Influenza
For several centuries, humans have recognized influenza-like diseases in horses. With the significant increase in the movement of horses, both nationally and internationally for competition and breeding, the incidence of equine influenza has increased dramatically over the last 25 years.
Clinical Signs - While it is necessary to confirm a diagnosis of equine influenza by laboratory examination, there are two common features of the disease: the extremely rapid spread of infection, and the frequent dry cough. Following a brief incubation period of 1 to 3 days, horses develop an elevated temperature (102.5 - 105.0 degrees F.) which persists for up to 5 days. A high temperature may be associated with loss of appetite and dullness. Both the severity and duration of these symptoms is dependent on the animal's exposure to influenza -- either by natural infection or vaccination. After the initial signs, horses develop a frequent, dry cough which persists with lessening frequency for several weeks. A "drippy" nose may also be observed with the discharge becoming thicker and profuse due to secondary bacterial infection, usually Streptococcus zooepidemicus.
Vaccination scheduling should include most horses. Foals at 3-6 months, then every 3 months. Traveling horses every 3 months. Brood mares biannually, plus booster 4-6 weeks pre-foaling. David G. Powell, BVSc, FRCVS, University of Kentucky.
Rhinopneumonitis
Rhinopneumonitis in horses describes the outward signs associated with infection by equid herpesvirus types 1 and 4. Equid herpesvirus 1 (EHV-a), was previously referred to as equine abortion virus (EHV-a subtype 1). However, in addition to causing abortion, this virus also causes respiratory disease and occasional paralysis. Equid herpesvirus 4 (EHV-4), previously referred to as equine rhinopnuemonitis virus (EHV-1 subtype 2), is the most common cause of respiratory disease or "snots" observed among foals and yearlings during the fall and winter months. On rare occasions it can cause abortion in pregnant mares.
Clinical Sings - Abortions attribute to EHV-1 usually occur between 8 and 11 months of gestation but can be as early as 4 months. These abortions may occur from 9 days to several months following infection. Mares abort suddenly without signs of illness, and the fetus shows no signs of degenerative change. At full term foals may be born alive, but if infected in utero the foals are very weak, have considerable difficulty in breathing, and invariably die from pneumonia within 48 to 72 hours. On rare occasions, EVH-1 invades the horse's brain and spinal cord producing signs of incoordination - which may progress to paralysis and recumbency. Neurological signs usually follow an earlier episode of respiratory disease or an abortion within a group of in-contact horses.
Vaccination scheduling - Foals at 2-4 months. Younger horses in training, repeat at 2 to 3 month intervals. All brood mares at least during 5th, 7th and 9th months of gestation. David G. Powell, BVSc, FRCVS, University of Kentucky
Encephalomyelitis
Encephalitis is an inflammation of the brain. There are many types of encephalitis, and a large number of the cases are caused by viruses. The predominant toga viral encephalitides in the western hemisphere are associated with the Eastern, Western and Venezuelan Equine Encephalitis virus. These viruses are classified as Tongaviradae, which are small, lipid - and protein-enveloped, ribonucleic acid particles. The structure of the viruses and the associated clinical presentations are fairly similar, but the character of epidemics and the immunology are distinct.
Clinical signs are more profound in unvaccinated animals. Acute clinical signs of EEE and WEE are nonspecific and include mild to severe fever, poor appetite, and stiffness. An incubation period of 1-3 weeks then occurs. Many cases of WEE do not progress beyond this point. With EEE, progression is more common. Once nervous signs develop, the viremia is past. It is unlikely that the animals can amplify the disease. In progressive cases the fever may rise and fall sporadically. Cerebral signs may develop at any time, but they often occur a few days after infection. Acute signs often range from propulsive walking, depression, and somnolence to aggression and excitability. Some horses may become frenzied after any stimulation. The later signs are evidence of the dynamic nature of these conditions and the increased severity of brain dysfunction. These signs include head pressing, propulsive walking, blindness, circling, head tilt and facial and appendicular muscle fasciculation. Paralysis of the pharynxx, and tongue are common. Death is often preceded by recumbency for 17 days. Animals that are comatose rarely survive. If animals are to survive, they show gradual improvement of function over weeks to months. Cases of VEE may have similar or different clinical presentations than WEE and EKE. This is most likely due to the difference in strain pathogenicity (the proportion of animals exposed to the virus that develop the disease). Diarrhea, severe depression, recumbency, and death may be prominent before neurologic deficits are evident. Neurologic signs occur at approximately 4 days following infection. Other associated signs include abortion, oral ulceration, pulmonary hemorrhage and bleeding from the nose.
Vaccination Scheduling All horses. Foals at 2-4 months. Annual in spring thereafter. Brood mares at 4-6 weeks before foaling. Joseph J. Bertone, DVM, MC, Ohio State University
Tetanus
Since horses have routinely begun to be vaccinated against tetanus, the disease has become increasingly rare. However, it still occurs sporadically and is highly fatal in the equine species. Tetanus is caused by a potent neurotoxin produced by the ubiquitous, grampositive, sporeforming bacterium Clostridium tetani. The organism is found in the intestinal tract of most mammals and in the soil.
Clinical Signs Most horses with tetanus have sustained a wound approximately 2 days to 1 month prior to the onset of the clinical signs. Puncturetype wounds to the hoof, as well as lacerations of the head, lower limbs or tail have been associated with tetanus. Physical evidence of a wound may not be present when the clinical signs of tetanus appear; however, there may be a history of an injury. In cases in which a wound could not be demonstrated, intestinal infections have been implicated. The clinical signs of tetanus are not difficult to recognize. An hyperresponsiveness to light, touch or sounds and prolapse of the third eyelids are consistent clinical signs of the disease in the horse. Gait stiffness, neck stiffness, fever, elevations in heart rate and respiratory rate, erect ears and tail, trimus (lockjaw), flared nostrils, muscle spasms and sweating are also common signs. The disease may rapidly progress (over hours to several days), and the signs may become so severe that they render the animal recumbent. Convulsions and respiratory or cardiac arrest precede death. The primary ruleouts based on the clinical signs should include rabies, meningitis, myositis, laminitis, ingestion of toxic substances or cervical (or other) vertebral fracture.
Vaccination Scheduling All horses. Foals at 2-4 months. Annually thereafter. Brood mares at 4-6 weeks before foaling. Sherril L. Green, DVM, University of CaliforniaDavis
Strangles
A highly contagious and dangerous disease. There may be some side effects associated with vaccination; therefore, it is important to discuss the risks versus benefits of vaccination with your veterinarian.
Vaccination Scheduling Foals at 8-12 weeks. Biannually for highrisk horses. Broodmares biannually with one dose 4-6 weeks prefoaling.
Rabies
A frightening disease which is more common in some areas than others. Horses are infected infrequently, but death always occurs. Rabies can be transmitted from Horses to humans.
Vaccination Scheduling Foals at 2-4 months. Annually thereafter.
Potomac Horse Fever
A seasonal problem with geographic factors. One third of affected horses die.
Vaccination Scheduling Foals at 2-4 months. Biannually for older horses. Brood mares biannually with one dose at 4-6 weeks prefoaling. Many combination vaccinations are available. Please check with your local equine practitioner. Appropriate vaccinations are the best and most costeffective weapon you have against common infectious diseases of the horse. A program designed with the help and advice of your local veterinarian will keep your horses and you happy and healthy for many years to come. Excerpts reprinted from the American Association of Equine Practitioners' Immunizations brochure and the Horse Industry Handbook.
From THE EQUINE NEWSLETTER, Volume 6, November/December, 1997.
