LECTURES PARASITOLOGY
LECTURE 1: CLASSIFICATION, LIFE CYCLES AND 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; (Micro)organisms and host.
- Commensalism: ‘eating at the same table’
o Benefit is uni-directional → Microorganism benefits, host is neither harmed nor helped.
- Mutualism:
o Benefit is bi-directional → Microorganism and host benefit.
- Parasitism:
o Benefit is uni-directional → Microorganism benefits, host is harmed
TYPE OF PARASITES
ENDO- VS ECTOPARASITES
- Endoparasites: Live IN the host → infection
o Protozoa (unicellular eukaryotes):
▪ Size: 1-100 uM
▪ Intra- or extracellular
▪ Sexual or asexual reproduction in host → binary fission of schizogony
▪ 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 → 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.
o 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.
o 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)
o 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 definitive host
▪ Fecal-oral auto-infection is possible
,LECTURE 2: DIAGNOSTIC CHALLENGES IN PARASITOLOGY
Lecture clips:
INTRODUCTION DIAGNOSTIC RESEARCH
PROTOZOA
Characteristics of protozoa
- single cell organism; 1-100 µm
o microscope needed to see
- intra/extra cellular
- multiply within host
- schizogony/sporogony or binary fission
Lifestyle and reproduction:
Plasmodium: schizogony →
Intestinal protozoa, like Entamoeba/Giardia: 2 stages:
- Trophozoites: moving around, causes morbidity
o Vegetative; motile, feeding
o asexual reproduction
o disintegrate → difficult to detect
- Cyst formation: dormant stage
o decreased metabolism; rounding, external cell wall
o resistance to environment => transmission of infection
HELMINTHS
Characteristics of helminths
- mm to meters
- multi cellular adult stage
- multiple organs
Lifecycle and reproduction
Adult worms: hermaphrodite or separate sex
- egg or larvae production
- eggs/larvae leave the host
- stable population => reflection of morbidity?
- Chronic disease
o depending on species adult worm 1 year => several decades
o the more worms, the more disease
INTESTINAL PROTOZOA DIAGNOSTIC RESEARCH
Diarrhoea causing protozoa
- Entamoeba histolytica
- Giardia lamblia
, - Cryptosporidium parvum/C. hominis
Clinical aspects: Entamoeba histolytica
- Travellers
- Relatives, family members: micro outbreaks in households
- Potentially invasive: ulcers intestines, bloody diarrhoea
- Abdominal pains, dysentery
- Liver abscess
Clinical aspects: Giardia lamblia
- Endemic in Netherlands (children)
- Travellers
- Gastro-intestinal complaints
- Malabsorption
- (Chronic) diarrhoea
Clinical aspects: Cryptosporidium parvum/ C. hominis
- Endemic in Netherlands (children)
- Water related outbreaks → summer outbreaks
- Gastro-intestinal complaints chronic diarrhoea
- Self limiting in healthy individuals
- Severe in non-immono competent
- Detection of Oocyst via acid fast staining
Microscopy diagnosis of diarrhoea causing protozoa
- Cysts and trophozoites can be found in faeces
- Trophozoites cannot survive in environment → disintegrate within an hour
o Mix stool with fixative → will still be visible
Specific problem microscopic diagnosis of E. histolytica
- Entamoeba hystolica and dispar not morpholically distinguishable
- Dispar causes no diarrhoea
- Only histolytica can go into red blood cells: hematophagous → differentiate from dispar
Microscopy
- Advantages:
o Available
o Affordable
o Specificity (not for E. histolytica)
- Disadvantages:
o Sensitivity!!!!: Day to day variation in parasites → 3 different samples from 3 different days
o Specificity for E. histolytica
o Staining procedures
Antibody detection (serology)
- Advantages:
o Fast
LECTURE 1: CLASSIFICATION, LIFE CYCLES AND 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; (Micro)organisms and host.
- Commensalism: ‘eating at the same table’
o Benefit is uni-directional → Microorganism benefits, host is neither harmed nor helped.
- Mutualism:
o Benefit is bi-directional → Microorganism and host benefit.
- Parasitism:
o Benefit is uni-directional → Microorganism benefits, host is harmed
TYPE OF PARASITES
ENDO- VS ECTOPARASITES
- Endoparasites: Live IN the host → infection
o Protozoa (unicellular eukaryotes):
▪ Size: 1-100 uM
▪ Intra- or extracellular
▪ Sexual or asexual reproduction in host → binary fission of schizogony
▪ 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 → 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.
o 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.
o 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)
o 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 definitive host
▪ Fecal-oral auto-infection is possible
,LECTURE 2: DIAGNOSTIC CHALLENGES IN PARASITOLOGY
Lecture clips:
INTRODUCTION DIAGNOSTIC RESEARCH
PROTOZOA
Characteristics of protozoa
- single cell organism; 1-100 µm
o microscope needed to see
- intra/extra cellular
- multiply within host
- schizogony/sporogony or binary fission
Lifestyle and reproduction:
Plasmodium: schizogony →
Intestinal protozoa, like Entamoeba/Giardia: 2 stages:
- Trophozoites: moving around, causes morbidity
o Vegetative; motile, feeding
o asexual reproduction
o disintegrate → difficult to detect
- Cyst formation: dormant stage
o decreased metabolism; rounding, external cell wall
o resistance to environment => transmission of infection
HELMINTHS
Characteristics of helminths
- mm to meters
- multi cellular adult stage
- multiple organs
Lifecycle and reproduction
Adult worms: hermaphrodite or separate sex
- egg or larvae production
- eggs/larvae leave the host
- stable population => reflection of morbidity?
- Chronic disease
o depending on species adult worm 1 year => several decades
o the more worms, the more disease
INTESTINAL PROTOZOA DIAGNOSTIC RESEARCH
Diarrhoea causing protozoa
- Entamoeba histolytica
- Giardia lamblia
, - Cryptosporidium parvum/C. hominis
Clinical aspects: Entamoeba histolytica
- Travellers
- Relatives, family members: micro outbreaks in households
- Potentially invasive: ulcers intestines, bloody diarrhoea
- Abdominal pains, dysentery
- Liver abscess
Clinical aspects: Giardia lamblia
- Endemic in Netherlands (children)
- Travellers
- Gastro-intestinal complaints
- Malabsorption
- (Chronic) diarrhoea
Clinical aspects: Cryptosporidium parvum/ C. hominis
- Endemic in Netherlands (children)
- Water related outbreaks → summer outbreaks
- Gastro-intestinal complaints chronic diarrhoea
- Self limiting in healthy individuals
- Severe in non-immono competent
- Detection of Oocyst via acid fast staining
Microscopy diagnosis of diarrhoea causing protozoa
- Cysts and trophozoites can be found in faeces
- Trophozoites cannot survive in environment → disintegrate within an hour
o Mix stool with fixative → will still be visible
Specific problem microscopic diagnosis of E. histolytica
- Entamoeba hystolica and dispar not morpholically distinguishable
- Dispar causes no diarrhoea
- Only histolytica can go into red blood cells: hematophagous → differentiate from dispar
Microscopy
- Advantages:
o Available
o Affordable
o Specificity (not for E. histolytica)
- Disadvantages:
o Sensitivity!!!!: Day to day variation in parasites → 3 different samples from 3 different days
o Specificity for E. histolytica
o Staining procedures
Antibody detection (serology)
- Advantages:
o Fast
