Lectures parasitology
Lecture 1 introduction 2
Lecture 2: Diagnostic Challenges in Parasitology 3
Lecture 3: Pregnancy-associated Malaria 18
Lecture 4: Controlled Human Infection Models 24
Lecture 5: Metabolism of Parasites 1 26
Lecture 5.1: Metabolism of Parasites 2 33
Lecture 6: Malaria Transmission to Mosquitoes: A Bottleneck in Parasite Survival 38
Lecture 7: Survival Strategies of Parasites 43
Lecture 8: The Role of Helminth Parasites in the Hygiene Hypothesis anno 2018/2019 51
Lecture 9: Biology of Ectoparasites: Nuisance and their Role in Disease Transmission 57
Lecture 10: Emerging Zoonoses in the Netherlands 60
Lecture 11: Epidemiology, Prevention, and Control of Parasitic Diseases, an example:
Schistosomiasis 65
Lecture 12: T. Solium Elimination vs. Control: Field Experience in Zambia 73
,Lecture 1 introduction
Parasites: Eukaryotic organisms that have to live in or on other organisms (hosts) to complete its
natural life cycle. Doesn’t always cause harm; can also cause benefit. Main goal of parasites: is to get
to the next host. Medical Parasitology: eukaryotic organisms that infect human hosts
Symbiosis: organisms living together
Close association between two organisms; (micro)organisms and host
1. Commensalism: eating at the same table
Benefit is uni-directional -> (micro)organism benefits, host is neither harmed nor helped
2. Mutualism: a form of commensalism
Benefit is bi-directional -> (micro)organism & host benefits
3. Parasitism
Benefit is uni-directional -> (micro)organism benefits, host is harmed
Endoparasite: live in the host (protozoa and metazoa) → infection (ex. Plasmodium falciparum)
Ecto parasite: live on the host (Insecta (lice, fleas), Arachnida (mites, ticks)) → infestation (ex.
Pediculus humanus capitas; teek)
Facultative: the parasite may exist in a free living state
Obligate: the parasite cannot survive without its host
Different types of hosts
• Definitive host: in which sexual replication takes place
• Intermediate host: only asexual replication takes place (so no sexual replication)
• Accidental host: parasite is seldom found in this host (host was infected by ‘accident’)
Taenia solium: human is accidental and definitive host.
It is a hermaphrodite and can live on its own and reproduce themselves.
Protozoa: unicellular eukaryotes
• Rhizopods
• Cilliates
• Flagellates
• Sporozoans
organelles of locomotion
reproduction – binary fission or schizogony
Metazoa: helminths (multicellular)
• Trematodes (fluke)
• Cestodes (tapeworm):herma
• Nematodes (roundworm); either male/female + have
alimentary tract
Morphology, sex: or or hermaphroditic, alimentary tract
Protozoa can reproduce in the host; the population in
the host grows. Helminths don’t do that;
Helminths have a stable population, because if you are
infected with one egg, you get one parasite.
Life cycles: direct (One host)
Direct: parasites need ONE host to complete its life cycle.
E.g. Enterobius vermicularis: children -> get itchy around
the anus -> scratch and don’t wash hands -> parents get infected -> children get reinfected.
,Life cycles: indirect (2 or more hosts)
Indirect: parasites need TWO (or more) hosts to complete its life cycle.
E.g. Taenia solium or Taenia saginata
T. Solium: pig is intermediate host, humans are definitive host (you can see the adult worm), but
when infected with eggs humans can also be an intermediate/accidental (dead-end for parasite) host.
T. Solium is hermaphrodite; they can reproduce on their own, therefore sexual reproduction in
humans and therefore humans as definitive hosts.
Hermaphrodite: can reproduce itself.
Life cycle Malaria
125 plasmodium species, but only 5 can infect humans. Only P. falciparum is lethal.
Malaria parasites have an indirect life cycle: mosquitoes (definitive host) and humans.
In what kind of cell does it survive?
Liver cycle takes 6 days and only happens one time.
The red blood cycle is associated with the symptoms.
Parasite is in Blood Cell -> blood cell has no nucleus -> so parasites proteins are not visible for the
immune system
The mosquito cycle can take 9-10 days.
Parasite is not transmissible between humans, because you need the mosquito.
For diagnosis we use blood stages -> smears.
Lecture 2: Diagnostic Challenges in Parasitology
Dr. Lisette van Lieshout
Voorbereiding:
Important from article Verweij:
Real-time PCR significantly reduces the risk of contamination but also reduces labour time, which in a
busy diagnostic laboratory allows for task reallocation. Also possible to combine the detection of
different targets. Additionally, real-time PCR gives a (semi)-quantitative indication of the DNA
representing the parasite load in the sample.
In a Dutch laboratory receiving stool samples from patients presenting with gastrointestinal complaints
to the general practitioner the detection rate for Giardia lamblia increased from 5·7% to 9·3%
comparing microscopy and real-time PCR, respectively.
In rural nonindustrialized settings, differences between detection rates obtained by microscopy
compared with PCR can be more extreme; in Ecuador, Mejia et al. found 5·8% G. lamblia with
microscopy compared with 31·5% with real-time PCR
Or maybe better, PCR on one sample provides a true positive or negative test result with the same
confidence interval as obtained by microscopy of three samples. This implies that when PCR is used
in some cases pathogens remain undetected in a first sample and will only be detected in a second or
even a third sample.
A positive PCR result found with a high (> 35) Ct-value (i.e. a low DNA load).
Sometimes in the third sample the parasite DNA is detected, with a low DNA load. The question
remains, however, would a patient or medical practitioner be willing to wait with treatment against E.
histolytica even if detected at very low DNA load and be willing to take the risk of a liver abscess when
regarding a high Ct-value for E. histolytica as being negative?
Sometimes DNA can be present for very long time, for example, remaining Schistosoma eggs in the
gut wall could cause ‘leakage’ of parasitic DNA for longer periods. In a recent study in the
Netherlands, G. lamblia DNA could not be detected one week after metronidazole treatment in
children and adults that were diagnosed with giardiasis using real-time PCR.
One of the most discussed tensions between microscopy and molecular diagnostics is the overall
capacity of microscopy to detect ‘all’ parasites and the high target specificity of PCR, i.e. you’ll find
just the thing you are looking for and nothing more.
, One of the most appealing benefits of molecular diagnostics is the possibility of automation providing
a short sample-to-answer time with limited handson time. Furthermore, bacterial, viral and parasitic
targets can be detected using one overall technique combined in setting-specific panels.
Soil-transmitted helminths
- Parasitic worms: transmitted through soil contaminated with eggs
- 1.5 billion people in the world are infected with worms; mainly affecting poor and
disadvantaged communities in the world. They are common in tropical and subtropical
countries, where the circumstances are warm and moist and there is poor sanitation and
hygiene.
Three main types:
● Roundworms: Ascaris lumbricoides
● Whipworms: Trichuris trichiura
● Hookworms: Necator americanus and Ancylostoma duodenale
Transmission: Faeces with eggs -> soil -> infective form eggs (of roundworm or whipworm) or larvae
(from hookworms) -> eggs: mouth (food, water, hands); larvae: skin (walking barefoot)
People can be infected with more than one type of worms at the same time.
Worms can feed on tissues, blood or nutrients. This leads to blood loss, inflammation.
Diagnose: microscopic examination
Prevention: best long term strategies -> clean uncontaminated water etc.
Deworming has been effective. -> ½ times a year.
Schistosomiasis (Bilharzia)
Tropical disease. The parasitics worms are called schistosomes = blood flukes
- Over 200 million infected, over 200000 deaths each year.
- Life cycle includes: humans, snails and freshwater
- 5 types of schistosomes are responsible for most human diseases. They differ in distribution,
diseases they cause and types of snails they live in.
1. Schistosoma haematobium:
● mostly Africa and Middle East
● Urinary and genital disease
2. S. mansoni:
● mostly Africa, South America, Caribbean
● Bowel and liver
3. S. japonicum:
● China and South-East Asia
● Bowel and liver
4. S. mekongi:
● Cambodia and Laos
● Bowel and liver
5. S. guineensis:
● Central Africa
● Bowel and liver
Life cycle Schistosoma: infected humans pass schistosome eggs through their urine or feces into
fresh water. These eggs hatch into larvae and infect certain species of snail. After development in the
Lecture 1 introduction 2
Lecture 2: Diagnostic Challenges in Parasitology 3
Lecture 3: Pregnancy-associated Malaria 18
Lecture 4: Controlled Human Infection Models 24
Lecture 5: Metabolism of Parasites 1 26
Lecture 5.1: Metabolism of Parasites 2 33
Lecture 6: Malaria Transmission to Mosquitoes: A Bottleneck in Parasite Survival 38
Lecture 7: Survival Strategies of Parasites 43
Lecture 8: The Role of Helminth Parasites in the Hygiene Hypothesis anno 2018/2019 51
Lecture 9: Biology of Ectoparasites: Nuisance and their Role in Disease Transmission 57
Lecture 10: Emerging Zoonoses in the Netherlands 60
Lecture 11: Epidemiology, Prevention, and Control of Parasitic Diseases, an example:
Schistosomiasis 65
Lecture 12: T. Solium Elimination vs. Control: Field Experience in Zambia 73
,Lecture 1 introduction
Parasites: Eukaryotic organisms that have to live in or on other organisms (hosts) to complete its
natural life cycle. Doesn’t always cause harm; can also cause benefit. Main goal of parasites: is to get
to the next host. Medical Parasitology: eukaryotic organisms that infect human hosts
Symbiosis: organisms living together
Close association between two organisms; (micro)organisms and host
1. Commensalism: eating at the same table
Benefit is uni-directional -> (micro)organism benefits, host is neither harmed nor helped
2. Mutualism: a form of commensalism
Benefit is bi-directional -> (micro)organism & host benefits
3. Parasitism
Benefit is uni-directional -> (micro)organism benefits, host is harmed
Endoparasite: live in the host (protozoa and metazoa) → infection (ex. Plasmodium falciparum)
Ecto parasite: live on the host (Insecta (lice, fleas), Arachnida (mites, ticks)) → infestation (ex.
Pediculus humanus capitas; teek)
Facultative: the parasite may exist in a free living state
Obligate: the parasite cannot survive without its host
Different types of hosts
• Definitive host: in which sexual replication takes place
• Intermediate host: only asexual replication takes place (so no sexual replication)
• Accidental host: parasite is seldom found in this host (host was infected by ‘accident’)
Taenia solium: human is accidental and definitive host.
It is a hermaphrodite and can live on its own and reproduce themselves.
Protozoa: unicellular eukaryotes
• Rhizopods
• Cilliates
• Flagellates
• Sporozoans
organelles of locomotion
reproduction – binary fission or schizogony
Metazoa: helminths (multicellular)
• Trematodes (fluke)
• Cestodes (tapeworm):herma
• Nematodes (roundworm); either male/female + have
alimentary tract
Morphology, sex: or or hermaphroditic, alimentary tract
Protozoa can reproduce in the host; the population in
the host grows. Helminths don’t do that;
Helminths have a stable population, because if you are
infected with one egg, you get one parasite.
Life cycles: direct (One host)
Direct: parasites need ONE host to complete its life cycle.
E.g. Enterobius vermicularis: children -> get itchy around
the anus -> scratch and don’t wash hands -> parents get infected -> children get reinfected.
,Life cycles: indirect (2 or more hosts)
Indirect: parasites need TWO (or more) hosts to complete its life cycle.
E.g. Taenia solium or Taenia saginata
T. Solium: pig is intermediate host, humans are definitive host (you can see the adult worm), but
when infected with eggs humans can also be an intermediate/accidental (dead-end for parasite) host.
T. Solium is hermaphrodite; they can reproduce on their own, therefore sexual reproduction in
humans and therefore humans as definitive hosts.
Hermaphrodite: can reproduce itself.
Life cycle Malaria
125 plasmodium species, but only 5 can infect humans. Only P. falciparum is lethal.
Malaria parasites have an indirect life cycle: mosquitoes (definitive host) and humans.
In what kind of cell does it survive?
Liver cycle takes 6 days and only happens one time.
The red blood cycle is associated with the symptoms.
Parasite is in Blood Cell -> blood cell has no nucleus -> so parasites proteins are not visible for the
immune system
The mosquito cycle can take 9-10 days.
Parasite is not transmissible between humans, because you need the mosquito.
For diagnosis we use blood stages -> smears.
Lecture 2: Diagnostic Challenges in Parasitology
Dr. Lisette van Lieshout
Voorbereiding:
Important from article Verweij:
Real-time PCR significantly reduces the risk of contamination but also reduces labour time, which in a
busy diagnostic laboratory allows for task reallocation. Also possible to combine the detection of
different targets. Additionally, real-time PCR gives a (semi)-quantitative indication of the DNA
representing the parasite load in the sample.
In a Dutch laboratory receiving stool samples from patients presenting with gastrointestinal complaints
to the general practitioner the detection rate for Giardia lamblia increased from 5·7% to 9·3%
comparing microscopy and real-time PCR, respectively.
In rural nonindustrialized settings, differences between detection rates obtained by microscopy
compared with PCR can be more extreme; in Ecuador, Mejia et al. found 5·8% G. lamblia with
microscopy compared with 31·5% with real-time PCR
Or maybe better, PCR on one sample provides a true positive or negative test result with the same
confidence interval as obtained by microscopy of three samples. This implies that when PCR is used
in some cases pathogens remain undetected in a first sample and will only be detected in a second or
even a third sample.
A positive PCR result found with a high (> 35) Ct-value (i.e. a low DNA load).
Sometimes in the third sample the parasite DNA is detected, with a low DNA load. The question
remains, however, would a patient or medical practitioner be willing to wait with treatment against E.
histolytica even if detected at very low DNA load and be willing to take the risk of a liver abscess when
regarding a high Ct-value for E. histolytica as being negative?
Sometimes DNA can be present for very long time, for example, remaining Schistosoma eggs in the
gut wall could cause ‘leakage’ of parasitic DNA for longer periods. In a recent study in the
Netherlands, G. lamblia DNA could not be detected one week after metronidazole treatment in
children and adults that were diagnosed with giardiasis using real-time PCR.
One of the most discussed tensions between microscopy and molecular diagnostics is the overall
capacity of microscopy to detect ‘all’ parasites and the high target specificity of PCR, i.e. you’ll find
just the thing you are looking for and nothing more.
, One of the most appealing benefits of molecular diagnostics is the possibility of automation providing
a short sample-to-answer time with limited handson time. Furthermore, bacterial, viral and parasitic
targets can be detected using one overall technique combined in setting-specific panels.
Soil-transmitted helminths
- Parasitic worms: transmitted through soil contaminated with eggs
- 1.5 billion people in the world are infected with worms; mainly affecting poor and
disadvantaged communities in the world. They are common in tropical and subtropical
countries, where the circumstances are warm and moist and there is poor sanitation and
hygiene.
Three main types:
● Roundworms: Ascaris lumbricoides
● Whipworms: Trichuris trichiura
● Hookworms: Necator americanus and Ancylostoma duodenale
Transmission: Faeces with eggs -> soil -> infective form eggs (of roundworm or whipworm) or larvae
(from hookworms) -> eggs: mouth (food, water, hands); larvae: skin (walking barefoot)
People can be infected with more than one type of worms at the same time.
Worms can feed on tissues, blood or nutrients. This leads to blood loss, inflammation.
Diagnose: microscopic examination
Prevention: best long term strategies -> clean uncontaminated water etc.
Deworming has been effective. -> ½ times a year.
Schistosomiasis (Bilharzia)
Tropical disease. The parasitics worms are called schistosomes = blood flukes
- Over 200 million infected, over 200000 deaths each year.
- Life cycle includes: humans, snails and freshwater
- 5 types of schistosomes are responsible for most human diseases. They differ in distribution,
diseases they cause and types of snails they live in.
1. Schistosoma haematobium:
● mostly Africa and Middle East
● Urinary and genital disease
2. S. mansoni:
● mostly Africa, South America, Caribbean
● Bowel and liver
3. S. japonicum:
● China and South-East Asia
● Bowel and liver
4. S. mekongi:
● Cambodia and Laos
● Bowel and liver
5. S. guineensis:
● Central Africa
● Bowel and liver
Life cycle Schistosoma: infected humans pass schistosome eggs through their urine or feces into
fresh water. These eggs hatch into larvae and infect certain species of snail. After development in the
