(O) 30: Parasitology II Flashcards
Flagellates
have one or more whiplike flagella
- sometimes has an undulating membrane
Amebae
use pseudopodia or protoplasmic flow to move
Sporozoa
undergo a complex life cycle w/ alternating sexual + asexual reproduction
move by GLIDING
Ciliates
have cilia distributed in rows or patches
Trypanosoma
Flagellate w/ intermediate + definitive host
- unicellular parasitic flagellate protozoa
- most are HETEOXENOUS and transmitted via a VECTOR
Some diseases they cause are:
- African trypanosomiasis (aka African Sleeping Sickness) caused by Trypanosoma brucei - vector is Tsetse fly
- American trypanosomiasis (aka Chagas disease) caused by Trypanosoma cruzi
African Trypanosomiasis
there are two types - East and West African
- BOTH are transmitted by the tsetse fly
- both are eventually fatal if not treated
East African trypanosomiasis is caused by Trypanosoma brucei RHODESIENE
West African trypanosomiasis is caused by Trypanosoma brucei GAMBIENSE
Tsetse fly and disease burden
Tsetse flies get nutrition from bloodmeal - reproductive cycles in their own body + eggs are laid in soil
Animals can host the human pathogen of Trypanosoma genus
T brucei brucei infects CATTLE in both West and East Africa - disease is Nagana
Trypanosomiasis in animals, especially cattle, is a major obstacle for economic devlopment
Trypanosoma life cycle
- infected tsetse fly ingests blood and injects parasites
- primary chancre develops at bite wound, in lymph
- trypomastigotes invade bloodstream (use our glucose + spreads asexually)
- humans are INTERMEDIATE hosts. tsetse fly bites + acquires infection
- undergoes sexual reproduction IN fly - tsetse fly is DEFINITIVE host
Signs and Symptoms of Trypanosoma infection
- Winterbottom’s sign (early onset): swollen lymph nodes at back
- perivascular cuffing in brain (late onset)
Antigenic Switching
T. brucei cell surface is covered by a variant surface glycoprotein (VSG)
if they switch, immune system can’t identify it fast enough to eradicate it
West vs East African Sleeping Sickness Symptoms
Both infections occur in 2 stages (initial hemolymphatic stage then CNS involvement)
- second stage symptoms: reversal of sleep-wake cycle, motor, sensory, mental + neurological disturbances
Main difference is time of symptom appearance + progression
West (T. brucei GAMBIENSE)
- symptoms develop over MONTHS post bite (headache, weakness, fevers)
- progress to 2nd stage in 300-500 days
East (T. brucei RHODESIENE)
- symptoms develop 1-3 WEEKS post bite
- progress to 2nd stage in 30-60 days
Diagnosis and Treatment of Sleeping Sickness
- no vaccine or drug for prophylaxis (can’t prevent)
- treatment depends on type of infection and stage
Staging is done by microscopic exam of CSF
- parasite in CSF = progressed to 2nd stage (if not, parasite in blood)
Giardia Lamblia
Flagellate, strict anaerobe = thrives in GI TRACT of humans
- infections by FECAL-ORAL route thru contaminated water
- giardiasis is frequent in travellers and immunocompromised ppl
G. lamblia is common in domestic animals - many infected ppl remain undiagnosed
Giardiasis Symptoms
Some ppl have no symptoms at all
Usually develop 1-2 weeks after infection: (all GI related)
- diarrhea
- gas
- foul-smelling, greasy stools
- stomach cramps or pain
- upset stomach or nausea
- vomiting
- dehydration
Treatment of Giardiasis
If you have diarrhea, drink lots of fluid to avoid dehydration
Effective pharmaceutical treatments exist
Entamoeba Histolytica
Amoeba, anaerobic
Causes AMOEBIC DYSENTRY (bloody diarrhea) in humans
- many members of this genus live in human large intestine but ONLY E. histolytica is clearly pathogenic
Transmitted via FECAL-ORAL route
Amoebiasis
Most exposed ppl are ASYMPTOMATIC but some may be chronic carriers
- most common symptom is DIARRHEA
Symptomatic amoebiasis is considered invasive so treatment agent is active achainst tissue invasive forms = METRONIDAZOLE is drug of choice for intestinal and extra-intestinal infection
Treatment of Amoebiasis
METRONIDAZOLE
Symptomatic amoebiasis is considered invasive so treatment agent is active against tissue invasive forms
Balantidium coli
Ciliate protozoan
- ONLY known PARASITIC ciliate
- infects GI tract/large intestine where it causes DYSENTRY
- transmitted via FECAL-ORAL route by contaminated food/water
- Balantidiasis is mostly ASYMPTOMATIC but ppl w/ other sicknesses can have persistent diarrhea, abdominal pain + sometimes a perforated colon
Parasitic metazoa
Metazoan parasites are MULTICELLULAR organisms w/ BOTH ecto- (insects) and endoparasitic (worms, helminths) lifestyles
- macroscopic, multi-cellular organisms
- includes helminths and arthropods
Classification of helminths
- nematodes
- cestodes
- trematodes
Nematodes
aka ROUNDWORMS
non-segmented roundworms
- fluid-filled body cavity
Cestodes
aka TAPEWORMS
segmented flat worms
- rings around body
- very long
Trematodes
aka FLUKES
non-segmented flatworms
- leaf-like shape
Mechanisms of entry and niche selection w/ helminths
Transmission
- fecal-oral (cyst - larva - adult worm)
- transdermal (cyst - larva - adult worm)
- verctor-borne (larva - adult worm)
- predator-prey (egg - larva - adult worm)
Helminth reproduction
- male and female reproduce by mating followed by egg production
- most trematode and cestode parasites contain male AND female sex organs but often need another worm to exchange sperm w/ before egg production
- some species produce both sperm and eggs and self-fertilizing (are HEMAPHRODITIC)
Mechanisms of helminth survival
Immune evasion strategies
- incorporation of host serum proteins on surface - hide from immune response
- inhibition of complement system
- secretion of anti-inflammatory molecules
Non-immune evasion strategies
- avoiding direct contact w/ host tissue (ex. living in lumen of small intestine)
- PAUSING LIFE CYCLE when host develops resistance
Ascariasis
Nematode/roundworm
Main specie that infects humans is A. lumbricoides
- a soil-transmitted helminth (geohelminth)
- very large nematodes that parasitize the human intestine
Ascariasis is the most COMMON helminth infection in the world and HUMANS are the DEFINITIVE host
Ascariasis life cycle
- Eggs are ingested - go into stomach
- Larvae hatch in small intestine, enter bloodstream + go to liver
- Larvae migrate to heart - start to mature in tissues
- Larvae reach lung capillaries
- Larvae enter alveolar spaces
- Larvae migrate up trachea + are swallowed down into esophagus then back into stomach and small intestine
- Adults mature in small intestine
- Eggs pass out in feces + embryonate in soil
Symptoms of Ascariasis
- parasitic infection occurs thru ingestion of eggs via fecal contamination of soil, food or water
- mostly ASYMPTOMATIC (could have mild abdominal discomfort)
- problems when it is untreated or other factors = high worm burden
Treatment of Ascariasis
ANTHELMINTIC medications (drugs that remove parasitic worms from the body) like
- albendazole
- mebendazole
Taenias
Cestodes/tapeworms
- humans are DEFINITIVE hosts for different types of Taenia
- humans pass the tapeworm segments/eggs in feces and contaminate soil
- Taenia eggs can survive in MOIST environment and remain infective for days to months
- can form cysts in muscle tissue
- humans can be infected w/ tapeworms when they eat raw or undercooked beef or pork
Types of Taenias
Taenia saginata (beef tapeworm)
Taenia solium (pork tapeworm)
Taenia asiatica (Asian tapeworm)
Taenias Life Cycle
- Cysticerci are ingested w/ raw or undercooked beef/pork
- Cysticerci are released from muscle in stomach
- Worms mature + live in SMALL INTESTINE
- Scolex contains four suckers
- Proglottids (male + female characteristics needed to produce) pass in feces
- Cow ingests embryonated eggs, then oncospheres migrate to tissues and develop to cysticerci
back to #1
Symptoms + Treatment of Taenias
- most ppl w/ tapeworms have NO or mild symptoms
- most common treatment are ORAL medications that are toxic to the adult tapeworm
Schistosomiasis
Trematode parasite
- infection occurs transcutaneously when skin comes in contact w/ contaminated freshwater in which certain types of snails (INTERMEDIATE host) that carry the parasite are living
- freshwater becomes contaminated by schistosome eggs when infected ppl URINATE or DEFECATE in the water
humans are DEFINITIVE host
- snails are intermediate host in water to keep larva
Symptoms + Treatment of Schistosomiasis
Most ppl have no symptoms when first infected
- within days after, they may get a RASH or ITCHY SKIN
- within 1-2 months of infection, they might get fever, chills, cough and muscle aches
Can develop into chronic schistosomiasis
Treated w/ PRAZIQUANTEL for 1-2 days to treat infection
oChronic Schistosomiasis
repeated infection or not being treated
Symptoms include
- abdominal pain
- enlarged liver
- blood in stool or urine
- problems passing urine
can also lead to increased risk of LIVER FIBROSIS or BLADDER CANCER
Anti-parasitic measures
- clean water
- better sanitation
- better hygiene
- vector control
Vector control
- reduction of areas where vectors breed (especially mosquitoes)
- access to bed nets
- treatment of areas w/ pesticide
- introduction of genetically modified mosquitoes (offspring w/ natural mosquitoes are STERILE)
