Parasitology

symbiosis

how two different organisms live together

What are the four categories of symbiosis?

1. Commensalism
2. phoresis
3. parasitism
4. mutualism

Commensalism

a. independent survival
b. "eating at the same table"
c. spacial proximity allows to feeds on substances captured and ingested by host
EX: sea anemone on hermit crab shell

Phoresis

a. "to carry"
b. phoront (smaller) carried by other organism (larger), host
c. no dependency in acquiring food
d. no physiology interaction or dependency
EX: fungi growing on aquatic arthropods

Parasitism

a. between two organisms
b. parasite (smaller) and host
c. parasite physiologically dependent
d. relationship: permanent (tapeworms) or temporary (mosquitos)
e. immunological response to the host to reduce number of parasites

Ectoparasite

A parasite that lives on but not in their host. Attaches to the outer surface of the host or are superficially embedded in the body.

Endoparasite

Live within the body and tissues of their hosts. At sites such as the alimentary tract, liver, lungs and urinary bladder.

Definitive Host

The species in which parasite undergoes sexual production.

Intermediate Host

The species in which a part or whole of asexual reproduction occurs.

Transfer or Paratenic Host

Not necessary for the completion of parasite's life cycle but it utilized as a temporary refuge and a vehicle for reaching an obligatory, usually the definitive, host in the cycle.

Vector

An arthropod or some other invertebrate that serves as a host as well as a carrier for a parasite (not a transfer host, needed to complete the life cycle).

Reservoir Host

Animals that serve as sources of infective organisms for humans. The two types are sylvatic (wild animal) and domestic (domestic animal).

Incidental Host

An unnatural host to which the parasite may not be adapted for replication; unusual pathology.

Mutualism

Association in which the parasite and host depend on each other physiologically. For example, flagellated protozoans and the termites in whose gut they live. The flagellate receives nutrients (carbs) from wood chips, and synthesizes and secretes cellulase

What are the routes of parasite transmission

1. Oral/fecal route
2. aspiration (unusual)
3. blood burne

What are general characteristics of a protozoa?

a. single celled
b. reproduce by fission
c. classified on basis of locomotion
d. maybe extracellular or intracellular
e. may be invasive or non-invasive

What are the general replication stages of protozoa?

1. Trophozoite
2. Cyst
3. Excystation
4. Schizogony (merogony)
5. Schizont
6. Sporogony (gametogony)

Trophozoite

motile stage (feeds and multiplies) of replication, maintains colony

Cyst

immobile stage of replication, transmitted, survives outside of body

Excystation

Stage of replication when the trophozoite emergences from the cyst.

Schizogony (merogony)

intracellular, stage of asexual replication of protozoa

Schizont

Stage of replication where mammalian cell contains intracellular replicating protozoa

Sporogony (gametogony)

stage of replication with formation of male and female gametocytes

Kinetoplast

Flagellated protozoan parasite where flagella varies depending on developmental stage. Mitochondrion, interconnected minicircle or maxicircle DNA, species - species molecular diagnosis contain parasite at the base of their flagella. The few that cause hum

What are other stages of hemoflagellates?

1. amastigote
2. promastigote
3. epimastigote

Amastigote

Leishmanial rounded intracellular stage of hemoflagellates.

Promastigote

Flagellated extracellular stage of hemoflagellates, kinetoplast at anterior end.

Epimastigote

More elongated extracellular stage of hemoflagellates with short undulating membrane and kinetoplast placed most posterior near the nucleus.

Helminthic

Multicellular organisms, the worms. Reproductive via hermaphroditic or sexual reproduction. Classified on the basis of their body shape. Further classified on the basis of their intermediate host. May be "non-invasive" or "invasive". Includes Nematodes.

Cestode

Flat segmented bodies with head (called scolex) + segments (called proglottids). Live in intestines of many vertebrates. Usually hermaphroditic. Lack of digestive system. include Trematodes (flukes) and Cestodes (tapeworms).

Nematodes

cylindrical (like earth worms), bilaterally symmetric. Barely macroscopic up to 8-10 inches (A. lumbricoides). Well developed (mouth, esophagus, anus). Tubular and linear. Separate male and female. Non-invasive: intestinal sites (lumen, mucosa, submucosa)

Trematodes (flukes)

Leaf-shaped (dorsoventrally flat). Bilaterally symmetric. Rudimentary. Blinded pouch (no anus). Food and excrement in and out the same opening (stoma). Hermaphrodites. Except for blood fluke, which have male and females. Visceral sites (liver, intestine,

Cestodes (tapeworms)

elongated and flattened dorsoventrally (like a ribbon). Segmented (proglottids), starting at the neck. Millimeters to meters. No internal digestive system. Exterior surface of the proglottids directly absorbs digested food metabolic products. Organism tak

Mycology

Study of Fungi. Fungi in general are beneficial to mankind in breaking down and recycling organic matter. Provide useful bioactive secondary bioactive metabolites such as antibiotics and immunosuppressive drugs.

Fungi

ALL are eukaryotic. Each cell contains at least one nucleus and nuclear membrane, ER, mitochondria, and secretory apparatus. Can be obligate or facultative aerobes. Also have chemotrophic properties. Relative to bacteria, fungi are slow growing with cell

Obligate aerobe

Aerobes require oxygen for aerobic cellular respiration in which they use oxygen to oxidize substrates (for example sugars and fats) in order to obtain energy.

facultative anaerobes

Can use oxygen, but also have anaerobic methods of energy production.

Chemotrophic

secrete enzymes that degrade organic material into soluble substrates that are passively taken into the cell by active transport.

What are the four types of heterotrophs?

1. Saprobes
2. Symbionts
3. Commensals
4. Parasites

Saprobes

Organisms that live together in which the association is mutual

Symbionts

Organisms that live together and in which the association is of mutual advantage.

Commensals

Organisms living in a close relationship in which one benefits from the relationship and the other neither benefits nor is harmed.

Parasites

Organisms that live on or within a host, from which they derive benefits without making any useful contribution in return: in the case of pathogens the relationship is harmful to the host.

How is Fungi classified?

1. The kingdom is Fungi (Myceteae)
2. Can be ID'd from other eukaryotes by: a rigid cell wall composed of chitin and glucan AND a cell membrane in which ergosterol (fungi) is substituted for cholesterol (animal).

How is a fungal infection treated?

1. treat underlying disease
2. reduce other risk factors

What are the three antifungal targets?

1. Beta(1,3)-D-glucan synthase -- membrane
2. Ergosterol -- membrane
3. C14-alpha-demethylase (ERG11) -- ergosterol synthesis

echinocandins (caspofungin)

Disrupts cell wall synthesis at Beta (1,3)-D-glucan synthase.

Polyenes (amphotericin B)

Binds to ergosterol to disrupt the membrane by creating a transmembrane channel that leads to monovalent ion (K, Na, H, and Cl) leakage, which is the primary effect leading to fungal cell death.

Azoles (fluconazole)

Inhibits C14-alpha-demethylase preventing lanosterol from being oxidized and synthesizing ergosterol.

Fungal Taxonomy

Relies on morphology and mode of spore production.
1. unicellular or multicellular
2. yeast form
3. mould form
4. dimorphic (both mold and yeast forms) - many fungi of medical importance fall into this category

Yeast

1. usually unicellular
2. reproduced by budding or fission in which the progenitor/mother cell pinches off a portion of itself to produce a progeny or daughter cell - asexually
3. daughter cell may elongate to form pseudohyphae
4. usually produce round, p

Mold

1. Multicellular
2. consist of threadlike structures called hyphae - branching cylindrical tubes
3. hyphae elongate by a process known as apical extension
4. coenocytic - hollow and multinucleate
5. septate - divided by partitions or cross walls
6. hyphae

vegetative hyphae

penetrate supporting medium and absorb nutrients

aerial hyphae

project above the cell surface of the mycelium and usually bear reproductive structures . May produce specialized structures known as conidia (Asexual reproductive organs). Can easily become airborne and serve to disseminate the fungus. Size, shape, and c

What are the five major classes of fungi for medical importance?

1. Zygomycetes
2. Ascomycetes
3. Archiascomycetes
4. Basidiomycetes
5. Dueteromycetes

How are fungi reproduced?

By the formation of spores

Sexual Reproduction

Involves meiosis preceded by the fusion of the protoplasm and nuclei of two compatible mating types

Asexual Reproduction

Involves mitosis only

Fungi Reproduction

Produce sexual and asexual spores

Teleomorph

form of the fungus that produces sexual spores

anamorph

form of the fungus that produces asexual spores

Mycoses

Fungal infections. Most pathogenic fungi are exogenous (natural habitats are water, soil, and organic debris). Can be classified as superficial, cutaneous, subcutaneous, systemic, and opportunistic. There is overlap in these classifications since systemic

Mycoses is classified by location of the fungal infection. What are the six locations?

1. Superficial (skin, hair)
2. Cutaneous (skin, nails)
3. Mucosal (oral, vaginal)
4. subcutaneous
5. respiratory (inhalation)
6. systemic

Superficial Mycoses

Infection of the stratum corneum (outermost layer of epidermis). EXAMPLE: White piedra - yellow nodules on hair

Cutaneous mycoses

Caused by dermatophytes, involve deeper layers of skin, hair, or nails. While limited to the keratinized layers, they may invoke host immune reactions causing localized irritation, leading to secondary bacterial infections. EXAMPLE: tinea pedis - athlete'

Subcutaneous mycoses

Caused by fungi that normally reside in soil. Enter the skin or subcutaneous tissue by traumatic inoculation with contaminated material. Usually confined to subcutaneous tissue but in rare cases become systemic. EXAMPLE: sporotrichosis - caused by Sporoth

primary pathogens

capable of initiating infection in a normal, healthy, immunocompetent host. Will colonize in suitable microenvironmental niche where it can avoid host defense mechanisms and multiply. When large numbers are inhaled infection, colonization, tissue, invasio

Saprobic Phase

characterized by filamentous septate hyphae typically found in soil or decaying vegetation, that produces the airborne infectious cells.

Parasitic Phase

adapted to grow at 37C and to reproduce asexually in the alternative environmental niche of the host respiratory mucosa

What are two stains for Coccidioides immitis?

1. Gomori methanamine silver (GMS)
2. Periodic Acid Schiff (PAS
3. Hematoxylin and eosin (H&E)

Gomori methanamine silver (GMS)

more advantageous since it stains old and nonviable fungal elements more efficiently than the other two

Hematoxylin and eosin (H&E) stain

very useful to visualize the host's response but is not a special fungal stain. It does not stain most of the fungi, except the aspergillus spp. and the zygomycetes.

Why use both GMS and H&E stains?

Can visualize both tissue reaction and the infecting fungus

Opportunistic Pathogens

state of host is of primary importance in determining the pathogenicity of opportunistic fungal pathogens (Candida spp., Aspergillus spp.). In most cases these organisms may exist as benign colonizers or as environmental saprobes and only cause serious in

What are the three types of Candidiasis?

1. Mucosal
2. cutaneous
3. disseminated

Mucosal Candidiasis

1. oral-pharyngeal
2. vaginal
3. esophageal, gastrointestinal, and urinary tract

Oral-pharyngeal candidiasis (oral thrush)

white adherent patches on oral mucous membrane, red lesions beneath. common in infants, immunocompromised individuals

vaginal candidiasis

often following antibiotic therapy that reduces the normal bacterial vaginal flora

Cutaneous candidiasis

especially in warm, moist skinfolds; erythema

disseminated candidiasis

fungemia (catheter-associated), peritonitis (GI perforation), hepatitis (transported to liver via portal vein, form abscesses detectable by MRI), endocarditis (heart valves), pulmonary, meningitis, ophthalmitis. compromised individuals, especially acute l

CHROMagar Candida

Based on how candida spp. metabolize the chromogenic substrates in the agar (C. krusei - orange; C. albicans - green; C. tropicalis - black)