From Bats to Humans: Understanding the Nipah Virus in Kerala

The recent emergence of the bat-borne Nipah virus in the southern Indian state of Kerala has caused concern as six individuals have already been infected, resulting in two deaths. Efforts to contain the virus have involved testing over 700 people, including healthcare workers, and implementing closures of schools, offices, and public-transport networks.

Understanding Nipah

This outbreak is the fourth to impact Kerala in the last five years, with the most recent occurring in 2021. Although these outbreaks typically affect a relatively small geographic area, they can be highly fatal. Scientists are apprehensive that further person-to-person transmission may make the virus more contagious. Nipah virus is known to have a fatality rate of 40% to 75%, depending on the strain. Rajib Ausraful Islam, a veterinary physician specializing in bat-borne pathogens at the International Centre for Diarrhoeal Disease Research, Bangladesh, states that every outbreak raises concerns as it provides an opportunity for the virus to mutate.

Symptoms of Nipah virus infection include fever, vomiting, respiratory issues, and brain inflammation. Although fruit bats are the primary carriers, it can also infect humans and domestic animals such as pigs. The virus spreads through contact with bodily fluids from infected animals or humans. Currently, there are no approved vaccines or treatments, but research is underway to develop potential candidates.

Historically, the first reported outbreak of Nipah virus occurred over two decades ago among pig farmers in Malaysia. It subsequently spread to Singapore through infected pigs, resulting in almost 300 cases and over 100 deaths. Malaysia has not experienced any further outbreaks, but since 2001, Bangladesh and India have seen periodic flare-ups. In Bangladesh, outbreaks occur almost every year and have been linked to the consumption of fermented date-palm sap contaminated with bat urine. Although it is unclear when and how the virus crossed over from bats to humans in the current Kerala outbreak, investigations are ongoing.

Nipah vs. COVID-19

Stephen Luby, an epidemiologist at Stanford University, explains that the strain of Nipah virus circulating in India and Bangladesh differs from the one that caused the Malaysian outbreak. While the Malaysian strain primarily spread from animals to humans, there was minimal transmission between people. Conversely, the strain responsible for the recent Kerala outbreak can transmit from person to person and is significantly more lethal. Danielle Anderson, a virologist at the Royal Melbourne Hospital, reassures that Nipah virus is less likely to spread globally than other animal-borne infections due to its lower person-to-person transmission rate. A study conducted in Bangladesh between 2001 and 2015 found that only about one-third of human infections were passed on to others. Anderson believes that Nipah virus will not have the same global impact as COVID-19.

The high fatality rate of Nipah virus restricts its ability to rapidly spread among populations. Christopher Broder, an expert in emerging infectious diseases, explains that the virus is not inclined to kill all who become infected as it is not in its best interest. The strain currently circulating in Kerala has not undergone significant changes since its emergence in Bangladesh over two decades ago. However, there is a possibility of future outbreaks involving a milder but more contagious strain if the virus mutates. It is also likely that undetected variants are already in circulation.

Preventing Nipah and other bat-borne virus outbreaks relies on improved management of wildlife living close to communities. Andrew Breed, a veterinary epidemiologist, suggests that stress in infected bats can lead to higher shedding of the virus, which increases the risk of transmission to domestic animals and subsequently humans. One approach to prevent future outbreaks is to restore forest areas to provide more habitat for bats, keeping them at a safe distance from humans. Additionally, planting more fruit trees that are appealing to bats but not to humans can help reduce the risk of contaminated food. In this way, it is essential to learn how to coexist safely with bats.