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 18-4

Common Vectors That Transmit Disease MosquitoTick MouseDeer

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 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.Genetic resistance

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 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