“Kerala battered by Covid now on alert for Nipah virus.” - The Times of India September 7, 2021
“Since 70% of people who are infected with Nipah virus die, the risk is that a new strain that is more efficiently transmitted person to person could generate the worst pandemic humanity has ever faced.” - Dr. Stephen Luby, Professor of Medicine (Infectious Diseases), Stanford University
As devastating as SARS-CoV-2 (the virus that causes COVID-19) continues to be, it has a low mortality rate of 2%. In early September, an outbreak of a far more virulent virus called Nipah virus was reported in India. This is especially alarming because the mortality rate of Nipah virus infection is about 70%. As is often the case in infectious diseases, geography—where you live or travel—along with whom and what you’ve contacted are key.
If you live in Kerala, India, and were in contact with the patient who died of Nipah infection or any of his close contacts, or if you’ve recently consumed date palm sap, you have serious cause for concern. For the rest of the world, however, the biggest concern is whether Nipah virus could mutate and cause another pandemic. In this week’s Germ Gems post, I will provide you with a brief overview of Nipah virus infection.
What is Nipah virus and where has it surfaced? Nipah virus is one of an estimated 140 human pathogens that emerged in the past 50 years. It is a type of RNA virus in the genus Henipavirus. It normally circulates among certain species of fruit bats but it can spread both from person to person and from other animals (pigs, in particular) to people. Like SARS-CoV-2, which is also an emerging RNA virus that is zoonotic (passed from animals to humans), Nipah virus arose in Asia, specifically Malaysia.
Nipah is one of the most lethal of all viruses—50-75% of those infected die. Humans infected by Nipah virus typically develop a fever and headache lasting for several days, followed by respiratory symptoms. The condition swiftly progresses to encephalitis (inflammation of the brain) leading to drowsiness, confusion, and then possible coma and death.
In 1998, a team of researchers at the University of Malaysia Faculty of Medicine first identified the disease during an outbreak in the village of Sungai Nipah, Malaysia, which ultimately gave rise to the name “Nipah” virus. The following year, Dr. Chau Kaw Beng and his colleagues, including collaborators at the Center for Disease Control and Prevention, isolated and identified the virus in pigs. Because pigs were identified as a source of human infection, in 1999 the Malaysian authorities slaughtered millions of pigs to stop the spread of disease—a measure that proved to be successful. Nonetheless, in this outbreak, nearly 300 human cases occurred with over 100 deaths among abattoir workers alone.
In the 21 years since its discovery in Malaysia, the geographical range of human cases of Nipah has continued to grow with outbreaks occurring in Bangladesh, India, and the Philippines. Multiple spillover events occurred in these countries from fruit bats. Human consumption of raw or fermented date palm sap that was contaminated with the urine or saliva of infected bats also played a role in some of these outbreaks.
In 2018, there was an outbreak of Nipah in Kerala, India, and only two of the 19 infected people survived. Therefore, in early September 2021 when it was reported that a 12 year-old boy had died of Nipah, panic ensued. Authorities quickly sealed off an area within a two-mile radius of the boy’s home. They also identified 188 people who had come in contact with the boy. Many of these people were hospitalized or held under strict quarantine. These measures seem to have worked. A risk assessment by the World Health Organization (WHO) on September 24 concluded: “India has experienced and contained Nipah virus disease outbreaks in the past and has demonstrated the capacity to carry out outbreak control activities, including case identification, laboratory testing, case management, contact tracing and risk communication. This event is an isolated case and the risk is low at a national level and low at the regional level.”
How to prevent Nipah virus infection. Spillovers of the Nipah virus from animals, such as bats and pigs, can usually be avoided. But it is the capacity of Nipah virus to be transmitted from person to person that has caused the WHO to list Nipah virus as one of the most dangerous emerging viruses.
While only about 10% of Nipah patients transmit the virus to others, transmission is highly variable and super-spreaders have infected dozens of people. Close care-givers are at highest risk for acquiring the infection, which most likely occurs through contact with respiratory secretions. In hospitalized patients, strict infection control strategies are therefore essential.
In a Journal of Infectious Diseases article in May 2020, “Twenty Years of Nipah Virus Research: Where Do We Go From Here?,” Emily Gurley, a Professor of Epidemiology at the Johns Hopkins Bloomberg School of Public Health, points to investments in promising vaccines as a high priority strategy in the prevention of Nipah virus infection. Given the recent success of RNA vaccines in preventing SARS-CoV-2 infection, researchers are also working on a vaccine strategy for Nipah virus (see https://www.gavi.org/vaccineswork/next-pandemic/nipah-virus). Also, in parallel with research on antivirals for SARS-CoV-2, a monoclonal antibody, m102.4, and remdesivir have shown promise in treating Nipah virus infection in non-human primates research models.
Will climate change play a role? An additional and potentially much bigger challenge for the prevention of the spread of Nipah virus beyond its current, geographical borders is climate change. Scientists warn that as the climate warms and humans destroy more natural habitats of species like the fruit bats in Asia, opportunities increase for new zoonotic variants of Nipah virus to emerge. According to Emily Gurley, “new henipaviruses continue to be discovered, including Cedar, Mojiang, and Ghanaian bat viruses. . . . These newly discovered henipaviruses, have radically expanded our understanding of the geographic range of henipaviruses, which now extends into the Far East and Africa.”
Emerging infections constantly remind us of our interdependence on other animals and the environment. In his book, “Spillover: Animal Infections and the Next Human Pandemic,” David Quammen put it this way, “People and gorillas, horses and duikers and pigs, monkeys and chimps and bats and viruses: We’re all in this together.” I couldn’t agree more, and it is crucial that humans maintain this perspective as we work to address the related crises in global health and climate change.
