Preventative Medicine in the Older Horse Vaccination and Deworming Frank M. Andrews, DVM, MS Diplomate ACVIM Professor of LA Medicine The University of Tennessee, CVM

Activities of the Older Horses Equestrian Sports Reproduction Broodmare, Stallion Pleasure Horses

Demographics of the older horse Increase in geriatric horses presented to veterinary hospitals (4 to 6 fold, up 55%) NAHMS*-7.5% of horse population is ≥ 20 yrs 75% between 20-29 years (old horse) 25% ≥ 30 years (very old horse) Average age = 25 years (71 human years) 1 horse year  2.85 human years *NAHMS=National Animal Health Monitoring System, 1988, USDA

Demographics (as of January 1, 1999) Equine population in US: 5.32 million ~400,000 old horses and ponies in the US Tennessee 3rd in horse inventory behind Texas and California, 190,000 (7th in value of horses sold) 14,250 old horses in Tennessee 10,688 old horses 3,572 very old horses Economic impact: $189.3 million ($2,711/head)

Changes with Advancing Age Decline in body condition Decreased muscle tone Decline in immune system Increased susceptibility to infections Decreased antibody production Decreased immune response to vaccines Vaccine failure rate ~50%

Vaccination

Variation in Vaccine Response Genetic variation with age Health status Parasitism Equine Cushings Disease Dental disease Arthritis External stress factors Weather Nutrition

Vaccination – General No vaccine offers absolute protection Lessen the effects of disease Shorten duration and signs of disease Good vaccine will stimulate immunity while minimizing secondary reactions Swelling at site of injection Injection site abscesses Anaphylactic reaction Fever and illness with loss of appetite

Vaccine Older Horses and Ponies Relative risk of exposure What diseases will your horse be exposed to? Pastured horse vs. Stabled horse Use attenuated vaccine products Inactivated and killed vaccines Likely to be safer in older horses

Eastern and Western Encephalitis (EEE, WEE) West Nile Virus Important Diseases Tetanus Rabies Influenza Eastern and Western Encephalitis (EEE, WEE) West Nile Virus Rhinopneumonitis (Equine Herpes Virus 1)

Caused by Clostridium tetani Abundant in environment, manure Tetanus Caused by Clostridium tetani Abundant in environment, manure Often fatal Infection through wounds Yearly booster New study suggests that yearly booster is essential for protection in horses

Always fatal in infected horses Humans can get disease from horses Rabies Caused by a virus Always fatal in infected horses Humans can get disease from horses Infection from bite of infected animal Skunk, raccoon, bats, etc. Yearly booster-Pastured horses??

Endemic in the US, stabled horses? New horses brought onto premises Influenza Caused by a virus Endemic in the US, stabled horses? New horses brought onto premises Respiratory disease, 3 day incubation Booster every 6 to 12 months Depending on exposure Killed vs. Modified live vaccine

Eastern and Western Equine Encephalitis Caused by a virus-”sleeping sickness” Spread via mosquitoes Regional areas WEE-West of Mississippi EEE-East of Mississippi (2003 outbreak in SE US) Fatality- EEE=75-100%; WEE=25%-50% Boosters every 4-6 months during mosquito season in endemic areas

Eastern Equine Encephalitis Over 200 cases reported this year in ten US States Florida, Alabama, Georgia, Tennessee, North Carolina, South Carolina, Mississippi, Virginia, Indiana, and Wisconsin Florida outbreak = 66% fatalities All have residual neurologic deficits

West Nile Virus Caused by a virus Spread via mosquitoes Throughout the US 2003 – over 4,000 cases in horses 2002 – over 14,000 cases in horses Fatality-30%, 40% may have lasting deficits **Horses over 18 years had a 2.8X greater likelihood of dying or being euthanatized

Incubation period -- 3 to 15 days West Nile Virus Transmission Cycle Mosquito vector Incidental infections West Nile virus Incidental infections Bird reservoir hosts Incubation period -- 3 to 15 days

Spread of West Nile Virus: Birds

Epidemiology Horses cannot spread West Nile Virus to other horses, people, or pets Dead-end Host

Prevention of West Nile Virus Client Education a must Not just a source of vaccine and meds No stagnant water 4 days required for mosquito breeding Old tires--and other Redneck landscaping materials Gambusia fish eat larvae in tanks and ornamental pools Topical spraying on horse—permethrins Mosquito Magnet (www.frontgate.com) Stalls at night fans in stalls Mosquito Magnet

West Nile Virus Vaccines (USDA Approved) New Vaccine “Innovator vaccine is 92% effective”

Rhinopneumonititis Latent infections in horses Caused by a Equine Herpes Virus 1 Respiratory disease is most common Neurologic, abortion, and weak foal forms Latent infections in horses May be reactivated by vaccination in older horses May precipitate neurologic disease Not recommended in older horses because most horses have been exposed to virus **Broodmares should be vaccinated during pregnancy to prevent abortion

Vaccine Protocol: Older Horse Spring: (March 15-31) 4 – Way Vaccine Tetanus Eastern Equine Encephalitis Western Equine Encephalitis Influenza Rabies West Nile Virus Summer: (July 31-August 15) West Nile Virus (most cases in Sept. and Oct.)

Vaccine Protocol: Optional for Older Horse Spring: (March 15-31) Potomac Horse Fever Pastured horses on endemic farms Questionable effectiveness Summer: (July 31-August 15) Influenza Stabled horses with new arrivals

Deworming

Deworming-General Resistance-Many of today’s parasites are resistant to some dewormers Adaptation: faster reproduction, environmental changes, to dewormers Parasites must pass into environment to complete life cycle Infection in related to quantity of parasites in environment that horse is exposed to!! Older horses are more susceptible to infections

Parasites- What problems do they cause?? Colic Diarrhea Poor hair coat Weight loss Suboptimal performance

Minimize environmental contamination of the parasite offspring Deworming-General Minimize environmental contamination of the parasite offspring Treatment vs. Prevention Preventing infection of larval stages is key Killing adult parasites important because it prevents them from laying eggs

Specific Parasites Large Strongyles Small Strongyles Bots Tapeworms

Large Strongyles (blood worms) Strongylus vulgaris Most common large strongyle Larva stages lodge in main blood vessel that supplies the small intestines Strongylus equinus Triodontophorus spp. Discovery of avermectins (Zimecterin®, Equvalan®, Quest®) have pushed to near extinction

Bots Gastrophilus intestinalis Gastrophilus nasalis Larva stages live in stomach and small intestine Larva released in manure in spring and become flies Flies lay nits (eggs) on front legs of horses Not a big problem in horses Associated with ulcers?

Small Strongyles (most important) Cyathostomum spp. Affect all grazing horses Infections are acquired from pasture only not stalls or dry lots Eggs hatch at temperatures 45 F to 85 F Temperatures > 85 F larva die Horses are safe from infection during summer in Southeastern United States Eggs resistant to freezing Encyst in large intestine

Normal Large Intestine wall Inflamed Large Intestine Wall Small Strongyles Normal Large Intestine wall Encysted Stage Inflamed Large Intestine Wall

Tapeworms Anoplocephala perfoliata Anoplocephala magna Most common tapeworm Can reach up to 3” in length Ileocecal junction Anoplocephala magna Paranoplocepha mamillan

Tapeworms Life Cycle:

Tapeworms Clinical signs, What to look for in your horse? Colic Spasmodic – 22% associated with tapeworms Ileal impaction – 80% associated with tapeworms Intussusception – blockage associated with telescoping intestines Weight loss Abnormal hair coat

Tapeworms: Where are they found?

Tapeworm Treatments All are FDA approved

Specific Deworming Agents Benzimadazoles Fendbendazole (Panacur®) - Resistance Pyrantel pamoate (Strongid®) - Resistance Avermectins Ivermectin (Zymecterin®), moxidectin (Quest®) Cestode dewormers Praziquantel (Contained in Zimectrin Gold®, Quest Plus®, and Equimax®) Daily dewormers Pyrantel tartarate (Strongid-C®)

Don’t be fooled – Read the label!! These all contain Ivermectin and Praziquantel Get all parasites including Tapeworms

Suppressive Deworming Deworming should be based on: Egg Reappearance Period (ERP) Length of time in which the eggs appear in the manure after deworming Panacur and Strongid = 4 weeks Ivermectins = 6 to 8 weeks Moxidectin = 8 to 10 weeks Scheduling deworming based on ERP

Protocol for Strategic Deworming September 1st Ivermectin + Praziquantel (Zimecterin Gold) October 24th Moxidectin (Quest) December 17th Ivermectin (Zimecterin) March 1st

Protocol for Strategic Deworming (cont) May 1st through August 31st Limited exposure to develop immunity Parasites cannot live on pastures in summer Fecal egg counts can be done to determine resistance of parasites Egg count before treatment Egg count 7-10 days after treatment Deworming can be adjusted based on egg counts

Strategic Deworming-Alternative 2 September 1st Moxidectin + Praziquantel (Quest Plus) November 1st Ivermectin December 25th Strongid Paste January 20th Panacur February 15th Ivermectin + Praziquantel (Zymectrin Gold)

Strategic Deworming-Alternative 2 (cont) March 1st through August 31st Limited exposure to develop immunity Take advantage of summer heat

Strategic Deworming-Alternative 2 September 1st through August 31st Strongid C daily dewormer Colic protection policy by Pfizer Farnham

I am vaccinated and I have no parasites When horses dream?? I am vaccinated and I have no parasites