Biological Hazards Environmental Science Unit 7.2

The Environment’s Role in Disease  We have altered our environment in ways that encourage diseases to spread  Pathogens – organisms or viruses that cause disease  How diseases spread  Air  Ex: tuberculosis, whooping cough  Drinking water that contains the pathogen  Secondary host transmission  Ex: mosquito  Host – organism in which a pathogen lives

 Most infectious deadly diseases:  Respiratory infections – 4.3 million deaths/yr  Ex: pneumonia, flu, whooping cough  Diarrheal diseases – 2.2 million deaths/yr  Ex: cholera, typhus, typhoid, dysentery  AIDS – 2 million deaths/yr  Tuberculosis (bacteria) – 1.5 million deaths/yr  Malaria – 900,000 deaths/yr  Childhood diseases – 800,000 deaths/yr  Ex: measles, diphtheria

Infectious Disease  Most infectious diseases are transmitted through water  In developing countries the local water supply is used for drinking, washing, and sewage disposal  Vector – organism that transmits a pathogen or parasite to another organism  Ex: mosquito

 Cholera  Deadliest waterborne diseases are from water polluted w/ human feces  Cholera and dysentery cause diarrhea and vomiting, which leads to dehydration  Most infant deaths worldwide  Malaria is caused by parasitic protists and is transmitted by a bite from infected female mosquitoes

Environmental Change and Disease  We alter the environment to make it more suitable for pathogens to live and reproduce  Soil erosion  Parasites are spread through soil contaminated with feces  Hookworm is caused by walking barefoot on soil contaminated w/ human and animal feces

 Antibiotic resistance  Antibiotics are fed to livestock each year to speed their growth  Salmonella, E. coli, etc. evolve resistance to antibiotics and spread through contaminated meat  We use enormous amounts of antibiotics to treat human illnesses  1979 – 6% of pneumonia strains resistant  1989 – 44% of pneumonia strains resistant

 Some strains of staphylococcus aureus are resistant to all antibiotics except one  Some organisms are resistant to ALL available antibiotics  Over-prescription of antibiotics by doctors

 Vector-borne diseases  Malaria was common in U.S. before mosquito control  Mosquitoes have evolved resistance to most pesticides  Spread growth regulators that prevent mosquito larvae from maturing into adults

 Emerging viruses are those that were unknown 100 years ago  Ex: AIDS is caused by HIV  Main defense against viral diseases is vaccination  Vaccinations are very specific

 Cross-species transfers – pathogens that have moved from one species to another  HIV, West-Nile virus  Hemorrhagic fever  Herbicides were sprayed on crops in Argentina  Killed native grasses and allowed other plants to invade farmland  Attracted rodents carrying virus for hemorrhagic fever  Flu spreads from humans to animals and back to humans  Outbreak of new, virulent strain is predicted to be greatest threat to human health