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Transmission of Viruses

Transmission of Viruses. Introduction Vocabulary Routes of transmission Some examples “Biology” of Viruses. Introduction: Why is transmission important to a virus?. Finite life span Host response/immunity Maintain propagation Spread within population A dead host is no good to a virus.

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Transmission of Viruses

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  1. Transmission of Viruses • Introduction • Vocabulary • Routes of transmission • Some examples • “Biology” of Viruses

  2. Introduction: Why is transmission important to a virus? • Finite life span • Host response/immunity • Maintain propagation • Spread within population • A dead host is no good to a virus

  3. Vocabulary • Portal of entry • Route of infection • Receptors • Susceptible/ non-susceptible cell (receptor) • Permissive/non-permissive (replication) • Abortive/incomplete vs productive/complete infection • Tropism • Localized/systemic infection • Vector/fomite

  4. Some routes of infection for animal (human) viruses • Distinctions are somewhat artificial and arbitrary-they are for virologists not for viruses • What is the “natural” route?-not the “lab” route • Viruses may use more than one

  5. 1. Direct contact transmission • Viruses persist in environment • Host comes in contact • Surfaces or fomites • Human rhinovirus (the “common cold virus”) • Evidence from volunteer studies

  6. 2. Respiratory route • Adenoviruses eg adenovirus 5 • 5-10% of urt infections in humans • conjunctivitis • Localized infections due to tissue tropism • Progeny virions released into secretions • Inflammations/irritations

  7. Respiratory droplets contain active virus!

  8. Other respiratory route virus examples • Paramyxoviridae (measles, mumps, respiratory syncytial virus RSV) • Orthomyxoviridae (influenza A, B, C) • Poxviridae (variola virus-smallpox) laboratory outbreaks in Britain-1973 and 1979 clinical practice of variolation illustrates adaptibility of viruses

  9. Family Paramyxoviridae has Two Subfamilies Paramyxovirinae Genus Rubulavirus Mumps Virus Genus Morbillivirus Measles Virus Rinderpest Virus Pneumovirinae Genus Pneumovirus Respiratory Syncytial Virus

  10. Measles • Japanese Measles = rubeola, 14-day measles, “true” measles • a very serious disease • Historical effects

  11. Pneumonia in rare cases Rash on Face and bodies of Children Measles symptoms and Disease Syndrome Contagious 1 to 2 days before symptoms appear. Continue to transmit virus for four days after rash appears. Transmission is by respiratory secretions: Aerosol. Incubation is 10 to 14 days. Cough, Fever, 2 to 4 days malaise - Pronounced rash.

  12. Measles Virus History • Humans are the only measles virus reservoir in nature. • Measles infection results in solid, life-long immunity. • A minimum population size of about 500,000 is required to maintain measles. Measles probably could not have existed solely in humans before human populations reached this size. • This may have occurred about 5000 years ago well after plant and animal domestication. • When the virus was first introduced into the Americas during European exploration 500 years ago, the death toll was enormous. Measles and smallpox caused massive depopulation of the North American Indians. • Measles is also a leading cause of death in developing nations. • http://www.who.int/topics/measles/en/

  13. http://www.slate.com/blogs/bad_astronomy/2014/02/19/measles_confirmed_case_in_sf_area_may_have_exposed_thousands_to_the_contagious.htmlhttp://www.slate.com/blogs/bad_astronomy/2014/02/19/measles_confirmed_case_in_sf_area_may_have_exposed_thousands_to_the_contagious.html

  14. Measles-a candidate for eradication • Measles is one of the leading causes of death among young children even though a safe and cost-effective vaccine is available. • In 2012, there were 122 000 measles deaths globally – about 330 deaths every day or 14 deaths every hour. • Measles vaccination resulted in a 78% drop in measles deaths between 2000 and 2012 worldwide. • In 2012, about 84% of the world's children received one dose of measles vaccine by their first birthday through routine health services – up from 72% in 2000. • Since 2000, more than 1 billion children in high risk countries were vaccinated against the disease through mass vaccination campaigns ― about 145 million of them in 2012.

  15. Efforts to stem measles have been successful, but uneven political commitment, lack of funds and public fear threaten to undermine the progress.

  16. “German” measles • German measles = rubella, 3-day measles • caused by a togavirus, mild initial disease but may cause birth defects (CRS) • Vaccine prevention

  17. Impact of vaccine in US

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