This presentation intends to explore the application of virus in different biomedical fields and research with special reference to vaccine production and plant viral diseases.
1. APPLIED VIROLOGY
Economic importance of viruses with reference to
vaccine production, role in research, medicine and
diagnostics, as causal organisms of plant diseases
By
N. Sannigrahi, Associate Professor,
Department of Botany,
Nistarini College, Purulia (W.B.) India.
2. VIRUS
Viruses (Latin Venum – poisonous fluid) are simplest forms of
life. They are not cells, but their study has provided a great
deal of information about cells. Study of viruses is a branch of
biology called Virology. Viruses are cellular parasites. They
are smaller than bacteria and have a much more simplified
organization. Russian Botanist Iwanowsky (1892) was first to
give clear cut evidence of virus. He demonstrated their
occurrence in tobacco leaves suffering from mosaic disease.
Mayer (1886), Beijerinck (1898) and Loeffler & Frosch (1898)
established the existence of viruses by discovering many viral
diseases in plants and animals.
Schlesinger (1933) was first to determine the chemical
composition of virus. W. M. Stanley, an American
microbiologist crystallized tobacco mosaic virus (TMV) after
isolating from infected tobacco leaf juice. He thus showed that
viruses are not like typical cells. Stanley was awarded Nobel
prize for this work.
4. GENERAL CHARACTERS
On the whole viruses are much smaller than bacteria. Most
animal and plant viruses are invisible under the light
microscope. Some of smaller viruses are only 200Å in
diameter. Variable. Most viruses are much smaller than
bacteria. The size ranges in between 100A to 250 mu. Some
viruses are larger than bacteria, for example the psittacos is a
virus measuring 0.75 mu in diameter
Viruses cannot multiply outside a living cell. No virus has
been cultivated in a cell-free medium. Viruses do not have an
independent metabolism. They are metabolically inactive
outside the host cell because they do not possess enzyme
systems and protein synthesis machinery. Thus viruses are
obligatory intracellular parasites.
Viruses have a very simple structure. They consist of a nucleic
acid core surrounded by a protein coat.
5. GENERAL CHARACTERS
In this respect they differ from typical cells which are made up
of proteins, carbohydrates, lipids and nucleic acids.
Myxoviruses have a membranous envelope consisting of
proteins, carbohydrate and lipid outside the usual protein coat,
but this envelope is derived from the host cell.
Viruses usually have only one nucleic acid, either DNA or
RNA. Typical cells have both DNA and RNA. Rous Sarcoma
virus (RSV), producing certain cancer, is the only virus having
both DNA and RNA.
SS DNA------------------ph I x174
DS DNA----------------- Pox virus, Herpes, Adeno
SSRNA-------------------TMV, Influenza
DS RNA-----------------Retrovirus of animals, Rice dwarf virus
DNA-RNA -------------Leukovirus, Rous sarcoma virus
6. ANIMAL VIRUS
The common animal viruses are small pox virus, influenza
virus, mumps virus, polio virus and herpes virus. In many
animal viruses an extra envelope surrounds their protein coat.
The membrane consists of proteins, lipids and carbohydrates
and is derived from the host plasma membrane. Animal
viruses may enter cells by attaching to the surface. Some are
then engulfed by the cell through pinocytosis or phagocytosis.
In such cases, uncoating of the viral nucleic acid might occur
within the cell. Inside the host cell they may multiply and form
numerous new viral particles. Usually, animal viruses release
from the host cells by the rupturing and subsequent death of
the host cells. The different diseases of animals in general and
human beings in particular are caused by this biologist puzzle
element and the unfortunate COVI19 is the dreadful viral
pandemic that becomes nightmare to the whole world.
7. PLANT & BACTERIAL VIRUS
Plant Viruses: They are parasites of plant cells. Their genetic
material is RNA which remains enclosed in the protein coat.
The most important plant viruses are tobacco mosaic virus
(TMV), tobacco rattle virus (TRV), potato virus (PV),
southern bean mosaic virus (SBMV), beet yellow virus (BYV)
and turnip yellow virus (TYV).
Bacterial virus: They are parasitic on bacteria and so also
called bacteriophages. There are many varieties of
bacteriophages. Their size and shape varies from species to
species. Some phages are spherical, some comma-shaped
whereas majority of them have tadpole-like appearance.
8. VACCINES
Prevention is better than cure” .Vaccine (L. vacca = cow) is a
preparation/suspension or extract of dead/attenuated
(weakened) germs of a disease which on inoculation
(injection) into a healthy person provides
temporary/permanent active/passive immunity by inducing
antibodies formation. Thus antibody provoking agents are
called vaccines. When the vaccine enters into the body, it
either totally prevents or reduces the effect of the disease. This
type of immunity developed is called acquired immunity.
Since the discovery of vaccine by Edward Jenner (1796),
several vaccines have been developed to provide immunity
against the different type of diseases. Either bacterial or viral
vaccines, it may be two types-
Attenuated live virus vaccine
Inactivated or killed virus vaccine
10. ATTENUATED VACCINES
The live virus activities and virulence have been attenuated
through different treatments. Most of the viral vaccines are
attenuated and the advantages of this vaccines are-
Requires single dose,
No need of adjuvant,
Duration of immunity is longer,
Produce both IgA and IgG type of antibodies,
No mucosal immunity,
Cell mediated immunity greater but the most important
problem is the presence of undesirable components remain and
high cold chain and difficult production level,
Vaccines of measles. Mumps, yellow fever, rubella etc .
11. INACTIVATED OR KILLED VACCINES
Vaccines are designed by the inactivation of viral infectivity
by the treatment of different chemicals like mild formalin,
ethylemines etc , heat, radiations or antibiotics by ensuring the
purity and potency during inactivation. Vaccines of Chlorea,
rabies, polio, influenza, bubonic plague, hepatitis A etc are
belonged to this category. Killed vaccines are available in two
forms-whole virus vaccines or sub-unit vaccines. Sub-unit
vaccines are separated from purified virus by detergent , then
centrifuged keeping the components to stimulate protective
antibody. Vaccines fore Hepatitis B, Human Papiloloma virus
(HPV) belong to this group. Toxoid vaccines are also belonged
to this group as it contain toxic compounds rather than
pathogen .It requires in multiple doses, need adjuvant for
better effectively, short term immunity, produce only IgG.
12. NEW TRENDS IN VACCINES
antibody with narrow range of application. etc are also used to
prevent the infection Recently synthetic vaccines,
Recombinant vaccinia virus, DNA vaccines are also being
used by the application of genetic engineering.
Production of vaccine needs the following steps-generation of
antigen, isolation and purification, formulation and packing.
The new trends in vaccine production are-
Development of vaccine for different age groups,
Production of combination vaccines to reduce the quantities of
antigen,
Focus on mammalian cell cultures rather than conventional
chicken egg embryos culture,
new method of administration,
Development of edible vaccines.
13. VIRUS IN DIAGONOSIS AND RESEARCH
Virus can be extensively use in the different fields like
microbiology, molecular biology, immunology, genetic
engineering and others.
USED AS PROBES: Probes are short oligonucleotides
sequences (10-30 bases) of DNA or RNA used to detect
complementary sequences present in unknown genetic
material. Southern blotting, Northern blotting, dot blots,
DNA/RNA sequencing, construction of genomic library etc
use the different types of probes for identification of genetic
materials. The probes are nothing but dsDNA or SSDNA or
ssRNA strands and labeled with radioactive or non-radioactive
substances for detection. The short sequences of probes are
generally obtained from viral genomes. Complementary DNA
(cDNA) arte prepared using mRNA which can be cloned in
E.coli using bacteriophage.
14. VIRUS IN DIAGNOSIS
PRODUCTION OF ENZYMES: The enzyme reverse
transcriptase produced by retrovirus has been extensively used
in the generation of cDNA which is frequently used for
research works and chemical diagnosis.T4 phage virus also
produce enzyme ligase which is used in recombinant DNA
technology as well as in ligase chain reaction.
BACTERIOPHAGE TYPING: The particular virus can
infect a particular bacteria. This technique is used in
identifying the bacteria species and this is used in clinical
samples in analysis and research. The pathogenic bacterium to
be identified in cultured .The plate is then marked into squares
and each square is inoculated with a particular phage and plate
is incubated for 24 hours. After the stipulated time, the plaque
formation is observed and phage typing is recorded to the
phage sensitivity of the bacterium.
15. VIRUS AS VECTORS
VIRUS AS VECTORS: Virus has the ability insert their content
into the host cells. Vectors are automatically replicating DNA
fragments to which genes of interest can be integrated for cloning.
Besides, the vector DNA should be capable of manipulation , easily
isolated and inserted into the host , carry sites for restriction
endonuclease enzymes and possess selectable markers for easy
identification. The lamda phage and M13 phages are mostly used as
vectors .Since phage vectors are naturally infective, can
accommodate large DNA fragments for cloning and identification of
recombinant viral vectors , it is comparatively easy. They are mostly
preferred as plasmid vectors. Lamda bacteriophages are used in
DNA cloning research. This phage virus is a temperate phage and
can perform both lytic and lysogeny cycle which infect host. The
linear lamda phage genome becomes circular on entering the host
bacterium E.coli8 and can accommodate large
16. TRANSGENEICS SCIENCE
DNA insert and generate different types of lamda vectors .
M13 vectors are used to get single strands of cloned DNA
which have uses in DNA sequencing. Several modified vectors
like M13, mp1m mp8, mp9 etc are the modified vectors
produced from M13 genome. Different cosmid vectors (with
cos site), phagmid vectors also used in recDNA technology.
TRANSGENIC PLANTS& ANIMALS: Viruses are regularly
used for the designing of genetic modified organisms. During
this process, viruses are used as shuttle vectors through which
desired genes enter into the bacterial host and then to the target
organism. Baculoviruses are used to design vectors for
production of recombinant protein in insect cell line.
For bio-pesticides designing, in gene therapy, virotherapy in
cancer and bacteriophage therapy, virus play a very crucial
role in medical science
17. PLANT VIRAL DISEASES
Plant viruses, like other viruses, contain a core of either DNA
or RNA. As plant viruses have a cell wall to protect their cells,
their viruses do not use receptor-mediated endocytosis to enter
host cells as is seen with animal viruses. For many plant
viruses to be transferred from plant to plant, damage to some
of the plants’ cells must occur to allow the virus to enter a new
host. This damage is often caused by weather, insects, animals,
fire, or human activities such as farming or landscaping.
Additionally, plant offspring may inherit viral diseases from
parent plants.
Plant viruses can be transmitted by a variety of vectors:
through contact with an infected plant’s sap, by living
organisms such as insects and nematodes, and through pollen.
When plant viruses are transferred between different plants,
18. PLANT VIRAL DISEASES
this is known as horizontal transmission; when they are
inherited from a parent, this is called vertical transmission.
Symptoms of viral diseases vary according to the virus and its
host. One common symptom is hyperplasia: the abnormal
proliferation of cells that causes the appearance of plant
tumors known as galls. Other viruses induce hypoplasia, or
decreased cell growth, in the leaves of plants, causing thin,
yellow areas to appear. Still other viruses affect the plant by
directly killing plant cells; a process known as cell necrosis.
Other symptoms of plant viruses include malformed leaves,
black streaks on the stems of the plants, altered growth of
stems, leaves, or fruits, and ring spots, which are circular or
linear areas of discoloration found in a leaf.
21. THANKS A LOT FOR YOUR JOURNEY
Viruses are important microbial predators that influence
global biogeochemical cycles and drive microbial
evolution, although their impact is often under appreciated.
Viruses reproduce after attaching and transferring their genetic
material into a host cell. The identification of virus needs the
understanding of multiple characters-potential infectious
nature, shape, size, structure and symmetry, envelope nature
of genetic material and other features. The recent pandemic of
COVID19 has brought the devastation and destruction of
millions has again raised a trillion dollar questions about the
acellular entity and the scientists become very much anxious
to manage this entity for the best of the human civilization.
More researches are needed to explore the puzzle of this
ultramicroscopic entity. Better late than never’-------------
