Chapter 23 - Parasitic Protozoa Flashcards
What are the general characteristics of protozoa?
- Protozoan and helminthic parasites exist worldwide
- Occur among people in rural, undeveloped, or overcrowded places\
- Emerging as serious threats in developed nations
- Parasitic infections often involve several hosts:
Definitive host: Mature forms of parasite are present and usually reproducing
Intermediate host:Immature parasites undergo various stages of maturation
Parasites can infect humans in one of three ways:
1. Ingestion
2. Vector-borne
3. Direct contact
What are the two morphological forms of protozoa?
Trophozite: feeding and reproducing stage that lives within the host
Cyst: Dormant infective form that survives in the environment, and undergo excytment when ingested developing into trophozoites
- Trophozoites undergo encystment before leaving the host in feces
- Parasites presented based primarily on their mode of locomotion
- Ciliates, amoebae, flagellates, and apicomplexans.
Do you know the flow chart to characterize Parasitic Protozoa?
Ciliates –> Balantidium coli
Amoebae — (Entamoeba histolytica, Acanthamoeba, Naegleria)
Flagellates — (Trypanosoma cruzi, Trypanosoma brucei, Leishmania, Giardia, Trichomonas)
Apicomplexans – (Plasmodium, Toxoplasma)
What are come of the characteristics of Ciliates?
- Protozoa use cilia in their trophozoite stage.
Disease: Balantidium coli
- Only known ciliate to cause disease
- Found in animal intestinal tracts
- Humans infected by food or water contaminated with feces containing cysts
- Trophozoites attach to muscoal epithelium lining the intestine
- 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 about Amoebae?
- Protozoa with no truly defined shap
- move and acquire food through the use of pseudopodia
- Found in water sources throughout the world
- Few cause disease
What are the characteristics of Entamoeba?
- 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 can result from infection:
- *1. Luminal amebiasis
2. Invasive amebic dysentery (bloody mucus stools and pain)
3. Invasive extraintestinal amebiasis** - Diagnosis through identification of cysts or trophozoites
- Treatment: drug paromomycin
- Maintaining clean water is important in prevention
What are the characteristics of Acanthamoeba and Naegleria diseases?
Acanthamoeba disease:
- Occurs through cuts, scrapes, the conjunctiva, or inhalation
- Acanthamoeba keratitis due to conjunctival inoculation
- Amebic encephalitis more common disease
Naegleria disease:
- Infection occurs when swimmers inhale contaminated water
- Amoebic meningoencephalitis
Diagnosisi by detection of trophozoites in corneal scrapings, CSF
Prevention difficult since organisms are environmentally hardy
What are some of the characteristics of Trypanosoma cruzi?
- Causes Chagas’ disease
- endemic in Central and South America
- Opossums and armadillos primary reservoir
- Transmission occurs through bite of insect in genus Tritoma
- “Kissing bugs” feed preferentially from blood vessels in the lips
What is Chagas’ Disease?
Progressive through four Stages:
- Acute state characterized by chagomas (swelling at the bite site)
- Generalized stage: fever, swollen lymph nodes
- An asymptomatic chronic stage
- Symptomatic stage characterized by congestive heart failure follwing formation of pseudocysts (clusters of amastigotes in heart tissue)
Diagnosis: Microscopic identification of trypomastigotes in blood, lymph… and Xenodiagnosis
Treatment: earliest stages can be treated with benznidazole or nifurtimox
Parasite-induced heart disease is a leading cause of death in Latin America
What is Trypanosoma brucei?
- Cuases African sleeping sickeness
- The insect vector is the tsetse fly
- Humans usually infected when bitten by infected tsetse flies
What is African sleeping sickness?
Progresses through three stages if left untreated:
- Site of the fly bite becomes a lesion with dead tissue
- Fever, lymph node swelling, and headaches
- Meningoencephalitis
Infections characterized by cyclical waves of parasitemia
The parasite changes its surface antigens with each cycle
Immune system incapable of clearing infection
Diagnosis: Microscopic identification of trypomastigotes in blood, lymph
Clearing tsetse fly habitats reduce the cases of disease
What is Leishmania?
- Causes leishmaniasis
- Endemic in parts of teh tropics and subtropics (Central and South America)
- Wild and domestic dogs and small rodents are comon hosts: Is a zoonosis, transmitted by sandfly
- Leishmania* has two developmental stages:
1. Amastigotes (Lack flagella) : multiply in host’s macrophages and monocytes
2. Promastigotes (flagellated): develop extracellularly within a vector’s gut
What are three clinical forms of leishmaniasis?
The three forms are:
- Cutaneous Leishmaniasis: large painless sores on head and face region
- Mucocutaneous leishmaniasis
- Visceral leishmaniasis (kala-azar) fatal
Most cases heal without treatment
Diagnosis by microscopic identification of amastigotes in samples from cutaneous lesions, spleen, bone marrow
Prevention limitined to reducing exposure to reservoir and vector
What are some of the characteristics of* **Giardia intestinalis?*
- Found in intestinal tract of animals and environment
- Causative agent of giardiasis (beaver fever)
- Common **gastrointestinal disease in US**
- Ingest cysts in contaminated water or when swimming
- Range from asymptomatic infection to GI disease
- Giardia have a similar life cycle to Entamoeba
- Trophozoites multiply in the small intestines (resemble a face)
- Foul smelling stools (“rotten egg” smell)
- Treatment: Metronidazole drug of choice
- Prevent infection by filtering water
What are some of the characteristics of Trichonmonas vaginalis?
- Most common protozoan causing human disease in industrialized nations
- Lives in the genitourinary system of men and women
- Transmitted almost exclusively via sex
- Occurs in people with preexisting STD or multiple sex partners
- Infection of women results in vaginosis
- Infection of men is typically asymptomatic
- Diagnosis by microscopic observation of actively motile trophozoites in vaginal and urethral secretions
- Trophozoites are flat, possess five flagella and a sail-like undulating membrane
- Prevention involves abstinence and safe sex
How does a apicomplexan undergo schizogony?
Multiple mitoses form a multinucleate schizont; then cytokinesis occur
Release numerous uninucleate daughter cells called merozoites
