The efficiency of transmission for any respiratory virus has important implications for containment and mitigation strategies. A study by Li and colleagues indicates an estimated basic reproduction number (R0) of 2.2, which means that, on average, each infected person spreads the infection to an additional two persons. As the authors note, until this number falls below 1.0, it is likely that the outbreak will continue to spread. Recent reports of high titers of virus in the oropharynx early in the course of disease arouse concern about increased infectivity during the period of minimal symptoms.
Anthony S. Fauci, Clifford Lane, and Robert R. Redfield
New England Journal of Medicine, February 28, 2020
The United Nations has launched a £1.5 billion global humanitarian response that will combat the spread of coronavirus in the world’s most vulnerable countries, as the organization insisted that it was time for humanity to “fight back” against the deadly pathogen.
Covid-19 has already upended life in some of the world’s wealthiest countries. It is now reaching places where people live in warzones, cannot easily access clean water and soap, and have no hope of a hospital bed if they fall critically ill.
To leave the world’s poorest and most vulnerable countries to their fate would be both cruel and unwise. If we leave coronavirus to spread freely in these places, we would be placing millions at high risk, whole regions will be tipped into chaos and the virus will have the opportunity to circle back around the globe.
Mark Lowcock, United Nations Secretary-General for Humanitarian Affairs, March 25, 2020
A novel and sometimes deadly respiratory illness that originated in a live animal market in China is rapidly spreading throughout that country with cases now being reported around the world.
In December of 2019, an outbreak of viral pneumonia was reported in Wuhan City, Hubei Province, China. In January 2020 a novel coronavirus was identified as the causative agent of the outbreak. The virus, temporarily named 2019-nCoV but now called COVID-19 (which stands for coronavirus disease-2019), has caused a widespread epidemic throughout China, with exported cases occurring on four other continents, including North America.
Chinese health officials have reported tens of thousands of cases in China. At the start of the epidemic, most of the COVID-19 infections outside of Wuhan were associated with travel from that area. Now, the virus is spreading person-to-person in many parts of China and other parts of the world (NIH, 2020a).
China has taken the unprecedented measure of quarantining nearly 60 million people but the virus is still spreading beyond its borders. Though the vast majority of cases are in mainland China, there have been hundreds of cases confirmed outside of China and those numbers increase daily (CNN, 2020a).
The United States reported the first confirmed instance of person-to-person spread on January 30, 2020. On the same day, the World Health Organization (WHO) declared the novel coronavirus outbreak a public health emergency of international concern. “The main reason for this declaration is not because of what is happening in China but because of what is happening in other countries. Our greatest concern is the potential for the virus to spread to countries with weaker health systems, which are ill-prepared to deal with it,” WHO Director-General Tedros Adhanom Ghebreyesus said (CNN, 2020a).
“A public health emergency of international concern” is an event that poses a global health risk that may require a coordinated international response as happened with Ebola, Zika, and H1N1 (CNN, 2020a).
On January 31, the United States declared a public health emergency to aid the nation’s healthcare community in responding to COVID-19 and the President of the United States signed a presidential “Proclamation on Suspension of Entry as Immigrants and Nonimmigrants of Persons who Pose a Risk of Transmitting 2019 Novel Coronavirus” (CDC, 2020b). On March 13, 2020, a national health emergency was declared in the United States.
“The goal of the measures we have taken is to slow the introduction and the impact of the disease in the U.S.,” said Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases. She added that at this time, “Most of the disease is in China. However, we can and should be prepared for this new virus to gain a foothold in the U.S. At some point, we are likely to see community spread here or in or other countries.” (CDC, 2020c).
The number of confirmed COVID-19 cases as of March 28, 2020 include:
- Globally, there are 640,589 confirmed cases; 29,848 deaths; 137,270 recovered.
- Western Pacific Region had 100,018 confirmed cases and 3,567 deaths.
- European Region there are 286,697 confirmed cases and 16,105 deaths.
- South-East Asia Region there are 2,932 confirmed and 105 deaths.
- Eastern Mediterranean Region there are 35,249 confirmed cases and 2,336 deaths.
- Region of the Americas there are 81,137 confirmed cases and 1,176 deaths.
- African Region there are 2,419 confirmed cases and 39 deaths.
Source: WHO, March 27, 2020; Center for Systems Science and Engineering, Johns Hopkins University, March 28, 2020
United States Epidemiology
The number of confirmed COVID-19 cases as of March 28, 2020 include:
- Total confirmed cases: 112,468 (918 recovered)
- Total deaths: 1,841
Source: Center for Systems Science and Engineering at Johns Hopkins University, March 28, 2020.
For global and regional coronavirus cases in real time check out the Johns Hopkins University Center for Systems Science and Engineering.
What Is a Coronavirus?
There are hundreds of coronaviruses, most of which circulate among animals including pigs, camels, bats, and cats. Sometimes these viruses jump to humans—a spillover event—and can cause disease, as happened with Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and now COVID-19 (NIH, 2020b).
Source: CDC, 2020.
Coronaviruses are named for the crown-like spikes on their surface. There are four main sub-groupings of coronaviruses, known as alpha, beta, gamma, and delta. Only seven of these viruses are known to cause human disease—four of which cause mild to moderate upper-respiratory tract illnesses, like the common cold. However, three times in the twenty-first century, coronavirus outbreaks have emerged from animal reservoirs to cause severe disease and global transmission concerns: SARS, which emerged in late 2002 and disappeared by 2004; MERS, which was first identified in 2012 and consistently jumps from dromedary camels to people; and the 2019 novel coronavirus, that emerged in December 2019 from China (NIH, 2020b).
While most coronaviruses only infect animals, MERS and SARS are notable for their ability to infect a variety of species, including humans. Recent research at the National Institute of Allergy and Infectious Diseases (NIAID) shows how the MERS virus can adapt to infect cells of a new species, which suggests that other coronaviruses might be able to do the same (NIH, 201). It appears that COVID-19 has done just that. A global effort is under way to contain its spread (NIH, 2018).
How Coronaviruses Adapt to Infect Other Species
To cause infection, a virus must first attach to a receptor molecule on cells of the host species. This interaction is highly dependent on the shape of the receptors, which the host genes control (NIH, 2018b).
To evaluate how MERS evolves to infect host cells, scientists from NIAID tested 16 bat species and found that the virus could not efficiently enter cells with receptors from the common vampire bat, Desmodus rotundus. They then grew virus on cells that had vampire bat receptors and observed the virus evolving to better infect the cells. After a few generations, the virus had completely adapted to the vampire’s receptors (NIH, 2018).
This illustration shows the bat species used in the study, Desmodus rotundus, or vampire bat, and representations of MERS-CoV (purple) interacting with host receptor DPP4 (gold).
Source: NIAID, 2020.
By studying how the shape of the MERS virus changed over time in order to attach to the new host receptor, the scientists found similarities with prior studies of the SARS virus. Thus, while these two viruses are different, they use the same general approach to enter the cells of new species (NIH, 2018).
The new cluster of viral pneumonia cases originating in Wuhan, China, marks the third time in 20 years that a member of the large family of coronaviruses has jumped from animals to humans and sparked an outbreak.
Anthony S. Fauci, Director
National Institute of Allergy and Infectious Diseases (NIAID)
- 229E (alpha coronavirus)
- NL63 (alpha coronavirus)
- OC43 (beta coronavirus)
- HKU1 (beta coronavirus) (CDC, 2020e)
- Runny nose
- Sore throat
- General feeling of being unwell (CDC, 2020e)
These human coronaviruses can also cause lower-respiratory tract illnesses, such as pneumonia or bronchitis; complications more commonly seen in people with cardiopulmonary disease and/or weakened immune systems, infants, and older adults (CDC, 2020e).
- MERS-a beta coronavirus
- SARS-a beta coronavirus
- COVID-19- a beta coronavirus (CDC, 2020e)
Evidence suggests that both SARS and MERS viruses originated in bats before transmitting to civets and camels, respectively.
Source: NIH, 2018.
Human coronaviruses historically have been regarded as relatively benign causes of the common cold. In 2002, however, a novel, highly pathogenic beta coronavirus emerged in China that caused 8,098 recorded cases of SARS, including 774 deaths, and cost the global economy billions of dollars. Symptoms often included fever, chills, and body aches which usually progressed to pneumonia. Classic public health measures of isolation and containment are likely what brought the outbreak to an end. No human cases of SARS have been reported anywhere in the world since 2004 (NIH, 2020c).
MERS, another beta coronavirus, jumped from animals to humans in 2012. It causes severe respiratory illness with symptoms of fever, cough, and shortness of breath. About 3 or 4 out of every 10 patients infected with MERS have died. The virus spreads from ill people to others through close contact, such as caring for or living with an infected person. These patients have ranged in age from younger than 1 to 99 years old(NIAID, 2020).
Unlike SARS, which was eliminated within several months of the initial outbreak, MERS continues to smolder due to sporadic transmission from camels—the virus’s intermediate host—to people, and limited chains of person-to-person transmission with a roughly 35 percent fatality rate (NIH, 2020c).
The first known cases of MERS occurred in Jordan in April 2012 and so far all cases of MERS have been linked through travel to, or residence in, countries in and near the Arabian Peninsula. The largest known outbreak of MERS outside the Arabian Peninsula occurred in the Republic of Korea in 2015. That outbreak was associated with a traveler returning from the Arabian Peninsula (CDC, 2019a).