Microbial pathogens 1 Flashcards
a pathogen
a microorganism that is able to cause a disease in a plant or animal or insect
pathogenicity
the ability to produce disease in a host organism
more virulent ∝
more capable of causing disease
microbes express their pathogenicity by means of
virulence
virulence =
term which refers to the degree of pathogenicity of the microbe
determinants of virulence
any genetic, biochemical or structural features that enable it to produce disease in a host
Two main mechanisms underlying bacterial pathogenicity
-The ability to invade tissues (invasiveness)
-ability to produce toxins (toxigenesis)
invasiveness =
-ability to bypass host defence mechanisms
-production of extracellular substances which facilitate invasion (like adherins)
toxigenesis the two types are
-two types of toxin EXO/ENDOtoxins
exotoxins
released from bacterial cells and may act at tissue sites removed from the site of bacterial growth
botulinum and cholera toxin
endotoxins
cell-associated substances that are structural components of the cell walls of GRAM NEGATIVE bacteria (capsule on LPS)
human pathogens can enter through (main sites)
-respiratory
-gastro-intestinal
-urinary or genital tracts
human pathogens can enter broken skin …
-by insect bites
-accidental surgical trauma
opportunistic pathogens are carried as
part of the normal human flora
acts as ready source of infection in compromised host
transmission of bordetella pertussis (more complex)
-respiratory
-requires contact with infectious material since the organisms survives poorly in environment
for pathogens where the primary source is environmental (infection follows ingestion) pathogens MUST
remain viable in different environmental conditions
the environment that can be colonised by a pathogen are critical in determining its reservoirs and potential modes of transmission
Psychrophile
grow best at low T
psychotroph
able to grow at low T but prefer moderate T
mesophile
most bacteria live in animals
thermophile
amount all thermophiles is wide variation in optimum and maximum T
growth rate curves for temperates effect
not symmetrical
-linear increase until optimum where the cell can’t function at high temps
cold shock adaptation
-inhibition of protein synthesis
-causes a growth lag known as the acclimation phase during this a group of cold shock proteins (Csp) are dramatically induced
chaperone
protein that check other proteins are folding correctly
cold shock proteins class 1
ensure ribosome/DNA/RNA synthesis is working correctly
cold shock proteins class 2
conditioning ribosome to conduct protein synthesis in cold conditions
Listeria
-non spore forming gram positive bacilli
causes LISTERIOSIS
risk:pregnant/immunocomprimised
CAPABLE OF GROWTH OVER A WIDE RANGE FROM 2 TO 40°C
how is listeria spread
infected foods
listeria virulence factors-escape from single membrane vacuole
slide 16 for detail
proteins and enzymes that punch holes in membrane
listeria virulence factors-cell to cell spread
slide 16 for detail
-Protein polymerising actin in wrong place (at base of cell allowing it to propel)
listeria virulence factors-required for escape from double membrane vacuole
slide 16 for detail
a phospholipase that cleaves the head group from many different kinds of lipids
listeria virulence factors-regulation of virulence factors
slide 16 for detail
positive regulator of virulence genes
how is listeria controlled in food
-high temps while cooking
-grow foods with 12% NaCL and with ph range of 4.4 to 9.8
-cook meat thoruoughly
Legionella pneumophila
-motile aerobic gram negative rod
-lives in phagocytic cells (macrophages)
-live in air conditioning units
CAUSES- pneumonia
temp and legionella
-humans are accidental hosts as CELLS EXPRESS MORE FLAGELLIN RNA and protein at 30°C than 37°C
-adherence is also temp dependent
Gram positive bacteria simple definition
only inner membrane
pH of natural environments varies from
0.5(acid) to 10.5 (alkali)
pH 0 = compared to pH 14 =
pH 0 = 1 mole per litre of Hydrogen ions (10^-14) moles per litre of OH^-
pH 14 = 10^-14 mole per litre of Hydrogen ions (1) moles per litre of OH^-
most free-living prokaryotes can grow over a range of _ pH units
3
pH growth rates are a _______ curve
symmetrical due to subtle effect of pH
Acidophile =
acid loving
most cells are _____philes
neutro
Thiobacillus species
-Acidophiles
-require low pH for growth because their membranes dissolve and the cells lyse at neutrality
obligate alkali-holes can grow around pH
10
-in an alkaline bacillus species a Na+ gradient (instead of pmf) supplies the energy for transport and motility
pmf
proton motor force
-electrochemical gradient forced due to ETC
optimal growth pH is the pH of the
extracellular environment
-extremes are 4.6 (acidophil) and 9.5 for (alkaliphile)
most are NEUTROPHILES
problems posed by acidic conditions
3
-capacity for nutrient acquisition and energy generation
-cytoplasmic pH homestasis
-protection of proteins and DNA
acidic conditions effecting protection of proteins and `DNA two mechanisms that can help achieve this
chaperone proteins
alkalisation of the periplasm
helicobacter pylori
-gastric pathogen
-gram negative curved rod
highly motile due to flagella
helicobacter pylori causes what
-gastric and duodenal ulcers
-ulcers associated with development of gastric cancer
helicobacter pylori main virulence factors
-flagella
-urease = helps neutralise the acidic pH of the stomach
-adhesins
-vacuolating toxin
Koch’s postulates
-the organism is always present in animals suffering from the disease but not in healthy
1)organism cultivated in pure culture away from the animal
2)susceptible animals should initiate the disease characteristics
3)organism re-isolated from experimental animals and cultured (same as ORIGINAL)
Barry Marshall
-drank culture of helicobacter pylori and shown to have an inflamed stomach two weeks later
how does H. Pylori survive in the acidic pH of the stomach - WHERE DOES IT GO
colonises mucin layer that covers the gastric mucosa
-mucus resists diffusion of protons from stomach acid because it is composed of negatively charged sulphated polysaccharides
how does H. Pylori survive in the acidic pH of the stomach - short term pH protection during motility
urease hydrolyses the urea secreted by gastric cells to produce ammonia and CO2- the ammonia neutralises stomach acid in its immediate vicinity
how does urease work?
urease is intracellular so the organism takes up urea and exports ammonia very efficiently to the periplasm where the pH can rise to approx 6
H. Pylori adhesions and neutrophils
BabA: adhesin recognising lewis b antigens which binds sulphated mucin sugars on epithelial cells
-NAP: neutrophil leads to inflammation
-VacA: vacuolating cytotoxin produces large vacuoles in mammala cells
UreI is a H.Pylori sensor
-an inner membrane protein that facilitates urea entry in a pH-controlled way
-UreI consists of 6 transmembrane regions
-Periplasmic loops and carboxy terminus contain a number of histidine and acidic residues that act as pH sensors through their ionisation
Salmonella typhimurium characteristics
-Gram negative rod
-motile
-causes gastroenteritis
Salmonella typhimurium main virulence factors
-acid tolerance responses
-adhesins
-invasion of mucosal cells
-type III secretion system = contact dependent (like a syringe)
effectors that pathogens produce are proteins (hard to diffuse through membrane)
Salmonella typhimurium acid tolerance response type III is induced when …
within acidified phagosomes of macrophages
cultured Salmonella typhimurium grown at neutral pH and shifted to lower pH survives well at pH values down to 4 but …
if cells are able to ADAPT (by growth at pH 6 for a generation) they can survive down to pH 3
DNA-binding protein fur
regulates a subset of acid shock proteins so fur senses pH as well as iron
mechanisms of acid resistance in gram positive - proton pumps
F1/F0 -ATPases from tolerant bacteria are less sensitive to low PH
-glutamate decaboxylases (GAD) : consume protons via glutamate decarboxylation the reaction product (GABA) is exported
mechanisms of acid resistance in gram positive - regulators
often of glycolytic enzymes to facilitate rapid growth recovery when pH stress is removed
mechanisms of acid resistance in gram positive - CELL DENSITY
a quorum sensing system and biofilm growth allow for increased acid tolerance in S. mutans
mechanisms of acid resistance in gram positive - envelope alterations
s mutans has increased levels of monounsaturated and longer chain fatty acids
Obligate aerobes
-require O2 for growth; they use O2 as final electron acceptor
obligate anaerobes/aerophobes
-do not need or use O2 as a nutrient
-O2 is TOXIC
-kills or inhibits growth
obligate anaerobes may live by
-fermentation
-anaerobic respiration
-bacterial photosynthesis (H sulphate as terminal e acceptor)
-methanogenesis (methane from acetate)
facultative anaerobes/ facultative aerobes
-organisms that can switch between aerobic and anerobic types of metabolism
aerotolerant anaerobes
-bacteria with an exclusively anaerobic (fermentation) type of metabolism but they are insensitive to the presence of O2 they live by fermentation alone
ROS
reactive oxygen species
what is generated by cells in the presence of O2
oxygen radicals can kill the cell
FAD
flavodeninedinucleotide
-cofactors involved in oxidation reactions therefore can be inhibited
all cells contain enzymes capable of reacting with O2
-oxidation of flavoproteins by O2 invariably results in the formation of H2O2(hydrogen peroxide)
singlet oxygen
-produced by chlorophyll and other pigments in cells that react with O2 in the presence of light
ANOTHER RADICAL which is potent oxidising agent in biological systems
superoxide dismutase (SODS)
enzyme
-all organisms that can live in teh presence of O2 contain superoxide dismutase prevents lethal accumulation
catalase
decomposes H2O2
certain aerotolerant bacteria such as lactic acid bacteria lack catalase so instead
they decompose H2O2 by means of peroxidase
enzymes which derive electrons from NADH2 to reduce peroxide to water
Obligate aerobes lack
superoxidase
dismutase
catalase
all photosynthetic and some non are protected from lethal oxidations of singlet oxygen by their possession of
carotenoid pigments which physically react with the singlet oxygen radical and lower it to its non-toxic triplet state
clostridium spp. - obligately anaerobic pathogens
-most clostridia lack respiratory chain cytochromes and the ENZYMES
-they obtain ATP by substrate-level phosphorylation
-a number of clostridia ferment sugars producing butyric acid ; other ferment amino acids
-clostrdia are in soil and some in human flora
substrate-level phosphorylation
the formation of ATP from ADP and a phosphorylated intermediate
-due to high energy phosphate bonds from organic intermediates are transferred to ADP
Clostridium botulinum
-most fatal food poisoning
-commonly found in soil and aquatic sediments
-extremely potent (1mg of pure toxin can kill 1 million guinea pigs)
Clostridium botulinum how can it be in food
-poorly canned foods create an anaerobic environment unfilled spores germinate and produce toxin
Clostridium botulinum different strains produce …
7 exotoxin types (A,B,C1,D,E,F,G)
types C and D are encoded by lysogenic bacteriophage that infect the bacteria
lysogenic bacteriophage =
inserts itself into genome
bacteriophage = viruses that target bacteria
botulism =
results from the ingestion of bacterially produced neurotoxins
exotoxin - types A, B, E and F are
the most toxic for humans these protein exotoxins are often released in an inactive form ; proteolytic cleavage activates them
type A exotoxin
the most potent known
10 ng can kill a normal adult
exotoxins block
the release of the neurotransmitter acetylcholine resulting in
-double vision general weakness
botulism- paralysis with accompanying respiratory failure
can be fatal in 20% of those affected
botulism food poisoning can be observed about
18-36 hours after ingestion which is heat labile(one that is capable of changing or destruction when subjected to heat)
action of botulinum toxin from Clostridium botulinum
-acts at motor end plates and prevents release of acetylcholine from vesicles resulting in a lack of stimulation of muscle fibres leading to flaccid paralysis
botulinum toxin is expressed as an
-inactive 150 kDa polypeptide
-comprising a 100kDa heavy chain (HC)
-50 kDa light chain(LC)
-linked through a disulphide bridge
botulinum toxin process
1)Hc binds the toxin to the presynaptic receptor
2)toxin enters the cell and the disulphide bond is cleaved
3)cleavage liberates the LC into the cytoplasm and endosomal compartment
4)LC acts as zinc endopeptidase cleaving SNAP/VAMp and syntaxin
prevents fusion of AC vesicles at membrane
clostridium tetani
-causative agent of tetanus
-from trauma or a puncture wound
-tetanus caused by the release of a SINGLE EXOTOXIN
-adheres to neuronal receptors
what does clostridium tetani fit to
-gangliosides thereby blocking the release of the neurotransmitters glycine and gamma-amino butyric acid(GABA)
-glycine normally prevents contraction of muscles therefore muscle spasms and convulsions occur
the action of tetanus toxin
blocks release of glycine (an inhibitory neurotransmitter) so that Acetylcholine release cannot be inhibited therefore muscle is irreversibly contracted
tetanus toxin physiology
-synthesised as 150 kDa polypeptide chain
-100 kDa HC = c terminal domain binds to gangliosides whilst teh n terminal domain of teh HC allows the LC to cross into the cell cytoplasm
-50 kDa LC
tetanus vs botolism
-one exotoxin compared to many
clostridium tetani how does the host die
-from respiratory paralysis though teh underlying tetani infection is elsewhere
-toxin secretion occuring
-the killing of the human host allows C.tetani to multiply as these anaerobic microbes can only grow in tissues that are anaerobic
most at risk of tetanus
herion addicts
clostridium difficile
-gram positive, obligately anaerobic, spore former
-antibiotic use reduces concentrations of normal microbiota C.difficile overgrows produces toxins A and B
clostridium difficile toxins causes
-diarrhoea and lesions on colon surface which coalesce- forming extensive tissue damage known as pseudomembranous colitis
-can be fatal
clostridium difficile toxins A and B are
large exotoxins that modify host cell membrane G proteins
-mode of action is to alter actin cytoskeleton of mammalian cells
clostridium difficile G-proteins
-mediated by toxins glucosylating G-proteins
-Glucosyl groups (from UDP-glucose) added to specific threonine residue on the G protein
flagellated protozoa
African trypanosomes
vector borne disease
-have arthropod /insect/vector which transmits parasites
African tryps-
trypanosoma brucei species HAT(human african trpanosoiasis
american tryps
trypanosoma cruzi and chagas disease
communicable disease =
infectious
vector of disease can be
biological or mechanical
zoonotic
transmissible from animals
arthroponotic
transmissible from human to human
a biological vector includes an
extrinsic incubation period which forms part of vectorial capacity
horse flies transmit
mechanically (interruptive feeding)
-where the fly sucks upinfected blood and injects bacteria on next feed
non-resevoir host
-dead end host
-parasite goes in but doesnt come out
-may not be susceptible but do provide blodd
-strong evolutionary force to find blood source
global warming assits the
extrinsic incubation period (ideal temps)
kinetoplastids-DIAGNOSTIC TOOL
-flagellated forms (locomotion by flagella)
-kinetoplastids distinguished by kinetoplast - a large DNA containing structure
morphological forms of hemoflagellates
-some forms are highly motile pulled by FLAGELLUM
HAT morphological form
epimastigot when developing in vector
-trypomastigote when blood form in host
epidemiology and distribution of African trypanosomes
DISEASES
-sleeping sickness in humans
-lagana in cattle
trypanosoma brucei
GAMBIAN
-central and W.Africa
-humans
-sleeping sickness (CHRONIC)
-glossina palpalis
trypanosoma brucei
RHODESIENSE
-East and S.Africa
-humans (zoonosis)
-sleeping sickness (ACUTE)
-glossina morsitans
nagana in cattle results in
-subacute,acute or chronic disease: anaemia, intermittent fever, diarrhoea, rapid loss of condition and often death
Nagana in cattle- T.b Brucei
-chronic to mild in cattle
-incubation 5-10 days
-acute in donkeys, horses
NO AQUIRED IMMUNITY WITH AGE
Nagana in cattle- T. congolense
-severe
-incubation 4-24days
-single important cause in E. AFrica
-major cause in W. Africa
-NO AQUIRED IMMUNITY WITH AGE
Nagana in cattle- T vivax
-less pathogenic than T.congolense:
-incubation 4-24 days
-most important in cattle in W. Africa
-partial immunity with age
emaciation
the state of being abnormally thin or weak.
Tsetse belt significant to africa
-1.6 million DALYs
-agricultural production losses worth US 4.75 bill
-when shipping out cows died within months
distribution of trypanosoma congolense and subgroups causing bovine trypanosomiasis
(Nagana-_______)
chronic
predominantly in east africa
distribution of trypanosoma vivax and subgroups causing bovine trypanosomiasis
(nagana-______)
acute
in south america and south africa
distribution of trpanosoma evansi causing
sura
across globe
epidemiology and control of human african trypanosomes
-60 million at risk
-in 36 countries
-500,000 cases pa
-deaths 50,000 pa
trypanosoma brucei
gambiense vs rhodesiense
G
G
-endemic in 24 countries of west and central africa
->90% of reported cases of sleeping sickness worldwide
-chronic disease lasts for several years
-athroponotic transmission (human resevour and vector borne)
-rivereine tsetse vector
-FATAL if untreated
trypanosoma brucei
gambiense vs rhodesiense
G
R
-endemic in 13 countries of east and south africa
-<10% of reported cases globally
-acute disease lasts for months
-zoonosis transmission (domestic and wildlife reservoirs, vector-borne)
-savannah tsetse vector
-FATAL if untreated
tsetse fly -
morsitans group
-savannah woodland
-highly mobile
-visual/olfactory cues
tsetse fly -
fusca group
-humid forest ecology
tsetse fly -
palpalis group
-riverine woodlands
less mobile
visual cues
HAT pathology
-two phases
-early stage (haemolymphatic or stage
-late stage (encephalitic or stage 2) SLEEPING SICKNESS
sleeping sickness
biological clock interrupted and oly sleep during day
the early stage of infections
parasite spreads through lymphatic system and invades the bloodstream
-chancre arises at site of bite in 50% of R infections (rarely in gamb)
early general symptoms
-enlarged lymph glands
-local oedema
-cardiac abnormalities
-general malaise
-headaches
-fever
late stage neuropathology
acute haemorrhagic leucoencephalopathy (AHL)
there is widespread fibrinoid necrosis in the walls of small blood vessels in teh affected regions of the brain
T.b gambiense (C and W africa)
pathology
-long asymptomatic period (months to years) emergent disease advanced
necessitates early diagnosis
T.b grhodesiense (E and S africa)
pathology
-acute virulent infection
-incubation 1-4 weeks
quickly detectable
no aquired immunity no vaccine
fatal without treatment
mechanisms of HAT
variant surface glycoprotein (VSG) the decoy antigen
-covers entire parasite surface including flagellum
-10^6 produced per cell
-molecule is highly immunogenic
-elicits highly strong antibody responses from infected host
-stage-specific
VSG the decoy antigen how does it work?
-parasite is able to switch VSG expression
-there are»_space;200 VSG genes
-under transcriptional control
VSG expression switching leads to
undulating fever which can last for months
-parasites from each peak of infection are antigenically distinct
diagnosis of HAT
-serological test:card agglutination (CATT) for gambiense only
-rapid serological tests (sticks in blood samples)
-microscopy
on clinical or serological positive evidence
-diagnosis of the stage is necessary step to identify appropriate treatment
-inspection of CSF obtained by lumber puncture to define disease stage
-trypanosomes (or high WBC count) demonstrated in CSF indicates 2nd stage of disease
different approaches to control HAT
GAMBIENSE
-reduce person to person transmission
- requires active identification of cases
-active or passive case detection and treatment
-vector control plays little to no part of control (low cost effectiveness)
-large scale epidemics in 20th century controlled by 1960s by active case detection and treatment programmes
different approaches to control HAT
RHODESIENSE
-to reduce transmission from zoonotic reservoirs
-vector control is central (NEED TO INTERRUPT TRANSMISSION CYCLES)
-cattle treatment becoming more common
-case screening conducted for humanitarian reasons
vector control prevents initial infection
whereas case treatment reduces circulation of parasites
both should reduce disease
vector control rationale
-low density
-low reproductive potential
-4% sustained mortality of females per day should cause extinction
K strategists
-dont have millions of offspring
-produce large larvae
insecticide applications
-traps/targets
-dips or pour on topical treatment
-ultra low volume (ULV) spraying
NOT USED ANYMORE, COSTLY AND ENVIRONMENTAL IMPLICATIONS
-sterile insect technique
standard tsetse traps
-electrified black target with flanking net
-biconical trap with flanking electrified grid
sterile insect techniques
8 million
-zanzibar
-1988 tsetse population suppressed using insecticide treated cattle and traps
-seriel release of sterlizid males by aircraft per week
1994-1997 8.5 mill males released
-1995 sterile to normal male ratio 100:1 >70% barren females
1996-7 tsestse population crashed glossina austeni eradicated
current gambiense situation in africa
-control seems to be working in many places with active foci being generally well known and reducing in size
-political instability makes monitoring less of a priority therefore may hide scale of problem
-most important areas of disease burden in DRC with 85% transmission
model predictions of gambiense to achieve elimination
-active screening to treat reduced incidence of new human infections by 52-53% over a 15 year period
-model projections indicate elimination goal may not be met until later this century under the current strategy
Flagellated protozoa African _____
trypanosomes
trypanosomes- Uganda two subspecies overlap…
making diagnosis essential for treatment
Geographical distribution of two HAT subspecies
-T.b gambiense west african tyrpanosmiasis
-T.b rhodesiense East african
Major epidemics of sleeping sickness in last century
modelling sleeping sickness in SE uganda
-human sleeping sickness SRA analysis (0.6%)
-fly biting prefernce human 9% cattle 23%
-cattle 234x more likely to be source of human rhodesiensis than humans
-predicted that 20% of cattle need treatment to achieve R0<1
through time subspecies of Rhodesiense are getting
closer together
Stamp out sleeping sickness (SOS) initiative
-public-private partnership launched in uganda 2006
-response to possible convergence of rhodesiense and gambiense in N.Uganda because treatment where human infections are mixed is more difficult
SOS drugs early stage disease 1st line drugs
-Suramin efficacious against rhodesiense
-pentamidine efficacious against gambiense
-pentamidine is not effective against early stage rhodesiense
SOS drugs late stage 1st line
-melarsoprol (arsenic so side effects) efficacious against both
-late stage treatment failures of gambiense increasing
-an alternative is eflorinithine but not effective against rhodesiense
Restricted application protocol (RAP)
cows dipped in insecticide
-convenient however large amount required $$$
-need knowledge of other ticks to kill off multiple things
Babesiosis in cattle
-incubation 3-21 days
-high fever anorexia, seek shade, weight loss, abortion, poor milk production
-extensive erthrocytic lysis :75% erthrocytes destroyed in a few days
-most survive but mortality up to >50% known slow recovery (AGIRCULTURE QUESTION IF WORTH TREATING)
-carrier status (low parasitaemia) for years
cattle babesiosis tick vectors
-Babesia pass into ovaries/eggs - vertical or transoverial transmssion
-migrate into salivary glands to reproduce in larvae
-larvae await on grass stalks to attach
-babesia from salivary glands injected into mammals bloodstream
___ _______ cattle in tropical and subtropical regions of the world are at risk to infection with babesia bovis and babesia bigemina
300 million
complexcity of insecticide treatment of cattle
-insecticides kill both ticks + tsetse
-need to maintain tick exposure while preventing tick bites
-insecticide costs
TBD endemic.enzootic stability CRITERIA
1)disease is more likely or more severe in older rather than younger susecptibles
2)following infection the probability that subsequent infection results in disease is REDUCED
endemic stability descrbes
a dynamic epidemiological state in which clinical disease is rare in spite of a high incidence of infection within a population
Criteria met by babesiosis
-1-2 met by babesiosis, cowdriosis and anaplasmosis
-uncertain for theileria
-nagan (t.b brucie, t.b congolense, t vivax) age not related to severity and no conferred immunity
Cattle age-dependent tick fever severity
-calf exposure to infected ticks is key to immunity
-the age of first exposure determines severity
-if exposed by 9 months long lasting immunity
measure to maintain endemic stability
WHERE TO TARGET INSECTICIDe
1)Tsetse more suspecitble to pyrethroid-treated cattle than are ticks - increasing intervention interval lowers impact on ticks
2)tsetse preferentially feed on different sites of body particularyly legs- avoid tick attachment sites
porportion of tsetse blood meals on cattle increases with
cattle weight
daily probability of tryp infection if in a mixed cow age herd
-more liekly to be infected if ox than cow than calf
solution towards sustainable control by farmers
-tsetse preferentially feed on older and larger herd members - leave young cattle untreated to become exposed to ticks
-treating half the herd (insecticide to larger individuals) would only be slightly less effective and cheaper
-selective treatments of hosts with restricted application protocol (RAP) reduce insecticide costs by 90% compared with teh current regime of treating entire herd)
vector control in absense of cattle
-minimum densities of 10 cattle/km^2 are necessary for cattle to be an important part of tsetse blood source depending on availability of zoonotic hosts
-precludes the use of RAP in many gambian HAT foci
-traditional biconial traps and deplyment is expensive costing an estimated US556 dollows per kilometre squared
-one recent disovery is theuse of tiny insecticide impregentaed targets against gambian transmission)
Tiny traps
look on slides lecture 6
Apicomplexan parasites
-Eukaryotic
-obligate parasites (have to have a host)
-one or multiple hosts depending on the species
-extremely important as disease agents
-malaria parasites (plasmodia)
-coccidia
-Prioplasms
Apical complex
-distinctive to apicomplexans
-key cellular machinery for host cell invasion
-some apicomplexans are motile and apical complex is essential for movement
-includes secretory organelles
-subpellicular membranes enable parasite feeding from host
host cell invasion
-conoids protrude into host cells in response to calcium
-rhoptries are secretory organelles releasing rhoptry protein sinto host during invasion
-micronemes also secrete proteins into host cell
-parassitophorus vacuole is formed
-parasite moves into parasitophorus vacuole
-polar ring is a microtubule organising centre
Apicomplexan life cycles
-can involve one or more hosts (human and mosquito)
-sexual - gametes fuse to form zygote
-asexual - sporozoites differentiate to form merozoites
-merozoites undergo multiple rounds of replication
-some merozoites differentiate into gamonts
-gamonts differentiate into gametes
malaria intro
-life thretening
-caused bt PLASMODIAN APICOMPLEXAN PARASITES
-mosquito vectors are becessary for disease transmission
-half of worlds population at risk - mainly in tropical areas
-disease can acuse considerable morbidity and mortality
morbidity =
having disease or illness
malria most often occurs in
tropics
malaria - causative agents and vector
majority of morbidity and mortality is caused by Plasmodium falciparum and vivax
-vector is female anopheles mosquito
plasmodium life cycles
-always involves mammal and female mosquito as hosts
-in insects -> gametes fuse to form zygote which forms oocyst
-in humans
sporozoites differentiate to form merozoites
-merozoites undergo multiple rounds of replication
-some merozoites differentiate into gamonts
-gamonts differentiate into GAMETES
disease presentation
-asymptomatic malaria -
circulating parasites but no symptoms (could be due to previous immunity)
disease presentation
-uncomplicated malaria
-nonspecific symptoms
-fever,shaking chills, profuse sweating, headache, nausea, vomiting, diarrhoea and anaemia (due to RBCs popping)
disease presentation
complicated malaria
-as above with additional organ damage and anaemia associated with hyperparasetemia and increased mortality
-extreme tiredness and fatigue
– impaired consciousness
– multiple convulsions
– difficulty breathing
– dark or bloody urine
– jaundice (yellowing of the eyes and skin)
– abnormal bleeding
hyperparasetemia
higher parasite load
Plasmodium falciparum specific complications
-cerebral malaria
(often fatal) high temps with convulsions and coma infected erythrocyte’s adhere to capillary endothelial cells-erythrocytes become knobbly, as a result of parasite proteins exported to the membrane these bind to ligands on host cells
Plasmodium falciparum specific complications
-blackwater fever
-massive lysis of erythrocytes causes high levels of free haemoglobi. in the blood and renal failure
-presence of haemoglobin in the urine gives the condition its name
Co-evolution of plasmodia and humans results in arms race
plasmodia
-plasmodia adaptations include array of hypervariable membrane proteins to switch between and evade immune system
Co-evolution of plasmodia and humans results in arms race
human
-higher proportions of people lacking duffy (dont have receptor for p vivax to bind to) therefore cant invade cells
-several inherited erthrocyte disorders in endemic areas offering protection against infection
-Eg sickle cell anaemia in malarial endemic aress as having heterozygous alleles offers protection from plasmodia
apicomplexian - an arms race
-the plasmodium falciparum genome contains a large family of 60 var genes that encode hypervariable. P. falciparum erthrocute membrane protein 1(PfEMP1)
-during the erythocytic stage each parasite expresses one of its var genes at a time
-by switching between different var genes during the course of infection the parasite is able to evade destruction by host immunity
-protective immunity lasts only as long as residual population of parasites is present, if the person is completly cured susceptibility returns (this is the reason most vaccines are ineffective)
arms race continued
- P. vivax can only enter erythrocytes with genetically determined receptor sites known as Duffy blood groups.
- Individuals which lack these antigens are refractory.
- A large proportion of the populations in western Africa are Duffy negative,
accounting for the low levels of P. vivax in west Africa. - This innate resistance led to the identification of the Duffy antigen as the
erythrocyte receptor for merozoite invasion. - Several inherited erythrocyte disorders are found predominantly in malaria endemic areas and at frequencies much higher than expected.
sickle cell anaemia
-sickle cell anaemia is protective against malaria a glutamic acid residue is in the amino acid sequence of haemoglobin is replaced by a valine which reduces oxygen carrying capacity
-those with homozygous alleles often die before 30 but those with heterozygous alleles have some normal haemoglobin and have 80-95% protection against p.vivax
-sickled cells tend to get stuck in narrow blood vessels, blocking flow of blood
malaria diagnosis
-WHO criteria: fever and presence of parasites
-light microscopic examination of a blood smear
-rapid diagnostic test
treatment recommendations
-P.falciparium- artmisinin combination (ACT) artemisinin derivative plus quinine derivation
-p vivax and p ovale- chloroquine unless drug resitance issue in area then ACT
-drug resistance is a major concern
malaria vector control
-widespread insecticide/ larvicide
-destruction of breeding grounds
-indoor residual spraying (IRS)
-long acting insecticide treated bednets (ITN)
-experimental methods in pipeline
insecticide treated bednets (ITNs)
-shown to reduce devere disease and mortality due to malaria in endemic regions
-reduce mortality by 20%
-currently only pyrethroid insecticides ae appropved due to low mammalian toxcity and may have knock on effect on insects
-Long-lasting insecticidal nets (LLINs) are the preferred form of ITNs for public health programmes.
Pyrethroids
have a high residual effect: they do not rapidly break down unless washed or exposed to sunlight.
*The need for frequent retreatments (6-12 months) was one of the most difficult barriers to full implementation of ITNs in endemic countries.
drugs used for malaria prophylaxis can work in one of three ways
1)kill parasites in liver (causal prophylaxis)
2)kill asexual parasites in RBCs suppressive prophylaxis
3)kill sexual parasites (gametophytes) in RBCs gametocytocidal prophylaxis
malaria vaccines
-recent vaccine developments offer hope
-RTS, S
-virus like particle (VLP) vaccine based on teh P falciparum circumsporozoite protein (CSP)
-tagets sporozoites injected by mosquito
-three primary doses plus booster
-efficacy 55%
R21 vaccine
-based on the falciparum cicumsporozite protein (CSP)
-three primary doses plus booster
-efficacy 75%
malaria impact of covid
-fragile health system capacity overwhelmed
-misdiagnosis as covid-19 or flu
-decreased funding
-malaria controld delivery systems impact by supply chain disruption
experimental approaches to control
-endectocides (systemic insecticides to kill mosquito feeding of them)
-sterile insect techniques
-CRISPR/CAS9 gene drives
-biocontrol using bacteria or fungi that infect the mosquito and prevent development of the plasmodium
sterile insect techniques
-irradiated males
-GM spermless males
-are not as competitive in mating flights
gene drive
-all male off-spring
-females sterile
-mosquitos resistant to plasmodium parasite
-ethics concern about relase and food chains
