Posts Tagged Bats
The Ebola virus was “discovered” in 1976 causing trouble for people living near the Ebola River in the Democratic Republic of Congo (DRC). Since then it has popped up several times in the DRC, Sudan and Uganda. The current outbreak is the first to involve Guinea, Liberia and Sierra Leone.
The virus itself is a filovirus, a group of long filamentous RNA viruses that are surrounded by a lipid envelope. It causes a severe disease in people characterised by vomiting, abdominal pain, fever, headache and bleeding. Symptoms usually appear eight to 10 days after infection but this can range from two to 21 days. Mortality rates can be as high as 90%. Unlike influenza, people tend not to be infectious until they are symptomatic.
The virus is spread via direct contact with blood and body fluids, although there was a publication indicating airborne spread between pigs and monkeys (Weingartl et al 2012). Although not in direct contact the two groups of animals were caged only eight inches apart. According to a second report it appears that the Ebola virus causes a different disease in pigs compared with primates (http://www.vox.com/2014/8/10/5980553/ebola-outbreak-virus-aerosol-airborne-pigs-monkeys/in/5712456). The virus hits the lungs of pigs, whereas the liver is the main target organ in primates. Therefore, while pigs can cough and sneeze out viral particles, primates tend to shed large numbers of virus in the blood and faeces, making airborne transmission unlikely. This is borne out by the current situation. If the Ebola virus was as contagious as the influenza virus we would all be drowning in our own blood by now. Instead the outbreak has remained relatively localised.
The main reservoir of Ebola virus is unknown although, as with most emerging diseases nowadays, bats have been fingered as the main culprit. Ebola has been found in gorillas, chimpanzees and duikers but, as they also develop clinical disease and die, they are unlikely to be a reservoir. However, as they are part of the bush meat cycle they represent a great way for the virus to spread to people.
The virus itself is not particularly hardy. It can survive for several days at room temperature but is destroyed by boiling for five minutes, and common disinfectants such as bleach, phenolics, glutaraldehyde, formaldehyde and 3% acetic acid (vinegar is 4-8% acetic acid). Alcohol hand wipes and washing with soap and water are also effective at killing the virus.
Unfortunately there is no vaccine and no treatment. ZMapp, a drug made of monoclonal antibodies, has been used experimentally but, oddly, there appears to be some debate over the ethics of using this unlicensed drug on people. I know that if I was infected with Ebola and someone waved a drug at me that might or might not work, I would certainly risk it.
The biggest problem in controlling the current epidemic is a lack of infrastructure and knowledge. I can imagine that it is not easy to convince people with very little or no education that a thing that is far too small to see is killing off your family, friends and community. And no, it is not us, the aid workers, who are bringing it in. And yes, you really should stop eating bush meat, even though it is a centuries old tradition. And no, if someone dies don’t wash the body by hand. And yes, we really need you tell us if you, or someone you know, is feeling sick so we can stop them spreading the virus to other people. Please don’t hide them at home. With early medical care they do stand a chance of recovery. Previous Ebola outbreaks had mortality rates of 90%. This one is running at 60%. So it is possible to survive an Ebola infection.
As an interesting aside to the Ebola issue, in 1989 shipments of monkeys were imported into a holding facility in Reston in the US from the Philippines. Those monkeys died with symptoms similar to those caused by an Ebola virus infection. It turned out they were full of a related filovirus subsequently named Reston virus. Interestingly, 14% of the people who had contact with the monkeys had filovirus antibodies, indicating they had also been exposed to the virus. It was just lucky that this, closely related virus, does not appear to cause disease in people. It is amazing that such a small change in viral structure can turn a harmless virus into a lethal one.
Dr. F. Bunny
Weingartl H.M., C. Embury-Hyatt, C. Nfon, A. Leung, G. Smith, and G. Kobinger. 2012. Transmission of Ebola virus from pigs to non-human primates. Scientific Reports 2, 811; DOI:10.1038/srep00811.
From the South China Morning Post: http://www.scmp.com/news/world/article/1352671/us-wind-energy-turbines-killed-600000-bats-last-year-study-says.
More than 600,000 bats were killed by wind turbines across the United States last year, with the highest concentration of kills in the Appalachian Mountains, according to new research.
In a paper published in the journal BioScience, University of Colorado biologist Mark Hayes used records of dead bats found beneath wind generators and statistical analysis to estimate how many bats were struck and killed by generator propellers each year.
“Dead bats are being found underneath wind turbines across North America,” Hayes wrote. “This estimate of bat fatalities is probably conservative.”
The new estimate is among the highest yet for generator-related bat deaths. Previous studies have calculated mortality rates of between 33,000 and 888,000 a year.
The bat deaths were calculated on a per megawatt basis, and the highest rates were associated with generators in the Appalachian Mountains-Buffalo Mountain, in the state of Tennessee, and Mountaineer, West Virginia.
Hayes said his estimates were conservative for several reasons.
Little information on bat mortality was available for wind generators along the Sierra Nevada ranges and Rocky Mountains, he wrote, and scavenging animals likely carried away a percentage of dead bats before they could be counted.
Hayes also said that if a range of bat deaths were listed by a facility, he used the lowest one for his calculations.
There are 45 known bat species in the continental United States, but biologists do not have a firm handle on their total population. Experts say the animals’ small size and nocturnal habits make them difficult to survey.
Nonetheless, biologists suspect their numbers are decreasing because of changing climate and diseases such as white-nose syndrome.
Even under the best circumstances, bat populations grew slowly, as they give birth to one pup per year, and the mortality rate for young bats was high, Hayes said.
While they are not generally beloved by the American public, bats perform two highly valuable services: they eat enormous amounts of flying insects, and they help pollinate crops like peaches and avocados.
In a world of climate change we are all (well, maybe not the coal and oil companies) looking for alternative ways to generate energy that do not produce greenhouse gases. It seems ironic that the nuclear industry has seen this as a potential opportunity to appear green and a viable alternative to coal power. Apart from the fact that plutonium is still deadly for 250,000 years and countries like Germany appear to be winding their nuclear programs down in the wake of the Fukushima disaster, nuclear is no more sustainable than coal or oil. Uranium will run out just like all the fossil fuels, so why go down a potentially lethal path for the sake of a few years of power? Forget the nuclear nonsense and head straight to the technologies that will keep my computer alive and active long after I’ve nourished a few thousand worms.
Which brings me to wind farms and turbines. As usual, a lot of nonsense is being spouted by both sides. One memorable newspaper article described opposition to turbines because they would negatively affect the migrating orange-bellied parrot, with a lovely full colour photo of the parrot accompanying the article (http://www.theage.com.au/articles/2006/04/05/1143916574751.html). Interestingly these turbines were destined for a site east of Melbourne, in an area not visited by OBPs, who prefer the saltmarshes west of Melbourne for their overwintering grounds.
Nevertheless turbines do kill birds and bats, 100,000 to 440,000 birds each year according to the US Fish and Wildlife Service (http://www.nature.com/news/the-trouble-with-turbines-an-ill-wind-1.10849), generally through direct collisions. This is, however, considerably fewer than are killed by cars (60-80 million), building strikes (100,000 to 1 billion), power lines (up to 175 million) and our old friend, the pussy cat (365 million to 1 billion). Very rubbery figures to be sure, but significant nonetheless.
Bats, however, die in a more interesting way. The movement of the propellers generates a significant area of low pressure behind the turbine (five to 10 kilopascals less than the surrounding air). As nature abhors inequality, when the unsuspecting bat flies into this low pressure region the relatively higher pressure inside its body attempts to equalise with the lower pressure outside its body. It does this by expanding outwards, which leads to ruptured blood vessels and lungs filled with blood (http://www.scientificamerican.com/article.cfm?id=wind-turbines-kill-bats). I can certainly attest to this, having necropsied affected bats. There are no external signs of damage but their chests are certainly full of blood, caused by this barotrauma.
What to do? Do we sacrifice some birds and bats on the altar of climate change, because none of us want to return to pre-electricity days but we also don’t want our planet to heat up? You can’t make an omelette without breaking eggs, and all that. Rather than scrap a potentially important source of sustainable power one suggestion is to be smarter about placing wind turbines away from bird and bat flight paths in the first place. While this is sensible in principle we don’t know enough about their pathways to make this work reliably.
What shows more promise is redesigning the turbines themselves. On a recent ski trip to Copper Mountain in Colorado I saw some wind turbines on the very top of the mountain. But these turbines were different to the traditional horizontal axis turbines we are all familiar with. They were vertical axis turbines. Instead of having a big propeller spinning on a pole, they had vertically orientated blades which spun around the central pole. I had never seen this design before, but it could be the answer. According to a report these vertical turbines are less dangerous than the horizontal ones because they don’t use propeller-like blades to capture the wind, but rotating open-framed cylinders (http://www.msnbc.msn.com/id/44627832/ns/technology_and_science-innovation/t/upright-turbines-breathe-new-life-wind-farms/). The downside is that they don’t generate as much electricity as the traditional turbines. However, according to the article, “putting windmills upright and spacing them more tightly together can generate more electricity on less land, and kill fewer birds or bats than traditional horizontal rotating wind turbines.” These vertical turbines are also only 30 feet high, which is below the migratory level for birds and bats.
It is amazing how resourceful we can be when we have to. It’s just a shame that resourcefulness only materializes when we are faced with a catastrophe. But that is how we operate, I guess. Why waste time on things that might happen, like Y2K, when there are so many things that are happening to worry about? It does make preventative medicine particularly hard to sell, however.
Dr. F. Bunny
A recent literature survey identified 1407 recognised species of human pathogen, 58% of which are zoonotic i.e. transmissible from animals to people. Of these 177 are regarded as emerging or re-emerging, with 73% of these being zoonotic (Woolhouse and Gowtage-Sequeria 2005). At first glance bats appear to be over represented as reservoirs of disease, being maintenance hosts for potentially fatal viruses like Australian Bat Lyssavirus, Hendra virus, Nipah virus, and Menangle virus. Bats, not civets, may also be the natural reservoir for SARS and the ever popular Ebola virus (not great apes as was initially thought). So, what is it about bats that make them such popular hosts for some of our scariest diseases?
Bats, in fact, are not over represented as ungulates (cattle, sheep, goats, etc) support the majority of the world’s zoonoses (over 250) and emerging diseases (over 50). Bats harbor less than 2% of human pathogens (Dobson 2005). Unfortunately the ones they do carry are associated with high human mortality rates, making them of much more interest to the media.
It is important to remember that there are a lot of bats, approximately 1240 different species. This represents more than 20% of all known mammal species (second only to the rodents). Bats are also the only mammal that can fly. Therefore, they have more opportunity to contact animals at different locations, enhancing opportunities for spread and transmission. Bats live in large groups, which also increases the potential for disease spread. Just look at how quickly the common cold rips through human populations.
One interesting theory postulates that there are good viruses as well as bad (this is starting to sound like an episode of Red Dwarf – http://en.wikipedia.org/wiki/Quarantine_(Red_Dwarf)). Hendra virus causes no disease in bats but does stimulate the bat’s innate immunity. This may help to protect it from other disease agents. Hendra virus normally persists at low levels in bat colonies. However, under conditions of stress, such as habitat destruction or potential predation, viral load and, therefore, viral shedding increases. As the virus is particularly deadly to other species, such as horses and humans, its release could act like a protective umbrella for the colony (Wang et al 2011).
Most of these disease agents evolved with bats over a long period of time and cause them no trouble. As habitat continues to be cleared, these viruses will contact new hosts (i.e. humans) with no prior immunological knowledge of them with ever increasing frequency. Viruses, like the rest of us, don’t enjoy being kicked out of their comfortable homes and forced to live somewhere new and strange. They tend to get a bit grumpy and anti-social and attempt to demolish their new house. Unfortunately for them, as the house is destroyed, so are they.
Our ability to diagnose diseases is always improving. Incredibly a recent paper reported that 57.2% of fatal encephalitis cases in Australia between 1993 and 2006 were undiagnosed (Huppatz et al 2009). Some of these cases could have been caused by previously unrecognised viruses. It is also a case of the more you look the more you find. Now that our antennae are up we will be searching harder than ever before and are almost certain to turn up new viruses (in fact a relative of the Ebola virus popped up recently in bats in Spain (Negredo et al 2011)).
This should not, however, be interpreted as open season on bats. Bats perform an incredibly important function as seed dispersers, plant pollinators and consumers of vast quantities of insects, many of which harm agricultural crops (Wibbelt et al 2010). Their demise would be catastrophic for agriculture and the planet as a whole. As we expand into new habitats novel diseases will continue to pop up, not just in bats, but likely in a range of species. We need to be aware of the risks, take steps to mitigate them and, in the words of John Howard, “be alert but not alarmed.”
Dr. F. Bunny
If, like me, you want to keep abreast of the situation and have all the latest disease information at your fingertips there are a few excellent websites worth consulting. The Centers of Disease Control and Prevention site contains a wealth of information about every disease you can think of, and probably quite a few you can’t: http://www.cdc.gov/. ProMED provide twice daily alerts about new diseases as they break. They cover not just human diseases but animal and plant ones too. Truly a hypochondriac’s delight: http://www.promedmail.org/. And if all that isn’t enough to make you live inside a plastic bubble for the rest of your life download the HealthMap app to your phone for disease alerts near you: http://www.healthmap.org/en/.
Dobson A.P. 2005. What links bats to emerging infectious diseases? Science 310:628-629.
Huppatz C., Kelly P.M., Levi C., Dalton C., Williams D. and Durrheim DN. 2009. Encephalitis in Australia, 1979-2006: trends and aetiologies. Communicable Diseases Intelligence 33:192-197.
Negredo A., Palacios G., Vazquez-Moron S., Gonzalez F., Dopazo H., Molero F., Juste J., Quetglas J., Savji N., de la Cruz Martinez M., Herrera J.E., Pizarro M., Hutchison S.K., Echevarria J.E., Lipkin W.I. and Tenorio A. 2011. Discovery of an ebola-like filovirus in Europe. PLoS Pathogens 7:10:e1002304.
Wang L.F., Walker P.J. and Poon L.L.M. 2011. Mass extinctions, biodiversity and mitochondrial function: are bats “special” as reservoirs for emerging viruses? Current Opinion in Virology 1:649-657.
Wibbelt G., Moore M.S., Schountz T. and Voigt C.C. 2010. Emerging diseases in Chiroptera: why bats? Biology Letters doi:101098/rsbl.2010.0267.
Woolhouse M.E.J. and Gowtage-Sequeria S. 2005. Host range and emerging and reemerging pathogens. Emerging Infectious Diseases 11:1842-1847.