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
What are some characteristics of Trichomonas vaginalis?
Most common protozoan causing human disease in the industrialized nations
Lives in the genitourinary system of men and women- Transmiteted exclusively via sex
Women- vaginosis, Men- asymptomation
Diagnosis by microscopic observation of actively motile trophozoites in vaginal and urethral secretions
Trophozoites are flat, posess five flagella and sail-like undulating membrane
Prevention- safe sex and abstinence
What are general characteristics of Apicomplexans?
Alveolate protozoa
Infective form characterized by ornate complex or organelles at their apical end
Parasites of animals
Life cycles involve at least two types of hosts
Schizogony- major feature of apicomplexan life cycles, multinucleate schizonts form before cells divide
Two parasites: Plasmodium, Toxoplasma
How does a apicomplexan undergo schizogony?
Multiple mitoses without cytokinesis form a multinucleate schizont, then cytokinesis occurs
Release numerous uninucleate daughter cells called merozoites
What are some general characteristics of Plasmodium?
Causative agent of malaria
Four species that cause malaria- P. falciparum, P. vivax, P. ovale, and P. malariae
Endemic throughout tropics and subtropics
240 million people infected with Plasmoidum and 88,00 die annually
Vectors- Mosquitoes of genus Anopheles
Life cycle has three prominent stages- Exoerythrocytic stage, Erythrocytic cycle, sporogonic phase
What are the steps of the exoerythrocytic phase?
- Sporozoites injected into host during blood meal
- Sporozoites invade liver cells and under schizogony
- Liver cells rupture and release numerous merozoites into the blood
What are the steps of the erythrocytic phase?
- Free merozoites penetrate erythrocytes
- A merozoite becomes a trophozoite
- Trophozoites undergo schizogony to produce merozoites which are released
- Some merozoites develop into gametocytes within the erthyrocytes
What are the steps of the Sporogenic phase?
- Mosquito ingests gametocytes during blood meal
- Gametocytes becomes gametes that fuse to form zygote
- Zygote differentiates into ookinete, which becomes an oocyst in gut wall
- Oocyst forms sporozoites, ruptures, and sporozoites migrate to salivary glands of mosquitoes
What traits help increase malaria resistance?
Sickle cell trait- sickle-shaped cells resist penetration by Plasmodium
Hemoglobin C- two genes from hemoglobin C protect against malaria
Glucose-6-phosphate-dehydrogenase deficiency- needed by the trophozoites to synthesize DNA
Lack of Duffy antigens on RBCs- P. vivax requires Duffy antigen to infect erythrocytes
What are the symptoms associated with malaria? How is malaria diagnosed, treated, and prevented?
Symptoms associated with cycles of RBC lysis
P.falciparum can cause blackwater fever- high fever, RBC lysis, renal failure, dark urine
Cerebral malaria- tissue death in brain
Immunity develops if victim survives acute stage- periodic episodes become less severe over time
Diagnosis- microscopic detection of ring-like trophozoites with RBCs
Treatment- Chloroquine, mefloquine, or atovaquone with proguanil
Prevent malaria by limiting contact with mosquitoes
What are some characteristics of toxoplasma?
T. gondii is causative agent of toxoplasmosis
One of the world’s most widely distributed parasites- 25% of world’s population is infected
Wild and domestic mammals and birds are major reservoir
Cats are the definitive host
Infection due to consumption of undercooked meat containing the parasite, also ingestion or inhalation of contaminated soil
Protozoan can cross the placenta and infect the fetus
What are some characteristics of Toxoplasmosis?
Most infections are asymptomatic, Toxoplasmosis develops in a small number of people
Fever producing illness combined with other symptoms, usually is a self-limited infection
Most severe in two populations- AIDS patients, fetuses
Transplavental transfer can result in still births, abortions, mental retardation, blindness, jaundice, etc.
Prevent- cooking meats thoroughly, avoid contaminated soil
