Bats and the search for the zoonotic link

05/27/2020

Gabe Reyes, one of the primary field biologists researching native bat populations in Marin, can no longer handle bats under guidance handed down this month by the California Department of Fish and Wildlife. The fear is that Mr. Reyes and the state’s 50-some researchers permitted to handle the animals could introduce Covid-19 to North American bat populations.

“There are two concerns here related to bats and Covid,” said Dr. Scott Osborn, the small-mammal conservation coordinator for Fish and Wildlife who helped inform the recent guidance. “The first is that we may, as humans, actually infect our North American bats with the virus, creating problems for their populations. The other is that if the virus takes hold, they could serve as a wildlife reservoir for the disease, spreading it back to humans.”

So far, Dr. Osborn said there is no evidence that bats outside of Asia have been infected with SARS-CoV-2, and he considers the possibility in the United States unlikely. Yet until there is more research into the risk of transmission between bats and humans, prohibiting direct contact was necessary, he said. 

There is strong evidence to suggest that the novel coronavirus originated in bats. Scientists at the Wuhan Institute of Virology in January identified a genome sequence of a coronavirus in horseshoe bats that was 96 percent identical to the one at fault for causing the global pandemic. But how the virus transferred from bats to humans remains under study, and experts suggest a third species made the transfer. 

The World Health Organization last week called for collaborative field research to confirm the zoonotic source of the virus and the route of its introduction to humans.

The May 6 state bat directive prohibits a variety of activities until further notice. These include the capture of live bats by mist netting, hand netting and harp trapping. Measurements, tissue sampling, banding and other marking are also on hold. 

The directive includes new safeguards for other wild mammals, including disinfecting, handwashing, and—for carnivores—wearing face coverings.    

“I am missing the field work, missing running around, and, like most people, I’m going a little stir crazy,” said Mr. Reyes, who is employed by the United States Geological Survey. 

For the past four years, Mr. Reyes has participated in an interagency monitoring program intended to establish baseline data on seasonal bat roosting and nesting sites, behaviors, and species prevalence throughout Marin. The program is managed by the partners of the One Tam campaign, including the National Park Service, Marin County Parks, California State Parks, Marin Municipal Water District and the Golden Gate National Parks Conservancy. 

A 2016 report on the Mount Tamalpais area pointed out the dearth of data on bats locally. Bats are considered an indicator species for environmental degradation, because they can be heavily affected by climate change, habitat loss, roost disturbance, pesticides and insect declines, and disease.

Mr. Reyes had just finished his winter research when sheltering began in March. He conducts both winter and summer radio telemetry studies—whereby tiny transmitters are glued to the backs of bats caught in mist nets—to determine which types of habitats bats are using at different times of the year. 

Many of the 13 species found in Marin hibernate in the winter, making learning about their habitats especially difficult during those months. Yet Mr. Reyes said he successfully tracked several species this winter, and even caught a female hoary bat, a rare sight in Marin. 

Telemetry studies will not proceed this summer. But the monitoring of roosts, or breeding sites, will continue, since it does not require contact. In the Point Reyes National Seashore, two known maternity roosts are the Randall House, an abandoned farmhouse off of Highway 1 in the Olema Valley, and an uninhabited structure at Commonweal in Bolinas. 

Dr. Osborn said there are several studies in particular he has his eyes on.

A risk assessment expected for release this week, conducted by 13 experts in bat biology, physiology, virology and epidemiology convened by the U.S. Fish and Wildlife Service and U.S.G.S., which will address the possible transfer of SARS-CoV-2 between humans and bats. The assessment used the Delphi method, aggregating the opinions of the scientists.  

Dr. Osborn has seen the preliminary results. “In a nutshell, they think that without [personal protection equipment], the risk is somewhat high to spill over [into bats]. With protection, the risk is extremely low,” he said.

The assessment also contemplated the risk of spread within bat populations, and Dr. Osborn expressed concern. “That came up with a one-third probability,” he said. “If it does get into a native bat species, it could spread. That’s a high probability, in my opinion.”

Dr. Osborn said Fish and Wildlife is awaiting the results of a study out of the University of Wisconsin on big brown bats, also found in California. The researchers inoculated the bats with the coronavirus and are testing to see if they get sick, and how they may or may not spread it to each other. 

Internationally, there are widespread efforts to determine the species that may have transferred SARS-CoV-2 from bats to humans, and which native and domesticated species are susceptible to the virus and could become reservoirs for spread. To date, pangolins are a leading candidate for the intermediate host, and in a lab setting, ferrets, macaques and hamsters have been shown to be susceptible to infection. Outside the lab, pet cats and dogs, captive tigers and lions, and farmed mink have also caught the virus, likely from people. 

Researchers are also looking at other factors involved in species-to-species spillover. One team of scientists from the University of Saskatchewan in Canada published a study this month that argued that when bats are under stress, either from habitat loss or other diseases, the viruses in their bodies that don’t normally cause them sickness multiply and are more easily spread. 

Bats carry other types of coronaviruses, some of which are found in other mammal and bird species.

The viruses in wildlife often do not cause illness, but sometimes they do. Locally, a die-off of harbor seals in 2000 in the Point Reyes National Seashore was attributed to a type of coronavirus. Dr. Frances Gulland, a research associate at the University of California, Davis who co-authored a study on the die-off, said it made sense to study the event again. Around 100 seals died. 

“No one really cared at the time,” Dr. Gulland said. “But now, of course, it makes sense to screen more harbor seals, and to see how prevalent it is. Obviously, with the concerns now for human health, we want to know where it came from and why it happened so suddenly.”

The U.S.G.S. said in a bulletin last week that it will test for coronaviruses in the event of any unusual die-offs.  

As of this week, Dr. Osborn is the only bat researcher in the state who has been granted an exception to the bat handling prohibition. This is a key year in California to study white-nose syndrome, a deadly disease that has wiped out millions of bats nationwide. The fungus was first identified in 2018 in a population of bats in Plumas County; now, two years later, he says the work is essential to find out if it has taken hold locally. 

He plans to wear a mask, gloves and disposable coveralls. His work will involve catching the bats in nets and swabbing them with a sterilized solution to take samples. Basic protections, such as gloves, are typical.  

Mr. Reyes said that in recent years, the word about the importance of bat conservation has spread, but that he laments the stigma that’s reviving against the species in light of the pandemic. 

“I always try to stress the point that bats, like all wildlife, have diseases, just like people do, so you should have a cautious approach, appreciating wildlife from a safe distance,” Mr. Reyes said. 

He added, “Bats, just like any other wildlife, aren’t trying to introduce diseases to us. They provide a lot of important ecological services, like eating mosquitos and other forest pests. Considering them is really important in keeping a healthy ecosystem intact.”