Nipah has sparked a health crisis in southern India. Here's what we know about this deadly virus

The Indian state of Keralais battling its fourth outbreak of the Nipah virus since 2018. Two people have died and nearly 800 people have been tested over the last 48 hours in the state's district of Kozhikode.

Two adults and a child are in hospital for observation after testing positive.

It is listed by the World Health Organization (WHO) among thethose deemed to pose the greatest public health risk due to their epidemic potential anda lackofsufficient countermeasures.

Here's a look at what is known about the virusand whether people in Canada should be worried.

What is Nipahvirus?

Nipah is a zoonotic virus, meaning it can be transmittedbetween animals and humansbut can also spread through contaminated food orfrom human to human.

Itkills 40 to 75 per cent of people who become infected, according to the health organization.

Nipah was first identified in 1999 in pig farmers in Malaysia and Singapore. Most of those cases result from farmers coming into direct contact with their sick pigs or with contaminated pig tissues. About 300 people were confirmed infected and 100 people died.

There has not been another known outbreak in either country since, according to the U.S. Centers for Disease Control (CDC).

In 2001, Nipah was first identified in Bangladesh.Since then, the country has experienced yearly outbreaks, with cases generally occurring between December and May, according to WHO.

It's believed the infections in Bangladesh are caused bypeople consumingfruit or fruit products like raw date palm juice or date palm sapthat hasbecome contaminated by the urine or saliva of the fruit bats that feed on thesap.

According to WHO, the fruit bat is considered a natural host of the virus. Fruit bats from Kerala tested positive for the Nipah virus during the state's first outbreak in 2018, which killed 21 of the 23 people infected.

Subsequent outbreaks in Kerala, in 2019 and 2021, killed two people.

In the face of the current outbreak in the state, samples of bat urine, animal droppings and half-eaten fruit have been collected from the village of Maruthonkara, where thefirst victim of this outbreak lived. The community islocated beside a 120-hectare forest thatis home toseveral bat species.

"We are testing human beings ... and at the same time, experts are collecting fluid samples from forested areas that could be the hotspot for the spread," Veena George, Kerala'shealth minister, told Reuters.

About 800 people have already been tested in the past week, with at least 77 deemed as being at high risk for infection, according to George.

A Canadian government fact sheet about the virus says Nipah has never been found in Canada.

What are the symptoms?

Some people infected with Nipah can be asymptomatic, a complicationthatWHO says can hinder diagnosis and create "challenges in outbreak detection, effective and timely infection control measures, and outbreak response."

Initial symptoms of Nipahcan also benon-specific, and the diagnosis is often not immediately suspected at the time of presentation.

Symptoms usually occur four to 14 days after exposure and includefever, headache, and respiratory ailments such as sore throat, cough and difficulty breathing,according to the CDC.

In more serious cases, brain swelling (encephalitis) occurs, with patients falling into a coma within 48 hours. Though people who develop symptoms of encephalitis from Nipah can recover, the CDC says they can experience long-term effects, including convulsions and personality changes.

The CDC says there have also been deaths from Nipah months or even years after exposure.

How is it treated?

There is no drug treatment or vaccine for Nipah.

"This is what we would call a neglected tropical disease," said Dr. Isaac Bogoch, an infectious diseases specialist at Toronto General Hospitalwho specializes in tropical disease and global health. He was speaking to CBC from Tasmania where he is presenting at a conference.

"It impacts parts of the world that are lower resourced. And if you have limited funding and research dollars that are primarily spent in high-income countries, this is just not a priority unfortunately."

That means current treatment is limited to supportive care hydration, rest and treatment of respiratory and neurological symptoms.

According to the CDC, there are immunotherapeutic treatments (monoclonal antibody therapies) under development for Nipah. One has completed its first phase of clinical trials and been prescribed on a compassionate use basis.

Where are the current confirmed cases?

The current outbreak is in the southern Indian state of Kerala, in the district of Kozhikode.

Public offices, government buildings, schools and religious institutions have been closed in nine villages of the district. Public transport has been suspended.

The neighbouring states of Karnataka and Tamil Nadu have ordered tests for visitors from Keralaand planto isolate anywho show symptoms that could be associated with the virus.

Is there concern about wider spread?

Bogoch said this isn't the type of virus that sweeps through communitieslike a COVID-19, for example because it requires veryclose contact with an infected individual.

"There have been outbreaks of the virus for decades," he said. "They're all sad, they're frequently deadly, but they're rarely large."

Still,BogochcallsNipaha global problem that warrants attentionbecause it is carried by an animal that lives in many parts of the world.

"If you look at where the bat home range is, it's massive," he said. "There are lots of areas for potential spillover events and lots of people living in the area of the geographic range of the bat. And many of these areas are not well-equipped to rapidly detect and respond to cases."

WATCH | Efforts to slow the spread of Nipah in India:

Efforts to control Nipah infection in Kerala

12 months ago

Duration 1:05

Authorities have shut down schools, government offices and religious institutions and set up road blocks in parts of Kerala, as the southern Indian state battles its fourth outbreak since 2018 of the deadly Nipah virus.

Can further outbreaksbe prevented?

Nipah is not a virus that is likely to be eliminated, according to Bogoch, and there will continue to be what are called spillover events or transmission between species.

The keys to lessening Nipah's deadly impact are to reduce the number of those spillover events, have early recognition of the virus by health-care workers,offer good supportive care for patients, andwork to limit secondary infections, he said.

"Through community education, through early detection, through use of personal protective equipmentand maybe in the futurethrough vaccination, all of those goals could be accomplished," said Bogoch.