Follow Up On Iceland Outbreak
The massive outbreak of infectious upper respiratory tract disease that hit Iceland four months ago is finally slowing down, and there is now a little more information available about what they've been seeing and what authorities believe has been going on.
There is a fairly clear description of the clinical signs seen in affected horses (as previously described), although signs vary from horse to horse. Typically illness begins with a serous (clear) nasal discharge which then becomes mucopurulent (snotty). There is sometimes mild conjunctivitis (e.g. red puffy eyes) and most commonly a dry cough. Horses that are examined using endoscopy show signs of laryngitis. Signs generally last 4-6 weeks, but this can vary.
There's also more information about the epidemiology of the disease (i.e. the pattern of spread). Morbidity seems to be close to 100%, meaning almost every horse that is exposed gets sick. Fortunately no mortality has been associated with the disease, meaning all the horses eventually recover. The incubation period (the time from exposure to illness) is 1-4 weeks. It seems to be spread mostly by direct contact, but indirect transmission is also possible, as even free-roaming herds with little contact with other horses or people have been affected. Horses are not completely immune after recovering (meaning they can get sick again if they are re-exposed), but there is evidence that the "herd immunity" of the horse population in Iceland is increasing, and the outbreak seems to be dissipating. It is still lingering in some horse groups where there are naive (unexposed) horses coming into contact with infected horses.
The way this disease has spread is very typical of a virus burning through a naive population which has never been previously exposed to or vaccinated against the disease. Even the clinical signs are very typical of an upper respiratory virus. However, extensive testing has been done using both PCR and antibody titres for a multitude of viruses including (but not limited to): equine herpesviruses 1, 2, 4 and 5, equine arteritis virus, equine influenza virus, equine reoviruses, and equine rhinitis viruses. None of these viruses appear to be the culprit, despite early suspicions that the cause was in fact equine herpesvirus. They are still testing for new/unknown viruses using viral culture, but this is a difficult and very time-consuming task.
What authorities have been able to find in affected horses is Streptococcus equi subsp. zooepidemicus, which is what is currently being blamed for the outbreak. They say it has been cultured from almost all coughing horses and all horses with mucopurulent nasal discharge. But that's not really surprising, as S. zooepidemicus is a very common commensal bacterium that is even carried by healthy horses in their upper respiratory tracts. It's also a very common opportunistic pathogen in horses, meaning when the animal gets sick for another reason (for example, if a horse is infected with a respiratory virus), then S. zooepidemicus moves in and causes a secondary bacterial infection, which can make the clinical signs worse or last longer, and may lead to other complications. In this case they are trying to make S. zooepidemicus out to be the primary pathogen, but it would have to be a very unusual strain of the bacterium - very virulent, highly infectious and totally novel to the horse population in Iceland - to cause an outbreak of this scale. They are doing additional testing to characterize the strain they have isolated from infected horses and to compare it to other strains previously isolated from horses in Iceland.
The good news is that after the horse industry in Iceland was paralyzed by this outbreak for almost four months, equestrian activities are now resuming under the supervision of the Icelandic Food and Veterinary Authority. That shouldn't pose a problem to the Icelandic horses, as there are very few naive horses left in the country that would still be highly susceptible to this still somewhat mysterious disease. However, export of horses from Iceland is slated to recommence on September 15. There are still quarantine requirements preceding export (horses must not be sick nor be in contact with a sick horse for 30-60 days prior, depending on what country they're going to), which always are and will remain very important for infectious disease control. However, with the cause of the outbreak still being somewhat unclear, it is unknown if any horses may now be healthy carriers of the outbreak pathogen, be it an unusual strain of S. zooepidemicus or an unidentified virus. If horses in other countries start getting sick a few weeks after exposure to exported Icelandic horses, strict control measures will have to be rapidly implemented to possibly prevent similar outbreaks from developing.
Photo credit: David Blaikie (source: http://commons.wikimedia.org)

Following a repeating trend that has been ongoing over the past couple of years, piroplasmosis has been identified in more US horses with no clear source. 


Salmonella is the bane of existence of equine hospitals. It's the most common cause of infectious disease outbreaks, some of which can be devastating.
The Royal Canadian Mounted Police's famed Musical Ride has been hit with strangles
Despite initial declarations that known common causes had been ruled out, the investigation into the
The rather 







Strangles outbreaks are a pain. They can result in infection of a large number of horses and major hassles. Unfortunately, while many people behave properly during outbreaks, there are also people out there who either don't think, don't listen or don't care (or don't do any of these). 

Often, when someone calls and asks about management of strangles, one of the first questions is 



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Following on the heels of a few outbreaks of piroplasmosis in the US over the past year is
Equine Piroplasmosis Disease Investigation Continues
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.
At the ongoing 

The recent
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 

There is apparently still no evidence regarding the location of
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At least 21 ponies belonging to a Venezuelan polo team died shortly before a competition yesterday in Florida. Not much information about what happened has been released. It was reported that the ponies exhibited
The other day, I wrote about a few .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
"A two-day horse show is different than an eight-day fair exhibition.'" Two days is lots of time to transmit infectious diseases.
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.
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 (
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.
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.
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
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
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
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.
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.
As of this morning, no new cases of equine herpesvirus (EHV) infection have been identified at Laurel Park in Maryland. (
Equine herpesvirus type 1 (EHV-1) infection was confirmed in a filly at Laurel Park in Maryland (
Recently, I wrote about a
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.
Eastern equine encephalitis (EEE) was recently identified as the
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).
