Remembering the Nipah virus outbreak

While pigs were the main source of infection in the first Nipah outbreak in Malaysia, fruit bats also serve as a host for the virus and have been the source of more recent cases. — Photos: Filepic

In December 2015, the World Health Organization (WHO) came out with a list of emerging diseases likely to cause severe outbreaks in the near future, and for which few or no medical countermeasures exist.

The list included Crimean Congo haemorrhagic fever, Ebola virus disease, Marburg virus disease, Lassa fever, MERS (Middle Eastern respiratory syndrome), SARS (severe acute respiratory syndrome), Nipah virus (NiV) disease, Rift Valley fever and Disease X.

Disease X “represented the knowledge that a serious international epidemic could be caused by a pathogen currently unknown to cause human disease”.

The question of whether Covid-19 is Disease X itself or the precursor of a more deadly Disease X to come in 2021 was raised in my previous column.

Recent reports of the Health Ministry’s stretched resources in containing Covid-19 led to a feeling of déjà vu as the situation is similar to the NiV outbreak in Malaysia and the question of whether Nipah could be Disease X.

Malaysia was the first country in the world to encounter the virus in 1998.

It resulted in the near decimation of our pig-rearing industry, which was then the largest in Asean, with about a million pigs culled.

Many of the humans who survived the infection have been left with residual complications.

Infection

NiV causes severe disease in animals and can spread from animals to humans.

This is not a forest fire, but smoke from the burning of culled pigs that were infected by the Nipah virus at Gertak Sanggul, Penang, in 2011.

It can also be spread through contaminated food or directly from person to person.

The clinical features of the infection in humans range from having no symptoms (asymptomatic) to acute respiratory infection and fatal encephalitis.

The initial symptoms reported were fever, headaches, muscle pain (myalgia), vomiting and sore throat.

This can be followed by signs of encephalitis, i.e. dizziness, drowsiness, altered consciousness and other neurological signs.

Some sufferers can develop atypical pneumonia and severe respiratory difficulties.

Encephalitis and fits occur in severe cases with rapid progression to coma in 24 to 48 hours.

Most who survive the acute encephalitis will recover, but long-term neurological conditions have been reported, with about 20% of patients left with residual complications like fits and personality changes.

A small number subsequently relapse or develop delayed-onset encephalitis.

The death rate of NiV ranges from about 40% to 75%, depending on the clinical management capabilities.

There are currently no drugs or vaccines for NiV.

Severe respiratory or neurological complications are managed with supportive care.

Spread

A government worker putting up a notice to seal off a pig farm where the animals are suspected to be carrying the Nipah virus in Sungai Tiram, Penang, in 2010. — Nanyang Siang Pau

The initial NiV cases were reported near Ipoh, Perak, in September 1998.

Four out of 28 of these cases tested positive for IgM antibodies against Japanese Encephalitis (JE) and a JE outbreak was declared.

The pig rearers sold their pigs and transferred them out of Perak.

By the end of 1998, more cases were reported in Bukit Pelandok in the Port Dickson district of Negri Sembilan.

In March 1999, then-virology graduate student Dr Chua Kaw Bing isolated NiV from a Sungai Nipah village resident who was being treated at Universiti Malaya Medical Centre (UMMC).

According to a 2003 paper in the Journal of Clinical Virology, the outbreak eventually caused 283 cases and 109 deaths, i.e. a death rate of 38.5%.

An outbreak (11 cases, one death) was also reported in Singapore among slaughterhouse workers in March 1999.

Since then, there have been annual outbreaks in Bangladesh beginning in 2001, as well as cases in eastern India.

Most human infections in Malaysia resulted from unprotected exposure to secretions of sick pigs or their contaminated tissues.

Subsequent outbreaks in Bangladesh and India, however, were most likely due to consumption of fruits or fruit products from infected fruit bats.

These bats, which are the natural reservoir of NiV, have been found in Indonesia, the Philippines, Thailand, Cambodia, Ghana and Madagascar.

Human-to-human transmission has been reported among family and caregivers of the infected through close contact with their secretions and excretions.

NiV in Bangladesh and India has also been reported in healthcare settings due to transmission through providing care.

Outbreaks of Nipah have been reported in domestic animals like pigs, horses, goats, sheep, cats and dogs.

An infected pig can be asymptomatic, but some develop fever, difficulty breathing and neurological symptoms like trembling, twitching and muscle spasms.

The death rate in pigs is usually low, except in young piglets.

Prevention

Dr Chua (second from right), along with consultant neurologist Emeritus Prof Datuk Dr Tan Chong Tin (right), served as WHO consultants during the 2004 NiV outbreak in Bangladesh. — UMMC

The prevention of NiV in domestic animals falls under the purview of veterinary authorities, with the assistance of the Health Ministry.

An animal health and/or wildlife surveillance system is vital in providing early warning.

The prevention of infection in humans requires increased awareness of the risk factors and reduction of exposure to NiV.

Lowering bat-to-human spread would involve decreasing the access of bats to plants and other fresh food/fruits consumed by humans.

Food/fruits should be thoroughly washed and peeled before consumption and those with signs of bites should be discarded.

Protective coverings may also be helpful for fruits and plants used for human consumption.

Nosocomial (healthcare-acquired) spread to healthcare staff can be minimised by ensuring proper handwashing, use of personal protective equipment (PPE) and isolation of patients.

In a 2019 review of NiV in the Journal of Infection and Public Health, the authors concluded that environmental factors played a vital role in the spread of animal disease to humans as “climatic changes due to factors like drought or floods, deforestation, urbanisation and industrialisation on a large scale leads to destruction of animal habitats causing starvation and low immunity, increasing the viral load in their body, excreted in the secretions of bats, thereby infecting the fruits, animals or humans who come into contact with them”.

Many of these factors are applicable to Malaysia.

Although there has been no NiV outbreak in Malaysia for decades, only the very brave can vouch that it will not recur.

There appears to be no light at the end of the tunnel for the current Covid-19 situation.

It is pertinent to consider how Malaysia would respond if there is another, and possibly concurrent, NiV outbreak.

Dr Milton Lum is a past president of the Federation of Private Medical Practitioners Associations and the Malaysian Medical Association. For more information, email [e-mail]. 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.