This document discusses the evolution of coronaviruses and the adaptations of the host immune system, focusing particularly on SARS-CoV-2 and its entry into the human population through zoonotic transmission. It outlines the characteristics of various zoonotic viruses and their pandemic potential, comparing them to other circulating human viruses. The document also speculates on long-term immunity regarding SARS-CoV-2, drawing insights from historical data on other viral infections.

1. Evolution of Coronaviruses &
Adaptations of the host Immune
System
Part-III
Dr. Rashmi Kumari
Department of Zoology
Assistant Professor
College of Commerce, Arts & Science
Patliputra University, Patna

2. Questions to be answered in this lecture!!!
How do viruses such as SARS-CoV-2 enter
the human population?
How does SARS-CoV-2 relate to other
circulating and epidemic human viruses?
Based on other human viruses, what might
we expect for long-term immunity or co-
existence with SARS-CoV-2?
Source: Google Images

3. Entry of viruses such as SARS-CoV-2 in the human population??
or
Origin of Human Pandemic Viruses
Every human pandemic virus has originated in other
species
This is called “Zoonotic transmission” or “Zoonoosis”
For a human virus to become pandemic, it needs sustained
human to human transmission
Source: Wolfe et al., 2007

4. Source: Wolfe et al., 2007
Entry of viruses such as SARS-CoV-2 in the human population??
or
Origin of Human Pandemic Viruses
Spillover
Spillover Sustained human
transmission
Circulating animal viruses
•Many bat coronaviruses
•Assumed low case fatality rate
Zoonotic viruses with limited transmission
•Middle Eastern Respiratory Syndrome [MERS]
•1st case described in 2012; case fatality rate 30-
40%
Zoonotic viruses with pandemic potential
•Severe Acute Respiratory coronavirus 2 [SARS-CoV-2]
•1st case described in 2019; case fatality rate 1-3%
Circulating human viruses
•Human respiratory coronaviruses
•Common cold virus; low case fatality rate

5. Molecular Interaction Underlying Viral Adaptation
Spillover
Redrawn from Fundamentals of virology, Acheson
Coronavirus “spike”
protein
Host “ACE2”
protein
Cocrystal of the SARS-CoV RBD bound to human ACE2. Cyan indicates a region of the RBD
shared among group 2 coronaviruses, whereas red indicates the RBM, which is not homologous
to that of other group 2 viruses. ACE2 is shown in white, with its cleft bearing the enzyme-active
site facing forward and the membrane-associated C terminus at the bottom of the figure.
Evolved “spike”
protein
New host receptor
Human ACE2
Source: Huang et al., 2006

6. Spillover Sustained human
transmission
Other Circulating and Pandemic Viruses
Circulating animal viruses
•Many bat coronaviruses
•Avian and Swine influenza viruses
Zoonotic viruses with limited transmission
•Middle Eastern Respiratory Syndrome [MERS-CoV]
•H7N9 “bird” influenza, rabies virus, Nipah virus
Zoonotic viruses with pandemic potential
•Severe Acute Respiratory coronavirus 2 [SARS-CoV-2]
•1918 Spanish influenza, 1968 Hongkong flu, 2009
“swine” flu, Smallpox, HIV, Ebola
Circulating human viruses
•Human respiratory coronaviruses
•“Seasonal” influenza, measles, polio
Spillover

7. What Might We Expect For Immunity
It is still too early to early to know about long-term immunity to SARS-CoV-2, but we can get a hint from other
viruses:
Long-term protective immunity:
Smallpox, Rabies
Measles, Polio
Mumps, Rubella, several others
Serum can be administered and is protective:
Ebola
Limited short-term or unknown protective immunity:
Human respiratory coronaviruses
We don’t have much idea, but appears that people can be reinfected again after some time (a few years??)
Influenza viruses
Vaccine is effective, but virus evolves every year to escape
 Based on this, we can probably expect protective immunity, but unclear about long-term protection.

8. References:
1. World Health Organization (WHO) [https://www.who.int/emergencies/diseases/novel-coronavirus-
2019/technical-guidance/naming-the-coronavirus-disease-(covid-2019)-and-the-virus-that-causes-it].
2. Google Images.
3. Li, W., Wong, S-K., Li, F., Kuhn, J.H., Huang, I-C., Choe, H., Farzan, M. 2006. Animal Origins of the
Severe Acute Respiratory Syndrome Coronavirus: Insight from ACE2–S-Protein Interactions. J. Virol.
4211–4219.
4. Wolfe, N.D., Dunavan, C.P., Diamond, J. 2007. Origin of human infectious diseases. Nature 447:279-83.