Section 1: Parasites

Learning Outcomes: Compare the direct and indirect lifestyles of a parasite. Describe the role of vectors in the transmission of parasites. Describe the methods for the diagnosis and control of parasites in a clinical setting. Discuss the impact globally of parasites in healthcare.

oocyte def.

Oocyte : a cell in an ovary that may undergo meiotic division to form an ovum  

Trophozoite

• Trophozoite : a growing stage in the life cycle of some protozoan parasites, when they are absorbing nutrients from the host 

• Cyst

• Cyst : a stage in the life of certain parasites, during which they are involved in a protective wall 

Intermediate host

• Intermediate host : an organism that supports the immature or nonreproductive forms of a parasite 

Definitive host

• Definitive host : an organism that supports the adult or sezual reproductive form of a parasite 

Tachyzoite

• Tachyzoite : a cellular protozoan stage where organisms are motile, quickly multiplying, spreading through the blood, and responsible for population expansion  

Bradyzoite

• Bradyzoite (s) : the slowly dividing stage of the parasite that make up tissue cysts 

what is a parasite

• Parasites are organisms that live on or in another organism, the host, and derive a benefit and/or nutrients at the expense of the host.

T or F : parasites are not considered part of the normal flora 

T

what are the four ways parasites can be acquired

• Bites (tick, mosquito (malaria) )

• Water (ex Giardia lambilia) 

• Environment (ex strongyliodes stercoralis, contaminated soil) 

• Food (ex diphylobothrium latum contaminated fish) 

Based on location, how are parasites divided

1. Endoparasites 

2. Ectoparasites

what classification of parasite is this?

• Live within the host and cause infections 

• Anaerobic respiration 

• Usually permanent unless medical intervention (completed lifecycle in the host) 

• Undergo specialization to maximize their nutrient absorption Ex : loss of anus in flatworms and integument in helminths 

1. Endoparasites 

what type of respirtation do Endoparasites use

1. Anaerobic respiration (no o2)

T or F: Endoparasites are no permanent even without medical intervention

Usually permanent unless medical intervention (completed lifecycle in the host) 

what classification of parasite is this :

1.  live on the host and cause an infestation. 

2. aerobic respiration and can be temporary, intermittent, or permanent.

3. they do not have a readily available source of nutrients → acquired adaptations, such as penetrating the skin, to acquire their nutrients.

Ectoparasites, also known as exoparasites

example of Ectoparasites, also known as exoparasites

1. Examples of ectoparasites include fleas or lice. 

what type of respiration do ectoparasites use

aerobic respiration and can be temporary, intermittent, or permanent

T or F: There is generally less adaptation in ectoparasites when compared to endoparasites, but specialization does occur.

T: ectoparasites do not have a readily available source of nutrients → acquired adaptations, such as penetrating the skin, to acquire their nutrients.

give the pros and cons of endoparasites

• Endoparasites :are protected from the external environment because they are inside their host and can more easily access nutrients

  • BUT These organisms do have to deal with the host immune system and have troubles dispersing throughout their host.

give the pros and cons of ectoparasites

ectoparasites are protected against the host immune system and can be easily dispersed. 

• BUT vulnerable to the external environment and have difficulty feeding

what are the 2 divison of endoparasites

Endoparasites: Protozoa (single celled) and Helminths (multicellular)

are protozoa single or multicellualr

single celled

are helminths single celled or multicellular

multicellular

T or F: protozoa are single cells eukaryotic organisms 

T: Usually microscopic 

Protozoa examples (3)

• Plasmodium spp.

• Giardia spp

• Toxoplasma spp.

what is Plasmodium spp.

protozoa endoparasite Causes malaria via a vector mosquito 

what is Giardia spp

protozoa endoparasite

• Causes giardiasis (abdominal pain and diarrhea)

• Colonizing small intestine 

what is toxoplasma spp

protozoa endoparasite

causes toxoplasmosis

T or F: Helminths are large, multicellular organisms 

T: visible to the naked eye in their adult stages 

T or F: helminths proliferate within their host

F: do not proliferate within their hosts. Worms develop slowly, so any resultant diseases are slow-onset and chronic.

Examples of helminths (3)

• Cestodes

• trematodes

• nematodes

what helminths is this :

• Flatworm parasites most tape worms 

• Flat segmented worms 

• Live in intestines 

• Transmission by eating undercooked meat 

• asymptomatic can have diarrhea, vomiting, weight loss, abdominal discomfort 

Cestodes

what helminths is this?

• AKA flukes 

• Infect blood vessels, lungs, GI tract, liver 

• Ex : schistosoma spp → infects blood → schistosomiasis 

• Trematodes

what helminthis is this?

• Round worm 

• Contaminated food and water 

• Ex Stronglyoides spp  

• Ex Enterobius vermicularis 

Nematodes

What is a further classification of ectoparasites?

Arthropods

what are Arthropods characterists

• Exoskeleton 

• Segmented body 

• Paired jointed limbs 

• 2 types

what are the 2 types of arthopods

• Two types

  • 1) 6 legged insects : fleas, flies, lice which actively feed on host tissues and fluids 

  • 2) 8 legged arachnids: ticks and mites (which bite into tissues and feed off of host fluids) 

fleas, flies, lice are examples of what type of arthropods?

• 1) 6 legged insects : fleas, flies, lice which actively feed on host tissues and fluids 

ticks and mites are examples of what types of arthropods

8 legged arachnids: (which bite into tissues and feed off of host fluids) 

what kind of tissue do arthropods bite on too? what does that cause?

Bite dermal tissues = inflammation and hypersensitivity reactions 

T or F arthropods are either: Are either histophagus (tissue feeding ) or hematophagus blood sucking

T:

T or F: arthropods are usally involved either pathogen or vector 

T

what are 2 examples of arthropods

• Scaroptes scapiei : 

• Pediclus humanus 

what arthropod is this?

• an arthropod responsible for scabies, a contagious skin infestation that is also known as the seven-year itch.

• severe itchiness and a rash. Occasionally, tiny burrows may be seen in the skin.

• Scaroptes scapiei : 

T or F: lice feed on human blood

T: ediclus humanus 

• Human lice 

• Body or head 

  • Pediculus humanus corporis, which causes body lice 

  • Pediculus humanus capitis, which causes head lice

• Feed on human blood 

T or F: Pediculus humanus corporis causes head lice

T: Pediculus humanus corporis, which causes body lice 

• Pediculus humanus capitis, which causes head lice

breifly review the classifications of parasites

what is the difference btw a Facultative Parasites and an Obligate Parasites 

• Facultative Parasites 

  • Free living state or as a non parasite (commensal even) 

  • May be parasitic only during certain part of life cycle and free living other times  

• Obligate Parasites 

  • Can not survive as a free living 

  • Needs host to survive 

T or F: oligate parasite will often kill host quickly

F: Need to preserve the health of the host 

• Do not often result in death of host (bc need them for food and replication) 

  • however not the case when death of the host is need to be transmitted 

what are the 3 roles that host can take on in relation to the parasite 

1. Primary host / definitive host

2. Secondary host 

3. Reservoir host 

what type of host?

1. Host serves a source of infection 

2. Host has the infective stages of the parasite development but the parasite does not develop or cause disease here

Reservoir host 

what type of host?

1. Parasite reaches adult/sexual mature stage in

2. Can undergo sexual reproduction in the host

1. Primary host / definintive

what type of host?

1. Harbours larval/immature/asexual stages of parasite 

2. Undergoes asexual reproduction in a secondary host 

1. Secondary host 

Direct life cycle needs how many hosts

only need one host 

Indirect life cycle needs how many hosts

• 1+ intermediate host 

what are namatode trichostronglyus 

• Roundworm nematode in the intestines

what type of life cycle direct or indirect

1. Once in the host = lay eggs (ex if in the GI → eventually passed via stool) 

2. Eggs hatch → larva released in rhabditiform stage (early development not infective yet)(grown in feces or soil)

3. 5-10 days larvae = filariform larvae = infective 

4. Human host contact → larvae go through skin of feet → BV → heart → lungs → pulmonary alveoli → ascend the bronchial tree → pharynx → swallowed   

5. Larvae reach intestines, reside and mature into adults and live in the digestive tract 

Direct Life Cycle of namatode trichostronglyus 

what type of life cycle direct or indirect?

1. Unsporulated oocytes of the parasite are shed in the cat’s feces 

2. Oocytes takes 1-5 days to sporulate = infective, intermediate host = animal that ingest contaminated soil, water, plant material become infected 

3. Oocytes → tachyzoites after ingestion by intermediate host and localize in neural and muscle tissue → tissue cysts bradyzoites 

4. Cats become infected by consuming intermediate host that have tissue cysts (rats, birds, etc) 

5. Animals that humans eat can also become infected after eating sporulating oocysts from environment 

6. Humans get infected by: 

   1. By eating undercooked meat of animals harboring tissue cysts

   2. By consuming food or water contaminated with cat feces or by contaminated environmental samples

   3. By a blood transfusion or organ transplantation

   4. Transplacentally from mother to fetus

Stages of indirect Life Cycle : Toxoplasma gondii

what is a Tachyzoites

Tachyzoites: A cellular stage where organisms are motile, quickly multiplying, spreading through the blood, and responsible for population expansion.

what is a Bradyzoites

Bradyzoites: slowly dividing stage of the parasite that make up tissue cysts 

During the chronic portion of this stage, tachyzoites stage-convert to bradvoites to form tissue cysts

How do humans get infected by Toxoplasma gondii

Humans get infected by: 

1. By eating undercooked meat of animals harboring tissue cysts

2. By consuming food or water contaminated with cat feces or by contaminated environmental samples

3. By a blood transfusion or organ transplantation

4. Transplacentally from mother to fetus

order the life cycle of a direct life cycle

is the rhabditiform stage is non infective

The rhabditiform larva (first-stage or L₁ larva) of Strongyloides stercoralis is non-infective to humans, grown in feces or soil, eggs are hatched —> rhabditiform larva

filariform larvae form from what? are they infective?

egg —> rhabditiform larva —> filariform larvae ( they are infective)

order the life cycle of a indirect life cycle

what are tachyzoites formed from? fast or slow replication? are they infective? direct or indirect life cycle?

indirect life cycle (ex toxomplasma)

They are infective and transform from oocysts shortly after ingestion by an intermediate host

represent the rapidly dividing, mobile form of Toxoplasma gondii responsible for the acute phase of infection and systemic spread

tachyzoites —> bradyzoites

T or F: indirect life cycle parasites are easier to control

F: direct life cycle completes life cycle in 1 host. 

• easier to control with antiparasitic agents or interventions.

• indirect life cycle, need multiple hosts to complete their life cycle. 

  • tend to be more complex and more virulent as they have multiple hosts to continue propagation of infection. 

  • They don't have to worry about killing off their only host.

indirect life cycle sexual reproduction occurs exclusively inside the host.

(a lifecycle requiring two or more host species to complete),

definitive host

T or F: vectors are only biological

F: A vector transmits the parasite from host to host and can be either biological or mechanical 

T or F: Bio vectors are not needed for parasite to complete the life cycle 

F: Biological 

• Bio vectors are need for parasite to complete the life cycle 

• Mosquitoes 

• Ticks 

• Cats 

• Fish 

• Crabs 

what is a mechinical vector?

• Any unessential vectors to the parasites life 

• EX: 

  • Water 

  • Watercress

    • A dark leafy green grown in natural spring water 

Question: Give two examples of how an individual can become infected with a parasite, describing the mode of transmission and how the parasite replicates and matures. Include one example of a parasite with a direct life cycle and one example of a parasite with an indirect life cycle.