RT Micro Ch. 21 Parasite Infections

• An accidental host is a

living organism can serve as a host in a particular parasite's life cycle, but is not usual host in that life cycle.

Protozoa are classified taxonomically by their mode of

locomotion.

In the malarial parasite's life cycle, ____ are released from infected liver cells.

merozoites

• The trophozoite is the

motile, feeding, diving stage in the protozoal life cycle, and the cyst, oocyst, and spore are dormant stages. Protozoal infections are most often acquired by ingestion or inhalation of dormant stages.

sporozoans are

nonmotile.

• In general, parasitic infections are diagnosed by

observing and recognizing various parasite life cycle stages in clinical specimens.

• Of the three categories of organisms (parasitic protozoa, helminths, and arthropods) that are studied in a parasitology course, only

one category (parasitic protozoa) contains microorganisms.

·A facultative parasite is an

organism that can be parasitic but does not have to live as a parasite. It is capable of living an independent life (apart from a host). An obligate parasite has no choice. To survive, it must be parasitic.

Parasites are defined as

organisms that live on or in other living organisms (hosts), at whose expense they gain some advantage (usually by depriving the host of nutrients).

Helminths are

parasitic worms

Amebas move by

pseudopodia,

Helminths - parasitic worms - are divided into

roundworms (nematodes) and flatworms. Flatworms are further divided into tapeworms (cestodes) and flukes (trematodes.

In the malarial parasite's life cycle ____ are produced within female Anopheles mosquitoes.

sporozoites

In the malarial parasite's life cycle humans become infected when a female Anopheles mosquito injects _____ while taking a blood meal.

sporozoites

The typical helminth life cycle consists of three stages:

the egg, the larva, and the adult worm.

• The definitive host is defined as

the host that harbors the adult or sexual stage of the parasite or the sexual phase of the life cycle.

In the malarial parasite's life cycle, merozoites initially mature into ______ within red blood cells.

trophozoites

Leishmaniasis is caused by

various species of flagellated protozoa in the genus Leishmania, and is usually transmitted via the bite of an infected sand fly.

In the malarial parasite's life cycle, female Anopheles mosquitoes become infected when they ingest male and female____ (at least one of each) while taking a blood meal.

gametocytes

Scabies is caused by an insect. T/F

​False (scabies is caused by an arachnid—specifically, a mite; arachnids are not insects)

Mechanical vector

An arthropod vector (e.g., a housefly) that merely transports a pathogen from "point A" to "point B," and within which the pathogen neither multiplies nor matures

Biological vector

An arthropod vector (such as a flea or tick) within which a pathogen multiplies or matures

Obligate parasite

An organism that can exist only as a parasite; incapable of a free-living existence

Facultative parasite

An organism that is capable of being a parasite but is also capable of a free-living existence

Helminth infections are usually diagnosed by observing

(1) whole worms or segments of worms in clinical specimens - most often, fecal specimens, or (2) larvae or eggs in stained or unstained clinical specimens.

Nematodes

(round worms) round smooth body; have a tube within a tube body plan, separate mouth and anus; no circulatory system; some free living, some parasite

Arthropods may be involved in human diseases in several ways:

(1) they may be the actual cause of the disease, (2) they may serve as an intermediate or definitive host in a parasite's life cycle, or (3) they may serve as a mechanical or biological vector in the transmission an infectious disease.

Trematodes

A category of flatworms; often referred to as flukes

Ectoparasite

A parasite that lives on the external surface of its host

Endoparasite

A parasite that lives within the body of its host

Helminth

A parasitic worm (as a tapeworm, liver fluke, ascarid, or leech).

Cestodes

A subcategory of flatworms; includes tapeworms

A disease known as PAM is caused by a protozoan in the category of protozoa known as

Amebas

Protozoa in the category of protozoa known as _____ move by means of pseudopodia.

Amebas

In the category of protozoa known as ____ only one protozoan causes human disease.

Ciliates

African trypanosomiasis and American trypanosomiasis are transmitted by the same type of arthropod vector. T/F

False (African trypanosomiasis is transmitted by a tsetse fly, whereas American trypanosomiasis is transmitted by a reduviid bug)

In the malarial parasite's life cycle, humans serve as definitive hosts. T/F

False (in the malaria parasite's life cycle, humans serve as intermediate hosts and mosquitoes serve as definitive hosts)

The amebae that cause amebic keratitis and PAM are good examples of obligate parasites. T/F

False (the amebae that cause these diseases are good examples of facultative parasites)

African trypanosomiasis, American trypanosomiasis, giardiasis, and trichomo-niasis are caused by protozoa in the category of protozoa known as

Flagellates

Definitive host

In a parasitic relationship, the host that harbors the adult or sexual stage of a parasite, or the sexual phase of the parasite's life cycle

Intermediate host

In a parasitic relationship, the host that harbors the larval or asexual stage of a parasite, or the asexual phase of the parasite's life cycle

Cryptosporidiosis, malaria, and toxoplas-mosis are caused by protozoa in the category of protozoa known as

Sporozoa

In a parasite's life cycle, it is possible for a particular arthropod to serve as both a host and a biologic vector. T/F

True

In a parasite's life cycle, the definitive host harbors the adult or sexual stage of the parasite or the sexual phase of the life cycle. T/F

True

It is possible to acquire cryptosporidiosis, cyclosporiasis, and toxoplasmosis by ingesting oocysts. T/F

True

Toxoplasmosis could be acquired by eating raw or rare meat. T/F

True

Trichomonas vaginalis cannot survive very long outside of the human body because it has no cyst form. T/F

True

When causing infections, parasitic protozoa and helminths are endoparasites. T/F

True

Primary amebic meningoencephalitis is caused by an

ameboflagellate named Naegleria fowleri.

ciliates move by

cilia,

Some accidental hosts are

dead-end hosts, from which the parasite cannot continue its life cycle.

Parasites that live on the outside of the host's body are referred to as

ectoparasites,

Parasites that live on the inside are called

endoparasites.

flagellates move by

flagella,

Trichomoniasis is caused by a

flagellated protozoan named Trichomonas vaginalis, and is transmitted by direct contact with vaginal and urethral discharges of infected people.

The intermediate host is the

host that harbors the larval or asexual stage of the parasite or the asexual phase of the life cycle.