Nipah Virus

Overview

Nipah virus infection is a zoonotic illness that is transmitted to people from animals, and can also be transmitted through contaminated food or directly from person-to-person. In infected people, it causes a range of illnesses from asymptomatic (subclinical) infection to acute respiratory illness and fatal encephalitis. The virus can also cause severe disease in animals such as pigs, resulting in significant economic losses for farmers.

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.

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) contaminated with urine or saliva from infected fruit bats was the most likely source of infection.

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

Signs and Symptoms

Infection with Nipah virus (NiV) can cause mild to severe disease, including swelling of the brain (encephalitis) and potentially death.

Symptoms typically appear in 4-14 days following exposure to the virus. The illness initially presents as 3-14 days of fever and headache, and often includes signs of respiratory illness, such as cough, sore throat, and difficulty breathing. A phase of brain swelling (encephalitis) may follow, where symptoms can include drowsiness, disorientation, and mental confusion, which can rapidly progress to coma within 24-48 hours.

Symptoms may initially include one or several of the following:

• Fever
• Headache
• Cough
• Sore throat
• Difficulty breathing
• Vomiting

Severe symptoms may follow, such as:

• Disorientation, drowsiness, or confusion
• Seizures
• Coma
• Brain swelling (encephalitis)

The incubation period is from 4 to 14 days but an incubation period as long  as 45 days has been reported.

Most people make a full recovery, although some are left with residual neurological conditions after acute encephalitis. Some cases of relapse have been reported. 

The case fatality rate of Nipah virus infection is estimated at 40–75% but can vary by outbreak depending on surveillance and clinical management in affected areas.

Diagnosis

Nipah virus infection in human central nervous system tissue specimen, credit to CDC PHIL

Nipah virus (NiV) infection can be diagnosed during illness or after recovery. Different tests are available to diagnose NiV infection. During early stages of the illness, laboratory testing can be conducted using real time polymerase chain reaction (RT-PCR) from throat and nasal swabs, cerebrospinal fluid, urine, and blood. Later in the course of illness and after recovery, testing for antibodies is conducted using an enzyme-linked immunosorbent assay (ELISA).

Early diagnosis of NiV infection can be challenging due to the non-specific early symptoms of the illness. However, early detection and diagnosis are critical to increase chances of survival among infected individuals, to prevent transmission to other people, and to manage outbreak response efforts. NiV should be considered for people with symptoms consistent with NiV infection who have been in areas where Nipah is more common, such as Bangladesh or India—particularly if they have a known exposure.

Treatment

There are currently no drugs or vaccines that specifically target Nipah virus infection.

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

Nipah virus 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.

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.

Practice handwashing regularly with soap and water

• Avoid contact with sick bats or pigs
• Avoid areas where bats are known to roost
• Avoid eating or drinking products that could be contaminated by bats, such as raw date palm sap, raw fruit, or fruit that is found on the ground
• Avoid contact with the blood or body fluids of any person known to be infected with NiV

Because NiV can be spread from person-to-person, standard infection control practices and proper barrier nursing techniques are important in preventing hospital-acquired infections (nosocomial transmission) in settings where a patient has confirmed or suspected NiV infection.

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.

1. 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.

2. 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.

3. 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.

Controlling infection in health-care settings

Health-care workers caring for patients with suspected or confirmed infection, or handling specimens from them, should implement standard infection control precautions at all times

As human-to-human transmission has been reported, in particular in health-care settings, contact and droplet precautions should be used in addition to standard precautions. Airborne precautions may be required in certain circumstances.

Samples taken from people and animals with suspected Nipah virus infection should be handled by trained staff working in suitably equipped laboratories.

Who discovered Nipah virus?

In early March 1999, a local medical virologist at the University of Malaya named Dr Chua Kaw Beng finally found the root cause of the infection.

Is there a vaccine for Nipah?

Currently, there are no vaccines licensed for the prevention of Nipah disease. To date, there are no vaccine approved for humans but at least eight experimental preventive candidate vaccines against henipaviruses have been evaluated in preclinical animal models.

Can Nipah virus live in water?

Nipah virus would not be neutralized in well water but it won't also multiply. If the water is boiled, the virus would be destroyed.

How long does Nipah virus survive?

Nipah virus can survive for days in fruit juice or flying-fox urine (22). Since date palm sap is sold and consumed within a few hours of collection, consumers could ingest infectious virus.