St Louis encephalitis is a naturally focal viral neuroinfection that mainly affects the membranes and substance of the brain. Debuts acutely infectious, meningeal and cerebral symptoms. There are disorders of consciousness, headache, vomiting, spastic muscle hypertonus, paresis, depression of abdominal and tendon reflexes, episyndrome. The diagnosis is made taking into account epidemiological data, the results of neurological examination, clinical tests, examination of cerebrospinal fluid, serological tests and tomographic examination of the brain. Treatment is antiviral, symptomatic and neurometabolic.
ICD 10
A83.3 Encephalitis St. Louis
General information
St Louis encephalitis is an acute infectious lesion of the membranes and substance of the brain caused by a neurotropic virus of the arbovirus family. It is a natural focal disease. St Louis encephalitis is spread mainly in the USA, for which it received its second name – American encephalitis. It is also found in Argentina, Brazil, Panama, Colombia, the Caribbean, Suriname, Mexico and Jamaica.
The “geographical” name of encephalitis is associated with the city of St. Louis, Missouri, where an outbreak of the disease occurred in 1932-33, after which it was isolated as a separate nosology. St Louis encephalitis can affect people of any age, but it is most often observed in people over 35 years of age. In children and young people, it usually occurs in a mild and subclinical form, in the elderly it is much more severe with a high percentage of disability and mortality in one case out of five.
Causes
Encephalitis St. Louis has a viral etiology. The causative agent is a flavivirus that is resistant to drying and freezing, but dies at temperatures above 56 ° C. It is transmitted transmissively, by the bite of an infected mosquito of the genus Culex. The source of infection is birds (wild pigeons, jays, sparrows), much less often — mammals. Encephalitis St. Louis has a seasonality with the highest incidence in the period from July to October and a peak at the junction of August and September.
Pathogenesis
When a mosquito bites, the virus enters the blood and spreads hematogenically throughout the body. The nervous system is most affected. There is swelling and infiltration of the cerebral membranes with the development of serous meningitis. In the cortex, basal structures, brain stem and spinal cord, there is fullness, diapedesis point hemorrhages, edema, lymphoid infiltration; necrosis of neurons and their replacement with glial elements is possible.
Symptoms
St Louis encephalitis acutely manifests after the expiration of the incubation period, which on average takes from 10 to 15 days, but can vary in the range of 4-21 days. The clinic of the debut is nonspecific, corresponds to the beginning of any acute infection. There is a sudden rise in body temperature to 40-41 ° C, pronounced weakness, headache, general malaise, myalgia (muscle pain). High hyperthermia lasts from a week to 10 days. Already in the initial period, nausea, dizziness, vomiting occur.
General cerebral symptoms and meningeal syndrome manifest on the 2-3 day of encephalitis. The general cerebral symptoms are, first of all, various disorders of consciousness. Hypersomnia, confusion and deafness are more often noted, sometimes elements of delirium. Severe disorders of consciousness (coma), typical of Japanese mosquito encephalitis, are rarely observed. Meningeal syndrome includes hypertonus (rigidity) of the posterior neck muscles, photophobia, increased skin sensitivity, the presence of symptoms of Kernig and Brudzinsky. In about a quarter of cases, the clinical picture is limited to manifestations of meningitis.
Encephalitis is characterized by spastic musculotonic disorders that spread to all muscles of the limbs and trunk. Motor disorders occur according to the type of spastic paresis, rarely reaching the stage of complete plegia (paralysis). Hyperkinesis is possible — involuntary motor acts, tremor of the hands, lips, tongue. Sometimes epileptic paroxysms are noted, more often represented by Jackson’s epilepsy, which indicates irritation of the cerebral cortex. At the beginning of the disease, tendon reflexes increase, then fade away. Abdominal reflexes cease to be triggered, pathological stop signs of Gordon, Babinsky, Oppenheim appear. Dysarthria, cerebellar ataxia, and sometimes aphasia may be observed.
In more than 20% of cases, St Louis encephalitis is accompanied by symptoms of damage to the urinary system: dysuric phenomena, frequent urination. The addition of a secondary infection causes the development of nephritis and pneumonia. After suffering encephalitis, a stable immunity is formed.
Diagnostics
St Louis encephalitis can be diagnosed on the basis of anamnestic and epidemiological data revealed during the examination of the neurologist symptoms of meningoencephalitis, confirmed by laboratory and instrumental methods:
- Laboratory tests. There are signs of a pronounced inflammatory reaction in the blood (in clinical analysis, 14-20 thousand leukocytes per 1 mm3, a shift of the leukocyte formula to the left is noted). Serological and immunological blood tests make it possible to verify St Louis encephalitis and differentiate it from other viral encephalitis (California, Japanese and tick-borne encephalitis, equine encephalomyelitis, two-wave viral meningoencephalitis).
- Tomography. To exclude other cerebral diseases, an MRI or CT scan of the brain is performed, which makes it possible to refute the presence of an abscess, cerebral cyst, intracerebral tumor or hematoma.
- Lumbar puncture. Allows you to determine the pressure of the cerebrospinal fluid and analyze it. The latter reveals an increased protein content and lymphocytic pleocytosis (more than 300 lymphocytes in 1 ml). Analysis of the composition of the cerebrospinal fluid makes it possible to exclude purulent meningitis, subarachnoid hemorrhage, and other pathology. PCR studies are not carried out, because at the time of diagnosis, as a rule, neither the virus nor its antigens are present in the cerebrospinal fluid or blood.
Treatment
The therapy is carried out by specialists in the field of neurology and infectious diseases. In the acute period (7-10 days), bed rest is necessary. Etiotropic antiviral treatment with interferon pharmaceuticals, ribavirin and ribonuclease is carried out. With increased intracranial pressure, diuretics (acetazolamide, spironolactone, furosemide) are prescribed. Anticonvulsants (carbamazepine, valproates) are indicated for convulsive syndrome.
Neurometabolic therapy with vitamins g. B, glycine, hemodialysis from the blood of calves plays an important role. In the absence of seizures, it is possible to prescribe nootropics (pyritinol, piracetam, gamma-aminobutyric acid, etc.). In order to improve cerebral blood flow, pentoxifylline is indicated. In the recovery stage, physical therapy, massage of paretic limbs is carried out.
Prognosis and prevention
The average mortality rate is 7%. However, the outcome of the disease largely depends on the age of the patient. At a young age, the mortality rate is below 5%, in the elderly — above 20%. In some cases, St Louis encephalitis occurs in an abortive or erased form. Even in the case of an extensive encephalitis clinic, the disease usually does not leave behind any residual effects. The exception is persons over the age of 60. They have the most severe course of encephalitis with residual consequences in the form of memory and concentration disorders, mental lability, asthenia, mild paresis, tremor. In childhood, residual hydrocephalus and oligophrenia are sometimes observed (mainly when encephalitis occurs in the first 6 months of life).
Prevention is reduced to the destruction of vectors of infection — mosquitoes, wearing protective clothing and the use of repellents in areas of possible habitat of infected mosquitoes. There is no specific prevention.
