The Next Big One

As the world recovers from the COVID-19 pandemic, we cannot forget what happened. Our focus needs to fall on what the next pandemic could be and how and where it could occur. The World Health Organisation lists ten priority diseases that have epidemic potential, including:

  • COVID-19
  • Crimean-Congo Haemorrhagic fever
  • Ebola virus and Marburg virus
  • Lassa fever
  • MERS and SARS
  • Nipah and henipaviral diseases
  • Rift Valley fever
  • Zika
  • The unknown “Disease X” – Potentially a mutated flu virus.

These diseases are mostly found in Sub-Saharan Africa, the Middle East and South and Southeast Asia. The exceptions being Zika and Crimean-Congo Haemorrhagic fever (and ignoring COVID-19), which are slightly more spread out.

I’ll be writing about three diseases that I think have serious pandemic potential including MERS, Nipah virus and Swine flu (due to its’ link to the food industry). I would definitely read the part about Nipah virus because that is a very scary prospect.

The Big Potentials

MERS

This disease is on my list because of the continuous contact between humans and camels, a known reservoir of the disease (De Wit et al. 2016). This transmission likely occurs through contact with the camel’s nasal secretions and does not need an intermediate host to transmit to humans. Importantly, the exact reservoir of the disease is not know (Azhar et al. 2014).

The reason that MERS (in my opinion) is more likely to become a pandemic is that droughts will reduce the suitability of farming cattle and increase the dependency on camels. We’d be looking at larger farms, therefore more workers exposed to camels and more reliance on camel’s milk.

Currently, it is unclear whether MERS can be transmitted through milk, however it can survive for prolonged periods when introduced. Furthermore, a study on Nipah virus indicated that the virus can be transmitted through drinking which results in a respiratory tract infection, rather than intestinal tract infection. In the event that MERS could be transmitted through milk, it would likely contaminate the oral cavity before infecting the respiratory tract (van Doremalen et al. 2014).

The emergence of SARS and MERS. Unlike SARS which has an unreliable connection between reservoir and human, there is a continuous connection between camels and humans. (De wit et al. 2016)

Swine Flu

One of the criticisms that the World Health Organisation has faced is that it over-hyped the 2009 swine flu pandemic. However, people shouldn’t use this criticism to overlook swine flu for its’ pandemic potential. The virus that caused the 2009 outbreak is thought to be the legacy of the 1918-1919 influenza pandemic that has adapted over 91 years and undergone triple-reassortment, now containing genes from avian, swine and human influenza. Not only can it infect humans, but it can now spread between them (Sebastian et al. 2009).

Furthermore, a sampling of 2,500 European farms found influenza A viruses on more that 50% of the farms, particularly in areas of intense pork production. Their surveillance program identified that 30% of the pigs were positive for influenza A, suggesting that swine flu has been circulating around large farms for months or even years (Henritzi et al. 2020).

More worryingly, it turns out that pigs are a perfect vessel where viruses from different species and groups can mix and blend. In fact, one of the reasons why there are so many strains of influenza in European pigs is that they are catching human viruses from the farmers.

The reason that swine flu is on my list is that it is enabled through the global trade of live swine (Mena et al. 2016), which is only going to increase. The critical factor is that H1N1 has been triple-reassorted, potentially allowing it to jump between birds, pigs and humans. With such large potential, another swine flu pandemic is a simple probability game.

Nipah virus

On the topic of the global transport of pigs, we move onto a scarier virus called Nipah virus which originated in Malaysia in 1998. It has since evolved and caused five outbreaks in Bangladesh between 2001-2005, which has indicated that Nipah virus can now repeatedly spill over into human population in independent outbreaks, is likely seasonal, does not require an intermediate host and can transmit between humans (Epstein et al. 2006).

Bats provide a permanent reservoir for the virus and has been found in small flying foxes (Pteropus hypomelanus), large flying foxes (Pteropus vampyrus) and Indian flying foxes (Pteropus giganteus). This supports a previous hypothesis that heniparviruses exist within the entire distribution of pteropid bats, including India, southern China, southeast Asia (including all of the islands) and Australia (Epstein et al. 2006). Due to deforestation, these bats are increasingly dependant on cultivated fruits, exposing farmers and livestock to contaminated fruit. If you’re interested, watch the ending scene of the 2011 movie ‘Contagion‘, that is very similar to how the 1998 outbreak started.

Outbreaks in Bangladesh have likely been caused by people eating fruit or drinking date palm juice that has been contaminated by bat saliva. In Malaysia, perfect conditions have been created for the virus through increased deforestation, planting of fruit orchards and development of intensive pig farms (Epstein et al. 2006). South and southeast Asia is also home to some of the densest human populations on the planet, meaning the potential for pandemic levels is increasing.

One potential site of a Nipah virus outbreak are the markets of Battambang, Cambodia. Directly above the market stalls selling fruit are thousands of fruit bats and the roofs of the stalls are covered in faeces. Selling guano (bat droppings) is also popular, which further increases the risk of an outbreak (Constable, 2021).

There is also the possibility for the global transmission of the disease through tourism (e.g. the Battambang bat caves). The incubation period for Nipah virus can range from 4 days to 2 weeks (some say months), meaning a tourist could pick up Nipah through contaminated food or exposure to urine and then carry it back with them to their home country. They would then experience flu-like symptoms before developing more serious brain conditions.

In Bangladesh, human transmission accounted for 51% of cases and there is no treatment or vaccine. Based on the analysis of outbreaks in Bangladesh, the R0 is thought to be 0.48 minimum, assuming everyone exposed was located. One study stated “if a strain with an R0 > 1 spills over, or if a strain infecting a person develops an R0 > 1, then in our globally connected world, humanity could face its most devastating pandemic”.

References

Azhar, E. I., El-Kafrawy, S. A., Farraj, S. A., Hassan, A. M., Al-Saeed, M. S., Hashem, A. M., & Madani, T. A. (2014). Evidence for camel-to-human transmission of MERS coronavirus. New England Journal of Medicine370(26), 2499-2505.

Constable, H. (2021, January 12). The other virus that worries Asia. BBC Future. https://www.bbc.com/future/article/20210106-nipah-virus-how-bats-could-cause-the-next-pandemic

De Wit, E., Van Doremalen, N., Falzarano, D., & Munster, V. J. (2016). SARS and MERS: recent insights into emerging coronaviruses. Nature Reviews Microbiology14(8), 523-534.

Epstein, J. H., Field, H. E., Luby, S., Pulliam, J. R., & Daszak, P. (2006). Nipah virus: impact, origins, and causes of emergence. Current infectious disease reports8(1), 59-65.

Gibbs, A. J., Armstrong, J. S., & Downie, J. C. (2009). From where did the 2009 ‘swine-origin’ influenza A virus (H1N1) emerge?. Virology journal6(1), 1-11.

Henritzi, D., Petric, P. P., Lewis, N. S., Graaf, A., Pessia, A., Starick, E., … & Harder, T. C. (2020). Surveillance of European domestic pig populations identifies an emerging reservoir of potentially zoonotic swine influenza A viruses. Cell host & microbe28(4), 614-627.

Mena, I., Nelson, M. I., Quezada-Monroy, F., Dutta, J., Cortes-Fernández, R., Lara-Puente, J. H., … & García-Sastre, A. (2016). Origins of the 2009 H1N1 influenza pandemic in swine in Mexico. Elife5, e16777.

Sebastian, M. R., Lodha, R., & Kabra, S. K. (2009). Swine origin influenza (swine flu). The Indian Journal of Pediatrics76(8), 833-841.

van Doremalen, N., Bushmaker, T., Karesh, W. B., & Munster, V. J. (2014). Stability of Middle East respiratory syndrome coronavirus in milk. Emerging infectious diseases20(7), 1263.

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