Why are so many viruses appearing?

After decades of calm and effective vaccines, the world has been following the emergence of new viruses. In addition to the coronavirus, monkeypox (mpox), the H5N1 avian flu virus, and Marburg, a virus similar to Ebola, were some of the viruses that deserved space in the news and caused concern among the world’s population in recent months.

But what has changed in recent decades for new pathogens or variants of old ones to be able to strengthen and spread with ease? Understand, in five points:

1. International movement of people

“The connection between people all over the world has increased, so the speed at which viruses spread is much faster nowadays”, explains professor at the University of Brasília (UnB) Bergmann Ribeiro, a specialist in viruses.

Currently, a person can be infected with a virus in one country and, in hours, be on the other side of the world, transmitting the pathogen to a new population without defenses – that is what happened with the coronavirus, which in weeks was already present in almost the entire planet.

2. Very high population density

In an article published on the scientific dissemination platform The Conversation, professor of virology Lindsay Broadbent, from the University of Surrey, in the United Kingdom, says that the urbanization observed in recent years has created a very high population density.

With cities increasingly crowded, the population lives much closer together – just imagine the subway at rush hour, for example – creating the perfect opportunity for viruses to spread.

“The rapid development of cities often exceeds the speed of creating adequate infrastructure, including basic sanitation and medical care, further increasing the chances of viral outbreaks”, writes the professor.

3. Deforestation

Ribeiro says that the appearance of new viruses is strongly related to animals: more than two thirds of all infectious diseases are considered zoonoses. “Just to name a few, HIV came from monkeys, zika and chikungunya are transmitted by mosquitoes, and respiratory viruses usually come from birds, such as influenza, for example. Sars-Cov-2 came from bats. Animals are reservoirs”, explains Bergmann Ribeiro.

To make room for ever-larger cities and demands for food and raw materials, deforestation has been increasing. In addition to contributing to global warming, the cutting down of forests limits the habitat of animals, forcing the coexistence of species that have never encountered each other — then viruses can “jump” to new animals, mutating enough to infect humans in the future.

4. Interaction with wild animals

Deforestation also forces animals to look for food elsewhere, moving closer and closer to cities and people, facilitating contamination by new viruses.

Another problem is the trafficking of wild animals: many have pathogens not yet known to science that can generate outbreaks in humans. Viruses can also be endemic in some countries and reach new nations through the transport of animals, spreading without resistance among a population that lacks specific antibodies to fight infections.

5. Climate change

Global warming and climate change are also associated with the emergence of new viruses, mainly because they favor the survival of mosquitoes. “For example, some arboviruses are being detected in new areas because the climate allows mosquitoes to reach new countries,” writes Lindsay.

Ribeiro, who is part of a group of researchers from all over Brazil, says that he monitors yellow fever in monkeys and mosquitoes — when a dead animal appears, a blood sample is taken to check if it has yellow fever. The sample is sent to Brasília, where the professor carries out the genetic sequencing of the virus to find out if it originates in the Amazon or if it comes from another region.

“This virus is endemic to the Amazon, but from time to time it goes down through the Midwest, goes to Minas Gerais, Rio de Janeiro, down to Rio Grande do Sul. We recently detected it in the south of the country, ”he explains.

How to avoid new pandemics?

“We have known about these factors for a long time. The emergence of Sars-Cov-2 did not surprise any virologist or epidemiologist. It was a matter of when, not if, a pandemic was going to happen. What was unexpected was the scale of Covid-19 and the difficulty of effectively limiting the transmission of the virus”, says the British professor.

Ribeiro, from UnB, recalls that there are potentially more than 800,000 viruses in the world, and the only way to prevent them from causing pandemics or outbreaks is to monitor them.

“It doesn’t mean that all of them will cause serious diseases in humans. But it’s important to monitor and study what they do, how they get into human cells. From the moment the genome of the virus is known, it becomes easier to establish a platform for the production of vaccines”, he says.

For Lindsay, virus monitoring can be frightening at first, but it is essential to contain future pandemics. “Increased surveillance will result in more outbreaks being reported. But, if an outbreak happens in a region without adequate surveillance, the infection will likely spread more easily,” she writes.

She recalls that surveillance is just one of the important points: governments and international agencies need to have well-designed pandemic protocols to guide actions in case of a new public health emergency.