Animal to human:hidden diseases

Each year millions of people become infected by diseases transmitted by animals. These viruses can be found in nature especially in rodents.

To understand the risks involved , scientists are at work in the EDEN project to better understand the transmission paths. This week in futuris.

Despite the appearance of winter, here in a forest in central Finland, it is in fact spring. The only human activity consists of scientists on the hunt for rodents. They want to understand the increase in diseases transmitted from animals to humans, among the many known as emerging diseases.

Renaud Lancelot is the Coordinator of the EDEN project at the International Cooperation Centre in Agronomic Research for Development.

“ In the 1940’s there were very few emerging diseases these days the numbers are far higher”.

Renaud Lancelot has worked for many years in the field before becoming coordinator of the EU research project into emerging diseases in a changing environment. The researchers have noted that social change impacts disease transmissions as much as climate change:

“We have seen that in the central and Baltic European countries, because the collapse of the Soviet bloc, a lot of people suffered economically, loosing their jobs with no resources. So they started to go to the forest to pick mushrooms, blueberries, wild berries. This contact with nature introduced people to ticks and insects and rodents that could transmit certain diseases to humans”.

The project studies diseases transmitted by mosquitoes or ticks and rodents. Heikki Henttonen has been working with rodents for 40 years. They transmit diseases like haemorrhagic fever with renal syndrome, which most of the scientists on the team have contracted.

Esa Koskela is a Biologist at the University of Jyväskylä:

“I don’t know if I have ever been so sick before in my life, but I haven’t be too sick actually. After this one week being ill then it took me almost another week before I started to feel fine again”.

Rodents are the most widespread mammals on the planet and play a key role in the spread of diseases. A mosquito or tick bites an infected rodent, which in turn transmits the disease to a human via a bite or scratch.

Heikki Henttonen is a Forest Zoologist and Rodents expert at the Finnish Forest Research Institute:

“When we have a rodent peak we have human diseases. Then the rodents decline and there is no more disease in humans. But really it doesn’t disappear, it’s in the rodents, in the forest, but in low prevalence. It’s always there”.

In this way diseases thought to have been eradicated remain extant inside the rodents. Here biodiversity is important as it prevents virus carrying rodents becoming too numerous.

Heikki Henttonen:

“With deforestation and so on, you can have lots of species with low densities but when you destroy the forest for agriculture, for palm oil, or anything… then maybe one or two species remain, and they can reach high densities. If these species are carrying dangerous viruses, then we get a problem because the rodents’ density of the host species is much higher, and they can spread the virus to humans”.

To learn how to control these diseases scientists take rodent samples from across the globe. They combine it with rodent study in their natural habitats.

Heikki Henttonen:

“We have to understand the population dynamics of the rodents because when we understand the rodents then we know what happens and how the virus is transmitted to humans”

Some of these samples, which are sent from all around the world, end up here, in Helsinki. The Finnish capital has one of the best laboratories in Europe devoted to the of study of animal to human disease transmission.
It was here, 30 years ago, that the link between haemorrhagic fever with renal syndrome and rodent excrement was discovered. Scientists now study samples from both humans and animals.

Olli Vapalahti is a Zoonotic Virologist at the University of Helsinki:

“What we are specially doing, we are trying to combine the ecology work, the samples from nature with let’s say, basic virology, that we are studying the genomes of viruses. But we also study patient samples trying to discover: do these viruses cause diseases?”

The results of these genetic analyses are passed onto to Montpellier in the south of France. Here they study rodent genetics.

First they classify each rodent, a job that often leads to the discovery of new species. Then they see if the viruses found in one of these species could infect other species of rodents.

Nathalie Charbonnel is an Immunogeneticist working on the project:

“If we take one rodent species that colonises a new country or a new environment with all the diseases that they carry, it’s important to know if these viruses can be transmitted to the species that are already present in this new country or environment. Or if the disease will not be transmitted to local rodent species because this rodent species doesn’t have the genetic characteristics that make them susceptible.”

But how can rodents, or other animals, colonise a new environment? The answer is simple: in the same way as humans.

Renaud Lancelot:

“The rodents, but also mosquitoes and any other animal can take a plane or a boat in containers, and this is one of the causes of introduction of new species of insects, rodents, plants in new environments”.

Disease does not respect borders and that is why, from the very outset, scientists put the emphasis on international cooperation involving 48 institutes from 24 countries.

Heikki Henttonen:

“When we understand what happens locally in different parts of Europe, and other environmental causes of the disease patterns, then we can make predictive models and we can make risk assessments to help people to avoid the diseases”

The predictive models indicate when and where disease outbreaks may happen because of climate change, new habits or even new viruses or diseases to prepare us for future epidemics.

Renaud Lancelot:
“We build a network of scientists that are easy to mobilise, to act against any health crisis that can happens at any moment”.

Heikki Henttonen:

“If there is an outbreak, we can very quickly find out what is the cause of the disease. With the SARS (Severe Acute Respiratory Syndrome) it took a few weeks to find the virus. With the influenza the virus strains were found very quickly”.

The key is anticipation: to act before the introduction or spread of any new disease transmitted by animals.

Renaud Lancelot:

“The most effective way to prevent the disease in humans is to control the disease in the animals”.