What is Nipah virus?
Nipah virus (NiV) infection is a newly emerging zoonosis that causes severe disease in both animals and humans. The natural host of the virus is fruit bats of the Pteropodidae Family, Pteropus genus. The organism which causes Nipah Virus encephalitis is an RNA virus of the family Paramyxoviridae, genus Henipairus and closely related to Hendra virus. NiV was first identified during an outbreak of disease that took place in Kampung Sungai Nipah, Malaysia in 1998. On this occasion, pigs were the intermediate hosts. In Bangladesh in 2004, humans become infected with NiV as a result of consuming date palm sap that had been contaminated by infected fruit bats. Straw-coloured Fruit Bat (Eidolon helvum) Kasanka National Park, Zambia, in flight.
Pteropus are natural reservoir hosts of the Nipah and Henda viruses. The virus is present in bat urine and potentially, bat feces, saliva and birthing fluid. Transmission of Nipah virus to humans may occur after direct contact with infected bats, infected pigs or from other NiV infected people. The NiV strain identified in this outbreak appeared to have been transmitted initially from bats to pigs, with subsequent spread within pig populations. Incidental human infections resulted after exposure to infected pigs. People to people transmission of Nipah virus in Bangladesh and India have been regularly reported. This is seen mainly in the family and caregiver to infected one.
Fig: Transmission of Nipah virus
Signs and Symptoms
Infection with Nipah virus is associated with encephalitis (inflammation of the brain). After exposure and an incubation period of 5 to 14 days, illness presents with 3-14 days of fever and headache, followed by drowsiness, disorientation and mental confusion. These signs and symptoms can progress to coma within 24-48 hours. Some patients have a respiratory illness during the early part of their infections, and half of the patients showing severe neurological signs showed also pulmonary signs. Latent infections with subsequent reactivation of Nipah virus and death have been reported months and even years after exposure.
Virus isolation attempts and real time polymerase chain reaction (RT-PCR) from throat and nasal swabs, cerebrospinal fluid, urine and blood should be performed in the early stages of disease. Antibody detection by ELISA (IgG and IgM) can be used later on. In fatal cases, immunohistochemistry on tissues collected during autopsy may be the only way to confirm a diagnosis.
Treatment is limited to supportive care. As Nipah virus can be transmitted person-to-person, standard infection control practices and proper barrier nursing techniques are important in preventing hospital-acquired infection. Ribavirin has been in shown to be effective against the viruses in vitro, but human investigations to date have been inconclusive and the clinical usefulness of ribavirin remains uncertain. Passive immunization using a human monoclonal antibody targeting the Nipah G glycoprotein has been evaluated in the post-exposure therapy in the Ferret model and found to be of benefit.
Nipah virus can be prevented by avoiding exposure to sick pigs and bats in endemic areas and avoiding drinking of raw date palm sap. Additional efforts focused on surveillance and awareness will help prevent future outbreaks. Research is needed to better understand the ecology of bats and Nipah virus.
A subunit vaccine, using the Hendra G protein, produces cross-protective antibodies against HENV and NIPH has been recently used in Australia to protect horses against Henda virus. This vaccine offers great potential for Henipahvirus protection in humans as well.