Determinants of Disease Agent

Biological Security - AGENT Internal

Most Common Agents

External Quarantine

Isolation

En vir

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William J.A. Saville, DVM, Diplomate ACVIM, Ph.D. Veterinary Preventive Medicine

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Horse Populations 2

Dead Disposal

Traffic

All In/All Out

AGENTS From Within

• • • • •

Equine Influenza Virus Equine Herpes Virus Equine Arteritis Virus Streptococcus equi subsp. equi (strangles) Salmonella spp

From Without

Equine Influenza • Probably the most explosive problem we have in stables or show barns • Rapid spread • High morbidity, low mortality in most cases • Primarily young and aged horses • Higher incidence in winter and spring

1963 Outbreak • 70 to 90% morbidity • 52% of Thoroughbred meets affected in 5 months (longer epidemic) • 62% of Standardbred meets (shorter epidemic) • Does not indicate the off track morbidity

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Equine Herpes

Time

Equine Herpes • Reasonable protection from vaccinations for respiratory and abortion form • • No protection for neurologic form

Equine Arteritis Virus • Appears endemic in Standardbred population • Stallions are carriers • Vaccination provides good protection, however, is a problem for horses to be exported

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No. of Cases

Propagated Equine Influenza Outbreak

• Not as explosive as Influenza • May be sporadic or in groups • Some evidence to suggest virus is latent in lymph as well as neurologic tissue • Some suggest latency ≥ 6 months of age in all horses • Respiratory, abortions or neurologic

Equine Arteritis Virus • First outbreak in 1953 in Ohio • Later Kentucky in 1984 • Last outbreak in 1993 at Arlington Racetrack in Chicago • Led to quarantine of the track at that time • Respiratory & abortion form

Strangles • Most common 1 - 5 yrs age & older horses • Extremely contagious - direct contact or fomites • Morbidity 30 - 100% • Mortality 9 - 10%

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Strangles

Salmonella

• Can be excreted for extended periods after signs are gone • Difficult to remove from environment • Survives for long periods in discharges • Vaccines have been inconsistent and severe consequences may occur due to side effects

• > 2,500 serotypes • Ubiquitous in the environment • Some suggest 70% of normal horses harbor organism in mesenteric lymph nodes • Transport is a risk factor for shedding of the organism • May cause acute colitis & death

Salmonella

Bio security

Feed Water

Housing Bedding Nutrition

• Survives well in environment, particularly in organic matter (years)

Wild Life Population Waste Mgmt

Public Health

• Birds and rodents are carriers Sanitation Ventilation Vaccines Parasites

Risk Factor • Any factor that may increase or decrease the risk of development of disease • May be environmental effects such as weather, housing, bedding, etc. or host effects such as transport, stress

Sick Dead

Risk Factors • Subclinical infections are common in horses • Some infections are latent and do not express themselves until the animal is stressed (e.g. Herpes, Salmonella) • Every horse is raised in a different environment with different management schemes (none to all)

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Risk Factors

Risk Factors

• Transport is a stressor in many species including the horse • Whether it is a show barn or racetrack or sale barn, how clean is the environment? • Were any horses diseased at the farm of origin? • Were any horses diseased during previous show, rodeo, race?

• Number of horses gathered • Number of geographic regions from which the horses originated

Housing & Bedding Bedding

Housing Inside

Materials

Outside

Construction

Ventilation

Purchase

Dust Type

Animals Grass

Air Flow

Quality Bedding

Feed

Temperature Control

Dirt

Barn Types

• Local Standardbred farm with 2 styles of barn and a quarantine area

Barn Types

• Lexington style barn

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Ventilation

Ventilation

• Some have no airflow

• Some barns have airflow

Fly Control Wildlife & Pest Control

Insects

Rodents

Other

Pest Control

• Mice, rats and numerous other species of wild life need to be controlled as well

• Important aspect of disease control • Concerned about diseases caused by common bacteria or other organisms that may be spread by insects • Salmonella, E. coli, Toxoplasma, Sarcocystis

Bird Control • Bird control is advised for reduction of the risk for Salmonella • Also may be transport vectors for other organisms

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Nutrition

Feed & Water Management Feed

Harvested

Water

Purchase

Protein

Carbohydrates

Required

Public Health

Residues

Sanitation

Viruses

Bacteria

Buildings

Personnel

Parasites, etc. E. coli

Equipment

Campylobacter

Sick/Dead Animals

Vaccination & Parasite Control

Disposal

Isolation

Age Group Same Facility

Available

Zoonotic Diseases

Bacteria

Salmonella

Minerals

Availability

Storage Source

Food Safety

Vitamins

Separate Facility

Render

Bury

Purpose

Traffic

Resident Agents

Incinerate

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Important Risk Factor

Waste Management

Fertilizer

Environmental Impact

Disposal

Important Risk Factor

• Air transport has also made it easier to get across the country or to different countries

• Every weekend of the year some equestrian event takes place

Host (home) Immune Competent Management Agents

Travel Cortisols

Host (away) Immune Suppressed

T-cells

AGENT

Environment -Cleanliness -No. Animals -Agents Present

OUTBREAK

Conclusions • Most diseases have a multifactorial etiology • Simple vaccination is only 1 facet of disease prevention, if it is efficacious • The individual horse is important, however, taking an agent back home from some event is much more crucial

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