Medical Tuesday Blog
Corona-flu-virus in Perspective
Covid-19, Sars-CoV-2, MERS, Ebola, Marburg Virus
All have a natural reservoir in Bats
The common cold virus, the most ubiquitous of the upper respiratory infections, was first isolated in 1956. Subsequently, many more viruses involving the nose and throat (coryza or rhinoviruses) were isolated. They are contagious from 1-2 days before symptoms begin until they are resolved. The virus spreads from coughing or sneezing. There are 113 immunologically distinct but biologically related rhinoviruses. Many cold viruses have not yet been identified. They are part of the Picorna RNA group of viruses inactivated by acid which is probably why they do not invade the intestinal tract.
A second group of upper respiratory viruses are the Myxoviruses of which influenza is the most prominent causing the most devastating epidemics. There are three RNA types of Influenza viruses. Type C rarely if ever, gives rise to epidemics. They cause inapparent infections in small children and nearly everyone has antibodies by age 15. Influenza A epidemics tend to occur in 2- or 3-year cycles while Influenza B epidemics occur in 4- to 6-year cycles.
All pandemics of influenza have been caused by type A viruses. There have been four well documented epidemics. The first in 1889-90. Then the one in 1918-19, Spanish flu, the first H1N1 virus, which was the most devastating accounting for more than 20 million deaths. The third one was the Asian virus, H2N2, emerging from the central part of mainland China in 1957. It spread to Hong Kong and other parts of the world. It was brought to the United States by naval personnel arriving in Newport, Rhode Island, and then San Diego.
The initial outbreak of the Asian virus occurred on June 20, 1957, during a conference of high school girls in Davis, California, and spread to several outbreaks in California. Apparently, the Asian virus was carried from the Davis conference to another meeting at Grinnell, Iowa, which was attended by 1800 young people from 43 states and several foreign countries. These conferees returning home seeded the Asian virus in many parts of the United States and by September 1957, the epidemics swept the country.
A fourth influenza pandemic was the 2009-10 swine virus, a new strain of H1N1 which originated in Mexico and infected as many as 1.4 billion people across the globe and killed between 151,700 and 575,400 people, according to the Centers for Disease Protection and Control. In the U.S., between April 2009 and April 2010, the CDC estimates there were 60.8 million cases of swine flu, with over 274,000 hospitalizations and nearly 12,500 deaths — that’s a mortality rate of about 0.02%.
The influenza virus is transmitted by the inhalation of virus containing droplets ejected from the respiratory tract by coughing or sneezing. Symptoms occur abruptly after an incubation period of 1-3 days with chills, fever, rigors, headache with extreme prostration. The diagnosis is clinical and there is no basis for differential diagnosis caused by types A, B, or C. There is a new antiviral drug, Amantadine, which has shown some success with influenza A. It is now largely prevented with vaccines.
The third group of upper respiratory viruses were the coronaviruses first isolated in 1965 from a boy with a common cold. This virus had a characteristic electron microscopic appearance with petal-shaped projections around the capsid resembling a solar corona. They are medium sized RNA viruses with more than 20 strains obtained from adults with upper respiratory infections. They are responsible for 10 to 24 percent of upper respiratory tract diseases. They can, along with the other respiratory viruses, invade the bronchi and cause a bronchitis. They can also, on occasion, invade the small respiratory bronchioles and alveoli causing a viral pneumonia. There are no specific drugs for viral pneumonia and treatment is supportive. If the arterial oxygen (PO2) is depressed, oxygen will be required. If ventilation is compromised as reflected with carbon dioxide retention (PCO2 elevation) intubation of the trachea and connection to a ventilator will be required. This then is called ARDS (acute respiratory distress syndrome) which is the terminal event in most chronic lung diseases.
A major problem in controlling the current coronavirus epidemic is that the incubation period, initially thought to be four days, (contagious for the last 48 Hours) can be as long as 14 days (and contagious for the last 10 days). Therefore, to eradicate this epidemic means that everyone needs to wear a mask anytime they leave their home or their car.
Dr. Stuart Cohen, Chief of Infectious Diseases at UC Davis, has started a clinical trial on a compassionate basis with Remdesivir with favorable clinical response in roughly two-thirds of COVID-19 patients. Treatment is otherwise primarily supportive (treating symptoms as they occur) unless there is a complicating pneumonia. Control of spread is by self-isolation at home, and for all necessary contacts using a mask and gloves or sanitizing solution to hands.
Bats are ideal for spreading respiratory diseases. They are mammals, have long lives, up to 30 to 40 years, live in large crowds, and fly. One bat roost in Texas houses 20 million bats at certain times of the year. One quarter of all mammal species are bats. Bats are sold in markets and supplied directly to restaurants throughout China and southeast Asia. Bats have supplied some of the more dangerous new diseases of the 21st century. Not only are they the known reservoir of Rabies, but are also the reservoir Ebola, Marburg, SARS, MERS, and Covid-19 viruses. They were discovered in the Yunnan cave in 2013. Patrick Woo and colleagues at Hong Kong University surveyed the coronavirus found in bats and in their paper in February of 2019 came to a prescient conclusion: “Bat-animal and bat-human interactions, such as the presence of live bats in wildlife wet markets and restaurant in southern China, are important for interspecies transmission of [coronaviruses] and may lead to devastating global outbreaks.” (Ridley in the WSJ)
Businesses such as restaurants, bars, salons, barbershops or any that preclude the wearing of a face mask covering the nose and mouth should remain closed for the duration of the epidemic. Businesses that remain open during the coronavirus epidemic, should have door monitors or security guards and require a mask for all who enter including the staff. There should be sanitizing solution at the doorway so everyone will spray their hands. There are now infrared thermometers that don’t require skin contact. Everyone entering should have a temperature below 100.4 degrees or be turned away. These simple steps for two weeks should help prevent the spread of the coronavirus. When there are no new cases of coronavirus spread or Covid-19 infection for a two-week period, isolation procedures could be lifted. These precautions would also be effective to prevent the spread of the influenza virus during a flu epidemic.
Personal prevention of Coronavirus infection would consist of wearing a mask at all times whenever they leave their homes or their automobiles and have a small bottle of sanitizing solution in their car and home.
Delbert H Meyer, MD, Pulmonologist / Sacramento
References: Infectious Diseases, third edition, Paul D. Hoeprich, Editor
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