Microbiology Review: WORMS

[liveonearth]

helminthe = a parasitic worm, one of three types: cestode, nematode, trematode

NEMATODES

NEMATODE = ROUNDWORM
--Phylum Nematoda from Greek νῆμα (nema): "thread" + -ώδη -ode "like"
--one of the most common phyla of animals: over 80,000 species (15,000+ are parasitic)
--ubiquitous in freshwater, marine, and terrestrial environments
--found in locations as diverse as Antarctica and oceanic trenches
--many parasitic forms, including pathogens in most plants, animals incl. humans
--have been repeatedly reclassified
--unsegmented, bilaterally symmetric, triploblastic protostomes w/ complete digestive sys
--no circulatory or respiratory systems, breathe by diffusion
--nutrients are transported throughout the body via fluid in the pseudocoelom
--thin and round in cross section
--body cavity is a pseudocoelom (persistent blastula)
--with growth the worm molts
--most free-living nematodes are microscopic, though a few parasitic forms can grow to over a meter in length (typically as parasites of very large animals such as whales)
--no circular muscles, so the body can only undulate from side to side
--poor swimmers: contact with solid objects is necessary for locomotion
--eat bacteria, fungi and protozoans, although some are filter feeders

ASCARIS LUMBRICOIDES = Giant Intestinal Roundworm
--15-35 cm in length, female larger, lays 200,000 eggs/day, worm lives 1-2 years
--infests over 1 billion people worldwide and several million in the US.
--eggs pass via stool, infection can occur via ingestion or inhalation
--eggs hatch in small intestine, larvae migrate in blood to lungs
--larvae enter alveoli causing inflam, exudate, coughing, pneumonia
--larvae coughed up from lungs are swallowed into gut, mature into worms and lay eggs

ENTEROBIUS VERMICULARIS = PINWORM
--female is 1cm long, pin-shaped, off-white, male is 3mm long and hard to see
--female lives in cecum but migrates out anus at night to lay 20,000 eggs on bedding & peri-anally every 2 weeks
--S/Sx: perianal itching, (no intestinal damage)
--occasionally worms enter vagina and case inflam there or in uterus or ovarian tubes
--spreads easily and quickly

NECATOR AMERICANUS, ANCYLOSTOMA DUODENALE = HOOKWORMS
--filariform larvae live in moist soil
--transmission: burrow through skin of feet or legs
--S/Sx: microcytic anemia, fatigue, nutritional deficiencies
--larvae migrate to lungs to be coughed up and swallowed
--swallowed larvae marture, slide into intestinal wall and feed on capillary blood

TRICHINELLA SPIRALIS = TRICHINOSIS
--transmission: eating undercooked pork, bears
--1.2-2.2mm, live 4 weeks in small bowel
--S/Sx: fever, muscle pain, periorbital edema, eosinophilia, acute inflam & myositis
--pathogenesis: larvae migrate into striated muscle cells. can infect cardiac & nervous tissue
--control: limit carnivorous feeding of farm animals (rodents can be infected too)

FILARIASIS
--(three organisms & two diseases)
--ONCHOCERCA VOLVULUS --> onchocerciasis, river blindness
--worm 2-5 cm long, female produces 2000 microfilariae daily for 15 years! which burrow into subcu and eye for 2 years, then die and are ingested by black flies which transmit to new host, can become encysted adults in 6-12 months
--transmission: black flies
--S/Sx: nodules 10-100, firm, mobile, 1-3cm, painless, over bony prominences. Hypersensitivity rash and pruritus, lichenification (large hanging skin folds). Fibrosis of lymphatics with elephantiasis. Keratitis, iritis, retinitis, blindness.
--Dx: skin biopsy
--location: tropical Africa, Yemen, Latin America
--WUCHERIA BANCROFTI --> lymphaitc filariasis, elephantiasis
--threadlike worm, femal 1cm, male 40mm
--transmission: mosquitoes
--accumulate in pulmonary vessels and flood the body at night!!
--incubation: 8-12 months
--S/Sx: asymptomatic or fever, lymphadenitis, lymphangitis usu in femoral area spreading to legs, lymphatic obstruction causes gential and leg enlargement.
--Dx: Eosinophilia, demonstration of oranisms in blood or body fluids.
--location: Asia, Africa, Latin America
--BRUGIA MALAYI --> lymphatic filariasis, elephantiasis
--same as Wucheria except half as large
--located in coastal Asia and South Pacific

FLUKES

FLUKE = trematode
--one of two subclasses of parasitic worms in class trematoda, phylum Platyhelminthes
--around 20,000 species of trematodes
--most are parasites of molluscs and vertebrates incl turtles and fishes
--complex life cycles involving more than one species of host
--most are monoecious and alternately reproduce sexually and asexually. (exceptions: Aspidogastrea--no asex reprod, and schistosomes--dioecious).
--sexual reproduction occurs in definitive host, eggs are shed in feces
--eggs shed in water release free-swimming larval forms that are infective to the intermediate host, in which asexual reproduction occurs
--infections are found anywhere that human waste is used as fertilizer
--normally inhabit digestive system and/or liver but some seek lungs, heart, brain or skin
--in the GI or liver they disrupt digestion and nutrient absorption
--S/Sx: chronic diarrhea and abdominal pain
--S/Sx from long-standing infections: ulcers, hemorrage and abscessess of the intestional wall, and liver damage, toxemia from worm metabolites
--common meds to kill trematodes: praziquantel, niclosamide, or tetrachloroethylene.
--Transmission: (1) drinking infected water, (2) swallowing infected water while swimming; transmission from wet hands to mouth or nose, etc., (3) eating infected aquatic vegetation, or (4) eating infected raw meat or raw intermediate hosts (snails, shellfish, crustaceans, fish).
--Prevention: One can kill trematodes by thoroughly cooking meats and vegetable taken from suspect waters. Salting, pickling, drying, and smoking does NOT always kill parasites in meat.

SCHISTOSOMA spp.
--location: Africa, Latin America, Middle East, Asia
--adults 10-20mm long
--three species that infect mammals have snail as intermediate host
--transmission: burrows through skin to enter blood stream
--S/Sx: swimmer's itch at transmission, swimmer's ear, later urinary bladder, bowel and liver dysfunction, hypersensitivity rxns, polyps in intestine, enlargement of esophageal and gastric veins, hepato & splenomegaly
--Dx: in endemic area, eggs in fecal matter
--pathogenicity: these worms like mesenteric veins and veins draining the urinary bladder. Eggs induce granuloma formation and fibrosis, and are associated with a high incidence of cancer.

CESTODES

CESTODE = a member of the class cestoda = TAPEWORMS
-- = parasitic flatworms commonly called tapeworms
--live in the GI of vertebrates as adults and often in the bodies of animals as juveniles
--adults are segmented and band like
--juveniles grow in tissues and organs of vertebrates or humans as cysts or metacestodes
--Illness usu due to metacestode stages in tissues rather than the adult tapeworm
--Tapeworms take host nutrients and do not attack the intestinal mucosa or remove blood
--Low level infections are usu asymptomatic. A carrier can notice the segments (proglottids) in the feces or sometimes in underwear.
--high level infections can cause malnutrition, anemia, bloating

TAENIA SAGINATA AND SOLIUM = TAPEWORMS
--trans: ingestion of undercooks beef or pork
--S/Sx: malnutrition, cysticerciasis (cysts in various organ systems)
--pathogenicity: these worms don't hurt the intestine wall when they attach, they only cause problems when they get so large that the interfere with absorption of nutrients.
--Pork tapeworm (solium) eggs can migrate to many organs to encyst, forming space-occupying lesions that cause lots of trouble if they are in the brain

DIPHYLLOBOTHRIUM LATUM = fish tapeworms
--location: Scandinavia, Northern Russia, Japan, Canada and US
--transmission: eating contaminated raw fish
--pathogenicity: worm absorbs vit B12 causing deficiency in host -->megaloblastic anemia
--S/Sx: abdominal discomfort, weight loss, malnutrition
--Dx: eggs or segments in feces, Hx of eating raw fish