Date Palm Sap Collection – Credit FAO
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Earlier this week, in EID Journal: Nipah Virus Exposure in Domestic and Peridomestic Animals Living in Human Outbreak Sites, Bangladesh, 2013–2015, we looked at a study looking for potential animal vectors of the Nipah virus - a henipavirus carried by fruit bats in Southeast Asia and the Indian Subcontinent - that has sparked sporadic, and deadly (70%-90% fatal) outbreaks over the past 25 years.
Outbreaks often occur between December and May - which is date palm sap harvesting season - as infected bats often roost at night at the top of date palm trees, and collection containers (see photo above) can become contaminated with bat saliva and feces.
There are other routes of infection, as we saw in Malaysia in 1998 when the spread first from bat to pigs - and then from pigs to humans - eventually infecting at least 265 people, killing 105 (see Lessons from the Nipah virus outbreak in Malaysia).
Human-to-human transmission has also been reported, as in India in 2018 (see Nipah Transmission In Kerala Outbreak) where we saw apparently robust household and nosocomial transmission of the virus in Southern India, eventually infecting 19 people.Recent outbreaks in India have highlighted the risks of a seeing a large urban outbreak of Nipah - similar to what we saw with Ebola in West Africa in 2014-2015 (see Enhancing preparation for large Nipah outbreaks beyond Bangladesh: Preventing a tragedy like Ebola in West Africa by Halsie Donaldson, Daniel Lucey).
In 2018 WHO added Nipah (and other henipaviruses) to their List Of Blueprint Priority Diseases; 8 disease threats in need of urgent accelerated research and development. An updated list is expected later this year.
Although the number of Nipah cases reported out of Bangladesh has dropped in recent years (while the number in India has grown), this year they are reporting a resurgence of the virus (see Lisa Schnirring's CIDRAP report Bangladesh reports more Nipah virus cases).
In 2019, the CDC ranked Nipah as #20 (out of 56) Zoonotic Diseases Of Most Concern In The United States, well ahead of MERS-CoV (#27), Lassa Fever (#39) and Monkeypox (#29).
This weekend local media are reporting on a press conference by Health Minister Zahid Malek, quoting him as saying:
'Nipah virus is a deadly virus. The death rate of this virus is 75 percent. There is no vaccine, no medicine and no treatment for this virus. So we have to be careful. Nipah is spread through fruit and palm sap eaten by bats. So we have to be careful not to consume date palm juice.'
'8 people have been infected with Nipah virus in our country this time. 5 of them have died. There are no new cases. 25-bed units have been opened in 2 hospitals for Nipah virus and 28 districts have been alerted.'
Yesterday the Business Standard, in Major Nipah outbreak feared as infections hit eight-year high, is unofficially reporting a 9th infection, and indicated that `several patients have been admitted to hospitals' with `Nipah symptoms'.
Since only limited human-to-human spread has been reported with Nipah, this outbreak is unlikely to spread widely, but each human infection provides the virus with additional opportunities to better adapt to human hosts, and potentially increase its threat.
On Friday, in their weekly bulletin (Communicable Disease Threats Report Week 5, 30 January - 5 February 2023) the ECDC published the following update and risk assessment. I'll have a brief postscript after the break.
11. Nipah virus - Bangladesh - 2023Overview:Summary: On 29 January 2023, media reports quoting health authorities in Bangladesh reported that eight people have been infected with Nipah virus (NiV) in Bangladesh, including the deaths of at least three adults and two children. All victims had histories of drinking date juice. Of the five deaths, two were from Goalanda and Baliakandi upazilas in Rajbari, one is from Godagari in Rajshahi, one was from Naogaon in Sadar, and one was from Ishwardi upazila in Pabna.In Bangladesh, bats are the carriers of Nipah virus. The usual route of infection for humans is through the consumption of date or palm juice. Bangladesh authorities urged people to avoid date juice, according to the same media report. Since 2001, Bangladesh has reported 333 cases including 235 deaths (CFR: 71%), according to the Institute of Epidemiology, Disease Control and Research.Background: Nipah virus is a zoonotic virus of the family Paramyxoviridae, genus Henipavirus which can be transmitted to humans via contact with animals (such as bats, pigs), direct human-to-human contact, and consumption of contaminated food. Fruit bats in the Pteropodidae family are the natural host of the Nipah virus.NiV infection can cause mild to severe disease with symptoms typically appearing four to 14 days following exposure to the virus. However, incubation periods as long as 45 days have been previously reported. Initial symptoms including fever, headache, myalgia, vomiting, sore throat, and difficulty breathing, and can be followed by more severe symptoms, such as disorientation, drowsiness, altered consciousness, and neurological signs that indicate acute encephalitis.The case fatality usually ranges between 40 and 75% but can be higher depending on the NiV strain, the severity of the disease and the availability of adequate and high-quality healthcare facilities.NiV was first isolated and identified in 1999 during an outbreak in Malaysia and Singapore. Since the initial detection, three countries described single or sporadic reoccurring outbreaks: Bangladesh, India and the Philippines.In Bangladesh and India, the most likely sources of infection were fruits or fruit products (such as raw date palm juice) contaminated with urine or saliva from infected fruit bats. Human-to-human transmission was also reported.Nipah is one of the nine priority diseases that WHO has assessed to pose the greatest public health risk due to their epidemic potential and/or where there is no or insufficient countermeasures.Sources: Nipah Virus Distribution Map | Nipah Virus (NiV) , CDC, Nipah virus (who.int)ECDC assessment: The likelihood of exposure and infection by NiV for EU/EEA citizens travelling or residing in Bangladesh is currently very low. As a general precaution, EU/EEA travellers and residents in Bangladesh should not handle domestic or wild animals and avoid contact with their excreta. The virus may be present on food items contaminated by bats; washing, peeling, and cooking fruit and vegetables before consumption is generally recommended. Raw date palm sap (juice) should not be consumed.Although the disease is severe with a high fatality rate, the likelihood of exposure and infection by NiV for EU/EEA citizens travelling or residing in Bangladesh is currently very low. As a result, the risk of infection by NiV for EU/EEA citizens travelling or residing in Bangladesh is currently very low.
The most likely route of introduction of the virus into the EU/EEA would be via infected travellers. While importation of the virus cannot be excluded, it is currently very unlikely to occur. Should a case be imported, nonetheless, the likelihood of spread of the virus within the EU/EEA is considered to be very low.
It should be highlighted that the natural reservoir host of NiV is not native to Europe. As stated above, the risk for the EU/EEA is considered to be very low. The laboratory network EVD-LabNet has mapped the capability of its network members for the diagnosis of NiV infections and the result is available in EVD-LabNet directory. Eleven countries within the EU/EEA can perform laboratory diagnostics for NiV infection.
Actions: ECDC monitors this event through its epidemic intelligence activities.
There are two other henipaviruses we also follow with interest; Hendra in Australian bats, which occasionally spills over into horses and humans (see Australia: A Novel Variant Of the Hendra Virus) and the recently discovered Langya virus in China (see Virulence: Langya henipavirus - Is it a potential cause for public health concern?).
Henipaviruses are also considered to have at least some bio-warfare applications (see 2015's Blue Ribbon Study Panel Report on Biodefense) and while not currently a tier one select agent, some have suggested that Nipah be placed on that list.
