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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 Diarrheal diseases – 2.2 million deaths/yr Ex: pneumonia, flu, whooping cough 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 Malaria infant deaths worldwide 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
