W3 Flashcards
describe the history of disease
- infectious disease ravaged human life since we began farming food 11,000 years ago
- during the 1800s industrial revolution, most people died of disease
- europe began to escape disease in the late 1800s and other countries in the 1900s
- the US surgeon general in the 1950s thought we could close the book on infectious disease
- but not anymore, we have climate change, evolution and our economics
what do people need to do to not get sick?
- prevention is much more effective than medicines
- public understanding of preventing disease is vital
what are the key traits of a hunter gatherer life that lead to them living better with less disease
- humans were His for 5Myr
- moved around to find food so faeces and parasites were left behind (these could then be broken down by bacteria)
- small family bands, separated from others, therefore the disease might kill a few, but would then die out
- bands of equal members, shared. humans were evolved to cooperate with each other
- we had a few common diseases, low virulence STDs, gut words and malaria
- humans often survived to fairly old ages
what are the key traits of the agricultural evolution that lead to disease
- life in one place meaning there were high densities, sharing of food and water and excreta where others might contact it
- domestication of animals: therefore many diseases of animals were passed to us. eg. TB from cattle to humans. it is a trait that diseases flourish in crowded animals
- storage of water and grain: this would attract mecum rats, cockroaches and these extra animals can pass on disease
- traders between towns: therefore carried diseases between groups of humans
- restricted diets and lower immunity: therefore more grain and less fruit, proteins, fats and variety
what causes diseases?
- parasites cause infectious disease:
- microparasites are viruses, bacteria, protists and fungi
- macroparasites are worms and arthropods
- some parasites are internal and some are ectoparasites
- organisms that cause severe disease are known as pathogens - genetic mutations or envrionmental stress eg. diet, UV. these are non infectious diseases eg. Down syndrome, fragile X
what are the defining traits of parasites
- to survive, parasites need to infect new animal hosts. much easier when humans or animals are close together
- parasites can jump to similar animal hosts ie. zonoses. infecting humans became easier once they kept animals
- often carried in faeces and urine. transfer is easier once humans lived in towns
- they must be passed on before the host dies: need slow disease or carriers to pass it on or fast transport between places eg. roads and horses. note: ebola had a high mortality and thus, killed humans very quickly
what are some of the domesticated animals that cause disease
dogs, sleeps and goats, cattle, pigs, poultry, horses and rats/mice
note: since poultry are less like us, there is the lowest number of diseases
how were farmers affected by the agricultural evolution
- shorter life expectancy
- more infectious disease and parasite infestation
- human and animal waste contaminated water supplies eg. typhoid is a water borne disease
- shortage of protein and restricted diets lead to lower resistance to disease: Kwashiorkor characterised by an extended stomach, poor wound healing and poor mental development
- drought lead to crop failure and then starvation
describe the industrial revolution in terms of what initiated the process of causing disease later on
- nobles fenced land to farm sheep so the serfs were thrown off the land
- machines were used to pump water and produce goods: steam engines. serfs and small town artisans became unemployed
- factories employed many workers in cities for pittance pay
- Huge growth of cities, as rural areas became poor. this lead to POLLUTED AND CROWDED CITIES
- attitude of control of nature
what were the conditions of the industrial revolution that lead to disease
- migration into cities where there was dense living
- bedpans and cesspits emptied in stress leading to raw sewerage, this infected people
- water supply companies sold water taken from the river and the sewers ran into this
- few public taps for poor so people stored water and this went bad. people seldom washed.
what were the effects of the industrial revolution in terms of disease
- half of birds less than five died of disease eg. TB, typhoid, dysentary, measles
- everyone had human fleas and lice and there was no way to avoid them
- epidemics due to crowding and ignorance. so the flu ,killed 5,000 people
- new diseases arrived such as cholera from India. this was due to fast trade
describe the sanitary awakening in terms of a timeline
- increased awareness of links between disease and environment
- 1842: Chadwick noted that poor living conditions led to disease but this was preventable
- 1848: the first london health officer was appointed
- 1849: major cholera epidemic where the rich infected the poor. this changed the opinions of the rich and powerful
- 1853: in the next epidemic, there was evidence of the cause. John snow’s theory of contagion where the drinking water was polluted with sewerage
what came out of the sanitary movement
- improved conditions where there was reduced poverty and reduced disease
- public ownership of water supplies, aqueducts built
- public sewer system so sanitation was used to break disease transmission
- debar, pasteur, koch, lister: microbes cause disease, hand washing and antiseptic surgery, pasteurisation of mik
there was a push to preventions and not cures and also poverty alleviation
describe vaccinations
- activates the immune system without causing disease. this increases the number of resistant individuals thus decreasing disease transmission.
also protecting unvaccinated individuals - smallpox was eliminated by vaccination
describe smallpox and how it was eliminated
it was eradicated by vaccination and isolation of infected people, humans were the only host
- polio could be eradicated of distrust of vaccination programs could be overcome
describe how public knowledge can be good
don’t get into situations where can get infected, thereby cutting the roots of transmission
describe how public health measures are good
- vaccination can improve immunity when in good shape, thereby not suffer from stress. this is the same for poor diet which reduces the IS
describe the effect of density on disease
when there is a high density of humans, there is high density of hosts. thereby there is efficient transmission of disease. this is the same for chicken and pig farms
describe the effect of a huge population surge
- easier to spread disease
- decried fertility because people now know that their children will survive to grow up
describe the effect of diseases remaining in poor countries
these become reservoirs of new diseases
what are the three main things to a better health globally
public health measures, public knowledge and poverty reduction
describe the issues for health in the future
- evolution of resistant strains: massive over use in agricultural contexts, high density farms lead to virulent diseases in animals that can then pass to humans
- increased human density
- more urban and natural poverty and inequality. thus, there is less public health spending and less resistance
- less public awareness to less immunity.
- world-wide jet transport meaning fast transmission
- more wars over resources meaning more disease (because pekoe are in poor conditions and there is poor sanitation)
- increasing impact on animal ecosystems meaning there are new bugs eg. zoonoses
what are the key traits of a parasite?
- survive lethal attacks from immune cells
- shrive toxins, corrosives and other attacks
- reproduce and produce millions of eggs
- get your offspring and eggs safely out of the host
- survive outside of the host
- get into another host
- invade other host through huge barriers
- repeat
contrast viruses/bacteria with eukaryotic protists
viruses/bacteria:
- ideal characters for effective parasites
- simple organisms with short life cycles
- very rapid reproduction
- rapid mutation and thus genetic change
eukaryotic protists:
- less simple organisms
- more complex but short life cycles
- rapid reproduction
- alternation of sexual and asexual reproduction, thus high genetic variation
describe phylum Platyhelminthes including lineage, structure and key traits
- from kingdom Animalia
- 2 classes of interest:
1. trematoda: Flukes
2. Cestoidea: Tapeworms - 3 cell layers including the ectoderm, mesoderm and endoderm
- no coelom and is thus called an acoelomate (no enclosed body cavity)
describe the class Trematoda in terms of an example
- phylum platyhelminthes
- eg. fluke
suckers
branching gut
complex reproductive organs
hermaphrodites
describe the class Trematoda and its life cycle
life cycle:
- eggs out of faeces of human or cow
- these try to get into water where they hatch into ciliated miracidium
- find snail (intermediate host) to invade and reproduce asexually, thus, lots of copies made from single infection
- cersaria produced (from snail) which can burrow into flesh of other animals in water or invade vegetation by water at which it is called metacercariae
- find some way to get into new host
describe class cestoidea in terms of an example and key traits
- phylum Platyhelminthes
- tape worms
- scolex or head with suckers and hooks
- proglottids, each with male and female reproductive organs. thus, is called a hermaphrodite
- no gut: food absorbed through body wall
describe class cestoidea in terms of a typical life cycle
Taenia solium (in pigs) Taenia saginata (in cattle)
life cycle:
- humans with tapeworm proglottids in the gut pass out eggs into the environment
- eaten by the pig or cattle which would have ingested the contained eggs or gravid proglottids
- produce oncospheres in the muscles intestinal wall. these develop into cysticerci in muscle
- if meat is not cooked properly, it can infect humans
note: scolex is used to attach to intestine
describe phylum Nematoda
eg. roundworms: Ascaris lumbroicoides, common in children
eg. pinworms, hair worms
traits:
- moult their outer cuticle so are called ecdysozoans
- slender, round body that is tapered at both ends
- 3 body layers
- pseudocoelem:
+ space between muscle and gut
+no membrane around cavity
- simple gut
- large long reproductive organs full up most of the body
- many different lifecycles
describe the key infection by a nematode
elephantiasis caused by Wuchereria bancrofti
- microfilariae (larval worms) live in blood
- transmitted by mosquito
- adults live in lymphatic vessels and can cause blockage ie. elephantiases
describe the structure of phylum arthropoda
- has outer exoskeleton that the muscles attach to
- must moult the outer cuticle- ecdysozoan
- true coelom- body cavity lined by membrane
describe arthropods with reference to an example
(insects, mites, ticks)
- screw worm fly
- exoskeleton, which is moulted for growth- ecdysozoan
- jointed appendages
- mostly ectoparasites and are often vectors for micro parasites
describe class Hexapoda example and traits
- insects
- 3 body sections
- antennae, head and abdomen
- 3 pairs of legs
describe class arachnida structure and examples
- ticks and mites
- also spiders and scorpions
- 4 pairs of walking legs
- no antennae
- 2 body sections (head+thorax, abdomen)
describe a generalised arachnid structure
- 2 body sections
- no antennae
- wings never present
- two pairs of mouthparts
how do parasites invade our bodies
- mouth: usually through our fingers
- nose/mouth in the air
- through the skin
- sexual intercourse
- via intermediate host or vector
what/outline two examples of invasions into humans through the skin
- schistosomes in the larval stage can be burrow into the feet when walking and penetrate the skin
- hookworm larvae emerge on soil and can penetrate the skin into the blood via the foot. this is carried to the heart and then lungs where it can penetrate the airway and up to the throat. human swallows larvae which can then attach to the small intestine and mature. adults lay embryos that pass out in faeces
list out some examples of invasion into our bodies to get to the final host
- eaten by final host whereby the prey are the intermediate host
- carried onto the final host where they are scratched in
eg. ectoparasite such as lice is the vector - injected into the final host eg. blood sucking ectoparasite vector
- in the water which can then penetrate the skin eg. schistosomes from pond snails
outline how cestodes can get to us
ie. T.salium, T.saginata can use pigs/cows as intermediate hosts to get to humans
how can humans become the intermediate host?
- harmless cysts are in the meat we eat. then the worms will colonise in our guts
what if the eggs are put in our mouth?
- oncospheres develop in our muscles
what’s the deal with dog tapeworms?
- hydatid (big) cysts are even more dangerous as they develop in the liver and other organs. this needs surgery and chemotherapy
why are insects and ticks excellent ectoparasites?
- highly mobile
- actively search for new hosts
- mouthparts adapted to penetrate skin barrier
diseases transmitted: - testese fly: sleeping sickness mosquitos: malaria just to name sand flies: leishmaniasis assassin bug: chagas disease fleas: bubonic plague lice: typhus
what are the human lines of defence?
1st defnse: physical barrier: secretions and skin
2nd denefse: innate immune response
3rd defense: adaptive Immune response
how do parasites survive in our body
- many copies so genetically variable: very common
- avoid recognition: schistosome
- present a moving target Trypanosoma
- hide from defenders: tapeworms, malaria in RBc
- attack: HIV
Describe the technique of avoiding recognition
- schistosomes use camouflage
1. live in blood vessels where they:
A. coat themselves with the host antigen proteins, this takes 7 days
b. mouse monkey experiment
- USE temperorary strategy while coating themselves:
produce enzymes that destroy or detach complement protein. (complemet proteins attack a parasite by attaching to foreign surface components. they then attract phagocytes and Destry the tegument of theorem and ruture cells
describe the technique of presenting a moving target
trypanosomes of kinetoplastids
- make 1000 diff. surface antigens
- majority of individuals only present 1 form but there will be variation in the parasite population
- IS learns to recognise and destroy major antigenic type
- variation means a few individuals with different antigen can survive
- these increase in number until IS learns to recognise again
describe the technique of hiding from defenders
- in gut: tapeworms and hookworms are at a low risk from IS because IS not strong in gut. must still have tegument that can resist digestion.
- inside cells: plasmodium and Trichinella spiralis (nematode) in muscle cells. this allows them to grow and get extra blood supllie
describe the technique of attaching the IS
HIV, causes AIDS
- invades and divides in various IS cells
- T H cells, dendritic cells and macrophages
- disruption and destruction of cellular immune response
- leaves infected people vulnerable other infections
how do parasites get into new hosts?
- exit the body in faeces, urine, cough, sneeze, vector
- complex life cycle that includes some or all of:
- innert stages: survive a long time and wait for host
- free living stages: feed and wait for host
- use an intermediate host: a way to get into final host and multiply in humber in this stage
- asexual multiplication: produce many copies, many chances and for dispersal
- sexual reproduction: ensure variation, hermephrotidism to ensure mates, double number of egg produces
describe the process of anus to mouth. example one
Entamoeba histolytica
- mature trophozoite can undergo asexual reproduction
- cysts with 4 nuclei are produced and these are passed into faeces
- trophozoites that did not become cysts with 4 nuclei die AND the other cysts surive
- cysts that survives are EITHER DIRECTLY become contamination of fingers, food or water, or are first transported by the fly. cockroach and then become contamination of finger/food.water
- contamination ingested
- in small intestine, 8 young emerge from cyst
- become mature trophozoite
describe another example of anus to mouth transmission . example 2
ascaris: human/pig roundworms of phylum Nematoda
- infects 1 billion people worldwide
- eggs swallowed on food, hatches in gut, penetrates gut wall
- worm to blood, into lungs, up bronchi to throat, then swallowed to gut
- eggs pass out in faeces and get into raw vegetables
describe transmission involving one intermediate host
echinococcus- hydatid tapeworm. Platyhelminthes of class cestoidea
DOG/HUMAN HOST:
- cyst wall digested and scolexes released
- attach to intestine and grow into tapeworms via sexual reproduction
TRANSMISSION:
3. released eggs pass in dog faeces and eaten by sheep or HUMAN
SHEEP/HUMAN HOST:
- eggs hatch and larvae penetrate gut wall
- hydatid cysts form in organs via asexual reproduction
TRANSMISSION:
6. infected meat eaten
back to step 1
describe another example of one intermediate host. example 2
schistosome spp. Bilharzia. trematode
HUMAN HOST:
- cercariae penetrate skin, migrate>lungs>liver. male enfolds female
- go to bladder/gut wall and lay eggs wit thorns. sexual reproduction occurs here
transmission:
3. eggs puncture wall. pass in faeces ad urine. hatch in water
SNAIL host:
- miracidia go into snail and form many redia. this is where asexual reproduction occurs
- redia form many daughter redia. these form cercariaea
transmission:
6. cercariaea leave snail and swim to find warm skin
describe an example of a varied intermediate host for humans
trichinella spiralis- pinworms of nematoda
- juveniles in muscle cells
- adults live in gut
- pig is intermediate host for humans
describe an example of 2 intermediate hosts
kidney roundworms
- giant among nematodes- Dictophyme renale
- adults reside in the kidney
- eggs secreted in urine
describe an example of multiple intermediate hosts
life cycle of fish tapeworm. cestoidea
there are three larval stages:
- free swimming
- eaten by crayfish, first intermediate host
- fish eats crayfish, this is eaten by a larger fish
bear or human eats fish
then passed into faeces
describe how vectors work and transport disease
- intermediate host that transports parasites between final hosts
- testese fly in Africa carries trypanosomes. because it has two two in its mouth, one tube has the salary gland connection which inputs the disease. the other tube is for taking in the blood from host
describe mosquito borne disease
- malaria (protists)
- filiaris (nematode)
- dengue (virus)
- encephalitis (virus)
- yellow fever (virus)
- M.V encephalitis (virus)
- ross river fever (alpha virus)
how to answer parasite life cycle question
- how do they invade our body
- how do they stay there, in what tissue
- how do they get into new host
- stages in water, inert stages
- intermediate hosts?
- final hosts?
- what stage does asexual reproduction occur
