Parasitology- Study of Protozoa & parasitic worms

How many protozoan species are there?
Over 20,000; Few cause disease

Characteristics of Eukaryotic cells (pertaining to protista)
Unicellular; Motile at some stage of development; Water/soil dwelling; No cell wall; 3um-300um

What is the difference between a trophozoite and a cyst?
Trophozoite is the vegetative stage, and cyst is in the non-vegetative stage

What is a cyst?
A protective capsule that enables parasitic protozoan to exist outside host after defecation & prior to entering new host.

What is involved with asexual reproduction?
Binary fission; budding; schizogony
Schizogony- Nucleus undergoes multiple divisions, then multiple fissions occur. Single cell separates into many daughter cells.

What are gametocytes?
Haploid sex cells involved in sexual reproduction

What are the 4 types of hosts?
Host-where parasite lives
Definitive- Where parasite reproduces sexually
Intermediate- Where parasite

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reproduces asexually or matures
Reservoir- Parasite does not reproduce

Protozoa are categorized based on motility, what are the 4 categories?
Mastigophera- Move via flagella or undulating membrane
Rhizopoda- (protozoan amoebas); Move via pseudopodia
Ciliphera- Move via cilia arranged in rows on the cell
(largest group, but only one is parasitic to humans)
Apicomplexia- Non-motile in mature form, glides in part of life cycle. Requires both definite/interm. host. (sex/asex)

Describe Giardiasis
Etiology- Giardia Intestinali; flagellated protozoa
Transmission- Fecal shedding spreads cyst- may last 2 mos in environment. Untreated H2O/swimming. Fecal/oral. Dog-person, or person-person

What is the pathogenesis of Giardiasis?
Cyst is digested away thru stomach int duodenum->liberates giardia in trophozoite form. Receptor binds to receptor on duodenal mucosal cell-> then suction attachment->digests epithelial cells/tissue fluids->edema->malabsorption

What are the S/S of giardiasis?
Chronic diarrhea (weeks), dehydration, malaise, nausea, cramps, significant wt. loss (malabsorption), Hydrogen sulfide odor may be detected on breath or in stool
*Dx-String test, test for cysts in feces, ELISA

Describe trichomoniasis
Etiology- Trichomonas vaginalis; Only protozoan STD. Affects only women. A mastigophera w/ undulating membrane.

What is the pathogenesis of Trichomoniasis?
Increased pH may increase presence. ABs decrease bacterial microbiota->less Lactobacilli + less others->less acid. Feed on host tissue->erosion of epithelium

Transmission & S/S for trichomoniasis
STD, towel, toilet seat. No cyst, so short survival outside
S/S- yellow/green genital tract discharge…profuse due to leukocyte migration to area; Frothy w/foul odor (metabolic gas); Vaginal irritation/inflamm./itching/tender/red. Most or 1/2 cases are asymptomatic. Co-infected w/gonnorhea

What is Trypanosoma & how does it work?
Parasitic flagellate protozoa. Displays specific Ag when introduced to blood. W/in 2 wks, descendents are displaying a different Ag. Original AB’s not effective against new Ag. Microbe can make 100-1000 different Ag’s as it clones self. Turns on 1 glycoprotein at a time.
*Immune system always playing catch up. Infection can last for decade w/trypanosomes.

Which 2 protozoans are good at evading host defenses for a long time?
Trypanosoma & Giardia

What is the only pathogenic amoeba found in the human intestine?
Entamoeba histolytica (Amoebic Dysentery)

Describe Amoebic Dysentery
Etiology: Entamoeba histolytica.
Transmission-fecal/oral. Cysts are transmitted in human feces that eventually enters food/H2O. Ingested cysts’ wall is digested away in duodenum. Excystment frees trophozoite. Enters Large Intestines’ epithelial mucosal cell, multiplies intercellularly->secretes enzymes->causes lysis. Dissolves tissues->penetrates deeper layers of mucosa->erosive ulceritis

What are S/S of amoebic dysentery?
Frequent stools, bloody mucoid stools, intestinal ulceration-> erosive ulcerations can perforate bowel->hemorrhage, abdomial pain, wt. loss.
*5% of Americans are asymptomatic carriers

What is known as an amoebic neuro disease?
Naegleria meningoencephalitis

Describe Naegleria meningoencephalitis (Amoebic neuro disease)
Etiology: Naegleria fowleri
Transmission- Infiltrate brain thru olfactory mucosa->olfactory nerve->proliferates in brain->inflammation damages neurons->98% fatal

What are the S/S of Naegleria meningoencephalitis?
Neuro-related death
*Common victims are children who swim in ponds/streams
Cases reported most parts of world- a few each yr. in US

Describe Balantidium coli
Causes a severe form of dysentery. Ingested cyst ruptures in colon, trophozoite released, produces proteases, destroys gut cells, cyst excreted.
S/S- Causes inflammation/ulceration of colon. Leads to hemmorhagic diarrhea.

What is a ciliophera?
Parasite that moves via cilia arranged in rows on the cell.
(ie. Balantidium coli)

What is Rhizopoda?
Protozoan amoebas. Move via pseudopodia
(ie. Entamoeba histolytica, Naegleria fowleri)

What is Apicomplexa?
A protozoan that is non-motile in mature form. It glides in part of life cycle. Requires a definitive host & intermediate host.
*Obligate intracellular parasite. Tips of cells have apical organelles w/enzymes that pentrate host cell.
(ie. Toxoplasma gondii, Cryptosporidium parvum, & Plasmodium vivax/ Plasmodium falciparum (Malaria))

What are 3 examples of mastigopheras?
Giardia intestinali, Trichomonas vaginalis, & Trypanosoma brucei gambiense (African sleeping sickness)

Describe Toxoplasmosis
Etiology: Toxoplasma gondii
Infects 1/2 adults worldwide. Cats-culprits & definitive host. Parasite can only produce oocysts in cat.
Humans-interm./accidental dead end host

How is Toxoplasma gondii transmitted?
Ingestion of undercooked contaminated meat. Oocyst exists as pseudocyst in under-cooked muscle of rodent, bird, small animal.
Oocyst shed in cat feces->survives months in soil. Contaminates food, H2O. Fecal-oral Can be inhaled from air or dust contaminated w/ cat droppings. Rodents lose cat avoidance behavior, insuring transmission to cat.

What is the pathogenesis of Toxoplasmosis?
Oocyst ingested->excystment->trophozoite invades cell->trophozoite reproduces->ruptures cell->trophozoites released->distribute themselves throughout body(myocardium, brain, eye, skeletal muscle, any nucleated cell)

What is the immune response when infected w/ Toxoplasma gondii?
Human cell may form a tissue cyst to wall off, or isolate parasite (w/ membrane of ER). Numerous protozoans produced in cyst reproduce very slowly as bradyzoites. These can persist for yrs, perhaps life, especially in brain. Immune sys. never purges parasite.
S/S- Most asymptomatic due to immune system depression

What is the potential host response with Toxoplasma gondii in an immunosuppressed individual?
*Can cause severe neurological damage to unborn fetus if initial infection during pregnancy.
**Acute myocarditis, pulmonary necrosis, damaged retina, heavy cerebral involvement. Primary marker for AIDS

Describe malaria
Etiology: Plasmodium vivax & Plasmodium falciparum
*300,000,000-500,000,000 infected yearly
*2-4million annual deaths (mostly children)
Transmission- Anopheles mosquito- intense & constant in tropical area

Describe the Plasmodium life cycle
Female anopheles mosquito->trophozoite injected into blood->hepatocyte->asexual schizogony->infected cytes burst in 10 days-> enter RBC’s 10s->asexual repro.->RBC’s burst->new RBC’s (some into M/F gametocytes)->mosquito siphons blood->gametic sexual repro. in mosquito->trophozoites enter insect salivary glands

What are the S/S of malaria (Plasmodium vivax & falciparum)?
Shaking chills, fever up to 104 (pyrogenic effect), weakness, fatigue for wks w/out relief, possible shock, anemia, liver failure, death; Cerebral malaria->brain damage->RBC’s become sticky in capillaries->obstruction->coma->death; Hb->kidneys->black urine (likely fatal);
*Hepatocytes may harbor for 5 yrs.

What are helminths? Give 2 examples.
Multicellular, eukaryotic, parasitic animals specialized to live inside host
*Platyhelminthe (flatworm); Nematode (roundworm)

What are the characteristics of helminths?
*Some lack digestive system->rely on host
*Poor nervous system->host environment constant
*Poor locomotion- No food search
*Large # of eggs
*Dioecious (separate M/F)
*Monoecious- M/F repro organs same worm
*Complex life cycle- succession of intermediate hosts + definitive host. Hard to treat

What are 2 classes of platylhelminths?
Trematode (fluke); Cestode (tape worm)

How do flukes obtain nutrients?
They utilize suckers to attach & obtain nutrients. Incomplete GI system.
*Named according to host tissue (ie. Lung fluke)

Describe a lung fluke
Etiology: Paragonimus westermani
Undercooked crayfish eaten->encysted larvae freed->bores out of small intestines->blood->lungs->in bronchiole develops into adult lung fluke->produces eggs->cough up->swallows infected eggs->excretes in feces->eggs to H2O->larvae develops->enters interm. host (aquatic snail)->larval form into another larvae->develops into free swimming larva->larvae bores out of snail->penetrate cuticle of crayfish

What are S/S of Paragonimus westermani?
Fever, cough, bloody sputum.
Untreated- extensive lung damage->impaired breathing->death is always possible

Describe a cestode (tape worm)
Flat intestinal parasites. Completely lack digestive system. Have no mouth, and absorb nutrients through its cuticle.

What is a scolex?
Head of tape worm. Contains suckers &/or hooks. Buries itself into intestinal wall.

What is a proglottid?
A bag of eggs. Segments of tape worm that contain both M/F gametes & make up body of worm. Each monoecious proglottid may fertilize other proglottids. Distal proglottids are mature fertilized egg containers. They break off-> defecated
*1000+ proglottids w/ 1000s of eggs.

What is the classification of beef tapeworm?
Taenia saginata; Lives upt to 25 yrs in human intestine. Grows up to 6 meters.
s/s: nothing significant beyond vague abdominal discomfort.

What is the classification of pork tapeworm?
Taenia solium; Eggs shed by human ingested by another human or by pig. Larvae encysts in pig muscle->human eats encysted pork-> larvae encyst in human muscle, eye, brain
S/S: Eye-Retinocysticercosis
Brain- Neurocysticercosis. Mimics epilepsy, tumor. Not uncommon in S.America

Describe Nematodes
Round worms; Dioecious (separate M/F); Complete digestive system: mouth, intestine, anus. Infx of humans by-infective eggs & larvae

Which nematodes have eggs infective to humans via the oral route?
Pinworms (Enterobius vermicularis) & Ascariasis (Ascaris lumbricoides)

Which nematodes have larvae infective to humans?
Hookworms (Necator americanus) & Trichinosis (Trichinella spiralis)

Describe pinworms
Etiology: Enterobius vermicularis
most common worm in US. Nocturnal egg layers live in sigmoid colon. Entire life in human host- egg->mature adult. Female lifespan 1-2mos. One female pinworm may release 1000 eggs on perianal skin at night. Eggs can survive up to a wk in cool, moist atmos. Above 80F only viable for 24hrs.

How are pinworms transmitted, and what are S/S?
Transmission: Fecal/oral; Child scratches around anus->eggs on hands->plays w/fomite->another child puts object in mouth. Eggs may go airborne.
S/S: Possible abdom. discomfort, diarrhea.
DX. Sticky tape on perianal. View under scope.

Describe Ascariasis
Etiology: Ascaris lumbricoides; Largest of Nematodes. Up to 30cm in L/ 5mm diameter. More than 1bil infected. Not uncommon in US. Adults free & unattached in small intestine of humans only. Survive up to 1 year.

What is the pathogenesis/transmission of Ascaris lumbricoides?
Up to 200,000 eggs/day->can remain infective in soil for 3-10 yrs.->eggs shed in feces->ingestion->hatch in small intestine->Larva burrows thru mucosal wall->enters blood stream->Burrows into lungs & grow into alveoli->10-14days->bronchial tree->trachea->pharynx->swallowed larva->reaches small intestine/adult stage->eggs shed in feces.
*Takes 5-8wks after initial ingestion

What are S/S of Ascaris lumbricoides?
Mild, or possible pulmonary s/s. Severe inflammatory reactions might follow migratory route; Affinity for small orifices (pacreatic duct, common bile duct, possible blockage w/large infestation
Cardinal: Adult worm emerge from anus/mouth/nose/naval/ear

Describe Necator americanus (Hookworm)
Can penetrate through sweat glands, soles of feet. Also follicles, abrasions. Eggs excreted in feces->Hatch in soil (1-2days)->larvae burrow into + penetrate skin->through veins+carried to+penetrates lungs to mate->larvae ascend bronchial tree/coughed up in sputum into pharynx/swallowed. Enter GI tract, attach to mucosa of small intestine, sucks blood.

What are the S/S of hook worm (Necator americanus)?
Blood streaked sputum; heavy infestation can result in up to 100ml of blood loss/day; iron deficient anemia-lethargy, pica; exertional dyspnea, fatigue; increased eosinophil count; recurrent epigastric pain, nausea, headache, bloody stool. Most adult worms live 1-2yrs.

Describe Trichinosis
Etiology: Trichinella spiralis; forms cysts in muscles of animals
Transmission: Eat encysted larvae in poorly cooked pork, bears, game animals. Once eaten->digestive action frees larvae->matures in small intestine (1wk)->sexually reproduce->female gives birth to live nematodes->enter vascular system->become encysted throughout host, esp. in muscle. M/c diaphragm, eye, tongue (vascularized muscle).

What are S/S of Trichinella spiralis?
Most subclinical; Fever, GI upset, swell around eyes. Mass infiltration of muscle->intense muscle/ jt. pain-> maybe into heart, brain-> No cure once larvae encyst in muscle->but encysted larvae degrade over time.

Describe anthropods
1mil species. A few suck human blood & transmit microbial disease while doing so. They are vectors & carry pathogenic microbes.

What is a vector?
An animal, usually an arthropod which carries disease-causing microorganisms. Eradicate vector, then eradicate means of transmission.
(ie. Arachnida-eight legs (spiders, mites, ticks)
Insecta- six legs (lice, fleas, flies, mosquitoes)
Crustacea- 4 antennae (crabs, crayfish)

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