ORGANISM: Giardia lamblia

LIFECYCLE: 1) Trophozooite (non-infectious). Binucleate, aerotolerant anaerobe lacking mito. 2) Cyst - Quadrinucleate, infectious agent (ingestion of water contaminated with animal fecal material--TRUE ZOONOTIC DISEASE), environmentally rugged in aquatic atmosphere. Cyst is resistant to chlorine--must be filtered from water supply.

PATH: Epigastric pain, flatulence, diarrhea, steatorrhea.

DX: Microscopy for cysts in stool.

TMNT: Tinidazole with metronidazole alt.

ORGANISM: Trichomonas vaginalis.

LIFE: One stage, motile trophozoite. 4 ant., 1 post. flagellae. Aerotolerant anaerobe with REDUCTIVE METABOLISM (produces H gas in hydrogenosome), no mitochondria.

PATH: FEMALES: severe itching, burning in vulva, thighs with copious, frothy, malodrous discharge. MALE: Urethral discharge with prostatitis and ureteritis. BUT MAY BE ASYMPTOMATIC.

DX: Clinical diagnosis may be made. Recover vaginal discharge in TV pouch and examine microscopically.

TMNT: Metronidazole. TREAT SEXUAL PARTNERS!

AGENT: Cryptosporidium parvum

LIFE: Infective agent, sporulated oocyst, ingested fecal-oral. Quadrinucleate oocysts excyst in sm. int. releasing 4 sporozoites which are internalized by int. epithelial cells. Mature merozoites are released into gut lumen which infect other cells. Some merozoites differentiate into microgametes (male) and macrogametes (female) which combine to form a zygote which changes into an oocyst and is released into gut lumen to be defecated. OOCYST MUST MATURE IN ENVIRONMENT BEFORE IT BECOMES INFECTIVE. Humans are both intermediate and definitive host.

PATH: Profuse watery diarrhea, cramping nausea, vomiting and low-grade fever (no fever, vomiting in giardiasis). CAN BE LIFE-THREATENING IN IMMUNOCOMPROMISED esp. AIDS (secondary to extreme fluid loss).

EPIDEMIOLOGY: Infects wide variety of animals incl. MAMMALS, REPTILES, FISH. Oocyte resistant to chlorination and ozone. CAPABLE OF VERY LARGE OUTBREAKS.

DX: Modified Acid-fast stain of fecal material.

TMNT: WORLDWIDE distribution--difficult to control. NO EFFECTIVE THERAPY.

AGENT: Pneumocystis jirovecii (formerly PCP [carinii]). WAS considered a protozoa, now classified as a fungus.

LIFE: Not fully understood. Can be observed as a thin-walled trophozoite or a thick-walled cyst.

PATH: (almost) exclusively causes disease in immunosuppressed hosts, esp. HIV. Most likely airborne transmission, reservoir unknown. HALLMARK is DIFFUSE INTERSTITIAL PNEUMONIA (PJP).

DX: microscopic examination of bronchial-alveolar lavage or lung biopsy.

TMNT: Trimethoprim-sulfamethoxazole.

CAUSATIVE AGENT: Plasmodium falciparum, vivax, malariae, ovale. Obligate intracellular parasites as sporozoans. Intermediate host in man, definitive host in female Anopheles mosquito ONLY. Falciparum - malignant subtertian malaria (most mortality due to high reproduction, ability to infect reticulocytes and RBCs and tendency to block capillaries, also, there is drug resistant falciparum). Vivax - Benign tertian malaria (cycle of fever, chills every 3 days. Most widely distributed form. Rarely fatal but debilitating. If untreated, it recurs. Malariae - Quartan malaria. Paraoxysms every 4th day. Can recur decades after initial infection and without hypnozoite formation. Ovale - Tertian-type malaria. Similar to vivax. Recurs with hypnozoite formation.

LIFE CYCLE: ASEXUAL PHASE: Sporozoites from mosquito saliva into blood stream and uptaken by hepatocytes (within 30 mins--this is why vaccine is difficult). Multiplication (binary fission) and differentiation into merozoites occurs (vivax and ovale can form hypnozoites which remain in liver cells and cause relapse). Merozoites released from liver cells and infect RBCs (attachment at apical end-->in a parasitophorous vacuole) where they differentiate into ring-shaped trophozoites. In the RBC, schizogony, rapid series of nuclear divisions, occurs filling the RBC with merozoites which lyse the cell where further infection can occur (cause of recurrent bouts of fever, chills). SEXUAL PHASE: Eventually a merozoite will enter an RBC and become either a macrogametocyte or a microgametocyte. These gametes are passed back to animal host via another mosquito's blood meal. Infected RBCs release gametocytes into gut. Microgametes divide (exflagellate), and fuse with macrogamete to form a zygote. The zygote passes through bsmnt. membrane of gut and undergoes a series of divisions to mature oocyst which is released into hemocoel of mosquito. Resulting sporozoites migrate to the mosquito salivary glands completing the sexual cycle. MAZELTOV!

PATH: Main consequence is normocytic, normochromic anemia. Hemolysis of RBCs with suppression of erythropoeitin and increased splenic clearance of infected RBCs (splenomegaly). Initial sympt. include Headache, myalgia, irritability, chills, naus. vom. and dia. Later, high fever and triad of chills fever and sweating at regular intervals depending on species. Furthermore, falciparum infections increase stickiness of RBCs leading to vasoocclusion in cap. beds---> further organ damage.

DX: Microscopic examination of both thick and thin blood films. Should be considered first in the case of a febrile illness in a recent traveler.

New species recently jumped from monkeys to man, P. knowlesi.

Trematodes

Schistosomiasis

ORGANISM: Subclass Digenia, non-segmented worm. Two kinds: Separate sex (female resides in groove in the male trematode), schistosomes; hermaphrodites, flukes. No gut--obtain nutrition by transport through a surrounding tegument and attach via ventral and anterior suckers. Humans are definitive host, Snails are the intermediate host. Larvae directly penetrate or encyst to enter human host.

PATH: Schistosomiasis: Cercariae (free swimming, fork-tailed) directly penetrate human hair follicle. Then enter blood stream maturing into adult flukes. Females lay eggs in venous system. Eggs are defecated or urinated out where they hatch in fresh water. Ciliated larvae hatch and penetrate snail host where they develop into cercariae which swim in free water looking for human host.

CLINICAL: Asymptomatic. Acute disease: fever, flu-like, fatigue, night sweats. Usually self-limited, resolves without treatment, but may cause chronic infection of intestine. Human to human, animal to human transmission possible. Schistosoma mansoni: mesenteric vessels; S. haematobium: bladder. S. japonicum: causes cor pulmonale, CNS damage, Hepatosplenomegaly.

TMNT: Praziquantal--acts on tegument.

Trematodes

Fascioliasis

ORGANISM: Fasciola genus. Hermaphroditic.

LIFE: Ingestion of metacercariae encysted on aquatic vegetation. Eggs produced and shed into environment through fecal material. Hatch into a ciliated meracidium, picked up by snail host. Development in snail occurs and mature into metacercariae again.

PATH: Fasciola hepatica (lives on watercress). Transient dyspepsia followed by high fever and abd. pain. Chronic phase includes obstruction of bile ducts where maturity and egg shedding occurs.

TMNT: Praziquantel.

Trematodes

Paragonimiasis

ORGANISM: Paragonimus westermani (Lung fluke).

LIFE: Ingestion of undercooked/raw freshwater shellfish. Metacercariae are ingested migrate to lungs where parasite matures. Aspiration of lung and defecation or sputum with eggs transmits to snail host where sexual phase begins. 

CLINICAL: clinical signs of a lung infection.

TMNT: Praziquantal and Bithionol

Cestodes

Taeniasis

ORGANISM: Taenia saginata (Beef Tapeworm), Taenia solium (Pork Tapeworm). 

PATH: Ingestion of larvae living in muscle tissue of undercooked beef or pork. Man is definitive host. Some achieve lengths of 10m. Adult worm has head (scolex) and segmented body (strobila) called proglottids. No digestive tract. Head attaches via suckers, hooks or grooves to intestinal lumen. Proglottids are formed proximally (adjacent to head) and mature as they go away from head. Each proglottid has male and female properties. Eggs are produced (egg factories!) which are shed in fecal material.

CLINICAL: Asymptomatic.

DX: Observation of eggs in fecal sample.

TMNT: Praziquantal with Niclosamide.

Cestodes

Cysticercosis

PATH: Taenia solium (pork tapeworm) only. When eggs of this tapeworm are directly ingested (not larvae), the organism does not develop into adult form. Instead larvae deposit in various tissues.

CLINICAL: Symptoms that mimic brain tumor (if deposit there), also abdominal symptoms.

DX: Observation of eggs in fecal sample.

TMNT: Praziquantal with Niclosamide.

ORGANISM: Echinococcus, cystic larval stage.

PATH: Adult tapeworms found in carnivores' intestines, larval form found in intermediate hosts of various mammals' viscera. Man ingests eggs which develop into embryos which form a hyatid cyst. Cysts can cause path in various tissues by simply being a "mass" or rupture can cause anaphylaxis. Can cause liver enlargement.

TMNT: Surgical ressection of cyst most effective. May resolve spontaneously or abendazole can be effective sometimes.

ORGANISM: Diphyllobothrium latum (fish tapeworm).

LIFE: Man consumes raw or undercooked fish of a certain species, pike. Man is the definitive host, the parasite matures and resides in intestine where it sheds eggs. Copepods, small aquatic crustaceans are the first intermediate hosts and fish are the second intermediate host. LONGEST TAPEWORM 2-15 meters.

PATH: Asymptomatic or subclinical in most cases. Fatigue, diarrhea, weakness and sensation of hunger can manifest. Worm scavenges B-12 so pernicious anemia can develop.

TMNT: Praziquantal and Niclosamide are effective.

Large group of free living, non-segmented round worms with separate sexes.

Structurally similar among species with a thick, acellular cuticle coating. Adults have a complex gut with fore-, mid- and hind- components.

Both anaerobic and aerobic.

Some lay eggs some are born live.

Nematodes

Enterobiasis

ORGANISM: Enterobious vermicularis (Pinworm).

LIFE: Eggs ingested and hatch in small intestine, adults mature in large intestine. Females produce many eggs and migrate out of anus expelling them in the perianal region. Eggs swiftly embryonate and are infective within 6 hours. Itching of anal region make inoculation of self or others possible.

PATH: Pruritis ani, perianal dermatitis or GU infections in women.

DX: Demonstrate eggs or worms on perianal skin. Eggs are oval with flattened edge, think rugby ball.

TMNT: Pyrantel pamoate, mebendazole or albendazole. Sometimes whole families must be treated.

Nematodes

 Ascariasis

ORGANISM: Ascaris lumbricoides

LIFE: Ingested eggs hatch into larvae in small intestine. They enter the bloodstream and migrate to liver, lung and trachea where they can be swallowed again. Unembryonated eggs are passed into fecal mass. Embryonation occurs in soil where they can live for a long time.

PATH: Patients can have cough, dyspnea, fever, wheezing while the worms invade alveolar spaces. Mechanical obstruction possible with worms. Larva may cause granulomas.

DX: Find eggs in stool.

TMNT: Albendazole or mebendazole.

Nematode

Hookworm

ORGANISMS: Necator americanus and Ancylostoma duodenale.

LIFE: Filiform larva actively penetrate skin (usually through hair follicle). Through bloodstream to lungs where larvae break out into alveoli and migrate up to trachea and are swallowed. Larvae mature into adults in the intestine.

PATH: Classic symptoms: hypochromic, microcytic anemia. Acute infection causes macropapular rash and pruritis. Chronic infection: epigastric pain, edema, fatigue. Symptoms due to focal hemorrhage of intestinal surface, ingestion of RBCs by adults.

DX: Find eggs in stool.

TMNT: Abendazole, mebendazole, pyrantel pamoate.

Nematode

Strongyloidiasis

ORGANISM: Strongyloides stercoralis.

LIFE: Can live as parasite OR freeliving worm in environment. Adult lives embedded in columnar epithelium of small intestine. Direct penetration of skin as larvae infects man. Larvae travel through blood to alveoli then climb up to trachea where they are swallowed. Develop into adults in small intestine after ingestion. Eggs pass into intestinal lumen, develop into larvae and are expelled or burrow into intestinal lining.

PATH: Asymptomatic often. Mild to severe abdominal symptoms depending on dose.

DX: Infectious serology. Look for larvae in stool.

TMNT: Ivermectin or albendazole.

Nematode

Trichuriasis

ORGANISM: Trichuris trichura (whipworm).

LIFE: Ingestion of embryonated eggs. Larval worm hatches in intestine and penetrates columnar epithelium. Molts a few times and adult worm migrates to large int. where it penetrates mucosa. Fertilized eggs are passed in fecal material and live in soil for long periods.

PATH: Usually asymptomatic except in high inf. dose. Abdominal pain, distention, bloody diarrhea, weakness, wt. loss. Appendicitis may occur as worms fill lumen. Children may get prolapsed rectum from irritation and straining during defecation.

DX: Fecal microscopy shows bile stained eggs with plugs on each end.

TMNT: Occurs worldwide. Use albendazole or mebendazole.

Nematode

Guinea worm

ORGANISM: Dracunculus medinensis.

LIFE: Man infected by ingestion of water containing infected copepods. Larval form are freed in sm. intestine. Larva migrates in connective tissues for a year, then mature into adults and reside in subcutaneous tissues in extremities. Ulcer develops in skin and female releases larvae which are ingested by copepods.

PATH: abscess where worm emerges from skin. Associated bacterial infections occur. Worms that don't emerge may calcify in skin and interrupt nerve and/or organ systems.

DX: Visualizatoin of emergent worm.

TMNT: Roll up worm on stick, take mebendazole to alleviate sympt.

PREV: Keep people away from water sources when worm is emerging.

Nematode

Filiariasis

ORGANISM: Wuchereria bancrofti (elephantiasis), Brugia malayi (loa loa).

LIFE: Human to human infection via arthropod vectors.

CLINICAL: Lymphangiitis, lymphadenoma, elephantiasis, lymphadenopathy, keratitis, dermatitis.

PATH: Worm migrates through lymphatics so symptoms are caused by lymph system reaction to worm. Loa loa migrates to eye and can be seen in eye.

DX: ID of microfilariae in blood or skin biopsy.

TMNT: Diethylcarbamazine and Ivermectin are micro- and macrofiliaricides.

Nematode

Trichinellosis

ORGANISM: Trichinella spiralis.

LIFE: Unusual in that they live as intracellular parasites. Ingestion of raw/undercooked pig. Larvae are released by digestive enzymes in intestine. Adults reside in intestine and produce larvae which disseminate through blood throughout the body. Larvae penetrate tissues and form "Nurse cell" complex in muscle.

PATH: Abd. pain, diarrhea, fever, malaise. Infl. enteritis, vasculitis and hemorrhage in eyes, brain, pericardium, endocardium, lungs and muscles can occur.

TMNT: Abendazole, mebendazole.

Nematode

Ancylostoma braziliensis

Nematode

Toxocara canis and catis

Nematode

Swimmer's itch

ORGANISM: Toxoplasma gondii

LIFE: Ingest raw/undercooked meat or congenital transfer or blood transfusion or tissue transplantation or direct ingestion of oocytes from feces of cats (definitive hosts). Obligate intracellular parasite related to coccidia and malaria. Excystation occurs in intestine releasing trophozoites which develop into tachyozoites and subsequent internalization into intestinal epithelium. Then carried through blood to many tissues throughout body. In tissue, a pseudocyst develops, then many rounds of division filling up the cyst with bradyozoites. They may remain dormant in cyst for years. In cat, micro- and macrogametes develop intracellularly, resulting gamete is released in feces. Sporulation occurs in environment and resulting oocyst is infective to man.

PATH: MAJOR cause of congenital and perinatal disease. Major cause of choreoretinitis, major cause of death of HIV patients. FOUR BASIC  CLINICAL MANIFESTATIONS: 1) Acute acquired disease, "fever of unknown origin". 2) Congenitally acquired when mother gets primary infection during 1st trimester. 3) Ocular disease - unilateral or bilateral posterior choreoretinitis--may manifest later. 4) Immunosuppressed reactivation of infection (seen in HIV).

TMNT: Pyrimethamine with Sulfadiazine and Lecovorin for active infection. In immunologically normal, no treatment indicated unless organ damage occurs.

PREV: Children may get when playing in places where cats have defecated. i.e. sandboxes (giant litterbox) for feral cats to poop on.

ORGANISMS: Cutaneaous: Leishmania tropica, L. major, L. aethiopica. Mucocutaneous: L. braziliensis, L. braz. ssp. panamensis, L. braz. ssp. guyaniensis. Visceral: L. donovani, L. infantum, L. chagasi. All kinetoplastic flagellates, no sexual cycle and one mitochondrion. Endemic to Southern Europe and countries that abut the mediterranean sea. 

LIFE: Bite of sandfly vector introduces parasite in promastigote form. In human host, amastigote is found intracellularly in macrophages in a parasitopherous vacuole.

PATH: Cutaneous: Chronic skin ulcers at bite site and elsewhere on skin in some species. Lesions have raised margin and necrotic center. Mucocutaneous: Metastatic spread of primary lesions to the mouth, nose and pharynx. Tissue destruction and bacterial infection ensue. Visceral: Fever, wt. loss, hepatosplenomegaly, anorexia.

DX: Microscopy from lesion scraping/aspirate.

TMNT: Sodium stibogluconate.

Trypanosomes

African

ORGANISM: Trypanosoma brucei gambiense - West Africa. Trypanosoma brucei rhodesiense - East Africa.

LIFE: Both cause African Sleeping Sickness and transmitted by Tsetse fly (female). Transmission through blood meal as metacyclic trypomastigote which tranforms to trypomastigote. Lives extracellularly in blood stream. Defense against host is antigenic variation. Also contain a kinetoplast.

PATH: Chronic disease characterized by torpor, coma and death. Domestic cattle in Africa succumb to disease known as Nagana.

TMNT: Pentamidine, Suramin, Melarsoprol and Eflornithine. Severe side fx.

Trypanosomes

American

ORGANISM: Trypanosoma cruzi - Central and S. America. Zoonotic disease occuring in wild animals.

LIFE: Causes Chagas Disease. Transmission through blood meal of Reduvidae (kissing bug) as metacyclic trypomastigote which tranforms to trypomastigote inside of a macrophage. Carried to many tissues including myocardium. Lives extracellularly in blood stream. Defense against host is antigenic variation. Also contain a kinetoplast.

PATH: Acute and chronic manifestations--most important pathological effect is cardiomyopathy.

TMNT: Nifurtimox and Benznidazole.