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Hong Kong (H5N1),
Hong Kong (H5N1),
Netherlands (H7N7),
Vietnam and Thailand (H5N1)
Swine flu - 2009 worldwide (H1N1)
3 prerequisites for pandemic
• new virus must be transmitted to humans
• spread from human to human
• must replicate in humans causing disease
Emergent Environmental Diseases
Animals also experience widespread epidemics /pandemics:
TSE: Transmissible Spongiform Encephalopathies
Creutzfelt-Jacob (human)
Mad Cow Disease (cattle)
Chronic Wasting Disease (deer, elk)
Prions (not virus, not bacteria) are agents causing this disease
Agent à Vector à Disease
West Nile Virus in 21 century
USA:
2001-2002
2010-2013
Outbreaks in
Russia: Volgograd, Astrahan’ cases in Kazakhstan
West Nile Virus – западно-нильский энцефалит.
Slide: incidence of reporting of infected birds in US counties in 2001.
Infectious Disease Outbreaks
Nipah virus – pig flu
Ebola virus – symptoms for Ebola include high fever, severe headache, muscle, joint, or abdominal pain, severe weakness and exhaustion, sore throat, and nausea.
Main Causes of Emerging Diseases
Microbial adaptation & change
Human demographics & behaviour
Technology & industry (animal practice, food production)
International travel & commerce
Breakdown of public health measures
Climate and weather
Poverty & famines
Wars
Most Common Cancers in the world
Cancer: ~5 times more in men vs women
2: Toxins
TOXINS:
Dangerous chemicals, divided into two broad categories:
Hazardous means dangerous:
flammables, explosives, acids, caustics, etc.
Toxic means poisonous:
may be general or very specific (able to damage /kill cells).
5 Classes of Toxic Chemicals
Neurotoxins - class of poisons that attack nerve cells:
• Heavy Metals kill nerve cells (lead, cadmium).
• Chlorinated Hydrocarbons disrupt nerve cell membranes (DDT).
• Organophosphates inhibit signal transmission between nerve cells.
Mutagens - agents that damage or alter genetic material.
Radiation
Teratogens - cause abnormalities during embryonic growth and development.
Alcohol - Fetal Alcohol Syndrome (FAS)
Some toxins affect the nervous system and reduce the ability of the brain to function.
Certain hazardous chemicals cause mutations, which adversely affect the developing fetus: teratogens. Fetal alcohol syndrome is a major societal problem and babies born of alcoholic mothers typically have less ability to fight off diseases.
Carcinogens - substances that cause cancer.
Cigarette smoke, asbestos.
Allergens - substances that activate the immune system.
Dust, paints, chemicals:, formaldehide, pesticides,..
Carcinogens are substances that actually can cause cancer. Chemicals produced to kill certain insects or weeds may be dangerous for people: allergic reactions (negative response of human body). The chemical makes the body think it is being attacked by a disease and the body responds by producing histamines, or poisons, to kill the disease it thinks it has. Allergens are substances that cause allergic reactions.
Top 12 Toxic & Hazardous Chemicals
Lumber - древесина
Pesticides in Produce
Rank: 12 most contaminated foods
‘ Dirty dozen ’: 12 POPs (Persistent Organic Pollutants). Among them are 9 pesticides like DDT), dioxins, furans.
Radiation
Most dangerous types of radiation
Nuclear Weapons, Nuclear Energy
Medical Uses of Radiation
Radiation in the Home and Workplace
Radon
Construction materials, buildings
Noise Pollution
Measured in Decibels
Noise pollution - > 80-85 decibels
Pain threshold = 120 decibels
Two sources of excessive noise
• Workplace
• Large gatherings of people (concerts, sports events)
Toxins in our Life
Humans can encounter exposure by drinking water that contains a toxin, by breathing polluted air, by eating contaminated food, by taking recreational or medicinal drugs, or by putting things on the skin.
Bioaccumulation & Biomagnification
Bioaccumulation: organisms take up and accumulate toxins in their cells and tissues
Biomagnification – increase in concentration of toxins through food webs from low to higher trophic levels
Bioaccumulation – accumulation of toxin in a certain species.
Biomagnification occurs when toxins that are in relatively small concentrations in the environment increase in concentration when they move up through the food chain.
DDT: Powerful Insecticide, Harmless to Humans
In this case, DDT was being sprayed directly on people. The LD 50 for DDT is 50 mg/kg, so we know that there will not be an immediate lethal impact on people here at the beach; however, humans incur health problems with pesticides (DDT).
Minimizing Toxic Effects
Every material can be poisonous under some conditions: depends on dose.
Taken in small doses, toxins break down before they do much harm.
Liver - primary site of detoxification
Toxins that aren't broken down can affect tissues and organs – they disrupt their growth and possibly cause
Humans are well adapted to exposure of many substances that are very toxic to other organisms. F.e., if you give a dog Tylenol, you would almost kill it. Certain plants that humans eat are loaded with toxins: broccoli is composed of ~80% toxic substances. Humans are able to detoxify many substances. Every material can be poisonous under certain conditions.
If the dose of a toxin is low enough, it can often be broken down and/or passed through the organism without harm. In humans, the liver is the primary site where toxins are broken down before being excreted.
Measuring Toxicity
Toxicity – degree to which a substance is toxic
Animal Testing -
Most common method to measure toxicity (harm)
Expensive, Time consuming
Often inhumane
Difficult to compare toxicity of unlike chemicals or different species of organisms
We need to know what level of toxic substance is harmful. If we look at a toxin as it moves up thru the food chain or as it is absorbed from the environment, we need to know the concentrations at which it starts to become a problem. The typical way to measure toxicity of new substances (new cosmetic or food additive) is to use animals. In many cases (with lab rats, for example), it may be unreasonable to compare the toxicity to an animal with toxicity to a human.
A Typical Dose/Response Curve
Graph is a typical response of population of organisms to a chemical dose. Dose -in any units, but usually in mg per kg of body weight.
Y axis: # organisms responding. We start with 0 dose that has no impact, and we set this as the baseline to measure effect. As we increase the dose a little, a few individuals that are very sensitive show a negative response (they may get a rash or be slightly sick). As the dose increases more, a majority of the individuals experience negative effects. With higher concentrations, a few individuals would have no response – they are insensitive to the material.
Lethal Dose 50 (LD50)
LD50 - the dose
of a toxin that is
lethal to half of the
tested population
LD50 examples:
Alcohol: 10 g/kg
Caffeine (rats):~0.2 g/kg
Nicotine: ~1 mg/kg
The extreme response to a toxin is death. Lethal dose, or LD50 (concentration of a toxin at which 50% of the population dies) is used to describe the level of toxicity of a substance. The concentration is usually expressed in mg of toxin per kg of body weight. One point to note about the LD50 is that some of the organisms die before this 50% level is reached. Note: LD50 does not describe how healthy is the remaining 50% of the population that survives.
Acute vs Chronic Doses & Effects
Acute effect - immediate health effect caused by a single exposure to a toxin (can be reversible)
Chronic effect - long lasting or permanent health effect caused by (1) a single exposure to a very toxic substance or (2) continuous or repeated sub lethal exposure to a toxin
We divide toxic impacts into acute and chronic effects. Acute effects are those we can immediately recognize after a person has had a single exposure. Acute effects can be reversible. An example of an acute effect is the symptoms you would have if you swallowed some rat poison. An acute effect might be reversible, and you get well quickly after your body got rid of the poison.
Chronic effects are long lasting, caused by a single or by repeated exposures. A chronic effect might not show up for years after the exposure, and might continue over a long period of time. They are difficult to diagnose. Chronic effects are probably more widespread and less likely to be treated because they are less likely to be noticed
Risk Assessment and Acceptance
Risk - the probability of harm times the probability of exposure:
Risk = P(harm) x P(exposure)
Many factors influence how we perceive relative risks associated with different situations.
Accepting risks - we go to great lengths to avoid some dangers, while gladly accepting others
The very act of living involves risks. The concept of risk assessment and acceptance is important when we consider potentially toxic substances in the environment. For instance, the biggest risk we take every day (that is if we don't smoke or over eat) is driving. Driving involves high risks of accidents and potential for fatality.
The perception of risk is often very important in whether or not we are willing to accept them.
Establishing Public Policy
In setting standards for environmental toxins, we need to consider:
Combined effects of exposure to many different sources of damage
Different sensitivities of members of the population
Effects of chronic as well as acute exposures
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