New Disease – Nipah Virus Encephalitis

Dr KK Aggarwal
Padma Shri Awardee
Vice President CMAAO
President HCFI

The cause of death of two people, ostensibly suffering from fever, in Kozhikode has been confirmed to be due to the Nipah virus (NiV), spread by fruit bats and which caused severe disease in both animals and humans. The virus has been confirmed by the National Institute of Virology, Pune.

Transmission of Nipah virus takes place through direct contact with infected bats or from other NiV-infected people and people have been also cautioned that they should not consume fruits that have fallen to the ground.

Nipah virus caused an outbreak in pigs and humans in Malaysia and Singapore between 1998 and 1999, and has caused recurrent human outbreaks in Bangladesh and West Bengal, India since 2001.

Nipah virus was initially discovered when it caused an outbreak of viral encephalitis among pig farmers in Malaysia. The virus was named after a village in Malaysia, where the infected patient lived. Since then, there have been several outbreaks of acute Nipah encephalitis in various districts in Bangladesh, in the neighboring district of Siliguri in India, and in the Southern Philippines

The natural host is believed to be fruit bats of the Pteropus species, four of which have been demonstrated to have serologic evidence of infection with this virus. The virus has also been isolated from fetal tissue and uterine fluids of these bats

Nipah and Hendra viruses are two related zoonotic pathogens that have emerged in the Asia-Pacific region. Both are RNA viruses that belong to the Paramyxoviridae family.
The viruses jump the species barrier and infect a secondary animal host (eg, pigs or horses), and transmit infections to humans. In addition, the Nipah virus may be able to spread from human to human.

Nipah virus primarily causes an encephalitic syndrome with a high mortality rate. The characteristic MRI abnormalities are multiple, small (less than 5 mm), asymmetric focal lesions in the subcortical and deep white matter without surrounding edema.

The incubation period ranges from 7 to 40 days. The initial presentation is non-specific, characterized by the sudden onset of fever, headache, myalgia, nausea and vomiting. Meningismus is seen in approximately one-third of patients although marked nuchal rigidity and photophobia are uncommon. Patients infected with Hendra virus have presented with fever and influenza like illnesses, or with meningoencephalitis.

The diagnosis of Nipah virus can be established using an enzyme-linked immunoassay (ELISA). Supportive care is the mainstay of treatment and infected patients may require intensive care monitoring.

In the Malaysian outbreak, anti-thrombotic agents, aspirin and pentoxyfylline, were administered in some patients based upon the recognition that arterial thrombosis may play an important role in the CNS disease.

Ribavirin, a nucleoside analogue, was also given empirically as it has a broad spectrum of activity against RNA and DNA viruses. In the Malaysian outbreak, 140 treated patients were compared to 54 control patients who did not receive ribavirin. Fewer treated patients died (32 percent versus 54 percent) . However, treated patients were identified later in the outbreak so it is possible that they were given better general medical care compared to untreated patients seen earlier. Subsequent animal models found that ribavirin, as well as chloroquine, were ineffective.