Nipah Virus: An Emerging Zoonotic Disease

Nipah Virus: An Emerging Zoonotic Disease
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DR. KHURSHID AHMAD TARIQ

Various infectious diseases are shared between animals and human beings due to close associations between human and animals. These associations are in the form of pets, farming and animal husbandry, hunting, butchering, research, consuming meat, consuming animal contaminated plants and plant products, using animal products, and so on. Such a category of diseases transmitted from animals directly or indirectly to human populations are called as zoonotic diseases. Out of the known human pathogens including viruses, bacteria, protozoa, helminthes and arthropods, more than 60% are zoonotic in nature.
The Nipah virus commonly known as NiV is not a new name in the zoonotic infectious disease list of man. It is an emerging viral infection in human from wild reservoir hosts (fruit bats) with high mortality rate. It is a known cause of encephalitis (acute inflammation of brain) in humans; however, its infections remain restricted to few regions of the world particularly South East Asia. Its infection cases were earlier confused with Japanese encephalitis due to lack of proper diagnosis. However, the improvements in disease diagnostics due to recent technologies led to the identification of this virus. The Nipah virus is named after the village in Malaysia where the person from whom the virus was first isolated died due to this disease in way back in 1999.
Taxonomically NiV is a RNA virus belonging to family Paramyxoviridae. It is one of the emerging zoonotic diseases in man since last decade. In India, the first two outbreaks of Nipah virus encephalitis occurred in 2001 and 2007, both in West Bengal bordering Bangladesh. The last epidemic outbreak of its disease was reported in 2008 from Manikgonj and Rajbari (Bangladesh). This time the Nipah virus outbreak has been reported from Kerala where it has already led to about a dozen human deaths. India and Bangladesh have been recognised as the high risk regions of its infection in the world.
Nipah virus infection was first isolated and described in 1998 from Singapore and Malaysian pig farms and in other domestic animals including horses, goats, sheep, cats and dogs. It was subsequently reported in Bangladesh from the year 2001 onwards with periodic out breaks. Bats belonging to the genus Pteropus commonly known as flying foxes which are frugivorous in habit (eating fruits) are the main natural reservoir of their infection. However, there is no apparent disease reported in fruit bats.
Every time , different strains of this virus are responsible for causing epidemics. Transmission of its infection to humans and other animals generally occurs via bat urine, faeces, respiratory droplets, saliva, nasal secretions or contact with the tissues of a sick animal. Therefore, the fruits on which bats feed become contaminated and are the cause of infection in human beings. We need to be cautious as we consume plenty of dates during Ramadan, so utmost care should be taken while consuming these, as there is every possibility of their contamination by bat secretions and excretions. Research has shown that consumption of fruits or fruit products(raw dates, palm juice) contaminated with urine or saliva from infected fruit bats is the most likely source of infection. Transmission of Nipah virus from human to human occurs by close associations and sharing with infected people. Furthermore, transmission between farms may take place by carrying the virus on clothing, equipment, boots, vehicles and so on.
As of now, the NiV infection is diagnosed through tests including real time polymerase chain reaction (RT-PCR) from bodily fluids as well as antibody detection via ELISA and cell culture to isolate the viruses from human cells. The incubation period (time interval from infection to the onset of symptoms in man) of Nipah virus infection ranges from 4-14 days. Human infections range from asymptomatic infection, acute respiratory infection and fatal encephalitis. Infected people initially develop influenza-like symptoms of fever, headaches, muscle pain, vomiting and sore throat. This can be followed by dizziness, drowsiness, altered consciousness, and neurological signs that indicate acute encephalitis. Encephalitis and seizures occur in severe cases, progressing to coma within 24 to 48 hours. The unmanaged cases lead to immediate death of the victim.
It is already listed in the blueprint priority diseases which were published by World Health Organisation in the month of March. Currently, there are no vaccines and effective drugs available against Nipah virus. The WHO has recently approved the vaccine development in human against this viral infection. Reducing the risk of direct and indirect bat-to-human transmission, animal-to-human transmission and human-to-human transmission are the measures for immediate prevention and control. To conclude, the only way to reduce Nipah virus infection in people is by raising awareness through media and other means of its epidemiology (risk factors and routes of infection) and requisite measures and management to reduce exposure to NiV infection.

The author teaches Zoology at the Islamia College of Science and Commerce, Srinagar. He can be reached at: drkatariq@gmail.com.

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