The National Virology Institute, Pune, confirmed that the contagious fever that has killed several people in Kozhikode and Malappuram districts over the last fortnight is due to Nipah virus ( NiV). Six more people succumbed to symptoms suspected to be that of Nipah virus on Sunday.
It is the first detection in Kerala of the Nipah virus which has a high fatality rate and spreads mainly through bats, pigs and other animals. Its symptoms include fever, vomiting, headache, drowsiness, coma and respiratory problems.
Virus has an incubation period of 4 to 18 days. Health workers need to take the highest level of protection while handling patients. No specific treatment is available but intensive care support is required.
Origion and History of initial identification:
Nipah virus (NiV) is a member of the family Paramyxoviridae, genus Henipavirus. NiV was initially isolated and identified in 1999 during an outbreak of encephalitis and respiratory illness among pig farmers and people with close contact with pigs in Malaysia and Singapore. Its name originated from Sungai Nipah, a village in the Malaysian Peninsula where pig farmers became ill with encephalitis. Given the relatedness of NiV to Hendra virus, bat species were quickly singled out for investigation and flying foxes of the genus Pteropus were subsequently identified as the reservoir for NiV .
In the 1999 outbreak, Nipah virus caused a relatively mild disease in pigs, but nearly 300 human cases with over 100 deaths were reported. In order to stop the outbreak, more than a million pigs were euthanized, causing tremendous trade loss for Malaysia. Since this outbreak, no subsequent cases (in neither swine nor human) have been reported in either Malaysia or Singapore.
In 2001, NiV was again identified as the causative agent in an outbreak of human disease occurring in Bangladesh. Genetic sequencing confirmed this virus as Nipah virus, but a strain different from the one identified in 1999. In the same year, another outbreak was identified retrospectively in Siliguri, India with reports of person-to-person transmission in hospital settings (nosocomial transmission). Unlike the Malaysian NiV outbreak, outbreaks occur almost annually in Bangladesh and have been reported several times in India.
Symptoms and investigation
Nipah virus’s (NiV) symptoms in humans are similar to viral fever such as fever, headache and muscle pain. Perhaps, these symptoms should be taken seriously as they were a part of rare viral fever – identified as the Nipah virus (NiV) – that claimed lives in Kerala.
NiV infection is associated with encephalitis (inflammation of the brain) and can lead to disorientation and mental confusion, or coma in some cases – encephalitis may present as acute or late onset. While the later may be difficult to diagnose, those who may have recovered from an acute episode may also have a relapse.
Since the symptoms of Nipah virus are similar to that of influenza, it can be difficult to determine whether the person is affected by NiV based on symptoms alone. According to WHO, procedures for laboratory diagnosis of Nipah virus include a series of tests – serology, histopathology, PCR and virus isolation. Serum Neutralization Test, ELISA, RT-PCR are used for laboratory confirmation. Also, magnetic resonance of the brain can help differentiate Nipah encephalitis from other encephalitis as well as in defining between acute and late-onset or a relapsed form of the disease.
Prevention and control
Till date, there is no effective vaccine for Nipah virus disease, treatment is mostly focused on managing fever and the neurological symptoms. Ribavarin may help alleviate the symptoms of nausea, vomiting, and convulsions. Severely ill patients require hospitalisation and may require the use of a ventilator. Therapeutics and vaccine are said to be under development.
Adopting standard infection control practices is vital in preventing the spread of person-to-person transmission of the disease. As the main strategy is to prevent NiV in humans, establishing appropriate surveillance systems is necessary to detect the disease outbreaks quickly so that appropriate control measures are initiated in time.
Research is needed to better understand the ecology of bats and Nipah virus, investigating questions such as the seasonality of disease within reproductive cycles of bats. Surveillance tools should include reliable laboratory assays for early detection of disease in communities and livestock, and raising awareness of transmission and symptoms is important in reinforcing standard infection control practices to avoid human-to-human infections in hospital settings (nosocomial infection).
A subunit vaccine, using the Hendra G protein, produces cross-protective antibodies against HENV and NIPV has been recently used in Australia to protect horses against Hendra virus. This vaccine offers great potential for henipavirus protection in humans as well.