Bats. It’s at this time of year – especially with Halloween just around the corner, and when bat-shaped decorations (fairy lights, biscuit cutters, and costumes) start to appear in the shops – that these mysterious animals come to public attention. It’s great news for me of course, as a researcher who works on bats (and vampire bats at that), with so much choice for office décor to choose from! However, is this association that bats = horror doing more harm than good? It’s fitting that Bat Week – an annual international celebration of bats, including how they contribute to ecosystems, and their need for conservation – falls over Halloween (24th-31st October). It gives us in the bat research community a chance to set the record straight and give bats some fair press.
Halloween shopping and office decorating. Photo by Alice Broos.
First of all, bats are an incredibly diverse group of mammals with over 1400 species found in every continent apart from Antarctica. They vary greatly in both size and diet. Pipistrelle bats, which you’re likely to see nipping around Kelvingrove Park in the evening at this time of year, stocking up on insects before hibernation, are very small at ~5 grams and a wingspan of 20cm. At the other extreme, the large flying fox (confusingly named Pteropus vampyrus even though it’s entirely vegetarian) found in southeast Asia can weigh over 1 kilogram, with a wingspan of 1.5m! Whilst insect-eating bats help control populations of flying pests like midges, fruit/nectar-eating bats help pollinate hundreds of species of plants – including avocados, and even agave used to make tequila.
Out of all the hundreds of bat species, there are actually only three that are classic ‘vampire bats’ that need to drink blood to survive. Of these, it’s the common vampire bat Desmodus rotundus which tends to bite large mammals: mainly livestock such as cows, but yes, humans are on the menu as well. However, these bats are so small that even when they do bite, they can only drink about 1-2 tablespoons of blood before they’re full. That’s about 1/16th of the amount you’d donate when giving blood. Compare this to the > 150 species of bat that are hunted for food around the world, and you’ll see that bats have far more reason to fear us than we do them.
Common vampire bat Desmodus rotundus. Photo by Daniel Streicker.
So, whilst 99.99% of bats aren’t going to try to take a bite out of you, are there any other reasons to be afraid?
From a human perspective, bats have a rather unlucky relationship with viruses. They harbour several which can be transmitted to people (or to livestock and then us) and cause serious disease – these are known as ‘zoonotic viruses’. The most famous example of such an occurrence in recent times is related to horseshoe bats in China, identified as the natural host of SARS-CoV and proposed to be the host of SARS-CoV-2. Many of these viruses don’t harm the bats that carry them (as far as we know). For example, fruit bats in Australia host Hendra virus which can be transmitted to horses and humans causing respiratory disease, but bats don’t seem to experience symptoms themselves. Similarly, Marburg virus, which causes a highly lethal haemorrhagic fever in humans, also seems to be symptomless in its Egyptian fruit bat hosts.
Bats aren’t immune to all disease however, and there is one family of viruses in particular that causes severe disease and death in all of its hosts, bats included. This is the family lyssavirus, the most famous member of which is rabies virus. Most commonly associated with dog bites, rabies is fatal in almost 100% of human cases once symptoms have begun to show. Vampire bats, which are native to South and Central America, are hosts of rabies virus and they too can succumb to the disease. Unfortunately, they’re also quite good at transmitting rabies to other animals because they bite during feeding, and the virus is spread by saliva getting into open wounds. European Bat Lyssavirus – a cousin of rabies virus which can cause the same disease – is found in UK bats. Whilst none of our insect-eating bats are going to bite you deliberately, sick, injured, or trapped bats can lash out unexpectedly, so you should avoid handling bats and go straight to your GP for an incredibly effective post-exposure vaccine if you have such a run-in.
Deadly diseases? This is making bats sound worse, not better!
Like any other wild animal, bats need space. You wouldn’t walk up to a bear and expect to come away from the encounter unscathed! One of the reasons that disease outbreaks attributed to bats have risen is that human contact with bats has increased. Bats have been carrying viruses for tens, hundreds, even thousands of years, but deforestation and human agriculture means that we are in closer proximity than ever before and sharing viruses as a result. Habitat preservation is important not only to make sure that we don’t lose several species of endangered bats and their contribution to vulnerable ecosystems, but to reduce the chance of disease spillover.
In some places, where bats are learning to live alongside us, contact with bats is becoming unavoidable. For example, vampire bats may see the livestock that we’ve introduced as an easy meal – sitting in the same field night after night – and some fruit bats have found that commercial orchards provide an excellent buffet. In these situations, we must look to other methods to prevent disease transmission from bats to us. In some countries where bats aren’t protected and are considered pests (such as vampire bats in Peru), governments tried culling programmes to reduce the number of bats. However, this hasn’t helped with reducing rabies cases.
An alternative, which my lab group at the University of Glasgow and a couple of others around the world are working on, is giving vaccines to bats. The idea here is to make enough bats in an area immune to a virus that it can’t survive. No virus in bats = no virus being transmitted to humans. We’re treating bats not as enemies, but as our allies in the fight against disease.
The next time you see a plastic bat in a window, think about the real ‘flesh and blood’ bats outside and how we can help them to continue helping us.
Blog by Megan Griffiths.
Megan is a Postdoctoral Research Assistant at SBOHVM in the Streicker Group working on modelling the transmission of viruses in common vampire bats.