The deadly Nipah virus returns: what danger does it represent?

A new outbreak of the lethal Nipah virus, recorded in the Indian state of Kerala, has set off alarm bells. To date there are six confirmed cases, of which four are under treatment and two have died. Health authorities have been able to establish the point of contact of the last infected person, a 39-year-old man who was in the same private hospital where the first victim of the virus (another 47-year-old man) had sought treatment before dying on December 30. August 2023.

India has witnessed at least five Nipah virus outbreaks since 2001, one in West Bengal and four in Kerala. The government of this country is working to evaluate preventive measures to address the outbreak and has compiled a list with the names of 1,080 people who may have had contact with those affected. Of them, 297 are in the “high risk” category.

For now, authorities have launched mass testing to stop the spread of the virus, restricted public gatherings and closed schools, offices and public transportation. In the outbreak also recorded in the state of Kerala in 2018, of 19 people infected, only two survived.

An extremely dangerous virus

Nipah virus is an emerging zoonotic pathogen that belongs to the genus Henipavirus and the family Paramyxoviridae and that causes severe febrile encephalitis. It has single-stranded RNA of negative polarity. Due to their extremely short generation time and faster evolution, RNA viruses show a higher probability of infecting new host species. They are considered one of the main factors responsible for between 25 and 44% of recent emerging infectious diseases.

Infections with Nipah virus were first described during Pandemic outbreaks that affected pig farmers in Malaysia and Singapore between 1998 and 1999. This episode not only caused almost 300 cases and more than 100 deaths in humans, but also generated a substantial economic impact, as more than one million pigs had to be slaughtered to help control the outbreak. The name of the virus comes from Sungai Nipah, a town on the Malaysian peninsula where pig farmers who became ill with encephalitis lived.

The fatality rate in the various outbreaks recorded to date has varied from 33% to approximately 75%, so we are facing a very dangerous virus. Additionally, it is estimated that 25% of survivors suffer from residual neurological deficits.

Although some cases of Nipah virus infection may be asymptomatic or mild, the majority of those infected experience two main clinical syndromes: encephalitis and predominantly respiratory involvement, both with high mortality. The initial symptoms are similar to those of the flu, with high fever, headache and myalgia. Some patients experience drowsiness, disorientation, and seizures. Many go into comas.

How is it transmitted?

Fruit bats of the genus Pteropus, the so-called flying foxes, are the main reservoirs of the virus and can transmit the pathogen through excrement and saliva. Transmission can occur from bats to humans or through pigs, which are the intermediate hosts, but also from human to human. Spread between people raises concerns that the Nipah virus is capable of causing a new global pandemic.

There are three main transmission routes: consumption of contaminated food, contact with infected human or animal body fluids, and exposure to droplets or aerosols. The usual way of infection in people is through consumption of contaminated food that has been exposed to bats or through direct contact with infected domestic animals – particularly pigs –, probably through mucous membranes.

Contaminated drinks

One of the most likely sources of infection in outbreaks that have occurred in Bangladesh (where the pathogen was first recognized in 2001) and in India is the consumption of date palm juice, very popular in several Asian countries.

Unfortunately, it is also highly appreciated by fruit bats that fly over the plantations at night licking the sap spilled by the palm trees and which the natives collect through a bowl attached to the trunk. These animals are also likely to urinate or defecate near the bowl. Every day, early in the morning, local vendors begin selling fresh, unpasteurized juice, inadvertently causing a potential Nipah virus outbreak.

In the eleven outbreaks that emerged in Bangladesh between 2001 and 2011, 196 people were infected, of whom 150 died. This year, from January 4 to February 13, eleven cases, including eight deaths, were reported in two districts of Bangladesh. That means a fatality rate of 73%.

In the spotlight

Today, the Nipah virus is a worrying threat and has therefore been classified as a Risk Group 4/BSL4 pathogen, the highest that exists.

Additionally, it has been included by the World Health Organization in the research and development plan that identifies diseases and pathogens that may cause a public health emergency and lack effective treatments and vaccines. Currently, such treatments are limited to supportive care, including rest, hydration, and managing symptoms as they appear.

In areas where the pathogen is present and there have been recent outbreaks, people should take into account, among others, the following preventive measures: wash hands regularly with soap and water; avoid contact with sick bats or pigs; avoid areas where bats rest or are active; avoid contact with the blood or body fluids of anyone who may be infected with the virus or who has had contact with an infected person; and do not eat or drink products that may be contaminated by bats, such as raw date palm sap, raw fruit, or fruit that is on the ground.

Treatments and vaccines underway

Fortunately, there are treatments in development and under evaluation that may be useful in combating Nipah virus infections. One of them is the human monoclonal antibody M 102.4, which has completed phase 1 clinical trials and has been used on a compassionate basis (authorized on an exceptional basis), as it has demonstrated positive results.

For its part, the antiviral drug Remdesivir has proven effective in non-human primates when administered as post-exposure prophylaxis and can be complementary to immunotherapeutic treatments.

There are also several vaccines in development. In a trial carried out with African green monkeys, a vaccine based on the ChAdOx1 vector, the same one used by the AstraZeneca vaccine against covid-19, generated a strong humoral and cellular response in the apes from fourteen days after vaccination. initial vaccination.

In addition, another experimental vaccine against the Nipah virus, mRNA-1215, which is based on mRNA, is being tested, with good expectations, in healthy adults between 18 and 60 years old.

And finally, trials are underway with a live, attenuated and recombinant PHV02 vesicular stomatitis virus vector vaccine. Additionally, the International Center for Diarrheal Disease Research in Bangladesh is also studying about 50 Nipah virus survivors to better understand the body’s response to the virus and support vaccine development.

Given the current tools, we may soon have effective strategies to fight the Nipah virus.

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