September 21, 2021 – When humans and other species mix and viruses move between them, experts call it ‘overflow’. As humans move and seek new habitats where wildlife lives, and climate change shifts the boundaries of those habitats, scientists predict we will see more of these outgrowths.
Coronaviruses, which is common in bats, is no exception. But it is mostly thought that an intermediate animal bridges the transmission of the virus from bat to human. For example, the respiratory syndrome in the Middle East, or MERS, coronavirus probably passed from bats to camels, and then from camels to humans.
Most people infected with MERS have developed serious respiratory illnesses, including fever, cough and shortness of breath, and about 3 or 4 out of every 10 people with MERS died.
Researchers working on the controversial topic of how SARS-CoV-2 — the coronavirus that causes COVID-19 — made the jump from bats to humans have addressed the broader question of how often such jumps occur, especially directly between bats and people, and their estimate is striking.
According to a pre-print study posted online on September 14, which has not yet been evaluated by peers, as many as 400,000 people a year in South and Southeast Asia, SARS-related coronaviruses can pick up directly from bats. The study focuses on South Asia and Southeast Asia due to the high overlap between human butts there.
Most cases of these ‘unnoticed outbreaks’, as the study authors call them, do not make a public health radar because they simply stick out. The infections remain unnoticed, causing mild or no symptoms, or symptoms similar to those of common viruses. Man Immune system destroy it mostly, leaving antibodies against the virus behind as proof of victory.
In the work yet to be investigated by experts, the researchers, led by Peter Daszak, PhD, a British zoologist and president of EcoHealth Alliance, used various data sources to arrive at their estimate.
One was geographic information about where bats and humans overlap in their habitat. Another source was human blood samples with signs of coronavirus antibodies and information on how long the antibodies lasted. And the researchers also gathered information on how often bats and humans encounter each other.
When they wrote down all this information in the calculations of the risk of people getting a virus through a bat, they reached their estimate of 400,000 such encounters annually.
Recognizing that their work yields only estimates and involves many limitations, the authors say they hope the findings could lead epidemiologists and experts in infectious diseases to surveillance. Maps of where these risks are greatest can help focus resources on capturing infection groups before spreading.