Japanese encephalitis (JE) is one of the most important etiologies of endemic encephalitis, especially in Eastern and Southeastern Asia regions of the world.¹ The burden of disease in India was first recognized in the early 1950s and has thereafter been reported from various states like Tamil Nadu, West Bengal, Assam, Bihar, Uttar Pradesh, Andhra Pradesh, etc.¹ Either outbreaks or sporadic encephalitis occur in targeted geographic areas based on the distribution of the etiological agent causing JE.²

According to data published by the World Health Organization, the global incidence of JE is unknown because there is worldwide variation in the intensity and quality of Japanese Encephalitis surveillance and in the availability of diagnostic laboratory testing.³ Mortality of JE is reported to be between 20-30%, and significant neurologic sequelae occur in 30-50% of survivors.⁴ Under-reporting of JE cases is a major drawback resulting in incorrect epidemiological data. A part of the reason in under-reporting is due to lack of easily available and affordable microbiological testing for the agents responsible for viral encephalitis.⁵Other reasons include short viremia time-frames for direct testing (PCR, culture, microscopy), difficulty to perform lumbar puncture in low-resourced/ regional settings and cross-reactivity of endemic flavivirus antibodies: these also contribute to the difficulty of establishing a diagnosis. Even with expensive and specialized testing the etiology remains unknown in the majority of cases.

Clinical diagnosis of Japanese encephalitis should be supported with laboratory diagnosis by performing IgM capture ELISA on cerebrospinal fluid (CSF), serum, or both of suspected individuals.⁴ Alternative methods are available for diagnosis such as reverse transcriptase polymerase chain reaction (RT-PCR), virus isolation, etc. Although there is no specific treatment for JE, supportive management, vector control and prevention including vaccination are modes of containing the spread of infection.⁵Reporting of positive cases should be mandatory for effective surveillance of Japanese encephalitis in the community.²

Case reports

Case 1

A 23-year-old male patient from Chennai, South India presented to our hospital with history of fever for 5 days. His recent travel history was not known. He was conservatively managed with antibiotic therapy and antipyretic medication on an outpatient basis. The symptoms persisted and five days after the onset of fever he presented to the Emergency Department with expressive aphasia and altered sensorium, unresponsive to oral commands, in view of which he was shifted to the Multidisciplinary Critical Care Unit for further management. His GCS was 12/15, aphasia was present, bilateral pupils were reacting to light. Magnetic resonance imaging (MRI) showed an acute small infarct in the left thalamus. Computed tomography showed signs of meningitis with minimal hydrocephalus and prominent lateral and third ventricles on both sides. Doppler imaging of carotid and vertebral arteries was normal.

Cerebrospinal fluid (CSF) was relatively clear in appearance and analysis revealed an elevated WBC count (233 cells/µL) with a lymphocytic predominance (98%). CSF protein was elevated (237 mg/dL), glucose was normal (53 mg/dL), chloride was low (100 mEq/L); the concomitant serum glucose level of the patient was 123 mg/dL. CSF Gram stain showed moderate pus cells and no organisms; CSF for bacterial culture showed no growth.

On suspicion of tuberculous meningitis, acid-fast stain and GeneXpert MTB/RIF (Cepheid, Sunnyvale, CA, USA) on CSF were done and found to be negative. Mantoux test and interferon gamma release assay (QuantiFERON-TB Gold) were also negative. Rapid plasma reagin (RPR) test for syphilis was non-reactive, HIV 1 and 2 antibodies were negative. Herpes simplex virus 1 and 2 by quantitative real time PCR (q-RT PCR) on CSF was negative. Dengue NS1 antigen, Dengue IgM antibodies by ELISA and scrub typhus IgM antibodies were negative by ELISA.

Serum for IgM antibodies to Japanese encephalitis virus was sent to King Institute of Preventive Medicine, Chennai, India, and tested positive. The patient was treated conservatively with i.v. fluids, steroids, diuretic therapy and supportive care. The patient was symptomatically better and hemodynamically stable after two weeks of management and he was discharged after complete neurological recovery.

Case 2

A 61-year-old female patient from Neyveli, Tamil Nadu, South India presented to the emergency department with complaints of high grade intermittent fever of 3 days’ duration. Her recent travel history was not known. She had recurrent seizure episodes on the day of presentation for which she was managed at an outside hospital and referred thereafter. Vomiting and headache were present for three days prior to admission. She had a past history of seizure disorder, type 2 diabetes mellitus and systemic hypertension controlled with regular medication. A provisional diagnosis of meningoencephalitis with seizure disorder and status epilepticus was made and the patient was intubated and mechanically ventilated for airway protection. Upon admission to the Multidisciplinary Critical Care Unit she was sedated and started on empirical broad-spectrum antibiotics (ceftriaxone and vancomycin) along with antiviral therapy (acyclovir), anti-epileptic and other supportive medications.

MRI showed the possibility of meningitis and age-related cerebral atrophy. A small area of diffusion restriction in the left anterior temporal pole with another small gliotic focus in the left superior temporal gyrus was also observed. Cerebrospinal fluid (CSF) analysis revealed an elevated WBC count (110 cells/µL) with a lymphocytic predominance (96%). CSF protein was elevated (209 mg/dL), glucose was elevated (138 mg/dL), chloride was low (114 mEq/L). CSF Gram stain showed moderate pus cells and no organisms; CSF bacterial culture was negative.

On suspicion of tuberculous meningitis, acid-fast stain and GeneXpert MTB/RIF (Cepheid) on CSF were done and found to be negative. Interferon gamma release assay (QuantiFERON-TB gold) were also negative.

Herpes simplex virus 1 and 2 by q-RT PCR on CSF was negative. Blood cultures were negative. Serum Dengue NS1 antigen, Dengue IgM antibodies by ELISA was negative. IgM antibodies to Japanese encephalitis virus were positive in serum and CSF by IgM capture ELISA from King Institute of Preventive Medicine, Chennai, India.

Her baseline echocardiography showed adequate left ventricular function, regional wall motion abnormality was noted in the infero-septal and antero-septal region. She developed hypotension which was initially managed with fluid boluses and later requiring increasing vasopressor support. During the course of hospital admission, she developed acute antero-lateral ST elevation myocardial infarction for which she was thrombolyzed with tenecteplase as per cardiology opinion. Post thrombolysis, the patient’s condition deteriorated and was declared dead despite adequate resuscitative measures.

In India a high occurrence of emerging infections can be defined as ‘‘infections that have newly appeared in a population or have existed previously but are rapidly increasing in incidence or geographic range.’’¹Emerging viruses are more fatal and bothersome when compared to other agents such as bacteria, fungi and parasites. Most viral illnesses are generally self-limited, although some can lead to sequelae. On the contrary, a large number of bacterial pathogens can also lead to important sequelae following meningitis or meningoencephalitis. In most viral infections where no specific treatment is available, preventive measures and immunoprophylaxis need to be strengthened to prevent sporadic outbreaks and spread of microbial agents.⁶

In India, a high occurrence of Japanese encephalitis cases has been reported from Tamil Nadu, Andhra Pradesh, Karnataka.¹ Reports from Chennai have been limited, however reports form districts like Cuddalore have shown vector abundance in specific months of the year. There has been a positive association between occurrence of cases and beginning of rainfall when there is vector abundance.⁷ Both our patients presented within a period of one month from end of August and beginning of September signifying the vector prevalence in these months.

Japanese encephalitis virus is a neurotropic RNA virus belonging to Flaviviridae family. Five genotypes of Japanese encephalitis virus have been identified so far (GI to GV). In India, the prevalent genotypes are genotype I and III, although genotype III is the most common.⁸ Genotyping was not possible to establish the type causing infection in our patients.

Clinical features of Japanese encephalitis are divided into three main stages: prodromal stage, acute encephalitic stage, late convalescent stage.⁹Both our patients presented in the acute encephalitic stage with features of continuous high-grade fever, seizures, altered sensorium, nuchal rigidity with adverse outcome in one patient.

According to the World Health Organization, the criterion for laboratory confirmation of Japanese encephalitis is positive IgM antibodies in a single sample of serum or CSF.⁴ Our patients had positive IgM antibodies in serum and CSF thereby confirming the clinical suspicion of Japanese encephalitis. One patient was not subjected to lumbar puncture due to high intracranial pressure. WHO also recommends other types of supportive laboratory diagnosis for JE such as RT-PCR, isolation of JE virus, detection of JE virus antigens by immunofluorescence.⁴

Any suspected case of acute encephalitis syndrome is classified as laboratory-confirmed JE, probable JE, "acute encephalitis syndrome” – other agent, "acute encephalitis syndrome” – unknown. Both our patients are laboratory-confirmed JE cases due to the presence of IgM antibodies in the serum and/or CSF.

The usefulness of imaging studies in substantiating the diagnosis of JE has been described by few authors. Involvement of thalamus and edema was observed in one of our patients. MRI imaging in JE patients has shown lesions involving bilateral thalamus, pons, midbrain, basal ganglia, cerebral cortex and white matter edema.¹⁰

A study on seizures in patients with Japanese encephalitis has reported that 46% of patients presented with seizures. Multiple seizure episodes as well as status epilepticus were seen in few patients.¹¹ We observed both these patterns in one patient who later developed cardiac arrest and could not be revived in spite of adequate resuscitative measures.

Mortality or adverse complications including permanent brain damage due to Japanese encephalitis virus are inevitable because of the neurotropic nature of JE virus and due to unavailability of effective antivirals for treatment of JE.¹⁰ However, effective prevention of Japanese encephalitis has been achieved in various South East Asian countries after implementation of immunization programs.¹ Three licensed JE virus vaccines are available for use, but in India the vaccine available is a live attenuated SA-14-14-2 vaccine. In endemic areas, the two main modes of prevention of JE infection would be immunization and vector control in order to prevent occurrence of infection and spread of the virus respectively.

Acute encephalitis syndrome due to Japanese encephalitis virus is challenging to diagnose unless there is knowledge of the varied clinical manifestations of the disease. Another obstacle to the confirmation of a clinical diagnosis is the unavailability of diagnostic tests in most laboratories. A suspicion of JE should be raised when any patient presents with AES in an endemic region like ours. A collective application of all these will aid in effective management of Japanese encephalitis.

1. Mani RS, Ravi V, Desai A, Madhusudana SN. Emerging viral infections in India. Proc Natl Acad Sci Sect B Biol Sci 2012;82:5-21. [Crossref]

2. Ravi V, Mani R, Govekar S, Desai A, Lakshman L, Ravikumar BV. Aetiology and laboratory diagnosis of acute encephalitis syndrome with special reference to India. J Commun Dis 2014;46:12-23.

3. Campbell GL, Hills SL, Fischer M, et al. Estimated global incidence of Japanese encephalitis: a systematic review. Bull World Health Organ 2011;89:766-74E. [Crossref]

4. World Health Organization. Manual for the laboratory diagnosis of Japanese encephalitis virus infection. March 2007. Accessed on: 26 Dec 2017. Available from: http://www.wpro.who.int/immunization/documents/Manual_lab_diagnosis_JE.pdf. [Crossref]

5. Sharma S, Mishra D, Aneja S, et al. Consensus guidelines on evaluation and management of suspected acute viral encephalitis in children in India. Indian Pediatr 2012;49:897-910. [Crossref]

6. National Programme for Prevention and Control of Japanese Encephalitis/Acute Encephalitis Syndrome. Operational guidelines. Government of India 2014;2-3.

7. Gajanana A, Rajendran R, Samuel PP, et al. Japanese encephalitis in South Arcot district, Tamil Nadu, India: a three year longitudinal study of vector abundance and infection freuency. J Med Entomol 1997;34:651-9. [Crossref]

8. Fulmali PV, Sapkal GN, Athawale S, Gore MM, Mishra AC, Bondre VP. Introduction of Japanese encephalitis virus genotype I, India. Emerg Infect Dis 2011;17:319-21. [Crossref]

9. Singh A, Saxena SK, Srivastava AK, Mathur A. Japanese encephalitis: a persistent threat. Proc Natl Acad Sci Sect B Biol Sci 2012; 82:55-68. [Crossref]

10. Kalita J,Misra UK. EEG in Japanese encephalitis: a clinico-radiological correlation. Electroencephalogr Clin Neurophysiol 1998;106:238-43. [Crossref]

11. Misra UK, Kalita J. Seizures in Japanese encephalitis. J Neurol Sci2001;190:57-60. [Crossref]