Equine Encephalomyelitis

Equine Encephalomyelitis is an infectious disease observed originally in horses and subsequently in humans, other mammals, and birds. A type of encephalitis occurring epidemically, it is caused by a virus that attacks the central nervous system. The disease is transmitted by mosquitoes and possibly by other bloodsucking insects. Three strains of the causative virus have been identified. Two of the strains are confined to North America; one causes a rare but severe type of the disease common to the east, and the other a milder type common to the west. The third strain is responsible for a type that occurs in Venezuela. Each type is characterized by inflammation of the brain and spinal cord, with high fever, headache, muscle pains, and sometimes convulsions as the earliest symptoms. Within one or two days after onset of the disease, somnolence develops, often progressing to coma.

Equine encephalomyelitis can be controlled by annual vaccination of horses and mules before the advent of summer. An antiserum vaccine administered in the early stages of the disease is sometimes effective in the treatment of infected animals. The disease in humans is known popularly as sleeping sickness. A vaccine made from infected chick embryos gives temporary immunity to the disease.

Edema

Edema, general term for the accumulation of excess fluid in any body tissue, cavity, or organ, except bone. Accumulation in the pleural cavity is called pleural effusion; in the cranium, hydrocephalus; and in the abdominal cavity, ascites. Generalized edema is referred to as anasarca. Major causes are heart or kidney failure, low blood serum protein after starvation or liver failure, shock, and impaired return of blood from extremities. Treatment involves stimulating the kidneys to excrete excess fluid and the use of arterial tone reducers and digitalis for heart failure.

Eczema

Eczema, an inflammatory, chronic, noncontagious disease of the skin caused by allergy and hypersensitivity. The term is loosely used to include many skin conditions more properly included under dermatitis. Eczema is characterized by a number of cutaneous lesions, such as macules, papules, pustules, vesicles, scales, and crusts. Macules are nonelevated skin spots. Papules are hard, circular, and elevated. Pustules are papularlike lesions that contain pus, and vesicles are small skin blisters that contain fluid. Eczematous lesions are usually accompanied by an exudation of serous fluid and by intense itching. One-third to one-half of all cutaneous conditions are eczematous.

Inner Ear Diseases

Diseases of the inner ear can affect the sense of balance and cause symptoms of motion sickness. Anemia, tumors of the acoustic nerve, exposure to abnormal heat, disturbances of the circulatory system, skull injuries, poisoning, emotional disorders, and hyperemia, or increased blood flow, may also cause these symptoms. Ménière’s disease results from abnormalities in the semicircular canals and produces nausea, hearing loss, a disturbed sense of balance, and tinnitus, or a persistent ringing in the ears. Destruction of the inner ear by cryosurgery or ultrasound is sometimes used to combat intractable dizziness.

Damage to the organ of Corti in the inner ear accounts for the condition of many people who are either totally deaf or severely hearing-impaired. Scientists have addressed the difficulties of such people by developing an electronic device called a cochlear implant. This device is more sophisticated than a hearing aid, which merely increases the volume of the sounds that pass through the normal hearing organs. The cochlear implant works by translating sound waves into electric signals. These signals are relayed to electrodes that have been surgically implanted in the cochlea so that the auditory nerve is directly stimulated. After successful surgery, once deaf or severely hearing-impaired patients can usually detect a wide range of sounds, but results depend on factors that include the health of the auditory nerves and the duration of deafness. Nonetheless, lip-reading ability often improves, and implant users have varying degrees of success in using the telephone.

Otalgia, or earache, is not necessarily associated with ear disease; occasionally it is caused by impacted teeth, sinus disease, inflamed tonsils, infections in the nose and pharnyx, or swelling of the lymph nodes in the neck. Tinnitus may also result from these conditions. Permanent tinnitus is most often caused by prolonged exposure to loud noise, which damages the hair cells of the cochlea. A sound masker, worn like a hearing aid, may offer relief to some sufferers by blocking the perception of ringing in the ears.

Middle Ear Disorders

Diseases of the middle ear include perforation of the eardrum and infection. Perforation of the eardrum may be caused by injury from a sharp object, a blow to the ear, or by sudden changes in atmospheric pressure.

Infection of the middle ear, whether acute or chronic, is called otitis media. Acute otitis media with effusion includes all acute infections of the middle ear caused by pus-forming bacteria, which usually reach the middle ear by way of the eustachian tube. Bacterial infection of the mastoid process, a cone-shaped, honeycombed projection of bone behind the auricle, may occur as a complication of middle ear infections. Hearing impairment often follows because newly malformed tissues affect the mobility of the eardrum and the ossicles. Painful swelling of the eardrum may require a surgical incision to permit drainage of the middle ear. Since the use of penicillin and other antibiotics became widespread, mastoid complications have become much less frequent. Sometimes acute otitis media with effusion leads to a chronic infection that does not respond readily to antibacterial agents.

Acute and chronic nonsuppurative otitis media, which do not involve the formation or discharge of pus, are caused by closure of the eustachian tube due to conditions such as a head cold, diseased tonsils and adenoids, inflammation of the sinuses, or riding in airplanes without pressurized cabins. The chronic form can also result from bacterial infection. Because the watery discharge impairs hearing, chronic otitis media in young children may interfere with language development. A variety of treatments are employed, including use of antibiotics and antihistamines, removal of tonsils and adenoids, and insertion of tubes into the middle ear to allow drainage.

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