emma (L7-8)

Question 1

apicomplexan parasites

Answer 1

they need a host to survive
malaria has 2 hosts
paruvium causes intestinal disorders, really bad diarrhea. can affect humans and cattle
toxoplasma gondii infects cats, birds and rodents
with a complex life cycle like 3rd one, it’s important to understand their characteristics

All members of the Apicomplexa are parasitic, and some of them are extremely important as disease agents including the malaria parasites, the coccidia and prioplasms, the gregarines and Toxoplasma gondii

Question 2

Apicomplexan structure

Answer 2

The ‘apical complex’ includes secretory organelles known as micronemes and rhoptries, polar rings composed of microtubules, and in some species a conoid which lies within the polar rings.

At some point during their life cycle, members of the apicomplexa either invade or attach to host cells.

It is during this invasive (and/or motile) stage that these apical organelles are expressed as well as the subpellicular membranes.

unusual structure, links to their lifecycle and their parasitic
complex structure because it needs to invade other cells, so it needs the cellular machinery to do so

the conoid is associated with the polar ring and rhoptries
subpellicular membranes used for feeding and nutrient formation
this is very characteristic
LOOK AT STRUCTURE ON L7 S4

Question 3

function of

• apical pole
• conoid
• rhoptries

Answer 3

• Apicomplexan parasites actively secrete proteins at their apical pole as part of the host cell invasion process in response to free Ca++ in the parasite’s cytoplasm.
• When present the conoid is located in the center of the polar rings, with the short narrow end pointing anteriorly. The conoid intermittently protrudes beyond the apical end of the microtubules. Protrusion of the conoid is sensitive to parasite cytoplasmic calcium concentration.
• The rhoptries are club shaped secretory organelles, often located near the apical end of Apicomplexan intracellular parasites. Rhoptries are secreted during host cell invasion, and rhoptry proteins are found within the lumen and the membrane of very early stages of the forming parasitophorous vacuole.

Question 4

apicomplexan life cycle

Answer 4

Complex life cycles that are characterized by three distinct processes sporogony, merogony and gametogony.

Sporogony occurs immediately after a sexual phase and consists of an asexual reproduction that culminates in the production of sporozoites. Sporozoites will develop into forms that undergo another asexual replication known as merogony.

diff apicomplexa have diff lifecycles and different number of hosts. but there is a generalised lifecycle that has gametes (which involves two to lots of chromosomes, so this is the sexual part) and sporozoites (formed from zygotes) and merozoites (formed from sporozoites) - (asexual part)

Question 5

merogony / sporogony / gametogony

Answer 5

merozoites can have many cycles in the asexual part of the life cycle and this is called MEROGONY
Quite often there are multiple rounds of merogony and sometimes these multiple rounds involve a switch in host organism or a switch in the type of cell invaded by the parasite

sporogony and gametogony can involve different hosts or cell types. As an alternative to asexual replication merozoites can become gametes through a process variously called gametogony, gamogony or gametogenesis.

As in other types of sexual reproduction, the gametes fuse to form a zygote which differentiates into a form yielding sporozoites

Question 6

malaria is caused by ?

Answer 6

Malaria is caused by four distinct Plasmodium species in humans: small subunit rRNA gene sequence similarity suggests more closely related to Plasmodium of other animals that to each other

• P. falciparum, most virulent species
• P. vivax, concurrent infection is not uncommon
• P. malariae,
• P. ovale

2 main that affect us worldwide : falciparum and Vivax (cause most deaths, mostly in children under 10)
you can have both at the same time

Question 7

distribution of malaria

Answer 7

malaria is spread worldwide. needed worldwide contribution to eradicate it
1952 - last malaria death reported

Question 8

prediction for the future

Answer 8

warmer environment will help malaria spread more (mosquitoes survive better)
there are a lot of control measurements that are acting on malaria, and there are concerns that the areas where where temperatures are getting warmer malaria can survive better and the spread range will increase

BUT OTHER STUDIES ARGUE THAT IT WONT AFFECT IT SINCE MALARIA LEVELS INCREASED DURING AN ICE AGE

Question 9

Global burden of malaria (figures from WHO september 2015)

Answer 9

438 000 malaria deaths annually
Over 214 million clinical episodes
About 3.2 billion people – half of the world’s population – are at risk of malaria
Every 30 seconds a child dies of malaria
90% of all malaria deaths occurred in the WHO African Region, mostly among children under 5 years of age
Reduction in malaria mortality rates by 60% globally since 2000 and by 49% in the WHO African Region.

Question 10

WHO reports in 2017

Answer 10

the overall decline in the global malaria burden has leveled off
In some countries and regions, we are beginning to see reversals in the gains achieved.
216 million cases of malaria, an increase of 5 million cases over the previous year
445 000 deaths
90% deaths in African region

Question 11

life and spreading cycle of malaria in mosquitos

Answer 11

LEARN DIAGRAM AND VIDEO IN L7 S16

Question 12

Clinical Manifestations of malaria

Answer 12

LEARN DIAGRAM IN L7 S17

Question 13

pregnant women and malaria

Answer 13

Pregnant women are at high risk of dying from the complications of severe malaria. Malaria is also a cause of spontaneous abortion, premature delivery, stillbirth and severe maternal anaemia, and is responsible for about one third of preventable low-birth-weight babies. WHO recommends intermittent preventive treatment for pregnant women living in areas of high malaria transmission

Question 14

disease symptoms

Answer 14

• The blood-stage parasites within a host usually undergo synchronous schizogony. The simultaneous rupture of the infected erythrocytes and the release of antigens and waste products accounts for the intermittent fever associated with malaria occurring at either 48 or 72 hour intervals.
• The pathology and clinical manifestations associated with malaria are almost exclusively due to the asexual erythrocytic stage parasites. Tissue schizonts and gametocytes cause little, if any, pathology
• The disease has a tendency to relapse or recrudesce over months or even years

Question 15

how can the disease reoccur and relapse?

Answer 15

due to initial stage of infection in liver, you can have infected liver cells that hide from the immune system and re-emerge, merozoites released and we infect again the same host

Question 16

P falciparum

Answer 16

P. falciparum causes cerebral malaria which is often fatal, extremely high temperature is associated with convulsions and coma. Infected erythrocytes 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.

Blackwater fever is also caused by falciparum, massive lysis of erythrocytes causes high levels of free haemoglobin in the blood and renal failure. The presence of haemoglobin in the urine gives the condition its name.

Question 17

malaria ecology - intrinsic and extrinsic factors

Answer 17

LOOK AT DIAGRAM IN L7 S23

Question 18

vector control

Answer 18

1904-14 control by larviciding, large-scale environmental modification

1935-39 use of pyrethrum spraying

1946-57 Interruption of transmission by anti-mosquito measures; by indoor residual spraying with DDT, a new major strategy.

1987-2003 Multiple projects and programs using insecticide-impregnated bed nets demonstrating overall mortality reduction and decrease in several malaria indices

Question 19

Insecticide-Treated Bed Nets

Answer 19

insecticide-treated bed nets (ITNs) have been shown to reduce severe disease and mortality due to malaria in endemic regions.

ITNs have been shown to reduce all-cause mortality by about 20%.

Currently, only pyrethroid insecticides are approved for use on ITNs. These insecticides have very low mammalian toxicity but are highly toxic to insects and have a rapid knock-down effect, even at very low doses.

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.

Long-lasting insecticidal nets (LLINs) are the preferred form of ITNs for public health programmes

Question 20

malaria in sri lanka

Answer 20

DDT spraying has been very effective and dropped from very high levels to very low
very rapidly after the DDT was stopped, it took longer for the falciparum than the Vivax to increase in nmbr of cases again
another way to control malaria in Sri Lanka was to immediately treat the disease in its very early stages to stop the spread

• Sri lanka malaria free in 2016 with education and effective screening and rapid treatment to reduce onward transmission
• in 2001* the levels of falciparum dropped rapidly
  Sri Lanka is now declared a malaria free zone
  largely through controlling it within the human host (intrinsic control)

Question 21

4 types of insecticides

Answer 21

DDT
malathion
deltamethrin
pyrimiphos-methyl

Question 22

immunity

Answer 22

age-related changed in ani-malarial antibody levels in relation to parasite rate and mortality in a west african population

parasite rates show that older kids can be infected but are less likely to die

Question 23

the arms race between Plasmodium falciparum and its host

Answer 23

During the erythrocytic 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 a residual population of parasites is present, if the person is completely cured susceptibility returns. (This is the reason most vaccines are ineffective).

it is always an arms race between a pathogen and its host and in this case falciparum has some variable genes that can switch in and out
the proteins that they use bind to the red blood cells
by switching between different genes it can infect the same host more than once which is why it is very difficult to create a vaccine

Question 24

the arms race between Plasmodium vivax and its host

Answer 24

• 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.

Question 25

sickle cell anaemia

Answer 25

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.

Homozygous people often die before 30, but heterozygotes have some normal haemoglobin and have 80-95% protection against P. vivax.

The sickled cells tend to get stuck in narrow blood vessels, blocking the flow of blood. Those with disease suffer painful “crises” in their joints and bones, strokes, blindness, or damage to the lungs, kidneys, or heart.

Question 26

drugs used for malaria prophylaxis

Answer 26

can work in 3 ways:

• kill parasites in the liver (causal prophylaxis)
• kill asexual parasites in red blood cells (suppressive prophylaxis)
• kill sexual parasites / gametocytes in red blood cells

current recommendation
P falciparium - artemisinin combination therapu
P vivax and P ovale - chloroquine

Question 27

Antifolates

Answer 27

Folate metabolism is the target of several antimalarials as well as drugs used against other pathogens.

Reduced folates serve a co-factors in the biosynthesis of amino acids and nucleotides.

Due to its high rate of replication the malaria parasite has a high demand for nucleotides as precursors for DNA synthesis and thus is particularly sensitive to antifolates

Question 28

drug resistance

Answer 28

Drug resistance can develop quickly in situations where a single point mutation can confer resistance
OR
expressing higher levels of the target (increased transcription and translation or gene amplification)

Question 29

Factors contributing to treatment failure

Answer 29

• self treatment
• poor compliance
• mass administration
• long drug half life
• transmission intensity

Question 30

sterile insect technique

Answer 30

irradiated males
GM spermless males
are not competitive in mating flights

Question 31

Cryptosporidium

Answer 31

The most well-known species are Cryptosporidium parvum and Cryptosporidium hominis (formerly known as C. parvum anthroponotic genotype or genotype 1), which are severe waterborne pathogens that causes cryptosporidiosis

cryptosporidiosis:
a flu-like intestinal disorder.
associated with diarrhea

Question 32

cryptosporidiosis

Answer 32

In immuno-competent individuals this diarrhoea is self-limiting and last about two weeks.
The disease is quite serious and potentially life-threatening in immunodeficient patients (especially AIDS) and is characterised by a profuse watery diarrhoea.

cryptosporidium spores attached to the epithelial cells of the intestine and feed on them

Question 33

risk factors of transmission for Cryptosporidium

Answer 33

similar to other faecal-oral diseases.
risk factor are poor hand hygiene, occupations that are more exposed (labs or farmers) etc

contamination from human to human, or animal or water (usually from faeces)
oocytes, which is part of the lifecycle where it is transmitted between animals and humans is very resistant to cleaning up the water

Question 34

Factors that contribute to the increased risks of Cryptosporidium waterborne outbreaks

Answer 34

• small size of oocysts
• wide range of host specificity and monoxenous development
• close associations between human and animal hosts
• large number of oocysts excreted (up to 100 billion per calf)
• low infective dose
• robust oocysts which are resistant to chlorine (a complex protective barrier consisting of a double layer of a protein-lipid-carbohydrate matrix )

outbreaks because it is multifactorial, oocytes are very small, very difficult to clean out of water, we have a lot of contact with animals

Question 35

Cryptosporidium in potable water - filtration

Answer 35

SEDIMENTATION – because of small size and low density the settling rate of oocysts is extremely low and removal by sedimentation is insignificant.
FLOCCULATION - surface charge of oocysts is low, so clumping with other negatively charged particles should readily occur particularly in the presence of aluminium or iron hydroxide flocs.
RAPID FILTRATION - successful if applied after flocculation and sedimentation.
SLOW SAND FILTRATION - the top few centimetres support aerobic bacteria that produce a network of extracellular polymers forming a natural biological filter.
MEMBRANE FILTRATION - this may be seen as a final finishing process and as such is not often applied to public water supplies.

Question 36

Cryptosporidium in potable water - disinfection

Answer 36

CHLORINATION - Cryptosporidium oocysts are particularly resistant to chlorination, surviving in undiluted bleach for several hours.
UV LIGHT - to date there have been no reports on the effect of UV light on Cryptosporidium oocysts. This method is currently suitable only for small volume treatment work.
OZONISATION - ozone is the most effective disinfectant tested to date although the levels required for destruction of Cryptosporidium oocysts are more than those used for normal water treatment

Question 37

life cycle of cryptosporidium

Answer 37

DIAGRAM IN L8 S10

Question 38

therapy for cryptosporidium

Answer 38

No safe and effective therapy for cryptosporidial enteritis has been successfully developed.

Since cryptosporidiosis is a self-limiting illness in immuno-competent individuals, general, supportive care is the only treatment for the illness.

Oral or intravenous rehydration and replacement of electrolytes may be necessary for particularly voluminous, watery diarrhoea

Question 39

drugs for therapy

Answer 39

Spiramycin (macrolide antibiotic) has produced partial responses in patients (a partial decrease in diarrhoea or partial decrease in stool oocyst number), but have not yielded reliable, reproducible results.

Paromomycin (aminoglycoside antibiotic with anti-parasitic activity), has been shown to decrease the intensity of infection and improve intestinal function and morphology.

Nitoxazonide is partially effective in immuno-competent patients

Question 40

toxoplasmosis cause by T gondii

Answer 40

T. gondii causes chronic infections in up to one-third of the human population and in animals.

In healthy individuals, a primary infection with Toxoplasma causes relatively mild symptoms, whereas in the immunocompromised patient or in the developing foetus, it can cause life-threatening infections with severe neurological and ocular manifestations

Question 41

toxoplasmosis host and life cycle

Answer 41

Felines are the only definitive host. (so they are necessary for the lifecycle to continue)

Toxoplasma has a complex life cycle consisting of intestinal and tissue phases. The intestinal phase of the infection occurs only in felines and exhibits a typical intestinal life cycle consisting of merogony and gamogony. The sexual cycle produces oocysts which are excreted in the faeces.

Question 42

life cycle of T gondii

Answer 42

Intermediate hosts - ingestion of sporulated oocysts.

Sporozoites are released, penetrate the intestinal epithelium, and invade macrophages and other types of cells.

The parasite undergoes binary fission (i.e., merogony) to form tachyzoites. (Tachy means rapid.) The host cell will rupture and release the tachyzoites which will invade new host cells and repeat the replicative cycle.

Infected macrophages will disseminate the tachyzoites throughout the host during this acute infection.

DIAGRAM IN L8 S16

Question 43

route of human infection

Answer 43

• ingestion of material contaminated with sporulated oocysts, cat faeces.
• ingestion of undercooked meat containing tissue cysts or tachyzoites, (particularly lamb and pork)
• Infection rates of 50% or higher in domestic chickens, geese, cattle, goats, pigs, and sheep
• 38% of meat samples in UK positive
• Congenital transmission can only occur during an acute infection (ie, tachyzoites) acquired during pregancy. Mothers with a chronic infection acquired before the pregnancy are not at a risk for transmitting Toxoplasma.

Question 44

Congenital toxoplasmosis statistics

Answer 44

In the UK about 30% of people will be infected by the age of 30. In the US, about 30-35% have antibodies and in France more than 65% of women will have already had toxoplasmosis.

2 in 1000 women catch toxoplasmosis each year during pregnancy, about 1400 each year in the UK.

In only about 30-40% of women who catch toxoplasmosis during pregnancy, does the infection pass to the unborn baby

Toxoplasmosis infection may lead to miscarriage, stillbirth or survival with growth problems, blindness, water on the brain (hydrocephalus), brain damage, epilepsy, or deafness. This often develops after birth

Question 45

Dormant or resting stage

Answer 45

As the host develops immunity the replication rate will slow and the infected host cells will become encapsulated (ie, tissue cysts). These slowly replicating forms are called bradyzoites (brady means slow) and represent a dormant or resting stage.

Bradyzoites secrete chitin and other components to form a cyst wall

tachyzoites have a fast replication rate. bradyzoites have a slow replication rate.
this is how malaria hid out from the immune system
some tissues we have slow growing forms of the parasites with a chitin wall around it
a cyst from mouse brain shows a lot of bradyzoites. x ray shows the size of cyst
they hide out from the immune system when dormant
so when the immune system drops, they can become activated again and cause bigger problems

Question 46

reactivation

Answer 46

The reactivation of an infection associated with waning immunity, as seen during malignancies, transplantation, and acquired immune deficiency syndrome, results from the release of the encysted organisms and the initiation of the tachyzoite stage of the infection and is followed by local tissue damage and inflammation

Interferon - γ is the essential mediator of the immune response, necessary to maintain latency

Cytokine production by microglia, astrocytes and neurons, which control inflammatory resonses

Question 47

Ocular toxoplasmosis

Answer 47

Ocular toxoplasmosis occurs from activation of cysts deposited in or near the retina

The scars from which recurrent toxoplasmic retinochoroiditis arise may be the result of remote, acquired infections in many cases, rather than congenital infections, as commonly assumed

Question 48

symptoms and treatment

Answer 48

Early symptoms of toxoplasmic encephalitis include headache, fever, lethargy, and altered mental status with progression to neurological deficits and convulsions. The disease is almost always due to a reactivation of a latent infection and tends to remain confined to the CNS.

The recommended treatment is the synergistic combination of pyrimethamine plus sulfadiazine.

Interfere with folic acid synthesis by inhibiting the enzyme dihydrofolate reductase.

Spiramycin for prophylactic use during pregnancy

Question 49

Tissue invasion

Answer 49

In bioluminescence imaging (BLI), the use of internal biological sources of light, luciferases (light emitting enzyme from firefly), to tag cells constitutes in vivo indicators that can be detected externally.

shows how fast it can spread once reactivated
light emission shows cells that have been affected

Question 50

Reports of clinical toxoplasmosis in immunocompetent people statistics

Answer 50

In late 1994 and early 1995, an outbreak of toxoplasmosis occurred in a Canadian community (Bowie et al., 1997).

Serological evidence consistent with acute toxoplasmosis was demonstrated in 100 people. Of these, 74 had clinical signs of T. gondii infection, including 20 patients with retinal lesions and 51 with lymphadenopathy (swelling of the lymph nodes). Twelve cases of congenitally acquired toxoplasmosis were also identified.

Epidemiologic evidence implicated contamination of the city water supply with oocysts

Question 51

Rodent psychology

Answer 51

In comparison to uninfected rodents, infected rodents are more likely to investigate novel stimuli and appear less cautious when presented with signs of cats.

This behaviour is hypothesised to increase the susceptibility of infected rodents to predation by cats, and therefore to increase the odds of completing the T. gondii life cycle.

does little else (e.g. activity levels and mate seeking behaviour are unchanged). This is unlikely to be a nonspecific effect of encephalitis, and therefore behavioural alteration may be controlled by the parasite as a result of evolutionary adaptation

Question 52

infection consequences

Answer 52

Infections in most circumstances do not result in clinically apparent encephalitis, the organism infects the central nervous system and forms latent tissue cysts in neurons and other permanent cells

Question 53

Human psychology

Answer 53

Increased risk of traffic accidents in subjects with latent toxoplasmosis

Toxoplasma gondii infects 30–60% of humans worldwide. Latent toxoplasmosis
(( life long presence of toxoplasma cysts in neural and muscular tissues, leads to prolongation of reaction times in infected subjects.))

These results suggest that ‘asymptomatic’ acquired toxoplasmosis might in fact represent a serious and highly underestimated public health problem, as well as an economic problem

Question 54

Toxoplasma gondii and Schizophrenia

Answer 54

Recent epidemiologic studies indicate that infectious agents may contribute to some cases of schizophrenia

since 1953, a total of 19 studies of T. gondii antibodies in persons with schizophrenia and other severe psychiatric disorders:

• 18 reported a higher percentage of antibodies in the affected persons
• 11 reported a statistically significant difference

Some medications used to treat schizophrenia inhibit the replication of T. gondii in cell culture

42% of schizophrenic patients were T. gondii-positive compared with 11% of matched control subjects

Question 55

toxoplasmosis and children’s mental retardation

Answer 55

Children with subclinical infection at birth may have cognitive, motor, and visual deficits, which may go undiagnosed for many years. One case control study (845 school children in Brazil) found mental retardation and retinochoroiditis (inflammation of the retina) to be significantly associated with positive toxoplasma serology.

Maternal exposure to cats and contact with soil were associated with an increased risk of mental retardation

Question 56

Vaccine development and validation

Answer 56

A vaccine available in New Zealand and some countries in Europe is one of the most effective vaccines against any protozoal disease. Toxovax® is intended for the prevention of toxoplasmosis abortion in ewes

Another type of vaccine would be one administered to cats that could prevent or reduce the shedding of oocysts.

Unfortunately, the attenuated live bradyzoites used in the vaccine could only be grown in mice, so mass production and purification were difficult, costly, and unprofitable for the manufacturer.