Equine Biosecurity

Biography: Dr. Martin Furr

The following information was given at a Seminar on Equine Nutrition and Health sponsored in part by the Virginia Horse Industry. It was held on October 17, 2008 at The Middleburg Agricultural Research and Extension (MARE) Center, Middleburg, Virginia. The following is being posted on HorseHints with the permission of the lecturer. This Seminar was beyond outstanding. My husband, Bill and I, feel so fortunate to have been able to attend.

"Biosecurity refers to the processes and procedures taken to ensure that people and our horses are protected from acquiring an infectious disease, or transmitting to another. We are concerned about biosecurity for a number of reasons, including the effects of the illness upon the individual horse, the substantial costs of treatment, including the effects of the illness upon the individual horse, the substantial costs of treatment, and the economic impact upon the industry resulting from restricted movement of animals for breeding and showing, cancelled competitions, and disrupted careers. Human illness is also a concern. There are a number of infectious and contagious diseases of concern for horse owners. The viruses equine Herpes virus 1 and equine influenza are prominent and can result in catastrophic financial losses. Bacterial infections such as streptococcus, salmonellosis, and Clostridium difficile are important. The parasite cryptococcus is not common in horses, but it does occur and can also cause human illness.

Equine herpes virus is a common virus that occurs in equine populations worldwide It has been estimated that up to 70% of adult horses may have the virus in their system, yet not show clinical illness. While there are several strains, the two most common are EHV-1, which causes abortions, respiratory disease and nervous system disease, and EHV-4 which primarily causes respiratory disease. The most common signs of infection with either form are fever, depression and loss of appetite. Cough and nasal discharge are frequently seen as well.

In horses affected with EHV-1, these initial signs may be followed by nervous system disease which is characterized by stumbling and an incoordinated gait in the rear limbs. Urine dripping and an inability to defecate can also be seen. In more recent severe cases, the horse may be unable to stand. The severity of the nervous system is quite variable, and depends upon the animal's general health and immune status, and perhaps factors related to the virus itself. Most patients recover with supportive care, but fatalities do occur. Late term abortions are sometimes seen with equine herpes virus infection, or foals that are born weak may die within a few days of birth.

EHV is highly contagious and can be readily transmitted from one horse to another. The most common methods of transmission are by aerosol or direct contact. Indirect transmission can occur when the virus contaminates hands, feed and water buckets, etc. Aborted fetuses and associated placental membranes are also significant sources of infection. This rapid transmission requires that once an affected animal has been identified, nearby animals and properties must be quarantined to prevent spread to other horses and farms.

The typical infected horse will usually not shed the virus for longer than 14 days after the fever subsides. Routine cleaning with soap and hot water is typically adequate to kill EHV which lives for only a few days in most environments.

The most effective method of on-farm infection control is to limit horse movement onto the farm, and to minimize co-mingling of new arrivals until a two or three week isolation period has been completed.

Equine influenza: Another major cause of influenza worldwide is equine influenza. Infection with any of several strains of equine influenza virus leads to clinical signs of a high fever, coughing, nasal discharge, poor appetite and muscle stiffness. Equine influenza is highly infectious, and is shed in nasal secretions; hence coughing, nose-to-nose contact or transmission on hands is adequate to spread the infection.

Streptococcus equi (aka "strangles") for the "strangling" cough and breathing noise associated with infection of the upper airway has been recognized for generations. Illness is caused by infection of the lymph nodes of the head with the bacteria Streptococcus equi. This infection leads to swelling and abscessation of the nodes, with associated fever, cough, weight loss, etc. may spread to other areas of the body ("bastard strangles") causing pneumonia, encephalitis, diarrhea, peritonitis, bone infections, etc. The organism is shed from nasal secretions and survives in the environment for long periods of time, in contrast to the viruses, which survive for only a very short time (days).

Infectious causes of diarrhea are of particular concern, due to the severity of the illness produced, leading to death in some cases. The bacterial agent of most concern is Salmonella. The organisms are shed in the feces and new cases become infected by ingestion of the organism from contaminated feed or forage, or from transfer to them on fomites (inanimate objects on which organisms can be transferred, e.g., feed buckets, hands, feet, clothing, etc.). Horses stressed due to concurrent illness, travel, heavy work schedules are all much more susceptible to infection. In addition, treatment with antibiotics may predispose horses to developing diarrhea from Salmonella, which can be carried asymptomatically.

All of the infectious agents above share the common ability to spread from horse to horse directly, or with the aid of people. Understanding and interrupting this central feature is the key to eliminating the spread of infection between horses. This is achieved by following a few basic tenets of biosecurity. Identify and isolate infected or POTENTIALLY infected horses. This includes new arrivals (don't know their history), sick horses, or horses that have been away from the farm. Isolating means physically preventing horses, or their infectious secretions, from contact with other horses. In addition, it is important to minimize contamination of the environment (some organisms live a long time in the environment), and to prevent any potential contamination of human caretakers.

Identifying potentially infected animals early is key to minimizing the extent of any outbreak. Horses should be monitored daily for signs of illness, and temperatures taken if there is any concern. Horses should be observed for coughs, nasal discharge, changes in feces, or loss of appetite and colic (a prelude to diarrhea in many cases). Fevers or other signs of illness should prompt a visit by your veterinarian, who may suggest a variety of diagnostic tests, depending upon their clinical findings. Culture of nasal discharge, scoping of the upper airways and guttural pouches, PCR testing of nasal secretions, etc. are all routine tests intended to identify specific causes of infection early. This is not the time to pinch pennies! Aggressively find out what is causing the illness so that control measures can be taken.

Isolation of infected animals is essential to prevention of spread. This is achieved by physical separation, barriers, and management practices intended to minimize transfer of infectious agents. Isolated horses should not share feed or water tanks, or running streams. Direct contact must be avoided, and the isolated horse should be kept at least 10 yards from other horses. If a horse is found to have an infectious disease, remove them from the group, but keep the remainder of the group together. Moving a horse away from the group at this point just spreads the infection faster!

A stall or small paddock can be identified for the isolated horse. There should be limited entry to this area, with only necessary movement in and out. Use barrier protection (gloves, overalls) and care for the isolated horse last, and then go change before dealing with other horses. Wash hands frequently using a disinfectant soap, and do not share any equipment with other horses. Feed and water buckets should be disinfected before using with other horses. If the isolated horse has (or had) diarrhea, the feces should be collected and disposed of where other horses can't get to it, and where it will not drain into the horses' field or water. Bedding from a horse with herpes virus (respiratory or abortion form) or strangles should be disposed of in a similar manner, or can be burned. Use a stall or turnout area that can be left empty for several weeks, if necessary. Once empty, stalls should be cleaned, allowed to dry thoroughly, and limed. Walls and stall doors can be scrubbed with soap and water, and then disinfected. A variety of commercial disinfectants are available and effective, or a 1:10 dilution of bleach is very effective, although somewhat caustic.

Don't forget to clean and disinfect trailers after shipping infected or unknown animals. Cleaning (e.g. removal of gross debris) is a must before disinfection, so clean, hose and scrub, then disinfect with commercial disinfectants or 1:10 bleach solution.

There are few equine infections that can affect a human, and which can be acquired directly from an infected horse. Clostridum difficile (an infectious cause of diarrhea) can theoretically infect humans, and the parasite Cryptosporidium certainly does. Barrier protection such as gloves and good hygiene (frequent hand washing, etc.) helps to reduce any risk to humans acquiring these infections. Herpes virus and equine influenza do not infect humans. However, humans with immunosuppressive illnesses, receiving immunosuppressive medications are at a much greater risk, and need to be much more careful. It may be most prudent for people in such situations not to care for horses with such conditions.

Proactive biosecurity at the farm is the best approach. This should be at a minimum--involve isolation of new entrees before mixing with the resident animals (minimum 14 days), require health papers and appropriate vaccination before allowing horses on the property, avoid mixing groups when possible, isolate horses when they have been off the farm, and routine cleaning and disinfection of horse-keeping supplies like buckets, rakes, etc."

Equine Influenza
Equine Herpes virus EHV-1