Chapter 23- Parasitic Protozoa Flashcards
What are some general characteristics of protozoa?
Protozoan and helminthic parasites exist worldwide
Occur among people in rural, undeveleoped, or overcrowded places, emerging as serious threats in developed nations
Often involve several hosts:
Definitive- mature forms of parasite are present and usually reproducing
Intermediate host- immature parasites undergo various stages of maturation
Infect in one of three ways: Ingestion, Vector-borne, Direct contact
What are the two morphological forms of protozoan parasites?
Trophozoite- feeding and reproducing stage that lives within the host, undergo encystment before leaving in the feces
Cyst- dormant infective form that survives in the environment, undergo excystment when ingested developing into trophozoites
How are protozoa characterized?
Primarily on mode of location
Ciliates, amoebas, flagellates, and apicomplexans
What is the species parasitic ciliates?
Balantidium coli- only ciliate to cause disease in humans
Use cilia in their trophozoite stage
Commonly found in animal intestinal tracts
Humans infected by food or water contaminated with feces containing cysts
Trophozoites attach to the mucosal epithelium lining the intestine
Infections generally asymptomatic in healthy adults
Balantidiasis occurs in those with poor health- persistent diarrhea, abdominal pain, and weight loss, severe infections produce dysentery
Presence of trophozoites diagnostic
What are some general characteristics of amoebas?
Protozoa with no truly defined shape
Move and acquire food through the use of pseudopodia
Found in water sources throughout the world
Few cause disease
What are some characteristics of Entamoba?
Carried asymptomatically in the digestive tracts of humans
No animal reservoir exists
Infection occurs by drinking water contaminated with feces containing cysts
Three types of amebiasis- Luminal amebiasis, invasive amebic dysentery (bloody mucus stools and pain), invasive extraintestinal amebiasis
Diagnosis through identification of cysts or trophozoites
Treastment- druge paromomycin
Maintaining clean is important in prevention
What are some characteristics of Acanthamoeba?
Occurs through cuts, scrapes, the conjunctiva, or inhalation
Ancanthamoeba keratitis due to conjunctival inoculation
Amebic encephalitis is the more common disease
What is Naegleria disease?
Infection occurs when swimmer inhale contaminated water
Amoebic meningoencephalitis can result
Diagnosis by detection of trophozoites in corneal scrapings, CSF
Prevention difficult since organisms are environmentally hardy
What are some characteristics of Trypanosoma cruzi?
Causes Chagas disease
Endemic in Central and South America
Opossums and armadillos are the primary reservoir
Transmission occurs through bite of insects in genus Triatoma (insect)
“Kissing bugs” (Triatoma) feed preferentially from blood vessels in the lips
What are some characteristics of Chagas disease?
4 Stages:
Acute stage characterized by chagomas (swelling at the bite site)
Generalized stage: fever, swollen lymph nodes
Asymptomatic chronic stage
Symptomatic stage characterized by congestive heart failure following formation of pseudocysts (clusters of amastigotes in heart tissue)
Diagnosis- microscopic identification of trypomastigotes (flagellated form) in blood, lymph, Xenodiagnosis
Treatment- in early stages, with benznidazole or nifurtimox
What are some characteristics of Trypanosoma brucei?
Causes African sleeping sickeness
Insect vector- tsetse fly
Humans infected when bitten by infected tsetse flies
What is African Sleeping Sickness?
Three stages if left untreated:
Site of the fly bite becomes a lesion with dead tissue (necrotic)
Fever, lymph node swelling, and headaches (Severe)
Meningoencephalitis
Infection characterized by cyclical waves of parasitemia- parasite changes its surface antigens with each cycle, immune system is incapable of clearning infection
Diagnosis- microscopic identification of trypomastigotes in blood, lymph
Clearing tsetse fly habitats reduce the cases of disease
What are some characteristics of Leishmania?
Flagellate that causes leishmaniasis
Endemic in parts of the tropics and subtropics (Central and South America)
Wild and domestic dogs and small rodents are common hosts- zoonosis transmitted by sandfly
Two developmental stages:
Amastigotes (lack flagella)- multiply in host’s macrophages and monocytes
Promastigotes (flagellated)- develop extracellularly within a vector’s gut
What are the three clinical forms of leishmaniasis and how are they diagnosed and prevented?
Cutaneous leishmaniasis- large painless sores on head and face region
Mucocutaneous leishmaniasis
Visceral leishmaniasis (kala-azar)- fatal
Most cases of leishmaniases heal without treatment
Diagnosis by microscopic identification of amastigotes in samples from cutaneous lesions, spleen, bone marrow
Prevention limited to reducing exposure to reservoir and vector
What are some characteristics of Giardia intestinalis?
Found in the intestinal tracts of animals and the environment
Causes giardiasis (beaver fever)- Common gastrointestinal disease in the United States
Ingest cysts in contaminated water or when swimming
Similar life cycle to Entamoeba - Trophozoites multiply in the small intestines (resemble a face)
Foul smelling stools “rotten egg” smell
Treatment- Metronidazole
Prevent infections in endemic areas by use of filtered water
