Recent reports of Nipah virus (NIV) infections in Kerala state in India have attracted global attention.
Since it was first reported in August (2023), there have been six cases, two of whom have died, as of Sept 23 (2023), with more than 700 healthcare workers tested in the past week.
This deadly microorganism is a zoonotic virus, i.e. it is spread from animals to humans.
It can also spread through contaminated food or directly between people.
The first global outbreak occurred in Malaysia in 1998-1999.
The initial NIV cases occurred near Ipoh, Perak, in September 1998, with the Health Ministry then declaring it a Japanese B encephalitis outbreak.
The infected pigs were transferred to Bukit Pelandok, Negri Sembilan, leading to NIV spreading to the population of pigs there, which then infected the pig farmers.
This resulted in the near decimation of the local pig-rearing industry, which was then Asean’s largest, with about a million pigs culled.
The outbreak was reported to have eventually affected 283 people, of which 109 died – a case fatality rate of 38.5%.
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An NIV outbreak (11 cases, one death) was also reported in Singapore among slaughterhouse workers in March 1999.
An outbreak occurred in Bangladesh in 2001, following which there have been nearly annual outbreaks there.
NIV outbreaks have also occurred in eastern India and Kerala state since 2001.
The current outbreak is the fourth outbreak in Kerala in the past five years.
How it spreads
Most human infections in Malaysia resulted from direct contact with sick pigs or their contaminated tissues.
Transmission was thought to have occurred from unprotected exposure to pig secretions, or unprotected contact with the tissue of sick pigs.
In Bangladesh and India, the consumption of fruits or fruit products contaminated with urine or saliva from infected fruit bats was the most likely source of infection.
Human-to-human transmission has been reported among family members and caregivers of those infected.
Hospital staff or visitors were affected in three-quarters of the cases in Silguri, West Bengal, India, in 2001.
About half of the reported cases in Bangladesh from 2001-2008 were due to human-to-human transmission through provision of care to the infected.
The natural host of NIV are fruit bats that are found in Australia, Bangladesh, Cambodia, China, India, Indonesia, Madagascar, Malaysia, Papua New Guinea, Thailand and Timor-Leste.
The fruit bats themselves exhibit no apparent disease from the virus.
NIV is also found in domestic animals like pigs, horses, goats, sheep, cats and dogs, as was first reported in the Malaysian outbreak in 1999.
NIV should be suspected if pigs have an unusual barking cough or if there are human cases of encephalitis.
From nothing to death
The spectrum of NIV disease ranges from asymptomatic cases to acute respiratory infection, which can be mild or severe, and encephalitis (i.e. infection of the brain), which is often fatal.
The initial symptoms are non-specific and include fever, headaches, muscle pain, vomiting and sore throat.
This can be followed by dizziness, drowsiness, altered consciousness and neurological signs of acute encephalitis.
Some of those infected may experience atypical pneumonia and severe respiratory problems, including acute respiratory distress.
Encephalitis and fits occur in severe cases, progressing to coma within 24 to 48 hours.
The incubation period (time from infection to symptom onset) ranges from four to 14 days.
However, longer incubation periods have been reported.
The case fatality rate ranges from 40-75%, depending on the clinical management capability and capacity in the healthcare setting.
Most of those who survive acute encephalitis recover fully.
However, about one in five have residual nervous system complications, like fits and personality changes.
A small number who recover subsequently relapse or develop delayed-onset encephalitis.
Because of its non-specific initial clinical features, NIV diagnosis is often not suspected.
During Malaysia’s outbreak, the diagnosis of Japanese B encephalitis was the working diagnosis until Dr Chua Kaw Bing from Universiti Malaya Medical Centre, isolated the NIV from a patient from Sungai Nipah village in March 1999.
The accuracy of the laboratory diagnosis of NIV is affected by factors surrounding the collection of the clinical samples and the time needed to get the samples to the laboratory.
There is currently no cure for NIV infection.
All that is available is supportive treatment of the respiratory and neurological complications.
Being aware
The only prevention is to increase awareness of the risk factors and measures to reduce exposure to NIV.
These measures include:
This would mean limiting bat access to date palm sap and other fresh food products with protective coverings; boiling freshly collected date palm juice; and thoroughly washing and peeling of fruits prior to consumption.
Fruits with signs of bites should be discarded.
Gloves and personal protective equipment (PPE) should be used when handling sick animals and their tissues, and during slaughtering and culling.
Contact with infected pigs should be avoided.
Pig farms, including pig feeds, should be protected against bats.
Farmers who rear domestic animals should be educated about the necessary precautions to prevent transmission of diseases from animals to humans.
Close unprotected contact with those infected with NIV should be avoided.
Regular handwashing after visiting and caring for any sick person would not only prevent NIV, but also other infections.
Healthcare and laboratory staff should adhere to standard infection control precautions at all times when caring for patients or handling specimens from them.
Under certain circumstances, protective airborne precautions may be necessary.
Keeping updated with health and travel advisories about and from countries affected by NIV and other infections would help in determining whether precautionary measures need to be taken.
Vigilance needed
Although there has been no NIV outbreak in Malaysia since 1998-1999, only the very brave can vouch that it will not recur.
Considerable people-to-people contact have occurred following the lifting of Covid-19 restrictions.
For example, there are more than 60 weekly air flights between Malaysia and India, and also, flights between Malaysia and Bangladesh.
The Health Minister stated that the Health Ministry, Veterinary Department and Wildlife and National Parks Department have been sharing surveillance data on NIV infection in wildlife and domestic animals.
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It is crucial that the public be provided with updated detailed information about the surveillance of NIV in humans and animals.
Extra vigilance is necessary to ensure that the deadly NIV does not cause the havoc that it did in 1998-1999.
Dr Milton Lum is a past president of the Federation of Private Medical Practitioners Associations and the Malaysian Medical Association. For more information, email starhealth@thestar.com.my. The views expressed do not represent that of organisations that the writer is associated with. The information provided is for educational and communication purposes only, and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.
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