In the old days, a round-the-world trip took a year. Now we can do it in 24 hours. It is possible to travel to the other side of the globe within the incubation period of almost any disease.
“When we encourage free mobility for people and goods, we also promote free mobility for viruses and bacteria,” states Olli Vapalahti, professor of zoonotic virology at the University of Helsinki.
An individual infection becomes an epidemic when the pathogen arrives in a new environment where people have not developed a resistance to it. This is what happened with the Zika virus in South America. A Zika infection during pregnancy is highly likely to cause severe developmental problems for the fetus.
In addition to mobility, the spread of infection is stimulated by urbanisation. When many people congregate, bacteria and viruses can easily be transmitted from one person to the next.
Divine plagues
Epidemics, of course, are nothing new. For example, yellow fever arrived in South America from Africa with the slave ships. The most infamous case of zoonosis, i.e., a disease spreading from animals to humans, was the Black Death, which was spread by rats. In history, pandemics were rare but much deadlier, as no tools existed to combat them.
“Today we are much better at diagnosing, identifying and spreading the word about diseases. We have opportunities to treat them and to limit them from spreading. They used to be thought of as divine plagues,” Vapalahti says.
Diseases have been spread to humans by bats, rodents, birds, mosquitoes and ticks, among other means. Keeping large numbers of production animals in a single facility poses a risk of new zoonotic viruses mutating and spreading to humans.
Climate change has also had an impact on where some of these disease vectors are found. In Finland, both ticks and tick-borne encephalitis, or TBE, are appearing further and further north.
Expect the unexpected
Some zoonotic viruses can spread from animals to humans but not from one human to the next, while others can mutate to allow contagion between humans. The most dangerous pandemics arise from the latter group.
Not all viruses mutate in the same way. The influenza virus mutates every year, and vaccinations must be constantly updated. Meanwhile, other viruses remain largely the same, or at least one’s acquired immunity provides sufficient protection from minor mutations of the virus. Such stable viruses include TBE and probably the Zika virus. Vapalahti believes that developing a vaccination for Zika will be a fairly straightforward process.
Could we prevent epidemics before they happen? According to Vapalahti, the most important thing would be to detect the infection at an early stage and keep it from spreading before long chains of infection form, involving many people.
“Despite everything, most epidemics come out of the blue. Nobody foresaw the vast Ebola epidemic in West Africa, and we never thought that Zika would damage fetuses. Expect the unexpected, that’s my advice.”
The Studia Generalia lecture on 3 March will focus on contagious diseases (in Finnish). Professor Jussi Huttunen will discuss how diseases spread, flourish and die.