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parasitic protozoa
of the three categories of organisms (parasitic protozoa, helminths, and arthropods) that are studied in a parasitology course, only one category—_____________________________—contains microbes.
Parasitism
is a symbiotic relationship that is of benefit to one party or symbiont (the parasite) at the expense of the other party (the host).
Parasites
are organisms that live on or in other living organisms, at whose expense they gain some advantage.
ectoparasites
Parasites that live outside the host’s body are
.Arthropods such as mites, ticks, and lice
endoparasites
parasites that live inside the host are
Parasitic protozoa and helminths are examples
definitive host
If more than one host is involved, the __________ is the one that harbors the adult or sexual stage of the parasite or the sexual phase of the life cycle
intermediate host
harbors the larval or asexual stage of the parasite or the asexual phase of its life cycle.
accidental host
An _________________ is a living organism that can serve as a host in a particular parasite’s life cycle, but is not a usual host in that life cycle
dead-end hosts
. Some accidental hosts are __________, from which the parasite cannot continue its life cycle
Facultative parasites
are organisms that can be parasitic but are also capable of a free-living existence.
Obligate parasites
have no choice; to survive, they must be parasitic
Medical parasitology
is the study of parasites that cause human disease
Parasitology Section of the Clinical Microbiology Laboratory
The overall responsibility of the _________________________ is to assist clinicians in the diagnosis of parasitic diseases—primarily, parasitic diseases caused by endoparasites such as parasitic protozoa and helminths
parasite life cycle stages
In general, parasitic infections are diagnosed by observing and recognizing various__________________________ in clinical specimens.
locomotion
Protozoa are classified taxonomically by their mode of ________. Some move by pseudopodia, others by flagella, others by cilia, and some are nonmotile
pseudopodia
Amebas (amebae) move by means of ______(literally, “false feet”)
whiplike flagella
Flagellates move by means of
hairlike cilia
Ciliates move by means of
Sporozoa (sporozoans)
Protozoa classified as__________have no pseudopodia, flagella, or cilia, and therefore exhibit no motility
parasitic protozoal infections
. Most _________ are diagnosed by observing trophozoites, cysts, oocysts, or spores in the specimen
The trophozoite
is the motile, feeding, dividing 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
Leishmaniasis
is caused by various species of flagellated protozoa and is usually transmitted via the bite of an infected sand fly
Reservoirs include infected humans, domestic dogs, and various wild animals.
is usually transmitted via the bite of an infected sand fly.
Transmission by blood transfusion and person-to-person contact have been reported.
Patient Care. Use Standard Precautions for hospitalized patients.
amastigote
. The nonmotile, intracellular form of Leishmania is called an
cutaneous Leishmaniasis
starts with a papule that enlarges into a craterlike ulcer Individual ulcers may coalesce, causing severe tissue destruction and disfigurement
Acanthamoeba, Toxoplasma gondii
Protozoal infections of the eyes include conjunctivitis and keratoconjunctivitis (inflammation of the cornea and conjunctiva), caused by amebas in the genus __________, and toxoplasmosis, caused by the sporozoan, _____________________
Trichomoniasis
is a sexually transmitted protozoal disease affecting both men and women. The disease is usually symptomatic in women, causing vaginitis with a profuse, thin, foamy, malodorous, greenish-yellowish discharge.
Patient Care. Use Standard Precaution
is caused by Trichomonas vaginalis, a flagellate and is transmitted by direct contact with vaginal and urethral discharges of infected people
. Amebic conjunctivitis and keratoconjunctivitis
are amebic infections causing inflammation of the conjunctiva, corneal ulcers, pus formation, and severe pain. These infections can lead to loss of vision. The disease process is more rapid if corneal abrasions are present.
Patient Care. Use Standard Precautions for hospitalized patients.
are caused by several species of amebas in the genus Acanthamoeba
. The amebas enter the eye from ameba-contaminated waters.
Infections have occurred primarily in people who wear soft contact lenses and have used nonsterile, homemade cleaning or wetting solutions, or have become infected in ameba-contaminated spas or hot tubs
Toxoplasmosis
s a systemic sporozoan infection that, in immunocompetent persons, may be asymptomatic or resemble infectious mononucleosis
Disease typically involves the central nervous system, eyes (chorioretinitis), lungs, muscles, or heart
Patient Care. Use Standard Precautions for hospitalized patients
is caused by Toxoplasma gondii, an intracellular sporozoan
Cerebral toxoplasmosis
is common in AIDS patients. Infection during early pregnancy may lead to fetal infection, causing death of the fetus or serious birth defects
Entamoeba histolytica
•Infects colon with secondary infection of liver.
•Infected patients pass noninfectious trophozoites as well as infectious cysts in stools.
• Diagnosis by presence of characteristic cysts (containing one to four nuclei) in stools.
• Therapy: Iodoquinol, metronidazole.
Giardia lamblia
•Infection usually results from drinking contaminated water.
•Infects duodenum, with incubation time of about ten days.
• Acute infection shows sudden onset with foul smelling, watery diarrhea.
• Diagnosis by presence of cysts or trophozoites in stools.
• Therapy: Metronidazole
Cryptosporidium parvum
• Infects lower small intestine.
• Organisms are intracellular parasites in epithelial cells of intestinal villi.
• Diagnosis by modified acid-fast stain of stool sample.
• Therapy: : Paromomycin (often not effective)
Amebiasis or amebic dysentery
. is a protozoal gastrointestinal infection that may be asymptomatic, mild, or severe and is often accompanied by dysentery, fever, chills, bloody or mucoid diarrhea or constipation, and colitis. The amebas may invade mucous membranes of the colon, forming abscesses and amebomas, which are granulomas that are sometimes mistaken for carcinoma
Patient Care. Use Standard Precautions for hospitalized patients.
is caused by Entamoeba histolytica
, E. histolytica has two stages: the______which is the dormant, infective stage, and the motile, metabolically active, reproducing ________
cyst stage, trophozoite stage
Balantidiasis
is a protozoal gastrointestinal infection of the colon causing diarrhea or dysentery, colic, nausea, and vomiting.
Patient Care. Use Standard Precautions for hospitalized patients
is caused by Balantidium coli,
Cryptosporidiosis
is a gastrointestinal infection caused by a coccidial protozoan.
may be asymptomatic or may cause diarrhea, cramping, and abdominal pain. Less common symptoms include malaise, fever, anorexia, nausea, and vomiting.
standard and contact precautions
results from ingestion of oocysts of Cryptosporidium parvum
Cyclosporiasis
is a coccidial gastrointestinal infection, causing watery diarrhea (6 or more stools per day), nausea, anorexia, abdominal cramping, fatigue, and weight loss. Diarrhea lasts between 9 and 43 days in immunocompetent patients, and months in immunocompromised patients
Patient Care. Use Standard Precautions for hospitalized patients
s results from ingestion of oocysts of Cyclospora cayetanensis,
Reservoirs include fecally contaminated water sources and produce that has been rinsed with fecally contaminated water. Transmission is primarily waterborne, but outbreaks have involved contaminated raspberries, basil, and lettuce.
Giardiasis
is a protozoal infection of the duodenum (the uppermost portion of the small intestine) and may be asymptomatic, mild, or severe. Patients experience diarrhea, steatorrhea (loose, pale, malodorous, fatty stools), abdominal cramps, bloating, abdominal gas, fatigue, and possibly weight loss
standard and contact precautions
is caused by Giardia lamblia
Reservoirs include infected humans, possibly beavers and other wild and domestic animals
Transmission occurs via the fecal–oral route
Primary Amebic Meningoencephalitis
is an amebic disease causing inflammation of the brain and meninges, sore throat, severe frontal headache, hallucinations, nausea, vomiting, high fever, stiff neck. Unless diagnosed and treated promptly, death occurs within 10 days, usually on the fifth or sixth day
standard precautions
s is caused by an ameboflagellate named N. fowleri
class Insecta
Some people refer to all, or most, insects as bugs, but only one category of insects—________—actually contains bugs.
African Trypanosomiasis (African Sleeping Sickness)
s is a systemic disease caused by flagellated protozoa in the bloodstream, known as hemoflagellates. Early stages of the disease include a painful chancre at the site of a tsetse fly bite, fever, intense headache, insomnia, lymphadenitis, anemia, local edema, and rash. Later stages of the disease include body wasting, falling asleep, coma, and death if untreated.
standard precautions
T. brucei ssp. gambiense , T. brucei ssp. rhodesiense
. Two subspecies of Trypanosoma brucei cause African trypanosomiasis. __________in western and central Africa, causes most cases of sleeping sickness; the disease may last several years. ________, in eastern Africa
humans
Infected _____serve as reservoirs of T. brucei ssp. gambiense
wild animals and domestic cattle
are the primary reservoirs of T. brucei ssp. rhodesiense
American Trypanosomiasis
. In the acute stage of the disease, patients may present with an inflammatory response at the site of the reduviid bug bite, fever, malaise, lymphadenopathy, hepatomegaly (enlarged liver), and splenomegaly (enlarged spleen), although it may be asymptomatic
also known as Chagas’ disease, in honor of Carlos Chageas, who described the entire life cycle of Trypanosoma cruzi in 1909
The etiologic agent of American trypanosomiasis is T. cruzi,
standard precautions
Babesiosis
is a sporozoan disease that may include fever, chills, myalgia, fatigue, jaundice, and anemia. It is potentially severe and sometimes fatal, especially in splenectomized and elderly people. Patients may be simultaneously infected with Borrelia burgdorferi, the etiologic agent of Lyme disease, which is transmitted by the same species of tick.
Reservoirs include rodents for B. microti and cattle for B. divergens. Transmission occurs by tick bite and rarely, by blood transfusion.
s is caused by Babesia microti
Use Standard Precautions
Malaria
is a systemic sporozoan infection with malaise, fever, chills, sweating, headache, and nausea. The intermittent bouts of chills and fever are sometimes referred to as paroxysms.
Patient Care. Use Standard Precautions
a is caused by four species in the genus Plasmodium: Plasmodium vivax (the most common species), P. falciparum (the most deadly), Plasmodium malariae, and Plasmodium ovale.
Infected humans and infected mosquitoes serve as reservoirs.
Life cycle of malarial parasites
Infected mosquito injects sporozoites.
Sporozoites migrate to the liver where they form merozoites
Merozoites are released and invade red blood cells.
In the red blood cell, the merozoite becomes a trophozoite.
In the red blood cell, the trophozoite multiplies, producing new merozoites. These are released when the red blood cell ruptures, and can infect other red blood cells.
Some merozoites become gametocytes.
The female mosquito picks up gametocytes from an infected human. The sexual cycle occurs in the mosquito, where sporozoites are formed
Helminths
The word ________-means parasitic worm
roundworms
(nematodes)
Flatworms
are further divided into tapeworms (cestodes) and flukes (trematodes).
The stages of the typical helminth life cycle are the _______, the ______, and the ______
egg, larva, adult worm
hermaphroditic
Cestodes and many trematodes are __________, meaning that adult worms contain both male and female reproductive organs. Thus, it only takes one worm to produce fertile eggs.
intermediate host, definitive host.
The host that harbors the larval stage is called the ____________, whereas the host that harbors the adult worm is called the
three-host parasite
The fish tapeworm, for example, is what is known as a ___________, having one definitive host (human) and two intermediate hosts (a freshwater crustacean called a Cyclops and a freshwater fish) in its life cycle
intermediate hosts, definitive hosts.
Fleas serve as___________ in the life cycle of the dog tapeworm, whereas dogs, cats, or humans can serve as ________________
Helminth infections
are usually diagnosed by observing (a) whole worms or segments of worms in clinical specimens—most often, fecal specimens, or (b) larvae or eggs in stained or unstained clinical specimens
Onchocerciasis (also known as “river blindness”)
HELMINTH THAT CAUSES THE DISEASE: Onchocerca volvulus (N); microfilariae (tiny prelarval stages of these helminths are found in the skin
ANATOMIC LOCATION: Skin
Trichinosis
HELMINTH THAT CAUSES THE DISEASE: Trichinella spiralis (N)
ANATOMIC LOCATION: Muscle and Subcutaneous Tissues
Dracunculiasis
HELMINTH THAT CAUSES THE DISEASE: Dracunculus medinensis (N); also known as the guinea worm
ANATOMIC LOCATION: Muscle and Subcutaneous Tissues
Onchocerciasis
HELMINTH THAT CAUSES THE DISEASE: Onchocerca volvulus (N); microfilariae enter the eyes, causing an intense inflammatory reaction
ANATOMIC LOCATION: Eyes
Loiasis
HELMINTH THAT CAUSES THE DISEASE: Loa loa (N); also known as the African eyeworm
ANATOMIC LOCATION: Eyes
Paragonimiasis
HELMINTH THAT CAUSES THE DISEASE: Paragonimus westermani (T); the lung fluke
ANATOMIC LOCATION: Respiratory System
Ascariasis infection
HELMINTH THAT CAUSES THE DISEASE: Ascaris lumbricoides (N); the large intestinal roundworm of humans
ANATOMIC LOCATION: Gastrointestinal Tract
Hookworm infection
HELMINTH THAT CAUSES THE DISEASE: Ancylostoma duodenale (N) or Necator americanus (N)
ANATOMIC LOCATION: Gastrointestinal Tract
Pinworm infection (enterobiasis)
HELMINTH THAT CAUSES THE DISEASE: Enterobius vermicularis (N)
ANATOMIC LOCATION: Gastrointestinal Tract
Whipworm infection (trichuriasis)
HELMINTH THAT CAUSES THE DISEASE: Trichuris trichiura (N)
ANATOMIC LOCATION: Gastrointestinal Tract
Strongyloidiasis
HELMINTH THAT CAUSES THE DISEASE: Strongyloides stercoralis (N)
ANATOMIC LOCATION: Gastrointestinal Tract
Beef tapeworm infection
HELMINTH THAT CAUSES THE DISEASE: Taenia saginata (C)
ANATOMIC LOCATION: Gastrointestinal Tract
Dog tapeworm infection
HELMINTH THAT CAUSES THE DISEASE: Dipylidium caninum (C)
ANATOMIC LOCATION: Gastrointestinal Tract
Dwarf tapeworm infection
HELMINTH THAT CAUSES THE DISEASE: Hymenolepis nana (C)
ANATOMIC LOCATION: Gastrointestinal Tract
Fish tapeworm infection
HELMINTH THAT CAUSES THE DISEASE: Diphyllobothrium latum (C)
ANATOMIC LOCATION: Gastrointestinal Tract
Pork tapeworm infection
HELMINTH THAT CAUSES THE DISEASE: Taenia solium (C)
ANATOMIC LOCATION: Gastrointestinal Tract
Rat tapeworm infection
HELMINTH THAT CAUSES THE DISEASE: Hymenolepis diminuta (C
ANATOMIC LOCATION: Gastrointestinal Tract
Fasciolopsiasis
HELMINTH THAT CAUSES THE DISEASE: Fasciolopsis buski (T); an intestinal fluke
ANATOMIC LOCATION: Gastrointestinal Tract
Fascioliasis
HELMINTH THAT CAUSES THE DISEASE: Fasciola hepatica (T); a liver fluke
ANATOMIC LOCATION: Gastrointestinal Tract
Clonorchiasis
HELMINTH THAT CAUSES THE DISEASE: Clonorchis sinensis (T); also known as the Chinese or Oriental liver fluke
ANATOMIC LOCATION: Gastrointestinal Tract
Filariasis
HELMINTH THAT CAUSES THE DISEASE: Wuchereria bancrofti (N) and Brugia malayi (N); microfilariae of these helminths are found in the bloodstream
ANATOMIC LOCATION: Circulatory System
Schistosomiasis (also known as bilharzia)
HELMINTH THAT CAUSES THE DISEASE: Trematodes in the genus Schistosoma
ANATOMIC LOCATION: Circulatory System
Cysticercosis
HELMINTH THAT CAUSES THE DISEASE: Cysts (the larval stage) of the pork tapeworm (Taenia solium) are found in the brain
ANATOMIC LOCATION: central nervous system
Hydatid cyst disease
HELMINTH THAT CAUSES THE DISEASE: Echinococcus granulosis (C) or Echinococcus multilocularis (C); in addition to the brain, hydatid cysts (the larval form of these helminths) can form in many other locations in the body
ANATOMIC LOCATION: central nervous system
The arthropod may actually be the cause of the disease.
Scabies, a disease in which microscopic mites live in subcutaneous tunnels and cause intense itching
The arthropod may serve as the intermediate host
Flea in the life cycle of the dog tapeworm. Beetle in the life cycle of the rat tapeworm. Cyclops sp. in the life cycle of the fish tapeworm. Tsetse fly in the life cycle of African trypanosomiasis. Simulium black fly in the life cycle of onchocerciasis. Mosquito in the life cycle of filariasis.
The arthropod may serve as the definitive host
Female Anopheles mosquito in the life cycle of malarial parasites
The arthropod may serve as a vector in the transmission of an infectious disease
Oriental rat flea in the transmission of plague. Tick in the transmission of Rocky Mountain spotted fever and Lyme disease. Louse in the transmission of epidemic typhus
insects
The ________studied include lice, fleas, flies, mosquitoes, and reduviid bugs. Arachnids include mites and ticks
Crustaceans
include crabs, crayfish, and certain Cyclops species.
Mechanical vectors
__________ merely pick up the parasite at point A and drop it off at point B, similar to an overnight delivery service.
For example, a housefly could pick up parasite cysts on the sticky hairs of its legs while walking around on animal feces in a meadow. The fly might then come through an open kitchen window and drop off the parasite cysts while walking on a pie cooling on the counter
biologic vector
is an arthropod in whose body the pathogen multiplies or matures (or both). Many arthropod vectors of human diseases are biologic vectors