professor in microbiology LECTURE (2) Medical Virology Dr.Dalia M. Mohsen professor in microbiology CLS (413)

Objective Comparison between viruses and bacteria Atypical virus like agents. Virus and cancer Discuss antiviral therapy Method of cultivation of viruses.

Comparison between viruses and bacteria No Property Viruses Bacteria 1 Size 20-300 nm 1000 nm 2 Genome (type of nucleic acid) DNA or RNA but not both DNA and RNA 3 Cell wall Envelope present in some viruses 4 Ribosomes No ribosomes 5 Sensitivity to antibiotics _ + 6 Growth in culture media Grow only in living host cell

Atypical virus like agents 1-Defective viruses: Are composed of viral nucleic acid and proteins but cannot replicate without a helper virus, which provides the missing function. These usually have a mutation or a deletion of part of their genetic material.

Atypical virus like agents 2- Pseudovirions : Contain host cell DNA instead of viral DNA within the capsid. They are formed during infection with certain viruses when the host cell DNA is fragmented and pieces are incorporated within the capsid. Pseudovirions can infect cell, but they don’t replicate.

Atypical virus like agents 3-Prions: Are infectious particles that are composed solely of protein. They contain no detectable nucleic acid.

virus and cancer Characters of transformed cells: Some DNA viruses that synthesize DNA during their replication are capable to induce malignant transformation of cells. Characters of transformed cells: Increase rate of multiplication and metabolism. Cells show morphological and chromosomal abnormalities

Viruses implicated in human cancer Tumor DNA Viruses: Human papiloma viruses(HPV) Epstein Barr virus (EBV) Hepatitis B virus (HBV) Carcinoma of skin Nasopharyngeal carcinoma Hepatocellular carcinoma RNA viruses: Human T-cell Lymphotropic Retrovirus (HTLV-1 ) Hepatitis C virus (HCV) Adult T-cell leukemia lymphoma Liver cancer

Antiviral therapy Since viruses are obligate intracellular parasites, it is difficult to find an antiviral drug that selectively inhibits the virus without affecting the cell (selective toxicity).Few antiviral drugs are in clinical use. They act by stopping virus attachment, penetration, uncoating or intracellular synthesis.

The potential points of inhibitory action of antiviral drugs Interference with virus adsorption or attachment to the receptor- binding site on the cell. Inhibition of viral uncoating. Inhibition of viral nucleic acid, transcription and replication. Prevention of virus budding or interference with virus maturation

Interferon Interferon : are proteins made and released by host cell in response to the presence of pathogen such as viruses, bacteria, parasites and tumor cells.

Interferon Therapeutic uses of interferon: With recombinant DNA technology, interferon was now commercially produced. Interferon(INF-ὰ) treatment may be helpful in certain severe viral infections(herpes), in chronic virus infection (hepatitis Band C viruses).

Method of cultivation of viruses: Laboratory animals Since viruses are obligate intracellular parasites, they have to be grown in living cells. There are three systems for their cultivation: (1) Laboratory animals (2) Embryonated eggs (3) Cell culture

Method of cultivation of viruses Laboratory animals: Some animal viruses can be cultured only in living animals, such as mice, rabbits, and pigs. Most experiments to study the immune system's response to viral infections must also be performed in virally infected live animals. After the animal is inoculated with the specimen, the animal is observed for signs of disease or is killed so that infected tissues can be examined for the virus.

Method of cultivation of viruses Some human viruses cannot be grown in animals or can be grown but do not cause disease.

Method of cultivation of viruses 2.Embrionated eggs: If the virus will grow in an embryonated egg, this can be a fairly convenient and inexpensive form of host for many animal viruses. A hole is drilled in the shell of the embryonated egg, and a viral suspension or suspected virus-containing tissue is injected into the fluid of the egg. There are several membranes in an egg, and the virus is injected near the one most appropriate for its growth

This method was once the most widely used method of viral isolation and growth, and it is still used to grow viruses for some vaccines. For this reason, you may be asked if you are allergic to eggs before receiving a vaccination, because egg proteins may be present in the viral vaccine preparations.

Method of cultivation of viruses 3. In Cell Cultures: Cell cultures consist of cells grown in culture media in the laboratory. Cell culture lines are started by treating a slice of animal tissue with enzymes that separate the individual cells. These cells are suspended in a solution that provides the osmotic pressure, nutrients, and growth factors needed for the cells to grow.

Method of cultivation of viruses 3. In Cell Cultures: Normal cells tend to adhere to the glass or plastic container and reproduce to form a monolayer. Viruses infecting such a monolayer sometimes cause the cells of the monolayer to deteriorates they multiply. This cell deterioration is called cytopathic effect (CPE) ,

Diagnosis of virus infections The laboratory procedures used in diagnosis of viral diseases include: (A) Direct detection of viruses (B) Serologic detection of antiviral antibodies

Direct detection of viruses Direct detection of viruses can be Achieved by different techniques: Light microscopy: This can be used to visualize some large viruses e.g. poxviruses

2. Electron microscopy: Is used to demonstrate virus particles in vesicular fluid or tissue extracts treated with special stain. Its only successful if large numbers of particles are present.

3. Immunofluorescence microscopy: Detection of virus in smears from lesions using fluorescein labeled specific antisera

5. Polymerase chain reaction: This technique involves amplification of a short sequence of a target DNA or RNA (which may be in low concentration e.g. one copy) leading to accumulation of large amounts of that sequence, so it can be easily detected. PCR can be used to determine the quantity of viruses in patients blood i.e. virus load e.g. in HIV patients. This is used to monitor the course of the disease and to evaluate treatment and prognosis.

(B)Serologic detection of antiviral antibodies: Serologic diagnosis used in virology: 1. Enzyme linked immunosorbent assay(ELISA): Enzyme linked immunosorbent assay (ELISA) can be used for detection of viral antigens in different clinical specimens e.g. detection of HBV ,HIV, HCV and Rota virus.

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