Lecture 22- Common Parasitic Diseases Flashcards
1
Q
Parasites
A
- parasitism is a relationship in which one of the participants either harms the hosts or lives at the expense of the host
- protozoan: unicellular eukaryotic organisms
- metazoan: multicellular animals, helminthology, and Arthropoda
2
Q
Hosts
A
- definitive host: the host in which the parasite reproduces sexually
- intermediate host: the host in which the parasite reproduces asexually
- reservoir host: animals that harbour the same parasite and which may serve as a source of infections for humans
3
Q
Classification of parasite by human habitat
A
- intestinal parasites: tapeworm, flukes, round worms, protozoan
- blood and tissue parasites: plasmodium, strongyloides, leishmania, echinococcus, toxoplasma
4
Q
Parasitic protozoa: classification by motility
A
- amoeba: irregular shape, moved by pseudopodia
- flagellates: move by means of filamentous flagellate
- ciliates: complex, unicellular organisms, move by means of cilia on cell surface
- apicomplexa: no locomotory organelles
5
Q
Parasitic metazoa
A
- Helminths: Platyhelminthes (flat worms: Trematoda and cestodes) and nematodes (round worms: hookworm, pinworm, ascaris, filariae parasites)
- arthropods: ticks, mites, fleas, lie
6
Q
Giardia duodenalis: assemblages
A
- eukaryotes: flagellate: reproduce by asexual reproduction
- 2 forms: motile (trophozoite) and cystic forms). Trophozoite: 10-20 microns long and 5-15 wide, cyst 8-12 by 7-10 microns
- characteristic features include the 2 nuclei with prominent nucleoli, flagellate
7
Q
Epidemiology of G duodenalis
A
- worldwide distribution
- most commonly identified intestinal parasite, up to 30% prevalence in
8
Q
Giardia duodenalis life cycle
A
- infective cyst state passed in faeces
- usually transmitted by faecal oral route but water-borne transmission occurs as well
- incubation period around 1-2 weeks
- cysts survive for months in cold water but are sensitive to dessication and UV light
9
Q
Pathogenesis of Giardia duodenalis
A
- cysts from environment excuses in proximal SI
- attach to brush border of enterocytes by suction disk
- not invasive
- disrupt absorptive surface and induce apoptosis
- immunity occurs by humoral and CMI: IgA likely a critical element in controlling infection. Able to switch antigenic expression
10
Q
Presentation: Giardia duodenalis
A
- trophozoite resides in small intestine
- asymptomatic cyst passer
- acute diarrhoea with epigastric pain, nausea, bloating and flatulence 1-2 weeks or
- chronic giardiasis: intermittent diarrhoea, weight loss, malaise for months
11
Q
Giardia duodenalis diagnosis
A
- detection of cysts or trophozoite in faeces by microscopy, yield improved by concentration techniques
- detection of trophozoites in duodenal aspirates
- detection of antigens in faeces
- clinical diagnosis is not possible - symptoms are too non-specific
12
Q
Giardia duodenalis treatment
A
- metronidazole
- Trinidazole
- albendazole
13
Q
Entrobius vermicularis
A
- intestinal roundworm (nematode)
- requires no external host
- ooscysts usually hatched into infective larva by the time they are passed in stool
- infective for 3 weeks
- concentrate around perianal skin
- worldwide distribution, more common in developing world
14
Q
Enterobius vermicularis lifecycle
A
1) eggs on perianal folds. Larvae inside the eggs mature within 4-6hr
2) embryonated eggs ingested by human
3) larvae hatch in small intestine
4) adult in lumen of caecum
5) Gracie female migrates to perianal region at night to lay eggs
15
Q
Enterobius: clinical correlates
A
- nocturnal pruritis ani
- spread by direct digital inoculation
- association with appendicitis
