chapter 22 module 8

Question 1

22.1 One Health

Answer 1

the concept that the health of humans, animals, and the environment (including plant life and ecosystems) should be viewed in a holistic (all-inclusive) way is called One Health

disruption of an environment can lead to transmission of pathogens to animals
and humans

evolution of new microbial traits can occur in response to changes in the environment

Question 2

Global Mixing Bowl

Answer 2

human activities in particular can promote the emergence of infectious diseases, for example through ecological disturbances and movement of animals

ie. influenza viruses; mixing of strains of influenza viruses in birds, swine, and humans results in the evolution of new recombinant strains with the potential to spread globally every year

we use term “mixing bowl” b/c within last few decades humans have created an incredible array of unique opportunities and challenges for microbes

ie. we fly across continents quickly (with out microbes)
ie. we use antimicrobial drugs that put selective pressure on microbes
ie. we transport microbes across oceans in ships
- -> the result has been the dawn of a new era of emerging and reemerging diseases

Question 3

Emerging and Reemerging Infectious Diseases - 2020

Answer 3

Babesiosis - protozoan tick-borne disease
Bartonella henselae - bacterial cat scratch disease
Candida auris - fungal disease causing local and bloodstream infections (multiply drug-resistant)
Chikungunya and Mayaro - two arbovirus diseases that have recently moved into the Americas
C. difficile - endospore-forming bacterium causing severe GI infection

SARS-CoV-2 - acute resp distress, damage to other organ systems
Ebola virus disease - hemorrhagic ever; large epidemic in 2014-2015
Ehrlichiosis - tickborne bacterial disease
Elizabethkingia - common environmental bacterium causing HAIs
Lassa fever - viral hemorrhagic fever; currently confined to Africa
Leishmaniasis - protozoan disease of skin and tissue
Marburg virus - viral hemorrhagic fever, similar to Ebola
Measles - threatens to reemerge b/c of lower vax rates
MERS - Middle East resp syndrome
Mumps - threatens to reemerge; partially due to lower vax rates
Nipah Virus - encephalitis and resp illness; Asia and Africa
SARS - sudden acute resp syndrome, emerged suddenly in 2003
Shiga-toxin producing E. coli - foodborne and water-borne infection
Zika Virus - mosquito-borne illness affecting fetuses most severely

Question 4

patterns of newly emergent infectious diseases

Answer 4

often reflect contemporary demographic and environmental changes – more people living closer together and in greater contact with wild and domesticated animals, and habitat destruction

–> another issue is the multipurpose use of resources – such as using the same water for waste disposal, irrigation, and human consumption

over the past 4 decades, the rate of infectious disease emergence has increased in both humans and animals

Question 5

22.2 Animals and Infectious Disease: Zoonoses

Answer 5

zoonosis describes the transfer of disease-causing microorganisms from animals to humans

worldwide diseases that humans acquire from animals result in millions of cases illness, and perhaps a million deaths each year

however, we also recognize that microbes can transfer back and forth between animals and humans

over the last three decades, approx. 75% of newly emerging human diseased have been zoonotic

likely 1 million vertebrate diseases and many more to discover

once introduced to human populations, some zoonotic agents can spread from human to human - in some cases causing global pandemics
ie. HIV/AIDS originated as a chimpanzee retrovirus, that jumped species and adapted itself to human-to-human transmission

Question 6

Lyme Disease

Answer 6

classic example of zoonosis

• in 1976 a number of children living near Lyme, Connecticut began developing arthritis-like symptoms
• because arthritis is not infectious, an underlying microbial cause was suspected
• –> soon recognized as bacterial infection caused by spirochete Borrelia burgdorferi and given name Lyme Disease

now most commonly reported arthropod-borne illness in US and Europe, and is also found in Asia

• ->lifecycle of bacterium involves ticks, small mammals, and large mammals
• ->more highly populated areas push houses to be built closer to woods which is good for ticks to come in contact with humans
• ->increases in temperature in recent decades in some areas = increased population of ticks
• ->warmer conditions mean that larval ticks are more likely to survive to maturity

Question 7

COVID-19

Answer 7

seems to originally have been a bat virus and then cycled in intermediate mammalian hosts before jumping to humans in 2019

• -> new to humans so no adaptive immunity
• -> many measures taken, including social distancing: decreasing the density of people in the same space to limit transmission
• -> a factor pushing high transmissibility is that it can be spread asymptomatically or presymptomatically

–> flattening the curve as to not overwhelm and exceed healthcare capacity

Question 8

22.3 The Environment and Infectious Disease

Question 9

Clean Water and Infectious Disease

Answer 9

every drop of water we drink contains thousands of microbes

large population of world does not have access to safe drinking water
–> WHO reports that more than 1 billion people lack access to clean water and 2.6 billion lack access to basic sanitation

poor water sanitation and lack of safe drinking water take a greater human toll than war and terrorism

• waterborne diarrheal diseases along cause great burden
• U.N. reports that 4000 children die each day as a result of infectious diseases acquired by drinking contaminated water

in many developed countries water is disinfected and tested and a filtration system is used or treatment with chlorine

boil water advisories come out when there is a breach in the water delivery system and the quality of water can not be ensured

Pathway for water purification = coagulation, sedimentation, filtration(sand, gravel, charcoal), disinfection(chlorine, UV light), distribution

Question 10

Indicator bacteria

Answer 10

routine bacterial monitoring of potable waters involves testing for INDICATOR BACTERIA, that is microorganisms normally found in mammalian GI tracts, whose presence would indicate likely contamination with fecal matter

testing for pathogens of concern like protozoa: Giardia and Cryptosporidium; bacteria like Salmonella, Shigella, Vibrio, and Campylobacter; viruses like Hep A and Norwalk – would be hard because it may not provide the necessary margin of safety given the large volumes of water that are distributed

intestinal bacteria most useful in the routine monitoring of microbial pollution are gram-negative rods called coliforms (E. coli and similar bacteria), which ferment lactose and produce gas
–> when significant numbers of coliform bacteria or fecal streptococci are detected the water is not considered safe to drink

important to differentiate between coliforms that can be naturally found in soils and uncontaminated water (Klebsiella, Enterobacter, Citrobacter) AND fecal coliforms that live mainly in human and animal intestines
–> although most E. coli strains are not pathogenic, they almost always come from a mammal’s intestinal tract so their presence in a sample is a clear indicator of fecal contamination

Biosensors: new tech developed that detects structures on specific microbes and transmit electrical or physical signals that are easily read (uses PCR, genome techniques, or electrochemical signaling)

Question 11

what is tested for in water

Answer 11

side from microorganisms,
chemical levels (ie. lead)

Question 12

Microbial Contamination of the Food Chain

Answer 12

E. coli outbreaks from beef are caused when cattle are infected
E. coli outbreaks associated with vegetables are generally triggered when crops are watered with unclean water containing fecal matter, or possibly when infected animals or birds have access to the crops

food can also carry harmful microbes

• Hep A virus can be transmitted through food or water contaminated with human fecal matter
• -> Hep A numbers are very high in areas where there is no sewage treatment, and have especially high numbers in developing countries and rural areas (in rural areas of South Africa, the seroprevalence is 100% - this means everyone in that area is infected, but some are asymptomatic and just carriers

Question 13

Global Climate Change and Biology

Answer 13

over past 40 years, the concentrations of carbon dioxide and methane in the atmosphere have increased

• -> now at highest level since the first humans set foot on earth
• -> as a result climate is changing, and the compounds are absorbing long-wavelength energy coming from Earth’s surface and reflect some of it back to earth, WARMING EARTH LIKE A GREENHOUSE

climate change can be detected in weather: more rainfall and generally higher average temperatures over the year with more variable weather patterns

in some areas increased rainfall will lead to increases in some pathogens and vectors of infectious disease

ie. Vibrio cholerae, for example, thrives in warm water
ie. mosquito populations will likely increase in areas with more rainfall and the incidence of infectious diseases like yellow fever and malaria will increase (potentially by several hundred million)

Hantavirus outbreak in 1993:

• weather phenomenon El Nino, warming trend that originates over the Pacific Ocean, caused wetter weather conditions, which led to an increase in pine nut population
• ->pine nuts are a favorite delicacy of deer mice, by the spring and summer of 1993 there was a very large pop. of deer mice which are the reservoir for hantavirus and their feces or urine exposed to humans = disease and potentially death
• note interconnectedness of environment, plant world, animal world, and humans

Question 14

22.4 Microbes to the Rescue

Answer 14

non-disease-causing microbes are of extreme importance in saving us from the wastes and pollutants we produce

Question 15

Liquid Waste Treatment - Sewage

Answer 15

each year trillions of gallons of human waste released into environment
-low levels of human wastes can be accommodated b/c natural waters have self purification capacities
naturally occurring nonpathogenic microbes in those ecosystems can degrade the wastes

• -> when waters are overwhelmed by concentrated inputs of organic matter a high amount of oxygen is required
• exhaustion of the dissolved oxygen occurs and water becomes putrid and septic = pathogens also spread

so to minimize this happening,

• -> rural and suburban areas with relatively low population densities rely on septic tanks (containers into which sewage flows)
• the solid material settles and is subject to microbial decomposition and the liquid, with its greatly reduced organic content, is allowed to overflow and is distributed through a series or perforated pipes into the surrounding area
• -> as long as the houses are far enough a part, the reduction in organic matter is sufficient to reduce concentrations or organic matter being released to levels that can be accommodated without causing harm
• but these systems are not good for largely populated areas

some cities pump sewage away into offshore areas of the ocean away from shellfish beds and sometimes into agriculture fields away from the city
-some have extensive sewage treatment plants

Question 16

main aim of wastewater treatment

Answer 16

to reduce organic matter content, that is, to lessen biological oxygen demand (or requirement of oxygen) when the wastewater is eventually released into the environment

Question 17

primary phase of wastewater treatment

Answer 17

involves physical separation of solid materials, largely through settling

Question 18

secondary phase of wastewater treatment

Answer 18

liquid portion of waste is subjected to microbial decomposition that is largely aerobic

Question 19

third (optional) phase of wastewater treatment

Answer 19

may be chemical, physical, or biological, to remove additional inorganic substances like ammonia, nitrate, and phosphate, and to eliminate pathogens

• removes nutrients that could support algal blooms and is important if the wastewater is going to be released into a pristine lake
• may also involve disinfection ie. by filtration or chlorine tx to eliminate pathogens

Question 20

trickling filter system

Answer 20

relatively simple and inexpensive secondary treatment system

• liquid waste is spread out over a porous bed of rocks and allowed to flow downward for collection directly into the groundwater
• the rocks are covered by a biofilm of microorganisms and as the waste percolates down, the biofilms degrade the organic compounds reducing the oxygen demand
• -> not suitable for high volumes of wastewater

Question 21

high volume wastewater treatment (activated sludge process)

Answer 21

activated sludge process is used in secondary stage

• liquid waste is placed into large tanks and the wastewater is rigorously mixed to ensure aerobic conditions
• an active microbial community develops that degrades the organic compounds in the wastewater
• sludge forms and is allowed to settle, most sludge is removed for further treatment, but a portion of it containing high number of microbes is reintroduced into the aerated tx tank along with the next batch of wastewater
• -> this component is called activated sludge b/c the microbes are already adapted to degrading the organic compounds in the wastewater

this process generally reduces the biological oxygen demand by 85-90% and greatly reduces the number of pathogens which are largely outcompeted by nonpathogens
–> concentrations of Shigella and Salmonella are generally 90-99% lower than when first came in

Question 22

anerobic digesters

Answer 22

closed chambers used in microbial process that converts organic sludge from waste tx plants into useful fuels such as methane and hydrogen gases, also called bioreactors

Question 23

Solid Waste Treatment - Composting and Landfills

Answer 23

garbage is material like glass, metal, and plastic that is not subject to microbial degradation

the rest of decomposable organic compounds such as food scraps and paper

• -> today we attempt to remove the nonbiodegradable material from the solid waste and recycle it
• this includes paper that is relatively difficult for microbes to decompose

Question 24

aerobic process in which air and inorganic nutrients support the growth of diverse aerobic microbial communities of bacteria and fungi that are able to decompose the organic wastes

Answer 24

composting

Question 25

composting cont’d.

Answer 25

wastes are generally arranged in a heap or pile that can be managed to ensure adequate aeration and moisture retention

• -> process carried out by mesophilic organisms (grow in moderate conditions)
• but as decomposition process proceeds, heat builds up and there is shift to thermophiles (grow at higher temps)
• -> end result of decomposition of the organic wastes is a material that can be added to soils a a soil conditioner or fertilizer

alternative to composting or decomposition is to send wastes to a landfill
–> generally organic and inorganic solid wastes are deposited together on land that has minimal real estate value

b/c exposed waste can cause odors and draw insects and rodents, a layer of soil is added onto each day’s waste and eventually a hill is formed
–as the buried waste decomposes, largely by anerobic microbes, the land mass subsides

–> after 30-50 years, the land is often stable and suitable for other uses like housing development

Question 26

Biodegradation and Bioremediation: Oil and Chemical Spills

Answer 26

microbes have an amazing capacity to degrade and to transform chemicals that enter our environment through either natural processes or human activities
–> without these microbial activities, all life would cease on earth within a few weeks

yet things like fossil fuels, and major oils spills, and the release of xenobiotics into the environment, chemically synthesized compounds that do not naturally occur
–> proving to be challenging to microbial BIODEGRADATION and the sustainability of environmental equality

BIODEGRADATION: breaking down of materials through the action of microbes or insects

Question 27

xenobiotic compounds

Answer 27

some are totally resistant to microbial attack

• when they enter environment they accumulate and can cause harm to enviro
• some cases it is possible to redesign the compounds and make they biodegradable

ie. laundry detergents now have linear alkyl benzyl sulfonates which are readily biodegradable instead of previous detergents that had nonlinear ones that were not biodegradable
- nonbiodegradable ones were recalcitrant and accumulated in the enviro

• today we also have biodegradable plastics and various other substances that have been designed to be vulnerable to microbial attack
• > microbes can degrade many compounds in petroleum, but large amounts of oil at once can overwhelm natural system
• • in some cases when natural microbes are not enough inorganic nitrogen and phosphate-containing fertilizers can be added to stimulate the growth of naturally occurring oil-degrading microbes
• no microbes added, just something to help natural ones grow
• –>this is called BIOREMEDIATION

Question 28

Counteracting Climate Change?

Answer 28

some scientists believe that is may be possible to manage microbial activities in soils and oceans to combat global warming

• microbes are responsible for the production and consumption of major greenhouse gases including CO2 and methane
• -> some microbes produce CO2 whereas others like cyanobacteria and algae consume it

some microbes like the archaea in the guts of herbivore animals, produce large amounts of methane

• > cows release more methane into the atmosphere than automobiles (example of microbes contributing to climate change)
• but others lessen it
• unclear whether scientists will be able to help or should they help manipulate microbes to help counteract climate change
• -> it is also unclear whether the balance of microbial production and consumption of CO2 and methane can be controlled

–> if concentrations of greenhouse gases continue to increase, human, plant, and animal, and environmental health will change – and the ultimate outcome may well depend on microbes