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 Route of infection Portal of entry 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, red measles, morbilli
a very serious disease
Historical effects

11. 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.
Rash on Face and bodies of Children
Pneumonia in rare cases

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 250,000 is required to maintain measles. Measles probably could not have existed solely in humans before human populations reached this size.
“critical community size”
This may have occurred as late as 1000 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 native Americans .
Measles is also a leading cause of death in developing nations.

14. Unvaccinated people can spread the virus
Measles death in the US-2015

15. 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 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.

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

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

19. Impact of vaccine in US