topic 14 Flashcards
What are two types of parasites? What are subtypes of these? examples?
Endoparasites
Protozoa – single-celled
Metazoa (helminths) – multicellular
Cestodes (segmented worms)
Trematodes (flatworms)
Nematodes (roundworms)
Ectoparasites
Hexapoda: Lice 6-legged; e.g. - “Crabs” Arachnida: Mites & Ticks 8-legged, e.g.- “Scabies” Numerous disease vectors
What are the general features of parasitic infections?
Major world problems Complex life cycles Co-evolution with hosts Chronic infections Immunopathology No effective vaccines
What are some examples of adaptability of parasitic infections?
Drastic life stage changes Antigenic variation Immunosuppression Immunological camouflage Drug resistance
What are some ways in which parasites are passed from human to human?
Fecal-oral
Fecal cutaneous
vector borne
What are some ways in which parasites are passed from animals to humans
fecal-oral
fecal-cutaneous
vector borne
improper cooking
What are some general stages of the parasitic lifestyle? What are some points of intervention in that lifecycle
extrahuman life stages
amplification/differentiation-public health measures
Human life stages
Infection-prophylactic vaccines (malarial chemoprophylaxis)
Maturation
Replication-Drug treatment of clinical disease
What type of immunity combats intracellular and extracellular parasitic infections? What cytokines are involved? What are some examples?
Intracellular parasites controlled by Type 1 immunity
CD4+ T cells inhibit endosomal replication
CD8+ T cells target cytosolic replication
Th1 cells. Protozoa. IFN-Gamma
Extracellular parasites controlled by Type 2 immunity
Antibody initiates complement/ADCC mechanisms
Mast cells and eosinophils release toxic granules
Helminths. Th2. Ab. IgE. IL-4.
What are some general characteristics of protozoa?
Single-celled pathogens
Complex life cycles
Intracellular/Extracellular
Vector-borne/environmental
What are 3 types of protozoa with examples?
Blood and tissues
- Plasmodium sp. (Sporozoans; malaria)
- Babesia sp. (Sporozoans: Babesiosis)
- Leishmania sp. (Flagellates; chronic ulcers/visceral)
- Trypanosoma sp. (Flagellates; African & American)
- Toxoplasma gondii (Sprorozoan; OIs)
Intestinal
- Entamoeba histolytica (Ameba; dysentery; liver abscess)
- Giardia lamblia (Flagellate; chronic diarrhea)
- Cryptosporidium parvum (Sporozoan: OI/diarrhea)
Urogenital
-Trichomonas vaginalis (Flagellate; STD)
What is the lifecycle of plasmodium falciparum? Where do the clinical manifestations occur?
Sporozoites are injected from a mosquito into human blood stream during a blood meal.
Exoerythrocytic stage: They enter hepatocytes and either continue onward as merozoites into the blood or stay latent in liver as cryptozoites (only 6-12 months)
Erythrocytic stage: The merozoites are able to target all RBCs and thus this stage is more serious in P. falciparum. They infect RBCs in signet ring stage, and go through a cycle of amplification become trophozoites, shizonts, merezoites, and then infecting more cells. This cycle is short in falciparum.
Some merozoites dont enter RBCs and are taken up by a mosquito as macrogametocytes and microgametocytes.
The clinical manifestations are mainly due to the erythrocytic cycle: anemia due to loss of RBCs, and RBCs can get sticky and cause microthromboses, etc.
What is the lifecycle of Plasmodium vivax? How does it differ from falciparum?
It is similar to falciparum. Some differences:
In the liver stage, some cryptozoites will stay latent for the whole life of the host, so they must be treated as well.
The merozoites can’t target all RBCs and thus infect less. The erythrocytic cycle is also slower making the clinical manifestations a little less serious (no microagglutinization).
If a blood smear is taken, P. vivax will have schizonts and merezoites, whereas P. falciparum will only have merezoites.
P. falciparum associated with drug resistance
What are some challenges for developing malaria vaccines? What is one solution?
Distinct life stage antigens Antigenic variation between strains Replicates in RBCs (no class I or II) Th1/CTL attack infected hepatocytes only Polyclonal gammopathy dilutes Ag-sp Ab
Use a mosquito net
What are characteristics of all metazoa (helminths)?
Multi-cellular animals
Eggs/Larvae/Adults lifestage
Type 2 immunity
Eosinophilia
Waht are characteristics of nematodes? What are some examples?
Nonsegmented, roundworms Acellular/collagen-rich cuticle Separate sexes 4 larval molts Intestinal & tissue infections
Ascaris lumbricoides (Giant roundworm)
Trichuris trichiura (Whipworm)
Enterobius vermicularis (Pinworm)
Strongyloisdes stercoralis (Small roundworm)
Ancylostoma duodenale & Necatur americanus
(Old World and New World Hookworms)
What is the lifecycle of Ascaris lumbricoides?
Eggs are ingested.
Larvae hatch in small intestine, enter bloodstream, go to liver, go to heart, reach lung capillaries, enter alveolar spaces, migrate to trachea, are swallowed
Adults mature in small intestine, cause obstruction
Eggs pass out in feces and embryonate in the soil
What is the lifecycle of enterobius vermicularis?
Eggs are ingested
larvae hatch in SI
adults mature in colon then migrate out of anus onto perineum
adults lay eggs on perineum–>itching–>scratching–>eggs on fingers–>eggs in mouths
What is the lifecycle of trichinella spiralis?
Larvae are ingested in raw or uncooked meats
Larvae live and mature in SI
Female sheds newborn larvae that enter lymph and blood (CNS damage, heart failure)
newborn larvae are carried through bloodstream and enter skeletal muscle
larva matures in muscle and nurse cell/larva complex formed.
Causes cysts. discoloration of fingernails
What is the lifecycle of wuchereria bancrofti?
mosquito takes a blood meal, larvae deposited on skin then enter bite wound.
larvae enter lymph, mature in lymph (can lead to elephantiasis)
microfiliariae enter bloodstream
mosquito takes a blood meal, get larvae, infecting larvae develop in mosquito
What is the lifecycle of onchocerca volvolus?
Blackfly takes blood meal, larvae crawl into wound.
adult worms mature in subcutaneous tissue
Adults shed microfilariae into subcut. tissue
microfil. migrate through subcutaneous tissue (can damage eye)
Blackfly takes blood meal, ingests larvae, infecting larvae mature in black fly
What are some examples of tissue nematodes?
Trichinella spiralis (Trichinosis) Dracunculus medinensis (Guinea fire worm) Toxocara canis (Dog worm/Visceral Larva Migrans) Wuchereria bancrofti (Filarial worm/Elephantiasis) Brugia malayi (Filarial worm/Elephantiasis) Onchocerca volvulus (Filarial worm/River blindness) Loa loa (Filarial worm or African eye worm)
What are some characteristics of trematodes and what are some examples?
Nonsegmented flatworms (flukes) Adults have 2 suckers Snails/shellfish are intermediate hosts Miracidia infectious stage for shellfish Cercaria infectious stage for mammals
Schistosoma mansoni/japonicum (Blood/liver fluke)
Schistosoma haematobium (Blood/bladderfluke)
Clonorchis sinensis (Oriental liver fluke)
Paragonimus westermani (Lung fluke)
What is the lifecycle of Schistosoma Mansoni?
snails release cercariae, cercariae enter skin, migrate (basically burrow through tissue) to lungs, then liver via blood stream.
Adults mate in liver, then migrate to mesenterics, adults live in mesenteric venules
Eggs enter SI, are released in feces into fresh water, eggs hatch in fresh water, snails take up miracidium
Liver disease, hepatomegaly
What are characteristics of cestodes (tapeworms)/ What are some examples?
Segmented flatworms Scolex = head Proglottids = body segments Proglottid = infectious unit Humans = definitive hosts Animals = intermediate hosts
Taenia saginata (Beef Tapeworm)
Taenia solium (Pork Tapeworm)
Diphyllobothrium latum (Fish tapeworm)
Echinococcus granulosus (Dog tapeworm)
What is the lifecycle of taenia saginata (cow)/solium (pig)?
Humans ingest raw or undercooked beef containing cysticerci
Cysticerci are released from muscle into stomach
Worms mature and live in small intestine (scolex contains four suckers so it stays in SI)
Adults grow up to 10 m in length, proglottids pass in feces
Cows take up embryonated eggs——->cysticerci
