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Equine Vaccinations
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Equine Vaccinations

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  1. 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 diseasea 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

  3. Protecting Against Infectious Disease • Three goals when it comes to protecting your horses againstinfectious 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

  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

  5. Killed or inactivated • Modified live or attenuated • Genetically engineered • Mono or multi-valent • IM / IN • Tetanus • WNV • EEE/WEE/VEE • EHV1&4 • Influenza • Rabies • Strangles • Potomac Horse Fever • Botulism • Rotavirus

  6. 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.

  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)

  8. Population Dynamics • Closed herd • Only resident horses • Uniform vaccination/ deworming protocols • Open herd • Outside horses • Recipient or Nurse mares • Performance/ show horses • Young horses

  9. 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

  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

  11. 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 Adjuvants

  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

  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

  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

  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. 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

  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!!

  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

  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

  29. Strangles: Vaccination • Vaccines • SeM protein extract vaccines (Bacterins) • Intramuscular • Reactive: use hindlimb • Attenuated live vaccine • Intranasal • Accidental contamination of other injection sites

  30. 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!

  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 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

  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%)

  33. 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 1 - 2 (3) times/yr depending on risk of disease and length of mosquito season • Booster beforemosquito 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. 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

  41. 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