Biology 1A - infection Biology Flashcards
what are the tow domains of prokaryotes
- bacteria
- archaea
where can prokaryotes thrive
almost everywhere
including too acidic, salty, cold or hot conditions for other organisms
how much bacteria on earth
more than 5x 10^30
what would happen without microbes
all forms of life would die
what is a mutualistic relationship
both organisms benifit
what is a commensal relationship
one organism benefits and the other is not significantly harmed or helped
what is a parasitic relationship
one organism benefits while the other is harmed
what are mutual symbionts
Mutual symbionts are species that benefit from each other in a symbiotic relationship
what are oblique aerobes O2 requirements?
require O2 for cellular respiration
what are oblique anaerobes O2 requirements?
they are poisoned by O2
what are facultative anaerobes O2 requirements
can survive in + or - O2 conditions
how do prokaryotes lay a major role in recycling elements between living and non living ecosystem compounds?
chemoheterotrophs - decompose corpses, dead vegetation and waste products
N-fixers - fix N2 from air to unstable ammonia - a fertilizer
what effects do prokaryotes have on nutrients
- increase availability of N, P, and K for plant growth
- can immobilise / decrease nutrient availability
where are microbes found?
- agriculture
- disease
- biotechnology
- energy/environment
- food
what are the size comparisons of cells
biggest = eukaryotic cell (by a lot), can see with naked eye/light microscope
middle = prokaryotic cell, can see with light microscope
smallest = virus (by a lot), can see with electron microscope
what is the biggest independent eukaryotic cell?
caulerpa - green alga
can grow to 3m
describe the basic structure of a eukaryotic cell?
- nuclear membrane is present
- contain several chromosomes of DNA per cell
- contain membrane bound organelles
- have interior cytoskeletal structures that support cell physically and organise and move internal components
what are the organelles in a typical eukaryotic cell
nuclear membrane
ribosomes
mitochondria
cytoplasm
membrane bound organelles
cytoplasmic membrane
several chromosomes
what is the largest bacterium?
Thiomargarita namibiensis
can grow to 1mm diameter
describe the basic structure of a bacterial cell?
- single large, double stranded molecule
- sometimes additional DNA is in small circular plasmids
-generally lack membrane bound organelles with a few exceptions (Acidocalcisomes, Anammoxosomes)
-typical size = 1-10 micrometres
what are the basic organelles in a bacterial cell
flagellum
single chromosome
ribosomes
cytoplasm
cytoplasmic membrane
cell wall
plasmid DNA
capsule
what are the main components of bacterial flagellum
basal apparatus
hook
filament
how do motile bacteria propel themselves
by flagella
many bacteria exhibit taxis. What does this mean
the ability to move towards oraway from certain stimuli
what is fimbriae
some prokaryotes have fimbriae
this is attachment pili
allows them to stick to their substrate or others in a colony
what is sex pili
longer than fimbriae
on prokaryotic cells
allow prokaryotes to exchange DNA
describe the basic function/structure of the cell wall in bacteria
- gives the bacteria shape
- protects them from 1) osmotic lysis 2) toxic substances
- contain a unique polymer (peptidoglycan). bacteria are classified into two groups based on the composition of this polymer in the cell wall
- an additional polysaccharide or protein layer called a capsule covers many prokaryotes
what are gram stains?
bacteria can be gram-positive (crystal violet) or gram-negative (crystal violet rinsed away revealing red/pink)
this is dependant on the composition of the cell wall
what makes up a gram-positive cell wall
peptidoglycan layer
what makes up a gram-negative cell wall
carbohydrate portion of lipopolysaccharide
outer membrane
peptidoglycan layer
what are the basic stages of bacteria’s asexual reproduction?
1) DNA replication
2) cell elongation
3) septum formation
4) completion of septum with formation of distinct walls
5) cell separation
what different shapes can bacteria adopt?
coccus (round)
rod
spirochete (long and thin)
what are some gram negative bacteria
alpha Proteobacteria
beta Proteobacteria
gamma Proteobacteria
delta Proteobacteria
epsilon Proteobacteria
what are some gram positive bacteria?
- actinomycetes
- bacillus anthracis
- clostridium botulinum
- some staphylococcus
- mycoplasmas
describe what a virus is
- not cells
- very small infectious particles
- consist of nucleic acid enclosed in protein coat and in some cases a membranous envelope
- are obligate intracellular parasites
- can reproduce only within host cells
- each type of virus can infect only a limited number of host cell types
what are the two types of viruses and what does this depend on
viruses can have
- double or single stranded DNA
- double or single stranded RNA
depending on its type of nucleic acid, a virus is called a DNA virus or an RNA virus
what is a capsid
a protein shell that encloses a viral genome
what are capsids built from?
protein subunits called capsomeres
what are bacteriophages (aka phages)
viruses tat infect bacteria
describe the viral capsids of bacteriophages
- most complex viral capsids
- elongated capsid head that encloses their DNA or RNA
- have protein tailpiece that attaches to host and injects phage DNA
- can have a membranous envelope
what are the two reproductive cycles of bacteriophages (phages)
- lytic
-isogenic
describe the lytic reproduction of bacteriophages?
- the phage reproductive cycle that culminates in host cell death
- produces new phages and digests hosts cell wall , releasing progeny
- virulent phages reproduce only by the lytic cycle
- bacteria have defences against phages (restriction enzymes that can recognise and cut certain phage DNA)
what are the stages of the lytic cycle?
1) attachment of phage
2) entry of phage DNA and degradation of host DNA
3) synthesis of viral genomes and proteins
4) assembly of phages
5) release from the cell
describe lysogenic reproduction in bacteriophages?
- replicates phage genome without destroying the host
- viral DNA incorporated into host cell chromosome
- integrated viral DNA = prophage
- every time host cell divides, it copies phage DNA and passes it to daughter cells
- temperate phages use both lytic and lysogenic cycles
- an environmental signal can trigger viral genome to exit bacterial chromosome and switch to lytic mode
what environmental triggers can cause a bacteriophage to switch from lysogenic to lytic mode?
UV exposure / mutagenic chemicals / desiccation
what type of reproductive cycles can virulent phages and temperate phages use?
virulent = just lytic
temperate = lysogenic and lytic
describe the stages of the lysogenetic cycle
1) phage DNA integrates into bacterial chromosome becoming a prophage
2) bacterium reproduces, copying prophage and transmitting to daughter cells
3) cell divisions produce population of bacteria infected with prophage
4) occasionally prophage exits bacterial chromosome, initiating lytic cycle
describe the general features of the animal virus reproductive cycle
1) viral genome enters cell
2) cell begins to manufacture viral proteins (replication)
3) virus makes use of the hosts enzymes, ribosomes, tRNAs, amino acids, ATP etc
4) transcription and manufacture of capsid proteins (viral DNA/RNA capsomeres self-assemble)
5) new virus produced and exit from cell
what are viral envelopes
- membranous envelope
- some formed from the host cell plasma membrane as capsids exit
- help virus evade host immune system
- viral glycoproteins on envelope bind to specific receptor molecules on host cell surface
where is the broadest variety of RNA genomes found?
in animal viruses
what is a retrovirus?
virus that uses reverse transcriptase to copy their RNA genome into viral DNA
what is an example of a retrovirus?
HIV that causes aids
what is a provirus
viral DNA integrated into host genome
what is the difference between a prophage and a provirus
unlike prophage, provirus remains permanent resident of the host cell
what are the functions of RNA and RNA polymerase in terms of viruses
RNA polymerase = transcribes proviral DNA-RNA
RNA =
1. mRNA for synthesis of viral proteins
2. functions as a genome for new virus particles
what are the two major surface antigens of influenza virus?
hemagglutinin (HA), neuraminidase (NA)
what kind of genome does influenza have and what does this mean
RNA genome
meaning high mutation rates and frequent genetic reassortment = variability in HA and NA (its surface antigens)
what type of virus is influenza
-ve sense, enveloped RNA virus
why does influenza have repetitive localised outbreaks?
minor changes in protein structure occur frequently allowing influenza to evade immune recognition
minor changes in HA caused by reassortment from different influenza A subtypes
what can cause outbreaks of new human viral diseases
existing viruses that expand their host territory
viral strains that jump species can exchange genetic information with other viruses to which humans have no immunity
what type of virus is SARS-CoV-2
single stranded +ve sense enveloped RNA virus
what are Viroids?
- one of the simplest infectious agents
- single circular RNA molecule
- a few 100s of nucleobases
- doesn’t include any proteins
- mostly infects plants and disrupts growth
what is hepatitis D thought to originate from
a viroid
describe hepatitis D
- caused by sub-viral satellite
- -ve sense, single stranded RNA virus
- can propagate only in presence of HBV
- causes complications in HBV infection - liver cirrhosis, liver cancer
what are prions
- slow acting, virtually indestructible infectious proteins that cause brain diseases in mammals
- propagate by converting normal form of protein to prion version
- cause scrapie, mad cow disease, Creutzfeldt-Jakob disease
what are the different niches for microbes on the human body
skin - dry and salty
armpits - damp, warm, salty, low pH
respiratory tract - moist, neutral pH, high in O2
GI tract - wet, warm, low pH, Low in O2
describe the densities of microbes in the body
stomach = very low
small bowel = low
large bowel = medium
anus = high
what is the role of microbiota
protects surfaces from physical colonisation by pathogenic bacteria from other humans, animals, environment etc.
what is a microbiome
microbes, their genome and environmental interactions in a defined environment ( eg. the gut)
what is the human microbiome project
studied the role of microbiomes in human health and disease
did whole genome sequencing:
Bacteria, archaea, yeasts, protozoa, helminth parasites, viruses (including phage)
describe the relationship between the gut microbiome and the host
symbiotic relationship:
human host:
- provides food/warmth
microbes:
- prevent colonisation by pathogenic bacteria
- train developing host immune system
- regulate gut development
- ferment unused energy substrates
- produce vitamins for host
- produce hormones to direct host to store fats
- thought to have a role in prevention of allergy and IBS
what are the principles of pathogenesis
1) attach to/ enter / invade host
2) evade immediate (innate) local defences and spread throughout body
3) multiply
4) evade long term adaptive immune defences long enough to complete life cycle
5) leave body and spread to fresh hosts
what is tooth decay
attachment of pathogen
bacterial micro-colonies growing on tooth surface
ferment sugar to lactic acid causing decalcification of enamel
what is cholera toxin
produced by gram -ve vibrio cholerae infected with bacteriophage
toxin gene phage is encoded
induces severe diarrhoea
what is necrotising fasciitis
caused by bacteria that invades the body and make substances that lyse red blood cells
what causes systemic infections
invasion of microbes into the blood
how do vaccines prevent infection
stimulate bodies own protective defences
generates memory response
what disease was eradicated by vaccines
smallpox
describe antibiotic sensitivity
if antibiotic growth is inhibited, bacteria is antibiotic sensitive
if antibiotic growth is not inhibited, bacteria is antibiotic resistant
what are antiviral agents
must inhibit multiplication of virus but not infected host cell
what foods are microbes involved in making?
bread, beer, wine, chocolate = yeast
cheese, yogurt, soy sauce etc.
how is beer made (microbes)
- malted barley (partially germinated)
- heat to 65 degrees to kill dangerous microbes
- add yeast
- yeast ferments sugar in barley
- by product fermentation alcohol production
. after fermentation, yeast removed, beer filtered, pasteurised and bottled
how is cheese made (microbes)
- produced from pasteurised milk by separation of curds (solids) and whey (liquids)
- this is done by the addition of rennet, mainly chymosin = aspartic acid protease
-the flavouring and form of cheese is dependant on the microbes present during maturation
eg. penicillium Roqueforti for Roquefort and stilton
how was vinegar originally made (microbes)
produced when wine exposed to air
wine contaminated with Acetobacter, oxidised alcohol to acetic acid
how Is vinegar made (microbes)
- ethanol produced by yeast
- converted to acetic acid by addition of acetobacter
what is Pruteen (microbes)
- single-cell protein animal feed
- made from methylophilus methlyotrophus bacteria + methanol
- 72% protein content
how are microbes used in sewage works
- to break down organic material in sewage
- if sewage was released, prevents it providing food for microbes in lakes/rivers, organisms would grow really fast, remove all oxygen and all plant/ animal life would die
what is the activated sludge process (microbes)
a biological method for treating wastewater. It uses microorganisms and oxygen to break down organic compounds and nutrients in sewage
what microbes are involved in the activated sludge process (microbes)
- autotrophs
- heterotrophs
- fungi
- rotifers
- protozoa
what is an autotroph (microbes)
organism that requires CO2 as a carbon source
use inorganic compounds for energy
what is a heterotroph (microbes)
require an organic nutrient to make organic compound
use organic carbon for energy
what is biomediation
use of microbes to break down dangerous chemicals, oil, pollution etc
eg. certain microbes can use oil as an energy source converting it to a less harmful form
what is an example of bio mediation going wrong (microbes)
oil spill in gulf of México 2010, used microbe Alcanivorax borkumensis to clean it up
resulted in residents having persistent rash possibly caused by reaction to A. borkumensis cell wall
why do bacteria make great microbial factories
- can produce compounds already encoded in bacterial genome
- can be genetically manipulated to make them produce useful non-native (exogenous) molecules
- can grow to very high densities
describe bacterial production of an exogenous protein (microbes)
1) expression vector is extracted from bacteria (microbial factory) and cut open
2) gene of interest is extracted and copied by PCR
3) gene of interest is inserted into expression vector
4) expression vector is returned to the original organism
5) organism grows; produces enzyme/ drug of interest
6) bacterium expressing exogenous protein is grown to high density
7) bacteria is Broken open and exogenous protein is purified
how are microbial factories used in the pharmaceutical industry (microbes)
1) production of vaccines - genes for protective antigens are identified by genome sequencing of pathogens
2) production complex vitamins
3) production of antibiotics
what protein drugs have been made through use of microbes (safer than originals as not purified from blood)
- insulin (diabetes)
- growth hormone (GH deficiency)
- FSH (fertility stimulating drug)
how are viruses used in human gene therapy (microbes in medicine)
- alteration of faulty versions of genes
- potential for treating disorder’s traceable to a single defective gene
- vectors used for delivery of genes into specific cell types
(ethical: should germline cells be treated to correct defects in future generations)
describe the process of using viruses for human gene therapy
1) insert RNA version of normal gene into retrovirus
2) let retrovirus infect bone marrow cells that have been removed from the patient and cultured
3) viral DNA carrying the normal gene inserts into chromosome
4) inject engineered cells into patient
what are some early issues with human gene therapy with viral vectors (microbes)
safety and efficacy issues
- DNA can be short lived so patients need multiple transfections
- immune response to virus/DNA, limits repeat transfections and possibly fatal
what are some risks with human gene therapy with viral vectors (microbes)
- possibility that viral vector may recover ability to cause disease
- vector may load gene near to oncogene, triggering cancer
- is easier for single-gene defects, multigene disorders not as easily treated
define epidemic, endemic and pandemic
1) epidemic = outbreak of disease that affects a large number of individuals at the same time, usually infectious disease
2) disease that is always present in an area, low to no spread
3) a global epidemic spreading across continents, sudden increase
what can cause an outbreak of disease to occur (epidemics)
changes to our interactions with our environment
- exploration
- warfare
- famine
- poverty, overcrowding and poor living conditions
- deforestation and encroachment on jungles
- changes in trade patterns
what is zoonosis (epidemics)
- a disease or infection that can be naturally transmitted from animals to humans, or from humans to animals
- accounts for a large percentage of new and existing infectious diseases
- 60% of human infections estimated to have animal origin
how are zoonotic diseases transmitted?
human/ animal interactions:
- hunting
- farming
- domestic animals
- exotic pet trade
transmitted:
- food-borne infection
- water-borne infections
- vector-borne infections
- proximity or indirect contact with animals
- direct contact with animals
what are roots of emergence for infectious diseases (epidemics)
- zoonic (animal to human)
- reappears after period of absence (plague)
- from an isolated population to native population (zika)
- mutation and adaption (influenza)
- natural disasters (cholera)
describe some diseases caused by bacteria (epidemics)
1) plague = tersinia pestis, transmitted via fleas and rodents
2) typhoid = salmonella typhi, transmitted via contaminated food or drink
3) cholera = vibrio cholerae, transmitted via contaminated food or drink
describe some diseases caused by viruses (epidemics)
1) smallpox = variola virus, transmitted via airborne water droplets
2) polio = poliovirus, transmitted via person-person contact
3) Ebola = Ebola virus, transmitted via body fluids
what pandemics have caused the most deaths
- black death (bubonic plague)
- HIV/AIDS
- COVID-19
- Cholera
what disease has been eradicated by vaccination, describe it
smallpox
mortality = 30%
transition = person to person via droplets
incubation period = two weeks
symptoms = high fever, fatigue, back pain, rash develops with fluid filled pustules over body (now infectious)
who developed the vaccine for smallpox and how did they do that
Edward Jenner
used vaccinia virus to create vaccine which is a related poxvirus
describe cholera (epidemics)
agent = Bacterium Vibrio cholerae
mortality = 25-50%
transmission = contaminated drinking water or food
incubation period = 2 hours to 5 days
symptoms = diarrhea, vomiting, circulatory collapse, shock
who is john snow (epidemics)
identified water pump as source of cholera in London
credited with the development of the germ theory of disease and the beginning of epidemiology
what can prevent water Bourne infections (cholera and typhoid)
supplying safe drinking water and proper disposal of sewage
what is a reproduction number/ratio/rate (RO)(epidemics)
epidemiologic metric used to describe the contagiousness or transmissibility of an infectious agent
estimated with complex mathematical models
what factors can affect reproduction dumber (RO) (epidemics)
biological factors
sociobehavioral factors
environmental factors
when is an outbreak expected in relation to RO value (epidemics)
expected to continue if RO has a value >1
expected to end if RO had value <1
what are some surveillance methods for epidemics/ outbreaks
digital media = monitor social media platforms and internet searches for symptoms
mathematical modelling = predicting the rate of increase in cases so can plan ahead for resources needed
how is information about epidemics/ outbreaks shared
online platforms: eg global public health intelligence network
WHO’s early warning and response system (EWARDS) = a box of electronic surveillance equipment for rapid deployment
Oxford-Nanopore minION = a credit card device powered from a laptop USB connection that provides live maps of outbreak movement
define a parasite
an organism living in or on another living organism, obtaining from it part or all of its organic nutrition, commonly exhibiting some degree of adaptive structural modification and potentially causing some degree of damage to its host
what is prevalence of infection
proportion % of a population infected
what is incidence of infection
the frequency of a population acquiring infection in a unit of time
eg. 3% per week or 100,000 per annum
what is intensity of infection
measure of the number or density of parasites per host
what is mortality of a disease
number of deaths in a given time, or percentage of deaths among all cases of infection
what is the morbidity of a disease
the level of ill health or disability among all cases of infection, or among general population
and is DALYs of an infection
Disability Adjusted Life Years
a measure of overall disease burden. number of healthy years lost to disease, disability or early death
describe the prevalence, mortality and DALYs of malaria
malaria is vector Bourne transmitted by mosquitos
prevalence = 219M
mortality = 435k
DALYs = 55M
what are all parasites?
eukaryotes
what are protozoa
single cell parasites
the can either live in intracellular habitat or extracellular habitat
what are helminths
worms
multicellular parasites
can be round worms or flatworms (tapeworms)
what are arthropods
multicellular
ectoparasites such as ticks and lice
small invertebrate animals. can attach to mammal body and abstract blood
what are the three categories of protozoa (parasites)
amoeboid = faecal/ oral transmission and multiply in intestinal tract
Kinetoplastid = flagellated causing motility, common parasites, invades cell so can multiply rapidly
Apicomplexa = at apex they have a complex, set of proteins allowing them to invade a target cell (eg. malaria, invades red blood cell)
what are the types of helminths (parasites)
nematoda = roundworms
platyhelminths = flatworms (tapeworms)
what are the types of ectoparasites
lice
fleas
ticks
what are examples of zoonic parasites
toxocara canis (dogs) = helminth
fleas and ticks (mice and deer) = ectoparasites
toxoplasma gondii (cats) = protozoa
what is polyparasitism
when a single host is infected with more than one species of parasite at the same time
what is toxocara canis
- predominant intestinal roundworm in dogs and foxes (helminth)
- infection by ingesting eggs from soil
- humans are an accidental host, infants are particularly at risk (eating soil/sand)
- larvae migrate in soft tissues (in humans)
- eggs have resilient coat, can survive in soil for months and resist chemical treatment
what are the two types of larvae migrants of toxocara canis (parasites)
visceral larva migrants - invades liver, causes fevers
ocular larva migrants - enter the eye and impair sight
describe the life cycle of toxocara canis
1) eggs ingested
2) eggs hatch in stomach releasing larvae
3) larvae migrate to lungs/ liver/ brain
4) in dogs move to small intestine and migrate to mature adult worms
5) adult females release eggs in faeces
when is toxocara canis larvae “reawakened” in dogs
remains arrested until pregnancy
larvae cross placenta to infect pups before birth
also migrate into colostrum to infect milk
what is Echinococcus granulosus
tapeworms
dog is definitive host
what disease does Echinococcus granulosus cause
hydatid disease
describe the life cycle of Echinococcus granulosus/ how it is transmitted
1) dog (definitive host) releases embryonated eggs in faeces
2) sheep accidentally take up eggs (intermediate host) parasites don’t develop life cycle in sheep
3) in sheep (intermediate host) eggs hatch in intestinal tract, invade body and form hydatid cysts in various organs (multiplied)
4) ingested by dogs eating sheep
5) humans can be infected by embryonated eggs (accidental host) and can become subject to hydatid cysts
what is a definitive host of a parasite
the species in which a parasite completes its full life cycle
where can hydatid cysts of Echinococcus granulosus grow in humans (parasites)
lung
brain
liver
what is toxoplasma gondii
protozoan parasite
zoonotic
cosmopolitan (found in all countries)
definitive hosts; cats
describe the life cycle of toxoplasma gondii (parasites)
1) cat is infected and toxoplasma parasite infect epithelial cells of intestinal tract and shed oocysts in faeces
2) oocysts can infect farm animals, rodents, humans (intermediate hosts)
3) cat eats rodents and is re-infected
what happens to toxoplasma gondii in hosts other than its definitive host (cats)
1) oocysts develop into tachyzoites to disseminate infection in host
2) parasite attaches to cells and invades it (broad cell specificity)
3) can escape cells defence mechanisms and avoid fusion with lysosomes that would break it down by forming Parasitophorous vacuole
4) rapid multiplication and rupture of host cell
5) can then infect wide range of tissue (heart, brain, eye etc.)
6) in time tachyzoites (fast) become bradyzoites (slow) which form dormant cysts in tissues, waiting for tissue to be consumed by cat
what is congenital toxoplasmosis
caused by toxoplasma gondii crossing placenta and attacking developing foetus
causes swelling of brain and visual/ mental impairment
what are the pathological consequences of toxoplasma gondii cysts infecting brain
change rodents behaviour
mice lose aversion to cats (more likely to be consumed)
car drivers may be less rick averse (more antibodies for toxoplasma infection)
describe the life cycle of head lice (ectoparasite)
egg/nit => 7-10 days => nymph => 10 days => adult => 50-150 eggs
what disease do ticks spread and how (ectoparasite)
Lyme disease caused by bacterium borrelia burgdorfi
causes erythema, bulls eye inflammation
can cause chronic arthritis, neuropathy and fatigue
treatable will early antibiotic treatment
what are neglected tropical diseases (NTDs)
- a group of diseases that causes substantial illness for more than one billion people globally
- affecting the worlds poorest people in communities lacking infrastructure and sanitation
- can impair physical and cognitive development
what are the three main soil transmitted helminths (tropical parasites)
Ascaris lumbricoides
Trichuris trichiura
Ancylostoma/Necator (hookworms)
describe the life cycle of Ascaris lumbricoides
- simple/ direct life cycle
1) environmentally resistant egg
2) egg containing larvae hatches in stomach acid and invades body
3) from intestinal tract it migrates to lung => coughed up and swallowed down oesophagus and into gut
4) males and females mate, females produce eggs which exit in faeces
5) in environment fertilised egg becomes larvae inside egg
what is Ascaris lumbricoides
type of tropical helminth
roundworm
soil transmitted
highest number of infected people
what is the treatment for Ascaris lumbricoides (tropical parasites)
medication:
Oral Albendazole
Mebendazole
Ivermectin
what is an issue with the drugs used to treat Ascaris lumbricoides
drugs don’t change susceptibility to reinfection
only adult parasites in the intestinal lumen are removed
reinfection can be rapid
what is Schistomiasis (tropical parasites)
helminth
one of the 3 big tropical parasites that are soil transmitted
2nd highest no. of infections
what type of life cycle of schistosomiases have?
indirect life cycle
lives through intermediate host (freshwater snail)
source of life cycle stage cercariae
what is cercariae (tropical parasites)
the life cycle stage of schistosomiasis that is able to penetrate human skin
describe the life cycle of schistosomiasis
1) parasitic eggs in fresh water
2) larvae called miracidiae hatch from egg and search out species of snail
3) infect snail, miracidiae multiply producing larvae called cercariae
4) cercariae released into water, penetrate human skin , transform into larvae called schistosomulae
5) penetrate human skin
6) schistosomulae mature into worms in blood supply of liver, intestines and bladder
7) lay hundreds of eggs that damage and work through tissue
8) eggs released into water by urine or faeces
describe schistosomiasis pathology - what diseases can it cause
eggs released by adult worms in the vasculature become lodged in liver causing granuloma formation, fibrosis and hepatomegaly
who is most susceptible to infection of schistosomiasis
children as they play in water
what are the prevention methods for schistosomiasis
drug - praziquantel
molluscide treatment of snail breeding sites
public health measures - education and infrastructure
describe the life cycle of malaria in both mosquito and human
in human:
1) bitten by mosquito whose salivary gland contains malaria parasites (sporozoites)
2) only infects specific cell in liver (hypnozoite)
3) parasite enters this liver cell and differentiates into into different form of malaria parasite (merozoite) takes couple weeks
4) merozoite enters red blood cell, multiplies and bursts red blood cell
5) merozoite creates cycle of infection and reinfection of red blood cells
6) merozoite enters 3rd life form called gametocytes (male and female)
in mosquito:
1) if gametocytes is taken up by mosquito they fuse forming a gamete
2) gamete creates sporozoites in midgut of mosquito
(if merozoites enter mosquito nothing happens)
describe the erythrocytic cycle of malaria (disease causing cycle)
1) merozoite initial contact with red blood cell through apical complex (surface proteins allowing parasite to attach to and invade red blood cell)
2) once inside multiplies and changes surface of red blood cell creating adhesive knobs which allow it to attach to the vascular endothelium (hiding strategy)
3) rupture
(takes 48 hours)
when does fever occur in the cycle of malaria
during erythrocytic cycle (schizont stage) when the red blood cell ruptures and merozoites are release
what is cerebral malaria
blood vessels in brain obstructed by parasites
- high grade fever
- seizures/ comas
- mortality: 25-50%
- rapid: 24-72 hours
- in children and travellers
what are the treatments for malaria
mosquito nets with insecticide
insecticide spraying
genetic strategies: create sterile males to mate with females and prevent future generations (small environments)
most recent drug: Artemesin (malaria creates resistance to most drugs, produce more)
what are the different targets for potential malaria vaccines
Sporozoite Vaccine = targets live sporozoites
Merozoite Vaccine : targets proteins
required for cell invasion
Gametocyte Vaccine : transmission
blocking vaccine, can target parasites in mosquito
what could be an observed benefit of tropical parasites
in other countries inflammatory diseases are becoming more common such as multiple sclerosis, but not in countries that have high levels of parasites
suggested that individuals with low levels of pathology are in a healthy state because parasites are dampening immune system
(hypothesised they could be used for treatments)
what is the solution to tropical parasites
block transmission
better drugs
ideally new vaccines
why aren’t there malaria vaccines yet
- Complex life cycles, with multiple stages in different tissues
- malaria has High level of antigenic variation
- Multiple immune evasion strategies
- Parasites are able to suppress the immune system
