- The progression from mild or moderate to severe can occur “very, very quickly.”
- About 10-15% of mild-to-moderate patients progress to severe and of those, 15-20% progress to critical.
- Patients at highest risk include people age 60 and older and those with pre-existing conditions such as hypertension, diabetes and cardiovascular disease.
This illustration provided by the Centers for Disease Control and Prevention in
January 2020 shows the 2019 Novel Coronavirus (2019-nCoV). (CDC via AP)
January 2020 shows the 2019 Novel Coronavirus (2019-nCoV). (CDC via AP)
The new coronavirus causes little more than a cough if it stays in the nose and throat, which it does for the majority of people unlucky enough to be infected.
Danger starts when it reaches the lungs.
By PATRICK PERRON | pperron@bayareanewsgroup.com | Bay Area News Group
PUBLISHED: | UPDATED:
PUBLISHED: | UPDATED:
One
in seven patients develops difficulty breathing and other severe
complications, while 6% become critical. These patients typically suffer
failure of the respiratory and other vital systems, and sometimes
develop septic shock, according to a report by last month’s joint World
Health Organization-China mission.
The
progression from mild or moderate to severe can occur “very, very
quickly,” said Bruce Aylward, a WHO assistant director-general who
co-led a mission in China that reviewed data from 56,000 cases.
Understanding the course of the disease and identifying individuals at
greatest risk are critical for optimizing care for a global contagion
that’s killed more than 3,500 people since emerging in central China in
December.
About 10-15% of mild-to-moderate patients progress to severe and of those, 15-20% progress to critical.
“The clinical picture suggests a pattern of disease that’s not dissimilar to what we might see in influenza,” said Jeffery K. Taubenberger, who studied the infection in Spanish flu victims, including one exhumed more than 20 years ago from permafrost in northwestern Alaska.
Covid-19 most likely spreads via contact with virus-laden droplets expelled from an infected person’s cough, sneeze or breath.
Infection generally starts in the nose. Once inside the body, the coronavirus invades the epithelial cells that line and protect the respiratory tract, said Taubenberger, who heads the viral pathogenesis and evolution section of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland. If it’s contained in the upper airway, it usually results in a less severe disease.
But
if the virus treks down the windpipe to the peripheral branches of the
respiratory tree and lung tissue, it can trigger a more severe phase of
the disease. That’s due to the pneumonia-causing damage inflicted
directly by the virus plus secondary damage caused by the body’s immune
response to the infection.
“Your body is immediately trying to repair the damage in the lung as soon as it’s happening,” Taubenberger said. Various white blood cells that consume pathogens and help heal damaged tissue act as first-responders. “Normally, if this goes well, you can clear up your infection in just a few days.”
In
some more-severe coronavirus infections, the body’s effort to heal
itself may be too robust, leading to the destruction of not just
virus-infected cells, but healthy tissue, Taubenberger said. Damage to
the epithelium lining the trachea and bronchi can result in the loss of
protective mucus-producing cells as well as the tiny hairs, or cilia,
that sweep dirt and respiratory secretions out of the lungs.
“You have no ability to keep stuff out of the lower respiratory tract,”
Taubenberger said. As a result, the lungs are vulnerable to an invasive
secondary bacterial infection. Potential culprits include the germs
normally harbored in the nose and throat, and the antibiotic-resistant
bacteria that thrive in hospitals, especially the moist environments of
mechanical ventilators.
Secondary
bacterial infections represent an especially pernicious threat because
they can kill critical respiratory tract stem cells that enable tissue
to rejuvenate. Without them, “you just can’t physically repair your lungs,” Taubenberger said. Damaged lungs can starve vital organs of oxygen, impairing the kidneys, liver, brain and heart.
“When you get a bad, overwhelming infection, everything starts to fall apart in a cascade,” said David Morens, senior scientific adviser to the director of the National Institute of Allergy and Infectious Diseases. “You pass the tipping point where everything is going downhill and, at some point, you can’t get it back.”
That
tipping point probably also occurs earlier in older people, as it does
in experiments with older mice, said Stanley Perlman, a professor of
microbiology and immunology at the University of Iowa in Iowa City, who
has studied coronaviruses for 38 years.
Still,
even healthy younger adults have succumbed to the illness. Li Wenliang,
the 34-year-old ophthalmologist who was one of the first to warn about
the coronavirus in Wuhan, died last month after receiving antibodies,
antivirals, antibiotics, oxygen and having his blood pumped through an
artificial lung.
Some
people may be more genetically susceptible, possibly because they have a
greater abundance of the distinctly shaped protein receptors in their
respiratory epithelial cells that the virus targets, Taubenberger
said. It’s also possible certain individuals have some minor
immunodeficiency or other host factors that relate to underlying
illnesses.
https://www.twincities.com/2020/03/08/there-is-a-tipping-point-before-coronavirus-kills/___
Ei kommentteja:
Lähetä kommentti