Equine Vaccinations

Equine Health Management

September 21, 2011

Controlling Infectious Disease

What is an infectious disease? Contagious disease Virus, bacteria, parasite, fungi and protozoa

When is infectious disease a problem? When a horse or group of horses experience a

challenge from an infectious agent at a dose sufficient to overcome resistance

Where do horses acquire resistance? Previous natural exposure or vaccination

Protecting Against Infectious Disease

Three goals when it comes to protecting your horses against infectious disease:1. Reduce exposure in the environment2. Minimize factors that decrease resistance3. Enhance resistance through the use of

vaccines** What causes increased incidence?

Management Animal Environment

Vaccinations

Vaccination minimizes risk but does not prevent disease

Follow instructions re: primary series (vaccines and boosters) before likely exposure

Not all horses respond the same or are protected for the same length of time

All horses in a herd should be vaccinated on the same schedule when possible to optimize herd immunity

Tetanus WNV EEE/WEE/VEE EHV1&4 Influenza Rabies Strangles Potomac Horse

Fever Botulism Rotavirus

• Killed or inactivated

• Modified live or attenuated

• Genetically engineered

• Mono or multi-valent

• IM / IN

Types of Immunity

Humoral Immunity: B lymphocytes and plasma cells produce antibodies to

foreign agents and stimulate T lymphocytes to attack them Cellular Immunity:

Immune response that involves enhanced activity by phagocytic cells and does not imply lymphocyte involvement.

Mucosal Immunity: Resistance to infection across the mucous membranes.

Dependent on immune cells and antibodies present in the lining of the urogenital tract, gastrointestinal tract and other parts of the body exposed to the outside world.

Contagious: Horse to Horse

Spread horse to horse Influenza virus: respiratory secretions, equipment Herpes virus: respiratory secretions, equipment, aborting

mares shed via uterine fluids, latent infections, asymptomatic shedders

Strangles: nasal discharge, draining abscesses, equipment, water troughs, environment , asymptomatic shedders

Rotavirus: manure, fomites Salmonella: manure, fomites (people, stall cleaning

equipment)

Population Dynamics

Closed herd Only resident horses Uniform vaccination/

deworming protocols Open herd

Outside horses Recipient or Nurse mares Performance/

show horses Young horses

Vaccinations Core Vaccines

Tetanus, EEE, WEE, WNV, EHV1&4, Influenza, Rabies

Regional Botulism: Mid-Atlantic area PHF: areas of fresh water

Endemic Strangles Rotavirus

Breed (WmB) EVA

Inactivated (Killed) Vaccine

Organisms not replicating Adjuvants added to boost

immune response Advantages:

Safety, stability Disadvantages:

Slower onset of protection, shorter duration of immunity

Reactions associated with adjuvants

Adjuvants

Immunomodulation Stimulate or slow the immune

response Increase response to vaccine No antigenic effect itself

Interaction between adjuvants? Different companies use different

adjuvants Local reaction to adjuvants Wide variety

Aluminum salts. Saponins, Oil emulsions, Liposomes

Attenuated (MLV) Vaccine Attenuated: organism is modified so it is non-pathogenic but still

causes immune response - replicates within the host Advantages:

Rapid onset of immunity Longer duration of immunity No adjuvant

Disadvantages: Potential for inactivation Reversion to virulence Requires reconstitution

Examples: Flu-AVERT® intranasal influenza vaccine Pinnacle® intranasal Strangles vaccine Rhinomune® intramuscular EHV-1 vaccine

Genetically Engineered Vaccines: A new breed of vaccines!

Category I: Subunit Category II: Gene deletion Category III: Clone genes into vector (bacteria or

virus); vector transports genes & expresses the antigens when administered to host Recombitek®: Canary pox virus vector used

Advantages: Safety Antigenic specificity Longer duration

Toxoids vs. Antitoxins

Toxoid: Deactivated toxin - vaccine Tetanus toxoid

Antitoxin: preformed antibody - treatment Tetanus antitoxin Botulinum antitoxin R. equi hyperimmune serum Rapid, but short-lived protection

Immunization Failures Host:

Compromised host; steroids? Maternal antibody interference

Vaccine: Inappropriate strain (PHF) Improper storage & handling; outdated Bell curve: some horses respond better than others!

Human Error: Misuse Too frequent administration: wait a minimum of 2 wks

between doses or between different vaccines

Foal Vaccination Program:

Dam’s vaccination status Colostrum quality/FPT Risk of diseases

Regional Endemic to farm Husbandry practices

Vaccine used/age at initial vaccination/ number of doses

Foal’s immune response

Foal Immunity

Passive Immunity Maternally derived antibodies in colostrum Temporary protection Immunity gap / window of susceptibility: the

period during which MDA have fallen below protective levels but still interfere with the foal’s response to immunization Varies with different antigens (diseases) and different

vaccines

Impact of MDA on Immune Function in the Foal

Maternally derived antibodies (MDA) provide passive protection while suppressing the foal’s ability to synthesize its own antibodies

Rate of decline of MDA varies for both individuals and antigens

[MDA] fall below protective levels for most antigens by 3 months of age, but remaining antibody levels may still block the foal’s response to vaccination

Maternal Antibody Interference

EEE / WEE Tetanus EHV-1&4 Influenza Rabies Rotavirus

Misdirected Immune Response

Inactivated vaccines administered to young foals (< 6mos) stimulate mostly IgG(T) and little to no IgGb which is the most immunoprotective antibody

Immunosuppression by high levels of colostral IgGb Foal [IgGb] lagged behind adult levels for > 6mos Recommend delaying primary vaccination

with inactivated vaccines until foals are at least 6 mos old

Diseases: What protects?

Humoral antibody EEE / WEE / WNV Tetanus Rabies Botulism

Combination EHV1&4: Humoral, cellular, mucosal Rotavirus: IgA, humoral Influenza: Humoral, mucosal Streptococcus equi: Humoral, mucosal

EHV-1: What we know…

EHV-1 becomes latent in ~80% of horses infected Latency established in trigeminal ganglion & lymphocytes

Natural immunity is short lived (3 – 6 months) but may increase after repeated exposure

In broodmares, immunity against abortion appears to be more durable following natural infection.

Infection is spread by direct contact between horses and infected equipment

“

EHV-1

Fetal Infection

Fetal death

Abortion of virus (+) fetus or dying foal

Maternal endothelial cell infection

Endometrial vasculitis, thrombosis, ischemia

Abortion of virus (-) fetus

Placenta

“Red Bag”

EHV: Vaccines

Killed Vaccines: Respiratory claim Prestige®: IM Calvenza®: IM / IN Innovator®: IM

Modified Live: Respiratory claim Rhinomune®: IM

Killed Vaccines : Abortion claim; approved for pregnant mares Prodigy®: IM Pneumabort K® : IM

Herpes vaccines Should I use a vaccine with EHV-1 and 4 or

just EHV-1? EHV-4 causes the majority of herpes respiratory

disease in young horses EHV-1 causes abortion and CNS disease as well

When should I use a EHV-1 only vaccines? During pregnancy: months 5, 7, 9 To reduce the risk of neurological EHV-1 disease? There is cross protection between EHV-1 and 4

NO vaccine has a label claim to prevent the neurological form of EHV-1!!

Influenza

Not a clinical problem in foals No longer necessary to have Influenza A type

1 in vaccines; should have clinically relevant A/equine 2 subtype in current vaccines

MLV Intranasal provides rapid onset of immunity (within 7 days) & longer duration of immunity

Use IM influenza vaccines to booster dam’s immunity

Modified Live Influenza Vaccine

Stimulates local immunity Rapid onset of immunity within 7 days Safe in stressed animals (e.g., transportation,

weaning) Single dose for primary immunization

Begin vaccination at 11 months; booster every 6 months

Strangles: Immunity & Vaccination

Immunity following recovery from disease Dependent upon inoculum dose, virulence, and pre-

existing immunity Solid immunity for 5 yrs or longer in 75% of animals

Foals born to recovered mares Colostrum contains IgG & IgA; milk contains IgA

Foals generally protected until weaned

Foals born to vaccinated mares Varies depending upon mare’s response Variable protection for 3-6 months

Strangles: Vaccination Vaccines

SeM protein extract vaccines (Bacterins)

Intramuscular

Reactive: use hindlimb

Attenuated live vaccine

Intranasal

Accidental contamination of other injection sites

Complications

Purpura Hemorrhagica Necrotizing vasculitis –

immune complex Edema, petechial &

ecchymotic hemmorrhage May develop after

vaccination or exposure to clinical disease

High titers predispose Do not over-vaccinate!

Strangles Protection on Hi-Risk Farms

Yearlings and Performance horses: IN every 6 mos; IM every 4-6 mos

Broodmares: IM booster last 4-6 wk of pregnancy

Foals: IN begin at 6 mos with 2 doses @ 3wk intervals IM begin at 4-6 mos with 3-dose series

Avoid vaccinating horses with high serum titers Horses with very high titers due to natural infection or

vaccination are at increased risk of purpura and other immune mediated complications

TETANUS (Lock-jaw)

Not contagious; organism lives in the environment in low oxygen conditions

C. tetani enters via puncture wounds (especially in the foot), lacerations, surgical incisions (e.g. castrations), umbilicus of foals

Horses are the most susceptible species

Very high mortality (80%)

Tetanus Vaccine is safe Good immunity; at least 1 year, probably longer

• Disease can be fatal and is expensive to treat

• All horses should be vaccinated for tetanus

• Check vaccination status before any surgery and after any deep penetrating wound

Eastern & Western Encephalomyelitis

Affects all ages; uncommon in foals < 3 mos

Viral infection Spread by ticks &

mosquitoes; wild birds & rodents are reservoirs

Seasonal and geographic disease; year to year variation based on rainfall and temperatures

EEE / WEE Vaccine is safe and

effective; USE IT Foals receive an initial series

of 3 doses beginning at 4 – 6 months of age

Booster 1 - 2 (3) times/yr depending on risk of disease and length of mosquito season

Booster before mosquito season begins

Insect control

Potomac Horse Fever: Distribution

• Cases reported in over 40 states, Canada and Europe

• Disease appears to be spreading

• Cases tend to occur near bodies of water

Potomac Horse Fever Vaccination

Commercial vaccines contain an older strain of PHF; Field strains of E. risticii continue to change

More than 28 new E. risticii isolates have been identified in field cases of PHF

Vaccinated horses often showed a milder form of PHF when exposed

Adults: Vaccinate once or twice a year depending on risk of disease and length of vector season

Booster pregnant mares 4 – 8 wks pre-foaling

Rabies: Important Facts

It is a ZOONOTIC DISEASE that can be spread from animal to man as well as from animal to animal

Public health concernNo treatment available once neurologic

signs developVaccinate ALL horses

Rabies Vaccine Killed intramuscular vaccine: safe,

effective Duration of immunity at least 1 yr;

annual boosters recommended Unvaccinated animals: primary series of 2 doses Colostral antibodies interfere with foal’s immune

response: Foals born to vaccinated mares: 1st dose at 6mo,

2nd dose 1 mo later, 3rd dose at 1yr of age

Rotavirus: MDA

Highly contagious Fecal-oral transmission Damages tips of villi in SI;

self-limiting Vaccinate pregnant mares: mos

8, 9, 10; repeat for each pregnancy; no “annual booster”

Herd immunity waxes and wanes

Botulism: Vaccine is safe and effective Protect foal by vaccinating mare & ensuring foal

ingests adequate colostrum Initial series of 3 doses given to 4 – 6 wks apart;

administer during last trimester Thereafter, annual booster for mares 4 – 8 wks pre-

foaling Can begin foal vaccinations at 3 – 4 mos if risk of

disease is high Series of 3 doses given 4 wks apart Foal relies on MDA for protection against “Shaker

Foal” syndrome