Research finds that bats carry Nipah virus across Bangladesh and can shed the virus at any time of the year
While the country is still grappling with the first wave of the novel coronavirus and preparing for a possible second wave of the infection, the threat of a Nipah virus (NiV) epidemic is looming large over it.
The deadly virus that caused repeated outbreaks in the country, with a fatality rate greater than 70%, has the likelihood of spreading not only in the Nipah belt but across the country as well, according to a recent study.
Claiming that the strain of the virus has changed over the years, the study says NiV could cause another epidemic in Bangladesh, India and other South Asian countries.
The study, entitled "Nipah virus dynamics in bats and implications for spillover to humans", was published in The Proceedings of the National Academy of Sciences (PANS) of the United States on 2 November this year.
The six-year study by EcoHealth Alliance – a non-governmental organisation which protects people, animals and the environment from emerging infectious diseases – was conducted from January 2006 to November 2012.
Research shows that outbreaks in bats are driven by increased population density, loss of immunity over time, and viral recrudescence, resulting in multiyear inter epizootic periods.
Even though incidence is low, bats carry NiV across Bangladesh and can shed the virus at any time of the year, it says, highlighting the importance of routes of transmission to the timing and location of human NiV outbreaks.
According to the research report --- edited by Dr Anthony Fauci, renowned infectious disease specialist and director of the National Institute of Allergy and Infectious Diseases in the US --- NiV cases in Bangladesh have shown more strain diversity than in Malaysia, which could be due to greater virus diversity.
Human NiV infections have been identified in India, Bangladesh, Malaysia, Singapore and the Philippines, it added.
Previous studies said human outbreaks occur almost annually in Bangladesh, and the seasonal timing (November to April) and spatial distribution of outbreaks coincide with patterns of raw date-palm-sap consumption in a region termed the "Nipah belt"(Meherpur, Naogaon, Rajbari, Faridpur, Tangail, Thakurgaon, Kushtia, Manikganj, Rajshahi, and Lalmonirhat).
But new findings suggest that NiV can be shed by bats at any time of the year and that viral dynamics are cyclical, but not annual or seasonal.
In Bangladesh, infection occurs when people drink date-palm sap contaminated with bat excreta.
Bangladesh first identified NiV cases in 2001.
In the last 20 years Bangladesh recorded 319 cases of the virus infection. Of them, 225 or 70.53% have died.
This year, six cases have been recorded, while four of them have died so far.
Professor Dr Mahmudur Rahman, one of the researchers of the PANS study, told The Business Standard that the Nipah virus spreads to all parts of the country through bats.
Mentioning that transmission of the Nipah virus from bats to human beings happens through contact, he said, "Nipah virus is spread in our country through date-palm juice. Bats carry NiV across the country, giving rise to a risk of the virus being spread among people of all regions. Increased contact with bats increases the risk of contracting the virus."
"People living around a place where bats live can also be infected with the virus after getting in contact with bats' urine and stool. The risk of the Nipah virus has increased due to the density of bats and the proximity of humans to bats," he added.
Mahmudur Rahman, who is a member of the WHO's taskforce on Nipah virus research and development, said the case fatality rate of NiV infection is considerably high.
The death rate from Ebola is not so high, he continued.
"We find that Nipah virus outbreaks have occurred almost every two years. The outbreak of the virus is more common in winter, mainly from November to April, as people drink raw date juice at this time," he said.
He also advised people to refrain from drinking raw date juice to stay safe from the infection.
"Drinking date juice is not necessary for us. Official advice has been given not to drink raw date juice. There is no alternative to this. Because the disease has such a high mortality rate, we can't advise people to drink date juice even after collecting it safely."
Currently, there is no drug or vaccine specific for Nipah virus infection, even though the WHO has identified it as a priority disease for the WHO Research and Development Blueprint.
According to sources at the Institute of Epidemiology, Disease Control and Research (IEDCR), the ICDDRB and the IEDCR are working to monitor the outbreak of the Nipah virus in the country.
Surveillance activities have been strengthened during the winter season, they said, adding that samples are collected from every case among those who are admitted to hospitals with encephalitis in the surveillance site.
They further said that the surveillance sites are now being expanded in Barisal and Sylhet.
Dr ASM Alamgir, principal scientific officer of the IEDCR, said bats now move everywhere in the country and so the Nipah virus is no longer confined to the Nipah belt.
"Our surveillance sites are being further expanded. Symptoms of Nipah include headache, convulsions, delirium, and shortness of breath in some cases. If one develops any such symptom, one should inform the IEDCR of this by dialing the hotline number.
Referring to the fact that there is no vaccine or specific treatment for Nipah, he urged people not to drink raw date juice in order to prevent NiV contraction.
"Precaution and awareness are the keys to preventing and controlling this disease," he concluded.