astounding that people will spend what is often a great deal of money to buy a horse that they expect will get sick, and then (more often than not) put it in the same barn as their other horses, thereby putting all the animals at risk of infection..jpg)
Strangles is an infection caused by the bacterium Streptococcus equi subsp equi, which is often simply called Strep equi or S. equi for short. This pathogen is always circulating somewhere in the equine population, and it can cause sporadic cases of strangles in individual horses, or large outbreaks in groups. It is transmitted mainly by nasal secretions and pus from infected horses when they come in contact with other horses. The classical and most prominent feature of strangles is the formation of large abscesses in the lymph nodes between the jaw bones.
The downside of this kind of treatment is, while it stops the immediate infection from developing, the horse does not develop immunity against S. equi like it would if its body had to fight the infection. This is not a problem if good infection control measures are in place to prevent further S. equi transmission. However, if transmission is not controlled, then the horse is at risk of being re-exposed, and could be infected again after the antibiotics are stopped. This can lead to a vicious cycle of exposure-treatment-susceptiblity-exposure-treatment... I've seen farms where this goes on for a long time with horses receiving multiple courses of antibiotics, and they often eventually getting the disease anyway.
As of this morning, no new cases of equine herpesvirus (EHV) infection have been identified at Laurel Park in Maryland. (.jpg)
Respiratory tract disease is a very common problem in horses that has a wide range of causes, including bacterial and viral infections, as well as non-infectious conditions. Nasal discharge (i.e. a "snotty nose") is often one of the first signs of respiratory disease noticed by owners. Unfortunately, the nasal discharge itself cannot tell you what the problem is, nor how to deal with it. If your horse develops nasal discharge, you should contact your veterinarian to determine the best approach to diagnose the cause and the best way to treat the animal. Here are just a few of the factors that need to be considered:
As we encounter more infections caused by antibiotic-resistant bacteria (e.g. 
Equine herpesvirus type 1 (EHV-1) infection was confirmed in a filly at Laurel Park in Maryland (
A two-year-old filly at a racetrack in Maryland has been 
The discovery of antibiotics was one of the most important medical advances in history, and these drugs have had an immense impact on human and animal health. While antibiotics have saved countless lives, their use can also be associated with some very serious side effects and complications. For example, in horses, antibiotic-associated diarrhea (colitis) is a major issue.
Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging problem in horses. This antibiotic-resistant bacterium can cause disease in both horses and the people in contact with them. In the early 2000s, virtually all reports of MRSA in horses in North America, and many from Europe, involved one particular "strain" of MRSA. This strain goes by different names in different places, but in Canada its called CMRSA-5, and in the US it's called USA500. This is actually a strain that originated in people but which seems to be well adapted to horses.
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The described clinical signs in affected horses are very non-specific, so it's hard to speculate about the causative pathogen. There are a variety of potential culprits, including equine influenza virus (EIV), but so far testing has not detected EIV or any other known pathogens. This "mystery" disease does not appear to affect other animals or people (but without knowing what is causing it, this is difficult to say for certain). It is possible that this is a "new" disease, but the vast majority of infectious disease outbreaks are caused by pathogens that we already know about. Specialists from Britain have been called in to help with the investigation. Hopefully more information will be available soon.
One area that people often ask questions about is the ability of S. equi to survive outside of a horse, and how to handle the general environment (e.g. barn, paddocks) during an outbreak of strangles. Two older studies reported that S. equi can survive on environmental surfaces for up to 60 days. This has led some people to recommend prolonged quarantine of pastures that have been used by infected horses. However, these studies were conducted in the controlled and relatively hospitable environment of a laboratory, without exposure to sunlight, temperature changes and competing bacteria that are found in the "real world".
Eastern equine encephalitis (EEE) was recently identified as the 
You may notice a recurring theme on equIDblog anytime we talk about infectious disease control, particularly when it comes to zoonotic diseases (those that can be transmitted between animals and people): an emphasis on handwashing. There is increasing emphasis on hand hygiene (i.e. hand washing and use of alcohol hand sanitizers) education in hospitals because the hands of healthcare workers are a major (if not the most important) means of disease transmission between patients. Despite hand hygiene being easy, cheap and effective, people rarely wash their hands as often as they should, and they often don't do it properly.
Many people in the horse world have heard the hype about methicillin-resistant Staphylococcus aureus (MRSA) in horses. MRSA can cause infection in horses, just like it can in people, dogs, cats and many other animals. It’s usually what we call an “opportunistic” pathogen, meaning it usually takes advantage of a person or an animal that is already sick or injured, like someone who’s in the hospital and has just had surgery. And because MRSA is resistant to many different antibiotics, the infection can be difficult to treat. The big concern with MRSA in recent years is that infections are now sometimes occurring in people who aren’t sick, and who don’t have wounds or incisions, which is where MRSA usually likes to move in. It’s very important to find out from the start if an infection is being caused by MRSA, so that it can be prevented from spreading to other people and animals, and so that it can (if necessary) be treated with the right kind of antibiotic.
In adult horses, botulism is caused by ingesting a toxin produced by the bacterium Clostridium botulinum. This bacterium will not grow in the presence of oxygen, however in can grow in conditions that are sometimes present in improperly fermented haylage and silage. As the bacterium grows, it produces botulinum toxin, one of the most potent toxins on the planet. Ingestion of botulinum toxin leads to progressive paralysis (i.e. severe weakness and flacid muslces).
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