Examples of Viral Pathogens Filovirus This newly emerged group of viruses, include the dangerous Marburg and Ebola. Hepatitis viruses The viruses responsible for hepatitis A, B and C. Herpesvirus Nearly 100 herpesviruses are known. Types found in humans include those that cause cold sores, chickenpox, shingles, and genital herpes. Influenzavirus This virus causes influenza in humans. Rapid mutation has resulted in many strains. Papillomavirus This virus causes the formation of warts in humans. Rhinovirus More than 100 rhinoviruses have been identified. They are the most common cause of colds. HIV The human immuno- deficiency virus (HIV) causes AIDS. Lyssavirus This bullet-shaped virus causes rabies.

The Human Immunodeficiency Virus (HIV) HIV and AIDS AIDS (Acquired Immune Deficiency Syndrome) was apparently a new emerging disease when it first appeared in the human population. AIDS was first detected in Los Angeles, USA in 1981. By 1983 the pathogen causing the disease (shown right) had been identified as a virus that selectively infects helper T cells. The virus, which causes a collapse of the immune system, was given the name Human Immunodeficiency Virus (HIV). As yet, there is no cure for AIDS. The disease is now a global pandemic. The Human Immunodeficiency Virus (HIV)

The Economic Cost of AIDS The UN estimates that the medical and human costs of AIDS have already reversed social and economic development in twenty countries. In Brazil, more than US$500 million is spent on anti-HIV agents annually, and medications still fall short of demand. In 2010, South Africa's Gross National Product (GNP) is more than 17% smaller than it would have been without the impact of AIDS. In sub-Saharan Africa, household incomes have fallen by 50% and business profits have decreased by 20% as a result of AIDS deaths. Zimbabwe has 1.8 million people living with AIDS, but despite an increase in health funding, only 24, 000 of the 500, 000 people in immediate need of retroviral drugs are being treated. Photo: CDC AIDS has left many African communities without adults to maintain an economic base. Source: UNAIDS, WHO.

The Social Cost of AIDS 25 million men, women, and children have died from AIDS since the onset of the pandemic. AIDS now kills more people worldwide than any other infectious disease (3.1 million deaths in 2004). 39.4 million people are living with HIV (including nearly 3 million children). Nearly all will die from AIDS-related complications within the next two decades. About 13,000 new HIV infections occur a day. 40 million children have been orphaned by AIDS Sub-Saharan Africa continues to be the most affected globally with 64% of new infections occurring here. Swaziland 38.8% Botswana 37.3% Zimbabwe 33.7% Lesotho 28.9% South Africa 21.5% % Adult Prevalence Rate Source: UNAIDS, WHO.

Origins of HIV AIDS researchers have recently confirmed that the origin of the two types of HIV virus resulted from cross-species transmission (zoonosis) to humans from other primates Viruses related to HIV have been found in many species of non-human primate and are named Simian Immunodeficiency Viruses The killing of primates as bush meat for human consumption allows the virus to infect humans when they handle infected carcasses with open wounds on their hands. Photo: ArtToday.com

Structure of the HIV Virus Capsid Protein coat that protects the nucleic acid (RNA) within Viral envelope A piece of the plasma membrane budded off from the last human host cell. Surface proteins These spikes allow HIV to attach to receptors on the T cells and macrophages. Reverse transcriptase Two copies of this important enzyme transcribe the RNA into DNA once inside a host cell. Nucleic acid Two identical strands of RNA contain the genetic blueprint for making more HIV viruses.

How HIV Infects a T Cell Infecting HIV New HIV HIV particle is attracted to CD4 receptors on a helper T cell. CD4 receptors Infecting HIV How HIV Infects a T Cell Reverse transcriptase causes the formation of viral DNA (using the RNA as a template). RNA The double stranded DNA is incorporated into the host cell's chromosome. Nucleus A complementary strand of DNA is formed. DNA Viral genes are translated into HIV proteins Budding of the new viruses from the host cell. New HIV

HIV Infection HIV infection results in a huge range of symptoms Fatigue HIV infection results in a huge range of symptoms Individuals affected by the virus may have no symptoms, while medical examination may detect only swollen lymph glands. Some individuals may experience a short-lived illness when they first become infected. The symptoms of HIV/AIDS arise from an onslaught of secondary infections as a result of the depleted helper T cell population and suppressed immune system. These infections are usually caused by rare fungi, viruses, and bacteria. Full blown AIDS can also feature some rare forms of cancer (e.g. Kaposi’s sarcoma). Kaposi’s sarcoma

Stages of HIV Infection Category A: HIV positive with little or no symptoms Category B: Some symptoms, low helper T cell count Category C: Clinical AIDS symptoms appear The progress of infection has three clinical categories, shown on the graph AIDS is occurs in the final stage of infection HIV population>Helper T Cell population Death is caused by secondary infection Helper T cell population HIV population Helper T cell concentration in blood (cells mm–3) Years

Modes of HIV Transmission HIV is transmitted in: blood vaginal secretions semen breast milk across the placenta Heterosexual activity now accounts for over 80% of new infections. Photo: Art Today In many African communities, men travel from rural settlements into the cities in search of work. These men often develop sexual networks while they are away and bring HIV with them when they return.

Treating HIV Infection HIV's ability to destroy and evade the cells of the human immune system make it difficult to treat. AZT is a widely used anti-retroviral drug. AZT blocks the production of an enzyme called reverse transcriptase (RT). RT is needed by the virus to splice its DNA into the chromosome of the T cell. Without the enzyme, HIV cannot reproduce. Slows progress—does not cure. Gene therapy, using genetically altered T-cells, which can kill HIV, is also being investigated to treat HIV. HIV Vaccines are currently being trialed on humans in Africa and the UK—successful results thus far