A reservoir of contagion
As dusk descends over the little orchard, the first bats emerge in the bluish grey haze, silently slipping out from the shining thickets of fruit trees that have finished bearing for the season. I stay still on a warm rock seat watching the various varieties, some in pairs, sweep across to start hunting insects such as the hordes of mosquitoes that followed the last heavy rains.
Over 500 plant species rely on bats to pollinate their flowers, including cocoa, banana, guava, cashew and my favourite delight, mango, about a dozen types of which, including a miniature Buxton spice, are crammed in the tropical plot of green reserve within the busy borough, where we live.
I see them at night constantly flitting past as I walk around the yard, or expertly manoeuvring through the house and unerringly back out when I forget to close the front door and windows. The only mammals to have developed powered flight, bats arose about 50 million years ago and today number more than 1,400 species distributed worldwide, except in Antarctica.
While they are a key part of a balanced natural environment, they continue to mysteriously coexist with the highest number of viruses among mammals, including SARS-CoV-2, the novel or new coronavirus which causes the conditions associated with COVID-19 that has infected at least 219 million (M) and killed 4.6M people to date, among them unvaccinated individuals including the 36 Guyanese who died in just one week recently.
Another two patients succumbed yesterday with about 360 new cases being reported, as baffling vaccine hesitancy and entrenched disinformation through unfounded conspiracies increasingly claim fresh victims, providing the breeding ground for wilful ignorance and viral variants that could prove even harder to beat. The reservoir of contagion, it seems, is not only among the unique bats.
Researchers believe that the bat has evolved a super immune system, with special adaptations such as during high-powered flight when they release tremendous energy causing the creature’s body temperature to soar over 100 degrees Fahrenheit, and its heart rate to top an incredible 1,000 beats per minute.
In us, one tenth of such a rate would be immediate cause for concern, while the temperature reaction would amount to a high fever, prompted by pathogens such as Sars-CoV1 and 2, which are known to induce excessive inflammation that can eventually lead to human death.
Three years ago, scientists including the foremost authority nicknamed “Batman,” Professor Lin-fa Wang, discovered an intriguing genetic mutation that manages the antiviral response in bats. Mr Wang is a Professor in the Programme in Emerging Infectious Diseases at Duke-NUS Medical School, Singapore, and one of the world’s leading specialists in bat immunology, and zoonotic diseases or infections that are transmitted between species from animals to humans or vice versa.
Found in a group known as the stimulator of interferon genes (STING) which plays an important role in innate immunity, the bat mutation dampened the production of specific inflammation-causing proteins called interferons. “The nature of the weakened, but not entirely lost, functionality of STING may have profound impact for bats to maintain the balanced state of ‘effective response’ but not ‘over response’ against viruses,” the researchers said.
International experts dispatched to China by the World Health Organization (WHO) in a major investigation this year, concluded it was most likely that the SARS-CoV-2 virus jumped from bats to humans through an intermediate animal, within the festering markets that sold live and dead creatures, such as at Huanan in Wuhan. The WHO declared the pandemic in March, 2020. As likely intermediaries, the WHO listed pangolins, mink, rabbits, raccoon dogs and domesticated cats.
Termed a “spillover event,” scientists like Professor
Wang have long warned about the consequences of transmission of a deadly disease from one species to humans, given the estimated 1.6 million different viruses circulating in the animal kingdom. His team found that SARS-CoV-2-related coronaviruses are in bats and pangolins in Thailand. One of the closest known relatives of SARS-CoV-2 is a coronavirus strain found in a bat sample from Yunnan province, China, in 2013, that is 96 per cent genetically identical. This week, researchers from the Pasteur Institute and the University of Laos reported that horseshoe bats living in a cave in that country, bordered by Myanmar and China carry a similar pathogen to SARS-CoV-2 that could potentially infect humans directly.
Coming from a big family of viruses that usually cause mild to moderate upper-respiratory tract illnesses, coronaviruses mostly circulate among animals such as bats, pigs, civet cats and camels, but three of the seven that seriously affect us have popped up over the past 20 years. These are the two SARS coronaviruses, the first in late 2002, and the second leading to COVD-19 some 18 months ago; and the Middle East Respiratory Syndrome (MERS) caused by the MERS coronavirus (MERS-CoV), identified in 2012 and transmitted from an animal reservoir in camels.
In the mid-1990s, an earlier novel virus began affecting horses and humans in Brisbane, Australian. Another emerged in Malaysia. Professor Wang helped confirm that these, the Hendra virus and Nipah virus named for the places where they had first broken out originated with bats. The Nipah virus may have leaped to humans after forest fires to clear land forced bats beyond their normal habitat.
“If a bat is stressed, bad things can happen,” Professor Wang told the New York Times in an interview. “We need to take care of bats. Then we can take care of humans.”
ID looks back to the Tacaribe virus, first isolated from bats and mosquitoes during a rabies surveillance survey conducted in Trinidad from 1956 to 1958. An unusual virus it has never been associated with a rodent host but studies spotted it in Florida’s ticks and there is evidence it is still among bats in Trinidad and Tobago.