Exam 3 Flashcards
1
Q
Nematoda: Form and Function
A
- bilaterally symmetrical, posses a pseudocoel
- most are dioecious; considerable sexual dimorphism
- elongated, tapered at both ends; from < 1 mm to > 10 meters
- digestive tract usually complete; mouth at extreme anterior and anus near posterior tip
- noncellular cuticle that is secreted by an underlying hypodermis
- chitinous cuticle is shed 4 times during ontogeny (4 molts)
2
Q
Nematoda: Form and Function
Bodv Wall
A
- nematode body wall consists of cuticle, hypodermis, and body wall musculature
- an important function of the hypodermis is secretion of cuticle.
- hypodermis is syncitial in adult worms; nuclei lie in 4 epidermal cords
- epidermal cords run longitudinally and divide body into 4 quadrants
- dorsal and ventral cords contain longitudinal nerve trunks
- lateral cords contain lateral canals of the excretory system in most species
3
Q
Nematoda: Form and Function
Musculature
A
- muscles of the body wall are all longitudinally with no circular layer
- nematode muscles have a contractile portion and a noncontractile cell body (myocyton)
- muscle contraction occurs similar to vertebrate striated muscle with myosin & actin
- cuticle, hypodermis, somatic musculature, fluid filled pseudocoel functions as a hydrostatic skeleton
4
Q
Nematoda: Form and Function
Pseudocoel and Hydrostatic Skeleton
A
- pseudocoel differs from a true coelom in that it has no peritoneal (mesodermal) lining
- pseudocoel is a fluid-filled cavity enclosed by body wall
- pseudocoelomic fluid in known as hemolymph
- pseudocoel functions as a hydrostatic skeleton that depends on:
(1) enclosed volume of non-compressible fluid
(2) ability of muscle contraction to apply pressure to that fluid
(3) transmission of the fluid pressure in all directions - alternation of contraction and relaxation in dorsal and ventral muscles produces the characteristic S-shaped motion seen in nematode locomotion
*water balloon *
5
Q
Nematoda: Form and Function
Nervous System
A
- nervous system is relatively simple
- 2 main concentrations of nerve elements; connected by longitudinal nerve trunks
one in esophageal region
one in anal region - nematodes have a variety of sensilla (small sense organs)
- sensilla are most prominent in the cephalic and caudal regions
6
Q
Nematoda: Form and Function
Digestive System and Acquisition of nutrients
A
- digestive system is complete; mouth, gut, and anus
- buccal muscles and anterior esophageal muscles contract to open mouth; suck in food
- hydrostatic pressure in pseudocoel closes the mouth and esophageal lumen
- food passes down the esophagus via muscle contractions until it reaches the intestine
- posterior bulb, one-way valve
- hydrostatic pressure pushes food posteriorly; newly ingested food & locomotor helps
- intestine constructed of a single layer of intestinal cells
- depressor ani (anal dialator muscles) contracts to open anus
- hydrostatic pressure causes defecation when the anus is opened
- food of nematodes include blood, tissue cells, fluids, and intestinal contents
7
Q
Nematoda: Form and Function
Secretory-Excretory system
A
- most excretion occurs through the intestine
- no flame cells or nephridia
- 2 long canals in the lateral hypodermis connect near the anterior end
- secretory-excretory canal opens to the excretory pore
- ability to osmoregulate varies greatly; depends on habitat
8
Q
Nematoda: Form and Function
Reproduction
A
- most are dioecious
- females generally larger; tail of males is more curled
- most nematodes are oviparous
- gonads of nematodes are solid cords of cells; germ cells move via rachis
- testes are generally paired, but some species only have one
- nematode spermatozoa use pseudopodium
- males have cloaca, ejaculatory duct opens into rectum
- the female reproductive system opens through a central vulva
- copulatory spicules of male are used in copulation
9
Q
how young develop
A
-Oviparous: Animals that lay eggs, which hatch and develop outside of the parent’s body.
-Viviparous: Animals that give birth to live young after developing inside the parent’s body
-Ovoviviparous: Animals that produce eggs that hatch inside the parent’s body.
10
Q
Nematoda: Trichuris trichiura
Whipworm
A
- tissue parasite
- 3 to 5 cm in length; adults live several years
- females produce 3,000 to 20,000 eggs per day
- embryonation, 21 days in moist and shady soil
- swallowed, hatch in small intestine, and enter intestinal crypts of large intestine
- slender anterior end embeds in gut mucosa; enlarged posterior portion in lumen
11
Q
Nematoda: Trichuris trichiura
Pathology
A
- < 100 worms, often asymptomatic
- heavy burden may result in death; 200 to 1,000 in small children
- trauma to intestinal epithelium and underlying mucosa; chronic hemorrhage
- intense trichuriasis: dysentery, anemia, growth retardation, rectal prolapse, finger and toe clubbing, adversely affect cognitive function
12
Q
Nematoda: Trichuris trichiura
Epidemiology
A
- poor standards of sanitation; night soil for fertilizer
- physical conditions for egg survival include: warm, high rainfall and humidity, moisture retaining soil, dense shade
- house flies can serve as mechanical vectors
- prevalence may reach 20-25% in small children in Southeastern US
- prevalence estimated at 795 million worldwide
13
Q
layers of GI tract
A
-mucosa
-submucosa
-muscularis
-serosa
14
Q
Nematoda: Trichinella spiralis
Porkworm
A
- smallest nematode parasite of human
- world’s largest intracellular parasite
- same individual host can be both intermediate and definitive host
- juveniles (J1) reside in “nurse cells” of skeletal muscle fibers of intermediate host
-increases angiogenesis factor (more blood cells grow) J1 gets fed - definitive host eats contaminated meat with nurse cells
- infective juveniles (J1) are released from nurse cells in stomach
- undergo 4 molts in small intestine, then copulation within mucosal epithelium
- adults are intramulticellular parasites in intestinal epithelium
- female gives birth (ovoviviparous) to thousands of juveniles over 4 months
- juveniles carried by hepatoportal system through liver, heart, lungs and arterial system
15
Q
Nematoda: Trichinella spiralis
Pathology
A
Pathogenesis of trichinosis in 3 stages
(1) penetration of adult females into mucosa
- traumatic damage to host tissue
- host reacts to their waste products: nausea, vomiting, sweating & diarrhea
(2) migration of juveniles
- damage to blood vessels: localized edema
- wandering juveniles: pneumonia, encephalitis, meningitis, etc.
- death can result from myocarditis
(3) penetration and nurse cell formation
- intense muscular pain, difficulty breathing or swallowing
- heavy infection suppresses muscle contractibility
16
Q
Nematoda: Trichinella spiralis
Epidemiology
A
- zoonotic disease: humans not important for life cycle
- eating infected pork is most common source of infection
- solid meat is safe when all traces of pink have disappeared
- well known in Mexico, parts of South America, Africa, southern Asia, & Middle East
17
Q
Nematoda: Ascaris lumbricoides
A
- females up to 49 cm long
- unembryonated develop into J3s in 13 days
- juveniles molt twice to become infective J3 inside egg
- infection occurs when unhatched juveniles are swallowed
- hatch in duodenum and penetrate small intestine and enter venules
- enter pulmonary circulation and break out of capillaries
- juveniles usually molt once in lungs, migrate up trachea and swallowed (must molt to J4 or they’ll be killed by gastric juices)
- pass through stomach and mature in small intestine
18
Q
Nematoda: Ascaris lumbricoides
Pathology
A
- many worms get lost and cause acute tissue reactions, inflammatory response
- breaking out of lung capillaries causes a small hemorrhage at each site
- small pools of blood accumulate in lungs causing edema, clogging air spaces
- lung can become diseased and result in bacterial infection, death
- massive infections can cause fatal intestinal blockage
19
Q
Nematoda: Ascaris lumbricoides
Epidemiology
A
- contamination is the typical means of infection
- eggs infective after 10 years in soil
- cockroaches can be mechanical vectors
- dogs are reservoir host
- one quarter of world population infected
20
Q
Nematoda: Strongyloides stercoralis
Threadworm
A
- parasitic females burrow into submucosa of small intestine
- parthenogenic females release eggs in mucosa, hatch and migrate to lumen
- J1s are passed in feces and become either:
•non-infective rhabditiform in soil that give rise to free-living adults in soil
•infective filariform J3s in soil - both free-living and parasitic females can produce free-living and parasitic juveniles (ambient temperature <34C then free-living)
- infective filariform J3s continue development after they penetrate skin
- migrate to small intestine usually via lungs, coughed up and swallowed
- autoinfection may occur if juveniles molt twice before exiting in feces
21
Q
Nematoda: Strongyloides stercoralis
Pathology
A
-Strongyloidiasis can be described in 3 stages:
(1) invasive: intense itching at site of entry, slight hemorrhage & swelling
(2) pulmonary: burning sensation in chest, nonproductive cough, and possible bronchial pneumonia
(3) intestinal: worms migrate randomly through mucosa, intense localized burning sensation in abdomen, intestinal ulceration and septicemia
22
Q
Nematoda: Strongyloides stercoralis
Epidemiology
A
- contacting filariform juveniles in contaminated soil
- transmammary infection in dogs, and presumably humans
- present under conditions of low sanitation standards
- cats and dogs serve as reservoir hosts
23
Q
Nematoda: Onchocerca volvulus
A
- females up to 50 cm long; males up to 42 cm long
- adult worms located under the skin; become encapsulated by host (onchocercomas)
- encapsulated nodules are located at site of black fly (Simulium spp.) bite
- adult females produce microfilariae (ovoviviparous)
- microfilariae concentrate in skin where black flies bite
- black fly becomes infected when it takes tissue fluid / blood meal
- microfilariae penetrate fly midgut and molt twice in black fly thoracic muscles
- infective filariform J3s move to fly mouth parts to infect new host
24
Q
Nematoda: Onchocerca volvulus
Pathology
A
- River Blindness; not fatal, but does cause disfigurement and blindness
- most middle-aged people and older are blind in some communities
- adult worms stimulate the growth of benign subcutaneous nodules (onchocercomas)
- onchocercomas consist of collagen fibers surrounding up to several adult worms
- pruritus and severe dermatitis occurs because of degenerating juveniles in skin
- degenerating juveniles in eyes resulting in sclerosing keratitis
- true elephantiasis may occur and also hanging groin
25
Nematoda: Onchocerca volvulus
Epidemiology
- significant public health problem in Africa and South America
- black fly larval stages only in clear, fast-running streams
- adult flies survive in high humidity and plenty of streamside vegetation
26
Nematoda: Dirofilaria immitis
- females up to 30 cm long; males are shorter
- adult worms located in right side of heart and pulmonary arteries
- adult females produce microfilariae (ovoviviparous)
- microfilariae are found in peripheral blood circulation
- mosquitoes get infected when they ingest blood meal
- microfilariae develop into J3s inside Malpighian tubules
- infective filariform J3 moves to mosquito proboscis to infect new host
27
Nematoda: Dirofilaria immitis
Pathology
- dangerous pathogen for dogs
- prevalence & intensity is typically lower in cats
- cats need fewer adults to cause serious disease
- symptoms include: respiratory distress, vomiting, chronic cough, & exercise intolerance
- adults worms may prevent proper sealing of tricuspid and semilunar valves
- pulmonary arteries often show signs of inflammation and thickening
28
Nematoda: Dirofilaria immitis
Epidemiology
- host specificity is low for species of mosquito vectors
- within the U.S. prevalence is highest in southeastern US & Gulf Coast (ave. 3.9%)
- heartworm has been diagnosed from domestic dog in all 50 U.S. states
- 60 cases of human pulmonary dirofilariasis documented in U.S.
29
Nematoda: Wuchereria bancrofti
- females up to 10 cm long; males up to 4 cm long
- adult worms located in lymphatic ducts of humans
- found in afferent lymph channels near major lymph glands in lower half of body
- adult females produce microfilariae (ovoviviparous)
- microfilariae show periodicity in their migrations to peripheral blood circulation
- night-feeding mosquitoes get infected when they ingest blood meal
- microfilariae penetrate gut and molt twice in mosquito thoracic muscles
- infective filariform 3s move to mosquito proboscis to infect new host
30
Nematoda: Wuchereria bancrofti
Pathology
- lymphatic filariasis can be described in 3 phases:
(1) Asymptomatic: seen in large proportion of infected endemic individuals where
microfilaremia and symptoms are not present
(2) Inflammatory (Acute): caused by antigens (Wolbachia) released from adult worms
- adult worms cause dilation of lymph channels
- may result in lymphedema and hydrocele
- invasion of bacteria from skin surface
(3) Obstructive: infiltration of the affected area with fibrous connective tissue
- elephantiasis results from repeated attacks of acute lymphatic inflammation
31
Nematoda: Wuchereria bancrofti
Epidemiology
- 2018 global prevalence was estimated at 51 million cases
- mosquito vectors are primarily night feeders
- tropical areas provide suitable breeding sites for mosquitoes
- prevention involves protection against mosquito bites in endemic areas
32
Nematoda: Loa loa
- known as "eye worm"
- females up to 7cm long; males are up to 3.5cm long
- adults actively migrate throughout subcutaneous connective tissue of body
- microfilariae appear in peripheral blood during day, in lungs at night
- several species of deer fly, genus Chrysops, are intermediate hosts
- microfilariae develop into J3s thoracic muscles of deer fly & migrate to mouthparts
33
Nematoda: Loa loa
Pathology
- adults live in subcutaneous and intermuscular connective tissues, including back, chest, axilla, groin, penis, scalp, and eyes in humans
- Calabar "fugitive swellings" result as worms wander through subcutaneous connective tissue
- intense pruritis, arthralgia, and fatigue are common
- infection of deep tissues, including fatal encephalitis is known
34
Nematoda: Loa loa
Epidemiology
- distributed in rain forest areas of Central and West Africa
- several species of deer fly, genus Chrysops, serve as vectors
- microfilariae have diurnal periodicity, (daylight in peripheral blood vs. night in lungs)
- control of deer flies breeding in swampy areas is extremely difficult
35
Nematoda: Anisakis simplex
- eggs produced by females worms embedded in stomach of marine mammal
- eggs become embryonated in water and juveniles molt once to become J2's in egg
- J2's hatch out of egg and become free-swimming and are ingested by crustaceans
- J2's molt once inside crustacean to become J3's and are eaten by fish or squid
- J3's migrate to peritoneal cavity and grow up to 3cm in fish or squid
- upon death of host the J3's migrate to the muscle tissues
- J3's are transferred via fish to fish predation and then finally to marine mammal
36
Nematoda: Anisakis simplex
Pathology
- symptoms begin within 1 to 12 hours when juveniles begin to penetrate the stomach
- symptoms of intestinal penetration may commence up to 14 days after ingestion
- symptoms include extreme gastric pain, nausea, vomiting, diarrhea, and hives
- Anisakis-associated severe IgE-mediated hypersensitivity reactions may occur
37
Nematoda: Anisakis simplex
Epidemiology
- eating undercooked or raw fish, such as sushi and ceviche, is a risk factor
- 'Sushi parasites' have increased 283-fold in past 40 years (Fiorenza, et al. 2020)
- in US, majority of anisakiasis cases are due to ingestion of Pacific salmon
- in Western Europe, majority of anisakiasis cases are due to ingestion herring
- in Spain, most cases have been related to the consumption of pickled anchovies
38
Nematoda: Enterobius vermicularis
Pinworm
- females up to 13 mm long; males up to 4 mm long
- adult worms congregate in the ileocecal region of intestine
- attach to mucosa and feed on epithelial cells and bacteria
- after copulation males die; females lay eggs onto perianal skin then die
- eggs laid have partially developed juveniles; in 6 hours they are infective J3s
- eggs can become airborne and accidentally swallowed; retroinfection can occur
39
Nematoda: Enterobius vermicularis
Pathology
- one-third of infections asymptomatic
- very large numbers of worms can cause pathogenesis in 2 ways
(1) damage caused by worms attached within the intestine
- minute ulcerations lead to mild inflammation and bacterial infection
(2) damage resulting from egg deposition around the anus
- perianal tickling sensation causes intense itching resulting in bacterial infection
- common for pinworms to wander into the vulva causing mild irritation
- cases have reported wandering up vagina, uterus, and oviducts into coelom
40
Nematoda: Enterobius vermicularis
Epidemiology
- humans can inhale and subsequently swallow eggs
- clothing and bedding rapidly becomes contaminated with eggs
- curtains, carpet, and dust are sources of infection or reinfection
- all bed linens, towels and clothes must be washed in hot water
- entire household needs chemotherapy, mebendazole (Vermox) or pyrantel pamoate
41
Nematoda: Ancylostoma duodenale
Hookworm
- females up to 13 mm long; males up to 11 mm long
- mature and copulate in small intestine of host
- direct life cycle, eggs passed with feces
- eggs require warmth, shade, and moisture for continued development
- newly hatched J1s live in the feces and feed on fecal matter
- undergo 2 molts to become infective J3s; can live for several weeks in soil
- penetrate skin, get to heart via blood vessels, then to lungs, coughed up, & swallowed
- in small intestine they molt twice to become adults
42
Nematoda: Ancylostoma duodenale
Pathology
- presence and severity depends on 3 factors:
(1) number of worms present
(2) species of hookworm
(3) nutritional condition of infected person
- hookworm disease manifests in 3 main phases
(1) Cutaneous phase: "ground itch" caused by bacterial infection of invading juvenile
- cutaneous larva migrans "creeping eruption", from cat and dog hookworms
(2) Pulmonary phase: dry coughing and sore throat as worms break out of capillaries
(3) Intestinal phase: attach to mucosa, suck blood producing iron deficiency anemia
- 0.26 ml blood loss per day (0.26 ml x 100 worms = 26 ml blood loss)
43
Nematoda: Ancylostoma duodenale
Epidemiology
- lack of adequate sanitation
- economic dependence on night soil
- 23°C to 30°C optimal for juveniles
44
Nematoda: Ancylostoma sp.
Anderson, Foster & Forrester (2003) performed a study of feral cats in Florida.
-75% were infected with Ancylostoma tubaeforme
-33% were infected with Ancylostoma braziliense;
most commonly associated with cutaneous larval migrans
45
Anhelmintics
Albendazole (Albenza)
- developed by SmithKline in 1972
- broad-spectrum anhelmintic
- on the World Health Organization's List of Essential Medicines
- recommended drug by CDC effective against: Trichuriasis, Trichinosis, Strongyloidiasis, Ascariasis, Anasakiasis, Enterobiasis, Ancylostomiasis, Loiasis
- binds to colchicine-sensitive site of tubulin eliminating its polymerization into microtubules leading to impaired uptake of glucose
- available in the United States as Albenza by GlaxoSmithKline
(1 dose pack - 2 tablets - $215.00)
46
Anhelmintics
Ivermectin (Stromectol, Mectizan, Heartgard)
- broad-spectrum anhelmintic
- on the World Health Organization's List of Essential Medicines
- recommended drug by CDC effective against: Trichuriasis, Strongyloidiasis, Ascariasis, Anasakiasis, Onchocerciasis, Wuchereriasis, and Dirofilariasis
- only effective against microfilariae, but can sterilize female macrofilariae (adults)
- binds to and activates glutamate-gated chloride ion channels present on neurons and myocytes, thus enhancing inhibitory neurotransmission
- available in the United States as Stromectol by Merck Sharp & Dohme
(1 pack - 4 tablets - $42.00)
47
Anhelmintics
Pyrantel pamoate (Reese's Pinworm Medicine)
- on the World Health Organization's List of Essential Medicines
- recommended drug by CDC effective against: Enterobiasis, Ascariasis, hookworms (all species), and Acanthocephaliasis
- acts as a depolarizing neuromuscular blocking agent, which causes sudden contraction, followed by paralysis of the helminths
- (Reese's Pinworm Medicine Suspension, 1.0 oz. - $8.99)
- over-the-counter product
48
Trypanosomatidae : Form and Function
- hemoflagellates
- heterotrophic, eukaryotic, single celli
- heteroxenous: a parasite that lives within more than 1 host during their life cycle
- monoxenous: living within a single host during a parasite's life cycle
- kinetoplast: a dark staining mass of DNA within the single mitochondrion;
situated at the base of the flagellum
- kinetosome (basal body): centriole from which the axoneme arises
- axoneme: core of cilium or flagellum, composed of microtubules
- undulating membrane: a finlike ridge across the surface of the cell with axoneme
49
Trypanosomatidae : Trypanosoma brucei
- 3 morphologically indistinguishable subspecies
(1) T. b. brucei : humans are not susceptible; causes nagana in livestock
(2) T. b. gambiense : Human sleeping sickness (chronic form)
(3) T. b. rhodesiense : Human sleeping sickness (acute form)
- inside vertebrate host trypomastigotes live in blood, lymph nodes, spleen, and cerebral spinal fluid
- transmitted by tsetse fly (Glossina spp.); > 90% flies refractive to infection
- trypomastigote sucked up by tsetse fly; multiplies in midgut of insect
- migrate to salivary glands and transform into epimastigotes and multiply
- epimastigotes transform into metacyclic trypomastigotes; infective to vertebrate host
50
Trypanosomatidae : Trypanosoma brucei
Pathology
- small chance at site inoculated; lesion disappears in 2 weeks
- fever, swelling of lymph nodes, generalized pain, headache, weakness, and cramps
- Winterbottom's sign: swollen lymph nodes at base of skull
T. b. rhodesiense : Human sleeping sickness (acute form)
- rapid weight loss, heart problems; death within few months of infection
T. b. gambiense
: Human sleeping sickness (chronic form)
- invades CNS, initiates chronic sleeping sickness
- increased apathy, mental dullness, tremor, paralysis, coma, death
51
Trypanosomatidae : Trypanosoma brucei
Epidemiology
- reservoir hosts for T. b. rhodesiense
- presence of tsetse fly
- brush removal and trimming
52
Trypanosomatidae: Trypanosoma cruzi
- triatomine bug "kissing bug" gets blood meal and passes metacyclic trypomastigote in feces
- trypomastigotes penetrate various cells at bite wound site
- amastigotes form within monocytes beneath epidermis and multiply
- trypomastigotes released and enter cells of spleen, liver, lymphatics, cardiac, smooth and skeletal muscle
- inside cell trypomastigotes transform into amastigotes and multiply; form pseudocyst
- trypomastigotes released are sucked up by "kissing bug" and become epimastigotes
- epimastigotes divide in midgut then transform to metacyclic trypomastigotes in rectum
53
Trypanosomatidae : Trypanosoma cruzi
Pathology
Chagoma: acute local inflammatory reaction where parasite enters through bite
Romana's sign: swelling and edema when parasites enter conjunctiva of eye
- disease known as Chagas' disease
- rupture of pseudocysts causes acute local inflammatory response resulting in necrosis
(1) destruction of autonomic ganglia causes megaesophagus or megacolon
(2) heart disease caused by destroyed nerve ganglia; heart enlarges
54
Trypanosomatidae : Trypanosoma cruzi
Epidemiology
- thatched roofs and cracked walls; ideal breeding for triatomine bugs
- dogs, cats, opossums, armadillos, and wood rats are reservoir hosts
- blood transfusion
55
Trypanosomatidae : Trypanosoma cruzi
"The New HIV/AIDS of the Americas",
- Chagas disease and HIV are health disparities
- Both are chronic conditions
- Require prolonged treatment
- Treatment is expensive
56
Trypanosomatidae : Leishmania donovani
- sand fly (Phlebotomus sp.) are vectors for Leishmania donovani
- promastigotes injected in new vertebrate host with the sand fly's bite
- promastigotes are immediately engulfed by macrophages
- promastigotes transform into amastigotes and divide by binary fission
- escaping from dead macrophage, parasites are engulfed by other macrophages
- sand fly ingests amastigotes in blood meall
- transform into promastigotes in midgut of sand fly; block gut, enter buccal cavity
- promastigotes ready to be injected in new host with the sand fly's bite
57
Trypanosomatidae : Leishmania donovani
Pathology
- disease known as kala-azar (visceral leishmaniasis)
- disease typically begins with low grade fever and malaise
- destroys phagocytic cells (Kupffer cells, dendritic cells, microglia cells, etc.) of reticuloendothelial (RE) system including spleen, liver, mesenteric lymph nodes,
intestine, and bone marrow
- hypertrophy of liver and spleen (hepatosplenomegaly)
- progressive wasting and anemia
- death in 2 to 3 years if untreated
58
Trypanosomatidae : Leishmania donovani
Epidemiology
- occurs in Mediterranean basin, China, India, Pakistan, Sumatra, Thailand Africa, and South America
- control of sand flies and reservoir hosts in endemic areas
- dogs are the main important reservoir host in most areas
- 2.5 million dogs may be infected in countries around Mediterranean
- fatal outcome is most frequent in infants and young children
59
Hexamitidae : Giardia lamblia
- direct life cycle
- dorsoventrally flattened; ventral surface has bilobed adhesive disk; two nuclei
- parasite is cosmopolitan; occurs mostly commonly in warm climates
- most common flagellate of the human digestive tract
- lives in the small intestine, with adhesive disk fitting over surface of epithelial cell
- trophozoites divide by binary fission; found in loose stool
- when feces enter colon and dehydrate the parasite encysts
- infective stage is the cyst; found in hard stool
60
Hexamitidae : Giardia lamblia
Pathology
- disease is known as giardiasis; typically not fatal
- some cases asymptomatic (protective immunity)
- may damage intestinal epithelium
- interferes with absorption of fats and other nutrients
- increases mucus production, diarrhea (sometimes incapacitating), dehydration, intestinal pain, flatulence, weight loss
- gallbladder may become infected causing jaundice and colic
61
Hexamitidae : Giardia lamblia
Epidemiology
- giardiasis is highly contagious
- if one family member infected, others will also
- children are especially susceptible
- prevention depends on high level of sanitation
- reservoir hosts include: beavers, dogs, cats, and sheep
62
Trichomonadidae : Trichomonas vaginalis
- cosmopolitan species; primarily transmitted by sexual intercourse
- direct life cycle; has trophozoite stage, but no cyst stage
- found in reproductive tracts of both men and women
- lives in the vagina and urethra of women
- lives in the prostate, seminal vesicles, and urethra of men
- acidity of normal vaginal (pH 4.0 to 4.5) discourages infection
- once established pH shifts toward alkalinity (pH 5 to 6), encourages growth
63
Trichomonadidae : Trichomonas vaginalis
Pathology
- most strains have low pathogenicity so person is asymptomatic
Men:
- infection is usually asymptomatic, but may have irritating urethritis or prostatitis
Women:
- in several days there is degeneration of vaginal epithelium
- followed by leukocytic infiltration; secretions become abundant and white or greenish, and tissues become intensely inflamed
- some strains cause intense inflammation, itching, copious white discharge (leukorrhea), burning, and chafing
64
Trichomonadidae: Trichomonas vaginalis
Epidemiology
- transmitted by sexual intercourse
- infections can be contracted from soiled washcloths, towels, and clothing
