Nipah virus (NiV) infection is a newly emerging zoonosis (disease or infection that is naturally transmissible from vertebrate animals to humans) that causes severe disease in both animals and humans.
Nipah virus is closely related to Hendra virus. Both are members of the genus Henipavirus, a new class of virus in the Paramyxoviridae family.
The natural host of the virus are fruit bats of the Pteropodidae Family, Pteropus genus.
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.However, in subsequent NiV outbreaks, there were no intermediate hosts.
In Bangladesh in 2004, humans became infected with NiV as a result of consuming date palm sap that had been contaminated by infected fruit bats.
Human-to-human transmission has also been documented, including in a hospital setting in India.
Human infections range from asymptomatic infection, acute respiratory infection (mild, severe), and fatal encephalitis. Infected people initially develop influenza-like symptoms of fever, headaches, myalgia (muscle pain), vomiting and sore throat. This can be followed by dizziness, drowsiness, altered consciousness, and neurological signs that indicate acute encephalitis. Some people can also experience atypical pneumonia and severe respiratory problems, including acute respiratory distress. Encephalitis and seizures occur in severe cases, progressing to coma within 24 to 48 hours.
The incubation period (interval from infection to the onset of symptoms) is believed to range between from 4-14 days. However an incubation period as long as 45 days has been reported.
Most people who survive acute encephalitis make a full recovery, but long term neurologic conditions have been reported in survivors. Approximately 20% of patients are left with residual neurological consequences such as seizure disorder and personality changes. A small number of people who recover subsequently relapse or develop delayed onset encephalitis.
The case fatality rate is estimated at 40% to 75%; however, this rate can vary by outbreak depending on local capabilities for epidemiological surveillance and clinical management.
Initial signs and symptoms of NiV infection are non-specific and the diagnosis is often not suspected at the time of presentation. This can hinder accurate diagnosis and creates challenges in outbreak detection and institution of effective and timely infection control measures and outbreak response activities.
In addition, clinical sample quality, quantity, type, timing of collection and the time necessary to transfer samples from patients to the laboratory can affect the accuracy of laboratory results.
NiV infection can be diagnosed together with clinical history during the acute and convalescent phase of the disease. Main tests including real time polymerase chain reaction (RT-PCR) from bodily fluids as well as antibody detection via ELISA. Different tests include:
There are currently no drugs or vaccines specific for NiV infection although this is a priority disease on the WHO R&D Blueprint. Intensive supportive care is recommended to treat severe respiratory and neurologic complications.
Fruit bats of the family Pteropodidae – particularly species belonging to the Pteropus genus – are the natural hosts for Nipah virus. There is no apparent disease in fruit bats.
It is assumed that the geographic distribution of Henipaviruses overlaps with that of Pteropus category. This hypothesis was reinforced with the evidence of Henipavirus infection in Pteropus bats from Australia, Bangladesh, Cambodia, China, India, Indonesia, Madagascar, Malaysia, Papua New Guinea, Thailand and Timor-Leste.
African fruit bats of the genus Eidolon, family Pteropodidae, were found positive for antibodies against Nipah and Hendra viruses, indicating that these viruses might be present within the geographic distribution of Pteropodidae bats in Africa.
Nipah outbreaks in pigs and other domestic animals (horses, goats, sheep, cats and dogs) were first reported during the initial Malaysian outbreak in 1999.
Nipah virus is highly contagious in pigs. Pigs are infectious during the incubation period, which lasts from 4 to 14 days.
An infected pig can exhibit no symptoms, but some develop acute feverish illness, labored breathing, and neurological symptoms such as trembling, twitching and muscle spasms. Generally, mortality was low except in young piglets. These symptoms are not dramatically different from other respiratory and neurological illnesses of pigs. Nipah should be suspected if pigs also have an unusual barking cough or if human cases of encephalitis are present.
Controlling Nipah virus in domestic animals
Currently, there are no vaccines available against Nipah virus. Routine and thorough cleaning and disinfection of pig farms (with appropriate detergents) may be effective in preventing infection.
If an outbreak is suspected, the animal premises should be quarantined immediately. Culling of infected animals – with close supervision of burial or incineration of carcasses – may be necessary to reduce the risk of transmission to people. Restricting or banning the movement of animals from infected farms to other areas can reduce the spread of the disease.
As Nipah virus outbreaks in domestic animals have preceded human cases, establishing an animal health surveillance system, using a One Health approach, to detect new cases is essential in providing early warning for veterinary and human public health authorities.
In the absence of a licensed vaccine, the only way to reduce infection in people is by raising awareness of the risk factors and educating people about the measures they can take to reduce exposure to and decrease infection from NiV.
Public health educational messages should focus on the following:
First symptomatic case of Nipah virus infection manifested on 2nd May 2018 near Perambra in Kozhikode district of Kerala. The index case was a 26 - year - old male who initially presented with fever, myalgia and respiratory distress. He died in Calicut Medical College, Kerala within the next few days. Subsequently, four other family members and close contacts were admitted within the next two days, of which three tested positive for Nipah virus at Manipal Centre for Virus Research and were subsequently confirmed at ICMR - National Institute of Virology, Pune.
As on May 31, 2018, there are 19 reported cases (18 lab confirmed). Out of 19 reported cases 17 died, from the two affected districts of Kozhikode and Malappuram in Kerala State. The Kerala State Govt. as well as the Union Ministry of Health & Family Welfare have immediately come into action. Steps taken are as follows:
Advice to people:
The Government of India has issued the following guidelines.