Japanese Encephalitis: Clinical Presentations, Prognosis, Diagnosis And Treatment
Symptoms Of Japanese Encephalitis
Clinical Features Of Japanese Encephalitis
The incubation period ranges from 5 to 15 days. Three stages are recognizable- prodrome, acute encephalitis and convalescence.
Prodromal stage: The onset may be gradual (4 to 5 days) or acute (12 to 24 hours) or abrupt (1 to 6 hours). The disease starts as a fever with chills, headache, meningism, convulsions, psychotic behaviour and coma. Majority of cases recover in 4 to 5 days and clinical diagnosis can be made only during epidemics.
Acute encephalitis stage: The fever persists at 400 to 410C, the pulse is rapid and neurological manifestations predominate. Symptoms such as convulsions (70%), altered sensorium (90%), focal neurological deficits, signs of meningeal irritation (30%) and coma supervene. Supra-nuclear ocular palsies are common. Cranial nerve palsies and papilledema are uncommon. These features help to identify JE from tiberculous meningitis. Rapid onset of paralysis such as hemiplegia or monoplegia is characteristic. Plantar responses are bilaterially extensor. Other manifestations of brain involvement include cerebella signs, extrapyramidal signs and dystonic postures.
Convalescence: Days to weeks after the encephalitic phase, the neurological manifestations subside to recover completely with time.
Prognosis: Complete recovery occurs in one-third of the cases, neurological sequelase in another one-third and mortality in the rest. In India, mortality rate is 25 to 45%, death being due to neuronal damage, cerebral edema, pulmonary edema or intercurrent complications. Prognosis has to be guarded since it is not always possible to predict the outcome from the clinical features. Neurological sequelae such as intellectual impairment, motor deficits, extra-pyramidal features and cerebella disturbances are common. Parkinsonism is uncommon and this stands in contrast to encephalitis lethargic. The first attack of JE produces immunity, but second attacks do occur since the immunity is not lifelong.
The Prophylaxis Against Japanese Encephalitis With Vaccine
Diagnosis, Treatment And Prevention Of Japanese Encephalitis
The clinical diagnosis is easy during epidemics, since disease often occurs sporadically, JE should always be considered in cases of encephalitis. Blood shows neutrophil leukocytosis. CSF shows lymphocytic pleocytosis. The cell count varies from 10 to 1000 cells/cmm, with an average of 100 to 200 cells. The CSF abnormalities may not be evident at the onset and repeat examination within 3 to 4 days may be necessary to demonstrate them. The CSF proteins may be raised to 50 to 150 mg/dl, sugar is usually normal.
Electroencephalographic abnormalities are present in the acute phase. The EEG findings are not helpful in predicting the outcome. The ECG may show nonspecific ST-T wave changes indicating myocarditis.
The final diagnosis is established by demonstrating the virus in autopsy or biopsy speciments of brain by fluorescence antibody techniques, or isolating the virus from CSF, or rarely from blood collected early in the disease.
Hemagglutination inhibition (HI) or complement fixing antibodies can be demonstrated in paired sera and these gives evidence of infection in retrospect.
Differential Diagnosis: Features of JE have to be distinguished from various types of meningitis and encephalitis, cerebral malaria, toxic encephalopatheis, cerebral tumours and Reye’s syndrome.
Treatment And Prevention
Treatment: There is no specific treatment. Supportive measures include the correction of fluid and electrolyte abnormalities, measures to control cerebral edema, anticonvulsants and maintenance of nutrition. Use of human immunoglobulin in a dose of 150 to 200 mg/Kg body weight early in the disease has been claimed to reduce the severity and mortality of the disease.
Prevention: Killed vaccines using Nakayama JE stain of the virus are available for prophylaxis. The frozen dried vaccine can be stored at 200C without losing potency for 3 to 4 years. The course of vaccination consists of two injections of 1 ml for adults and 0.5 ml for children given at an interval of 2 weeks.
Protection starts one month after the second dose. Booster doses are given at one year and subsequently at 3 to 4 year intervals. Vaccines using India strains of the virus are being tried experimentally. Vaccination should be performed during inter-epidemic periods in endemic areas. Anti mosquito measures help in avoiding outbreaks.
© 2014 Funom Theophilus Makama