·  Legal News, Analysis, & Commentary

Health & Medicine

The Frequency of Spillover is Difficult to Track

— September 29, 2021

Scientists are trying to figure out how often viruses are transmitted to humans by other species.

Scientists refer to the transfer of viruses and diseases from animals to humans as a “spillover,” and suggest that this phenomenon is actually more common than many people may think.  Moreover, spillover is getting worse as humans move into wildlife habitats and share space with certain species known to transfer unwanted health conditions.

Of course, the coronavirus is likely the first thing that comes to mind.  Scientists believe that the virus was transmitted to human by bats.  Spillover has also caused the deadly Middle East respiratory syndrome, (MERS), which likely moved from bats to camels to humans.  Similar to SARS-CoV-2 (the coronavirus), individuals who are infected with MERS experience severe respiratory distress, fever, coughing, and shortness of breath.  A MERS outbreak occurred in 2002 and 2003 and led to more than 8,000 infections worldwide, leading to the deaths of nearly 10% of those infected, according to data.  Of course, COVID-19 is also associated with a respiratory illness that may lead to pneumonia and acute respiratory distress syndrome (ARDS).

A major difference between MERS and SARS-CoV-2 is that the spread of MERS was limited to the Arabian Peninsula and there have been less than 200 reported cases.  Of course, now that the coronavirus has spread worldwide, scientists are taking a closer look at why spillover continues to occur.

The Frequency of Spillover is Difficult to Track
Photo by cottonbro from Pexels

Plus, a study recently published in PLOS online monitored 431 adults with confirmed cases of SARS-CoV-2 between February and August 2020 in Zurich, Switzerland.  At the time of the study, all participates had fully recovered.  The researchers evaluated the proportion reporting fatigue using the Fatigue Assessment Scale, dyspnea using a mMRC dyspnea scale, or depression using the DASS-21 at six to eight months after diagnosis.  They also evaluated for health complications post-infection.

The team found that “more than half of the participants reported symptoms of fatigue.  One fourth suffered from some degree of dyspnea or had symptoms of depression.  Overall, more than two thirds had not recovered or experienced fatigue, dyspnea or depression at the time of follow-up, with only partial overlap between these outcomes.”  Furthermore, “two fifths of study participants had at least one further healthcare contact related to COVID-19 after acute illness.”  These findings indicate that those who become infected with the coronavirus have a high probability of experiencing both mental health and physical health symptoms after the fact.  The research also supports the need for more information on how spillover might occur and, hopefully, how it can be avoided to prevent long-term health issues.

Most infections never get to the level global coronavirus outbreak has, and thus, it is hard to determine how often spillover occurs.  However, according to a study that was posted online this month (which has yet to be peer-reviewed), as many as “400,000 people each year in South and Southeast Asia might pick up SARS-related coronaviruses directly from bats.”  The research team, led by Peter Daszak, PhD, a British zoologist, and president of EcoHealth Alliance, pulled several data sources to determine this estimate.

The authors have acknowledged that their estimate is just that – an estimate.  Because it is so difficult to factor in undetected cases of spillover, this number would be even greater.  However, the team hopes these findings can serve as a guide for epidemiologists and infectious disease experts as their knowledge of the novel coronavirus continues to develop.


Viruses May Jump From Bats to People More Often Than Realized

MERS vs. SARS: Compare and contrast

Burden of post-COVID-19 syndrome and implications for healthcare service planning: A population-based cohort study

Join the conversation!