What is Nipah virus?

What is Nipah virus?

Nipah virus (NiV) is a zoonotic virus that can be transmitted from animals to humans.

Nipah virus infection in humans causes a range of clinical presentations, from asymptomatic infection (subclinical) to acute respiratory infection and fatal encephalitis.

The case fatality rate is estimated at 40% to 75%. This rate can vary by outbreak depending on local capabilities for epidemiological surveillance and clinical management.

Nipah virus can be transmitted to humans from animals (such as bats or pigs), or contaminated foods and can also be transmitted directly from human-to-human.

Fruit bats of the Pteropodidae family are the natural host of Nipah virus.

There is no treatment or vaccine available for either people or animals. The primary treatment for humans is supportive care.

The 2018 review of the WHO list of Blueprint priority diseases indicates that there is an urgent need for accelerated research and development for the Nipah virus.

Although Nipah virus has caused only a few known outbreaks in Asia, it infects a wide range of animals and causes severe disease and death in people, making it a public health concern.

Past Outbreaks

The disease was first identified in 1998 during an outbreak in Malaysia while the virus was isolated in 1999. It is named after a village in Malaysia, Sungai Nipah. Pigs may also be infected, and millions were killed in 1999 to stop the spread of disease. No new outbreaks have been reported in Malaysia since 1999.

It was also recognized in Bangladesh in 2001, and nearly annual outbreaks have occurred in that country since. The disease has also been identified periodically in eastern India.

As of 2013 a total of 582 human cases of Nipah virus are estimated and 50 to 75 percent of those who were infected died.

Other regions may be at risk for infection, as evidence of the virus has been found in the known natural reservoir (Pteropus bat species) and several other bat species in several countries, including Cambodia, Ghana, Indonesia, Madagascar, the Philippines, and Thailand.

In 2018, an outbreak of the disease resulted in at least 13 deaths in the Indian state of Kerala.

Transmission

During the first recognized outbreak in Malaysia, which also affected Singapore, most human infections resulted from direct contact with sick pigs or their contaminated tissues.

Transmission is thought to have occurred via unprotected exposure to secretions from the pigs, or unprotected contact with the tissue of a sick animal.

In subsequent outbreaks in Bangladesh and India, consumption of fruits or fruit products (such as raw date palm juice/ palm toddy) contaminated with urine or saliva from infected fruit bats was the most likely source of infection or using water from wells infested by bats.

Natural Host: Fruit Bats

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 virus(NiV) in domestic animals

Outbreaks of the Nipah virus in pigs and other domestic animals such as horses, goats, sheep, cats and dogs were first reported during the initial Malaysian outbreak in 1999.

The 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 is low except in young piglets.

These symptoms are not dramatically different from other respiratory and neurological illnesses of pigs.

Nipah virus should be suspected if pigs also have an unusual barking cough or if human cases of encephalitis are present.

Human-to-human transmission of Nipah virus has also been reported among family and care givers of infected patients.

During the later outbreaks in Bangladesh and India, Nipah virus spread directly from human-to-human through close contact with people's secretions and excretions.

In Siliguri, India in 2001, transmission of the virus was also reported within a health-care setting, where 75% of cases occurred among hospital staff or visitors.

From 2001 to 2008, around half of reported cases in Bangladesh were due to human-to-human transmission through providing care to infected patients.

Signs and symptoms

Humaninfectionsrangefrom asymptomatic infection to 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 from 4 to 14 days.

However, an incubation period if 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.

Diagnosis

Initial signs and symptoms of Nipah virus infection are nonspecific, and the diagnosis is often not suspected at the time of presentation. 

This can hinder accurate diagnosis and creates challenges in outbreak detection, effective and timely infection control measures, and outbreak response activities.

In addition, the quality, quantity, type, timing of clinical sample collection and the time needed to transfer samples to the laboratory can affect the accuracy of laboratory results.

Nipah virus infection can be diagnosed with clinical history during the acute and convalescent phase of the disease.

The main tests used are real time polymerase chain reaction (RT-PCR) from bodily fluids such as throat swabs, cerebrospinal fluid, urine and blood analysis during acute and convalescent stages of the disease and antibody. 

(IgG and IgM) detection can be done after recovery to confirm Nipah virus infection detection via enzyme-linked immunosorbent assay (ELISA).

Other tests used include polymerase chain reaction (PCR) assay, and virus isolation by cell cultures.

Immunohistochemistry on tissues collected during autopsy also confirms the disease.

Viral RNA can be isolated from the saliva of infected persons.

Treatment

There are currently no drugs or vaccines specific for Nipah virus infection although WHO has identified Nipah as a priority disease for the WHO Research and Development Blueprint. 

Intensive supportive care is recommended to treat severe respiratory and neurologic complications.

Prevention

Controlling Nipah virus in pigs

Currently, there are no vaccines available against Nipah virus. Based on the experience gained during the outbreak of Nipah involving pig farms in 1999, 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 have involved pigs and/or fruit bats, establishing an animal health/wildlife surveillance system, using a One Health approach, to detect Nipah cases is essential in providing early warning for veterinary and human public health authorities.

Reducing the risk of infection in people

In the absence of a vaccine, the only way to reduce or prevent infection in people is by raising awareness of the risk factors and educating people about the measures they can take to reduce exposure to  the Nipah virus.

Public health educational messages should focus on:

Reducing the risk of bat-to-human transmission
.

Efforts to prevent transmission should first focus on decreasing bat access to date palm sap and other fresh food products. Keeping bats away from sap collection sites with protective coverings (such as bamboo sap skirts) may be helpful.

Freshly collected date palm juice should be boiled, and fruits should be thoroughly washed and peeled before consumption. Fruits with sign of bat bites should be discarded.

Bats are known to drink toddy that is collected in open containers, and occasionally urinate in it, which makes it contaminated with the virus. Surveillance and awareness are important for preventing future outbreaks.

Reducing the risk of animal-to-human transmission.

• Gloves and other protective clothing should be worn while handling sick animals or their tissues, and during slaughtering and culling procedures.
• As much as possible, people should avoid being in contact with infected pigs.
• In endemic areas, when establishing new pig farms, considerations should be given to presence of fruit bats in the area and in general, pig feed and pig shed should be protected against bats when feasible.
   

Reducing the risk of human-to-human transmission.

• Close unprotected physical contact with Nipah virus-infected people should be avoided.
• Regular hand washing should be carried out after caring for or visiting sick people.

WHO response
WHO is supporting affected and at-risk countries with technical guidance on how to manage outbreaks of Nipah virus and on how to prevent their occurrence.

Reference:

http://www.who.int/csr/disease/nipah/en/

"WHO Nipah Virus (NiV) Infection". www.who.int. Archived from the original on 18 April 2018. Retrieved 21 May 2018.

Diagnosis Nipah Virus (NiV)". CDC. 20 March 2014. Retrieved 24 May 2018

"Prevention Nipah Virus (NiV)". CDC. 20 March 2014. Retrieved 24 May 2018

"Nipah virus outbreaks in the WHO South-East Asia Region". South-East Asia Regional Office. WHO. Retrieved 23 May 2018