Viral Diseases and Immunity

In gene therapy trials, the retrovirus is used as a vector to treat X-linked severe combined immunodeficiency (X-SCID) represent the most successful application of gene therapy. The retrovirus genetic material is in the form of RNA molecules, and their hosts genetic material is in the form of DNA. When a retrovirus infects a host cell, it will introduce its RNA together with some enzymes, namely reverse transcriptase and integrase, into the cell. This RNA molecule from the retrovirus must produce a DNA copy from its RNA molecule before it can be integrated into the genetic material of the host cell. The process of producing a DNA copy from an RNA molecule is termed reverse transcription.

An antiviral drug is used to treat genital herpes outbreaks stay symptom-free longer. These drugs can also reduce the severity and duration of symptoms when they do flare up. Drug therapy is not a cure, but it can make living with the condition easier. Because of lack of research about the Herpes virus action mechanism, there is no cure for Herpes but it is inhibited by acyclovir. It is one of the most common sexually transmitted infections. 

Viruses are obligate parasites. They are acellular and are only made of a genetic material surrounded by a protein capsid. Viruses use the host cellular machinery for survival and replication. They also undergo mutation within the host. They have no energy metabolism nor do they produce waste products. Hence they are considered non-living. Thus the correct answer is option C.

HIV infection leading to AIDS  can be transmitted through the blood transfusion because HIV virus infects blood and multiplies in blood cells only.

H5N1 is a subtype of the influenza A virus that causes highly pathogenic avian influenza, commonly known as bird flu.

The Western blot is a widely used analytical technique used to detect specific proteins in a sample of tissue homogenate or extract.
HIV - Human Immunodeficiency Virus
AIDS- Acquired Immuno Deficiency Syndrome.

The encounter of B cell with a specific antigen activates its clonal expansion which in turn gives rise to plasma cell and memory cells.  Memory cells are the B cells (antibodies) responsible for long-term immunity and confirm the previous encounter of a person with the specific virus. Antigens are foreign substances that induce the immune system to produce antibodies. Disease-causing organisms are called as pathogens. Natural killer cells and macrophages are components of immune system. So, the correct answer is option D.

Retroviruses operate a central dogma reverse. RNA of these viruses first synthesis DNA through reverse transcriptase or RNA dependent DNA polymerase. This DNA synthesised on RNA template is called c-DNA or retroposons.

HIV (Human Immunodeficiency Virus) is a retrovirus with a viral envelope, matrix proteins and core. The viral core consists of two single strands of RNA. Retroviruses containing RNA genome have reverse transcriptase enzyme that synthesizes a DNA copy (cDNA) of viral RNA. This cDNA can be introduced in the hosts' genome and allowed to replicate to form viral proteins. Influenza and vaccinia viruses are not retroviruses.

Once inside a CD$ _4$ cell ( helper T cell ), HIV releases and uses reverse transcriptase  to convert its genetic material—HIV RNA—into HIV DNA. The conversion of HIV RNA to HIV DNA allows HIV to enter the CD$ _4$ cell nucleus and combine with the cell’s genetic material—cell DNA.

Graft versus host disease (GVHD) occurs when immunocompetent cells from a donor graft recognize the recipient's tissues as foreign. This is most common in allogenic transplants where the donor and recipient are not genetically identical.

• Immunity to viral infection is caused by a variety of specific and nonspecific mechanisms. 
• The activation of different immune functions and the duration and magnitude of the immune response depending on how the virus interacts with host cells. 
•  Cytotoxic T lymphocytes, natural killer (NK) cells and antiviral macrophages can recognize and kill virus-infected cells.
•  Hence, Body cells infected by viruses are destroyed mostly by Natural Killer cells.
• So, the correct answer is 'Natural Killer cells'.

• Condoms are the barrier method of birth control. Use of condoms block the sperm from entering the uterus. 
• Sexually transmitted diseases can be prevented by using condoms as they make a physiological barrier between two individuals and prevents the entry of sperm into the female body. 
• Thus, the correct answer is option A.

Variolation was an early method of immunization against smallpox where material from a smallpox pustule was introduced into the body, typically through a scratch on the skin.