STORY SO FAR: Kerala has reported a fatality from a case of infection by the Nipah virus in the northern district of Kozhikode bringing back memories of the chaos in May-June 2018 when the same district reported 18 confirmed cases of which there were 17 laboratory-confirmed deaths. It’s the high mortality associated with the virus that triggered panic across the State and the country and when it was controlled the State’s healthcare surveillance system came in for praise though, as it turned out, it was only a test-run for the pandemic of 2020.
What do we know about Nipah virus outbreaks?
The human Nipah virus, as it is called, is classified as an “emerging zoonotic disease”, meaning that it can transfer to people after being incubated in other species. It was first recognised in a large outbreak of 276 cases in Malaysia and Singapore from September 1998-1999.
Prior to the Kerala outbreak of 2018, there have been several Nipah virus outbreaks in Bangladesh with spillovers into India particularly in 2001 and 2007 at Siliguri and Nadia in West Bengal. During the outbreak in Siliguri, 33 health workers and hospital visitors became ill after exposure to patients hospitalised with Nipah virus illness. At least 70 people died in the outbreaks in these two districts. In the 2018 outbreak in Kerala, four from the family of the first person confirmed with the infection succumbed to the viral disease.
How does the Nipah virus originate and spread?
Nipah virus (NiV) is classified as a “highly pathogenic paramyxovirus” and handling the virus requires the highest grade of facilities called BS-4. The natural reservoir for the virus are large fruit bats of Pteropus genus. From here the virus may pass on to pigs who may be infected after eating fruits that are bitten on by infected bats.
The initial outbreaks were reported among pig breeders whereas in Bangladesh the virus was suspected to have jumped to humans who directly consumed fruits that may have been contaminated by bat saliva or urine. The virus takes from 6-21 days to incubate and manifest as disease.
Drinking of raw date palm sap contaminated with NiV and close physical contact with Nipah-infected patients are believed to be the two main modes of spread. The person-to person transmission may occur from close physical contact, especially by contact with body fluids.
Unlike in the case of the novel coronavirus which is more airborne and can spread among great distances, the Nipah virus isn’t a very efficient spreader. Contact with body fluids and an infected person’s respiratory droplets, that aren’t expected to travel very far, are said to be the main sources of spread which explains why close family members in a house are said to be at highest risk along with the infection spreading in hospital settings between patients.
In pictures: Nipah’s deadly grip on Kozhikode
What are the symptoms of the disease and how is it diagnosed?
Fever, delirium, severe weakness, headache, respiratory distress, cough, vomiting, muscle pain, convulsion, diarrhoea are the main associated symptoms. In infected people, Nipah virus causes severe illness characterised by inflammation of the brain (encephalitis) or respiratory diseases which is why it is associated with a high fatality rate. Because of the lethality of the virus, very few labs such as the Pune-based National Institute of Virology are equipped to confirm it by isolating the virus.
Antibody tests that detect the presence of antibodies in the serum of cerebrospinal fluid can be used to detect infection or the RNA of the virus can be detected from respiratory secretions, urine or cerebrospinal fluid.
What treatment exists?
Currently there is no known treatment or vaccine available for either people or animals. Ribavirin, an antiviral may have a role in reducing mortality among patients with encephalitis caused by Nipah virus disease, according to a fact sheet by the National Centre for Disease Control.
The thrust of treatment relies on managing symptoms.
There are, however, immunotherapeutic treatments (monoclonal antibody therapies) that are currently under development and evaluation for treatment of NiV infections. One such monoclonal antibody, m102.4, has completed phase 1 clinical trials and has been used on a compassionate use basis. In addition, the antiviral treatment remdesivir has been effective in nonhuman primates when given as post-exposure prophylaxis, according to the U.S. Centres for Disease Control. There are no approved vaccines or even test-vaccines as part of human trials for the virus.
