Basics

Pathogens on the move

People now travel around the globe in just a few hours. And dangerous pathogens accompany them. But bacteria and viruses are not just stowaways on planes and in ships – animals also spread them around the world.

In many of the Earth’s regions, people and farm animals live side by side, such as here in China’s largest freshwater lake, Poyang Lake in Jiangxi province. This means pathogens can easily be transferred from animals to humans. Zoom Image
In many of the Earth’s regions, people and farm animals live side by side, such as here in China’s largest freshwater lake, Poyang Lake in Jiangxi province. This means pathogens can easily be transferred from animals to humans. [less]

This is frequently not a problem for the animals themselves; however, some of these pathogens pose a major risk to humans. Many fatal infections, like Ebola, HIV or influenza, originally stem from animals. When humans and animals live in close contact, the germs can easily jump to humans. In Asia and Africa in particular, humans and animals live in close proximity, often even in the same room. Such cases are particularly dangerous and often trigger symptoms of a fatal disease.

Pathogens frequently cover thousands of kilometres in the company of migratory birds, marine animals or hoofed animals. While they can infect humans directly, a more likely scenario is the transfer to household pets, as viruses and bacteria are well adapted to the domesticated relations of their original host. They can then move easily from household pets to humans.

For a number of years now, scientists have been using computer models to calculate the spread of epidemics based on the global airline network. However, it is not only the routes travelled by humans that play a role in the spread of disease; the movements of animals are also increasingly important in the prediction of epidemics.

For example, between 2005 and 2010, an international team of researchers studied the outbreaks of the H5N1 virus among wild and domestic birds, a virus that is also dangerous to humans. They then compared the outbreaks with the flight paths of two bird species. The scientists tracked the flight paths of the bar-headed goose (Anser indicus) and the common shelduck (Tadorna tadorna) with the help of GPS transmitters. Their research showed that the water birds fly together with many other species from India and Bangladesh in a northward direction over Tibet and China to Mongolia. Most of the outbreaks that occurred among poultry in South Asia during the period studied were also on this flight path. According to the results, the bar-headed geese and the common shelducks could transport many viral strains from an arbitrary bird resting area in Central China to Mongolia.

Shelducks can become infected with bird flu from poultry on their annual flights and spread the virus over large distances. Zoom Image
Shelducks can become infected with bird flu from poultry on their annual flights and spread the virus over large distances. [less]

The scientists assume that the common shelduck is infected by poultry in its wintering areas in Bangladesh. The bar-headed goose, on the other hand, comes into contact with the H5N1 pathogen mainly in the Tibetan capital of Lhasa and brings it from there to China. The study shows therefore where the wild birds are likely to be infected and consequently where the contact between wild and domestic animals should be prevented. This contact arises primarily due to the fact that poultry are driven to graze on harvested rice fields or swamplands and forced to come into contact with their wild relatives.

But the avian flu is not only rife in Asia: in the winter of 2005/2006, wild birds in Europe also fell victim to the virus. The extraordinarily low temperatures during this winter probably increased the risk of infection, as the cold causes water birds to move particularly close together. However, scientists still do not know which route was taken by the pathogen from Asia to Europe and who brought it to Europe.

It is hoped that Icarus will now help determine the flight paths of other bird species and thus the way in which viruses are spread. Scientists participating in the Icarus project want to attach transmitters to northern pintails (Anas acuta) and mallards (Anas platyrhynchos) in Siberia for example and observe them on their flights to their winter quarters in tropical Africa, India and Southeast Asia. The results that they obtain will reveal not only the routes taken by infectious diseases but also the spread of antibiotic-resistant bacteria. Mallards are particularly susceptible to being infected with antibiotic-resistant bacteria by their relatives in poultry farming.

Fruit bats can transmit dangerous diseases to humans. They can transport the pathogens over hundreds of kilometres on their flights. Transmitters attached to the back of the animals enable researchers to trace their flight paths. Zoom Image
Fruit bats can transmit dangerous diseases to humans. They can transport the pathogens over hundreds of kilometres on their flights. Transmitters attached to the back of the animals enable researchers to trace their flight paths. [less]

Fruit bats are another animal group that act as reservoirs for pathogens. SARS, rabies and the Nipah virus can potentially be transmitted from these bats to humans. They are also possible carriers of the Ebola virus. Thanks to telemetry studies using tagged fruit bats in Ghana researchers now know that the animals there commute hundreds of kilometres every day between their roosting place and their feeding place. Viruses could rapidly cover great distances in this way. The researchers want to use Icarus to find out more about the life of fruit bats, for example where the infection risk is particularly high. Contacts between animals and humans could be minimised with this information.

The health of millions of people around the world could thus be protected if the necessary knowledge about animals and their migrations were available. For this to become a reality, however, researchers need to know even more about the behaviour and routes of a wide variety of species. This can only be achieved with a global satellite-based system like Icarus, which can observe thousands of animals using transmitters and analyse the data in real time.

 
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