1. Equine Health Management September 21, 2011
Equine Vaccinations
Equine Health Management
September 21, 2011

2. 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
define contagious
Transmission of an infectious disease may occur through one or more pathways including physical contact with infected individuals. These infecting agents may also be transmitted through liquids, food, body fluids, contaminated objects, airborne inhalation, or through vector-borne spread (i.e., ticks, mosquitoes, etc.)

3. Protecting Against Infectious Disease
Three goals when it comes to protecting your horses against infectious disease:
Reduce exposure in the environment
Minimize factors that decrease resistance
Enhance resistance through the use of vaccines**
What causes increased incidence?
Management
Animal
Environment
**vaccination alone will not prevent disease!! You must also have good management to reduce risk of exposure.
Management includes: stocking densities, movement of horses off/on farm
Animal: age, breed, sex, use, previous exposure
Environment: climate, geography, layout of facility

4. 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
How do you know when to administer to prevent disease prior to exposure??
Know how vaccines work! They are not instantaneous protection!

5. 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
There is no such thing as a “standard” vaccination protocol – it all depends on the type of facility and animals you are dealing with!
Choice of a variety of different types of vaccines directed against a variety of antigens; determine the age of susceptibility for various diseases

6. Types of Immunity Humoral Immunity: Cellular 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.

7. 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)
A fomite is any inanimate object or substance capable of carrying infectious organisms (such as germs or parasites) and hence transferring them from one individual to another
With this kind of disease, a humoral response would be ideal (protects the entry routes – i.e., throat, nasal passage, etc.)

8. Population Dynamics Closed herd Open herd Only resident horses
Uniform vaccination/ deworming protocols
Open herd
Outside horses
Recipient or Nurse mares
Performance/ show horses
Young horses
Rhodococcus equi and Strangles are most prevalent in open herds

9. Vaccinations Core Vaccines Regional Endemic Breed (WmB)
Tetanus, EEE, WEE, WNV, EHV1&4, Influenza, Rabies
Regional
Botulism: Mid-Atlantic area
PHF: areas of fresh water
Endemic
Strangles
Rotavirus
Breed (WmB)
EVA
WmB = warmblood

10. 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
Slower onset  protection generally is not achieved until 2 to 3 weeks after completion of the primary series or 1 or more weeks after administration of a booster dose.
*Work better when given as a 3-dose series than as a 2-dose series!
*3 to 4 week interval between the first and second doses of vaccine followed by a longer interval of 3 to 5 months between the second and third doses  optimize priming of the immune system and protection.

11. Adjuvants Immunomodulation Interaction between adjuvants?
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
an adjuvant is an agent that may stimulate the immune system and increase the response to a vaccine, without having any specific antigenic effect in itself. The word “adjuvant” comes from the Latin word adjuvare, meaning to help or aid. "An immunologic adjuvant is defined as any substance that acts to accelerate, prolong, or enhance antigen-specific immune responses when used in combination with specific vaccine antigens."

12. 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

13. 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

14. 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

15. 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
Never vaccinate a sick horse or one on steroids (i.e., prednisone)
OK to give multiple vaccines in one day, but don’t come back in 5 days and give another; wait at least 2 weeks!

16. 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
FPT = Failure of Passive Transfer

17. 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

18. 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

19. Maternal Antibody Interference
EEE / WEE
Tetanus
EHV-1&4
Influenza
Rabies
Rotavirus

20. 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
Foal production of IgGb not detected until at least 63 d of age

21. 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

22. 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

23. Abortion of virus (+) fetus or dying foal
EHV-1
Maternal endothelial cell infection
Fetal Infection
Placenta
Fetal death
Endometrial vasculitis, thrombosis, ischemia
Abortion of virus (+) fetus or dying foal
“Red Bag” “
Abortion of virus (-) fetus

24. 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
Prodigy and Pneumabort are for EHV-1 ONLY;

25. 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!!
Use of EHV-1 only vaccine may improve immunity, but not necessarily so!

26. 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
Generally only a problem in yearlings  about 3 years old (sometimes older); not usually a problem in adult horses

27. 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

28. 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
Only vaccinate if at risk or unknown farm status (i.e. endemic problems)

29. Strangles: Vaccination
Vaccines
SeM protein extract vaccines (Bacterins)
Intramuscular
Reactive: use hindlimb
Attenuated live vaccine
Intranasal
Accidental contamination of other injection sites
When you use the IM vaccine always use hindquarters and then get horse out and moving.
Don’t give ANY other vaccine at the same time as the intranasal (see photo) – can cause a massive pus-filled nasty mess.

30. Complications Purpura Hemorrhagica Do not over-vaccinate!
Necrotizing vasculitis – immune complex
Edema, petechial & ecchymotic hemmorrhage
May develop after vaccination or exposure to clinical disease
High titers predispose
Do not over-vaccinate!
Vasculitis = inflammation of the blood vessels
Petechial = is a small (1-2mm) red or purple spot on the body, caused by a minor hemorrhage (broken capillary blood vessels)
Ecchymotic = A small haemorrhagic spot, larger than a petechia, in the skin or mucous membrane forming a nonelevated, rounded or irregular, blue or purplish patch
Titer = number of antibodies present (concentration)

31. 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 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

32. 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%)
- Clostridium tetani bacteria is a normal contaminant of the horses intestinal tract and feces.

33. Tetanus All horses should be vaccinated for 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

34. 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

35. 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 (3) times/yr depending on risk of disease and length of mosquito season
Booster before mosquito season begins
Insect control

36. 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

37. 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

38. 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 concern
No treatment available once neurologic signs develop
Vaccinate ALL horses

39. 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

40. West Nile Virus Vaccination
Initial series of 2 vaccinations followed by a booster every 6 – 12 months depending on risk and length of mosquito season
Mosquito control
Remove areas of standing water

41. 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

42. 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