Lecture 8: Pathogenesis and Diagnosis of Parasitic Infections in Biology

Disability-adjusted life-years (DALYs)

a composite measure of disease burden capturing both premature mortality and prevalence and severity of ill health

the health loss due to a specific disease or injury

What does DALYs quantify?

thorough differntial diagnosis

what is important for applying the appropriate treatment, especially because some antiparasitic agents are quite toxic?

exogenous

Most protozoan and helminthic infections are:

tsetse fly

how is African sleeping sickness transmitted?

duffy antigen

protein on RBCs where parasites latch onto to get into the RBC

Less malaria caused by p. vivax

People who do not have Duffy antigen have:

intermediate host

when a human has a worm larvae in the tissue what kind host is the human?

helminths

TH2, complement, IgE response, mast cells, eosinophils

TH2 responses

through igG and IgA are important for preventing parasite binding to tissue to block binding and entry into cells, to activate complement and as an opsonin

IgE

bound to mast cells and eosinophils binds parasite and parasite antigen, and releases histamine and toxic substances to promote expulsion

mucus secretion

TH2 responses activate _____ ____ into colon to promote expulsion.

TH1 responses

especially important for intracellular infections (leishmania) but promote inflammation

granuloma formation

what is important for intracellular infections (schistosome)

TH17 responses

reinforce epithelial and neutrophil action for extracellular parasites

anaphylactic reaction (type 1)

TH2, complement, IgE response, mast cells, eosinophils

eosinophils

what are one of the major defense mechanisms against worms that have major basic protein?

eosinophilia

what do we see often with worm infections?

cytotoxic reaction (type 2)

Antibody + antigen on cell surface: complement activation or antibody-dependent cellular cytotoxicity

Lysis of cell-bearing microbial antigens

Result of cytotoxic reaction

anaphylactic shock

what can occur with some helminth infections?

immune complex reaction (type 3)

Antibody + extracellular antigen complex

Inflammation and tissue damage; complex deposition in glomeruli, joints, skin vessels, brain; glomerulonephritis, and vasculitis

result of immune complex reaction

cell mediated reaction (delayed type 4)

Sensitized T-cell reaction with antigen, liberation of lymphokines, triggered cytotoxicity

Inflammation, mononuclear accumulation, macrophage activation - Tissue damage

Result of cell mediated reaction

antigenic variation

Variation of surface antigens within the host

molecular mimicry

Microbial antigens mimicking host antigens, leading to poor antibody response

concealment of antigenic site (masking)

Acquisition of coating of host molecules

intracellular location

Failure to display microbial antigen on host cell surface

Immunosuppression

Suppression of parasite-specific B-cell and T-cell responses - degradation of immunoglobulins

microscopic exam

wet mounts, permanent stains of stool, stool concentrates, blood, tissue

immunodiagnostics

antigen detection, antibody response

molecular diagnostics

nucleic acid hybridization or amplification for detection/ identification

immunoassays

what can be very effective for parasitic identification?

fecal specimen collection

(three specimens recommended) under appropriate conditions (fast delivery to lab, preservatives, absence of certain medications, drugs)

sputum

what should be used for certain parasites?

ova and parasites (O&P)

Microscopic stool examination for ____ ___ ____ might miss certain parasites

duodenal, small bowel

sometimes even a ______ content aspiration or ____ ____ biopsy is necessary

proctoscopic or sigmoidoscopic

what examinations can be used in some cases?

urine or urogenital specimens (trichomonas)

additionally, what specimens can be taken to aid?

parasitic infections of blood and tissue

blood films for staining, CSF, tissue specimens, sputum

trypanosomes

animal inoculation for:

chagas disease

xenodiagnositcs for:

kissing bug

what is the vector of chagas disease? through the fecal matter of the vector