RA3: Intro to Clinical Parasitology Flashcards
Endoparasite
Live within body of host, mostly protozoa and helminths
Ectoparasite
Live on the surface of their host, usually arthropods (ex. ticks and mites)
Obligate vs. facultative
Obligate must spend at least part of their life cycle in association with host, while facultative are capable of leading both free or parasitic existence
Vector
Insect that transmits infectious agent from one host to the next
Protozoa
Unicellular eukaryotic microbe
Helminths
Worms that can vary in length and are covered in cuticle
Nematode
Roundworm
Cestode
Tapeworm
Trematode
Fluke (complex flatworms)
Definitive host
Host in which the parasite reaches sexual maturity
Intermediate host
Host that harbors larval or asexual stages of parasite
Reservoir host
Definitive host (animal) that serves to maintain parasite’s life cycle in environment
Cysts
Environmentally resistant, facilitate transmission to hosts (normally protozoa)
Trophozoite
Metabolically active, motile, feeding stage of parasitic protist
4 classes of protozoa
- Amoeba (pseuodopodia)
- Flagellates (flagella)
- Sporozia (gliding)
- Ciliates (cilia)
Schizogony
Asexual reproduction process of sporozoans and amoebas
Sporogony
Sexual form of reproduction that entails multiple nuclear divisions followed by cytokinesis after zygote formation
3 factors in transmission of parasitic diseases
- Source of infection
- Mode of transmission
- Presence of susceptible host
Ingestion
Oral transmission due to consumption of food/water contaminated with parasite eggs or cyst; fecal contamination implicated in transmission of parasitic diseases
Penetration/inoculation
Larval forms of some helminths found in soil or water can penetrate skin of host
Direct transmission
Trichomonas vaginalis, causative agent of common STD, is transmitted through sexual contact
Congenital transmission
Transmission from mother to infant (toxoplasmosis, malaria)
Transfusion and transplantation
Potentially any blood or tissue dwelling parasite, seen in malaria and trypanosomes
Mechanical damage by parasites
Caused by presence or movement of parasite (lots of worms)
Damage caused by parasite products
Helminths and intestinal protozoa produce products aiding in establishment and persistence of infections
Immunopathology
Response of host to parasitic infection; ex. granulomas can disrupt blood flow
Immune responses to protozoal infection
- Neutralizing antibody
- Antibody + complement
- Antibody/complement opsinization
- Activated macrophages
- CD8+ cytotoxic T cells
What problems do helminthic infections pose?
- -Too big for phagocytosis
- -Often covered with protective cuticle or sheath to protect against complement-mediated lysis
- -Eosinophilia is hallmark of these
Size in evasion of immune defense
Helminths unlikely to be phagocytosed or destroyed by macrophages or neutrophils due to large size
Anatomical location in evasion of immune defense
Residing in lumen makes difficult to reach them
Intercellular sequestration in evasion of immune defense
Residing for a period of time sequesters from destruction by humoral defenses
Formation of cyst in evasion of immune defense
Provide impenetrable barriers to immune system
Avoidance of phagolysosomal destruction in evasion of immune defense
Some parasites can survive and replicate in inhospitable environment of lysosomes
Antigenic variation in evasion of immune defense
Different forms of malaria have different antigens, African trypanosomes have new waves every so often that has different antigens
Antigenic masking in evasion of immune defense
Larval and adult forms of helminths will cost in proteins or lipids to mask antigens from immune system
Immunosuppression in evasion of immune defense
Infected individual can become susceptible to secondary infections
Anti-protozoal drugs
Target rapidly proliferating metabolically active cells
Anti-helminths
Targeted at non-proliferating adult helminths
