Inhoudsopgave
,Introduction: Classification, life cycles &
definitions
Definitions
Parasites: Eukaryotic organisms that have to live in or on other organisms to complete their natural
life cycle.
Medical parasitology: Eukaryotic organisms that infect humans hosts.
Symbiosis
Symbiosis: Organisms living together Close association between two organisms; Microorganisms
and host. Three forms of symbiosis:
Commensalism: Benefit is uni-directional Microorganism benefits, host is neither harmed
nor helped.
Mutualism: Benefit is bi-directional Microorganism and host benefit.
Parasitism: Benefit is uni-directional Microorganism benefits, host is harmed
Type of parasites
Endo- vs ectoparasites
Endoparasites: Live IN the host Leads to infection.
o Protozoa (unicellular):
Size: 1-100 uM
Intra- or extracellular
Sexual or asexual reproduction in host
Increase parasite load
Classification based on movement organelles and type of reproduction
Types:
Rhizopods
Cilliates
Flagellates
Sporozoans
o Metazoa (multicellular):
Size: mm – meters
Hermaphroditic or males and females
Reproduction: Eggs or larvae
Stable population
Classification based on morphology, sex and digestive tract
Types:
Trematodes (flukes)
Cestodes (tapeworms) Flat worms and hermaphroditic (they can
still produce off-spring with only one egg)
Nematodes (roundworms)
Ectoparasites: Live ON the host Leads to infestation.
, o Insecta (lice, fleas)
o Arachnida (mites, ticks)
Obligate vs facultative parasites
Obligate: The parasite cannot survive without its host.
Facultative: The parasite may exist in a free living state.
Type of hosts
Definitive host: In which sexual reproduction takes place, that is, the fertilization process.
Two gametes form a zygote. This is preceded by sexual multiplication/gametogony
(formation of gametes). If in a host only sexual multiplication takes place (such as in malaria)
and not fertilization, it’s not a definitive host but an intermediate host.
Sexual multiplication and fertilization are two distinct processes in sexual reproduction.
Intermediate host: In which asexual reproduction takes place.
Accidental host: Parasite is seldom found in this host (host was infected by accident)
These hosts are often a dead end and the lifecycle stops here. In these hosts, often disease is
caused which is neither beneficial for the hosts nor the parasite as disease can cause death.
Life cycles
Direct: Parasite needs only one host to complete its life cycle.
o Enterobius vermicularis Fecal-oral auto-infection.
Indirect: Parasite needs two (or more) hosts to complete its life cycle (often an intermediate
and definitive host).
o T. saginata and solium Humans are the definitive host. Fecal-oral auto-infection is
possible.
,Lecture 2: Diagnostic Challenges in
Parasitology
Diagnostic Research in Parasitology
Intestinal protozoa
Malaria
Soil Transmitted Helminths
Schistosomiasis
Characteristics of protozoa
Single cell organism: 1-100 uM You need a microscope to visualize them.
Intra- and extracellular.
Multiply within host
Lifecycle and reproduction
Schizogony/sporogony: In malaria; or binary fission: In Entamoeba/Giardia (intestinal
protozoa). In Giardia:
o Trophozoites:
Vegetative: motile, feeding
Asexual reproduction.
Causing the pathology.
Disintegrate: it can’t survive outside
the host and therefore is difficult to
detect in feces.
o Cyst formation (= dormant stage):
Decreased metabolism, rounding,
external cell wall
Resistance to environment
Transmission of infection (auto-
infection or to another person).
Cysts differ from oocysts Oocysts
are not dormant.
Characteristics of helminths
Mm to meters.
Multi-cellular adult stage.
Multiple organs.
Lifecycle and reproduction
Adult worms: Hermaphrodite or separate sex.
Produce eggs or larvae.
Eggs or larvae leave the host To complete the lifecycle (sometimes elsewhere, such as in
an intermediate host).
It’s a stable population, unless there’s repeated exposure. Quantification is possible.
, Often cause chronic disease.
o Depending on the worm load.
Intestinal protozoa
Diarrhea causing protozoa:
o Entamoeba histolytica
o Giardia lamblia
o Cryptosporidium parvum/C. hominis
Entamoeba histolytica Giardia lamblia Cryptosporidium parvum
Travellers Endemic in Netherlands Endemic in Netherlands
Relatives, family members (children) (children)
Travellers Water-related outbreaks
Potentially invasive
Bloody diarrhea (only E. Gastro-intestinal complaints Gastro-intestinal complaints
Clinical aspects
histolytica, E. dispar is not Malabsorption Sticking to Chronic diarrhea
invasive) intestine wall Self-limiting in healthy
Abdominal pains (Chronic) diarrhea individuals
Liver abscess Severe in non-immuno
competent
Trophozoites can be visible when
stool is very fresh or is fixed.
Then the trophozoites won’t
Microscopy
disintegrate.
diagnosis
Cysts of different species of
Entamoeba can’t be
differentiated under the
Microscopic microscope. This also goes for
problems the small trophozoites. Large
trophozoites can ingest red
blood cells. Only histolytica can
do this.
Diagnosis 1. Microscopy:
Advantages: Available, affordable, specificity (not for E. histolytica: false positive for one of the types).
Disadvantages: Sensitivity (false negatives; need at least 3 stool samples for confirmation), specificity for
, E. histolytica (no distinction possible between species), and staining procedures.
2. Serology (Antibody detection: ELISA) A reaction of the host to the invaders and this takes some
time:
Advantages: Fast, sensitive
Disadvantages: Only for invasive species (such as E. hystolitica), miss non-targeted parasites (because it’s
very specific), however a-specific after treatment Cross-reactivity with other antibodies and the
presence of antibodies for a long time (false positives), and not always sensitive.
3. Antigen detection (ELISA or Rapid Test) Molecules excreted by the pathogen:
Advantages: Fast, sensitive (that is, more than microscopy; only 1 stool sample required), less training
required, reproducible.
Disadvantages: Sensitivity still not optimal (some infections are still missed; false negatives), miss non-
targeted parasites and costs.
4. Molecular diagnosis (q-PCR) Pathogen DNA:
Advantages: Fast, sensitive & specific, multiplex setting, reproducible, (semi) quantitative, high
throughput, QC options.
Disadvantages: Molecular set-up of laboratory. This is not feasible in developing countries.
Microscopy can be an additional tool for travelers:
Malaria
Plasmodium falciparum is the most dangerous species.
Mainly in tropical regions.
Children, pregnant women and travelers are at risk, because they are immunological naive.
Seroconversion (production of Abs) is too late (approx. 10 days) to fight the disease.
Microscopy
Detection of the parasite in a blood sample:
1. Thick blood smear:
