Health Minister Veena George flagging off the mobile virology lab. Image: Facebook / Veena George
Reappearance of Nipah virus cause for significant concern in Kerala
Large fruit bats of Pteropus genus are the natural reservoir of the Nipah virus. Pigs are identified as intermediate hosts.
Nipah Virus (Niv) infection was recognised as a deadly infection in 1998 with no vaccine or treatment protocol, and received more attention in Kerala with the outbreaks in 2018, 2019, and 2021. This recent one is its fourth comeback, and this zoonotic disease has already claimed 20 lives in the last five years. Nipah is a highly pathogenic RNA virus, belonging to the Paramyxoviridae family and grouped under the genus Henipavirus.
According to the Nipah management plan document prepared by the department of health, Kerala, ‘two NiV clades (a group of organisms) have been proposed so far; B genotype in Bangladesh, and M genotype in Malaysia. The complete NiV genome of the Kerala strain had 85.14 per cent - 96.15 per cent similarity with M and B NiV genotype’.
High mortality rate
The 1998 outbreak in Malaysia claimed the lives of nearly 40 per cent of those affected. Subsequent outbreaks in Bangladesh, beginning in 2001, have exhibited an overall mortality rate of approximately 70 per cent. But contrary to this, the 2018 outbreak of Kozhikode had a mortality rate of around 90 per cent, compelling the researchers to believe that the Kerala strain was even more lethal. But by adapting a swift and effective identification and isolation method, Kerala could contain the disease in a span of 60 days even though 17 valuable lives were lost.
Large fruit bats of Pteropus genus are the natural reservoir of the Nipah virus. Pigs are identified as intermediate hosts. In a study conducted during the outbreak of 2018, the high positivity of Nipah virus was detected in bat throat swabs, and showed persistence of the virus for a couple of hours on contaminated fruits, which enhance the chances of human infection. NiV positivity was identified in bats from the north-eastern states and Kerala.
"The cause behind the majority of encephalitis cases in Kerala remains unidentified. However, with improved infrastructure for intensive care and disease detection post the COVID pandemic, we now have the opportunity to harness these resources to investigate the underlying reasons for the recurring Nipah outbreaks," said Dr KP Aravindan, a pathologist and the former president of the people’s science movement Kerala Sasthra Sahithya Parishad.
Nipah virus present in other parts of India – ICMR study
An ICMR study has detected the presence of the Nipah virus in bats not just in Kerala but also in various other parts of the country. There exists a significant likelihood that Nipah infections might be going undetected in many regions, possibly being mistaken for other fevers or forms of encephalitis. However, the proactive approach in Kerala, possibly due to its distinctive social characteristics, has led to the conduct of tests and the identification of the Nipah virus, observes Dr TS Aneesh, an Associate Professor of community medicine in Government Medical College, Manjeri.
A study conducted by the department of community medicine, Government Medical College, Kozhikode after the first Nipah outbreak had found person-to-person transmission was the key epidemiological feature of the outbreak which occurred in Kozhikode. Transmission occurred mainly in health-care settings and the mortality rate was high. The outbreak was contained by case isolation, early initiation of barrier nursing, infection control practices, contact surveillance, and home quarantine.
The study also stated that the fruit bats are known reservoirs of NiV but the exact mode of transmission from bats to the primary case was unclear. However, the researchers inferred that exposure may have occurred either in the process of cleaning of a bat-infested unused well by the patient zero (index case) or during visits to the nearby forest. Fruit bats were mapped in the area and specimen studies for the virus confirmed from captured bats by animal husbandry and national agencies.
Developmental activities have adverse impact on flora, fauna
A 2022 study published in Journal of Mammalogy that mapped the distribution of bat species in Kerala found 90 per cent of flying fox territory there is unprotected, vulnerable to development. Numerous other recent environmental-impact assessments conducted in Kerala, such as the one for the Silverline semi-high-speed railway project carried out by K-rail, have indicated that developmental activities have had an adverse effect on the state's flora and fauna including that of these flying fox habitats. Zoological experts are concerned that this type of stress on fruit bats could potentially lead to weakening of bats’ ability to fend off viruses, resulting in more and more virus spill overs.
"The Nipah virus first surfaced in Malaysia in 1998, prompted by the devastation of Malaysian forests – the natural habitat of fruit bats. This destruction was a result of the El Nino phenomenon, which forced the bats to seek shelter in human settlements. Factors contributing to epidemics like Nipah include population growth, encroachment into wildlife habitats, alterations in land use patterns, and climate change," observes Dr B Eqbal, former member of Kerala planning board and former vice chancellor of the University of Kerala.
"Based on the studies conducted thus far, it has been determined that Nipah is not a pandemic akin to influenza or COVID, which can be transmitted by asymptomatic carriers. The virus will only spread from individuals exhibiting severe symptoms. The government is taking all the possible precautions to contain the spread of the virus," Health Minister Veena George stated in the Kerala Assembly.
