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Which climatic factors promote the spread of zoonotic diseases?

A recent Europe-wide study has investigated the prevalence of protozoans, bacteria, and viruses in birds and bats that are potentially pathogenic to humans and domestic animals. The experts compiled the results of over 700 scientific articles and nearly half a million observations in varying climate conditions. 

The researchers identified specific climatic factors that can significantly alter the risk of succumbing to infectious diseases.

Pathogen occurrence 

By combining data on the occurrence of more than 75 pathogenic microbes across Europe from almost 400 bird and 40 bat species with climatic factors, the scientists discovered that the occurrence of most pathogens is associated with temperature and rainfall.

“In general, the occurrence of pathogenic bacteria increased in areas with a warm and dry climate. On the other hand, pathogenic viruses prefer moist climate,” said lead author Yanjie Xu, a postdoctoral fellow in Ecology and Evolutionary Biology at the Finnish Museum of Natural History from the University of Helsinki.

Climatic factors 

The link between climatic factors and pathogens could be reliably assessed on the 17 pathogen taxa with most data. According to the researchers, the observed associations significantly varied.


“Temperature was positively associated with occurrence of avian flu virus, malaria-parasite, and bacteria that cause chlamydia, salmonella, Q-fever, and typhus in birds and bats,” explained co-author Arto Pulliainen, an expert in Biomedicine at the University of Turku.


Rainfall had both positive and negative associations with the occurrence of different pathogens. For example, rises in rainfall increased the probability for the occurrence of Usutu-, Sindbis- and avian flu viruses and salmonella bacteria.

“Usutu- and Sindbis-viruses are vectored by mosquitoes, and rainfall can increase the occurrence of wetlands favored by mosquitoes. Similarly, avian flu and salmonella are prevalent particularly in waterfowl, for whom wetlands are also of importance,” said co-author Thomas Lilley, a professor of Ecophysiology at the Finnish Museum of Natural History.

Distribution ranges 

According to the scientists, climate change modifies the distribution ranges of both the pathogens and their hosts. For instance, the distribution ranges of birds have already been observed to shift northwards by more than a kilometer per year. 

“There is a possibility that for instance thermophilic pathogens become more common in northern Europe as a cause of climate change,” said senior author Aleksi Lehikoinen, a curator at the Finnish Museum of Natural History.

Study implications 

“Our results suggest that rising temperature and increasing precipitation will accelerate the threat of bird- and bat-associated bacterial and viral pathogens to wildlife, domesticated animals and humans, respectively,” said the study authors. 

“However, the idiosyncratic relationships with climatic conditions among pathogenic taxa highlight the need for pathogen-specific predictive models to understand future pathogen distributions.”

The study is published in the journal Ecography.

More about bat and bird viruses

Bats and birds are known to be reservoirs for various viruses that can sometimes spillover and infect other animals, including humans. 

Bat viruses


The most well-known of these is SARS-CoV-2, the causative agent of COVID-19. Bats are believed to be the natural reservoir for various coronaviruses, including the ones responsible for Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS).

Ebola and marburg viruses

These are hemorrhagic fever viruses with bats serving as a potential reservoir. They can be transmitted to humans and non-human primates leading to severe outbreaks.

Rabies and other lyssaviruses

Bats can be reservoirs for rabies virus and other related viruses. Transmission to humans is rare but can be fatal without treatment.

Nipah and hendra viruses

These viruses are found in fruit bats and can spill over to other animals and humans, causing severe respiratory and neurological disease.

Bird viruses

Avian influenza

Often referred to as “bird flu,” various strains of avian influenza virus can infect birds. Some of these strains, like H5N1 and H7N9, have caused severe illnesses in humans.

West Nile 

While this is primarily a mosquito-borne virus, birds are the main reservoir. Mosquitoes transmit the virus after biting infected birds and can then infect mammals, including humans.

The existence of these viruses in natural reservoirs emphasizes the importance of surveillance, understanding wildlife ecology, and the interactions between wildlife, livestock, and humans. 

Reducing the interface between wild animals and humans, like by limiting the wildlife trade or encroachment into natural habitats, can help minimize the risk of future outbreaks.

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