parasitic infetation: microscopic Flashcards
what are protozoa
- eukaryoites
- metabolic processes are more similar to those of the human host than prokaryotic bacteria pathogens
- less easily treated compared to bacterial infectsion
types of microscopic parasitic diseases from protozoan infectsions
Entamoeba (amoebiasis), Giardia (beaver fever) Trichomonas and Plasmodium (malaria).
what is entamoeba histolytica
- anerobic parasitic protozoan that causes amoebiasis
infects the GI tract: considered asymptomatic based on range of symptoms from mild diarrhea to blood and mucus in stool
- infects 500 million ppl yearly, 110,000 deaths
what are teh two forms on entamoeba histolytica?
cysts and trophozoites
- cysts are infective and surivve outside of human body, will transform into trophozoites
- trophozoites = non infective but invasive form that can reproduce and invade the wall of the large intestine and migrate to other tissues like the liver
*trophozoites can transform to cysts and be exreted in feces
what causes amoebiasis
entamoeba histolytica
descibe the life cycle of entamoeba histolytica
- Ingestion of cysts through fecal-ral route (drinking contaminated water)
- Whether intestinal invasion occurs function of number of cysts infested, stain of parasite and motility of host GI tract and presence of appropriate enteric bacteria to serve as nourishment for the maoeba
Disease results when active trophozoites (active stage of life cycle) invade intetinal epithelium and spread to liver via protal circulrion
Lyses and destroys human tissue
describe the clinical presentation of Ameobiasis
- asymptomatic intestinal infection, mild to moderate colitis, severe intestinal infection (dysentery), ameoboma, (psudotumoral lesion) and liver absecess or other extra-intestinal infection.
what is the difference between asymptomatic infection and invasive disease of ameobiasis
In asymptomatic infection
- ingested cysts excyst (mature) in small intestine but do not invade the intestinal mucosa
- the trophozoites encyst in the colon and excretion via feces
Invasive disease
- active trophozoites invade intestinal eithelium resulting in asymptomatic colonization
- intestinal amebiasis (amebic dysentery)—which is characterized by diarrhea and abdominal cramps—or intestinal perforation.
- Spread of infection via the portal vein can cause liver abscesses.
how is E. histolytica treated?
- amoebicidal drugs
Luminal Amoebicides: treat parasites in bowel lumen
- ex: iodoquinol, works against luminal stages which include trophozoites and cysts
- side effects = rash, diarrhea and dose related peripheral neutropathy (optic neuritis)
- evoid long term use
Systemic ameobicides: treat parasites in intestinal wall and liver
- ex treat liver abscess
- use high dose of metronidazole to eliminate trophozoites then iodoquinol
Mixed (luminal + systemic)
- choice for entamoeba distolytic infections
- kills trophozites but not cysts
what does Metronidazole treat
- parasitic infection of E. histolytica
- can also use to treat Giardia lamblia, Trichonomas vaginalis, anaerobic cocci, anaerobic gram-negative bacilli and pseudomembranous colitis such as Clostridium difficile.
*drug of choice for treating diarrhea or dysentery
what are the pharmacokinetics of metrondiazole
- can be administered orally and its readily abs
- extensive abs via simple diffusion, therapetuic concentrations reported in vaginal, seminal fluids, saliva and cerebrospinal fluids
- metabolized by depatic oxidation by mixed function oxidase
- phenobarbital enhances metabolism
- cimetidine inhibits hepatic mixed function oxidase so prolongs excretion
describe the mechanism of action of metrondiazole
- involves ferroxin like, low redox potential, electron transport proteins which transfer electons to nitro groups of metronidazole and form cytotoxic reduced products bind to DNA and proteins
* is a Mixed amoebicide but not reliably efective for liminal parasites, must use in combo with luminal ameobicide like iodoquinol or paramocylin (aminoglycoside)
what are the adverse effects of metrondiazole
nausea, vomiting, headache, abdominal cramps and metallic taste in mouyh
Nausea and vomiting also occur is alcohol is ingeted at same time
Drug is metagenic in bacteria so avoid if preg or nursing
what is gardia lamblia
- aka beaver fever
- Most common intestinal parasitic infection of people - does not involve tissue development
Life cycle:
- Two stages: trophozoites and cysts
- Infection occurs following cyst ingestion which are usually in water
- Both people specific and zoonotic genotypes of infection
- Many infections are asymptomatic but severe diarrhea can occur
what are risk factors for gardia lamblia
- ingesting contaminated water
- children in child care settings
- close contact with infected eprsons
swallowing contaminated pool water
outfoor activities like camping
how is gardia lamblia treated?
- metrondiazole
- dose much lwoer than for amoebiasis so better tolerated
- treated often not used for asymptomatic infections bc those will clear on own
what is trichomonas vaginalis
- anaerobic parasite that resides in lower genital tract of femals urethra and male prostate
- no cyst form, replicates via binary fission so does not survive well in external environment
*most common pathogenic protozoan infection of industrialied countries (common STI)
symptoms of trichomonas vaginalis
Symptoms - vaginal dischage, vulvar itching and discomfort during urination with occasional dysuria
In men no signs or symptoms but urethral dischange and burning during purination is possible
treatment of trichomonas vaginalis
- use metronidazole as single or multiple dose regimen
Single dose therapy more effective due to compliance
Resistant infections can occur, may need to treat with higher dose
Systemic treatment preferred over topical therapy due to multifocal nature of the infection. Simultaneous treatment of the sexual partner is very important as well.
what causes malaria
Caused by one of five species of plasmodial parasites: Plasmodium falciparum, P. vivax, P. ovale, P. malariae and P. knowlesi
P. falciparum is the most serious disease and results in the most deaths.
Resistance is major prophylactic and therapeutic problem
describe the lifecycle of plasmodia parasites
- involves parasite, mosquito vector and human host
- mosquito can ingest sexual forms of malarial parasites (gametocytes) from blood of infected human
- male and female gametocutes fuse and zygote matures within mosquito
- sporozoites released from an oocyst and migrate to mosquitos salivary gland, can be incolulated into blood of another human host (asymptomatic stage)
- 1-12 weks after ifnective bite the liver cells release parasites into bloodstream as merozoites
- infected erthyrocyte eventually reptures releasing another gen of merozoite that continue cycle
- Rare merozoites also mature into gametocytes and ingestion of these by an appropriate mosquito completes the life cycle.
whta do drugs that treat malaria target?
- different stages of ifnection
Liver stages = tissue schizonticides
Erythrocytic stages = blood schizonticides
Sexual stages = gametocides
- can also treat by killing erythrocytic parasites before they grow in number and cause disease, but this is based on the species that caused the infection
infection cycle of
One cycle of multiplication in liver
Liver infection ceases in less than 4 weeks
Elimination of erythrocytic parasites cures infection
decribe infection of P. vivax + P. ovale:
Dormant hepatic stage (hypnozoite) is not killed by most drugs
Must eliminate both erythrocytic and hepatic parasites
how do you prevent mosquito bites
insect repellents, insecticides, bed nets and appropriate clothing is necessary.
Preventatative medications include chloroquine, mefloquine (most malarious areas) and doxycycline (if high prevalence of multidrug-resistant falciparum malaria).
what is chloroquine
drug of choice for chemoprophylasis if chloroquine-S parasites are known to be found in the area (mainly in caribean and central america)
- synthetic 4-aminoquinoline that is admin orally
- concentrates in parasties acidic food vacuole to prevent polymerization of heme into hemozoin and results in oxidative damage which lyses the parasite and red blodo cell
*when parasite is in the RBC it digests host hemoglobin, heme is toxic to the parasite and it is polymerized to form homozoin in the food vacuole
pharmacokinetics of chloroquine, adverse effects and resistance
- Rapidly abs and distributed to tissues wehre it had blood schixonticide activity(but no activity against liver parasites)
- Drug is dealkylated by hepatic mixed-function oxidase system meaning that the parent drug and metabolites are eliminated in urine
- resistance v common due to mutations in membrane transporter
- adverse efects minimla @ low dose but nausea, vomiting and blurred vision can occur at higher doses
*Dosing after meals can reduce adverse efefct
what is mefloquine?
recommended chemoprophylatic drug in areas with chloroquine-R Plasmodium falciparum
- synthetic 4-quinoline methanol which means it is chemically related to quinine
has blood schizonticide activity against P. falciparum but not activity against hepatic stages of gametocytes.
MOA is unknown but believed to be due to concentration of parasite and inhibition heme polymerization with a final result of membrane damage
pharmacokinetics of mefloquine, adverse effects and resistance
Orally admin and well abs, showing extensive distribution to tissues
Very slow elimination
- resistnace uncommon escept in south east asia bc high rates of multidrug resistance associated w/ quinine and halofantrine but not chloroquine
*adverse effects are a concern
- neuropsychiatric toxicities, nausea, vomiting, dizziness and sleep and behaviour disturbances
* not known if the frequency of serious adverse effects is no higher compared to other anti-malarials.
*Contraindicted in pt with history of epilepsy and psychiatric disorders
what is doxycycline
standard chemopropylactic drug in areas of Southeast Asia with multidrug-R parasites (including mefloquine-R)
- oral administration, dont use as single agent based on slow action
- use with quinidine or quinine, allows for shorter but better tolerated course of these drugs
- MOA: inhibition of protein synthesis, also has blood schizonticide activity and is not active against liver stages
adverse effects gastrointestinal symptoms and photosensitivity.
