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

Often, when someone calls and asks about management of strangles, one of the first questions is "What disinfectant should I use?"

There are basically two answers that I give:

1) Streptococcus equi, the cause of strangles, is susceptible to most disinfectants, provided they are used properly. That means using them at the proper concentration, providing the recommended contact time (5-30 minutes, depending on the disinfectant) and ensuring that there is minimal organic debris (e.g. dirt, manure, pus) present on the surface to be disinfected. The latter is a key point, as disinfectants do not work well in the presence of debris, so it's therefore understandably very difficult to really disinfect a stable. Some stable surfaces (e.g. sealed solid walls and floors, buckets) are able to be disinfected if it is done properly, while other surfaces (e.g. dirt floors, unsealed wood walls, leather) are essentially impossible to disinfect.

2) Disinfection is a very minor component of strangles control. It is something to pay attention to and it should be done properly, but too often people to focus on disinfection as the key infection control measure. Just disinfecting surfaces, but ignoring aspects like cohorting exposed and unexposed horses, restricting horse movement, testing for carriers, regular temperature checks of all horses to detect early cases, using good personal hygiene and using protective outerwear, is bound to fail in terms of controlling an outbreak.

So, don't ignore cleaning and disinfection, but don't' rely on it as the main component of strangles control.

More information about strangles can be found on the equIDblog Resources page.

• Email This
• Print
• Comments
• Trackbacks

The latest edition of the journal Emerging Infectious Diseases contains a paper describing the 2008  Australian Hendra virus outbreak in horses and people.

In this outbreak, there were five horses infected and two humans infected. The horses predominantly had signs of neurological disease, not respiratory disease like some other reports describing this disease. Four horses died. One recovered but was euthanized for public health reasons.

Two people became infected after working with the sick horses, which represents 10% of the total veterinary staff that were exposed to the infected horses.  Both people started off with influenza-like illness, which seemed to improve initially, but then signs of severe neurological disease developed. They were treated with ribavirin, an antiviral drug, as part of an experimental treatment. One of them died after 40 days of illness, the other person survived.

The authors stressed that the effectiveness of ribavirin could not be determined, but they recommend it nonetheless because of the severity of Hendra virus infection and lack of other options. Ribavirin was also used in the 2009 outbreak, but it is clearly not 100% effective since one person died there also.

A number of concerning activities occurred that put people at risk of infection, including a "percutaneous blood exposure while euthanizing an infected horses" (they didn't explain exactly what this was, but it could have been a needlestick), low use of personal protective equipment, and contact with potentially infectious body fluids. This is unfortunately not surprising since the approach to infection control (particularly in terms of zoonotic infections) is often lax in equine medicine. That certainly has to change, particularly in areas where Hendra virus may be present.

Much more information about how to control this potentially devastating virus is needed. Fortunately, infections are uncommon and it is restricted to a fairly small geographic range in Queensland, Australia.

Image source: http://animalphotos.info/

• Email This
• Print
• Comments
• Trackbacks

Equine infectious anemia (EIA) virus, a chronic and potentially devastating bloodborne virus, was identified in two horses in Britain. The two affected horses were from a group of horses imported from Romania via Belgium. They were tested as part of standard import testing regulations designed to do exactly what happened here - diagnose this important infectious disease at the time of importation so that the infected horses cannot spread the disease in the country. The two positive horses will be euthanized, the unfortunate but standard response to this virus, because infected horses can pose a risk of infection to other horses for their entire lives. Other horses on the premises are under quarantine and are likely being tested further. The risk of transmission to other horses during the presumably short period of time they've been on the farm is probably low because, as an insect borne disease, biting fly activity has probably been pretty low during the cold British winter weather. (Transmission by sharing needles or other human-associated ways of cross-contamination of blood is also a concern, and has been a problem in other outbreaks.)

Chief veterinary officer Nigel Gibbens stated that these are the first imported cases of EIA identified since 1976. This is a good example of why we need to continue routine infection control measures such as import testing, even when nothing is found for years. Some people try to argue that since certain problems don't seem to be present, or at least are not identified, that infection control testing or activities should be decreased. This situation illustrates why that's bad thinking. Despite only picking up one incident in the past 34 years, this is a very important finding - failure to detect the positive horses could have lead to widespread infection in the country, which would ultimately make it very difficult and expensive to try to control. You never know when the next outbreak is lurking around the corner, and complacency is a big enemy of infection control.

Image source: www.collectgbstamps.co.uk

• Email This
• Print
• Comments
• Trackbacks

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.

An article in the International Journal of Infectious Diseases (Friederichs et al) describes infectious arthritis of the shoulder of a horse owner that was caused by Streptococcus zooepidemicus, a bacterium commonly found in horses but rarely associated with disease in people. The person didn't have a wound in the shoulder area or any other obvious route for the bacterium to get to the shoulder joint. They searched for a source of the infection and all they found was a chronic lesion on the person's foot. This, combined with the patient's history of taking care of his horses in "bare feet in boots", led them to implicate the foot as the source of infection.

The idea, I guess, is that socks would be a barrier to help prevent contamination of the foot wound. That makes sense to a degree - the person could contaminate his foot with S. zooepidemicus from his hands (probably acquired from touching the horse's nose) while removing the boots, or manure could work its way into boots and directly contaminate the wound. Both are possible, but we have to be a little cautious in interpreting these conclusions. However, this is a bacterium that is associated with horses and the foot lesion is certainly a possible route of entry.

Overall, this should be considered an interesting report of a very rare problem, not something that indicates a major concern. However, there are a few good points to take away from this story:

• If you have a wound or chronic lesion of any sort, make sure you take measures to reduce the risk of bacterial contamination when working around horses. This might be as simple as making sure it's covered by clothing, or something more involved like using an impermeable bandage.
• Hands are probably the major source of infection transmission, and good hand hygiene is important after horse or stall contact, particularly if you have an underlying disease.

This equIDblog entry was originally posted on our sister site, Worms & Germs Blog, on 20-Jan-10.

• Email This
• Print
• Comments
• Trackbacks

I received newsletter today from Intervet (a pharmaceutical company) that is targeted at equine veterinarians. One article discussed rabies in horses. It wasn't bad overall, but I thought the section on what to do when a horse might have been exposed to rabies was worth discussing.

The article asks, "If your client suspects that a horse has been bitten by a rabies-infected animal, what should be done?"

Answer: "Contacting you as the veterinarian is always the first step."

Great first step.  A second step that wasn't mentioned should be, "Try to identify and (safely) capture the animal that bit the horse." This is often impossible but certainly worthwhile if it can be done.  However, if you're trying to catch the offending animal, make sure you don't put yourself at risk of exposure to rabies in the process.  If the animal can be caught, it's rabies status at the time of the bite can be determined (either through testing or quarantine). If it can be shown that the animal wasn't rabid, a lot of stress, hassle and expense can be saved.

"If the horse was previously vaccinated... Then isolate and observe the animal for 45 to 90 days (your clinical evaluation will involve gait analysis, radiography and a spinal tap)."

Boosting the rabies vaccine is also a good idea. The next step, however, needs to be contacting local regulatory officials to find out what you have to do. They determine if, how and how long an animal needs to be quarantined - this is NOT the decision of the local veterinarian nor the animal's owner. Most likely, they will recommend a 45 day quarantine for a vaccinated horse, since this is what is recommended in the NASPHV Compendium on Rabies. The discussion of diagnostic testing makes no sense. There is absolutely no indication to perform diagnostic tests on a horse that has been bitten by a rabies suspect. None. There are no tests that can be used to diagnose rabies in live horses (also exposed horses don't instantly develop signs of rabies). Horses should be monitored closely for signs of rabies during the quarantine period, but that's it.

"...and have the client make a list of all people who had contact with the horse."

This is often done when horses have or are suspected of having rabies, but not horses that are potentially exposed. It is done to help public health personnel contact people that may have been exposed to rabies. A horse that was just bitten by an animal is not a risk for transmission of rabies.  (However, keeping a list of people who have contact with the horse after it's been bitten (i.e. durng the quarantine period) - which should be as short a list as possible - is a reasonable precaution in the unlikely event that the horse does develop rabies.)

"If the animal was not vaccinated, your options are to euthanize and perform a postmortem examination of the brain (the only way to definitely confirm rabies)..."

Euthanasia is one of the options that needs to be considered in an unvaccinated horse that has been exposed, which is one of the reasons that identifying the biting animal and testing it is critical, if it can be done. The last part of the above sentence (from the atricle) is complete nonsense. Why would you test the brain of a normal horse that has been euthanized because it's just been bitten by a potentially rabid animal? The horse isn't being euthanized because it has rabies, it's being euthanized because of the likelihood  of it developing rabies weeks to months later. Testing of the brain will tell you absolutely nothing if the animal was only bitten recently.

"...or isolate and observe the horse for six months and develop the human contact list."

Again, this needs to be decided based on discussions with regulatory personnel who are responsible for dictating what is to be done. A six-month quarantine is a pretty standard recommendation for an unvaccinated animal. Creating a human contact list should not be necessary, since quarantine involves severely restricting contact of people with the horse and only a few (ideally one) person would have any type of contact.

The article wraps up with the very true emphasis on vaccinating horses. It's a cheap measure to prevent a relatively rare but invariably fatal disease.

Click image for source.

• Email This
• Print
• Comments
• Trackbacks

At some point, the US is going to have to admit that piroplasmosis, the bloodborne parasitic infection caused by Theileria equi, is endemic in some regions of the country. It's a declaration that will have major impacts on horse movement to some areas but, it's better for everyone to know what's going on. Piroplasmosis is technically still considered an exotic disease in the US, but there have been many cases identified over the past year and a clear source for the individual outbreaks in lacking, indicating there must be a reservoir in some part(s) of the country.

The latest incident involves the diagnosis of piroplasmosis in three race horses in New Mexico, which were picked up as part of routine screening. There were only three positives out of about 1200 horses tested, so the disease is still rare, but the fact that it was there and none of the positive horses had any link with previous outbreaks is definitely a concern. The OIE report states that transmission is suspected to have been from "artificial" means like sharing needles between horses, not natural tick transmission. This could account for the multiple horses affected but doesn't explain where the disease came from it the first place, and it's unclear how solid that hypothesis really is.

It's quite interesting (surprising, frustrating...) that few comments are put forth in any of these outbreaks indicating where the infections may have originated and why we are seeing recurrent, unrelated infections. Is increased testing in different areas helping to pick up cases that would otherwise have been missed (i.e. were already there), or is piroplasmosis in the US an emerging problem? How confident are they that there are no ticks capable of transmitting T. equi in some of these areas? Is wider screening of horses required to determine the extent of the problem and to determine whether it can be controlled? Is broader screening of ticks in the affected areas needed to see if there are ticks known to be able to transmit T. equi? Are studies needed of other tick species in areas where unexplained cases have occurred to determine if some tick species that are not currently known to be able to spread the parasite can actually do so? Lots of questions... hopefully someone's trying to find some answers.

Click image for source.

• Email This
• Print
• Comments
• Trackbacks

A pony in New Jersey has been diagnosed with equine infectious anemia (EIA) and euthanized. Details are pretty scarce at this point and it's unclear whether the pony was sick or whether EIA was simply diagnosed through routine testing. There's also no indication of where the pony might have acquired the infection, which is a very important question.

Equine infectious anemia is a viral disease of horses and other equids that is characterized by recurrent fever, lethargy, decreased appetite and decreased red blood cell numbers (anemia). Sometimes, the first episode of disease (acute EIA) can be fatal, but most horses recover. Most survivors experience recurrent episodes of illness. In some horses, these episodes become frequent and severe.

A major problem with EIA is that horses are infected (and are infectious) for life. Even if they recover from the acute disease and rarely or never get noticeable recurrent disease, they are still carrying the virus in their blood. Biting flies are the main means of transmission from horse-to-horse, although human-associated transmission through reuse of needles or other procedures that cross-contaminate blood between horses can also be involved.

The combination of life-long infection and an insect vector is BAD. That's why, in areas where EIA is not endemic, infected horses are usually immediately euthanized. In some regions, affected horses can be branded or tattooed to permanently indicate their EIA status and housed at least 200 yards from any other horse (and often with strict insect control measures).

Control of EIA focuses on identification of carriers. Most jurisdictions require regular EIA testing (formerly the "Coggins test") for horses that are traveling or competing, as well as imported horses. While this disease is extremely rare and the vast majority of routine tests are negative, it's a disease that can silently spread in a population if people are not looking for it - routine testing is critical for keeping this disease at bay.

• Email This
• Print
• Comments
• Trackbacks

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.

Do all foal's need specific umbilical care? Not really. Most foals, especially those born normally in a clean environment to a healthy mare and who received adequate colostrum, don't need anything done. However, it's not always easy to differentiate these low-risk foals from others, and it is possible for the healthiest foal born in the cleanest environment with ingestion of an adequate volume of good quality colostrum to develop complications, so most people perform some form of post-birth umbilical care (and that's a good thing). The key is making sure that it's the right umbilical care.

The goals of umbilical care are pretty basic:

• Prevent bacteria from entering the umbilicus.
• Avoid damaging the umbilicus and other body tissues, and avoid delaying normal drying of the umbilicus.

What to use?

• Research has indicated that a 0.5% chlorhexidine solution is the optimal umbilical dip. Other disinfectants can also kill local bacteria on the umbilicus but may not be as effective, may not work as well in the presence of debris (dirt, manure...), or may be irritating to body tissues.

Read the label:

• Make sure you are actually using 0.5% chlorhexidine and that it's a solution (diluted in water), not a tincture (diluted in alcohol). If you don't have 0.5% chlorhexidine solution and are unsure about how to dilute it properly, ask your veterinarian.

More is not better!

• Don't think that since 0.5% is good, 5% must be 10 times better. The stronger the concentration, the greater the chance of damage to local tissues, which can increase the risk of complications. Stick with 0.5%.

More is not better! Part 2

• The umbilicus should be dipped in disinfectant, not marinaded in it! The goal is to cover the umbilicus and not other tissues (e.g. the abdominal wall). You don't need to soak the umbilicus or hold the disinfectant in place over it. Short term contact (dip) is adequate. Dip it and walk away. The umbilicus needs to dry up - repeated soaking isn't helpful.

More is not better! Part 3

• The umbilicus should be disinfected shortly after birth, then every 6-8 hours for the first 24 hours of life. That's usually enough. If the umbilicus still appears wet at that time, it can be dipped again. Continued dipping "just is case" is not needed.
  

Don't tie off the umbilicus:

• Tying off the umbilicus can actually increase the risk of complications such as infection and patent urachus (urination through the umbilicus).

Hands off!

• Don't touch, poke or otherwise make contact with the umbilicus with your hands. It's not needed and it's a great way of transferring bacteria to the umbilicus.

If in doubt, call your veterinarian:

• A proactive call to your veterinarian is much better and cheaper than an umbilical infection, umbilical abscess, septic foal or patent urachus. These are all expensive complications and  often difficult to treat successfully. Foals can change very quickly, and waiting to "see what happens" for a day or two can be the difference between a minor complication and a life-threatening problem.

• Email This
• Print
• Comments
• Trackbacks

Eradication of infectious diseases is a great goal, but it's rarely practical. The best known (and perhaps only) example of infectious disease eradication is the elimination of smallpox. So, why is it so hard to do?

The following general criteria need to be in place to eradicate a disease:

• It must have a clearly defined host range and that range is ideally only one species. A disease that can affect multiple species is very hard to control.
• It must predictably cause disease in individuals that are infected.
• There must be no long-term carriage state. Once a person/animal gets over the illness, he/she/it must get rid of the infection completely in a defined and predictable period of time.
• A highly effective vaccine should be available.
• There must be a commitment to put in lots of time, money and effort everywhere the disease exists.
  

This isn't the case with most diseases, and equine herpesvirus (EHV) has many characteristics that make eradication impossible:

• Unpredictable disease: EHV infection doesn't always cause signs of disease. When it does cause disease the signs can be quite variable and difficult to easily differentiate from other infections.
• Longterm carriage: This is the biggest problem with herpesviruses. EHV is able to survive in a latent (dormant) state in the body after infection. It can lie dormant for a long period of time, but infected animals can always start shedding the virus again. A large percentage of horses are carrying EHV in their bodies and there's no way to get rid of it.
• Vaccine: Vaccines are available but they are by no means 100% effective at preventing infection.
• Time, effort, money and cooperation are terms that are not commonly associated with disease control in horses. Getting everyone to follow a standard recommendation (if one were able to control disease) would be difficult to impossible. The entire horse-owning population would not be willing to spend the money for broad control measures, and there's no real impetus for governments to do so. Even getting people to agree to follow basic vaccination and infection control recommendations is difficult.  If there is any negative impact on use of horses, ease of management or any other minor inconvenience, 100% compliance with any recommendation becomes impossible to obtain.

We have to live with EHV. It will always be a risk to horses. Good infection control measures and vaccination of certain groups (e.g. pregnant mares) can help control the impact of the virus.

• Email This
• Print
• Comments
• Trackbacks

A colleague mentioned a rumour that is apparently going around some areas about horses getting H1N1 influenza. While we never say never with infectious diseases, there is no evidence that H1N1 can be spread to horses, nor do I have much concern about this. H1N1 can infect different species, including humans, pigs, poultry, cats, ferrets and dogs. That's a pretty impressive range, but it's mostly because the virus is made up of genes from human, swine and avian influenza viruses, and we know that other species like ferrets and cats are prone to occasionally (rarely) catching human or avian influenza. Horses have their own influenza, H3N8 equine influenza A. This virus has been remarkably stable in the horse population in that H3N8 has been the predominant equine influenza strain for a long time. There is little information indicating that horses are susceptible to the variety of seasonal flu viruses that circulate amongst the human population every year, or H5N1 avian influenza. No one has specifically tested H1N1on horses, and equine infections are not theoretically impossible, but it's pretty unlikely that this strain would be a major concern in horses, given what we know right now. Considering the number of people that have been infected with H1N1, horses have certainly been exposed to this virus, but there are no reports of suspected equine infections.

While the risk of horses contracting H1N1 is very low, it can be reduced further with common sense practices to reduce the risk of exposure. If you may have influenza, avoid contact with people and other animals, including pets and horses, and get a flu shot.

Image source: http://graphicshunt.com

• Email This
• Print
• Comments
• Trackbacks