Environmental Health Science Check-In 2

Seven Drivers of Disease Resurgance

1) Human Migration

2) Population Growth & Urbanization

3) Pesticide Overuse

4) International Travel

5) Antibiotic Overuse

6) Lack of Clean Water

7) Climate Change

Zoonosis

an infectious disease that passes from animals to humans, by direct contact with animals, their body fluids, or contaminated surfaces, or through a vector.

Vector-Borne Disease

a disease spread to humans by the bite of an infected arthropod (mosquito, tick, flea, sandfly) that carries the pathogen.

Vector vs. Reservoir

the vector carries the pathogen between hosts. The reservoir is where the pathogen lives long-term, often a rodent, bird, or bat.

Prions

misfolded proteins

Viruses

need host cells to replicate

Bacteria

single-celled; most treatable with antibiotics

Protozoa

single-celled parasites

Examples of Vector-Borne Diseases

Malaria, Leishmaniasis, Plague, Lyme Disease, Rocky Mountain Spotted Fever, Arboviruses

How a Pathogen Gets From an Animal to You

Reservoir Host —> Vector —> Human

Chain of Infection

Infectious Agent —> Reservoir —> Portal of Exit —> Mode of Transmission —> Portal of Entry —> Susceptible Host

Malaria

Vector: Anopheles Mosquito

Reservoir: Humans

Controlling Malaria

• Insecticide-treated nets

• Indoor residual spraying

• Larval source management

• Chemoprophylaxis

Leishmaniasis

Vector: Sand fly

Reservoir: Rodents, dogs, humans

Plague

Vector: Rodent fleas

Reservoir: wild rodents

Plage moves between these two cycles in nature

Enzootic cycle & Epizootic cycle

Lyme Disease

The most commonly reported vector-borne disease in the United States

Vector: backlegged tick

Reservoir: white-footed mice, chipmunks, birds

Rocky Mountain Spotted Fever

Vector: Dog & Wood Ticks

Reservoir: Ticks (pass it to their offspring)

Examples of Arboviruses

West nile virus, dengue, zika, yellow fever, japanese encephalitis, tick-borne encephalitis, rift valley fiver

Arboviruses

viruses carried by mosquitoes and ticks

Arboviral infections cause three main clinical pictures

1) Febrile Illness: high fever, headache, muscle and join pain, rash

2) Neuroinvasive Disease: Encephalitis, menigitis, or acute flaccid paralysis

3) Hemorrhagic Fever: Bleeding, Organ Failure, Shock

Dengue

Vector: Andes mosquito

Reservoir: humans (forest cycle in monkeys)

Why new zoonoses are emerging

• Human-driven

• Environmental

• Microbial & Host

Hantavirus

Route: inhaled rodent excreta

Reservoir: Deer mouse

Ebola disease

Route: Bodily Fluids

Reservoir: likely fruit bats

Mpox

Route: Close Skin Contact

Reservoir: likely rodents

Rabies

nearly 100% fatal once symptoms start, and nearly 100% preventable (vaccine)

Route: Bites, Scratches

Reservoir: bats, racoons, dogs

Anthrax

Agaent: Bacteria

a soil bacterium that is an occupational hazard for people who handle animals

Route: skin, inhalation, ingestion

Reservoir: soil; graving livestock and wildlife

H5N1 Influenza

Route: contact with infected animals

Reservoir: wild birds, poultry, cattle

West Nile

Vector: Culex mosquito

Reservoir: Birds

vCJD

Agent: Prion

Route: eating contaminated beef

Reservoir: Cattle

Heavy Metal

a metal with high atomic weight and a density at least 5 times that of water

Acute Exposure

a high dose over a short time, effects are fast and dramatic

Chronic Exposure

Low doses over months or years, effects are slow and easy to miss

Route of exposure

how a metal enters the body: inhalation, ingestion or skin contact

Media

what carries metals to people: air, soil and dust, water, food.

Bioaccumulation

buildup within one organism over time

Biomagnifictation

rising concentration at each step up a food chain

vertical transmission

passage from mother to fetus across the placenta

Carcinogen

something that causes cancer

Take-home exposure

workers carry dust home on clothes and shoes, exposing their families

Hierarchy of Control (How workers are protected)

Elimination (Strongest) —> Substitution —> Engineering Controls —> Administrative Controls —> PPE (weakest)

CERCLA

authorizes EPA to clean up sites contaminated with hazardous substances, pollutants or contaminants, and to respond to emergency releases.

Removal Actions

short-term responses to immediate threats

Remedial Actions

long-term, permanent cleanups at National Priorities List Sites

EPA

regulatory (enforcement)

How do we control and clean up the hazard?

ATSDR

non regulatory

are people exposed now, and how is it harming them?

How do the EPA and ATSDR work together?

ATSDR asses health risks at a site —> ATSDR recommends actions —> EPA Requires and oversees cleanup —> Community exposure is reduced.

Substance Priority List

1) Lead

2) Arsenic

3) Cadmium

4) Nickel

5) Beryllium

6) Manganese

FIRFA

registration and labeling of every pesticide

FQPA

pesticide residues on food, with an extra 10x safety margin for children

TSCA

industrial chemicals (not pesticides)

CERCLA (Superfund)

cleanup of hazardous waste sites; created ATSDR

EPCRA

Emergency planning and community right-to-know

Stockholm Convention

international treaty on POPs

Pesticide

any substance or mixture intended to prevent, destroy, reprel, or mitigate a pest

also: insecticide, herbicide, fungicide, rodenticide

Sodium Channels

Normally: open briefly to fire the signal

Pesticide: DDT and pyrethroids hold them open: repeated firing

GABA receptors

Normally: Calm nerve activity

Pesticide: Dieldrin blocks them: seizures

AChE enzyme

Normally: Clears ACh to end the signal

Pesticide: OPs and carbamates block it: ACh builds up

ACh receptors

Normally: receive the ACh signal

Pesticide: neonicotinoids overstimulate them, mainly in insects

Organophosphates

Irreversibly block AChE

Low persistance

#1 cause of pesticide poisoning

Carbamates

Reversibly block AChE

Low persistence

shorter-lived poisoning

Organochlorines

Disrupt nerve sodium channels or GABA receptors

Very High persistence

Chronic: endocrine disruption, cancer

Pyrethrins & Pyrethroids

Hold nerve sodium channels open

Low persistence

toxic to fish and bees

Neonicotinoids

overstimulate nicotinic ACh receptors

Moderate persistence

harms pollinators

How do organophosphates poison insects and people?

They block acetylcholinesterase, so acetylcholine builds up

Organochlorine Characteristics

1) Persistent

2) Fat-Soluble (bioaccumulate and biomagnify)

3) Travel Far (classified as POPs, spread far from where they were used)

Pyrethrins vs. Pyrethroids

Pyrethrins (natural) vs. Pyrethroids (synthetic)

Shared mechnaism: hold nerve sodium channels open —> nerves fire repeatedly —> paralysis

Glyphosate (herbicide)

• Blocks an enzyme plants need to make amino acids

• most used farm pesticide in the US

2,4-D (herbicide)

• Mimics a plant growth hormone; broadleaf weeds grow out of control

• half of the agent orange mixture

Paraquat (herbicide)

• restricted use: certified applicators only

• highly toxic if swallowed; studied for links to parkinsons

Why do IARC and EPA reach different conclusions about glyphosate and cancer?

IARC judges hazard

EPA judges risk at real-world exposures

Dioxins

unintended byproducts (POP)

PCBs

manufactured chemicals (POP)

Household Cleaning Products

top substance category in poison-center exposures for children 5 and under

Mixing bleach with ammonia-based cleaners releases which toxic gas?

Chloramine

Agent Orange

a tactical herbicide and defoliant used by the U.S. military during the Vietnam War to destroy dense tropical foliage and enemy food crops