Nipah Virus Disease

Nipah virus disease, caused by the Nipah virus, is a recently discovered zoonotic disease characterized by fever, constitutional symptoms and encephalitis, sometimes accompanied by respiratory illness.

Epidemiology

Nipah virus disease is endemic to south Asia, where sporadic outbreaks have been noted in Malaysia, Singapore, India, and Bangladesh since the virus was first isolated in 1999. Less than 20 cases are typically reported per year worldwide, although systematic surveillance is lacking.

Clinical description

The incubation period is typically 4-20 days. Patients usually present with fever, malaise, headache, myalgia, sore throat, nausea and vomiting, sometimes accompanied by vertigo and disorientation. Severe cases progress to encephalitis, which may be complicated by seizures and coma. Atypical pneumonia, sometimes leading to the acute respiratory distress syndrome, may be seen. Asymptomatic infections have been documented. Cases of relapse occurring weeks or even months after recovery have also been described. Neurologic sequelae occur in up to 20% of survivors of Nipah encephalitis and include persistent seizures and personality or mood changes.

Etiology

Nipah virus is a member of the Paramyxoviridae family, genus Henipavirus. The virus appears to be maintained in fruit bats (Pteropus genus), which may infect humans through direct exposure to their saliva or excreta, including through contaminated food, especially palm tree sap. Bats may also transmit the virus to intermediate hosts, especially pigs, which develop respiratory disease and may pass the virus on to humans. Serologic evidence of infection has also been noted in cats, dogs and horses. Swine farmers and abattoir workers are at increased risk. Human-to-human transmission has been occasionally noted through exposure to bodily fluids.

Diagnostic methods

Common diagnostic modalities include cell culture (restricted to biosafety level-4 laboratories), serologic testing by enzyme linked immunosorbent assay (ELISA) or indirect fluorescent antibody (IFA), and reverse transcription polymerase chain reaction (RT-PCR). Because no commercial assays are presently available, these tests are typically performed only in a few specialized laboratories.

Differential diagnosis

Nipah virus disease is difficult to distinguish from a host of other febrile illnesses, at least during its onset. More common causes of viral pneumonia, including adenovirus and influenza, and viral encephalitis, in particular Japanese encephalitis (see this term), which is also transmitted by swine, need to be excluded.

Management and treatment

Patients should be isolated and precautions (face shields, surgical masks, double gloves, surgical gowns and aprons) should be used to prevent nosocomial transmission. As there is presently no antiviral drug available for Nipah virus disease, treatment is supportive. Ribavirin has been used on a few patients but its efficacy for Nipah virus disease has not yet been determined.

Prognosis

The case-fatality varies from 40-70% depending on whether encephalitic or severe manifestations are noted and whether adequate healthcare facilities are available. Advanced age, underlying diabetes, and neurological symptoms confer a poor prognosis.