Nipah Virus: Will it cause the next pandemic and can it be stopped?

London: The dire and devastating consequences of the coronavirus pandemic were undoubtedly made worse by a substantial lack of pandemic preparedness, with the exception of East and Southeast Asia, which built up defenses in 2003 after their experience with SARS. That’s why it’s important that governments start developing strategies to protect us if other deadly viruses come to the fore.

recent outbreak nipah virus in india has raised the question whether we should start treating it as a future threat and build up our arsenal of defense now.

The rapid development of vaccines against the novel coronavirus, SARS-CoV-2, has provided a way out of this pandemic. So, if vaccines for other potentially dangerous viruses can be developed and stored, they can be rolled out as soon as a new outbreak is detected. Then we would be ahead of the curve and a pandemic could have been avoided.

This approach is plausible – but it assumes that viruses with pandemic potential can be identified earlier, which is not easy to do. And it also runs the risk that don’t worry, there is a vaccine mentality that can cause simple preventive methods to be overlooked.

Nipah virus was first identified in Malaysia in 1998. Cases such as the recent death of a boy in Kerala, India have raised concerns that it may increase the efficiency of mutation and transmission, leading to wider spread.

This scenario is frightening as the virus currently has a mortality rate of over 50% and there is no vaccine or tried-and-true treatment. But before we can invest resources in the development of a vaccine against Nipah, we need to assess whether it threatens a real pandemic. And even if it is, there are other viruses out there, so we must understand where to rank it on the list of priorities.

Epidemic Risk Assessment of Nipah

To assess risk we need to see how Nipah virus transmits and replicates. Nipah is a paramyxovirus. It is related to a human virus, the human parainfluenza virus, which is one of a handful of viruses that cause the common cold.

Its natural host is the fruit bat, large and small flying foxes that are distributed in South and Southeast Asia. So far, all cases of human infection with Nipah virus have been due to direct or indirect contact with infected bats. Infection in bats is sub-clinical, so goes largely unnoticed. The virus is excreted in the urine, which ensures transfer within and between colonies, through grooming and congestion.
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Fruit or fruit juice contaminated with bat urine is the major route of transmission of the virus to people.

Bangladesh study on Nipah virus outbreak

A long-term study in Bangladesh, where routine Nipah virus outbreak It occurs among people, suggesting that the population density of bats, the spread of the virus, and people who drink raw date palm juice are the main factors explaining the pattern of transmission.

Bats contaminate the juice while it is extracted from the date palm and then it is consumed locally. This is an important discovery. As we have seen with SARS-CoV-2, better transmitting viruses develop while the virus is circulating among its human, not animal, hosts.

Therefore, keeping the number of infections in people to a minimum not only reduces the mortality rate from Nipah, but also reduces the chances of virus adaptation. Stop transmission and you stop the threat of an epidemic. In cases of human infection, so far there has been limited spread only to close contacts of the primary infected person, such as family members or, if the person is hospitalised, hospital staff.

Normal transmission does not occur, mainly because Nipah virus uses proteins to enter cells, receptors, are concentrated in the brain and central nervous tissue. Nipah infection causes death from acute encephalitis in most cases because the virus replicates best in tissues where it is easier for the virus to enter cells.

The virus replicates somewhat in the vasculature, the blood vessels that provide a route for the virus to travel from the foods consumed to the nervous system. But central nervous system preference also explains why onward transmission is limited. The virus is not easily accessible from there.

Of course, a very sick person will have a virus everywhere, but with Ebola, the virus is not transmitted efficiently through the respiratory tract and needs to be touched or transferred to body fluids. Infecting someone else requires very close contact.

The likelihood of the virus repeating in the upper respiratory tract, from where it will most certainly be transmitted, is small, and although this does not rule out the possibility of an epidemic, it does significantly reduce its likelihood. Like other routine zoonotic infections, the spillover event itself is more of a problem than bat-to-human transmission, and the potential for epidemic spread to those immediately affected.

There is a case for the Nipah vaccine, but more for emergency use in those exposed to the primary case than for vaccination campaigns in general. The case against it hinges on the fact that the absolute numbers are low, the cost is high and the outbreak is so sporadic that conducting a clinical trial would be very difficult. Research has shown that the therapeutic antibody is effective and will make it a far more practical treatment option in the short term.

Nipah does not pose a high risk of causing an epidemic. The current pattern of outbreak is likely to remain the norm. Instead, as discussed elsewhere, we need to ensure that surveillance, improved awareness and effective public health measures are in place and followed. These will have a huge impact on the control of Nipah virus cases in the near future.

Researchers say that to prepare for pandemics in the medium and long term, we need to turn our attention to identifying which other viruses pose a threat and work to develop vaccines and other protective measures against them.

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