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Lecture_13_Superspreaders - PJH1 Contact networks and...

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2/24/2009 1 Contact networks and superspreaders of infectious disease 1. Heterogeneity in contact rates for STDs 2. Directly‐transmitted pathogens, superspreaders and contact networks 3. Superspreaders of vector‐borne disease and helminths The Disease: AIDS Main cause of death in 25 ­ 44 year olds Immunity collapse after 8 ­ 15 years Increases susceptibility to other infections The Aetiological agent: HIV Human Immunodeficiency Virus HIV/AIDS: Heterogeneity in STD Transmission A Retrovirus Cases … 16,000 new cases each day 90% in developing countries Transmission 80% via sexual intercourse Also : Intravenous drug use by sharing needles Blood transfusion ..but screening has reduced Vertical from mother to child during parturition or breast feeding …reduced through anti‐retroviral drugs during pregnancy 30 PJH1 AIDS HIV infection runs for many years Asymptomatic Acute Antibody T Helper Cells Acute phase: first infection similar to most viruses but virus enters CD4 cells Asymptotic phase: Body’s defenses strong. Virus production reduced AIDS: Immune defenses loses control, Virus replicates & immune system collapses. 0 1 2 3 4 5 6 7 8 9 10 11 12 Years HIV The HIV Pandemic International Pandemic 40 million living adults infected HIV/AIDS 2003 .. 20 million dead … Europe 0.6m Africa 26.5m E Europe 1.6m Asia 6.5m N. Am 1.0m Latin Am 1.4m The HIV Pandemic HIV in adults in USA The HIV Pandemic Age prevalence of AIDS in USA
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2/24/2009 2 Susceptible Infectious Acute β Asymptomatic Acute AIDS Modeling HIV Dynamics Simple SI model Infectious Asymptomatic Death Infectious AIDS 0 1 2 3 4 5 6 7 8 9 10 11 12 Years For sexually transmitted pathogen, Transmission does not depend on N R 0 = β / ( α + d) Wh β Heterogeneity in contact rates Where = ε c c = rate of sexual partner acquisition (contact rate) ε = per contact transmission probability Sexual transmission..
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