Coronavirus story: nocturnal mammals, camels and the common cold

Published on Wednesday, April 1, 2020

By: Gary Pettus, gpettus@umc.edu

Coronaviruses are not new, but when it comes to potential reach and scope, the one now spreading fear and uncertainty across the world may wear the crown.

While many people may know it as “COVID-19,” that is the name of the disease, or range of symptoms, caused by the virus identified as “SARS-CoV-2: Severe Acute Respiratory Syndrome Coronavirus 2.”

As the numeral 2 implies, this isn’t the first SARS virus to appear. The first one reared up during a 2002-03 outbreak, but no cases of SARS-1 have been reported anywhere since 2004.

In contrast, SARS-2, the virus that causes COVID-19, is still cranking up, at least in the United States and many other countries. The case count is increasing daily, along with the number of reported deaths.

“The coronavirus strain that causes COVID-19 is in the same group as the Severe Acute Respiratory Syndrome (SARS) virus, as well as several bat coronaviruses,” said Dr. Jose Lucar Lloveras, assistant professor of medicine in the Division of Infectious Diseases at the University of Mississippi Medical Center. “They also appear to use the same receptor (a structure that receives and binds, or attracts, a certain substance) to enter the human cells and cause disease.

“However, they do have some differences in their genetic material, some of which may make the current virus more transmissible. It is important to note that experts all around the world are currently studying this virus, so we will continue to learn more about the true mortality rates of COVID-19 over time.”                  

We began learning about coronaviruses in general more than 50 years ago when virologists first described them. While their stubble of protrusions, as viewed with an electron microscope, resembles another destructive force – sea mines – scientists, in the late 1960s, chose a less threatening image to identify them: a crown, or corona.

Four coronaviruses cause the common cold, but they do not represent the most common cause, Lloveras said. A virus whose name refers to another type of protuberance – your nose – does.

“There are over 200 viruses identified as causes of the common cold,” said Lloveras, who also serves as medical director of the Outpatient Antimicrobial Service at UMMC. “Certainly, rhinoviruses are the most common viruses associated with cold symptoms, and may explain up to half of those cases.”

Rhinoviruses originated in camels, as did one of the four coronaviruses responsible for colds, at least one study found. But Lloveras said with SARS 2, it is very likely that bats are the primary reservoir for the virus.

“Bats tend to get a number of diseases they tolerate fairly well,” said Dr. Donna Sullivan, UMMC professor emeritus in the Division of Infectious Diseases. “They seem to carry rabies without dying from rabies. Bats are unique: They can live as long as 50 years, depending on the species, and they fly, so they can migrate vast distances. They spread viruses through guano they leave behind.

“They seem to be a source of a lot of new viruses we have seen recently, like SARS and the Nipah virus.”

When it comes to human infection, camels are also a risk factor for the Middle East respiratory syndrome (MERS), discovered in 2012. It is also caused by a coronavirus.

As of 2020, more than 2,500 MERS cases had been reported in more than 20 countries, with about 860 deaths – a fatality rate of an estimated 30 percent, Lloveras said. But, as the Centers for Disease Control and Prevention reports, MERS poses a “very low risk” in the U.S.

By contrast, “the case-fatality rate of the SARS virus during the 2002-2003 outbreak was estimated to be slightly under 10 percent,” Lloveras said.

As for the currently raging SARS –SARS 2 – the fatality rate changes as more cases are diagnosed. It varies from age group to age group and even from country to country.

At one point, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, wrote that because of the high number of unreported cases, the death rate may be much lower than 1 percent. Early estimates, though, placed it between two to three times higher than that.

“Most people present a mild form of the disease, but people should keep in mind that these include cases of pneumonia that may not require hospitalization,” Lloveras said. “Some people who become infected may even remain asymptomatic, which means that they may carry the virus for several days without developing any symptoms.

“However, it is estimated that about one of every five people who develop symptoms may have a more severe form of the disease, and some of these will require admission to the intensive care unit.”

The pandemic’s starting point was China, in Wuhan City, Hubei Province, in December 2019. The virus appears to have passed from animals to humans and then from humans to humans.

“That seems to be appearing more and more frequently,” Sullivan said. “In China, it’s probably due to the ways agriculture is done. And there are the live markets, where you pick out your lunch while it’s still standing: It’s not like going to Kroger and buying your chicken wrapped in plastic.

“When a lot of people and animals are in one place, you increase the risk of these kind of species-to-species spillover events.”

Epidemics and pandemics have beset humans throughout history, Sullivan said. There was Justinian's Plague, which was transmitted by black rats and affected nearly half of the population of Europe in the sixth century. About 800 years later, one of at least three bubonic plague pandemics, the Black Death, transmitted from fleas to rodents to humans, killing as many as 30 million people, estimates say.

“It wiped out a significant portion of the planet, at least in Europe,” Sullivan said.

But the “Spanish” influenza pandemic of 1918-19 was the “Mother of All Modern Epidemics,” Sullivan said. About 500 million people, or one-third of the world’s population at the time, became infected. The fatality rate was above 2.5 percent, compared with less than 0.1 percent for other flu pandemics.

A report by the CDC said many flu pandemics since that time descended from the 1918 virus.

“The problem with pandemics like this one now is we really can’t predict where they’re coming from and how fast they will spread,” Sullivan said. “When you have a new disease, you have a population of humans who have never seen it before. They have no natural immunity.

“When it spreads readily and easily from one person to another, a lot of people will be infected.”

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