Environmental Hazards and

Human Health, Part 2

Causes of global deaths

Infectious diseases

Some definitions

• Disease– Chronic– Acute

• Epidemic• Pandemic

Transmissible (infectious) disease: one that is caused by a living organism

• Pathways for infectious disease in humans.

Figure 18-4Figure 18-4

Common Vectors That Transmit Disease

Mosquito Tick

Mouse Deer

Examples of Vector-Borne Diseases

• Mosquito-borne– West Nile Virus

– Malaria

– Dengue

– Yellow Fever

• Tick-borne– Lyme Disease

– Rocky Mountain Spotted Fever

• Hanta Virus (mice droppings)

• Bubonic Plague (fleas)Characteristic bull rash caused by Lyme disease

How Weather Affects Vector-Borne Diseases

• Tropical and subtropical regions• Temperature• Humidity• Surface water• What might happen with future predicted

climate changes?Climate Change–Larger geographic area where disease is common–Intensity and duration of outbreaks–Altered seasonal distributions

Examples

• Mosquitoes develop more rapidly

• Mosquitoes bite more frequently

• Viral load in mosquitoes is higher

• Because more people are infected, more mosquitoes become carriers that transmit disease

Historic Infectious Diseases

• Diseases of poor sanitation – Hepatitis– Cholera– Diarrheal

• Plague• Malaria• Tuberculosis

Plague

• Bubonic plague, Black Death• Caused by a bacterium carried by fleas and thus their

hosts

Malaria – Death by Mosquito

Tuberculosis

• Caused by a bacterium that infects the lungs

• Spread when someone coughs• Highly infectious• Bacterial cells can live in air for several

hours

Growing Global Threat from Tuberculosis

• The highly infectious antibiotic-resistant tuberculosis (TB) kills 1.7 million people per year and could kill 25 million people by 2020.

• Recent increases in TB are due to:– Lack of TB screening and control programs

especially in developing countries due to expenses.

– Genetic resistance to the most effective antibiotics.

Growing Germ Resistance to Antibiotics

Emergent infectious diseases

• Previously not described, or• Have not been common for at least

the previous 20 years• Examples:

– HIV/AIDS– Ebola– Mad Cow– Avian flu– West Nile– SARS

Emergent diseases

Ebola hemorrhagic fever

Bovine Spongiform Encephalopathy

• Mad Cow Disease• Caused by prions

Avian flu

• H1N1 virus• In 1918 killed an estimated 40

million people• 2006 a closely related (H1N5)

emerged from Asia, passed from domestic birds to people

• 2010 a new emergence of H1N1 first found in Mexico (swine flu)

SARS

• Sudden Acute Respiratory Syndrome

• Severe form of pneumonia first identified in 2003

• 8000 cases, 750 that year• Virus is passed from person to

person through airborne and surficial means

• Virus can live up to 6 hours in the open environment