Microbial Biotechnology Lecture:4 Microbial Biotechnology

Treatment for Viral Disease

Vaccines An attenuated virus is a weakened, less vigorous virus “Attenuate" refers to procedures that weaken an agent of disease (heating) A vaccine against a viral disease can be made from an attenuated, less virulent strain of the virus Attenuated virus is capable of stimulating an immune response and creating immunity, but not causing illness

Other Viral Treatments Interferon are naturally occurring proteins made by cells to fight viruses Genetic altering of viruses (attenuated viruses) Antiviral drugs (AZT) Protease inhibitors – prevent capsid formation

Antibiotics Antibiotics can only be used to treat bacterial infections! Target specific structures on bacteria to kill them. First made from a fungus (penicillin), now most are made artificially. Unfortunately, antibiotic resistance (where the antibiotic doesn’t kill the target bacteria anymore) is becoming a major problem.

Antivirals Antivirals can only be used to treat certain viral infections! Does not “kill” or disarm the virus permanently; only shortens symptoms by 1-2 days. Usually only prescribed to patients with life threatening symptoms or those that have a greater chance of developing complications (because of their age or they have a high-risk medical condition). Just like antibiotics, there is evidence of antiviral resistance too!

Influenza A virus Properties of the virus Myxovirus Enveloped virus with a segmented RNA genome Infects a wide range of animals other than humans Undergoes extensive antigenic variation Major cause of respiratory infections Influenza A virus is the second acute infection to be discussed. Myxovirus Enveloped virus with a segmented RNA genome Infects a wide range of animals other than humans Undergoes extensive antigenic variation Major cause of respiratory infections

Influenza A virus Infection Spread by respiratory route Virus infects cells of the respiratory tract Destruction of respiratory epithelium Secondary bacterial infections

Spread of influenza virus Respiratory aerosoles can be generated from the respiratory tract by various means – from speaking to sneezing. During a sneeze, millions of tiny droplets of water and mucus are expelled at about 200 miles per hour (100 metres per second). The droplets initially are about 10-100 micrometres diameter, but they dry rapidly to droplet nuclei of 1-4 micrometres, containing virus particles or bacteria. This is a major means of transmission of several diseases of humans.

Respiratory Tract There are various means by which the host is protected from infection by influenza virus. The droplets containg the virus may be filtered by fines hairs and cilia in the nasal cavity. Muco-cilliary cells lining the trachea can trap virus particles and sweep the virus to the back of the throat from where it is swallowed and excreted via the intestinal tract. Alveolar macrophages can engulf the virus if it enteres as far as the lower reaches of the lung and alveolar sac.

Nucleic acid replication Virus protein processing Virus maturation Antiviral Targets Attachment/Entry Nucleic acid replication Virus protein processing Virus maturation Attachment/Entry Picornaviruses Nucleic acid replication Human immunoideficiency virus (AZT) Herpes simplex virus (Acyclovir) Virus protein processing HIV (Protease inhbitors) Virus maturation Influenza A virus (Neuraminidase blockers) Problems of antivruals Dificuly in finding a virus specific site against which to direct the antivrial As with the use of antiiotics – resistant mutant scan be readily generated that are resistant to antiirals – this is particuarly a problem with those against HIV where the drug has to be used for prolonged periods of time.