Micro2 X4: Ch 50, 51, 52

Parasitic infections are....

globally prevalent

What major parasitic diseases cause significant morbidity and mortality?

malaria, schistosomiasis, hookworm

What does disease severity depend on? Esp in what?

parasite burden, especially in helminth infections such as hookworm anemia.

What do parasites tend to avoid doing?

avoid killing their host

What does parasitic disease usually result from?

chronic or heavy infection rather than acute toxicity.

What are many human parasitic infections the result of? What do they require?

-zoonoses

-requiring animal hosts

What host do Taenia saginata require?

cattle

What kind of hosts are humans considered for parasites?

dead-end hosts

How do protozoa replicate? What does this mean? Examples?

-replicate within the host, enabling disease from very small inocula

-Giardia, Cryptosporidium

What is the importance of cysts? Example of parasite that does this?

-enable environmental survival and fecal-oral transmission for many GI protozoa

-Giardia

Where do Helminths not multiply? Explain their infectious form?

-Helminths do NOT multiply within humans

-one infectious form → one adult worm; burden reflects cumulative environmental exposure.

What is central to a parasites ability for chronic infection? What are two examples?

-Immune evasion

-schistosomes coat themselves with host proteins

-trypanosomes undergo antigenic variation

What determine parasitic infection patterns? What are two examples?

-Tissue and species tropisms

-P. vivax requires Duffy antigen

-temperature differences dictate Leishmania disease forms

What may parasitic pathology result from? Especially in what case? Examples?

-Pathology may result from host immune responses

-especially chronic inflammation

-schistosomiasis, filariasis, cysticercosis

What is a characteristic of invasive helminth infections? What is it driven by?

-Eosinophilia

-driven by Th2 cytokines and IgE-mediated responses

When may long term complications from parasitic infections arise?

years to decades later

What are some potential long-term complications from parasitic infections?

portal hypertension, bladder cancer, neurocysticercosis, and chronic Chagas disease

What parasites are portal hypertension and bladder cancer associated with?

-portal hypertension = S. mansoni

-bladder cancer = S. haematobium

How to control parasitic diseases?

life-cycle interruption, including sanitation, vector control, mass drug administration, and (rarely) vaccines

What do bloodstream protozoa do? What does it cause? Examples of protozoa that do this?

-infect and destroy RBCs, causing anemia and systemic symptoms

-malaria and babesiosis

What are examples of tissue-invasive protozoa and what do they cause?

Toxoplasma, Trypanosoma brucei, and T. cruzi

-cause organ-specific disease--> brain, heart, eyes

What five plasmodium species infect humans?

P. falciparum, P. vivax, P. ovale, P. malariae, P. knowlesi.

How is malaria transmitted?

via the female Anopheles mosquito, injecting sporozoites, the infectious stage

Describe the hepatic and erythrocytic stages of malaria?

-Hepatic stage is asymptomatic

-erythrocytic stage produces symptoms--> fever, anemia, paroxysms

What do P. vivax and P. ovale form? What does this cause? Treatment?

-P. vivax and P. ovale form hypnozoites, causing relapsing malaria

-treatment requires primaquine/tafenoquine

What does P. falciparum infect? What does it lead to?

-infects RBCs of all ages, leading to the highest parasitemia and greatest mortality risk

What does PfEMP-1-mediated cytoadherence cause?

-sequestration, microvascular obstruction, and severe complications (e.g., cerebral malaria)

What is classic malarial paroxysm?

synchronized RBC rupture → cytokine surge (TNF, IL-1) → fever/chills.

diagnosis of malaria

-Microscopy (thick & thin smears) = gold standard

-Rapid Antigen Detection Tests are rapid but less sensitive at low parasitemia

What does Chloroquine do? How? What issue may occur?

-kills parasites by blocking heme detoxification in the food vacuole

How does Chloroquine resistance occur?

via efflux pumps

What does Chloroquine-resistant P. falciparum require for treatment?

alternative agents (atovaquone- proguanil, artemether-lumefantrine, quinine + doxycycline)

What must malaria prophylaxis match? What does this mean?

-match regional resistance patterns—chloroquine ineffective in most of Africa, Asia, South America

What does Babesia microti do? How is it transmitted? What else has the same vector?

-infects RBCs directly (no liver stage)

-transmitted by Ixodes tick--> same vector as Lyme disease

What do Babesia form and what are these called? What is it often confused with?

-forms tetrads--> "Maltese cross"

-can be confused with P. falciparum on smear

Babesiosis treatment

-atovaquone + azithromycin

-severe cases may require exchange transfusion

Toxoplasma gondii transmission and host

-ingestion of tissue cysts (undercooked meat) or oocysts (cat feces)

-cats are the definitive host

What are the risks for immunocompromised patients (eg AIDS patients) with toxoplasmosis? How are they treated?

-ring-enhancing brain lesions

-treated with pyrimethamine + sulfadiazine/clindamycin

How are intestinal/ vaginal protozoa classified by?

classified by motility and life cycles

What are examples of intestinal/ vaginal protozoa?

amebae, flagellates, apicomplexans, and microsporidia

What do entamoeba histolytica cause, via what? What is significant about this?

-amebiasis with classic flask-shaped ulcers and potential liver abscesses via portal spread

-microscopy cannot distinguish it from nonpathogenic look-alikes

E. histolytica transmission

fecal-oral

Main reservoir of E. histolytica?

asymptomatic cyst shedders are the main reservoir—diarrheal patients mostly shed noninfectious trophozoites

What is needed for E. histolytica pathogenesis?

-adherence via Gal-GalNAc lectin

-contact-dependent killing (amebapores),

-phagocytosis of host cells

What type of immunity is essential for E. histolytica?

Cell-mediated immunity

What should individuals infected with E. histolytica not do? Why?

-take steroids

-they predispose to severe disseminated amebiasis by blunting this cell-mediated immunity

diagnosis of amebiasis

requires antigen detection or PCR, since microscopy cannot distinguish pathogenic from nonpathogenic Entamoeba species

treatment of amebiasis

-requires two steps: metronidazole for tissue disease followed by a luminal agent (paromomycin/iodoquinol) to clear cysts

What does Giardia lamblia cause? Why?

causes malabsorptive diarrhea due to non-invasive attachment to the duodenum/jejunum

What is significant about Giardia lamblia cysts?

cysts are chlorine-resistant, enabling waterborne outbreaks

Giardia pathogensis is (blank) not (blank)

functional, invasive

Giardia pathogenesis? What can this lead to?

-tight junction disruption, villous blunting, and fat malabsorption

-steatorrhea (excretion of excess fat in stool) and vitamin deficiencies

Why can cryptosporidium oocysts cause large outbreaks?

-Cryptosporidium oocysts are chlorine-resistant, causing major waterborne outbreaks (e.g., Milwaukee 1993)

What can cryptosporidium oocysts cause in AIDS patients?

evere persistent diarrhea in AIDS patients

Where does Cryptosporidium complete its life cycle?

intestinal microvilli

What does severity of Cryptosporidium infection depend on?

determined by immune status—self-limited in immunocompetent patients, chronic in immunocompromised

What does Cyclospora require for maturation? What does this mean?

-requires environmental maturation (sporulation), so freshly passed oocysts are noninfectious

What are Cyclospora outbreaks strongly associated with?

contaminated produce

How is Trichomonas vaginalis transmitted? Symptoms?

-sexually transmitted only

-causes frothy vaginitis in women

-is often asymptomatic in men

Trichomonas vaginalis diagnosis

wet mount or Nucleic Acid Amplification test

treatment of Trichomonas vaginalis

-Metronidazole (single dose) is first-line for trichomoniasis,

-both partners must be treated to prevent reinfection