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Biosecurity for Horse Owners

September 2017 by Dr Brett Tennent-Brown, BVSc, MS, Dip ACVIM, Dip ACVECC, U-Vet Werribee Equine Centre, University of Melbourne

Why is a biosecurity plan important for your property?

Until 2007, Australia was one of a handful of countries that had never experienced an outbreak of Equine Influenza (EI), a highly contagious viral disease of the respiratory tract. 

In animals that have been exposed to the virus previously and have, therefore, developed some degree of immunity, infection with the EI virus generally causes only mild disease. 

However, in horses with no immunity to the virus, disease is often more severe. Australian horses are highly susceptible to EI because they have not been exposed to the causative virus and they are not vaccinated against it; Australian horses are, therefore, immunologically ‘naïve’ with regards to EI. 

In August 2007, the virus causing EI escaped into this country’s horse population following a breakdown in quarantine procedures. Because Australian horses had no immunity to the virus, it was able to spread very rapidly across thousands of properties and infected over 76,000 horses in New South Wales and Queensland. 

Once the outbreak had been recognised, a control and eradication scheme, based on movement restrictions and strategic vaccination, was implemented. This included a complete ban on all horse movements and cancellation of all equine events. While these measures were very effective in preventing further spread of the virus, it has been estimated control and eradication of EI from Australia cost over $1 billion. 

The history of EI in Australia illustrates just how critical effective biosecurity protocols are in protecting both our horses’ health and the financial viability of equine-related businesses. However, it also provides some insight into the difficulties of implementing and maintaining effective biosecurity measures nation-wide. 

Broadly speaking, the goals of a biosecurity protocol are to: 

  1. Prevent entry of infectious diseases into a group or population of horses. 
  2. Limit spread within a population should disease occur. 

There are a large number of diseases that are ‘exotic’ to Australia (i.e. they do not occur normally in this country) and that have important implications for our livestock industries (such as Equine Influenza, Foot and Mouth Disease, etc.). Regulations to prevent the entry of these diseases into the country are developed at a state or federal level. 

This aim of this article is to provide some advice on implementing effective biosecurity procedures to owners or managers of privately owned stables and farms. However, it is important to realise the first appearance of an exotic disease, such as EI, might occur at a private property (visit the Animal Health Australia website for more information). 

In addition, some diseases that are present in Australia and occur commonly (such as Strangles) must be reported to the appropriate government body (to contact the Emergency Disease Watch Hotline, call 1800 675 888).     

Preventing the entry of infectious diseases: managing new arrivals

Preventing entry of an infectious disease into a population of horses requires the establishment of appropriate quarantine procedures. All horses arriving on a property for the first time should be quarantined separately from resident horses until you are confident the new arrival is not carrying an infectious, disease-causing organism. 

Ideally, horses returning from events at which they had contact with horses from other properties should also be quarantined. However, this is often very difficult to achieve, particularly in busy stables with lots of horse movement. In these situations, returning horses (and their immediate neighbours) should be carefully monitored so if they did acquire an infection, they can be quickly isolated to limit the spread of disease. 

When developing protocols to manage new arrivals, it is important to understand:

  • The specific diseases that we should be concerned with,
  • How those diseases are transmitted from one horse to another, 
  • The incubation period for each of those diseases. 

Diseases caused by the respiratory viruses (such as Herpes and Rhinitis) and Streptococcus equi (the bacteria that causes Strangles) are common, and have tremendous disruptive potential. Because they are common, these organisms are probably the most important to consider when developing biosecurity protocols. 

However, other disease-causing organisms might be important under some circumstances. With the relatively frequent and rapid movement of horses from Queensland and New South Wales, we all need to be mindful of Hendra virus. Furthermore, with a very fluid flying fox population, there is always the risk of a case outside of the areas in which the disease is considered endemic.

Some of the bacteria that infect the intestinal tract (such as Salmonella) can cause severe, life-threatening disease. These bacteria are usually spread in faeces and are often extremely contagious. 

Therefore, it is critical new arrivals are monitored very carefully for signs suggestive of gastrointestinal disease (i.e., fever, decreased appetite and a change in the consistency of manure).    

Gastrointestinal parasites should also be considered in a comprehensive biosecurity plan as parasite resistance to many of the current anthelmintics (de-wormers) is a huge and increasing issue for horse owners and the equine industry. 

Faecal egg counts and strategic de-worming protocols should be considered when new horses arrive at a property to prevent the introduction of resistant parasites. As you develop a plan for your property, you should consult with a veterinarian who is familiar with your particular operation. 

The incubation period is the time from when an animal is first exposed to an infectious organism (e.g. a virus or bacteria) until it begins shows detectable signs of infection (e.g. a fever or a cough). 

For most viruses and bacteria, the incubation period ranges from several days up to several weeks. Knowledge of the incubation period is important when determining the appropriate duration of quarantine. In most cases, a quarantine length of 3-4 weeks is sufficient. 

It is important to recognise a horse infected with a particular organism might be able to infect other horses before showing any obvious signs (i.e. horses are infective to others within the incubation period of the disease). 

Therefore, unless quarantined horses can be strictly isolated from one another, an ‘all-in, all-out’ policy - that is, all quarantined horses should arrive together and then leave together at the end of the quarantine period - is usually required to limit the chances of introducing a disease into the resident population. 

Many of the diseases we are concerned about are transmitted on airborne particles when an infected horse coughs or sneezes. However, people and equipment are also important in the transmission of infectious organisms from one horse to another. 

Quarantined horses must, therefore, be physically separated from resident horses and, ideally, attended by staff that have no or little contact with other horses on the farm. It is not known for certain how far particular matter carrying viruses or bacteria can travel, and remain infective when a horse sneezes or coughs, but 10 meters has been suggested.

If staff members must attend both resident and quarantined horses, horses in quarantine should be attended after resident horses. Staff members should wear separate clothes and boots when working with horses in quarantine and equipment (e.g. feeding, cleaning, grooming and tack) used in the quarantine area must not be used with resident horses. Hand washing between animals (even between apparently healthy animals) is essential as this is one of the most common means of transferring bacteria and viruses. 

Quarantined horses should be examined at least twice daily for evidence of an infectious disease, such as decreased appetite, nasal discharge, swollen sub-mandibular lymph-nodes (the glands beneath the jaw), coughing, a change in demeanour or in the characteristics of the horse’s manure. 

New arrivals should also have their temperature taken at least twice daily while they are in quarantine. A veterinarian should be consulted if there are any signs of disease or if a horse’s temperature is greater than 38.5°C on more than one occasion.   

Limiting the spread of disease: managing sick horses in the barn or on the farm

Unfortunately, disease can occur in horses even on very well managed properties with robust quarantine and biosecurity procedures. In some cases, the disease-causing organisms are ubiquitous in the environment and are, therefore, difficult or impossible to eliminate completely. In other cases, they might be carried by wildlife. 

Some infectious organisms can also cause ‘latent infections’; that is, the organism lies dormant within the horse, but can be reactivated under some circumstances. Reactivation of latent infections is particularly common with the Herpes viruses and is often associated with stressful events. 

Additionally, some horses carry the bacteria causing Strangles and, although these ‘carrier’ animals are clinically normal, they are able to transmit the bacteria to other horses without signs of the disease.

In addition to a good quarantine routine, general recommendations for limiting disease spread through groups of horses include: 

  • Separation of age groups (e.g. weanlings, yearlings and adults),
  • Limited mixing of horses from different groups (e.g. on breeding farms where mares might be managed in small bands),
  • Limiting access of wildlife to feed stores and water supplies,
  • Good, basic hygiene practices (e.g. regular hand washing, and routine disinfection of feeding and cleaning equipment, etc.). 

Young animals are often more susceptible to disease than older animals and so separating age groups makes good sense. Separating age groups and avoiding mixing of animals from different groups also reduces social stress, which can increase susceptibility to disease. 

Detection of latent infections can be very challenging, but if horses are maintained in strict groups with limited mixing, the spread of infection can be minimised should disease occur.

If disease does occur in a stable or on a farm, eliminating contact between infected and uninfected horses is the cornerstone of control and limiting spread of the disease. It is important to recognise there are three groups of horses to consider:

  • The clinically infected horse or horses.
  • Horses that have been exposed (i.e. those that have had contact with an infected horse) and might be habouring the disease-causing organism, but are not yet showing clinical signs.
  • Horses that have had absolutely no contact with the infected horse. 

The clinically infected horse or horses must be completely quarantined from uninfected horses, but exposed horses must also be quarantined from unexposed horses. Exactly how those horses are quarantined will depend on the individual situation and will be influenced by a range of factors, including housing (e.g. horses kept at paddock as opposed to in a busy barn) and how the disease is transmitted. 

Personnel access to both the sick and exposed horses must be strictly controlled. Feeding and cleaning equipment is easily contaminated, and must not be shared between the groups. Care should also be taken to ensure uninfected horses are not exposed to contaminated bedding. And, once again, hand-washing is essential!

The ‘in contact, but not yet sick’ horses need to be kept separate from both the sick horses and horses that have not had any contact with the sick horses. These ‘in contact, but not yet sick’ horses must be monitored extremely carefully for the signs of disease and cannot be considered disease-free until the maximum possible incubation period has elapsed without signs of disease. 

Laboratory testing can sometimes be used to identify horses in this group that have been infected. Quarantined ‘in contact, but not yet sick’ animals should have their temperature taken frequently (at least twice daily) and should be carefully assessed for clinical signs of disease (e.g. lymph node swelling, nasal discharge, loss of appetite, change in faecal consistency, etc). 

Cleaning up: cleaning and disinfecting stalls

Cleaning paddocks that have been contaminated by sick horses is obviously very difficult. 

Exposure to the sun and elements will kill many, but not all bacteria and viruses - although sometimes that can take a very long time. 

To prevent disease spread to other horses, the safest thing to do is to ‘close’ that paddock. The length of time that a contaminated paddock will need to be closed for will depend on the disease-causing organism involved and you should always consult with your veterinarian for more specific recommendations to limit exposure. 

If a horse was in a stable when disease occurred, there are a number of critical steps to follow when cleaning that stall. 

The first step is to thoroughly remove organic matter, such as manure and soiled bedding, since most disinfectants are inactivated by this material. 

The walls and floors should be washed in a careful and systematic manner with a detergent (soap) and then rinsed with water to ensure all surfaces are clean. 

The stall should then be allowed to dry before it is disinfected. A wide range of disinfectant are available, but phenolic- and quaternary ammonium-based products are often the most effective. 

It is absolutely essential disinfectants are used according to label directions, particularly with regards to dilution and contact times. Many of these products are relatively toxic to people and so safety instructions must be adhered to.

If your farm or stable has an isolation stall, the same steps should be followed after every horse kept in that stall. Recognise that porous materials (wood, unpainted concrete blocks, unsealed concrete floors) can be extremely difficult or impossible to completely disinfect. 

This is an important consideration if you are planning to build an isolation stall or building new stables. It can be virtually impossible to satisfactorily eliminate disease-causing organisms from dirt floors and a dirt floor would not be suitable for a permanent isolation stall.   

Conclusions

If appropriately implemented, a quarantine protocol that includes strict isolation of new arrivals and frequent health checks will reduce the risk of introducing an infectious, disease-causing organism into a property. 

Effective biosecurity processes require an understanding of the diseases that we should be concerned about, how those diseases are transmitted and what their incubation period is. 

Unfortunately, despite the best efforts, infectious diseases will occasionally occur in a population of horses. The principles used to develop quarantine protocols can be also used to develop procedures that will limit the spread of disease. However, these are much more effective if developed ahead of time, rather than in the face of an outbreak.