Introduction to Parasitology Extraintestinal-

Symbiosis- Relationship between diff. organisms A. Amoebic liver abscess

 Commensalism- No benefit nor harm(host) B. Amoebic pneumonitis
 Mutualism- mutual benefit Diagnosis- Direct Fecal smear
 Parasitism- harm on host A. Loose watery- Trophozoite
B. Formed- cyst
Classification of parasites Treatment- Drug of choice- Metronidazole
1. Based on habitat Alternative- Tinidazole
 Ectoparasites- outside, infestation
 Endoparasites- inside, infection  Giardia lamblia
2. Based on dependency *Trophozoite has a Old man facies with sucking disc
 Obligate- needs host to complete life cycle *Falling leaf motility
 Facultative- can live without a host IS- Cyst
3. Based on mod of living PS- Trophozoite
 Permanent- remain inside from early life to MOT- Fecal-oral ( contaminated water)
maturity - sexual transmission
 Intermittent- invades during feeding time Pathogenesis
 Incidental- unusual host Giardiasis(Traveler’s diarrhea)
 Transitory- uses host only for development Diagnosis- DFS- cyst & trophozoite
 Erratic- unusual invasion site String test- alternative
Treatment- Metronidazole, Tinidazole, Nitazoxanide
Types of Host
 Definitive- Harbors the adult/sexual stage  Trichomonas vaginalis
 Intermediate- Harbors larval/asexual stage *only protozoa with no Cyst stage
 Reservoir- Harbors parasite as carrier, may act as IS- Trophozoite
additional source of infection PS- Trophozoite
 Paratenic- Means of transport MOT- Sexual transmission
- Vertical transmission
Source of exposure- Most common is soil Pathogenesis
Mode of Transmission- Most common Fecal-oral route Trichomoniasis
Portal of Exit- Most common is Anus -Vaginal mucosa in women
Pathogenecity- dynamics of disease process -Prostate & Urethra in men
- Strawberry cervix with watery to foul
Classification of parasites- greenish yellow discharge
 Protozoa- single celled Diagnosis- Wetmount (Vaginal, urethral, prostatic
 Metazoa(helminths)- multi celled discharge and/or urine sample)
Treatment- Metronidazole
Classification of Protozoa- based on motility
1. Amoeba- Pseudopods (crawling)  Balantidium coli
2. Flagellates- Flagella (crawling) *Largest protozoa
3. Sporozoa- no motility organ (gliding) *Cytostome- primitive mouth & with boring motility
4. Ciliates- Cilia IS- cyst
PS- Trophozoite
Classification of Helminths- based on shape and Reservoir- Pig/ monkey
structure MOT- Fecal-oral ( contaminated water/food)
1. Nematodes (roundworms) Pathogenesis
2. Platyhelminthes Balantidiasis- Same manifestation with E.
a) Trematodes (Flukes) histolytica but without extraintestinal invasion
b) Cestodes (Tapeworms) Diagnosis- DFS
Treatment- DOC- Oxytetracycline & Iodoquinol
Protozoa Blood and Tissue
Intestinal & Urogenital  Acanthamoeba castellani
 Entamoeba histolytica *can invade through contact lenses
*Classic flask shaped ulcer on Cecum & Colon IS- Cyst
IS- cyst PS- Trophozoite
PS- Trophozoite MOT- Aspiration/direct invasion of eye(soil/cold water)
MOT- Fecal-oral ( contaminated water/food) Pathogenesis
- sexual transmission Granulomatous Amoebic Encephalitis
Pathogenesis -immunocompromised host with brain abscess
Amoebic Dysentery-bloody mucoid stool Keratitis- Eye infection thru direct contact
Amoeboma- mass inside cecum
Diagnosis- CSF smear, Brain tissue, corneal scrapings
stained with Calcoflour white Chronic
Treatment- Pentamidine, Ketoconazole, Flucystosine Myocarditis with cardiac arrhythmia
Propamidine- eye and skin infection Diagnosis- PBS finding trypomastigotes
Treatment- Benznidazole & nifurtimox
 Naegleria fowleri
IS- Trophozoite T. Brucei gambiense & rhodesience
DS- Trophozoite Vector- Tsetse fly (Glossina)
MOT- Transnasal Reservoir- human
Pathogenesis Pathology
Primary Amoebic Meningoencephalitis Gambiense Rhodesience
Kernig’s sign (meningeal irritation), altered sense West african sleeping East african sleeping
of smell & taste sickness sickness
Mortality within 1 week if untreated Chronic Rapidly fatal
Diagnosis- CSF Less virulent More virulent
Treatment- Amphotericin B + Miconazole + Rifampicin Chancre- indurated ulcer at insect bite
Intermittent fever
 Leishmania spp. Winterbottom sign- enlarge post. Cervical LN
IS- Promastigote Kerandel’s sign- delayed pain sensation
PS- Amastigote Diagnosis- Giemsa stained PBS
Vector- Phlebotomus sandfly (Epimastigote) Treatment- Melarsoprol, Suramine, pentamidine &
Reservoir- rodents, ant eater, dog, cat Eflornithine
MOT- Insect bite
I. L. donovani complex Plasmodium spp.
Pathogenesis DH- Anopheles mosquito (vector)
Visceral Leishmaniasis (Kala-azar) IH- Human
Incubation- 2weeks- 18months IS- Sporozoite
Fever, weakness, weight loss PS- Merozoite
Hepato & splenomegaly
Kala-azar- Hyperpigmentation of skin Type of Dse Fever
Diagnosis- screening- Montenegro skin test RBC spike
Definitive- giemsa stained PBS P. falciparum Old & Malignant Irregular
Treatment- Liposomal amphotericin B(Ambisome) young Tertian
II. L. braziliensis complex P. vivax young Benign 48h
Pathogenesis Tertian
Mucocutaneous Leishmaniasis (Espundia) P. ovale young Benign 48h
Distinguishing ulcer lesion at nasal cartilage Tertian
(Tapir nose) P. malariae old Quartan 72h
Diagnosis- Giemsa stained ulcer biopsies
Treatment- Ambisome, Na stibogluconate
MOT- insect bite
III. L. Tropica complex
Pathogenesis
Pathogenesis
Malaria
Old world cutaneous Leishmaniasis
Cold stage- 10-15mins- chills, headache , myalgia,
(Oriental sore)
arthralgia
Pus containing ulcer(self healing)
Hot stage- 2-6hrs- Fever, abd. Pain, nausea,
Diagnosis- Giemsa stained ulcer fluid
vomiting
Treatment- Na stibogluconate
Sweating stage- Dreanching sweats
Paromomycin ointment- ulcer treatment
Diagnosis- Giemsa stained PBS (Gametocytes)
Treatment- DOC- chloroquine
Trypanosoma spp.
Ovale & vivax- primaquine
IS- Trypomastigote
Prophylaxis- Doxycycline
PS- Amastigote
Vector- Epimastigote
Toxoplasma gondii
DH- domestic cats
T. cruzi
IH- human and other mammals
Vector- reduviid “kissing” bug
IS- oocysts
MOT- insect bite with fecal content
PS- Trophozoite (Tachyzoite & bradyzoite)
Pathogenesis
MOT- ingestion of raw meat or cont. Water
Chagas dse(American Trypanosomiasis)
Pathogenesis
Chagoma- unilateral bite site nodule
Toxoplasmosis
Romana’s sign- eyeldi swelling with conjunctivitis
Fever chills, lymphadenitis, chorioretinitis
Diagnosis- Giemsa stained PBS may manifest as fever, Upper abdominal pain,
Treatment- Pyrimethamine + Sulfadiazine anorexia, hepatomegaly, diarrhea, eosinophilia.
Chronic- hepatomegaly, Cholangiocarcinoma
Helminths diagnosis- DFS
treatment- Praziquantel
Trematodes
General properties  Fasciola hepatica
 Unsegmented, leaf-like CN- Sheep liver fluke
*All are hermaphroditic except Schistosoma DH- Sheep, Human
(dioecious). 1st IH- snail
*All require two intermediate hosts except Schistosoma 2nd IH- Kangkong, watercress
*The infective stage is metacercariae except for IS- Metacercariae
Schistosoma (cercariae). PS- Adult worm
*The diagnostic stage is embryonated egg Except for DS- Ova
Paragonimus, Fasciola, Fasciolopsis, and Echinostoma MOT- Ingestion of infected aquatic plants
(unembryonated egg) pathogenesis
 The first intermediate host is always a snail. Acute or invasive phase: Triad of high fever,
 The second intermediate host may be a fish, hepatomegaly, marked eosinophilia
crustacean, another snail, or fresh water plants. Chronic or latent phase: adults in bile ducts→
 The DOC is praziquantel except for Fasciola which obstruction
is triclabendazole. Halzoun/ marrara: hemorrhagic nasopharyngitis
and dysphagia due to ingestion of raw Fasciola
 Schistosoma spp. adult-infected liver
*Adult schistosomes exist as separate sexes diagnosis- DFS
CN- Oriental blood fluke (S. japonicum) treatment- Triclabendazole
Urinary blood fluke (S. haematobium)
Manson’s blood fluke (S. mansoni)  Paragonimus westermani
DH- Human CN- Oriental lung fluke
IH- Snail (Oncomelania hupensis quadrasi, Bulinus, DH- Human
Biomphalaria) 1st IH- Antemelania asperata (snail)
IS- Cercariae 2nd IH- Sundathelphusa philippina (mountain crab)
PS- Adult worm IS- Metacercariae
DS- Ova PS- Adult worm
MOT- Cercarial skin penetration DS- Unembryonated Ova
Pathogenesis MOT- Ingestion of undercooked/raw crab meat
Main pathology: host granulomatous reaction to eggs Pathogenesis
o Liver granulomas lead to presinusoidal Paragonimiasis
obstruction, hepatomegaly and portal Chronic cough with bloody sputum
hypertension (S. japonicum, S. mansoni) Ectopic: cutaneous and cerebral paragonimiasis
o Bladder granulomas lead to nodules, polypoid diagnosis- Sputum concentration with 3% NaOH
lesions, and ulcerations in the lumens of the preparation
ureter and bladder, which in turn causes urinary treatment- Praziquantel
frequency, dysuria and end stream hematuria (S.
haematobium)  Fasciolopsis buski
Diagnosis- Kato-katz, Circumoval precipitin test (ovoid *Largest intestinal fluke of humans and pigs
egg with small hook) CN- Large intestinal fluke
Treatment- Praziquantel DH- Human
1st IH- snail
 Clonorchis sinensis 2nd IH- watercress, lotus
CN- Chinese liver fluke/Oriental liver fluke IS- Metacercariae
DH- Human PS- Adult worm
1st IH- Parafossarulus, Bulinus (snail) DS- Ova
2nd IH- Cyprinidae (fish) MOT- Ingestion of infected aquatic plants
IS- Metacercariae Pathogenesis
PS- Adult worm Gland abscesses in the mucosa
DS- Ova Intoxication from absorption of worm metabolites
MOT- Ingestion of undercooked/raw fish → generalized toxic and allergic symptoms (edema
Pathogenesis of face, abdomen, lower ext.)
Clonorchiasis diagnosis- DFS
mostly asymptomatic treatment- Praziquantel
Cestodes IS- plerocercoid
General properties PS- adult worm
Segmented, ribbon-like DS- unembryonated egg
All are hermaphroditic. MOT- Ingestion of undercooked fish
Structures: Pathogenesis
o Scolex: main organ of attachment to definitive host Diphyllobothriasis
o Neck: region of growth Abdominal pain and diarrhea
o Segments or proglottids: becomes more mature Hyperchromic, megaloblastic anemia (due to
distally, most distal are gravid segments vitamin B12 deficiency) with thrombocytopenia
and leukopenia
 Taenia saginata diagnosis- Stool examination
*T.saginata is irritated by alcohol leading to passage of treatment- Praziquantel
proglottids after a drinking bout
CN- Beef tapeworm  Hymenolepis nana
DH- Human CN- Dwarf tapeworm (smallest tapeworm)
IH- Cattle DH- Human
IS- cysticercus bovis IH- none
PS- adult worm IS- Ova
DS- Gravid proglottids, eggs, scolex PS- adult worm
MOT- Larvae in undercooked beef (ingestion) DS- Ova
Pathogenesis MOT- Ingestion of infected rice or flour beetles/water
Taeniasis Pathogenesis
Epigastric pain, vague discomfort, hunger pangs, Hymenolepiasis
weight loss, loss of appetite, pruritus ani mostly asymptomatic
Intestinal obstruction- Proglottids are actively nausea, weakness, loss of appetite, diarrhea, abd.
motile → can cause obstruction in the bile and pain, pruritus ani
pancreatic ducts andappendix diagnosis- Stool examination
diagnosis- Stool examination, perianal swabs treatment- DOC- Praziquantel alt- Niclosamide
treatment- Praziquantel
 Echinococcus granulosus
 Taenia solium *Man is an accidental intermediate host.
CN- pork tapeworm CN- Dog tapeworm or hydatid tapeworm
DH- Human DH- Dog
IH- Human, Pig IH- Sheep/man
IS- cysticercus cellulosae, eggs IS- Ova
PS- adult worm PS- Hydatid cyst
DS- Gravid proglottids, eggs, scolex DS- Hydatid cyst
MOT- Larvae in undercooked pork, water/food cont. MOT- Ingestion of eggs
human feces (ingestion) Pathogenesis
Pathogenesis Echinococcosis, Hydatidosis
Taeniasis Cysts acts as space occupying lesions (SOLs)
Mild non-specific abdominal complaints if the cyst ruptures, life-threatening anaphylaxis
Proglottids are not as active → No obstruction of can occur
bile and pancreatic ducts and appendix diagnosis- Ultrasonography
Cysticercosis Gold standard serology: detection of IgG antibodies to
Most serious: neurocysticercosis hydatid cyst fluid
Seizures, visual and motor deficits, vomiting treatment- Surgical resection, Albendazole
Most serious: Racemous (subarachnoid) PAIR procedure: Puncture, Aspiration, Injection,
Eyes: retinal or subretinal Respiration
diagnosis- Stool examination, CT scan MRI
treatment- Praziquantel Nematodes
Neurocysticercosis: Praziquantel or albendazole + General Properties
corticosteroids Elongated, cylindrical (roundworms)
 Diphyllobothrium latum With separate sexes
*Longest medically important tapeworm ASH (lung migration)- Ascaris, Strongyloides,
*All cestode eggs are non-operculated (no opening) Hookworms
EXCEPT for D.latum
CN- Broad fish tapeworm  Ascaris lumbricoides
DH- Human *Most common and largest intestinal nematode
1st IH: copepods (Cyclops) CN- Giant roundworm
2nd IH: fish DH- Human
IS- Embryonated egg Old world = teeth
PS- adult worm New world = semilunar cutters
DS- eggs, adult worm Blood-sucking nematodes
MOT- Ingestion of embryonated egg CN- N. americanus (New World hookworm)
Pathogenesis A. duodenale (Old World hookworm)
Ascariasis & Loeffler syndrome DH- Human
Principal site of tissue reaction is the lungs- IS- Filariform larvae
inflammation with an eosinophilic exudate occur PS- adult worm
Heavy worm burden may contribute to DS- eggs
malnutrition MOT- Larval penetration of skin
WANDERING WORMS: due to erratic behavior of Pathogenesis
adult worms→ hepatobiliary ascariasis, Major damage due to blood loss at site of
pancreatitis, appendicitis attachment, oozes in response to an anticoagulant
diagnosis- DFS, Kato Katz made by the worm
treatment- Albendazole Acute disease
Ground itch or dew itch at site of entry
 Enterobious vermicularis Eosinophilic pneumonia during transpulmonary
*Only intestinal nematode infection that cannot be passage(Loeffler’s syndrome)
controlled through sanitary disposal of human feces Wakana syndrome: vague GI disturbances and
CN- Pinworm, seatworm eosinophilia following peroral infection
DH- Human Chronic disease
IS- Embryonated egg Microcytic, hypochromic anemia by blood loss
PS- adult worm Hypoalbuminemia
DS- Eggs on perianal folds diagnosis- DFS, Harada-Mori culture
MOT- ingestion/inhalation of embryonated egg Treatment- Albendazole
Pathogenesis
Enterobiasis/oxyuriasis  Strongyloides stercoralis
Eosinophilic enterocolitis Ovoviviparous (lay eggs- hatch before leaving host)
Vulvovaginitis CN- Threadworm
Salpingitis DH- Human
Appendicitis IS- Filariform larvae
Female releases thousands of fertilized eggs on PS- adult worm
perianal skin DS- Rhabditiform larvae
Eggs develop into larvae, causing perianal pruritus MOT- Larval penetration of skin
Autoinfection can occur Pathogenesis
diagnosis- Scotch tape swab Strongyloidiasis
treatment- DOC- Pyrantel pamoate, Mebendazole > Acute disease
Albendazole Ground itch at site of entry, Mild watery diarrhea
Cochin China diarrhea: intermittent watery and
 Trichuris trichiura bloody diarrhea
Ova resembles a football or a Chinese lantern. Eosinophilic pneumonia (Loeffler’s syndrome)
CN- Whipworm Chronic disease
DH- Human Serpiginous track along buttocks, perineum and
IS- Embryonated egg thighs (larva currens)
PS- adult worm Duodenitis
DS- eggs Paradoxical asthma
MOT- Ingestion of embryonated egg Hyperinfection syndrome
Pathogenesis diagnosis- Harada-Mori culture
Trichuriasis Koga agar plate: most sensitive coprological method for
Trichuris dysentery syndrome:chronic dysentery larval detection
and rectal prolapse treatment- Ivermectin
Rectal prolapse: from increased peristalsis to expel
the worms  Capillaria philippinensis
Appendicitis *Only nematode with life cycle involving migratory bird
diagnosis- DFS CN- Pudoc worm
treatment- Mebendazole > Albendazole DH- Fish-eating birds, Human (incidental)
IH- Freshwater or brackish water fish
 Hookworms IS- Infective larvae
Necator americanus & Ancylostoma duodenale PS- adult worm
*Differentiated based on character of buccal spears of DS- Unembryonated egg
filariform larvae MOT- Ingestion of undercooked fish
Pathogenesis Fever, muscle pain, periorbital edema,
Capillariasis eosinophilia and hemorrhagic phenomena
Acute disease (subconjunctival, splinter)
Borborygmus, Intermittent diarrhea, Fever, Severe disease
abdominal pain, eosinophilia Myocarditis, encephalitis, pneumonia, respiratory
Chronic disease myositis
Chronic watery diarrhea, Edema, wasting diagnosis- Muscle biopsy
Protein-losing enteropathy treatment- Thiabendazole
Hypogammaglobulinemia
diagnosis- Direct fecal smear
Peanut-shaped eggs with striated shells and flattened
bipolar plugs
treatment- Albendazole
DOC: Mebendazole

 Filarial worm
W. bancrofti & B. malayi
Most debilitating nematode infection
CN- W. bancrofti (Bancroft’s filarial worm)
B. malayi (Malayan filarial worm)
DH- Human
Vector- Anopheles minimus flavirostris & culex spp.
(mosquito)
IS- 3rd stage larvae
PS- adult worm
DS- Microfilariae
MOT- Mosquito bite
Pathogenesis
Lymphatic filariasis
Acute disease
Acute adenolymphangitis/
dermatolymphangioadenitis
Filarial fever
Acute filarial lymphangitis (palpable cord)
Chronic disease
Lymphedema (most common manifestation)
which progresses to elephantiasis
Hydrocoele: common in Bancroftian filariasis
Milky urine (chyluria)
diagnosis- Peripheral blood smear
treatment- Diethylcarbamazine

 Trichinella spiralis
CN- Muscle/Trichina worm
DH- Pigs, Human(accidental host)
IS- Encysted larvae
PS- adult worm
DS- Encysted larvae
MOT- Ingestion of undercooked meat
Pathogenesis
Trichinellosis
Clinical conditions divided into 3 phases:
 Enteric phase (incubation, intestinal invasion)
 Invasion phase (larval migration, muscle
invasion)
 Convalescent phase (encystment and
encapsulation)
Cardinal signs and symptoms
Severe myalgia, periorbital edema, eosinophilia;
self-limiting
Mild disease