In December 2019 , many cases presented in Wuhan, china with symptoms of pneumonia. All cases were associated with the Wuhan Wholefood market ( Market for sea food and live and wild animals).
34 Ophthalmologist (Wenliang Li, RIP) started spreading alarms about SARS like disease cases going around, he warned his friend on the chat by sending group messages. But hours after hitting send, Wuhan city health officials tracked Li down questioning him about the information source and then got a call from Wuhan city police and let him sign document admitting that Li was spreading rumors online .
In Jan 25 of 2020 there was 1300 known cases and 41 deaths and it was already spreaded to Australia , France and United state.
Now, COVID-19 is a pandemic!
SARS-COV-2 is the name of the virus that lead to this pandemic.
What is SARS-COV-2 virus ?
SARS-COV-2 is corona virus , Which is RNA viruses , positive sense , enveloped with crown like spikes.
Corona virus belong to Coronaviridae family and it have 4 subgroups : Alpha, Beta, Gamma, Delta.
Alpha and Beta groups are the only groups can infect mammals.
There is seven species of corona virus that can infect humans :
- SARS-CoV -2
(1-4) are usually presented with mild flu like symptoms.
(5-6) caused a pandemic in 2003 and 2012 (respectively).
(7) is the novel corona virus ( often called Wuhan corona virus) that caused COVID-19 pandemic, now known as SARS-CoV -2 .
The genetic sequence of SARS-CoV -2 looks 79.5% like SARS-CoV .
The Origin of SARS-CoV-2 :
All corona viruses originate from animals, especially from bats and rodents. SARS-COV-2 origin is not know yet. Studies suggest, Based on genomic sequencing, that SARS-CoV-2 is a mutated version of RaTG13 sampled from bats (Rhinolophus affinis).
There was some theories that SARS-CoV-2 is biological weapon but there is no evidence and the origin is hard to be proved at this point according to author “it is currently impossible to prove or disprove the other theories of [the SARS-CoV-2] origin”
Pathogenesis of COVID-19 :
ACE-2 enzyme on respiratory epithelium lead to dis-regulation of fluid balance causing edema in alveolar space.
When virus ( SARS-COV-2) reach the alveoli by inhalation, it infect the alveoli and cause pnemonia, this virus have S protein on it surface (spikes) which help it to attach to special receptor on type 2 alveolar cell ( which produce surfactant), this receptor called ACE-2 ( angiotensin convering enzyme 2 ).
ACE-2 convert angiotensin 1 to angiotensin 7 .
Angiotensin 7 drops blood pressure by relaxing blood vessels .
The virus attaches to it’s receptor on type 2 alveolar cell , then it enters the cell and starts to replicate and asseble.
Once the SS-RNA genetic material released to cytoplasm , it uses the human cell transcriptional machinery (Ribosomes).
Ribosome will read SS-RNA from(5′ end to 3′ end)to produce 2 big polypeptide proteins. These polypeptide proteins can then read the SS-RNA from (3′ end to 5′ end) to produce many proteins , such as : S proteins , surface proteins and sugar and membrane materials. Those then reassemble and released from the cell into the alveoli .
Some times the type 2 alveolar cell burst and release pro-inflammatory chemicals to alveoli , such as cytokines ( IL, TNF). cytokines increase the permeability of blood vessels and lead to fluid leakage into alveoli which inhibit gas exchange .
The localized inflammation may become systemic and lead to Septic syndrome !
SARS-COV-2 Transmission :
SARS-COV-2 virus route of transmission risk is not completely understood. Initially cases were related to Wuhan seafood market ,it’s believed that cross-species jump happened there.
Person to person transmission was reported mainly through droplets, SARS-COV-2 can be transmitted nosocomially, fecal-oral route and airborne especially with aerosolizing procedure.
SARS-COV-2 remain viable in the air for 3 hours! and up to 72 hour on other surface.
SARS-COV-2 incubation period :
Incubation period is the duration between first exposure to the virus and when the sign and symptom of disease caused by the virus first appear.
SARS-COV virus incubation period is usually 2 to 9 days, however there was reported cases with more than 20 days incubation period, period can vary greatly among patients.
presentation of COVID-19:
pneumonia is the most serious presentation of COVID-19, but clinical features is not well known yet ! The most common sign and symptoms at the onset of the disease are :
- fever (99%)
- fatigue (70%)
- Dry cough (59%)
- Myalgias (40%)
- Dyspnea (31%)
Other symptoms such, headache, sore throat, and rhinorrhea were reported too but less commonly.
80% of COVID-19 recover from the disease without needing special treatment
There is secondary complication that can happen including:
- Acute renal failure
- Acute respiratory distress syndrome (ARDS)
- arrhythmias, acute cardiac injury, and shock
Imaging of COVID-19 patient :
COVID-19 Lab test :
the CDC recommends nasopharyngeal swab specimen to test for SARS-CoV-2 https://www.cdc.gov/coronavirus/2019-nCoV/lab/guidelines-clinical-specimens.html
SARS-COV-2 virus genetic material is detected by reverse-transcription polymerase chain reaction (RT-PCR) , false positive and false negative are possible.
COVID-19 patients have in common laboratory findings such:
- Leukopenia or leukocytosis
- Elevated lactate dehydrogenase
- Elevated ferritin
- High D-dimer levels and severe lymphopenia are associated with high mortality rate https://www.ncbi.nlm.nih.gov/pubmed?term=32007143
COVID-19 Treatment :
No medicine have yet been proven effective for treatment of illness caused by SARS-COV-2 . The current best strategy of treatment of patients with COVID-19 is purely supportive :
- Respiratory support
- Antibiotic ( for bacterial superinfection)
There are recommendations for critical care units, infection control, and minimization of nosocomial transmission in this link https://thorax.bmj.com/content/59/3/252