BMI3705 – VIROLOGY
QUESTION 1 [5]
Briefly outline the Baltimore classification system for viruses:
Based on their genomic makeup, strandedness, sense or antisense, and replication mechanism,
viruses are categorized using the Baltimore categorization system. Scientists can better
comprehend and arrange the diversity of viruses due to this classification scheme, which was
created in 1971 by Nobel laureate David Baltimore. According to the system, viruses are
categorized into seven groups:
1. Group I (dsDNA viruses): This category comprises viruses whose genetic material is
double-stranded DNA. This category of viruses includes, for example, adenoviruses,
herpesviruses, and poxviruses. Through a DNA intermediary, these viruses copy their
genetic material.
2. Group II (ssDNA viruses, sense): These are viruses that are single-stranded DNA and
have a positive sense strand. Parvovirus is a typical example of a group II virus. When
the host cell becomes infected, they can act as mRNA directly to synthesize proteins.
3. Group III (dsRNA viruses): Two strands of RNA make up the genetic material of viruses
in this category. The reovirus is one such. They utilize a double-stranded intermediary to
duplicate their RNA.
4. Group IV (+) ssRNA viruses: Positive-stranded RNA viruses that are single-stranded
fall within this category. PICRONAVIRUS and TOGAVIRUS are two examples. These
viruses can function as mRNA for translation right away.
5. Group V (-) ssRNA viruses: These viruses have a negative sense (antisense) strand in
their single-stranded RNA. Orthomyxoviruses and rhabdoviruses are two such instances.
Prior to translation, they must create a complementary positive sense RNA strand.
6. Group VI (ssRNA-RT viruses): These are positive sense strand single-stranded RNA
viruses that have a DNA intermediary in their life cycle. This category includes
, retroviruses such as HIV. Their DNA is created by reverse transcribed their RNA genome,
which subsequently combines with the host genome.
7. Group VII (dsDNA-RT viruses): This category includes viruses that replicate by reverse
transcription and have genomes made of double-stranded DNA. The hepadnavirus, which
includes the hepatitis B virus, is one example.
Understanding the genetic makeup and replication tactics of various viruses is important for
creating vaccines and antiviral medications. This can be done using the Baltimore categorization
system. Based on the kind of genetic material that they contain and how they multiply that
genetic material inside host cells, viruses are categorized.
QUESION 2 [15]
Describe the different types of vaccines used to prevent viral infections and provide two
examples for each type of vaccine:
,Vaccines can be used in a variety of ways to lower disease rates while still having the capacity
to stimulate a protective immune response.
Vaccinations that are inactivated or killed:
These vaccinations contain microbes that have been made incapable of reproducing by
treatment with chemicals, heat/radiation, or antibiotics. Vaccines against influenza, cholera,
bubonic plague, polio, hepatitis A, and rabies are currently administered inactivated or killed.
• Influenza Vaccine: Inactivated influenza viruses are used in influenza vaccinations. To
make these viruses non-infectious, heat or chemicals are applied to them. Without really
causing the illness, they encourage the immune system to generate antibodies. Annual
influenza vaccinations are frequently given to guard against seasonal flu viruses.
• Hepatitis A Vaccine: Inactivated hepatitis A virus makes up the hepatitis A vaccine.
Hepatitis A is a very contagious liver infection that is prevented with it. It is especially
advised that those who are at a higher risk of infection or who are visiting areas where
hepatitis A is more prevalent get this vaccination.
Vaccines containing live attenuated viruses:
These vaccines are made of live viruses that have been cultured in circumstances that lessen
their toxicity. More relevant regulatory mechanisms, such as cytotoxic CD8 T cells, are activated
by them. Most of these vaccinations are made from viruses, while some are made from bacteria.
These vaccinations produce a lasting immunological response. However, because they might
act like virulent opportunistic pathogens, they ae not suitable for immunocompromised people.
• The Measles, Mumps, and Rubella (MMR) comprises live attenuated viruses that cause
the measles, mumps, and rubella. These viruses have undergone modifications to lessen
their infectiousness without compromising their capacity to trigger an immune reaction.
To protect from all three of these viral illnesses, a combination vaccine is administered.
• The yellow fever vaccination. It has a weakened yellow fever virus that induces an
immunological response without spreading the illness. Travelers to areas where yellow
fever is endemic must get this vaccination.
Subunit or conjugate vaccines:
, The protein subunit that triggers an immune system reaction is made from an organism's
fragment. Recombinant vaccines are made by genetically modifying certain subunits.
• Hepatitis B Vaccine: The vaccine against hepatitis B is a subunit made up of the virus's
surface proteins. These proteins are created by using the method of recombinant DNA or
taken from the blood serum of individuals who have a persistent infection. The vaccination
offers protection against hepatitis B infection by inducing an immune response against
the hepatitis B virus.
• Vaccine against the human papillomavirus (HPV): HPV vaccines are subunit
vaccinations derived from the main capsid protein of HPV strains. Their purpose is to
provide protection against high-risk HPV strains that might cause cervical and other
malignancies. To prevent diseases associated to HPV, both males and females receive
the HPV vaccine.
QUESTION 3 [20]
Write briefly on the following topics providing appropriate examples where necessary:
3.1. Viral hosts (5)
Host cells of different kinds that viruses can infect are referred to as viral hosts. Specialized
locations for attachment on host cells and cell parts necessary for viral multiplication define a
virus's "host range," or the variety of host cells it can infect. Fascillae, flagella, cell walls, and
plasma membrane proteins are a few examples of these attachment sites. Remember that inside
a single host species, viruses only infect types of cells.
Viral hosts fall into one of two major categories:
• Eukaryotic viruses: These viruses affect protists, fungi, animals, and humans as well as
other eukaryotic organisms. For instance, the influenza virus mostly affects human
respiratory cells, whereas the rabies virus primarily affects mammal nerve cells.
• Prokaryotic viruses are those that infect prokaryotic microorganisms, including bacteria,
archaea, and other microbes. Phage-like viruses that infect bacteria are referred to as
bacteriophages. The T4 bacteriophage, which infects the bacteria Escherichia coli (E.
coli), is one instance.
The relationship between host cell receptors and viral surface proteins determines the
particularity of viral hosts. To limit the number of cells they can infect; viruses have developed
