Approximately 75% of newly emerging diseases currently affecting the global population are of animal origin. These viruses, like Covid-19, have been transmitted from an animal population to humans. Known as zoonotic diseases, they have been responsible for a number of global pandemics including Avian Influenza and the previous coronavirus outbreaks of MERS and SARS. Tropical regions such as Asia, with their biodiversity, are high risk areas for the emergence of new viruses.
Deforestation and population growth
Bats are a known pool for coronaviruses, but also harbour other deadly diseases such as Nipah virus. Nipah virus has a mortality rate of 40-75% in humans, and with no available vaccine, it is considered a major risk to human health by the World Health Organisation. Fruit bats are its natural host, but the virus can infect other animals, increasing its potential to spread to humans. The virus can be caught by direct contact or through contaminated food. There have already been outbreaks of Nipah virus in Asia but as the human population rapidly expands in places such as Cambodia, Thailand, Malaysia and Bangladesh, bats and people are coming into daily contact. As bat habitats are destroyed by deforestation, they move closer to the local population who are generally unaware of the risk bats pose. High risk situations such as the drinking of date palm juice contaminated with bat urine (thought to have caused a previous outbreak), and the collection of bat droppings for use as fertiliser, could lead to further outbreaks. A cull of the bat population would not be beneficial as they play a vital role in the ecosystem. Scientists based in Asia continue to monitor for Nipah virus, but also believe that educating the local population about the threat caused by bats would reduce the chances of another occurrence.
Global trade and international travel
Like bats, mosquitoes are also well-known disease vectors. Many mosquito species are only found in specific geographical regions; when the Aedes vittatus mosquito local to the Indian subcontinent was found in Cuba, it was the first time in had been seen in the western hemisphere. This species of mosquito is able to transmit a number of dangerous diseases to humans that are not spread by current mosquito species found in North America. Work to eradicate mosquito-borne diseases in North America saw reductions in disease, but more recently there have been new outbreaks of dengue fever, Zika virus and chikungunya virus in the Americas. It is thought they were caused by invasive species which have spread globally through carriage of mosquito eggs in shipping containers sent from countries where the viruses are endemic. Malaria has also been spread through international travel, with mosquitos travelling to new regions via commercial flights. Without measures to detect and destroy these mosquitos, a pandemic of a mosquito-borne disease is highly likely.
Increasingly warmer weather and milder winters are helping mosquitos thrive in the US. These environmental changes allow mosquitos to experience a longer breeding season, boosting local mosquito populations and thus the likelihood of mosquito borne illnesses. The rise in global temperatures is also a concern in the Middle East where there have been previous Mers outbreaks. Middle East respiratory syndrome (Mers) is a coronavirus that causes disease 10 times more deadly than Covid-19. It is carried by camels and due to climate change, the region’s reliance on camels has increased. Conditions are becoming too harsh to breed livestock which are not adapted to drought. In North African countries such as Kenya, camels are relied on as a source of income, not only for their meat and milk, but as an investment used for payments such as dowries. With a population of 3 million camels, the danger of Mers transmission from wildlife to camels, then on to camel herders is a real concern. Herders as well as being in close contact with the camels, are known to drink raw milk. To prevent a pandemic where Mers reaches the general population, education on the dangers of not boiling milk before consumption, as well as the continued surveillance of livestock for disease will be vital.
Intensive farming and movement of animals
Livestock was responsible for another pandemic, in 2009 swine flu killed over 100,000 people globally. The H1N1 Influenza A virus responsible, was thought to have spread to humans from infected pigs in Mexico. It was subsequently controlled by a vaccine but has not been eradicated and reoccurs as seasonal flu. The way we currently produce our food makes another pandemic far more likely. Population increases have led to a larger demand for meat, resulting in more intensive farming methods. Holdings have greatly increased in size over the last 25 years, now with 10 to 100 times more pigs that previously reared. This is problematic as pigs can act as mixing vessels for viruses from different species, leading to new strains. Intensive farming methods require pigs to be slaughtered at a young age, before their immune systems have developed enough to effectively fight influenza. Viruses once introduced, due to the number of young pigs farmed, are active for longer. A surveillance study of over 2,000 European pig farms found Influenza A viruses with pandemic potential in over 50% of holdings. Movement of pigs either for trade, or as part of the farming process, leads to more viral mixing between pigs from different geographical areas. These pigs infected with their local viral strains, infect each other and these viruses when combined may generate more deadly strains. Making the testing and reporting of swine flu mandatory for farmers and reducing the size of swine holdings may help reduce the risk of another swine flu pandemic.
These are just a few examples of why the modern world is more susceptible to pandemics. To deal with this threat, the PREDICT project was initiated by the US government in 2009. Led by UC Davis, it was a global collaboration of scientists supporting emerging pandemic threats preparedness. This 10-year project worked to improve monitoring and identification of established and newly emerging zoonotic diseases. It has improved response systems in the areas where they are most needed, enabling viral threats to be detected and dealt with in order to prevent a serious outbreak. As surveillance and early detection are key to preventing the next pandemic, it is global collaborative projects like this, as well as changes to lesson our environmental impact that could help keep us all safe.
Information sourced from BBC Future’s excellent series of articles entitled Stopping the next one: What could the next pandemic be?