The Government of India lowered the alarm yesterday regarding the "incorrect figures" circulating about cases of Nipah virus disease. It clarified that the situation is contained, after confirming that the nearly 200 people monitored for direct contact have tested negative. "All traced contacts are asymptomatic and have tested negative for Nipah virus disease," detailed in an official statement.
With this, India aims to reassure its Asian neighbors, who have tightened controls on citizens from outbreak areas, in the state of West Bengal, where the two cases were confirmed. Additionally, five cases have been confirmed in Calcutta.
Sílvia Roure, Director of International Health at the Fight against Infections Foundation, and María del Mar Tomás spokesperson for the Spanish Society of Infectious Diseases and Clinical Microbiology (Seimc), address the key points of this emerging pathogen on which "the WHO has focused to ensure that it does not spread beyond localized outbreaks," Tomás emphasizes.
The Nipah virus is a zoonotic virus, meaning a virus whose main reservoir is fruit bats of the genus Pteropus, mainly found in South Asia and Southeast Asia, and sporadically jumps to humans. It belongs to the Paramyxoviridae family. It was first detected in 1998 during an outbreak in Malaysia and Singapore, associated with pig farms.
The clinical presentation in humans is varied, "ranging from asymptomatic infection to acute respiratory illness and even cases of encephalitis," explains Roure. According to data from the World Health Organization, it can have a variable mortality rate between 40 and 75%.
It belongs to the BSL 4 pathogen risk group, the highest level that exists and which includes Ebola, for example, as it is considered a very dangerous emerging virus due to its high mortality rate and the lack of authorized treatment or vaccine.
Tomás from Seimc explains that there are ongoing "vaccine research programs with prototypes in advanced clinical studies, but there is still no approved commercial vaccine."
It is transmitted through direct contact with infected animals or people, or through contact with their fluids or secretions. "Mainly through the ingestion of fruit contaminated by bat saliva or urine, contact with sick pigs, and also through close contact with fluids from an infected person," points out Roure.
The transmission capacity among sick individuals makes healthcare workers a risk group, "as seen in the cases detected in India; these are nosocomial infections acquired in the hospital," explains Tomás.
To verify the type of virus, "tests such as RT-PCR and molecular virology techniques are performed to detect and classify it," explains the Seimc spokesperson.
What are the symptoms of Nipah?
The incubation period is 4 to 14 days, after which the first manifestations such as fever, headache, sore throat, and muscle pain begin. Therefore, "active surveillance in travelers is essential," emphasizes the Seimc microbiologist.
If the infection progresses, more severe symptoms begin, as Tomás enumerates, "it can cause respiratory difficulty, encephalitis with brain inflammation, confusion, drowsiness, and coma."
Why does it generate so much concern?
Because it combines several factors, as Roure lists, because "there are severe symptoms such as encephalitis; a high lethality is estimated; and there is no specific vaccine or treatment."
The WHO prioritizes it due to its significant lethality and "classifies it as a high-priority pathogen due to its epidemic/pandemic potential, high mortality, and its ability to be transmitted among humans under certain conditions," as Tomás states.
This microbiologist points out that it is not a virus that spreads like respiratory viruses with such transmission capacity, "it requires close contact with contaminated fluids or products," she insists.
What should be considered on a global scale?
The virus appears almost every year in areas of South Asia and affects countries with the presence of these bats. However, as Roure details, the global risk is considered very low due to the lack of natural reservoirs in most countries and that in the 27 years since its identification, around 750 human cases have been reported with a limited geographical distribution mainly in Asia (Bangladesh and eastern India).
The risk is very low in Spain and Europe for the general population, as long as controls or active surveillance in travelers are established to prevent the spread of outbreaks.
What are the recurring outbreaks that have occurred in India in recent years like?
India has recorded periodic outbreaks since 2001, especially in West Bengal, considered an endemic area. Tomás explains that "there have been recurrent outbreaks in Asia, especially in India and Bangladesh."
At least ten Indians died in Kerala due to an outbreak in 2018. Two years ago, at least two deaths and three infections were reported in the Kozhikode district of the southern state of Kerala.