Replication Learning Objectives: To be able to describe the process of replication of the influenza and HIV virusTo be able to describe the process of replication of the influenza and HIV virus To be able to describe the course of infection, signs, symptoms and transmission if Influenza and AIDSTo be able to describe the course of infection, signs, symptoms and transmission if Influenza and AIDS

Replication Though the details of virus infection and replication vary greatly with host type, all viruses share 6 basic steps in their replication cycles. These are:Though the details of virus infection and replication vary greatly with host type, all viruses share 6 basic steps in their replication cycles. These are: –Attachment –Penetration –Uncoating –Replication –Assembly –Release This is called lytic replicationThis is called lytic replication

The virus must first attach itself to the host cell. This is usually accomplished through special glycoprotiens on the exterior of the capsid, envelope or tail.The virus must first attach itself to the host cell. This is usually accomplished through special glycoprotiens on the exterior of the capsid, envelope or tail. Next, penetration occurs, either of the whole virus or just the contents of the capsid. If the entire capsid enters, the genetic material must be uncoated to make it available to the cell's replication machinery.Next, penetration occurs, either of the whole virus or just the contents of the capsid. If the entire capsid enters, the genetic material must be uncoated to make it available to the cell's replication machinery. Replication of genetic material takes place, as well as the production of capsid and tail proteins.Replication of genetic material takes place, as well as the production of capsid and tail proteins. Once all of the necessary parts have been replicated, individual virus particles are assembled and released.Once all of the necessary parts have been replicated, individual virus particles are assembled and released. Release often takes place in a destructive manner, bursting and killing the host cell.Release often takes place in a destructive manner, bursting and killing the host cell.

Lysogenic Some viruses, when they invade a cell do not undergo the full infective cycle.Some viruses, when they invade a cell do not undergo the full infective cycle. They integrate themselves into the hosts DNA.They integrate themselves into the hosts DNA. When the cell replicates, it also replicates the virus.When the cell replicates, it also replicates the virus. When the virus reassembles it re-enters the lytic phase, releasing new copies of the virus and rupturing the host cellWhen the virus reassembles it re-enters the lytic phase, releasing new copies of the virus and rupturing the host cell

Viral DNA injected into host cell Assembly of new viruses Lysis of cell Viral DNA integrated into hosts DNA Lytic cycle Lysogenic cycle

In the lytic phase virus particles infect host cells and are replicated.In the lytic phase virus particles infect host cells and are replicated. In the lysogenic phase viral genetic material that has entered the host cell becomes incorportated in the cell and lies dormant. It is then passed on to the progeny of the infected cells.In the lysogenic phase viral genetic material that has entered the host cell becomes incorportated in the cell and lies dormant. It is then passed on to the progeny of the infected cells. Eventually, the lytic phase will start again, and cells that were never infected themselves, but carry the viral genetic material will begin to produce new virus particles.Eventually, the lytic phase will start again, and cells that were never infected themselves, but carry the viral genetic material will begin to produce new virus particles.

What are the six steps in virus replication attachment, penetration, uncoating, replication, assembly and release. What is contained within the capsid of a virus? The capsid contains the genetic material, either DNA or RNA, and sometimes enzymes. How is the genetic material of viruses replicated? Viruses have no replication capabilities themselves, so they must use the replication machinery of their host cells.

Human Influenza Virus (type A,B or C) A type of myxovirus Influenza A viruses infect a wide variety of mammals, including man, horses, pigs, ferrets and birdsA type of myxovirus (any of a group of RNA viruses including those that cause influenza and mumps) Influenza A viruses infect a wide variety of mammals, including man, horses, pigs, ferrets and birds Influenza A viruses are a major human pathogen, associated with epidemics and pandemics.Influenza A viruses are a major human pathogen, associated with epidemics and pandemics. Influenza B viruses infect humans only and cause disease, but generally not a severe as A typesInfluenza B viruses infect humans only and cause disease, but generally not a severe as A types Influenza C viruses infect humans only, but are not believed to cause disease.Influenza C viruses infect humans only, but are not believed to cause disease.

Method of transmission Method of transmission Air-bourne droplets infection from the coughs and sneezes of infected individualsAir-bourne droplets infection from the coughs and sneezes of infected individuals Infected people are infected from a day before symptoms appear until a week afterwardsInfected people are infected from a day before symptoms appear until a week afterwards

Organ affected The virus invades the epithelial cells of the upper respiratory tract and reproduces inside them, killing many cells in the process. The dead cells increase the amount and thickness of the mucus produced which irritates the throat causing coughing. Secondary bacterial infection is common

Incubation time Infected people are infected from a day before symptoms appear until a week afterwardsInfected people are infected from a day before symptoms appear until a week afterwards Symptoms usually lasts about 7-10 days, with the fever and aches improving after 2-3 days and the cough and sore throat lasting longer.Symptoms usually lasts about 7-10 days, with the fever and aches improving after 2-3 days and the cough and sore throat lasting longer. However, some people have symptoms which go on for much longer - weakness and depression sometimes lasts weeks.However, some people have symptoms which go on for much longer - weakness and depression sometimes lasts weeks.

Symptoms Fever (usually above 38°C) Chills Muscle aches and pain Severe headache Weakness and tiredness Loss of appetite Sore throat Cough, and Chest pain

Treatment Most people got better on their own with simple relief for their symptoms. This includes: Rest. The most important thing in flu is to give your body a chance to heal itself by resting. Lie down and sleep if possible.Rest. The most important thing in flu is to give your body a chance to heal itself by resting. Lie down and sleep if possible. Regular pain relief with aspirin, paracetamol or ibuprofenRegular pain relief with aspirin, paracetamol or ibuprofen Keep well-hydrated with plenty of warm fluids.Keep well-hydrated with plenty of warm fluids. Remedies for sore throat, headache and blocked nose.Remedies for sore throat, headache and blocked nose.

Prevention Vaccination is difficult due to genetic changes in the influenza virusVaccination is difficult due to genetic changes in the influenza virus Vaccinations based on a variety of antigens are used to protect vulnerable groupsVaccinations based on a variety of antigens are used to protect vulnerable groups Prevention would require isolation of flu victims which is not practical.Prevention would require isolation of flu victims which is not practical.

Human immunodeficiency virus (HIV) HIV is a retrovirus (ie one that contains a single strand of RNA and the enzyme reverse transcriptase)HIV is a retrovirus (ie one that contains a single strand of RNA and the enzyme reverse transcriptase)

Through infected semen or vaginal secretions during sexual activityThrough infected semen or vaginal secretions during sexual activity Through infected blood in transfusions or contaminated needlesThrough infected blood in transfusions or contaminated needles Across the placenta or in breast milk from infected mothersAcross the placenta or in breast milk from infected mothers Method of transmission

HIV in the blood attaches to cells that carry the ‘CD4’ antigen. These include T Lymphocytes and macrophage white blood cells.HIV in the blood attaches to cells that carry the ‘CD4’ antigen. These include T Lymphocytes and macrophage white blood cells. Organ affected

Incubation time After entering the cell it becomes a provirus – that is a form of the virus which is capable of being integrated into the host genome.After entering the cell it becomes a provirus – that is a form of the virus which is capable of being integrated into the host genome. It is replicated over a period of 8 – 10 yearsIt is replicated over a period of 8 – 10 years Eventually the virus particles are reassembled and emerge into the blood, rupturing and killing the T cells in the process. This leaves the immune system compromisedEventually the virus particles are reassembled and emerge into the blood, rupturing and killing the T cells in the process. This leaves the immune system compromised

Symptoms During the latent period there are no symptoms, but the individual is infectious.During the latent period there are no symptoms, but the individual is infectious. After this period symptoms begin to appear that include:After this period symptoms begin to appear that include: –Tiredness –Fever –Weight loss –Diarrhoea This is followed by the more serious symptoms of AIDSThis is followed by the more serious symptoms of AIDS

AIDS As the immune system is no longer functioning there is no defence against a variety of opportunistic infectionsAs the immune system is no longer functioning there is no defence against a variety of opportunistic infections The most common are:The most common are: –Kaposi’s sarcoma –TB –Pneumonia All of these are usually fatalAll of these are usually fatal

Treatment There is, as yet, no cure or vaccination for HIV or AIDSThere is, as yet, no cure or vaccination for HIV or AIDS Drugs such as AZT can delay the onset of symptomsDrugs such as AZT can delay the onset of symptoms

Prevention Safe sexSafe sex Use only sterile needlesUse only sterile needles Screening of blood productsScreening of blood products

What is a bacteriophage? b)What do they infect? c)Why are bacteriophages important industrially? d)How do they infect a cell? e)Why is the life cycle of a bacteriophage described as lytic? Do you consider viruses to be alive? Give reasons to justify your answer. Read the information on RETROVIRUSES. a) Give 2 features of all retroviruses b) Name a retrovirus c)Why are reverse transcriptase and retroviruses widely used in genetic engineering?