People, horses and dogs, in that order, are the three species most likely to travel long distances, both nationally and internationally. Coupled with meeting and mixing with large numbers of the population, this provides ideal conditions for the spread of infectious diseases. For example, a single horse with a respiratory infection could spread the infection to many other susceptible horses at a show or event. If these horses then carry the infection home, it can spread yet further.
The ease and rapidity by which any infection can spread will depend on many variables, including the nature of the infectious agent, the way the infection spreads, the level of immunity among horses that are exposed to the infectious agent and environmental conditions. When shipping horses, a clear understanding of the importance of biosecurity is vital for all involved.
Currently in the UK there is a limited number of contagious equine diseases we need to be aware of and try to control. There exists the ever-present threat of new or exotic diseases, which could prove devastating, especially for horses that have not previously been exposed. There is always a huge focus on the risk of exposure to such diseases, but the endemic diseases, particularly respiratory infections, are a more common threat for our equine population. These include the equine influenza virus, equine herpes virus and strangles. The characteristics of these diseases are very different, so preventative strategies should be planned accordingly.
Equine influenza is an economically important cause of acute respiratory disease in the horse. It is highly infectious because large amounts of virus are sneezed and sprayed from an infected horse as it coughs, unpleasantly similar to a person with a bad cold. Widespread vaccination in the UK has reduced the incidence and severity of equine flu outbreaks, but they still occur. These can be controlled by rapid diagnosis, which is effectively assisted by the Animal Health Trust’s scheme, whereby samples can be sent into their lab free of charge by the vet in practice and text alerts are then sent out to equine vets nationwide. This is a useful surveillance measure.
Strangles is a highly contagious bacterial infection that is very different to the equine influenza virus. It is challenging because carrier animals may show no clinical signs but still spread the disease. This and other subclinical diseases remain a huge challenge for international trade. In 88 percent of reported events studied by the World Organisation for Animal Health (OIE; 2017), the infected horses did not show signs of clinical disease at the time of import.
Equine herpes virus is another very common infectious disease in horses. There are a number of different types of equine herpes viruses, but types 1 and 4 are the most important. Infection by equine herpes virus-4 usually produces respiratory disease, whereas type 1 can result in respiratory disease, abortion, the birth of sick foals and neurological disease. Recent outbreaks of equine herpes virus-1 neurological disease have highlighted the importance of this infection. When large transient horse populations gather for events, there is the potential for serious and widespread repercussions when the animals move elsewhere.
This is what happened at a 2011 American Cutting Horse event in Utah, USA. It is thought that exposure to a single horse shedding EHV1 at this event resulted in more than 165 horses developing clinical disease and, sadly, at least 13 horses died as a result. The outbreak spread to at least 10 US states, as well as parts of Canada, much to the huge consternation of show organisers worldwide. The one beneficial result of this has been a better general understanding of biosecurity with useful guidance becoming widely available.
Transportation is a necessary evil as far as horses are concerned. There are multiple factors to consider beyond biosecurity and the associated infectious disease risks. The Equine Vet Journal (Padalino et al., 2017) has recently published the results of an online survey that provides information on the risk factors for illness and injury associated with equine transportation. Of the 797 responses to the survey from both amateur and professional equestrians in Australia, all of whom transported horses at least once a month, there were 214 cases of a transport-related health problem over the previous 2 years.
Ten horses died during transit (two were found dead and the remaining eight were euthanised due to fractures). An additional 15 horses were euthanised within 1 week of the journey, seven within 24 hours. Journey duration and breed of horse were associated with transport-related health problems. Thoroughbreds, Arab and warmblood horses were more likely to develop illness than be injured during transportation when compared to Standardbreds. Illnesses, which included gastrointestinal and respiratory problems, and occasionally resulted in death and euthanasia, were significantly associated with longer journey times. Respiratory disease was the most common problem. Muscular problems were more likely on an intermediate length journey than a short one.
Journey duration was found to have no influence on the incidence of heat stroke. Injuries tended to occur on shorter journeys. This is likely to be associated with stress-induced behavioural problems or movement within the vehicle during the early part of the journey. Trailers and non-commercial transporters were more commonly used for shorter journeys. The overall conclusion was that transport-related health problems are significantly associated with longer journey times, with illness more likely on journeys over 24 hours’ duration and injuries more common on short journeys.
This study confirmed what has been shown previously – that respiratory disease is a significant issue, often labelled as the notorious ‘shipping fever’, to which horses are particularly susceptible for several reasons. If a horse’s head cannot be lowered during transport, normal so-called ‘postural drainage’ of material from the respiratory tract is prevented; this can have severe consequences for respiratory health due to colonisation of the lower airways with bacteria and the development of an inflammatory response. Many cars now have air conditioning, but it is far less common in horse transport. Poor lorry ventilation is detrimental to a horse’s airways and is made worse by the high stocking densities often seen in multi-horse transporters. Higher rates of the inhalation of potentially dangerous bacteria may occur in hot and humid conditions – due to an increase in the horse’s respiratory rate and depth associated with thermoregulation. Hot and humid conditions during transport may also lead to horses inhaling greater quantities of airborne moulds, which may trigger attacks of recurrent airway obstruction in susceptible animals.
Horses tend to drink and eat less during transport, sometimes causing discomfort and dehydration. Transportation over greater distances has been associated with weight loss, which increases with journey distance, in part due to dehydration. This dehydration can reduce the rate at which mucus is cleared from the airways, thus inhibiting one of the lungs’ major defence mechanisms against infections, exacerbating the risk of respiratory disease. In addition, the stress response associated with transport causes a rise in blood cortisol concentration, which has immunosuppressive effects that impede the horse’s ability to fight infections.
When reflecting on horse welfare and travel, remember how tiring transport is for horses. Research has shown that the effort required to maintain balance during a 300km road trip had the same impact on muscles as a 1.5km canter and caused a comparable increase in serum muscle enzymes. The effort required is even more on a stop/start journey with an inexperienced driver. Consequently, any opportunity to allow a horse a rest break to stretch their head and neck down is wise, ideally by unloading if safety permits, especially when the lorry design prevents this onboard (as with some angled designs of lorries and wagons with inbuilt tack lockers). This is recommended as a must every 4 hours. Equally, horses deserve at least a 3-hour recovery period after any lengthy journey. It is wrong to expect a horse to compete immediately after travelling.
In the event of an outbreak, traceability is important in controlling infection. Identifying in-contacts can be important to ensure appropriate monitoring and precautions. Horse travel is a justification for accurate horse identification so that a specific horse can be identified or traced.
In addition to correct identification, it is essential that the horses are fit to travel. The clinical examination prior to departure may seem routine, but it is crucial. The motto must be “sick horse setting off, sicker horse on arrival” – something that is best avoided.
