📚 Parasitology Syllabus • General Parasitology (Host, Parasite, Vector) • Protozoa (Amoeba, Naegleria flowleri, Giardia, Leishmania, Plasmodium, Toxoplasma, Trichomonas) • Helminths (Cestodes, Trematodes, Nematodes) • Important Parasitic Diseases (Ascariasis, Enterobiasis, Hookworm, Filariasis, Trichinellosis, Dracunculiasis, Chagas Disease) • Laboratory Diagnosis • Prevention & Control of Parasitic Infections

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📚 Complete Parasitology Notes

Sources: Quick Compendium of Clinical Pathology 5th ed., Medical Microbiology 9e (Murray), Sherris & Ryan's Medical Microbiology 8th ed., Jawetz Melnick & Adelberg's Medical Microbiology 28th ed.

PART 1 - GENERAL PARASITOLOGY

Key Definitions

Term	Definition
Parasite	An organism that lives in or on another organism (host) and benefits at the host's expense
Host	The organism that harbors the parasite
Definitive host	Host in which the parasite undergoes sexual reproduction (e.g., humans for Taenia, mosquito for Plasmodium)
Intermediate host	Host in which asexual reproduction or larval development occurs
Reservoir host	A non-human host that harbors the parasite and serves as a source of human infection
Paratenic host	Carries the larval form without further development; acts as a "transport" host
Vector	An arthropod that transmits the parasite (biological or mechanical)
Zoonosis	Infection transmitted from animals to humans

Types of Parasitism

Ectoparasite - lives on the surface (e.g., lice, scabies)
Endoparasite - lives inside the host (e.g., Plasmodium, Ascaris)
Obligate parasite - cannot survive without a host
Facultative parasite - can live free or parasitically (e.g., Naegleria)

Parasite Life Stages

Trophozoite - active, feeding, motile form (vegetative)
Cyst - dormant, infective, environmentally stable form
Sporozoite - infective stage injected by mosquito
Merozoite - released after hepatic schizogony; invades RBCs
Gametocyte - sexual stage; ingested by vector

Types of Vectors

Biological vector - parasite develops/multiplies inside (e.g., Anopheles mosquito for malaria, Aedes for filariasis)
Mechanical vector - parasite is carried without development (e.g., fly carrying cysts)

PART 2 - PROTOZOA

Overview

Protozoa are unicellular eukaryotes. Classified by mode of motility:

Sarcodina - move by pseudopodia (amoeba)
Mastigophora - move by flagella (Giardia, Leishmania, Trichomonas)
Ciliophora - move by cilia (Balantidium)
Sporozoa/Apicomplexa - non-motile adults (Plasmodium, Toxoplasma, Cryptosporidium)

2.1 ENTAMOEBA HISTOLYTICA (Amoebiasis)

Feature	Detail
Transmission	Fecal-oral; contaminated food/water
Infective stage	Cyst (4 nuclei)
Disease stage	Trophozoite (ingested RBCs = pathognomonic!)
Habitat	Large intestine
Disease	Amoebic dysentery, amoebic liver abscess

Pathogenesis:

Trophozoites invade colonic mucosa → flask-shaped ulcers
Portal spread → liver abscess ("anchovy paste" / chocolate brown pus)
Rarely: lung, brain abscess

Cyst morphology:

10-20 μm, 4 nuclei with central karyosome
Chromatoid bars (cigar-shaped) with rounded ends
Glycogen vacuoles

Trophozoite morphology:

15-60 μm, ingested RBCs visible inside
Eccentric nucleus with central karyosome

Diagnosis:

Stool O&P (3 specimens, ≥24 hrs apart)
Serology (positive in invasive disease)
Trichrome stain on stool

Treatment: Metronidazole + luminal agent (paromomycin or iodoquinol)

Non-pathogenic species to know: E. dispar, E. coli, E. hartmanni, Iodamoeba bütschlii, Endolimax nana

2.2 NAEGLERIA FOWLERI

Feature	Detail
Classification	Free-living amoeba (thermophilic)
Habitat	Warm stagnant freshwater, soil
Entry	Nasal mucosa → cribriform plate → olfactory nerve → frontal lobe
Disease	Primary Amoebic Meningoencephalitis (PAM)
Population	Children/young adults swimming in warm freshwater
Prognosis	Nearly always fatal (>97% mortality)

Key facts:

No cysts found in brain tissue (unlike Acanthamoeba)
Trophozoites: 10-35 μm, small nucleus with large dense central karyosome; can be mistaken for macrophages in CSF
Culture: grown on agar with E. coli lawn
CSF specimens must NOT be refrigerated before culture (organisms die in cold)

Diagnosis: Trophozoites in CSF; PCR; culture on E. coli

Treatment: Amphotericin B + azithromycin + rifampin (rarely successful)

Compare with other free-living amoeba:

Feature	Naegleria	Acanthamoeba	Balamuthia
Disease	PAM	GAE + Keratitis	GAE
Host	Immunocompetent	Immunocompromised	Both
Cysts in brain?	No	Yes	Yes
Entry route	Nasal (cribriform)	Hematogenous	Hematogenous
Course	Acute (days)	Subacute/chronic	Subacute/chronic
Contact lens risk?	No	Yes (keratitis)	No

Quick Compendium of Clinical Pathology 5th ed., p. 124

2.3 GIARDIA INTESTINALIS (syn. G. lamblia, G. duodenalis)

Feature	Detail
Transmission	Fecal-oral, contaminated water ("beaver fever")
Infective stage	Cyst (4 nuclei)
Disease stage	Trophozoite
Habitat	Duodenum and jejunum (NOT colon)
Disease	Giardiasis - fatty diarrhea, malabsorption, bloating, flatulence

Trophozoite morphology (classic):

Pear/teardrop-shaped, bilaterally symmetrical
2 nuclei (gives "owl-eye" or "monkey face" appearance)
4 pairs of flagella
Sucking disk (adhesive disk) - attaches to intestinal villi
Ventral concavity

Cyst morphology:

Oval, 8-12 μm, 4 nuclei
Intracytoplasmic fibrils

Pathogenesis: Mechanical blockade of intestinal epithelium + villous flattening → malabsorption (fat-soluble vitamins A, D, E, K)

Diagnosis:

Stool O&P (3 specimens - intermittent shedding)
String test (Enterotest)
Stool antigen ELISA / DFA - more sensitive
Note: no peripheral eosinophilia (intestinal protozoa don't invade)

Treatment: Metronidazole or tinidazole; nitazoxanide

2.4 LEISHMANIA SPECIES

Disease	Species	Vector	Geography
Visceral (Kala-azar)	L. donovani, L. infantum	Female Phlebotomus sandfly	Asia, Africa, Mediterranean
Cutaneous (Oriental sore)	L. major, L. tropica	Female Phlebotomus sandfly	Middle East, Africa
Mucocutaneous (Espundia)	L. braziliensis	Lutzomyia sandfly	South America

Life cycle:

Promastigote (flagellated) - in sandfly, infective stage
Amastigote (no flagellum) - intracellular in macrophages/reticuloendothelial cells of human host

Visceral leishmaniasis (Kala-azar):

"Kala-azar" = black sickness (Hindi)
Massive hepatosplenomegaly, fever, weight loss, pancytopenia
Hypergammaglobulinemia
Amastigotes in macrophages of liver, spleen, bone marrow

Cutaneous: Painless papule → ulcer with raised indurated borders ("volcano crater")

Diagnosis:

Giemsa-stained bone marrow/spleen aspirate (amastigotes within macrophages)
Culture on NNN medium
PCR, serology (rK39 antigen for visceral)

Treatment: Liposomal amphotericin B (drug of choice); pentavalent antimonials (sodium stibogluconate)

2.5 PLASMODIUM SPECIES (Malaria)

Five species infecting humans:

Species	Fever Pattern	RBC Change	Key Features	Relapse?
P. falciparum	Quotidian → malignant tertian (36-48h)	Smaller, multiple rings, Maurer's clefts	Most dangerous; cerebral malaria; banana-shaped gametocytes	No (no hypnozoites)
P. vivax	Benign tertian (48h)	Enlarged, Schüffner's dots	Widest distribution; DARC receptor	Yes (hypnozoites)
P. ovale	Benign tertian (48h)	Enlarged, fimbriated/oval edges, Schüffner's dots	Africa, milder	Yes (hypnozoites)
P. malariae	Quartan (72h)	Smaller, band trophozoites	Causes nephrotic syndrome	No (but recrudescence)
P. knowlesi	Daily (24h = quotidian)	Normal/small	Zoonosis (macaques), SE Asia	No

Life Cycle:

Mosquito bite → sporozoites enter blood → liver (exoerythrocytic schizogony, 8-25 days)
Hepatocytes rupture → merozoites released → enter RBCs
Erythrocytic cycle: ring → trophozoite → schizont → rupture → merozoites (fever paroxysm at this point)
Some merozoites → gametocytes (sexual stage)
Anopheles mosquito ingests gametocytes → sporogony in mosquito → sporozoites in salivary glands
P. vivax/ovale: some sporozoites become hypnozoites (dormant liver forms → relapse)

P. falciparum special features (most virulent):

Cytoadherence (knobs on RBC surface) → capillary sludging → cerebral malaria
Rosette formation
No persistent liver stage (no relapse, only recrudescence)
Infects all RBC ages; others are age-selective
Banana/crescent-shaped gametocytes

Complications:

Cerebral malaria (P. falciparum)
Blackwater fever: massive hemolysis → hemoglobinuria → dark urine
Nephrotic syndrome (P. malariae)
Splenic rupture
Severe anemia, thrombocytopenia

Diagnosis:

Thick blood film (screening - concentration): Giemsa or Wright stain
Thin blood film (speciation - morphology)
Rapid diagnostic test (RDT) - antigen detection (HRP2 for P. falciparum)
PCR (most sensitive/specific)

Treatment:

Chloroquine-sensitive: chloroquine
Chloroquine-resistant P. falciparum: artemisinin combination therapy (ACT)
P. vivax/ovale relapse prevention: primaquine (G6PD screen first - risk of hemolysis)
Severe malaria: IV artesunate (preferred) or IV quinine

Prevention: Mosquito nets, insect repellent (DEET), chemoprophylaxis (chloroquine, mefloquine, doxycycline, atovaquone-proguanil)

Fig. - Life cycle of Plasmodium species (Medical Microbiology 9e)

2.6 TOXOPLASMA GONDII

Feature	Detail
Definitive host	Cats (only host for sexual cycle/oocysts in stool)
Intermediate host	Humans, most warm-blooded animals
Infective forms	Oocysts (in cat feces), tissue cysts (in undercooked meat), tachyzoites (congenital)
Transmission	Ingestion of oocysts (contaminated soil, cat litter), undercooked meat, congenital (transplacental), blood transfusion/organ transplant

Forms:

Tachyzoite - rapidly replicating, active infection, crescent/banana shaped (active disease)
Bradyzoite - slowly replicating, in tissue cysts (latent infection, especially brain and muscle)
Oocyst - sexual form shed in cat feces; environmentally resistant

Disease presentation:

Population	Manifestation
Immunocompetent	Usually asymptomatic or mild mononucleosis-like (cervical lymphadenopathy)
AIDS/Immunocompromised	Toxoplasmic encephalitis (ring-enhancing lesions on MRI, basal ganglia)
Congenital	Triad: chorioretinitis, hydrocephalus, intracranial calcifications
Pregnant women	Can cause fetal death, spontaneous abortion

Congenital toxoplasmosis - Classic Triad:

Chorioretinitis + Hydrocephalus + Intracranial calcifications (periventricular)

Diagnosis:

Serology (IgM = acute; IgG = past/chronic)
PCR of CSF or amniotic fluid
Brain biopsy (ring-enhancing lesions)
Neonatal IgM (does not cross placenta)

Treatment: Pyrimethamine + sulfadiazine + leucovorin (folinic acid to prevent myelosuppression)

Prophylaxis in HIV: TMP-SMX (also prevents PCP)

2.7 TRICHOMONAS VAGINALIS

Feature	Detail
Classification	Flagellated protozoan (mastigophora)
Transmission	Sexually transmitted (STI) - most common non-viral STI worldwide
Infective/disease stage	Trophozoite only (no cyst stage)
Habitat	Vagina/male urethra
Morphology	Pear-shaped, 4 anterior flagella + 1 recurrent flagellum (on undulating membrane), axostyle

Clinical:

Women: vaginitis, yellow-green frothy vaginal discharge, "strawberry cervix" (petechiae), pH >4.5
Men: usually asymptomatic; urethritis possible
Characteristic jerky, tumbling, non-directional motility on wet mount

Diagnosis:

Wet mount (direct microscopy) - motile trophozoites; sensitivity ~60%
Nucleic acid amplification test (NAAT) - most sensitive/specific
Culture on Diamond's medium
Pap smear can detect incidentally

Treatment: Metronidazole (2g single dose) - treat both partners; tinidazole is alternative

PART 3 - HELMINTHS

Helminths are multicellular worms. Divided into:

Cestodes (tapeworms) - flat, segmented
Trematodes (flukes) - flat, unsegmented
Nematodes (roundworms) - cylindrical, unsegmented

General: Lab Finding - Eosinophilia

Eosinophilia is the hallmark of tissue-invasive helminth infections
Pure intestinal protozoa (Giardia, E. histolytica) do NOT cause eosinophilia
Highest eosinophilia: Trichinella, visceral larva migrans, Strongyloides, early Ascaris migration

3.1 CESTODES (Tapeworms)

All tapeworms have:

Scolex (head) - with suckers ± hooks for attachment
Neck - region of growth
Proglottids - body segments (immature → mature → gravid)

3.1.1 Taenia saginata (Beef Tapeworm)

Transmission: ingestion of undercooked beef containing cysticerci
Definitive host: humans; Intermediate host: cattle
Scolex: 4 suckers, no hooks (unarmed)
Proglottids: 15-30 uterine branches per side
Does NOT cause cysticercosis in humans (eggs not infectious to humans)
Treatment: praziquantel or niclosamide

3.1.2 Taenia solium (Pork Tapeworm)

Transmission: ingestion of undercooked pork (cysticerci) → intestinal tapeworm; OR ingestion of eggs (fecal-oral) → cysticercosis
Scolex: 4 suckers + hooks (armed/rostellum) - "armed tapeworm"
Neurocysticercosis = most common cause of acquired epilepsy worldwide
- Cysts in brain (ring-enhancing lesions, calcifications on CT)
- Treatment: albendazole + steroids + antiepileptics
Treatment of intestinal form: praziquantel or niclosamide

3.1.3 Echinococcus species (Hydatidosis / Cystic Echinococcosis)

Definitive host: dogs; Intermediate hosts: sheep, cattle, humans (accidental)
Transmission: ingestion of eggs from dog feces
Disease: hydatid cysts in liver (70%), lungs (20%), rarely brain
Cysts contain protoscoleces ("hydatid sand")
Never aspirate/needle biopsy - risk of anaphylactic shock + dissemination
Diagnosis: imaging (CT/US) + serology (IHA, ELISA)
Treatment: PAIR (Puncture, Aspiration, Injection, Re-aspiration) + albendazole; surgical resection

3.1.4 Diphyllobothrium latum (Fish Tapeworm)

Transmission: ingestion of raw/undercooked freshwater fish
Intermediate hosts: copepods (1st) → freshwater fish (2nd)
Largest tapeworm infecting humans (up to 10 meters)
Vitamin B12 deficiency → megaloblastic anemia (tapeworm preferentially absorbs B12)
Egg: oval with unshouldered operculum + abopercular knob
Treatment: praziquantel

3.1.5 Hymenolepis nana (Dwarf Tapeworm)

Smallest cestode infecting humans
Unique: can complete entire life cycle in one host (autoinfection possible)
Transmission: ingestion of infected beetles or person-to-person
Treatment: praziquantel

3.2 TREMATODES (Flukes)

All trematodes (except Schistosoma) are hermaphroditic.

3.2.1 Schistosoma species (Blood Flukes)

Unique: dioecious (separate sexes), the female lives in the groove of the male
Vector: freshwater snails (Biomphalaria, Bulinus, Oncomelania)
Transmission: cercariae penetrate intact skin while wading/swimming in freshwater

Species	Site of Eggs	Disease
S. mansoni	Lateral spine, stool	Intestinal/hepatic schistosomiasis, periportal fibrosis
S. haematobium	Terminal spine, urine	Urogenital schistosomiasis, bladder cancer (SCC)
S. japonicum	Small lateral spine, stool	Most eggs per worm; severe hepatosplenomegaly

Cercarial dermatitis ("swimmer's itch") = immediate hypersensitivity at entry site Katayama fever = acute schistosomiasis - fever, urticaria, eosinophilia (Serum sickness-like) Chronic: portal hypertension, "Symmer's clay pipe-stem fibrosis" (S. mansoni/japonicum)

Diagnosis: Eggs in stool/urine; Kato-Katz thick smear; serology; rectal biopsy

Treatment: Praziquantel (drug of choice for all species)

3.2.2 Fasciola hepatica (Liver Fluke)

Transmission: ingestion of aquatic plants (watercress) with encysted metacercariae
Intermediate host: freshwater snail (Lymnaea)
Disease: biliary obstruction, cholangitis, eosinophilia
Treatment: triclabendazole (NOT praziquantel - resistant)

3.2.3 Clonorchis sinensis (Chinese Liver Fluke)

Transmission: raw freshwater fish
Risk: cholangiocarcinoma (biliary)
Treatment: praziquantel

3.2.4 Paragonimus westermani (Lung Fluke)

Transmission: raw/undercooked crabs or crayfish
Disease: pulmonary paragonimiasis - hemoptysis, brown eggs in sputum (mimics TB)
Egg: oval, shouldered operculum
Treatment: praziquantel

3.3 NEMATODES (Roundworms)

Key concept: Nematodes have separate sexes. Eosinophilia during migration phase.

3.3.1 Intestinal Nematodes

Ascaris lumbricoides (Giant Roundworm)

Largest intestinal nematode (up to 35 cm)
Transmission: fecal-oral, ingestion of embryonated eggs
Löffler's syndrome (pulmonary eosinophilia) during larval migration through lungs
Worms may obstruct intestines, bile duct, appendix
Diagnosis: eggs in stool (mammillated outer coat), adults may be passed in stool
Treatment: albendazole or mebendazole

Enterobius vermicularis (Pinworm)

Most common helminth infection in the US
Transmission: fecal-oral, autoinfection; nocturnal perianal migration of female worm
Perianal pruritus (especially nocturnal) = hallmark
Diagnosis: Scotch tape test (cellophane tape applied to perianal area at night)
Eggs: asymmetrically flattened on one side ("D-shaped")
Treatment: mebendazole or albendazole (repeat dose in 2 weeks); treat entire household

Hookworm (Ancylostoma duodenale, Necator americanus)

Transmission: filariform larvae penetrate intact skin (walking barefoot)
"Ground itch" at entry site; Löffler's syndrome during lung migration
Adults attach to small intestinal mucosa → iron-deficiency anemia (blood-sucking)
A. duodenale also transmits via ingestion/breast milk; more aggressive blood-sucking
N. americanus = most common hookworm worldwide (Americas, Africa, Asia)
Diagnosis: eggs in stool (thin shell, 4-8 cell morula inside)
Treatment: albendazole or mebendazole + iron supplementation

Trichuris trichiura (Whipworm)

Transmission: fecal-oral (embryonated eggs)
Egg: "barrel/football" shaped with 2 polar plugs (pathognomonic)
Anterior end (thin/whip) embeds in mucosa; posterior (thick) hangs free
Heavy infection: "whip-worm dysentery," rectal prolapse in children
Treatment: mebendazole or albendazole

Strongyloides stercoralis

Unique: can cause hyperinfection/dissemination in immunocompromised hosts
Transmission: filariform larvae penetrate skin; unique direct development cycle
Autoinfection possible (larvae can penetrate intestinal wall without leaving host)
Hyperinfection in corticosteroid users, HTLV-1 infection, transplant recipients
Larva currens = rapidly migrating urticarial track in skin
Diagnosis: stool O&P (rhabditiform larvae); serology (ELISA); Baermann technique
Treatment: ivermectin (drug of choice); albendazole as alternative

3.3.2 Tissue Nematodes

Wuchereria bancrofti / Brugia malayi - Lymphatic Filariasis

Vector: Culex mosquito (W. bancrofti), Mansonia/Anopheles (B. malayi)
Disease: lymphatic obstruction → elephantiasis (lymphedema of limbs/scrotum)
Microfilariae show nocturnal periodicity (peak at night in peripheral blood)
Diagnosis: blood smear (thick film, midnight sample); microfilariae in blood
Treatment: DEC (diethylcarbamazine) ± albendazole; ivermectin + albendazole

Onchocerca volvulus - River Blindness

Vector: Simulium (blackfly), breeds in fast-flowing rivers
Disease: skin nodules (onchocercomas), dermatitis ("leopard skin"), blindness (keratitis, chorioretinitis from microfilariae dying in eye)
No blood microfilaremia (microfilariae stay in skin/eye)
Diagnosis: skin snip (not blood) - microfilariae in superficial skin; slit lamp exam
Treatment: Ivermectin (drug of choice, mass distribution program); kills microfilariae NOT adults; DEC is contraindicated (causes Mazzotti reaction → severe inflammation)

Loa loa (African Eye Worm)

Vector: Chrysops (mango fly / deer fly)
Disease: Calabar swellings (transient migratory subcutaneous edema), adult worm migrating across conjunctiva
Diurnal periodicity of microfilariae (peak during daytime)
Diagnosis: microfilariae in daytime blood sample; observing worm under conjunctiva
Treatment: DEC

PART 4 - IMPORTANT PARASITIC DISEASES (Detailed)

4.1 ASCARIASIS

Causative agent: Ascaris lumbricoides
Transmission: ingestion of embryonated eggs (fecal-oral); contaminated soil/vegetables
Life cycle highlights:
1. Eggs ingested → hatch in small intestine → larvae penetrate intestinal wall
2. Larvae migrate via portal blood → liver → heart → lungs (Löffler's syndrome)
3. Larvae migrate up trachea → swallowed → mature in small intestine
4. Adults (up to 35 cm) live in jejunum
Clinical:
- Pulmonary phase: cough, wheezing, eosinophilia (Löffler's syndrome)
- Intestinal phase: usually asymptomatic; heavy infection → malnutrition, obstruction
- Complications: biliary/pancreatic duct obstruction, intestinal obstruction, appendicitis
Diagnosis: Eggs in stool (fertilized egg: oval, brown, mammillated); unfertilized eggs also seen
Treatment: Albendazole (400 mg single dose) or mebendazole; pyrantel pamoate

4.2 ENTEROBIASIS (Pinworm)

Causative agent: Enterobius vermicularis
Epidemiology: Most common helminth in USA; mainly children, institutional settings
Transmission: Fecal-oral, autoinfection, airborne (eggs can float in dust)
Life cycle: Eggs ingested → mature in cecum → females migrate to perianal area at night to deposit eggs → pruritus ani
Complications: Secondary bacterial infection from scratching; rarely appendicitis; vaginal/pelvic migration in girls
Diagnosis: Scotch tape test (morning, before bathing) - asymmetric D-shaped eggs
Treatment: Mebendazole or albendazole (single dose, repeat in 2 weeks); treat all household members; hygiene measures

4.3 HOOKWORM DISEASE

Causative agents: Ancylostoma duodenale (Old World), Necator americanus (New World)
Transmission: Filariform (L3) larvae in warm moist soil penetrate intact skin
Life cycle:
1. L3 larvae penetrate skin → blood → lungs (Löffler's syndrome) → swallowed
2. Mature in small intestine; attach to mucosa by buccal capsule with teeth/plates
3. Blood-sucking causes iron deficiency anemia and hypoalbuminemia
Clinical:
- "Ground itch" (dermatitis at penetration site)
- Pulmonary migration symptoms
- Iron-deficiency anemia (most important complication): weakness, pallor, dyspnea
- Hypoproteinemia, growth retardation in children
Diagnosis: Eggs in stool; Harada-Mori filter paper technique to detect larvae
Treatment: Albendazole or mebendazole; iron supplementation; nutritional support

4.4 FILARIASIS

See tissue nematodes section above
Key summary:

Parasite	Vector	Microfilariae periodicity	Key disease	Dx sample
Wuchereria bancrofti	Culex mosquito	Nocturnal	Elephantiasis	Midnight blood
Brugia malayi	Mansonia/Anopheles	Nocturnal	Elephantiasis (arms)	Midnight blood
Loa loa	Chrysops fly	Diurnal	Calabar swellings, eye worm	Daytime blood
Onchocerca volvulus	Simulium blackfly	N/A (skin)	River blindness	Skin snip
Mansonella spp.	Midges (Culicoides)	Aperiodic	Mild/asymptomatic	Blood

4.5 TRICHINELLOSIS (Trichinosis)

Causative agent: Trichinella spiralis (and related species)
Transmission: Ingestion of undercooked pork (or bear, wild boar) containing encysted larvae
Unique: Humans are accidental dead-end hosts; the same individual is both definitive and intermediate host
Life cycle:
1. Encysted larvae in muscle → ingested → released in stomach → mature in small intestinal enterocytes
2. Female worms release larvae → penetrate mucosa → migrate via blood → encyst in striated muscle (preferred: diaphragm, intercostal muscles, tongue, extraocular muscles)
Clinical phases:
- Intestinal phase (day 1-7): nausea, vomiting, diarrhea
- Muscle invasion phase (day 7-21): myalgia (especially jaw, tongue, extraocular), periorbital edema (classic!), fever, eosinophilia
- Encystment phase: symptoms subside; calcified cysts remain in muscle
Classic presentation: Periorbital edema + myalgia + eosinophilia after eating pork
Diagnosis: Serology; muscle biopsy (encysted larvae "nurse cells"); CBC (marked eosinophilia); elevated CK
Treatment: Albendazole or mebendazole + corticosteroids (for severe cases)

4.6 DRACUNCULIASIS (Guinea Worm Disease)

Causative agent: Dracunculus medinensis
Transmission: Ingestion of cyclops (copepods/water fleas) in contaminated drinking water
Life cycle:
1. Cyclops in water ingested → larvae released in intestine → penetrate gut wall → mature in retroperitoneum
2. Gravid female (up to 1 m long!) migrates to skin (usually lower leg) over ~1 year
3. Female creates blister → ruptures on contact with water → releases larvae into water → cyclops ingest larvae
Clinical:
- Mostly asymptomatic during migration
- Blister and ulcer on lower extremity; intensely painful
- Secondary bacterial infection is the main complication
- Severe: arthritis, septicemia
Diagnosis: Clinical (visible worm emerging from skin); no effective serological test
Treatment: No drug treatment! Traditional slow extraction: wind worm around stick (a few cm/day over weeks); cannot pull quickly (worm breaks → anaphylaxis + severe infection)
Prevention/Eradication: Filtering drinking water through fine cloth/pipe filter; education; DEET in water sources to kill cyclops. Currently near-complete global eradication (Carter Center program)

4.7 CHAGAS DISEASE (American Trypanosomiasis)

Causative agent: Trypanosoma cruzi
Vector: Triatomine bug (Triatoma, Rhodnius, Panstrongylus) = "Kissing bug" / "Reduviid bug"
Transmission: Bug defecates near bite wound; parasite in feces enters wound (NOT the bite itself); also: blood transfusion, congenital, organ transplant, undercooked food
Distribution: Central and South America
Life cycle:
1. Trypomastigotes in bug feces enter wound → enter macrophages → transform to amastigotes (intracellular)
2. Amastigotes replicate in tissue cells (especially heart muscle) → rupture → release trypomastigotes → infect other cells or ingested by another bug

Clinical Phases:

Phase	Features
Acute	Romaña's sign (painless periorbital edema = entry via conjunctiva), chagoma (skin nodule at entry site), fever, lymphadenopathy, hepatosplenomegaly; rarely myocarditis/meningitis in children
Indeterminate	Asymptomatic, positive serology, normal ECG/imaging; most remain here
Chronic	Chagasic cardiomyopathy (dilated, arrhythmias, heart failure, sudden death); megaesophagus and megacolon (enteric nerve destruction)

Romaña's sign = unilateral painless periorbital edema = classic sign of acute Chagas "Megadisease" = hallmark of chronic Chagas (megaesophagus, megacolon)

Diagnosis:

Acute: blood smear (trypomastigotes with C/U shape), buffy coat; PCR
Chronic: serology (2 different tests required per WHO); xenodiagnosis (let clean bugs feed on patient then examine bug feces - gold standard historically)
ECG: right bundle branch block + left anterior fascicular block is classic Chagas pattern

Treatment:

Nifurtimox or benznidazole - effective in acute phase; limited efficacy in chronic phase
Chronic cardiomyopathy: standard heart failure treatment, ICD, transplant

Compare with African Trypanosomiasis:

Feature	Chagas (American)	African Sleeping Sickness
Agent	T. cruzi	T. brucei gambiense/rhodesiense
Vector	Triatome (kissing bug)	Tsetse fly (Glossina)
Transmission	Feces in wound	Bite
Reservoir	Many mammals	Humans (gambiense), animals (rhodesiense)
Target	Heart/GI tract (intracellular)	CNS (extracellular)
CNS disease	Rare	Hallmark (sleeping sickness)
Treatment	Nifurtimox/Benznidazole	Suramin, melarsoprol, eflornithine

PART 5 - LABORATORY DIAGNOSIS OF PARASITES

Stool Examination (O&P - Ova and Parasites)

Specimen requirement: 3 specimens collected at least 24 hours apart (to account for intermittent shedding)
Fresh specimen: examine within 1 hour; if delay, use preservative (formalin, PVA, SAF)
Do NOT refrigerate specimens if cultured for free-living amoeba

Techniques:

Technique	Purpose
Direct wet mount	Motile trophozoites (Giardia, Trichomonas, amoeba)
Concentration methods (zinc sulfate flotation, formalin-ethyl acetate)	Increase sensitivity for cysts/eggs/larvae
Permanent stains (Trichrome, Iron hematoxylin)	Morphologic identification of protozoa
Modified acid-fast stain	Cryptosporidium, Cyclospora, Cystoisospora (oocysts are acid-fast)
Giemsa stain	Blood parasites (malaria, Leishmania, trypanosomes, microfilariae)
Scotch tape test	Enterobius vermicularis (pinworm) eggs
Kato-Katz	Helminth egg counts (intensity of infection)
Harada-Mori	Culture of hookworm/Strongyloides larvae
Baermann technique	Strongyloides larvae (uses gravity and heat)
Skin snip	Onchocerca volvulus microfilariae
NNN/Diamond's medium	Culture of Leishmania (NNN), Trichomonas (Diamond's)

Blood Parasite Diagnosis:

Method	Detail
Thick blood film	Concentration; used for screening/detection
Thin blood film	Morphology; used for species identification
Giemsa stain	Standard for blood parasites
Wright stain	Alternative to Giemsa
Midnight blood sample	Wuchereria (nocturnal microfilariae)
Daytime blood sample	Loa loa (diurnal microfilariae)
Buffy coat	Trypanosomes, microfilariae concentration

Immunological Methods:

Serology (ELISA, IFA, IHA): Toxoplasma, Echinococcus, Leishmania (rK39), Schistosoma, Trypanosoma
Antigen detection: Giardia/Cryptosporidium (stool EIA/immunochromatography); Plasmodium RDTs (HRP-2)
PCR: Most sensitive/specific; used for malaria, Toxoplasma, Leishmania, microsporidia, Strongyloides

Parasite by Body Site Summary (from Quick Compendium of Clinical Pathology):

Body Site	Key Parasites
Intestinal tract	Entamoeba, Giardia, Cryptosporidium, Ascaris, Enterobius, hookworm, Strongyloides, Taenia, Schistosoma (eggs)
Blood	Plasmodium (RBCs), Leishmania (leukocytes), Trypanosoma, microfilariae
CNS	Naegleria fowleri, Acanthamoeba, Toxoplasma, T. solium (neurocysticercosis), Trypanosoma brucei
Liver/Spleen	Echinococcus, E. histolytica, Leishmania, Fasciola, Schistosoma
Muscle	Trichinella, Taenia (cysticercus), T. cruzi
Lungs	Paragonimus, Echinococcus, Strongyloides larvae, Toxoplasma
Skin	Leishmania, Onchocerca, microfilariae, Sarcoptes scabiei, Loa loa
Urogenital	Trichomonas vaginalis, Schistosoma haematobium (eggs)
Eye	Acanthamoeba (keratitis), Toxoplasma (chorioretinitis), Onchocerca, Loa loa

PART 6 - PREVENTION & CONTROL OF PARASITIC INFECTIONS

General Principles (Interrupting Transmission)

Strategy	Examples
Safe food/water	Boiling/filtering water (Giardia, Cryptosporidium, cholera), cooking meat well (Trichinella, Toxoplasma, Taenia), avoiding raw fish (Diphyllobothrium, Clonorchis)
Personal protection	Wearing shoes (hookworm, Strongyloides), insect repellent (DEET), bed nets (malaria, filariasis)
Vector control	Insecticides (indoor residual spraying - malaria), larval control, draining stagnant water
Sanitation	Proper sewage disposal, handwashing, avoiding open defecation
Mass drug administration (MDA)	Ivermectin (onchocerciasis, lymphatic filariasis), DEC + albendazole (LF elimination program)
Animal reservoir control	Treating dogs (Echinococcus, Leishmania), meat inspection (Taenia, Trichinella)
Chemoprophylaxis	Malaria prophylaxis (chloroquine, mefloquine, doxycycline, atovaquone-proguanil)
Water filtering	Dracunculiasis - filtering with pipe filter/cloth
Vaccination	No licensed human vaccines for most parasites; trials ongoing for malaria (RTS,S/AS01 = MosquirixTM)

Disease-Specific Control:

Disease	Key Control Measures
Malaria	Insecticide-treated bed nets (ITNs), IRS (indoor residual spraying), ACT treatment, RTS,S vaccine (partial efficacy), chemoprophylaxis
Filariasis	Annual MDA (albendazole + ivermectin or DEC), vector control, morbidity management (lymphedema care)
Onchocerciasis	Annual ivermectin MDA (CDTI - community-directed treatment); blackfly control (larviciding rivers)
Dracunculiasis	Water filtering, health education, case containment, ABATE (temephos) in water sources; near eradication globally
Chagas Disease	Triatomine bug control (insecticide spraying), blood screening, congenital screening
Schistosomiasis	Praziquantel MDA, snail control (molluscicides), avoiding contaminated water, sanitation
Soil-transmitted helminths	Periodic deworming (MDA with albendazole/mebendazole), sanitation, hygiene education
Giardia/Cryptosporidium	Water treatment (boiling, filtration, UV - NOT chlorination for Cryptosporidium), handwashing
Neurocysticercosis	Meat inspection, sanitation, pork cooking, taeniasis treatment in communities
Toxoplasmosis	Avoid cat litter in pregnancy, cook meat well, wash produce; screening of pregnant women

HIGH-YIELD MNEMONICS & QUICK FACTS

Malaria Species Memory Aid: "FaKt Vivid Oh My"

Falciparum - malignant tertian, cerebral, banana gametocytes
Knowlesi - quotidian, zoonosis (monkeys, SE Asia)
Tertian benign = Vivax - largest distribution, Schüffner's dots
Ovale - benign tertian, Africa
Mylariae (Malariae) - quartan (72h), nephrotic syndrome

Drug-Parasite Matches (High Yield):

Drug	Key Use
Metronidazole	Giardia, E. histolytica, Trichomonas
Praziquantel	Most cestodes and trematodes
Albendazole	Broad spectrum: roundworms, hookworm, Echinococcus, neurocysticercosis
Mebendazole	Soil-transmitted helminths (Ascaris, hookworm, Trichuris, pinworm)
Ivermectin	Strongyloides (DOC), Onchocerca (DOC), lymphatic filariasis, scabies
DEC	Lymphatic filariasis (W. bancrofti, Brugia), Loa loa
Pyrimethamine + sulfadiazine	Toxoplasmosis
Nifurtimox / Benznidazole	Chagas disease
Triclabendazole	Fasciola hepatica (NOT praziquantel)
Primaquine	Radical cure of P. vivax/ovale (kills hypnozoites)
Artesunate (IV)	Severe malaria
Liposomal amphotericin B	Visceral leishmaniasis (drug of choice)
Amphotericin B	Naegleria fowleri PAM

Vectors Summary:

Vector	Parasite
Anopheles mosquito	Plasmodium (malaria)
Aedes mosquito	Brugia timori; also Dengue, Zika (not parasitic)
Culex mosquito	Wuchereria bancrofti, Brugia malayi
Simulium blackfly	Onchocerca volvulus
Chrysops (deer/mango fly)	Loa loa
Phlebotomus sandfly	Leishmania (Old World)
Lutzomyia sandfly	Leishmania (New World)
Tsetse fly (Glossina)	T. brucei (African sleeping sickness)
Triatomine bug (kissing bug)	T. cruzi (Chagas disease)
Cyclops (water flea)	Dracunculus medinensis
Freshwater snail	Schistosoma (cercariae), Fasciola, Paragonimus
Ixodes tick	Babesia

Sources: Quick Compendium of Clinical Pathology 5th ed. | Medical Microbiology 9e (Murray, Rosenthal, Pfaller) | Sherris & Ryan's Medical Microbiology 8th ed. | Jawetz, Melnick & Adelberg's Medical Microbiology 28th ed.

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