Bats are the host to a lot of viruses but do we know much about that?

In an article in Science today, Kai Kupferschmidt reminds us that while the chiropterans (bats belong to the Order Chiroptera which comprise >1,200 species) are a fascinating bunch. As you might expect from animals that make up a fifth of all mammals and reside on all continents except Antarctica  they harbour a lot of viruses and yet we still know very little about how the flying fuzzballs interact with their own virome.

Bats have been found to harbour or were the likely source of a virus that became what we know as:

• Nipah virus 
• Hendra virus
• Rabies virus
• Australian bat lyssavirus
• Severe acute respiratory syndrome coronavirus (SARS-CoV)
• Numerous other bat CoVs
• Ebola virus
• Marburg virus
• Kasokero virus
• Duvengae virus
• Menangle virus
• Middle East respiratory syndrome virus

Intermediate hosts play a big role when these infections get to humans, mostly because we don't really have bats on our list of cute and cuddly animals with which we spend a lot of close contact time. 

Bats also live for decades, probably first emerged 50-million years in the past, may have a primitive immune system and seem to have an ability to host viruses without getting ill. This may have to do with a reduced repertoire of foreign (in this case, viral) gene-sensing molecules. In humans, these sentinel are always on or in cells, keeping a "non-specifically specific" lookout for bits and features of DNA or RNA. When found the sentinels act to scale up the body's immune response to the virus. But for bats, little of this process is really known because bats are a difficult animal to study. There are some bat cell lines that have been successfully used to examine bat immune responses in labs, but nothing beats observing and understanding the viral life cycle in its natural host.

Even very basic knowledge is lacking. Viruses have been isolated from bat urine successfully, and detected using sensitive PCR-based techniques (which don't prove an infectious virus is present) from bat urine and faeces etc, but do we know if bat faeces is infectious and if so, for how long? That knowledge may solve some riddles about transmission cycles for bat viruses. When I recently asked Prof Linfa Wang about this, he was pretty clear on what we don’t know:

“This is a tough question to answer. I don't think anybody has done any "hard science" on this and the answer will vary with viruses anyway.”

As humans move into or remove bat territories, we may be increasing our contacts with them by forcing them to move into areas shared with us. We may be forced to learn more about bats in the future; perhaps now would be a good time to fill in some of our knowledge gaps to make that learning curve a little less steep.