ch23 Flashcards
definitive n intermediate hosts
Parasitic infections often involve several hosts—a definitive
host in which mature (often sexual) forms of the parasite are
present and usually reproducing and, with many parasites, one
or more intermediate hosts in which immature parasites undergo
various stages of maturation.
In general, parasites infect
human hosts in one of three major ways
by being ingested, through vector-borne transmission, or via direct contact and
penetration of the skin or mucous membranes
protozoa
unicellular eukaryota diverse
group defined by three characteristics: They are eukaryotic, are
unicellular, and lack a cell wall.
Among the many protozoa that enter the body via __,
most have two morphological forms:
ingestion; A feeding and reproducing
stage called a trophozoite, which lives within the host,
and a dormant cyst stage, which can survive in the environment
and is infective to new hosts.
excystment
Once ingested by a host,
cysts undergo excystment and develop into new trophozoites, which resume feeding and reproducing.
encystment
In most cases, trophozoites
undergo encystment before leaving the host in the feces,
becoming available to infect other hosts.
parasitic diseases
Many protozoan and helminthic parasites exist
worldwide, especially in the tropics and subtropics, and particularly
among people living in rural, undeveloped, or overcrowded
places. Parasitic diseases are also emerging as serious
threats among developed nations in nontropical regions.
ciliates
Ciliates (sil´e@ats) are protozoa that in their trophozoite stages
use cilia for locomotion, for acquiring food, or both. Balantidium
coli is the only
ciliate known to cause disease in humans.
B coli detection
Paradoxically, cysts are few and usually cannot be recovered
from stool (fecal) samples, although they are the infective
stage. Noninfective trophozoites, by contrast, can be detected,
and their presence is diagnostic for the disease. Fresh stool
samples must be used for diagnostic purposes because the
trophozoites do not survive long outside the intestinal tract.
balantidiasis
In healthy adults, B. coli infection is generally asymptomatic.
For those in poor health, however, balantidiasis
occurs. Persistent diarrhea, abdominal pain,
and weight loss characterize the disease. Severe infections produce
dysentery (frequent and painful diarrhea, often containing
blood and mucus) and possibly ulceration and bleeding
b coli cycl
Following ingestion, excystment occurs in the small intestine,
releasing trophozoites that use their cilia to attach to (and then
burrow through) the mucosal epithelium lining the intestine.
Eventually, some trophozoites undergo encystment, and both
cysts and trophozoites are shed in feces. Trophozoites die
outside the body, but cysts are hardy and infective.
b coli host
Pigs are its most common
host, but it is also found in rodents and nonhuman primates
b coli trasmission
Humans become infected by consuming food or water
contaminated with feces containing cysts.
balantidiasis
Prevention of balantidiasis relies on good personal hygiene,
especially for those who live around or work with pigs. Additionally,
efficient water sanitation is necessary to kill cysts or remove
them from drinking water.
amoebae
protozoa
that have no truly defined shape and that move and acquire food
through the use of pseudopods. Although amoebae are abundant
throughout the world in freshwater, seawater, and moist
soil, few cause disease. The most important amoebic pathogen
is Entamoeba.
types of amebiasis
Depending on the health of the host and the virulence
of the particular infecting strain, three types of amebiasis can result
1. luminal
2 amebic
3. invasive extraintestinal
emtamoeba transmission
Infection occurs most commonly through the drinking of
water contaminated with feces that contain cysts. The parasite
can also be ingested following fecal contamination of hands or
food or during oral-anal intercourse.
entameboa cycle
Excystment in the small intestine releases trophozoites that
migrate to the large intestine and multiply. The organism uses
pseudopods to attach to the intestinal mucosa, where it feeds
and reproduces via binary fission. Both trophozoites and cysts
are shed into the environment in feces, but the trophozoites die
quickly, leaving infective cysts.
lumial amebiasis
The least severe form, luminal amebiasis,
occurs in otherwise healthy individuals. Infections are asymptomatic;
trophozoites remain in the lumen of the intestine,
where they do little tissue damage.
amebic dysentery
Invasive amebic dysentery
is a more serious and more common form of infection characterized
by severe diarrhea, colitis (inflammation of the colon),
appendicitis, and ulceration of the intestinal mucosa. Bloody,
mucus-containing stools and pain are characteristic of amebic
dysentery, which affects about 500 million people worldwide.
invasive extraintestinal amebiasis
In the most serious disease, invasive extraintestinal amebiasis,
trophozoites invade the peritoneal cavity and the bloodstream,
which carries them throughout the body. Lesions of dead cells
formed by the trophozoites occur most commonly in the liver
but can also be found in the lungs, spleen, kidneys, and brain.
Amebic dysentery and invasive extraintestinal amebiasis can be
fatal, especially without adequate treatment.
emtamoeba prevntion
Several preventive measures interrupt the transmission
of Entamoeba. Discontinuing the use of human wastes as fertilizer
reduces the transmission of amebiasis. Normal methods
of treating wastewater and drinking water are helpful
but not completely effective because the infectious cysts are
hardy. Effective processing of water requires extra chemical
treatment, filtration, or extensive boiling to eliminate all
cysts. Good personal hygiene can eliminate transmission via
intimate contact.
emtamoeba prevntion
Several preventive measures interrupt the transmission
of Entamoeba. Discontinuing the use of human wastes as fertilizer
reduces the transmission of amebiasis. Normal methods
of treating wastewater and drinking water are helpful
but not completely effective because the infectious cysts are
hardy. Effective processing of water requires extra chemical
treatment, filtration, or extensive boiling to eliminate all
cysts. Good personal hygiene can eliminate transmission via
intimate contact.
2 other amoebae
Acanthamoeba and Naegleria cause rare and usually fatal infections
of the brain
2 other amoeba env
Acanthamoeba and Naegleria are common free-living inhabitants
of warm lakes, ponds, puddles, ditches, mud, and moist
soil. They are also found in artificial water systems such as
swimming pools, air-conditioning units, humidifiers, and dialysis
units. Contact lens wearers who use tap water (as opposed
to sterile saline solution) to wash and store their lenses
create an additional focal point for infection.
acanthamoeba transmission
Acanthamoeba usually enters a host through cuts or scrapes
on the skin, through the conjunctiva via abrasions from contact
lenses or trauma, or through inhalation of contaminated water
while swimming.
keratitis
Acanthamoeba trophozoites when inoculated into the eye can invade and perforate the eye, resulting in keratitis.
Damage can be extensive enough to require corneal replacement.
2 other amoeba diseases
Acanthamoeba - keratitis, amebic encephalitis
Naegleria - amebic meningoencephalitis
amebic encephalitis symptoms
The more common disease caused by infection with Acanthamoeba
is amebic encephalitis (inflammation of the brain), characterized
by headache, altered mental state, and neurological deficit.
Symptoms progressively worsen over a period of weeks until the
patient dies
naegleria transmission
Infection with Naegleria occurs when swimmers inhale
water contaminated with trophozoites, which then invade
the nasal mucosa and replicate. the tropozoites migrate to the brain
amebic meningoencephalitis symptoms
(inflammation of the brain and its membranes). Severe headache,
fever, vomiting, and neurological tissue destruction lead
to hemorrhage, coma, and usually death within three to seven
days after the onset of symptoms.
2 other amoeba prevention
acanthamoeba, naeglria are environmentally hardy, control
and prevention of infection can be difficult. Swimmers and bathers
should avoid waterways in which the organisms are known
to be endemic. Nonsterile solutions should never be used to
clean or store contact lenses. Swimming pools should be properly
chlorinated and tested periodically to ensure their safety.
Air-conditioning systems, dialysis units, and other devices that
routinely use water should also be cleaned thoroughly and regularly
to prevent amoebae from becoming resident.
flagellates
protozoa that possess at least
one long flagellum, which is used for movement. The number
and arrangement of the flagella are important features for
determining the species of flagellate present within a host.
flagellates types
- trypanosoma, leishmania: kinetoplastids
- giardia: diplomonad
- tricomonas: parabasalid
interphase
during which the cells grow
and eventually replicate their DNA, and a stage during which
the cell’s nucleus divides.
prophase
- cell condenses its DNA molecules into
visible threads called chromatids - a set of microtubules is
constructed in the cytosol to form a spindle - In most cells,
the nuclear envelope disintegrates during prophase so
that mitosis occurs freely in the cytosol
chromosome
2 identical chromatids jointed together at centromere
metaphase
chromosomes line up on a plane in the
middle of the cell and attach near their centromeres to
microtubules of the spindle.
anaphase
Sister chromatids separate and crawl along the
microtubules toward opposite poles of the spindle. Each
chromatid is now called a chromosome.
telophase
The cell restores its chromosomes to their less
compact, nonmitotic state, and nuclear envelopes form
around the daughter nuclei.
meiosis early prophase I
homologous chromosomes line up side by side. An aligned pair of homologous chromosomes is
known as a tetrad.
meiosis late prophase I
Once tetrads have formed, the homologous
chromosomes exchange sections of DNA in a random
fashion via a process called crossing over. This results in
recombinations of their DNA. It is because of meiotic
crossing over that the offspring produced by sexual
reproduction have different genetic makeups from their
siblings. Prophase I can last for days or longer.
meiosis metaphase I
Tetrads align on a plane in the center of the
cell and attach to spindle microtubules. Metaphase I differs
from metaphase of mitosis in that homologous chromosomes
remain as tetrads.
meiosis anaphase I
Chromosomes of the tetrads move apart from
one another; however, in contrast to mitotic anaphase, sister
chromatids remain attached to one another.
telophase I meiosis
The first stage of meiosis is completed as the
spindle disintegrates. Typically, the cell divides at this
phase to form two cells. Nuclear envelopes may form.
Each daughter nucleus is haploid, though each haploid
chromosome consists of two chromatids.
meiosis 2
6 Prophase II. Nuclear envelopes disintegrate, and new
spindles form.
7 Metaphase II. The chromosomes align in the middle of
each cell and attach to microtubules of the spindles.
8 Anaphase II. Sister chromatids separate as in mitosis.
9 Telophase II. Daughter nuclei form. The cells divide,
yielding four haploid cells.
meiosis 2
6 Prophase II. Nuclear envelopes disintegrate, and new
spindles form.
7 Metaphase II. The chromosomes align in the middle of
each cell and attach to microtubules of the spindles.
8 Anaphase II. Sister chromatids separate as in mitosis.
9 Telophase II. Daughter nuclei form. The cells divide,
yielding four haploid cells.
cytokinesis
typically occurs simultaneously with telophase of mitosis,
though in some algae and fungi it may be postponed or may
not occur at all. In these cases, mitosis produces multinucleate
cells called coenocytes
cell plate
In plant and algal cells, cytokinesis occurs as vesicles deposit
wall material at the equatorial plane between nuclei to
form a cell plate, which eventually becomes a transverse wall
between daughter cells
cytokinesis of protozoa and some fungal cells
Cytokinesis of protozoa
and some fungal cells occurs when an equatorial ring of actin
microfilaments contracts just below the cytoplasmic membrane,
pinching the cell in two
yeasts cytokinesis
Single-celled fungi called
yeasts form a bud, which receives one of the daughter nuclei
and pinches off from the parent cell
scizogony
In schizogony, multiple mitoses
form a multinucleate schizont (skiz´ont); only then does cytokinesis
occur, simultaneously releasing numerous uninucleate
daughter cells called merozoites
schizogony in plasmodium
Some protozoa, such as Plasmodium—the
cause of malaria—reproduce asexually within red blood cells
and liver cells via a special type of reproduction called schizogony. The body of an
infected host responds to the release of huge numbers of merozoites
with the cyclic fever and chills characteristic of malaria.
the organisms we
commonly refer to as protozoa are classified in six kingdoms:
Parabasala, Diplomonadida, Euglenozoa, Alveolata, Rhizaria,
and Amoebozoa.
formed largely according to similarities
in nucleotide sequences and ultrastructure.
algae are
distributed among the kingdoms
Stramenopila, Rhodophyta,
and Plantae
water molds and slime modls kingdom
water molds are in the kingdom Stramenopila;
and slime molds are in the kingdom Amoebozoa
most species of protozoa
Protozoa require moist environments; most species live worldwide
in ponds, streams, lakes, and oceans, where they are critical
members of the plankton—free-living, drifting organisms
that form the basis of aquatic food chains. Other protozoa live
in moist soil, beach sand, and decaying organic matter, and a
very few are pathogens—that is, disease-causing microbes—of
animals and humans.
most species of protozoa
Protozoa require moist environments; most species live worldwide
in ponds, streams, lakes, and oceans, where they are critical
members of the plankton—free-living, drifting organisms
that form the basis of aquatic food chains. Other protozoa live
in moist soil, beach sand, and decaying organic matter, and a
very few are pathogens—that is, disease-causing microbes—of
animals and humans.
some ciliates
Some ciliates have two nuclei: a larger macronucleus,
which contains many copies of the genome (often more than
50n) and controls metabolism, growth, and sexual reproduction,
and a smaller micronucleus, which is involved in genetic recombination, sexual reproduction, and regeneration
of macronuclei.
protozoa: Several groups lack mitochondria,
whereas all the others have mitochondria with
discoid or tubular
cristae rather than the platelike cristae seen in animals,
plants, fungi, and many algae.
contractile vacuoles
some protozoa
have contractile vacuoles that actively pump water from the cells,
protecting them from osmotic lysis
all __ protozoa
All free-living aquatic and pathogenic protozoa exist as a motile
feeding stage called a trophozoite (trof@o@zo´ıt), and many
have a hardy resting stage called a cyst
cyst
hardy resting stage of protozoa. characterized
by a thick capsule and a low metabolic rate. Cysts of protozoa
are not reproductive structures because one trophozoite forms
one cyst, which later becomes one trophozoite. Such cysts allow
intestinal protozoa to pass from one host to another and to survive
harsh environmental conditions such as desiccation, nutrient
deficiency, extremes of pH and temperature, and lack of oxygen.
most protozoa are __trophic
Most protozoa are chemoheterotrophic; that is, they obtain nutrients
by phagocytizing bacteria, decayed organic matter, other
protozoa, or the tissues of a host
protoz and botanists
Because the protozoa called
dinoflagellates and euglenids (discussed shortly) are photoautotrophic,
botanists historically classified them as algal plants
rather than as protozoa.
protozoa reproduction
Most protozoa reproduce asexually only, by binary fission or
schizogony; a few protozoa also have sexual reproduction in
which two individuals exchange genetic material. Some sexually
reproducing protozoa become gametocytes (gametes)
that fuse with one another to form a diploid zygote.
(specific protoz agroup) reproduction
Ciliates,
such as Paramecium, reproduce sexually via
a complex process called conjugation
parabasala
Parabasalids lack mitochondria, but each has a single nucleus
and a parabasal body, which is a Golgi body–like structure.
trichomonas
parabasalid. lives in the human vagina
(see Figure 23.9). When the normally acidic pH of the vagina is
raised, Trichomonas proliferates and causes severe inflammation
that can lead to sterility. It is spread by sexual intercourse and is
usually asymptomatic in males.
giardia
diplomonad. a diarrheacausing
pathogen of animals and humans that is spread to new
hosts when they ingest resistant Giardia cysts.
diplomonadida
- lack mitochondria,
Golgi bodies, and peroxisomes - have rudimentary mitosomes in the cytoplasm and mitochondrial
genes in the nuclear chromosomes, a finding that suggests that
diplomonads might be descended from typical eukaryotes that
somehow lost their organelles
euglenozoa
- euglenids and some flagellated protozoa called kinetoplastids
- eukaryotic microbes that share certain characteristics of
both plants and animals. - have a crystalline rod of unknown
function in the flagella, and mitochondria with
disk-shaped cristae
knetoplastids
- trypanosoma, leishmania
- have a single large mitochondrion that contains a
unique region of mitochondrial DNA called a kinetoplast. As
in all mitochondria, this DNA codes for some mitochondrial
polypeptides. - live iside aimals, some r pathognic
euglenids
photoautotrophic,
unicellular microbes with chloroplasts containing
light-absorbing pigments—chlorophylls a and b and carotene.
For this reason, botanists historically classified euglenids in the
kingdom Plantae.
y euglenids not i plantae
euglenids store food as a unique polysaccharide
called paramylon instead of as starch.
Euglenids are
similar to animals in that
they lack cell walls, have flagella, are chemoheterotrophic phagocytes (in the dark), and move
euglenoid movemnt
move by using
their flagella as well as by flowing, contracting, and expanding
their cytoplasm. Such a squirming movement, which is similar to
amoeboid movement but does not involve pseudopods, is called
euglenoid movement.
pellicle
A euglenid has a flexible, proteinaceous, helical pellicle that
underlies its cytoplasmic membrane and helps maintain its shape.
eyespot
Typically each euglenid also has a red “eyespot,” which plays a
role in positive phototaxis by casting a shadow on a photoreceptor
at the flagellar base, triggering movement in that direction.
alveolates
protozoa with small membranebound
cavities called alveoli16 (al@ve´o@lı) beneath their cell
surfaces.
Alveolates share at least one other characteristic—tubular
mitochondrial cristae. This group is further divided into three
subgroups: ciliates, apicomplexans, and dinoflagellates.
ciliates
alveolates. All ciliates are
chemoheterotrophs and have two nuclei—one macronucleus
and one micronucleus
apicomplexans
alveolates. all chemoheterotrophic pathogens of animals.
infective forms are characterized by an ornate complex of
organelles at their apical ends, that enables them to penetrate host cells.
- plasmodium, toxoplasma, cryptosporidium cyclospora
- major feature: schizogony
- all have complicated life cycles
involving at least two types of hosts
dinoflagellates
alveolates. unicellular microbes that have photosynthetic pigments,
such as carotene and chlorophylls a, c1, and c2. make up a large proportion of freshwater and marine plankton.
- botanists have historically classified
the dinoflagellates as algae because dinoflagellates are photoautotrophic
- manny r bioluminescent
- some produce neurotoxins
red tide
Other dinoflagellates produce a red pigment, and their abundance
in marine water is one cause of a phenomenon called a
red tide.
