PPT 1 - PARA Flashcards by Atasha Mae Aposaga

Medical Parasitology consists of?

Protozoa
Helminths
Arthropods

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Six major tropical diseases to which WHO pays great
attention include? All of them are parasitic except? Where are they prevalent?

⚫ malaria,
⚫ schistosomiasis,
⚫ filariasis,
⚫ leishmaniasis,
⚫ trypanosomiasis and
⚫ leprosy.

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⚫ Any association more or less permanent is called a
symbiosis, with each member a symbiont.
⚫ Two different organisms live together and interact
⚫ one partner lives in or on another one’s body.

Symbiosis

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Three types of symbiosis.

⚫ Mutualism
⚫ Commensalism
⚫ Parasitism

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⚫ Permanent association between two different
organisms that life apart is impossible,
⚫ Two partners benefit each other,
⚫ The mutuals are metabolically dependent on one
another;
⚫ One cannot survive in the absence of the other.

Mutualism

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⚫ Association of two different organisms
⚫ One partner is benefited while the other neither
benefited nor injured, such as E. coli and man.

Commensalism

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⚫ Association of two different organisms
⚫ One partner is benefited while the other is injured,
such as Ascaris lumbricoides and man.

Parasitism

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It is an animal organism which lives in or on the host in order to obtain nourishment and shelter from the host as well as does harms to the host.

Parasite

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A small organism () has the potential to harm a larger organism () and relies on it for nutrients and shelter (_).

Parasite, host, niche

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Types of Parasites according to their habitat.

Endoparasite, Ectoparasite

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⚫ Lives inside the body of the host
⚫ May be just under the surface or deep in the body
⚫ Tapeworms, flukes, protozoans

Endoparasite

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⚫ Stays on outside surface of the host
⚫ leeches, ticks, fleas, brood parasites

Ectoparasite

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Types of parasites based on dependency on the host.

Obligate parasite, facultative parasite

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⚫ Requires finding and invading the host to complete its
life cycle
⚫ Most of the parasites we will cover

Obligate parasite

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⚫ May become parasitic if it is given the chance but does
not require a host.

Facultative parasite

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Types of parasites based on amount of time spent.

Permanent parasite, temporary parasite

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⚫ Lives entire adult life stage on or in a host
⚫ Usually endoparasites
⚫ One exception is eyelash mite

Permanent parasite

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⚫ Spends only a short time on a host
⚫ Usually ectoparasites

Temporary parasite

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Types of parasites according to their pathogenicity.

Pathogenic parasites, non-pathogenic parasites, opportunistic parasites.

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• Cause disease in the host.
• Can lead to significant symptoms, tissue damage, or organ dysfunction.
• Example: Plasmodium (causes malaria).

Pathogenic parasites

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• Live in or on the host without causing harm.
• Do not trigger disease under normal conditions.
• Example: Entamoeba coli (found in the human intestine but does not cause disease).

Non-pathogenic parasites

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• Usually harmless but can cause disease in immunocompromised hosts.
• Take advantage of weakened immune systems, poor health, or disrupted microbiomes.
• Example: Toxoplasma gondii (harmless in healthy individuals but dangerous for those with weakened immunity, such as HIV/AIDS patients).

Opportunistic parasites

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Types of parasites based on their life cycle.

Monoxenous, heteroxenous, heterogenetic

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⚫ Those with direct life cycles (i.e., with one host).

Monoxenous

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⚫ Those with indirect life cycles requiring an intermediate host (i.e., involves 2 or more hosts).

Heteroxenous

⚫ One with alteration of generations e.g., Coccidial parasites and Strongyloides.

Heterogenetic

Types of parasites based on their host range.

Euryxenous, stenoxenous

⚫ Those with a broad host range.

Euryxenous parasites

⚫ Those with a narrow host range.

Stenoxenous parasites

⚫ Found in locations in the host where they normally do not occur; ⚫ e.g., Ascaris larvae may migrate to the brain

Aberrant parasite

⚫ Occurs in hosts where it does not normally occur; ⚫ e.g., Fasciola normally does not occur in man but is incidental if found in man’s liver.

Incidental parasite

Examples of aberrant and incidental parasite

e.g., Ascaris larvae may migrate to the brain e.g., Fasciola normally does not occur in man but is incidental if found in man’s liver.

Are organism which harbors the parasite, the injured partner.

Host

Types of Hosts

⚫ Definitive host: ⚫ Intermediate host:

⚫ Where sexual reproduction takes place. ⚫ Normally where the adult parasites live. ⚫ Normally the larger of the hosts, usually a vertebrate. ⚫ Convention - (parasites which only reproduce asexually) ⚫ Specificity - frequently, a large number of host species can act as intermediate host and only one or a few can act as a definitive host.

Definitive host

⚫ sexually immature or larval stage of a parasite ⚫ Asexual multiplication takes place ⚫ may harbor many immature stages of a parasite; ⚫ e.g., Cercaria, Redia and Sporocysts which are all immature stages of Fasciola in the snail intermediate host. ⚫ Some parasites: ⚫ require more than one intermediate host which are then designated as first, second intermediate,

Intermediate host

Example of paratenic host.

Toxoplasm species in cattle

⚫ No development occurs but parasite remains alive and infective to another host ⚫ May go dormant ⚫ May cause damage

Paratenic or Transport Host

⚫ Parasite is in the “wrong” species. ⚫ Parasite usually wanders around and causes great damage because it doesn’t know where to go then dies.

Accidental or Incidental Host

⚫ Any animal that carries a parasite that can cause infections in humans. ⚫ Even if it is the normal host for that parasite. ⚫ Related to the medical perspective of parasitology

Reservoir Host

⚫ A person who harbors parasites has no any clinical symptom. He is an important source of infection in epidemiology Example??

Carrier Host e.g. human beings harboring cyst form of E.histolytica

⚫ The number of species the parasite can use as a definitive or intermediate host. ⚫ Parasites show varying degrees of host specificity ⚫ A few parasites will infect only one species ⚫ Most parasites will infect a few closely related species (or similar anatomy) ⚫ Some parasites can infect a large group of animals ⚫ A few parasites have little or no host specificity.

Host Specificity

an organism (usually an arthropod) which transfers infective forms of a parasite from one host to the other.

Vector

Classification of vectors.

1. Biological vectors:- 2. Mechanical (Parathenic or transport) Vectors

⚫ characterized by the development of the parasite before its transfer to another host

Biological vector

Three under biological vectors and give examples each.

Propagative, cyclopropagative, cyclodevelopmental

• The parasite multiplies inside the vector but does not undergo developmental changes. • Example: Yersinia pestis (causes plague) multiplies in the digestive tract of fleas before being transmitted to humans.

Propagative

• The parasite multiplies and undergoes developmental changes inside the vector before being passed to the next host. • Example: Plasmodium vivax (malaria-causing parasite) undergoes both multiplication and development inside Anopheles mosquitoes before transmission to humans.

Cyclopropagative

• The parasite undergoes development but does not multiply inside the vector. • Example: Onchocerca volvulus (causes river blindness) develops inside black flies (Simulium species) before being transmitted to humans.

Cyclodevelopmental

⚫ no parasitic development of reproduction occurs

Mechanical vector

⚫ No development occurs but parasite remains alive and infective to another host ⚫ May go dormant ⚫ May cause damage

Paratenic host

it is a stage when a parasite can invade human body and continue to live there. The infective stage of ascarid is the embryonate egg.

Infective Stage

the specific entrance through which the parasite invades the human body. Hookworms invade human body by skin. Man gets infection with ascarid by mouth.

Infective Route

means how the parasite invades human body, such as the cercariae of the blood fluke actively penetrate the skin of a swimming man and the infective ascaris eggs are swallowed by man.

Infective mode

⚫ refers to the helminths which complete their life cycles not requiring the processes of the development in intermediate hosts. ⚫ They have only one host and a simple life cycle, such as ascarid, hookworm, pinworm and etc.

Geohelminth

⚫ refers to the helminths which have to undergo the development in intermediate hosts to complete their life cycles, such as filaria, liver fluke, pork tapeworm and so on

Biohelminth

⚫ In life cycles of some parasites, there is the regular alternation of sexual and asexual reproductions, e.g. Plasmodium vivax

Alternation of Generation

is a living stage of protozoa when they can move, take food and reproduce. (It is usually the pathogenic stage.)

Trophozoite

is the resting stage of a protozoa with a protective wall. It is usually the infective stage. Its functions are protection, transmission and multiplication.

Cyst

Process where protozoa form a cysts

Encystation

Process where a protozoa emerge from cysts.

Excystation

The study of the patterns of diseases within populations

Epidemiology

A small ecosystem that possesses all the factors to maintain the parasite.

Nidus

⚫ parasite occur globally, ⚫ the majority occur in tropical regions,

Global distribution

Factors in Geographic Distribution

⚫ Favorable environmental conditions ⚫ poverty, poor sanitation and personal hygiene

Factors (Endemicity):

1. Presence of a suitable host 2. Habits of the host 3. Escape from the host 4. Favorable conditions outside of host 5. Economic and social conditions

Three key links of parasitic disease transmission

⚫ 1. Source of infection ⚫ 2. Mode of transmission ⚫ 3. Susceptible people

⚫ infected persons ⚫ carriers ⚫ animals

Primary source

Sources of Exposure in Parasitic Infections

1. Contaminated soil 2. Contaminated water 3. Raw or Insufficiently cooked meat of pork, beef, and fish 4. Blood-sucking arthropods 5. Animals (domestic or wild animals harboring the parasite), 6. Human beings:

Direct mode of transmission are classified as?

Horizontal direct mode of transmission Vertical direct mode of transmission

Transmission is mainly effected through:- ⚫ Fecal-oral route: most intestinal parasites transmitted in this way. ⚫ Sexual intercourse ⚫ Blood transfusion ⚫ Direct skin penetration

Horizontal direct mode of transmission Vertical

Transmission of the parasite is from the mother to child through: ⚫ Congenital / transplacental ⚫ Transmammary (breast milk)

Vertical Direct Mode of Transmission:

If the parasite ⚫ has complex life cycle ⚫ requires biological vectors and/or ⚫ one or more intermediate hosts

Indirect Mode of Transmission

⚫ requires 2 or more hosts (a vector or intermediate host ) to reproduce or grow in ⚫ Frequently this may involve passing through a number of developmental stages & Event

Indirect or heteroxenous life cycles

⚫ only one host is required to complete its cycle ⚫ the parasite often spends most of its life, usually as an adult, and where it reproduces ⚫ Transmitted from one host to another through the air, by a fomite, or in contaminated food or water.

Simple or Direct Life Cycle (monoxenous)

⚫ Common for bacteria and small protozoa

Macrophage endocytosis

rare parasites have been associated with cancer, but mechanisms are still unknown

Neoplasia (cancer)

edema and increase of leukocytes

Acute

monocytes and lymphocytes present, with fibrocytes binding parasite with collagen.

Subacute

plasma cells present and form a granuloma

Chronic

Round worms; appear round in cross section, they have body cavities, a straight alimentary canal and an anus

Nematodes

Flat worms; dorsoventrally flattened, no body cavity and, if present, the alimentary canal is blind ending

Platyhelminthes

Adult tapeworms are found in the intestine of their host They have a head (scolex) with sucking organs, a segmented body but no alimentary canal Each body segment is hermaphroditic

Cestodes

Non-segmented, usually leaf-shaped, with two suckers but no distinct head They have an alimentary canal and are usually hermaphroditic and leaf shaped Schistosomes are the exception. They are thread-like, and have separate sexes.

Trematodes

PPT 1 - PARA Flashcards

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