Why bats don’t get get sick from the deadly diseases they carry


Michelle Baker, CSIRO

Bats are a natural host for more than 100 viruses, some of which are lethal to people. These include Middle Eastern Respiratory Syndrome (MERS), Ebola and Hendra virus. These viruses are among the most dangerous pathogens to humans and yet an infected bat does not get sick or show signs of disease from these viruses.

The recent Ebola outbreak in West Africa showed the devastating impact such diseases can have on human populations.

As treatments in the form of therapeutics or vaccines rarely exist for emerging diseases, future outbreaks of disease have the potential to result in similar outcomes.

Understanding disease emergence from wildlife and the mechanisms responsible for the control of pathogens in their natural hosts provides a chance to design new treatments for human disease.

The path to discovery

Until recently, bats were among the least studied groups of mammals, particularly in regard to their immune responses.

But even early studies of virus-infected bats provided clues that there may be differences in the immune responses of bats. It was observed that some bats were capable of clearing viral infection in the absence of an antibody response.

Antibodies are one of the hallmarks of the immune response and allow the host to respond more rapidly to subsequent infection when the same pathogen invades the body. The absence of a detectable antibody response within the bat was striking and drew our attention to the earliest stages of the immune response, called the innate immune system.

The recent sequencing of the first bat genome provided some of the first clues that the innate immune system may be key to the ability of bats to control viral infection. There is intriguing evidence for unique changes in innate immune genes associated with the evolution of flight, and bats are the only mammal capable of sustained flight.

Flight is energetically expensive and results in the production of oxygen radicals. In the research we speculated that bats have made changes to their DNA repair pathways to deal with the toxic oxygen radicals.

A number of innate immune genes intersect with the DNA repair pathways. These genes have also undergone changes, so it appears that the evolution of flight may have had inadvertent consequences for the immune system.

Bat super immunity

In humans and other vertebrates, infection with viruses triggers the induction of special proteins called interferon.

This is one of the first lines of defence following infection. It starts the induction of a variety of genes, known as interferon-stimulated genes. These genes play specific roles in restricting viral replication in infected and neighbouring cells.

Humans and other mammals have a large family of interferons, including multiple interferon-alpha genes and a single interferon-beta gene. People have 17 type I interferons, including 13 interferon-alpha genes.

Analysis published today of the interferon region of the Australian black flying fox reveals that bats have fewer interferon genes than any other mammal sequenced to date. They have only ten interferon genes, three of which are interferon-alpha genes.

This is surprising given that bats have this unique ability to control viral infections that are lethal in people and yet they can do this with a lower number of interferons.

Although interferons are essential for clearing infection, their expression is also tightly regulated. This is to avoid over-activation of the immune system, which can have negative consequences for the host.

The expression of interferon-alpha and interferon-beta proteins, which account for the majority of the antiviral response generated following viral infection, is normally undetectable in the absence of infection. It is rapidly induced following detection of a pathogen.

Yet we again see a difference in bats. The three interferon-alpha genes are continuously expressed in bat tissues and cells in the absence of any detectable pathogen. Bats appear to use fewer interferon-alpha genes to efficiently perform the functions of as many as 13 interferon-alpha genes in other species. And they have a system that is constantly ready to respond to infection.

Continual activation of the interferon response in other species can lead to over-activation of the immune response. This frequently contributes to the detrimental effects associated with viral infection, including tissue damage. In contrast, bats appear able to tolerate constant interferon activation and are continually primed for viral infection.

The bat approach in others

We are familiar with the important role bats play in the ecosystem as pollinators and insect controllers. They are now demonstrating their worth in potentially helping to protect people from infectious diseases.

The ability of bats to tolerate a constant level of interferon expression is poorly understood at the moment. But the identification of the unique expression pattern of interferons in bats is a first step in identifying new ways of controlling viruses in humans and other species.

If we can redirect other species’ immune responses to behave in a similar manner to that of bats, then the high death rate associated with diseases such as Ebola could be a thing of the past.


Peng Zhou was a co-author of this article. He’s a researcher in pathogen discovery and antiviral immunity, formerly employed at Duke–National University of Singapore Medical School and CSIRO.

The Conversation

Michelle Baker, Research scientist, CSIRO

This article was originally published on The Conversation. Read the original article.

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Microbes: the tiny sentinels that can help us diagnose sick oceans


Katherine Dafforn, UNSW Australia; Emma Johnston, UNSW Australia; Inke Falkner, and Melanie Sun, UNSW Australia

Microbes – bacteria and other single-celled organisms – may be tiny, but they come in huge numbers and we rely on them for clean water, the air we breathe and the food we eat.

They are nature’s powerhouses but they have often been ignored. We previously lacked the capacity to appreciate truly their diversity, from micro-scales right up to entire oceans.

Recent advancements in genetic sequencing have revealed this diversity, and our research, published in Frontiers in Aquatic Microbiology this week, shows how we can use this information to understand human impacts on an unseen world – making microbes the new sentinels of the sea.

A sea of microbes

The great majority of bacteria and other microbes are extremely beneficial, performing vital roles such as recycling nutrients.

The number of bacteria on Earth is estimated at 5×10³⁰ (or 5 nonillion, if you prefer), and many of them live in the ocean. There are 5 million bacteria in every teaspoon of seawater, and more bacteria in the ocean than stars in the known universe.

Guess how many microbes?
Victor Morozov/Wikimedia Commons, FAL

There are yet more bacteria in the world’s soils and sediments, with estimates of between 100 million and 1 billion bacteria per teaspoon. These sediments are vital for recycling nitrogen, particularly in coastal sediments closest to human populations. Without bacteria and other microbes, sediments would turn into unsightly, pungent piles of waste.

Microbial services are not limited to recycling. Many microbes, including cyanobacteria, function like tiny plants by using sunlight to produce oxygen and sugars. Due to their extraordinary number in the world’s oceans, the amount of oxygen these organisms produce is equal to that of all plants on land.

Marine sentinels

Until recently, finding out just how many different types of microbes there are was relatively difficult. How do you identify and study millions of different organisms that are not visible to the naked eye?

Bacteria, for example, had to be grown in the laboratory in large colonies to be seen. But only 1-3% of bacteria can be cultured successfully.

Advances in genetics together with the development of molecular tools have allowed researchers to investigate marine bacteria in their natural environment. Microbial communities can now be grouped by the role they play in ecosystems and how these groups respond to environmental gradients.

We can use these new tools to measure ecosystem health, which is crucial to managing human impacts on our coastlines, particularly in estuaries. Early studies have found shifts in bacterial community composition to be good indicators of contaminants

Different areas of harbours, such as Sydney Harbour, have distinct bacterial communities. These patterns may be driven by circulation. The outer harbour, which is flushed with seawater on every tidal cycle, is dominated by photosynthetic cyanobacteria. The upper harbour, with less flushing and more runoff, is dominated by soil-related bacteria and those adapted to nutrient-rich environments.

In our waterways, pollutants such as metals bind to fine particles and settle as sediment. This exposes sediment-dwelling organisms to a multitude of toxic products. What effect do these toxic substances have on sediment microbes?

Recent evidence from a large survey of eight estuaries suggests that microbes are far more sensitive to contaminants than larger animals and plants. This survey also revealed that toxic substances were linked to changes in community structure and a reduction in community diversity. This is especially alarming given that a diversity of microbes is essential to nutrient recycling.

Diagnosing wounded seas

It would be great if we could use particular microbes to diagnose human impacts. For instance, certain microbes can indicate water quality.

A technique called metagenomics is revealing the true depth of microbial diversity by pooling DNA sequences from all the species in a sample. It then works backwards to construct a genetic overview of the entire community.

However, while metagenomics can give us important information about the identity of microbes in a community, it can’t tell us what they are doing or how their functions change in response to environmental stressors and human activities.

Metatranscriptomics takes the sequencing approach one step further and characterises gene expression in a microbial community, which can be linked to crucial ecosystem services such as nutrient cycling.

Similar to their use for diagnosis of ailments in humans, molecular tools are being used to diagnose human impacts on earth by observing changes in microbes across polluted and unpolluted environments. They can even detect very small amounts of toxic substances. Because of their diversity, they can potentially be used to detect a wide range of human impacts.

This allows us to identify environmental impacts early, potentially limiting greater loss in larger organisms.

With the new tools to “see” microbes and their importance, we are now perfectly poised to advance our understanding of how microbes are responding to environmental change. They are sentinels of our increasingly human-affected waterways.

The Conversation

Katherine Dafforn, Senior Research Associate in Marine Ecology, UNSW Australia; Emma Johnston, Professor of Marine Ecology and Ecotoxicology, Director Sydney Harbour Research Program, UNSW Australia; Inke Falkner, Community Outreach Coordinator for Sydney Harbour Research Program, Sydney Institute of Marine Science, and Melanie Sun, PhD Candidate – Environmental Research, UNSW Australia

This article was originally published on The Conversation. Read the original article.

Uluru: Not On


A little while back I posted about a planned trip to Uluru in the near future – sadly I have had to cancel the trip because I am concerned about my run of poor health. I have basically been sick since November last year and had pneumonia 4 times during this time. So the trip will be postponed for a year to ensure I recover fully.

Sick Again


Hi all – I have been trying to keep the Blog going in recent days despite being ill again – however, as I continue to get worse it is probably wise to have a complete break for the rest of the week and get as much sleep as I can.

I have had pneumonia 3 times since November last year (twice in November and once last month) and have come down sick again. Thought I was improving over the last couple of days but have once again developed the ‘shiver me timbers (chills and fever)’ tonight. So I plan to be away from the keyboard for the rest of the week in a bid to finally get over all of this illness. I apologise for the interruption to Blog posts in the mean time.

Back Very Soon


Hi all – my previous post suggested I would be away for about a week or so because of pneumonia. It turns out my absence was for a whole lot longer than that. I ended up with Double Pneumonia twice in 6 weeks and it has been a struggle to recover. I am feeling much better now and hope to return to Blogging over the next week, posting to each again over that time. Thanks for your patience.