16 Parasitology Flashcards
Understand the concept of parasitism and parasitic infections
Parasitism: An association between the populations of two species in which the smaller (parasite) is physiologically dependent on the larger (host)
The parasite has:
- higher reproductive potential than host
- potention of harming host
Understand the concept of parasitism and parasitic infections
Parasites are organisms that live off other organisms, or hosts, to survive.
Some parasites don’t noticeably affect their hosts. Others grow, reproduce, or invade organ systems that make their hosts sick, resulting in a parasitic infection.
There are three main classes of parasites that can cause disease in humans
There are three main classes of parasites that can cause disease in humans: protozoa, helminths, and ectoparasites
Define
-Parasite
-Host
-Vectors
Parasite: an organism that lives in or on an organism of another species (its host) and benefits by deriving nutrients at the other’s expense.
Define
-Parasite
-Host
-Vectors
In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist guest
What are two types of hosts in parasitology?
- Definitive (adult, sexual multiplication)
- Intermediate (larva, asexual multiplication)
The definitive host is the one which harbors the adult parasite and where the parasite reproduces sexually. The intermediate host is the host which harbors the larval stage or the asexual forms of the parasite. Few parasites require two different intermediate hosts in addition to a definitive host.
For a beef Tapeworm: what is the definitive host? the Intermediate host?
- Intermediate host = Ox or cow
- Definitive host = Human
For taxoplasma, who is the definitive host and who is the intermediate host?
Definitive host: Cat
Intermediate host: Human, other animals
Define
-Parasite
-Host
-Vectors
Vector is an (invertebrate) organism that spreads infection by transporting parasites
What is the difference between a mechanical vector and a Biological vector
- Biological vectors (B), such as mosquitoes and ticks may carry pathogens that can multiply within their bodies and be delivered to new hosts, usually by biting.
- Mechanical vectors (A), such as flies can pick up infectious agents on the outside of their bodies and transmit them through physical contact.
Outline a simple classification of parasites into:
- protozoa/metazoa
- ecto/endoparasites
- Provide an example of each
- Endoparasites: living inside the hosts (Roundworm (Ascaris))
- Ectoparasites: living on surface of the host’s body (Pubic louse (Phthirus))
Outline a simple classification of parasites into:
- protozoa/metazoa
- ecto/endoparasites
- Provide an example of each
Classification from a host parasite relationship angle
Protozoan parasites: eg toxoplasma gondii
- multiply w/in the host
- Intracellular (eg malaria) or extracellular (intestinal protozoa)
- Correlation between clinical symptoms & immune manifestation
- Acquisition of immunity critical to host survival
METAZOAN Parasites:
- Don’t multiply w/in host
- Extracellular existence
Parasitism = quatitative phenomenon, depending on: nr of infecting forms/antigenic burden of worm load; acquisition of immunity - little or no effect on host response (helminths)
Describe a parasitic life cycle and how it relates to their transmission and human disease
pending
Life cycle & classification of Toxoplasma gondii
Toxoplasma gondii (Protozoa)
- Infects most warm blooded animals but:
- Can only multiply sexually in cats - excrete millions of infectious oocysts
- Obligate intracellular lifestyle
- Ability to invade (all nucleated host cells) and evade (immune system)
- 1/3 population - may cause toxoplasmosis but usually asymptomatic
- CAN CAUSE: congenital toxoplasmosis and fetal damage
Lifecycle of Amoebae:
most are (?) inhabitants of (?); some (?) to humans, causing infections of the:
- ? (keratitis)
- ? (meningitis and encephalitis)
- ?
Most amoebae exist in two basic forms:
- ? (a naked cell, usually the form involved in tissue invasion)
- ? (a thick walled environmentally hardy form allowing survival outside the body of the host)
most are aerobic bacteriophagous inhabitants of soil, water, (incl sewage); some pathogenic to humans, causing infections of the:
- eye (keratitis)
- brain (meningitis and encephalitis)
- gastrointestinal tract
Most amoebae exist in two basic forms:
- Trophozoite (a naked cell, usually the form involved in tissue invasion)
- Cyst (a thick walled environmentally hardy form allowing survival outside the body of the host)
Most amoebae exist in two basic forms:
Most amoebae exist in two basic forms:
- Trophozoite (a naked cell, usually the form involved in tissue invasion)
- Cyst (a thick walled environmentally hardy form allowing survival outside the body of the host)
What are Acathamoeba and Nagleria? How are they contracted?
Free Living amoebae;
Have been found in ponds, pools, dust, tap water etc
- Nagleria: enters brain through nasal passages; may put you into coma
- Acanthamoeba: invade and destroys cornea when caught under contact lenses - blindness
Nematodes (roundworms)
Classification: ?
- Size and egg output
- lives in ?
- Parasitic relationship with host: ?
- Infection via: ?
Metazoa (helminths)
Ascaris sp
- pencil size worm w/ about 200,000 eggs/worm daily
- lives in GIT but larval stages travel through several organs before settling in gut to mature
- Adults usually coexist peacefully with host but may block hollow organs or migrate to unusual body sites
- Infection: fecal/oral by ingestion of thick walled environmentally hardy eggs
Life cycle of Ascariasis (roundworms/nematodes/metazoa/helminths)
- ingestion of eggs from feces
- Eggs hatch in intestines; burrow through gut wall; migrate to lungs via the blood
- Larvae break into alveoli and travel up trachea where they are coughed up and swallowed
- Larvae pass through the stomach into the intestines for a second time where they become adult worms
What is the anatomy of tapeworms (cestodes)?
Head ? Segments? Larval form?
- Ribbon-l.ike worms 3mm-25m long
- Head (scolex) w/ hooks and suckers
- Chain of segments (proglottids) full of eggs
- Encysted larval form called cystercercus
How do you get Taenia saginata and Taenia solium?
- Ingestion of undercooked pork (T. solium) or beef (T. saginata) == ingestion of encapsulated larvae - mature in intestine
- Accidental ingestion of eggs (T. solium only) === end up with larval form in tissues
5 methods of laboratory diagnosis of parasitic infection?
- All intestinal parasites: stool microscopy for ova and parasites
- Blood and tissue parasites: microscopical examination of biopsy tissues or body fluids including blood
- Parasite identification
- Molecular methods: PCR
- Serology (antibody response only in cases of tissue invasion)
