2. Objectives
By the end of this lecture, the students will be able to:
• Define virus.
• Describe the properties of virus.
• Identify different viral shapes.
• Identify DNA and RNA viruses
3. Virus
• Viruses may be defined as acellular organisms
whose genomes consist of nucleic acid, and
which obligately replicate inside host cells
using host metabolic machinery.
• Size: 20 ---- 14,000 nm in length
4. VIRUS PROPERTIES
• Infectious – transmissible horizontally or vertically
• Obligatory Intracellular – requires a living cell
• Nucleic acid –Either DNA or RNA, but not both
• DNA and RNA – Any of them may be double-
stranded or single-stranded
• Capsid – Most have protein coat called Capsid
• Lipid envelope---May or may not present
• No Metabolic machinery – No metabolic (ATP
generating) and biosynthetic (Protein synthesizing)
enzymes but use that of the host.
5. DNA and RNA Viruses
DNA Virus
• Smallpox virus
• Herpesviruses
• Hepatitis B virus
• Papilomavirus (wart virus)
RNA Virus
• Polio virus
• Rhabdovirus
• Mumps virus
• Measles virus
• HIV
• Influenza virus
• Hep C virus
• Rubella virus
15. MCs
• Molluscum contagiosum is a viral skin infection that causes either single or multiple raised, pearl-like bumps (papules) on the skin. It is a chronic
infection and lesions may persist from a few months to a few years. However, most cases resolve in six to nine months.
• Causes of Molluscum Contagiosum
• Molluscum contagiosum is caused by a virus (the molluscum contagiosum virus) that is part of the pox virus family. The virus is contagious through
direct contact and is more common in children. However, the virus also can be spread by sexual contact and can occur in people with compromised
immune systems. Molluscum contagiosum can spread on a single individual through scratching and rubbing.
• What Are the Symptoms of Molluscum Contagiosum?
• Common locations for the molluscum contagiosum papules are on the face, trunk, and limbs of children and on the genitals, abdomens, and inner
thighs of adults. The condition usually results in papules that:
• Are generally painless, but can itch
• Are small (2 to 5 millimeter diameter)
• Have a dimple in the center
• Are initially firm, dome-shaped, and flesh-colored
• Become softer with time
• May turn red and drain over time
• Have a central core of white, waxy material
• Molluscum contagiosum usually disappears spontaneously over a period of months to years in people who have normal immune systems. In people
who have AIDS or other conditions that affect the immune system, the lesions associated with molluscum contagiosum can be extensive and
especially chronic.
• Diagnosing Molluscum Contagiosum
• Diagnosis of molluscum contagiosum is based on the distinctive appearance of the lesion. If the diagnosis is in question, a doctor can confirm the
diagnosis with a skin biopsy -- the removal of a portion of skin for closer examination. If there is any concern about related health problems, a doctor
can check for underlying disorders.
• Treatment for Molluscum Contagiosum
• Molluscum contagiosum is usually self-limited, so treatment is not always necessary. However, individual lesions may be removed by scraping or
freezing. Topical medications, such as those used to remove warts, may also be helpful in lesion removal.
• Note: The surgical removal of individual lesions may result in scarring.
• Prevention of Molluscum Contagiosum
• To prevent molluscum contagiosum, follow these tips:
• Avoid direct contact with anyone who may have the condition.
• Treat underlying eczema in children.
• Remain sexually abstinent or have a monogamous sexual relationship with an uninfected individual. (Male and female condoms cannot offer full
protection as the virus can be found on areas not covered by the condom.)
16. Viral Particles
• Virion
A complete, fully developed viral particle having nucleic acid
surround by capsid.
• Prion
– No nucleic acid but self replicating protein
• Viroid
– An infectious agent of plant having ssRNA without a
protein coat.
