Quiz Study I: Diseases

We'll begin with an introduction to some common communicable diseases and vaccinations. I'm taking this from a lecture and sheet we were given about diseases at the ABC Retreat for Pony Club. The lecture was absolutely wonderful and was delivered by Dr. Liz Hoffman.

Please note: I am not a vet, and I don't play one on TV either. You need to talk to your own vet to figure out the best vaccination schedule for your own horse, etc etc etc. I am here for educational purposes only.
Also, this is definitely NOT a comprehensive list! Just the basics.

First, your vaccination program will vary by area. For example, around here, not everyone vaccinates for Rabies. According to my information, no cases of equine rabies have been reported in Oregon or Washington.

Vaccinations do not provide immediate protection. Many vaccines require a series of shots, and it takes up to 2 weeks for the immune system to begin creating antibodies.

For mosquito-borne diseases, it's best to time your vaccination just before the start of mosquito season. For us, that's usually sometime in March.

Most of this information comes from the AAEP, or American Association of Equine Practicioners guide to vaccinations.

First, the diseases for which a vaccination exists.

Tetanus
aka Lockjaw
Affects the nervous system. Caused by a bacteria that thrives in anaerobic environments, like soil. Transmitted by puncture-type wounds.
Symptoms: Tense muscles, inability to open jaw to eat properly, exposure of the 3rd eyelid. Eventually, the respiratory muscles become paralyzed, causing death.
Treatment: Antibiotics, supportive care.
Prevention: Yearly vaccination. Some vets recommend a booster vaccination if your horse sustains a puncture wound and it has been awhile since their last vaccination - check with your vet.

Encephalitis [Eastern, Western, Venezuelan]
aka Sleeping Sickness
Affects the nervous system. Caused by a virus. Carried by birds and transmitted by mosquito bites.
Symptoms: Fever and excitability which goes to depression, drowsiness, and paralysis.
Treatment: supportive care.
Prevention: In some areas [including Oregon], you don't need to vaccinate for the Venezuelan strain, but all horses should be vaccinated every 6 to 12 months.

West Nile Virus
Affects the nervous system. Caused by a virus. Carried by birds and transmitted by mosquito bites. A serious and often fatal disease.
Symptoms: Loss of coordination, abnormal gait, muscle tremors, depression, inability to get up.
Treatment: supportive care.
Prevention: Vaccination every 6 to 12 months, depending on mosquito exposure.

Rabies
Affects the nervous system. Caused by a virus. Transmitted by bites from infected animals such as bats, skunks, and raccoons.
Symptoms: Excitability, depression, inability to swallow, paralysis, death.
Treatment: None, always fatal.
Prevention: In areas where rabies is common, horses should be vaccinated yearly.

Influenza
aka Flu
Affects the respiratory system, caused by a virus. Usually affects young horses or those exposed to numerous other horses [showing, for example]. Transmitted through the air and by direct contact with mucus.
Symptoms: Similar to human flu. Fever, loss of appetite, depression, cough.
Treatment: Supportive care and antibiotics to prevent secondary bacterial infections.
Prevention: Vaccination every 6 - 12 months. [Interesting note: the Pony Club manual says every 2 - 3 months, but according to the most recent veterinary opinion this kind of frequency isn't really necessary.]

Rhinopneumonitis
aka Rhino
Affects respiratory, reproductive, and occasionally neurological systems. Caused by Equine Herpes Virus type 1. Usually affects horses under age 5 and pregnant mares. Transmitted through the air and through direct contact with mucus.
Symptoms: Similar to human flu including fever, loss of appetite, depression, and cough. Causes abortion in pregnant mares. Occasionally neurological symptoms.
Treatment: Supportive care and antibiotics to prevent secondary bacterial infections.
Prevention: 2 types of vaccine: a live virus for respiratory infections and a killed product for abortion prevention. Pregnant mares should be vaccinated at 5, 7, and 9 months of gestation with the killed product. Horses traveling or exposed to lots of other horses should be vaccinated every 6 to 12 months.

Potomac Horse Fever
This is a 'ricksettsial disease,' similar to a bacteria. It is transmitted by freshwater snails; horses contract Potomac Horse Fever by grazing on pastures that have been flooded and contain the snails.
Symptoms: Loss of appetite, fever, diarrhea, colic.
Treatment: Antibiotics and supportive care.
Prevention: Vaccination every 6 to 12 months where it is common.

Strangles
Affects the respiratory system. Caused by a bacteria, streptococcus equi. Transmitted by mucus from an infected horse and is highly contagious.
Symptoms: Fever, loss of appetite, nasal discharge, and nasty abscessed lymph nodes in the throatlatch area. Occasionally internal abscesses.
Treatment: Antibiotics, drain abscesses.
Prevention: Injectable and intranasal vaccines, given every 6 to 12 months. Intranasal is more effective, but if you use both, never introduce the intranasal material to the injection site as it causes horrible abscesses.
The AAEP only recommends vaccinating in high-risk situations; decreasing exposure and isolating infected horses works best.

Equine Viral Arteritis
Affects respiratory and reproductive systems. Caused by a herpes virus. This primarily affects breeding stock. It is transmitted through the air and in the semen of infected breeding stallions.
Symptoms: Fever, nasal discharge, swelling of the legs.
Treatment: Supportive care.
Prevention: Vaccination, testing of breeding stock, and avoidance of carrier stallions. Note that vaccinated horses will test positive, and are indistinguishable from infected horses; therefore routine vaccination is not recommended, and is often controlled by the government.
Generally not something to worry about if you're not a breeding farm.

Botulism
Affects the nervous system, caused by a toxin produced by the bacteria Clostridium Botulinum. Usually contracted by horses fed round bales of hay. It is transmitted by fermented feed or feed contaminated by animal carcasses [e.g. rodents that got caught up in the haying process and were baled in the hay].
Symptoms: Paralysis of mouth, inability to swallow, weakness; eventually the respiratory muscles become paralyzed leading to death.
Treatment: Antibiotics, supportive care.
Prevention: Yearly vaccination in areas botulism occurs in horses, especially if feeding round bales.


Now, here are some infectious diseases for which no vaccination exists.

Equine Infectious Anemia, or EIA
aka Swamp Fever
This is what your Coggins tests for. Caused by a virus; transmitted in blood from an infected horse via mosquito and fly bites or contaminated needles.
Symptoms: Fever, depression, loss of appetite, anemia, jaundice, paralysis. Incurable, often fatal. Can be acute (anemia and jaundice), chronic (lack of stamina, weight loss), or asymptomatic (appears to be totally healthy).
Treatment: none
Prevention: A positive-testing horse must be quarantined where it cannot be exposed to biting insects. Many states and shows require a negative Coggins to travel or compete. There are some exceptions, so check the state rules - for example, Oregon and Washington have an agreement that horses traveling between the two states do not need to have a test.

Pigeon Fever
The name comes from the abscesses on the chest that cause a swollen chest, not because it is transmitted by birds.
Affects the muscles and internal organs; caused by a bacteria living in soil, contracted by contact through routine abrasions. People don't get it but can carry it among horses on their clothing, boots, etc. It may be transmitted by fly bites (I believe the jury is still out on a consensus as to whether or not flies transmit this).
Symptoms: Lameness, fever, lethargy, weight loss. Usually accompanied by very deep abscesses and multiple sores along chest, midline, and groin. Can also develop internal abscesses.
Treatment: Hot packs or poultices applied to abscesses to encourage opening. Open abscesses should be drained and regularly flushed. Surgical or deep lancing may be required by a veterinarian. Antibiotics are controversial; they may prolong the disease by suppressing but not eliminating the abscesses.
Prevention: Buckets or other containers should be used to collect pus from draining abscesses [EW EW EW] and this should be disposed of properly. Consistent, careful disposal of infected bedding, hay, straw, or other material used in the stall is also important. Stalls, paddocks, all utensils and tack should be thoroughly disinfected. Pest control is also important.

Equine Protozoal Myelitis [EPM]
Affects the neurological system. Transmitted by opossum feces in a horse's feed. Has a low fatality rate, but many horses never return to full capability, and it can take years to recover.
Symptoms: Lameness, loss of balance, weakness, upward fixation of the patella.
Treatment: Marquis (ponazuril) or Navigator (nitazoxamide).
Prevention: No good vaccine currently available. Eliminate contact with opossums (because THAT's easy to do..)


So, in conclusion, some important management techniques to help prevent diseases:
Mosquito and fly control
Isolation of new horses [quarantine]
Regular vaccination schedule
Not reusing needles
Good sanitation in barn and show situations


Phew, that was a lot. Talk to your vets about this stuff. I learn new things every time I ask my vet a question, and she's always happy to explain things to me. Hope this was some good information for you guys.

PS, does anyone know what's up on encephalitis vs. encephalomyelitis? I have seen this spelled both ways and I'm not sure which is correct or if either one is acceptable.