Rapid urbanization and climate change have caused humans and animals, including bats, to come in contact more frequently, leading to outbreaks of Nipah Virus encephalitis
New Delhi: Rapid urbanization, coupled with changing climate in recent years, has played a key role in triggering the re-emergence of Nipah Virus in India. When health officials and scientists are busy in containing the Nipah Virus infection in Kerala that has already claimed over 10 lives, health and natural science experts are attempting to look at the reasons why the virus has emerged in India after 2001 and 2007.
“We are looking at the causes of the re-emergence of the virus. Specialized team at our strong network of laboratories are trying to find out the causes of outbreak," said A.C. Dhariwal, adviser, National Vector Borne Disease Control Programme. “India is witnessing a rapid urbanization and animals and birds including bats are losing their natural habitats. In recent years, humans are animals are coming in contact with each other which is also causing outbreak of diseases such as Nipah," he said.
The virus is named after the Malaysian village where it was first discovered and belongs to Henipavirus in the subfamily Paramyxovirinae. The major symptoms of the infection are fever, dizziness, headache and vomiting. Doctors say that the virus is capable of human to human transmission who are staying in close proximity.
According to World Health Organization (WHO), Nipah virus was first identified during an outbreak of disease that took place in Malaysia in 1998. Both animal-to-human and human-to-human transmission have been documented. From 1998 to 2015, more than 600 cases of Nipah virus human infections were reported. Subsequent outbreaks in India and Bangladesh have occurred with high case fatality. The first identification of Nipah virus as a cause of an outbreak of encephalitis was reported in 2001 in Meherpur district of Bangladesh. Since then, outbreaks of Nipah virus encephalitis have been reported almost every year in selected districts of Bangladesh.
India reported two outbreaks of Nipah virus encephalitis in the eastern state of West Bengal, bordering Bangladesh, in 2001 and 2007. Around 71 cases with 50 deaths (70% of the cases) were reported in two outbreaks. During January and February 2001, an outbreak of febrile illness with neurological symptoms was observed in Siliguri, West Bengal. A second outbreak was reported in 2007 in Nadia district of West Bengal. Around 30 cases of fever with acute respiratory distress and/or neurological symptoms were reported and five cases were fatal. All five fatal cases were found to be positive for NiV. In 2007 outbreak, a horde of bats were observed hanging from the trees around a patients’ residence which suggests direct contact of the liquor with bat fluids.
“In Malaysia NiV was first transmitted to pigs and from pigs to humans, however in Bangladesh and India NiV travelled directly from bats to humans. Even though humans and bats have co-existed for long, known cases of NiV are recent. In India and Bangladesh it has been found that the virus spreads through the consumption of date palm sap that is contaminated by bat urine or saliva," said Sanjana Singh, an environmental science expert who has studied Nipah virus and climate change closely. Her research paper , Nipah Virus: Effects of Urbanization and Climate Change, was showcased at the 3rd International Conference on Biological, Chemical and Environmental Sciences in 2015 in Malaysia.
Environmental experts claim that Nipah Virus has existed in the bats for centuries and this virus has not undergone an evolutionary change, but the question had deepened that why did this infection spread only now.
“There are many ecological factors that contribute to the emergence of Nipah virus, however the most prominent is human intervention into the bat infested areas due to rapid urbanization. In Malaysia the virus spread due to unplanned deforestation of pulp wood, which is the natural habitat for NiV carrying bats, and mismanagement of large piggeries," said Singh.
“The increase in the human-bat interaction could be one reason why the NiV outbreak occurred in Bangladesh and India where humans got this virus from drinking date palm juice contaminated by bat urine or saliva," she said.
The availability of data on the Siliguri and Nadia are less and hence the effects of Urbanization and Climate Change on these regions are unknown. However due to their proximity to the Nipah Belt‘ of Bangladesh there is high possibility of NiV travelling to India due to spill-over effect in Bangladesh. This doesn‘t only raise questions towards wildlife surveillance but also displays the potent interconnectedness of events in neighboring countries, Singh argues.
As till now there is no vaccine for prevention or cure and treatment is limited to supportive care, Nipah virus is one of the pathogens in the WHO Research & Development (R&D) Blueprint list of epidemic threats needing urgent R&D action. The Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, with support from the Wellcome Trust and in collaboration with the WHO, has been tasked with facilitating the collaborative development of a draft “Nipah R&D Roadmap".
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