protozoans
unicellular eukaryotic heterotrophic
microorganisms. A typical life cycle includes a vegetative
trophozoite stage and a resting cyst stage.
protozoan classification
Phylum Sarcomastigophora (including Subphylum
Mastigophora [the flagellates] and Subphylum
Sarcodina [the amoebas]),
Phylum Ciliophora (the ciliates), and
Phylum Apicomplexa (sporozoans and others).
- handout: amoebas, flagellates, ciliates, apicomplexa (complex life cycles, intracellular parasites, most stages are non motile)
amoebic dysentery
- Entamoeba histolytica
- amebiasis
- Identification is made by finding
either trophozoites or cysts
in a stool sample. - The extent of damage
determines whether the disease is acute, chronic, or
asymptomatic. In the most severe cases, infection may
extend to other organs, especially the liver, lungs, or
brain. Among the symptoms of amoebic dysentery are
abdominal pain, diarrhea, blood and mucus in feces,
nausea, vomiting, and hepatitis.
entamoeba histolytica in the body
Infection occurs when a human host ingests cysts,
either through fecal–oral contact or, more typically, contaminated
food or water. Cysts (but not trophozoites)
are able to withstand the acidic environment of the
stomach. Upon entering the less acidic small intestine,
the cysts undergo excystation. Mitosis produces eight
small trophozoites from each cyst.
The trophozoites parasitize the mucosa and sub -
mucosa of the colon, causing ulcerations. They feed
on red blood cells and bacteria.
asymptomatic carrier
Developing cysts undergo mitosis to produce mature
quadranucleate cysts, which are shed in the feces and are infective. They also may persist in the original host, resulting
in an asymptomatic carrier—a major source of
contamination and infection.
balantidiasis
- large intestinal infection
- Balantidium coli is the caus -
ative agent of balantidiasis and exists in two forms: a
vegetative trophozoite and a cyst. Laboratory diagnosis
is made by identifying either the cyst or the trophozoite,
with the latter being more commonly found - Symptoms of acute infection are bloody and
mucoid feces. Diarrhea alternating with constipation may
occur in chronic infections. Most infections probably are
asymptomatic.
b. coli trophozoites and cysts
The trophozoite is highly motile because of the cilia
and has a macronucleus and a micronucleus. Cysts
in sewage-contaminated water are the infective form.
Trophozoites may cause ulcerations of the colon mucosa,
but not to the extent produced by Entamoeba
histolytica.
giardiasis
- Giardia lamblia (also known as
Giardia intestinalis) - small intestinal infection
- Transmission
typically involves fecally contaminated water or food, but
direct fecal–oral contact transmission is also possible. Most infections are asymptomatic.
Chronic diarrhea, dehydration, abdominal pain,
and other symptoms may occur if the infection produces
a population large enough to involve a significant surface
area of the small intestine. Diagnosis is made by identifying
trophozoites or cysts in stool specimens.
g lamblia in the body
- Giardia lamblia (also known as
Giardia intestinalis), a flagellate protozoan - It is seen
most frequently in the duodenum as a heart-shaped
vegetative trophozoite with four pairs
of flagella and a sucking disc that allows it to resist gut
peristalsis. Multinucleate cysts lacking flagella are formed as the organism passes through the
colon. Cysts are shed in the feces and may produce
infection of a new host upon ingestion. - The organism attaches to epithelial cells but does not
penetrate to deeper tissues.
vulvoganitis
- Trichomonas vaginalis is the causative
agent of trichomoniasis (vulvovaginitis) in humans. - may affect both sexes but is more
common in females - inflammation of genitourinary mucosal surfaces—typically the vagina,
vulva, and cervix in females and the urethra, prostate,
and seminal vesicles in males. Most infections are
asymp tomatic or mild. Some erosion of surface tissues
and a discharge may be associated with infection. The
degree of infection is affected by host factors, especially
the bacterial flora present and the pH of the mucosal
surfaces. Transmission typically is by sexual intercourse.
t. vaginalis
It
has four anterior flagella and an undulating membrane.
- The trophozoite
is the only stage of the Trichomonas life cycle.
trypanosoma
Trypanosoma brucei (Figure 12-36) is a species of flagellated
protozoans divided into subspecies: T. brucei brucei
(which is nonpathogenic), and T. brucei gambiense and
T. brucei rhodesiense, which produce African trypano -
somiasis, also known as African sleeping sickness. The
organisms are very similar morphologically but differ
in geographic range and disease progress. Modern molecular methods that compare
proteins, RNA, and DNA are used to differentiate be-
tween them.
2 types of pathogenic t. brucei
West African
trypanosomiasis (caused by T. brucei gambiense) is
generally a mild, chronic disease that may last for years,
whereas East African trypanosomiasis (caused by T.
brucei rhodesiense ) is more acute and re sults in death
within a year.
trypanosome life cycle
Trypanosomes have a complex life cycle. One stage
of the life cycle, the epimastigote, multiplies in an in ter-
mediate host, the tsetse fly (genus Glossina). The infective
trypomastigote stage then is transmitted to the human host through tsetse fly bites. Once introduced,
trypomastigotes multiply and produce a chancre at the
site of the bite. They enter the lymphatic system and
spread through the blood, and ultimately to the heart
and brain.
trypanosomiasis
Immune response to the pathogen is hampered by
the trypanosome’s ability to change surface antigens
faster than the immune system can produce appropriate
antibodies. This antigenic variation also makes devel -
opment of a vaccine unlikely. Diagnosis is made from
clinical symptoms and identification of the trypomastigote
in patient specimens (e.g., blood, CSF, and chancre
aspirate). An ELISA and an indirect agglutination test
also have been developed to detect trypanosome antigens
in patient samples.
Progressive symptoms include headache, fever, and
anemia, followed by symptoms characteristic of the in-
fected sites. The symptoms of sleeping sickness—sleepiness,
emaciation, and unconsciousness—begin when the
central nervous system becomes infected. Depending on
the infecting strain, the disease may last for months or
years, but the mortality rate is high. Death results from
heart failure, meningitis, or severe debility of some other
organ(s).
The infective cycle is complete when an infected
individual (humans, cattle, and some wild animals are
reservoirs) is bitten by a tsetse fly, which ingests the
organism during its blood meal. It becomes infective
for its lifespan.
plasmodia
Plasmodia are sporozoan parasites with a complex life
cycle, part of which is in various vertebrate tissues while
the other part involves an insect. In humans, the tissues
are the liver and red blood cells, and the insect vector is
the female Anopheles mosquito.
- Four species of Plasmodium cause malaria in humans:
P. vivax (benign tertian malaria),
P. malariae (quartan malaria),
P. falciparum (malignant tertian malaria), and
P. ovale (ovale malaria).
plasmodium life cycle
The sporozoite stage of the pathogen is introduced
into a human host during a bite from an infected female
Anopheles mosquito. Sporozoites then infect liver cells
and produce the asexual merozoite stage. Merozoites are
released from lysed liver cells, enter the blood, and infect
erythrocytes. (Reinfection of the liver occurs at this stage
in all except P. falciparum infections.) Once in RBCs,
merozoites enter a cyclic pattern of reproduction in
which more merozoites are released from the red cells
synchronously every 48 hours (hence tertian—every
third day—malaria).
- The sexual phase of the life cycle begins when certain
merozoites enter erythrocytes and differentiate into male
or female gametocytes. The sexual phase of the life cycle
continues when ingested by a female Anopheles mosquito
during a blood meal. Fertilization occurs, and the
zygote eventually develops into a cyst within the gut wall
of the mosquito. After many divisions, the cyst releases
sporozoites, some of which enter the mosquito’s salivary
glands ready to be transmitted back to the human host
malaria
- A chill, nausea, vomiting, and headache are symptoms
that correspond to rupture of the erythrocytes. A spiking
fever ensues and is followed by a period of sweating,
after which the exhausted patient falls asleep. During
this latter phase, the parasites reinfect the red cells and
the cycle repeats. - Most malarial infections are cleared eventually, but
not before the patient has developed anemia and has
suffered permanent damage to the spleen and liver. The most severe infections involve P. falciparum. Erythrocytes
infected by P. falciparum develop abnormal projections
that cause them to adhere to the lining of small blood
vessels. This can lead to obstruction of the vessels,
thrombosis, or local ischemia, which account for many
of the fatal complications of this type of malaria—
in cluding liver, kidney, and brain damage.
t gondii life cycle
has sexual and asexual phases. The
sexual phase occurs in the lining of cat intestines where
oocysts are produced and shed in the feces. Each oocyst
undergoes division and contains eight sporozoites. If
ingested by another cat, the sexual cycle may be repeated
as the sporozoites produce gametocytes, which in turn
produce gametes. If ingested by another animal host (including
humans) the oocyst germinates in the duodenum
and releases the sporozoites. Sporozoites enter the blood
and infect other tissues, where they become trophozoites,
which continue to divide and spread the infection to
lymph nodes and other parts of the reticuloendothelial
system. Trophozoites ingested by a cat eating an infected
animal develop into gametocytes in the cat’s intestines.
Gametes are formed, fertilization produces an oocyst,
and the life cycle is completed
toxoplasmosis
Infection usually occurs by eating undercooked contaminated meat, exposure from infected cat feces, or mother-to-child transmission during pregnancy. Toxoplasmosis may cause flu-like symptoms in some people, but most people affected never develop signs and symptoms. For infants born to infected mothers and for people with weakened immune systems, toxoplasmosis may cause serious complications.
- Infection via ingestion of the oocyst typically is not
serious. The infected person may notice fatigue or muscle
aches. The more serious form of the disease involves
infection of a fetus across the placenta from an infected
mother. This type of infection may result in stillbirth,
or liver damage and brain damage. AIDS patients may
incur fatal complications from infection.
trypanosome cruzi
- People can become infected in various ways. In Chagas disease-endemic areas, the main way is through vectorborne transmission. The insect vectors are called triatomine bugs. These blood-sucking bugs get infected by biting an infected animal or person. Once infected, the bugs pass T. cruzi parasites in their feces. After they bite and ingest blood, they defecate on the person. The person can become infected if T. cruzi parasites in the bug feces enter the body through mucous membranes or breaks in the skin.
- consumption of uncooked food contaminated w/ feces from infected bugs
leishmania donovani
- flagellates; kinetoplasmids; euglenozoa
- Visceral leishmaniasis, black fever, and Dumdum fever
- The parasite migrates to the internal organs such as the liver, spleen (hence “visceral”), and bone marrow, and, if left untreated, will almost always result in the death of the host. Signs and symptoms include fever, weight loss, fatigue, anemia, and substantial swelling of the liver and spleen.
- bites from female phlebotomine sandflies
cryptosporidium parvum
- apicomplexa
- cryptosporidiosis (mammalian intestinal tract)
- Infection is caused by ingestion of sporulated oocysts transmitted by the faecal-oral route.
- small intestine, maybe respiratory tract
