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Dengue and Japanese encephalitis are considered as one of the most common arboviral diseases in tropics. Dengue viral infection presents in very unpredictable manner varying from silent infection to uncomplicated dengue fever, dengue hemorrhagic fever and fulminant dengue shock syndrome. Various neurological manifestations in dengue fever and dengue hemorrhagic fever have always been thought as secondary to vasculitis with extravasation of fluid, cerebral hypo-perfusion, edema, hypo-natremia, hepatic or renal failure, termed as dengue encephalopathy [1]. Japanese encephalitis, which is one of the major public health problems in most of the South East Asian countries including India, may present with similar clinical pictures mimicking dengue encephalitis. 

A 34 year old male was brought to the Emergency Department (ED) with complaints of high grade fever associated with chills and rigors since three days. Patient also complained of having multiple episodes of vomiting with streaks of blood. There was no history of bleeding from any other site. On presentation patient was conscious and oriented and had a heart rate of 120/min, blood pressure of 110/70 mm Hg, respiratory rate of 20/min,  temperature of 100^oF and oxygen saturation of 100% on room air. Rest of the systemic examination was unremarkable. During his stay in the ED the patient developed episodes of projectile vomiting, and went into a state of altered mentation. Repeat vital signs showed severe hypotension for which the patient received intravenous fluids and inotropes. In view of deteriorating mental status with an inability to protect his airway, the patient was electively intubated and attached to mechanical ventilator. Arterial blood gas analysis revealed severe metabolic acidosis. Blood investigation revealed a platelet count of 30 × 10⁹/L  and dengue virus NS1 antigen test was positive. Magnetic Resonance Imaging (MRI) brain was done which revealed  extensive bilateral symmetrical areas of relative restriction of diffusion and hyper-intense signal alteration on T2W and FLAIR in cerebral white matter, thalamus, brainstem and cerebellum; mass effect over lateral, 3rd and fourth ventricle with mild tonsillar herniation, suggestive of Japanese encephalitis [Fig.1].

A diagnosis of dengue fever with Japanese encephalitis was made and patient was admitted in Intensive Care Unit (ICU) under the neurology team. Treatment was continued with inotropic support, anti-pyretics, platelet transfusions and supportive care over the next few days but patient’s condition continued to deteriorate and he expired on the 4th day.

Dengue virus is a single stranded RNA virus belonging to the Flaviridae genus, and is classified into 4 serotypes [1-4]. Serotypes 2 and 3 are mostly responsible for all the neurological manifestations [4,5]. Even though, the complete mechanism through which dengue virus crosses blood brain barrier is not clear, it is proposed that the virus enters the blood brain barrier through infected macrophages [6]. Severe dengue infection can manifest with neurological complications. Management of dengue is supportive and vaccinations for prevention are under trials.

Japanese encephalitis (JE) virus is classically a neurotropic virus. It is responsible for most of the cases of viral encephalitis in many countries of Asia accounting for 68,000 clinical cases every year. JE virus doesn’t give rise to any systemic manifestations but has great affinity for midbrain, striatum, thalamus and anterior horn cells of spinal cord. JE doesn’t have any specific antiviral therapy and the management is mainly symptomatic, however it can be prevented by vaccination. Solomon et al. reported case series of 9 cases with dengue encephalitis [DE], out of which all patients were positive for dengue serology but virus/antibodies for dengue were seen only in cerebrospinal fluid of two patients. In their case series, seven patients didn’t have typical manifestations of DE [4].

Borawake et al. reported a case of DE that had MRI findings suggestive of lesions in bilateral thalamus, pons and cerebellar regions [7].  These findings are more sensitive in cases of Japanese encephalitis [8]. A study has been done which established a relationship between pre-existing JE virus antibodies and severity of subsequent dengue virus infection. It was noted that antibodies for JE virus were associated with increased prevalence of symptomatic dengue infection [9]. A recent study noted that patients who were admitted for dengue virus infection, also turned out to be seropositive for JE [10].

The case that we are reporting presented with fever and subsequently developed altered mental status and shock. Above stated MRI findings are seen in more than half of patients suffering from Japanese encephalitis [11]. In this case, the patient had atypical symptoms with dengue serology positive and MRI findings suggestive of features of JE.

There is a possibility of dual infection or cross reactivity between JE and dengue which needs to be considered, if clinical and serological evidences are seen in the same patient.  In a country known for dengue epidemics, it is important for emergency physicians to keep a differential of JE in dengue positive patients with altered mental status. 

Contributors: PS: manuscript writing, literature search; WRS, DN: manuscript editing, literature search; AV, SJ: Study designing and manuscript editing. PS will act as guarantor. All authors approved the final version of manuscript.

Funding: None; Competing interests: None stated.