How the Pentagon is planning to use bats in the battle against bioweapons
The last US military attempt to employ bats was a disastrous failure that involved miniature bombs. Now, their remarkable defensive abilities against disease are being eyed
The US military has a long history of enlisting the help of animals in warfare. The bottlenose dolphin’s sophisticated sonar enabled the Navy to detect and clear underwater bombs during the Iraq War, and homing pigeons played a vital role as secret messengers during both world wars, with some awarded medals for bravery.
But there is one animal that the military has had significantly less success in conscripting, and that is the bat.
In the wake of the Pearl Harbour bombing in 1941, hundreds of Mexican free-tailed bats were recruited as part of a hare-brained scheme to blow up Japanese cities by arming the flying insectivores with tiny bombs and releasing them from planes. The idea was that the bats would roost in buildings and explode, killing the enemy as they slept. What could possibly go wrong?
Undeterred, the scientists ran a test of “Project X-ray” using real bats and tiny bombs in June 1943. Things did not go as planned. A report on the experiment stated somewhat evasively that “testing was concluded … when a fire destroyed a large portion of the test material.”
It failed to mention that the barracks, control tower and several other buildings at the auxiliary field station in Carlsbad, New Mexico, were set spectacularly ablaze by escapee bat bombers. The need to maintain military secrecy prevented civilian firefighters from entering the scene, and fire leapt from building to building, incinerating most of the base. As a final insult, a couple of winged missiles went AWOL, taking up roost under a general’s car before exploding.
Project X-ray was later cancelled.
Today, the US military is again interested in bats, not as frontline attackers but as defenders against a potentially devastating threat: Russian bioweapons.
Fruit bats have an almost supernatural ability to harbour some of the planet’s most deadly viruses without getting sick themselves. Inject an Egyptian fruit bat with the Marburg virus – a haemorrhagic relative of the infamous Ebola virus – and nothing happens. Do the same thing to a human, and within a week, the patient is bleeding to death.
These bats’ extraordinary super-immunity has long fascinated virologists, and new research has shed light on how these flying frugivores achieve their supreme skill. Unpacking the mystery involved some cunning detective work from a coalition of scientists at Boston University and the US Army Medical Research Institute of Infectious Diseases. Their work was published in the journal Cell.
“What we are trying to do is to study bat immunology, but that turned out to be a very difficult thing to do when starting from scratch,” said Thomas Kepler, a professor of microbiology at Boston University. It took decades to create the reactive substances necessary to study human or mouse antibodies. With bats, he explained, they were starting from zero.
So Kepler’s team jump-started its work by examining the whole genome of the Egyptian fruit bat, chosen because it is a known reservoir for the lethal Marburg virus. It took two years just to assemble the genome. Once done, they compared it with other mammals’ genomes to hunt for idiosyncrasies, in particular an increase in size in any gene families that control the production of defensive proteins involved with immunity. They found significantly large interferon genes.
“These are interesting and very important, as they serve as the front line of anti-viral defence,” Kepler said. Once a cell has become infected by a virus, the interferons alert the surrounding cells. “They are basically a warning saying, ‘I’ve just been infected’,” he said. Neighbouring cells then start shoring themselves up for a viral invasion.
The other supersize set of genes in the fruit bat controlled the receptors on “natural killer,” or NK, cells. These are essentially the body’s police system for identifying infected cells. Typically, these receptors are activating, which means they trigger the NK cell to kill the damaged cell. But the fruit bat’s NK receptor genes appear to activate and inhibit NK cell function.
This suggested to Kepler and his team that the bat immune system may respond in a unique way to viral infection, offering what he calls “soft protection.” Instead of attacking and killing an infected cell, which leads to a cascade of inflammatory responses in the host, their NK cells might have a more nuanced response. They might, for instance, effectively starve the virus by turning down the host’s cellular metabolism.
The bat’s unique approach to viral infection could also explain why viruses that transfer from bats to humans, including Ebola, are so severe. “A virus that has co-evolved with the bat’s anti-viral system is completely out of its element in the human,” Kepler said. “That’s why it is so deadly – the human immune system is overwhelmed by the inflammatory response.”
Kepler believes that this insight into the fruit bat’s super-immunity could eventually lead to a cure for Marburg. “It’s possible that we could develop drugs that dampen down inflammation and arrest the virus by depriving it of what it needs to grow rather than trying to kill it outright,” he said.
So where do bioweapons come in? Natural outbreaks of Marburg virus infection have occurred in African countries and are rare but extremely deadly, with a fatality rate of up to 90 per cent. There is no antidote – and that has made the Marburg virus a prime candidate for biological warfare.
The Soviets had a keen interest in the Marburg virus in the 1980s and managed to develop an especially lethal strain after an accident at the Vector Institute, their germ warfare centre in Siberia. The chief scientist there, Nikolai Ustinov, accidentally injected his thumb with the virus, which was intended for a guinea pig he was holding.
Ustinov suffered a devastating death, but the Soviets managed to profit from the mistake by harvesting Ustinov’s organs for fresh samples of the virus. These proved to be even more powerful than the original strain. According to a former institute insider who wrote a book on his experience, Ken Alibek, the Soviets named it “Variant U” and sent it to be approved for use by the Soviet Defence Ministry in early 1990.
The Marburg virus is classed as a Category A bioterrorism agent by the Centres for Disease Control and Prevention, and Kepler’s study was supported by the Defence Threat Reduction Agency, a Defence Department division established during the Manhattan Project era to combat weapons of mass destruction.
If the virus is ever deployed as biological warfare, the fruit bat’s super-immunity may hold the answer to preventing its spread. But it may also go some way toward redeeming the bat in the eyes of the US military – and could even make the animal an unlikely hero.