Handling infectious diseases outbreaks at equine events (Proceedings)

Veterinarians are the first line of defense against infectious disease outbreaks. Current problem and case based equine medicine likely does not prepare new graduates in outbreak control. Control of an infectious disease is based on correct application of the principles of population biology and transmission dynamics of a particular infectious organism, basic microbiology, and basic epidemiology. Overall, training in diagnostic medicine is declining due to loss of state and federal support in our programs and reprioritization of veterinary student training programs that primarily focus on clinical programs. Unfortunately, this does not lighten the responsibility of the primary care veterinarian in control of infectious diseases and in the liability associated with failure to avert economic disaster or animal loss.

Event planning and disaster avoidance

The following information should be recorded for ALL horses at a particular EVENT even before clinical illness is apparent, preferably at arrival. Owner, trainer, and name of horse should be recorded. Origins of horses and destinations of horses should be recorded. All stalling locations of these individual animals on the respective grounds should be recorded both retrospectively and prospectively. The identities of all personnel in contact with the horse should be known by recoding stall entry, personnel records, and activities such as grooming care, veterinary care and husbandry (feed men, braiders, clippers, farriers, etc) should be maintained. While a horse show is public event, the stabling area should not be!

In addition, management should require a pre-event questionnaire that assesses immunization and health status of the horse BEFORE stalling.

     1. Does your horse have a fever today?

     2. Has your horse had a fever within the last 7-10 days?

     3. Does your horse have any of the following clinical signs (circle all that apply): loose stool, problems walking or keeping balance, snotty nose or cough?

     4. Has your horse been stabled with any horses that have had a fever within the last 7-10 days or has your horse been stabled with any horses that have had any of the following clinical signs (circle all that apply): loose stool, problems walking or keeping balance, snotty nose or cough?

     5. Has your horse been shipped within the last 2 weeks by commercial (or private transport with multiple horses)?

     6. Has your horse been vaccinated for the core immunizations that include Rabies, Eastern equine encephalomyelitis virus, Western equine encephalomyelitis virus, West Nile virus, and Tetanus yearly and within the last year? Has your horse been vaccinated within six months against herpesvirus, influenza, or Streptococcus equi? Has your horse had a Coggins test within the last 6 months?

Steps once possible infectious disease case is identified

Call the State Veterinarian right away. State veterinarians are very sensitive to the economics of disease outbreaks. Early communication is essential for disaster avoidance!

History assessment

In order to assess the potential for an infectious disease outbreak, a simple 12 point questionnaire is useful to require owners to answer for all horses are currently on the property which again goes over the pre-event history but identifies AT RISK horses.

Questions regarding the individual animal:

     1. Does your horse have a fever today?

     2. Has your horse had a fever within the last 7-10 days?

     3. Does your horse have any of the following clinical signs (circle all that apply): loose stool, problems walking or keeping balance, snotty nose or cough?

     4. Has your horse been stabled with any horses that have had a fever within the last 7-10 days?

     5. Has your horse been stabled with any horses that have had any of the following clinical signs (circle all that apply): loose stool, problems walking or keeping balance, snotty nose or cough?

     6. Has your horse been shipped within the last 2 weeks by commercial (or private transport with multiple horses)?

     7. Has your horse been to a racetrack, horse show, polo match, public riding trail, or comingled with other horses from other farms within the past two weeks?

     8. Has your horse been to a veterinary clinic or farrier shop within the past two weeks?

     9. Has your horse been tube dewormed, had teeth floated, body clipped or had another activity where the equipment must be shared between animals?

     10. Has your horse been vaccinated for the core immunizations that include Rabies, Eastern equine encephalomyelitis virus, Western equine encephalomyelitis virus, West Nile virus, and Tetanus yearly and within the last year?

     11. Has your horse been vaccinated within six months against herpesvirus, influenza, or Streptococcus equi?

     12. Has your horse had a Coggins test within the last 6 months?

     13. Obviously most of the answers to horses coming to a venue may not be factual but many owners are forthright and are willing to answer honestly. These documents provide outbreak veterinarians with a fast guide for AT RISK horses if something should occur. Also venue holders can use this information and understanding of the complex nature of their arriving horse population and will become more sensitive to steps to avoid future outbreaks.

Population assessment

Once a contagious disease is suspected, these are the ADDITIONAL assessments that must rapidly be made regarding the population.

     1. Origin of horse if shipped recently. This must also include all companies and professionals associated with the actual hauling.

     2. Complete immunization history of the whole barn or section. Preferably the information should provide you with an idea of how many vaccines specific for a disease were administered over the lifetime of these animals in question.

     3. Any history of non-infectious causes of increased rectal temperature within the population.

     4. An assessment of previous exposure to S. equi equi should be made no matter how long ago this occurred due to risk for chronic carrier status and recrudesce of shedding.

     5. State-wide and regional information regarding infectious disease activity.

Individual animal risk categorization

The goal of risk assessment is to develop a simple, translational formula that ranks an animal of unknown status caegorically into high, medium or low. Because many equine diseases are highly contagious diseases, febrile horses should always be considered at risk for carrying a contagious disease. In hot, humid areas environmental effects on non-infectious diseases should be taken into consideration.

Risk factors are many but several stand out in their high association with subsequent infectious disease. These include: 1) Shipment commercially with horses from multiple venues. 2) Recent association with venues that have historically been implicated in outbreaks including quarantine stations, rest farms for commercial shipping, veterinary clinics, race tracks, polo events and horse shows. 3) Very old and very young horses are risk factors. 4) Sudden stressful events which include changes in activity, feed, and management. 5) Recent exposure to sick horses including horses that only have increased rectal temperature without any other explanation such as recent surgery, vaccination, other medical conditions associated with fever. 6) Recent exposure to horses that have acute respiratory, diarrhea, and neurologic signs especially if a non-infectious cause has been ruled out.

Risk should be assigned to a defined criteria such as High, Medium and Low and then handling of the animals will follow logically (quarantine, isolation, and testing criteria) based on these categories. Box 1 provides examples of how risk could theoretically be assigned to horses in a barn, stable or show where an infectious disease outbreak is occurring:

Handling of risk groups

Once risk groups are defined, all horses on that site should be assigned a risk group. The only unknowns are memory lapses, either intentional or unintentional. Proceed as though you have the best information at hand, but take seriously any reports that deviate from the information at hand. The most omission concerns actual pre-outbreak congregation and transport events. In the end, shipping manifests and gate logs may be the only way to assess horse movement.

High risk horses should be quarantined and isolated until the infectious cause is completely eliminated. Quarantine means detention of an animal for the purpose of isolation because it harbors a suspected contagion. Isolation means that there is NO contact with other horses and no contact with handlers occurs that results in exposure of body fluids from that horse to other horses. The risk of spreading disease is logically higher when one co-mingles horses from different sources within an isolation unit that allows contact between horses. The latter situation is not isolation, although clients assume that isolation also means protection of their "isolated" animal from other infectious diseases. Nothing is solved by giving a client another infectious problem.

Horses classified as HIGH RISK should be transported directly to an isolation facility, unloaded, and placed in an isolation stall without contact with other horses during that time. Personnel in contact are also protected from spreading disease to other horses in the facility. All cleaning equipment will be designated to the stall of the HIGH RISK inpatient. All isolation wear (gowns included) should be used once and discarded. Tyvek suits should be mandatory (no surgical gowns). Any ante-room and common aisle ways will be cleaned and disinfected twice daily.

Horses classified as MEDIUM RISK can be placed in a 'Ward Isolation' that is at least 35 feet from the general population, closed to all through traffic, and full personal protection is worn. This consists of tyvek suits, gloves, booties, hair bonnets, and work is followed by hand cleansing. All pest and vermin are controlled in this area. All manure and waste is separate from the hospital barn. Separate personnel are recommended; in the absence of this, feed, cleaning and treatments should be low-risk patients first. Low risk horses require minimal preventative strategies.

Box 1. Example risk assessment for categorizing horses during an outbreak of infectious disease.

Disease containment

Perimeters work to decrease spread through limiting environmental contamination. Limiting environmental contamination limits infective dose for animals that come into contact with a pathogen. Limiting infective dose is at the heart of all microbiology. Perimeter implementation for contagious diseases work very effectively to prevent transmission.

Primary Containment

Stop horse movement between sick and healthy horses

     1. Confine horse to stall or move immediately to separate facility

     2. ALL horses with clinical signs no matter how mild must be placed in this area

Disease surveillance

     1. Take rectal temperature twice per day and record & centralize evaluation of all rectal temperatures daily

     2. If owner is recording, contact veterinarian immediately

     3. Veterinarians should perform physical examination on all suspect horses and run appropriate clinical and diagnostic testing.

Limit human access

     1. Access is limited to essential personnel only: veterinarians and caretakers

     2. All personnel should be trained and follow biosecurity protocols

     3. Security personnel may need to be placed at access points

Quarantine: confirmed cases

     1. Once a positive horse is identified either state or voluntary quarantine should be imposed.

     2. Length of quarantine: Viruses should be separated 21 days after the LAST clinical sign which is usually temperature. For Streptococcus equi or Salmonella, horse should be separate until three and five consecutive cultures are obtained, respectively.

     3. Expect any quarantine to last 28 to 35 days.

     4. Exit test requirements should be decided and strictly adhered to.

Implement secondary perimeter

It is extremely important to identify a secondary perimeter. This is important to allow exercise of horses and limited continuation of internal organized activities.

     1. Definition: entire facility, venue. ALL animals within the secondary perimeter are considered free of infection, but at increased risk exposure and development of disease. Thus enhanced surveillance is necessary.

     2. Movement: Horses can only travel from outside of this facility and under regulation of the veterinarian in charge

     3. Record arrival/departure of ANY horse: Date, Origin, Destination, Carrier Information

     4. Surveillance: all horses twice daily and daily physical inspection for disease

     5. Entrance Health Requirements: Health Certificate, Vaccination recommendation of veterinarian in charge

     6. Exit Health Requirements: Health certificate with disease endorsement

     7. Exit testing requirements: frequency and type of testing depends on disease.

All of these activities should commence immediately anytime a HIGH risk horse is identified. Activities up to step 4 will be most successful if carried out within 24 hours. The secondary barrier usually requires continuous assessment and re-administration. Finally, for successful implementation of these guidelines, leadership is important. Everyone involved must agree and adhere to any plan adopted and leadership must be designated and recognized in order to assign tasks, keep order and provide consistent communication. In these situations, it is the veterinarian that is called up to provide this expertise.

Finally, all veterinarians should devise a fees system. Implementation of these tasks takes time. As an expert, the venue should be charged a daily fee or each horse should be charged a biosecurity fee. It is recommended that any veterinarian involved in a public venue discuss this before agreeing to participate so that if a disease outbreak occurs the veterinarian does not bear the brunt of the cost of disease outbreak control.

Set up and maintain methods for daily assessment of all animals.

Data collection should be a completely separate step. This is extremely important and at the center of successful disease control. Most of the man hours will be tracing back exposure of animals and identification of the origin and contacts in order to gain information on possible avenues of additional spread after an index case is identified. This also allows for communication outside the venue to risk groups that may unknowingly have been exposed. This communication allows implementation of early intervention. Individual animal progress, status of unaffected animals, mapping of the disease within the population should be performed twice per day.

Release from quarantine.

Successful release of animals from a primary quarantine rests on the premise that enough time has passed that animal is no longer contagious. Venues generally opt to test free in order to attain this goal sooner. Often, the time and money spent on retesting is of little sound investment if the retest time is too soon; exposed animals are going to shed organism for a given length of time irrespective of the amount of retesting performed. If a test out procedure is pursued, then all animals within a quarantine must be tested simultaneously and released upon negative resulting simultaneously. In general most viruses will test negative in population within 3-4 weeks of the last clinical case. For bacterial infections, this is quite variable and initial quarantine and testing may focus on in contact horses. Often for bacterial infections, repeated culturing is necessary and movement from primary to secondary quarantine can occur. However, release of animals from secondary quarantine should be performed after several days or even weeks where no cases are identified within secondary containment.