ENCEPHALOMYELITIS HORSE

From Big Medical Encyclopedia

ENTSEFALOMIELYTY LOShADY-

NY (Greek enkephalos a brain + a myelitis[es]) — the infectious diseases which are characterized by damage of a head and spinal cord, and also a meninx.

AA. l. meet in the countries of America and usually consider them as group of the American horse encephalomyelitis. Distinguish east, western and Venezuelan horse encephalomyelitis that is connected with places of emergence and studying of the first epizooty of these diseases (east and the U.S. Western States, Venezuela).

East horse encephalomyelitis. The virus nature of a disease at horses is established to Ten-B a re-lump and Giltner (S. of Ten Broeck, L. T. Giltner) with sotr. in 1933 during an epizooty of encephalomyelitis among horses in Eastern States of the USA. Fotergill and Webster (L. D. Fothergill, L. T. Webster) with sotr. in 1938 it was proved etiol. role of a virus east E. l. in cases of encephalomyelitis of the person.

Diseases east E. l. at people in the form of sporadic cases or small flashes are registered in vost. and sowing. states of the USA, the districts of Canada, adjacent to them, in a number of the countries of Central and South America (Mexico, Cuba, Dominican Republic, Jamaica), on the lake of Trinidad. Such outbreaks of a disease at people quite often arise against the background of an epizooty among horses.

Activator east E. l. — the virus relating to group of an arbovirus (see) is transferred by arthropods. It belongs to the sort Alphavirus this. Togavirida^ (see Alpha viruses, t. 25, additional materials). Virions of a virus have spherical shape, diameter them apprx. 60 nanometers; contain infectious RNA. The virus is inactivated under the influence of formalin, beta propiolactone, UF-of radiation; it is long keeps infectious activity at low temperatures and in the dried-up look. He well breeds in many cellular cultures (fibroblasts of a chicken embryo, a cell of HeLa, mouse fibroblasts of the line L, a cell of kidneys of monkeys of macaques Rhesus factors and the person) and causes cytopathic effect; in single-layer cultures under an agar covering forms plaques. White mice, Guinea pigs, rabbits, hamsters, white and cotton rats, and also other laboratory animals are susceptible to a virus. Virus strains east E. l. divide into two antigenic groups, one of to-rykh combines North American strains, another — the strains revealed in Central and South America. In the northeast districts of the USA the large epizooty among pheasants caused by a virus east E often is registered. l.

Sources of activators east E. l. are not established, however numerous allocation of a virus east E. l. from wild birds of many types allows to assume that these birds are sources of a contagium. Besides, there is an opinion that horses and mules in the period of an epizooty east E. l. also can be a source of a contagium. As carriers of a virus serve mosquitoes (see Mosquitoes blood-sicking). Natural infectiousness is established at mosquitoes of 12 types; more often than others are infected mosquitoes with Culex nig-ripalpus, S. taeniopis, S. restuans,

S. salinarius, Culiseta melanura, Aedes vexans, Anopheles crucians u Mansonia perturbans.

Diseases of people arise preferential during the aestivo-autumnal period. More often inhabitants of rural areas, hl are surprised. obr. children. Number of reportable diseases east E. l. it is small, the importance of a disease is caused by damage of a brain and a high lethality. So, in 1938 — 1962 in the USA, Dominican Republic and in Jamaica 120 people got sick, them them apprx. 67% died; in 1964 — 1969 in the USA 33 are registered. a case, from to-rykh 18 ended letalno. Infection of the person with a virus east E. l. usually causes clinically expressed disease.

Virus east E. l. gets to blood of the person from the infected mosquitoes during a krovososaniye. Through an endothelium of capillaries it gets into tissue of a brain where there is its reproduction and the direct damaging action on nervous cells is shown.

The main of a stalemate morphological features east E. l. hypostasis and a plethora of a head and spinal cord, internals are. At microscopic examination of a brain reveal a diffusion encephalomeningitis with extensive involvement in process of neurons (from little changes in a kernel and cytoplasm before final fracture), and also perivascular accumulations of leukocytes.

In the course of an infection at east E. l. intense and long immunity is developed; in an organism of the patient anti-hemagglutinins, complement-linked and virus neutralizing antibodies are produced (see). Recurrent diseases are not observed.

The incubation interval lasts

5 — 15 days. The disease begins with sharp rise in temperature (to 39 — 41 °), vomitings. During 24 — 48 hours drowsiness or coma develops, spasms develop. At inspection of the patient find a stiff neck and a spastic condition of other muscles, lack of belly reflexes, a face edema and the lower extremities, cyanosis.

The diagnosis is established on the basis by a wedge, pictures, data of Epi-demiol. anamnesis (stay in the area of possible distribution east E. l.) and results of laboratory researches. In blood the polymorphonuclear leukocytosis, in cerebrospinal liquid — a lymphocytic pleocytosis comes to light (to 1000 cells in 1 mkl). For allocation of a virus take blood of in the fever patients. The studied material enter into a brain and into an abdominal cavity of white mice suckers, into an amniotic cavity of chicken embryos or into culture of susceptible cells (usually fibroblasts of a chicken embryo). At mice virus east E. l. causes a tremor, an ataxy and death; chicken embryos perish; in culture of susceptible cells the cytopathic effect develops. For identification of specific antibodies in blood serum of patients and had use the following reactions: reaction of suppression of hemagglutination (see Hemagglutination) — anti-hemagglutinins appear by the end of the 1st week of a disease; reaction of binding complement (see) — fixators are found by the end of the 2nd week of a disease; a neutralization test (see. Virologic researches) — neutralized antibodies come to light on

3 — the 4th week of a disease.

To differentiate east E. l. follows with western and Venezuelan E. l. (see below), serous meningitis (see Meningitis) and encephalitis of various etiology (see Encephalitis), rage (see). The final diagnosis can be established only after obtaining results of virologic and serological researches.

Treatment includes desintoxication (administration of solutions of glucose, salts, etc.), dehydration (appoint lasixum, Mannitolum, etc.) and symptomatic means.

A lethality at east E. l. reaches 75%. At children

5 years after the postponed disease often are younger the delay of intellectual development, paralyzes is observed.

For specific prevention east E. l. use the inactivated cultural vaccine (see Vaccines), to-ruyu apply to prevention of a possibility of a disease during the carrying out a lab. researches and at threat of infection east E. l. in the natural centers. Use also means of protection from attack of mosquitoes — repellents (see), protecting screens (see).

Western horse encephalomyelitis. Virus western E. l. it was allocated by Maier (To. F. Meyer) with sotr. in 1930 in California: (USA) from a brain of the horse who died from encephalomyelitis. In 1938 Mr. Hauitt (V. of F. Howitt) allocated a virus western E. l. from sick people. Large epidemics of this disease are known. So, in 1941 more than 3 thousand diseases in sowing were registered. the districts of the USA, in California in 1945 — 1950 — apprx. 500 cases, in 1952 — St. 375 cases. In 1964 — 1969 in the USA 342 cases western E are registered. l., from them 9 ended letalno. Usually during flash register from 5 to 15 cases of diseases on 100 000 population.

In addition to the USA, diseases of people are revealed in Canada, Brazil, Peru, Chile, Argentina.

Activator western E. l. — the virus belonging to the sort Alphavirus this. Togaviridae. It has many general properties with a virus east E. l. Among virus strains western E. l. the nek-ry antigenic distinctions allowing to distinguish 2 antigenic options — east and western are observed.

It is supposed that sources of a contagium in the natural centers western E. l. wild birds are what points allocation of a virus from blood of birds of many types to. In the antropourgichesky centers sources of an infection are horses and mules. In zap. states of the USA the main role in transfer of a virus to horses and the person belongs to mosquitoes of Culex tarsalis, in other districts a carrier is Culise-ta melanura. Infected there were also mosquitoes of Culex peus,

S. pipiens, S. quinquefasciatus, Aedes melanimon, A. nigromaculus and Anopheles freeborni that can indicate their possible role in transfer of a virus.

Diseases of people in the USA are observed preferential in summer months. Among the diseased inhabitants of rural areas prevail; to a quarter of cases make diseases of children 1 years are younger. Before use of specific vaccines the considerable number of diseases western E was registered. l. among employees virusol. laboratories. Infection of people with a virus western E. l. often leads to an asymptomatic infection, as a result a cut in an organism specific antibodies are developed. Rivs (W. Page of Reeves) and sotr. (1962) consider that in the centers western E. l. one case of encephalomyelitis among children under 5 years is the share approximately of 58 cases of infection; with age this relation changes and makes among persons 15 years 1:1150 are more senior.

Microscopic changes in a brain (gray matter, basal kernels, a mesencephalon and a cerebellum) consist in a focal necrosis with destruction of neurons and accumulation of one-nuclear, preferential microglial cells. At a bystry lethal outcome the microscopic hemorrhagic centers in the varoliyevy bridge are found (the bridge of a brain, T.) and in a myelencephalon.

Pathogeny and developmental character of immunity western E. l. are similar to east.

An incubation interval at western E. l. varies from 4 to 21 days, 5 — 10 days are more often. The disease usually begins with bystry short-term rise in temperature to

39 — 40 °. Spasms are observed more than at 90% of children aged till

1 year, at 40% of children — at the age of 1 — 4 years and is rare at adult patients. The headache, vomiting, muscle tension of a nape and back belong to frequent symptoms at children. At adults also drowsiness, block, development of coma are possible. The acute period proceeds 7 — 10 days. More than at a half of children aged till 1 year after the postponed disease the residual phenomena — spasms, convulsions, disturbances of motive function and mental activity remain. At more senior children and adults the residual phenomena are less expressed and short-term or completely are absent.

The diagnosis is established on the basis by a wedge, pictures, data of Epi-demiol. anamnesis (stay in the area of possible distribution western E. l.) and laboratory researches. Allocation of a virus and detection of antibodies carry out the same as at east E. l.; the picture of blood and composition of cerebrospinal liquid are similar from that nra east E. l. (see above). Differential diagnosis is similar described at east E. l. Treatment is carried out the same as at east E. l.

A lethality at western E. l. reaches 8 — 15%, among children — to 30%.

Specific prevention western E.l. it is carried out by means of the vaccine inactivated by formalin, a cut preferential vaccinate workers virusol. laboratories. Destruction of mosquitoes in the centers western E. l. promotes decrease in incidence. Use means of protection from attack of mosquitoes — repellents, protecting screens.

Venezuelan horse encephalomyelitis. Virus Venezuelan E. l. it was allocated in 1938 by Beck and Uikkoff (S. E. Beck,

R. W. G. Wyckoff) from a brain of the died horse during a heavy epizooty of encephalitis in Venezuela. The first studied cases Venezuelan E. l. at the person diseases of employees virusol were. the laboratories which caught during the work with a virus in 1943. After a disease of people owing to infection in the centers were registered in Colombia, Panama, Venezuela, Mexico and some other countries Central and South America. The most considerable epidemics of a disease were noted in

1962 in Colombia and Venezuela where ached apprx. 7 thousand people, and the lethality made 0,6%; in 1971 in Mexico where the St. 25 thousand people (from them 397 got sick — with the phenomena of encephalitis), at the same time the lethality made 0,2%.

Virus Venezuelan E. l. belongs to the sort Alpha virus this. Toga vir idae. Virus strains together with Mukabo and Piksun's antigenically related viruses form 4 antigenic groups.

The factors causing existence of the natural centers Venezuelan E. l., are studied insufficiently. The large number of wildings, apparently, takes part in circulation of a virus in the nature, however probably rodents and monkeys have the greatest value. The virus was repeatedly allocated from domestic animals — horses, mules, donkeys. Carriers of a virus are mosquitoes. Virus Venezuelan E. l. in the natural centers it was allocated from many species of the mosquitoes belonging to the sorts Culex, Aedes, Mansonia, Psorophora, Hae-magogus, Sabethes and Anopheles. Diseases arise preferential at inhabitants of rural areas, and among the diseased children and persons of young age prevail. Unlike east and western E. l. allocation of a virus Venezuelan E is established. to the h.p. nasopharyngeal separated what assumes a possibility of transmission of infection from the person to the person though documentary cases of such transfer are not described.

Pathogeny Venezuelan E. l. at the person it is studied insufficiently.

At a pathoanatomical research reveal symptoms of encephalitis — hypostasis and focal damages of a brain.

Immunity after the postponed disease resistant and long probably lifelong; in the course of a disease antigemag-glyutinina, complement-linked and virus neutralizing antibodies are developed.

The incubation interval makes 2 — 6 days, can be shortened to 1 days. The disease begins sharply, with a severe headache, a fever, short-term rise in temperature, muscular pains, nausea and vomiting. These phenomena are followed by a hyperemia of a conjunctiva and mucous membranes of a pharynx and throat. At a small part of patients symptoms of encephalitis are observed: spasms, disturbances of consciousness from drowsiness before development of coma. In case of the easy course of a disease these symptoms disappear in 3 — 5 days, in more hard cases — in 8 — 10 days.

The diagnosis is established on the basis by a wedge, pictures and data epidemiol. anamnesis. Confirm the diagnosis with allocation of a virus and detection of specific antibodies by the same technique, as at east E. l. The picture of blood and cerebrospinal liquid is similar to that at east E. l. (see above).

Treatment is carried out the same as at east E. l. Recovery is usually full. At a part of patients after the postponed encephalitis persistent headaches, an adynamy, attacks of spasms are observed.

Preventive measures include destruction of mosquitoes, protection against their attack in the centers Venezuelan E. l. and inoculation vaccine. It is established that destruction of mosquitoes constrains distribution of epidemics. For vaccination of the people who are put risk of infection use a vaccine from an attenuirovanny strain of the CU-83, and also the inactivated vaccine.

Bibliogrobshchy and private virology, under the editorship of V. M. Zhdanov and S. Ya. Gaydamo-vich, t. 2, page 49, M., 1982; The Management on a zoonosis, under the editorship of V. I. Pokrovsky, page 78, JI., 1983; Fedorov Yu. V. and With about l I am a N and to R. G. Biological properties and variability of viruses of horse encephalomyelitis, Tomsk, 1977, bibliogr.; Control of communicable diseases in man, ed. by A. S. Benenson, Washington,

1981. S.G. Drozdov, B. F. Semenov.

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