Before May 2018, Nipah virus encephalitis was not the household name it has become today. But the truth is that India has had two deadly brushes with the virus, one in 2001 and the other in 2007. Both the outbreaks claimed 50 lives in total, turning Siliguri and Nadia into ghost towns. This time around, the virus has claimed 18 lives in Kozhikode, Kerala the ground zero of the 2018 outbreak. Seven out of ten afflicted by the encephalitis don’t survive. The ones who do are doomed to suffer from severe neurological disorders and persistent convulsions for life. Without a single drug or treatment in sight, it’s too early to predict the course of the contagion.
In the midst of all the hullaballoo, an uncomfortable truth stares back at us – that perhaps, we have no one to blame but ourselves for unleashing the scourge of Nipah on humankind; that human ambitions coupled with an utter disregard for the environment has led to the rise of zoonotic infections, whether Nipah or Ebola.
Environmental Changes and Zoonotic Diseases
According to the World Health Organization (WHO), “zoonotic diseases are a group of infectious diseases naturally transmitted between animals and humans.” These diseases are transmitted to humans through exposure to infected animals, their products (meat, milk and eggs) or their environment. Approximately 60 percent of emerging human pathogen, are zoonoses in nature.
The human-animal interface is a complex one, affected by climate change, human and natural factors. Although there are many ecological factors contribute to the emergence of zoonotic diseases, the most prominent reason is unchecked population growth and resultant urbanisation. Dr. Om Shrivastava, Consultant of Infectious Diseases and Immunology says, “Rapid urbanisation and deforestation creates closer contact between humans and pathogens through bats, primates and other animals that could become hosts to new viruses.”
Rising temperatures change the dynamics of vectors like mosquitoes, ticks and sandflies. Higher temperatures have a direct effect on mosquitoes, which accelerates their activities like reproduction, feeding and digestion. Pathogens harboured by vectors like mosquitoes also mature faster. Warmer water temperature causes mosquito larvae to develop fasting, increasing the proliferation of vectors in the environment.
Climate change during the mid-14th century spurred the zoonotic disease called Bubonic Plague or The Black Death that killed 50 million people between 1347 and 1353. Even the more recent Ebola outbreak in African countries have been linked to deforestation.
In the case of hantavirus infectious, the rodents harbouring the dreaded virus sought shelter within human habitats since the protective environment provided by the snow was removed. This increased human-rodent interaction, which facilitated the transmission of the virus.
Nipah Virus and the Ecological Link
In the 2015 paper titled Nipah Virus: Effects of Urbanization and Climate Change authors Shweta Rana and Sanjana Singh pose a question: “Nipah Virus has existed in the bats for centuries and this virus has not undergone an evolutionary change, so why did this infection spread only now?”
As per a WHO report on the Nipah virus, bat-related viral infections that can be spread to humans and animals can be attributed to their loss of natural habitats. In Kampung Sungai Nipah, Malayasia, where the first outbreak was reported, rapid and unplanned deforestation of pulpwood drove the virus-carrying bats out of their homes and into human habitats.
According to findings of Indian Space Research Organisation, even in the Western Ghats of Kerala, between 1920 and 1975, the forest cover loss was 62.7 percent. Such a drastic change in the ecology could be one of the contributing factors of zoonotic illnesses like Nipah in the area.
When their homes are destroyed by human activity, the fruit bats are forced out of their homes where they were healthy and at a safe distance from humans. The loss of their habitat makes them stressed and hungry. This, in turn, makes their immune systems weaker and the virus that they are already carrying inside them overruns their body. The excessive viral load is then shed through their urine and saliva, which can enter the human body if the person comes in contact with them.
With the increased vilification of bats in the recent outbreak, people are reacting to these creatures with a mixture of derision and fear. Ecologists fear that this may lead to another pressing problem -- a mass culling of these flying animals. Fruit bats are “keystone species” which plays a crucial and unique role in the ecology. Their furry bodies help in dispersing seeds and pollen; without them, local ecosystems can collapse, compounding the problem.
A combination of unrestrained urbanisation, exploding population deforestation, changing climate conditions, all of which brings animals in close contact with humans, could a reason why the number of zoonotic infections like Ebola, SARS, Chikungunya and Nipah is on the rise. On World Environment Day, the denizens of the blue planet have to reflect on the impact of our choices. Should human progress happen at the cost of altering ecological systems, human health will be shaped by the changing environment, which is illustrated by the recent outbreaks. Way forward, we should focus on better ways to integrate ourselves into the environment instead of the other way round.
(References: Nipah Virus: Effects of Urbanization and Climate Change, Climate-driven introduction of the Black Death and successive plague reintroductions into Europe, The impact of climate change and other factors on zoonotic diseases)