Equine Diseases and Management

• Equine diseases and their management are covered.

Instructional Outcomes

• Explain how horses develop natural or induced immunity to common diseases from a scientific perspective.
• Describe how good management can prevent or control parasites in horses.
• Outline an acceptable vaccination program for a local area.
• Determine if a horse has internal parasites.
• Describe how to prevent diseases through sanitation.
• Generalize the differences among treatment, control, and prevention of equine diseases.
• Describe how diseases are transmitted among horses via vectors.
• Describe when to call a veterinarian and provide correct information.
• Describe symptoms, treatment, control, and prevention of common horse diseases and internal parasites.
• Explain the importance of proper equine dentistry for maintaining productivity.

Diseases in Horses

• A disease is any condition that impairs normal physiologic functioning.
• Infectious diseases are caused by pathogens (disease-causing agents) entering the body.
• Pathogens disturb body functions, resulting in symptoms.
• Common infectious pathogens include bacteria, viruses, and parasites.
• Non-infectious diseases may be caused by chemicals, poisons, injuries, or poor nutrition, or may be inherited.
• Overworked or stressed animals may develop disease due to reduced resistance to pathogens.
• Good horse management practices can minimize these problems.

How Diseases Spread

• Good management creates an environment that disrupts the chain of events causing disease.
• Infectious agents spread through direct contact, such as a diseased animal touching another.
• Venereal diseases are spread this way.
• Diseases can result from indirect contact, such as a susceptible animal encountering excretions or secretions from an infected animal.
• Contact with infected placentas, aborted fetuses, or manure can transmit disease.
• Breathing in small particles exhaled by a diseased animal can also spread disease.
• Contaminated facilities or improperly cleaned equipment can spread disease.
• Contaminated feed and water troughs are common sources of disease.
• Caretakers not wearing clean clothing or using properly sterilized syringes can spread disease.
• Vectors such as insects, ticks, and mites can spread disease.
• Vectors inject pathogens when they bite a healthy animal.
• Equine diseases needing a vector for transmission include Equine Infectious Anemia, Lyme's Disease, and Eastern and Western Encephalomyelitis.
• Diseases can be transmitted by flesh-eating animals that act as carrion feeders moving from infected to clean areas.

Pathogens That Cause Disease

• Viruses are disease-producing microorganisms visible only with an electron microscope.
• Viruses are tiny and can pass through filters that stop bacteria.
• Viruses live only in live tissue, parasitizing cells for growth and reproduction.
• Once inside a host's cells, viruses cause the cells to lose their ability to divide.
• Viruses are classified by their appearance, the host they infect, and the tissues they commonly attack.
• Dermotropic viruses attack skin cells, pneumonotropic viruses attack respiratory tract cells, and neurotropic viruses attack nerve cells.
• Equine Influenza (flu) is a viral disease in horses, and vaccination is used to control viral diseases.
• Bacteria are small, single-celled forms of life visible with a standard microscope.
• Bacteria vary in shape, are host-specific, and are environmentally sensitive, except when in a spore stage.
• Aerobic bacteria need oxygen to survive, while anaerobic bacteria die in the presence of oxygen.
• Once inside the host's body, bacteria reproduce and release toxins.
• Diseases caused by some bacteria can be prevented by vaccination.
• Antibiotics can be used to kill bacteria in a horse that is already infected.
• Tetanus is a bacterial disease in horses.

Common Viral Diseases of Horses

• Equine Influenza "Flu" is transmitted through contact with an infected animal or via airborne spread, and it can spread rapidly.
• Symptoms include fever, cough, and anorexia.
• Treatment involves rest, stall rest, and a dust-free environment.
• Prevention includes vaccination, quarantining new animals, and isolating sick animals.
• Equine Rhinopneumonitis ("Rhino") is transmitted through contact with an infected animal, aborted fetus, or placenta, or through infected equipment or hands of the caretaker. It can also be transmitted maternally.
• Symptoms include abortion, respiratory disease, neurologic disease, and blisters on reproductive organs.
• Treatment involves supportive care.
• Prevention includes vaccination, quarantining new animals, and isolating pregnant animals.
• Equine Infectious Anemia ("Coggins") is transmitted through insect bites, hypodermic needles, surgical instruments, maternal transmission, milk, or semen.
• Some animals may have no symptoms; others may show fever, weight loss, depression, and death.
• There is typically no treatment.
• Control of EIA involves isolating or destroying Coggins-positive horses and controlling biting insects.
• Encephalomyelitis (Eastern, Western, & Venezuelan "EEE", "WEE", & "VEE") is transmitted by the bite of an infected mosquito.
• Symptoms include neurological disease, depression, circling, excitability, blindness, and death.
• Treatment is supportive care.
• Prevention includes vaccination and insect control.
• Rabies is transmitted through bites from infected animals.
• Symptoms include neurological disease, paralysis, blindness, and inability to swallow.
• There is no treatment; humans must be treated immediately if in contact.
• Prevention includes vaccination and control of wild and stray animals.
• Equine Viral Arteritis ("EVA") is transmitted via airborne respiratory tract secretions, direct contact with infected animals, or venereally.
• Symptoms include fever, swelling, depression, anorexia, abortion, and skin rashes.
• Treatment is supportive care, but note that some animals can become chronic carriers.
• Prevention includes vaccination, isolation, and quarantine.

Additional Disease Information

• Horses are susceptible to tetanus due to the bacteria's formation of resistant spores and the commonality of wounds in horses.
• Routine vaccination is crucial for tetanus prevention.
• Tetanus leads to severe muscle spasms, "lockjaw," and a sawhorse stance, frequently resulting in death.
• Strangles is another bacterial disease characterized by fever and swollen, draining lymph nodes, commonly affecting young horses.
• Vaccination can prevent strangles.
• Parasites are living organisms that derive shelter and food from a host animal, though they rarely kill horses.
• Parasites lower food conversion efficiency and work performance, and interfere with digestive functions.

Classification of Parasites

• External parasites live on the surface of the body and obtain food via the skin.
• Internal parasites live inside the body for all or part of their life cycle.
• External parasites damage the skin, causing irritation, restlessness, allergy, and blood loss.
• Diseases can be transmitted through wounds from parasites.
• Ticks are one example of an external parasite, and can transmit Potomac Horse Fever.
• Internal parasites absorb nutrients, suck blood and lymph, and damage host tissue leading to internal bleeding or compromised organ function.
• Sufficient numbers of parasites can block the passageway of food throughout the digestive system.
• Important internal parasites include roundworms, tapeworms, bots, pinworms, and bloodworms, with bloodworms and roundworms being very common.
• Large Strongyles (Bloodworms) contribute to poor development and performance, anemia, anorexia, and death.
• Adult worms live in the intestinal tract, feeding on the gut wall and cause erosions and bleeding.
• Larval stages migrate and can block blood vessels supplying the intestines.
• This can lead to weight loss, colic, and death.
• Small Strongyles (Bloodworms) can occur in large numbers.
• These worms live inside the gut wall.
• Larvae leaving the gut wall can cause diarrhea with rapid weight loss.
• Small strongyles have a seasonal life cycle, with eggs being most visible in feces during winter/spring in northern latitudes and summer/fall in southern latitudes.
• Ascarids (Roundworms) usually occur in horses less than two years old and can cause emaciation, poor growth, a rough hair coat, diarrhea, and colic.
• Severe cases can cause intestinal blockage or rupture.
• Foals can be born with roundworms so deworming mares prior to foaling and deworming foals beginning at one month of age is recommended.
• Ascarid larvae migrate through the lungs, causing pneumonia, coughing, and snotty noses.

Determining if Horses Have Internal Parasites

• Internal parasites are a major cause of health problems.
• A regular schedule for deworming is imperative.

Developing Immunity Against Disease

• Immunity means an animal is less susceptible to a given disease.
• Acquired immunity develops after exposure to a disease.
• Active immunity results from direct contact with specific disease-causing organisms.
• The animal's body develops antibodies to combat the disease.
• Active immunity generally lasts throughout the animal's life.
• Vaccination is a way to give a horse active immunity by injecting a foreign substance to enhance its immunity.
• Passive immunity means an animal receives antibodies from its mother which protect it against the invasion of certain organisms.
• When foals get colostrum (first milk) they get antibodies that help fight disease.
• Passive immunity lasts as long as the antibodies remain in the animal's body, generally three to six months after birth.
• Maternal immunity doesn't disappear until the foal's immune system matures.
• If a foal doesn't nurse adequately or if the mare's colostrum drips out before birth, the foal becomes susceptible to infections.

Sanitation and Disease Prevention

• Maintaining the physiological well-being of a horse is key in maintaining good health.
• Good health is affected by many factors including infectious agents.
• Environmental factors such as nutrition, population density, stress, water, and temperature, general care, shelter and cleanliness are important.
• The nutritional state of the animal is important in determining its resistance to infection.
• Protein is needed to produce the products needed for the immune response.
• Caloric requirements of young animals is greater than for adults.
• Needs for nutrients such as protein, vitamins, and minerals for young animals are higher than for adults.

Population Density

• Population density determines the course of a particular disease within a population.
• High population density increases the severity and spread of infection or disease.
• High population density increases carriage of disease carriers.
• It increases the proximity of susceptible animals to contagious pathogens.
• It increases environmental contamination (food, water, air, and soil) with the pathogen.
• It increases the dose of infectious agents to susceptible animals.
• It increases stress and competition for food.
• Effects of increased population density can be lessened by better ventilation and removal of excreta.
• This can become more time consuming and expensive as population density increases.
• Most organisms that cause disease don't thrive in sanitary conditions.
• Parasites are hampered when facilities and equipment are sanitary.
• Proper cleaning and sanitization are important.
• Regular exposure of confined animals to certain diseases leads to a build-up.
• Cleaning premises is an important line of defense in equine disease and parasite control.
• Removing organic material is the first step in cleaning.
• Shovels, brooms, soapy water, and stiff brushes are useful tools.
• Steam cleaners are effective at removing dirt.
• Use of detergent with hot steam improves cleanliness.
• After removing dirt, the second step is to apply a disinfectant that works in the presence of organic material.
• Choose disinfectants that are compatible with detergents and soaps.
• Choose disinfectants that are harmless to materials and non-toxic to animals.
• Interchange of animals between populations is important in spreading disease.
• High-density populations have their own viral, bacterial, parasitic and protozoan flora.
• Animals from high-density populations can be carriers of disease agents.
• An animal taken from one population to another might spread new infections and is exposed to new organisms.
• Unfit environmental and host factors introduced into the new population ensure rapid infection spread.
• Animal interchanges can perpetuate diseases.
• Strangles outbreaks in horses can be an example of this.
• Intercurrent illness from infectious or non-infectious causes can influence resistance to infection.
• Disease saps body nutrients.
• In certain infections, like AIDS, and Equine Infectious Anemia the host's immune system is depressed.
• In other cases, one organism sets up an environment allowing other infection-causing organisms to invade tissues.
• In breeding farms, intercurrent infections are important because young animals in close proximity to older animals are more heavily impacted.
• Heritable or developmental anomalies can influence infection.
• Defects are rare but can have disastrous consequences.
• Some can occur in Arabian horses where defects can occur in white-blood cells and the ability to make antibodies.
• These foals can die from respiratory infection by adenovirus at the time immunity from colostrum disappears.

Additional Factors Influencing Disease

• Whether animals are brought together in cramped and poorly ventilated quarters.
• Stress can contribute to disease.
• Foal diarrhea can occur as a result of stress from shipping and introduction to new environments.
• The infectious agent’s virulence and the dose of the agent has influence on disease.
• Higher doses of infectious agents, higher infection rates, severe disease, and greater mortality.
• Caretakers must know and recognize characteristics present in healthy animals.
• Although signs are generally similar for horses, some have differences due to personality or environmental conditions.
• Diseases affect parameters of vital signs in predictable ways.
• From understanding those normal parameters, caretakers can determine the extent of change taking place.

When to Call a Veterinarian

• Call for professional assistance which is critical from time to time.
• Prompt intervention is more effective at lessening the severity and duration of illness.
• Call the vet if...
  • The rectal temperature is 103 °F or higher in the absence of exercise.
  • There is a frequent, deep or chronic cough.
  • The horse is noticeably depressed or showing abnormal posture.
  • The horse is off feed.
  • There is a thick nasal discharge.
  • There are signs of colic (abdominal pain)
  • The horse is severely lame or injured, or mildly lame for over five days.
  • Labor is exceeds 20 minutes after the water breaks or there are hard contractions.

Examining the Horse Before Calling the Vet

• Examining the horse before calling a vet can be useful to determine its overall condition.
• Follow a standard, planned procedure to uncover problems and symptoms of a disease.
• Consider:
  • Are the horse’s movements normal?
  • Has it’s appearance changed?
  • Are there lacerations or severe lameness?
  • Are feces present?
  • Is it eating well?
• Also important to check vital signs.
  • Is temperature normal?
  • Is pulse rate normal?
  • Is respiration rate normal?
  • Are adequate sounds coming from the abdomen?
• Remember that the assessment of these signs is affected by time of day, age, sex of the animal, amount of work or exercise, and weather conditions.

Tissue Color

• Look for bright, moist tissue that appears with a clear pink color.
• Look inside the inner eyelids, nostrils, inner lip and gums, and the vulva of a mare.
• Membranes mustn't appear dry or sticky.
• They mustn't appear yellow or brick red in color.
• Note foul or pungent odor.

Capillary Refill and Skin Pliability

• Complete a capillary refill and skin pliability test.
• While watching the mucous membranes, press the thumb against the upper gum.
• Remove the thumb after two seconds.
• If no color returns, wait for three seconds.
• Check for skin pliability on the side of the neck.
• Pinch skin with thumb and forefinger.
• If the fold doesn't disappear between two seconds the pliability is abnormal.