Nipah Virus Infection

Introduction

Nipah virus is an RNA virus belonging to the Paramyxoviridae family and Henipavirus group. Nipah virus caused an outbreak in pig and humans in Malaysia and Singapore between 1998 and 1999 and has been the cause of recurrent outbreaks in Bangladesh and West Bengal, India since 2001. It was initially discovered when it caused an outcome of viral encephalitis in pig farmers in Malaysia. The primary animal reservoir of Henipaviruses are bats of the genus Pteropus, Pteropodidae family. Other animals such as pigs and domestic animals such as dogs and cats can be intermediate hosts for the virus as well. Nipah virus is classified internationally as a biosecurity level (BSL) 4 agent. The pathogenesis of Nipah virus infection is based on its ability to infect blood vessels, and extravascular parenchyma, especially the central nervous system (CNS).

Clinical Features

Nipah virus causes an encephalitis syndrome with a high mortality rate, currently reported at 75% in India. The incubation period ranges from 7-40 days. The initial presentation is non-specific with sudden-onset fever, myalgia, nausea, and vomiting. It is suspected in a patient who has

• Fever with new-onset/altered mental status or seizure and/or

• Fever with headache and/or

• Fever with cough or shortness of breath.

Meningismus is seen in approximately one-third of patients but marked nuchal rigidity and photophobia are uncommon. In 60% of patients, the disease rapidly progresses with declining consciousness and can lead to a coma within 5-7 days. Generalized seizures occur in 20% of patients. Other neurological presentations include myoclonus, cerebellar dysfunction, tremors, areflexia. Brainstem involvement leads to pinpoint pupils, unreactive pupils, abnormal doll’s eye reflex, tachycardia, and hypertension which are signs of a poor prognosis. Few cases can have pulmonary involvement with atypical pneumonia and chest radiographs show diffuse interstitial infiltrates. Some cases may have non-encephalitic illness initially and have a late-onset neurological disease. Patients can have residual fatigue and day time somnolence after the illness. One of the complications of Nipah virus infection is relapsing encephalitis presenting with multiple episodes of neurological dysfunction in survivors.

Investigations

MRI: The characteristic MRI abnormalities are multiple, small (less than 5 mm), asymmetric focal lesions in the subcortical, and deep white matter without surrounding edema. These lesions most probably represent areas of micro-infarction that have also been observed on histopathology.

Electroencephalography:
Shows continuous diffuse slow waves with or without periodic bitemporal independent sharp wave discharges.

ELISA:
An IgM capture ELISA and an indirect IgG ELISA have high specificity for the diagnosis.

PCR:
RT PCRs can be used for the detection of viral sequences in fixed or fresh tissue or CSF diagnostic specimens or as an adjunct to the rapid characterization of viral isolates from cell culture.

Samples used for investigations include:

• Throat swab in viral transport medium

• Urine in universal sterile container (10 ml)

• Blood in plain vial (atleast 5 ml)

• CSF in sterile container (atleast 1 ml)

Treatment

Management of the Nipah virus is mainly supportive care and strict isolation of the infected patient. Mechanical ventilation for airway protection can be done in patients with neurological decline. In Malaysia, aspirin and pentoxifylline were administered for their anti-thrombotic properties as it was recognized that neurological symptoms could be due to thrombi. Ribavirin, a nucleoside analog is also given empirically as it has a broad-spectrum activity against RNA and DNA viruses.

Prevention

Since there is no specific treatment available yet, prevention is the mainstay of our approach.

• Avoid exposure to bats and sick pigs in endemic areas.

• Do not consume half-eaten or bitten fruits,

• Do not consume new palm sap (palm toddy) contaminated with bat fluids. Bats are known to contaminate toddy kept in open containers with their saliva or urine.

• Especially if caring for a patient: Wash hands regularly, wear gown, mask, cap, gloves, whenever in contact with patient.

• Since it is a BSL 4 agent, universal standard droplet and biocontainment precautions should be followed during contact with secretions, excretions and body fluids of suspected patients.