Today: Human Population

“Toxic Garbage Island” movie W 4/21 at 5pm in JES A121

What happens as populations approach their carrying capacity?

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UN Department of Economic and Social AffairsPopulation Division (2004)

Human Population GrowthFig 53.22

as of 4/15 at 1004pm:6,815,080,019

Spanish flu of 1918-1919

Spanish flu of 1918-1919•Killed between 20-50 million people worldwide; 675,000 in the U.S.(2.5%-5% of world population)

•Infected 1/5 to 1/4 of world population

•Was most lethal to people 20-40 years old

http://virus.stanford.edu/uda/

Spanish flu of 1918-1919People on their way to work suddenly developing the flu and dying within hours (Henig).

One physician writes that patients with seemingly ordinary influenza would rapidly "develop the most viscous type of pneumonia that has ever been seen" and later when cyanosis appeared in the patients, "it is simply a struggle for air until they suffocate," (Grist, 1979).

Another physician recalls that the influenza patients "died struggling to clear their airways of a blood-tinged froth that sometimes gushed from their nose and mouth," (Starr, 1976).

http://virus.stanford.edu/uda/

The high fatality rate from the Spanish flu was probably due to an immune system over-reaction

Viruses

Viruses are very simple, and come in a variety of shapes/compositions Fig 19.3

Living organisms must fit all of the following criteria: (modified from Campbell “Biology”)

1. They must have organization.

2. They must have metabolism.

3. They must respond to the environment.

4. They must be able to reproduce themselves.

Viruses only harm cells by invading them and using the cell to reproduce

Living organisms must fit all of the following criteria: (modified from Campbell “Biology”)

1. They must have organization.

2. They must have metabolism.

3. They must respond to the environment.

4. They must be able to reproduce themselves.

basic viral reproductive cycle

Fig 19.4

the relationship between viruses and disease

Virus 1 Virus 2

Virus1+2

During co-infection viral genomes can be mixed resulting in a new hybrid virus.

Spanish flu of 1918-1919

This influenza virus was similar to avian flu

Avian flu exists in two distinct forms:High pathogenicity AI virus that produce >75% mortality (HPAI)

Low pathogenicity is everything else (LPAI)

Public Health Risk from Avian Influenza Viruses by Perdue and Swayne in AVIAN DISEASES 49:317–327, 2005

Avian flu is maintained in wild birds as low pathogenicity, and occasionally mutates to high pathogenicity in domesticated birds.

Approximately 25 outbreaks since 195915 since 1990 and 6 since 2000

Public Health Risk from Avian Influenza Viruses by Perdue and Swayne in AVIAN DISEASES 49:317–327, 2005

Membrane protein

Viruses enter cellsvia membrane proteins.

virus

cell

Membrane protein

Viral genetic material can change allowing the virus to infect

different cells or organisms.

virus

cell

Virus 1 Virus 2

Virus1+2

During co-infection viral genomes can be mixed resulting in a new hybrid virus.

Virus 1 Virus 2

Virus1+2

One concern is a person who is infected with human flu and high pathogenicity avian flu.

Public Health Risk from Avian Influenza Viruses by Perdue and Swayne in AVIAN DISEASES 49:317–327, 2005

How is bird flu being spread?

To lower the chance of a pandemic, we need to understand the spread of the disease.

Declan Butler NATURE Vol 439 pg 772 February 16, 2006

http://news.bbc.co.uk/1/shared/spl/hi/world/05/bird_flu_map/html/1.stm

Bird Flu Spread

Migratory wild birdsorPoultry trade (black market)

Prevention efforts will only be effective if the source can be defined

If the flu is being spread by migratory birds, why are some migratory routes free of flu?

Bird migration is mostly N⇔ S

In 2004 an outbreak in Tibet was traced to illegal poultry transport from China.

Even with today’s vaccine technology and the knowledge that vaccines will prevent severe illness and death, only 300 million doses are produced and used worldwide.More than 95% of the world’s population remains at risk for infection.

Each year an estimated 250,000 to 500,000 people die worldwide as a result of influenza virus infections.

Public Health Risk from Avian Influenza Viruses by Perdue and Swayne in AVIAN DISEASES 49:317–327, 2005

It is estimated that in the United States, for example, the yearly economic burden caused by influenza deaths, infections, vaccinations, loss of productivity, and attendant health care costs is equal to 0.1%–0.5% of the gross domestic product.

Public Health Risk from Avian Influenza Viruses by Perdue and Swayne in AVIAN DISEASES 49:317–327, 2005

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UN Department of Economic and Social AffairsPopulation Division (2004)

Fig 52.17

“Toxic Garbage Island” movie W 4/21 at 5pm in JES A121