Micro 6 - Parasitic infections Flashcards
What is a parasite
Organism living in or on the host and dependent on it for nutrition - causing damage
What are the 2 classes of endoparasites
- Protozoa - amoeba, coccidiae, ciliate, flagellates
2. Metazoa - roundworms, flatworms, flukes
What is a protozoa
Single celled organism - they are eukaryotes (genome within a nucleus, complex organelles in cytoplasm).
NOT ASSOCIATED WITH EOSINOPHILIA
What is a metazoan
Multicellular organisms (e.g. helminths/worms)
Free living, intermediate hosts and vectors. Some just inhabit gut, others invade tissues
If they invade blood, they ARE associated with EOSINOPHILIA
What are the 4 groups of protozoa
- Amoebae - entamoeba histolytica, entamoeba dispar
- Coccidia - plasmodium species, toxoplasma, cryptosporidium
- Ciliates - balantidium coli
- Flagellates - trichomonas, giardia, trypanosoma, leishmania
Describe amoebae
Infection occurs by ingestion of mature cysts in food/water, or on hands contaminated by faeces
90% infections are asymptomatic
Incubation period - may be 7 days to 4 months (usually)
Humans are the only reservoir
Invasive amoebiasis - often affects liver (abscess), lung, heart, brain, UT and skin also affected sometimes
What is the cause of invasive amoebiasis
E. histolytica –> but be differentiated from entamoeba dispar (which is normal GIT commensal)
How is invasive amoebiasis (due to E. histolytica) diagnosed?
How is it treated?
By a wet mount
(mature cyst has 4 nuclei, immature = 1-3 nuclei)
Treated via nitroimidazole derivatives - act on trophozoite, but not cysts
Coccidial infections in humans are mostly?
Zoonoses.
e.g. coccidial organisms = plasmodium (malaria), toxoplasma (toxoplasmosis), cryptosporidium (diarrhoea)
Plasmodium is a type of coccidia. Describe the different types of plasmodium.
Also what are the hosts?
What are the stages in human?
P falciparum, p malariae, p ovale, p vivax, p Knowlesi
2 hosts - humans and female Anopheles mosquitoes
2 stages in human - liver and blood stages
What are the symptoms/complications of malaria
Fever/headache/vomiting/muscle pain
May also cause severe anaemia (RBC destroyed), cerebral malaria (swelling of brain, seizures, coma)
How is malaria diagnosed and treated
Diagnosis = blood film, giemsa stained
(Can also do rapid test - antigen detection tests)
Treatment:
uncomplicated malaria = chloroquine, mefloquine
Severe malaria - ACT
Toxoplasma is a type of coccidia. Describe its transmission
Eating undercooked meat
Immunocompromised patients may develop CNS disease, brain lesions, pneumonitis or retinochoroiditis. Can also be transplacentally transmitted
Cryptosporidium is a type of coccidia. It is mainly a problem in HIV patients. How is it diagnosed and treated/
Diagnosed via stool examination
Treated with fluid rehydration
Give an example of a ciliate (ciliates = type of protozoa)
Balantidium coli - causes balantidiasis
Reservoir hosts = pigs, rodents, primates
Most people infected => no symptoms (but may cause severe signs/symptoms if immunocompromised)
Diagnosis of balantidiasis = stool exam
Flagellates are a type of protozoa. Give examples of flagellates
Giardia lamblia - cause giardiasis (which causes diarrhoea). Also greasy stools, stomach cramps, etc. Diagnosed by stool examination. Treated with metronidazole / tinidazole. It has 2 stages, cysts and trophozoites (tablets for water purification only kill the trophozoites, must filter water)
- Trichomonas - STD. Many cases are asymptomatic. Can be odours. Associated with detrimental pregnancy. Infection may enhance HIV transmission. Diagnosed by microscopy, treated by metronidazole
Aside from giardia lamblia and trichomonas, name another flagellate
Leishmania
Give examples of metazoa (endoparasites)
Roundworms, flatworms, flukes
Describe helminths (metazoan)
Helminths = complex multicellular parasites.
Cycles - both vectors and intermediate hosts. Majority = humans, some are zoonoses
Adult worms CANT multiply in man - number of adults related to infection
Helminths lay eggs, microfilaria, larvae
Name some roundworms (nematodes)
Ascaris, hookworm, filaria, strongyloides
Describe ascariasis
Adults live in SI lumen –> F make eggs that are passed in lumen.
After swallowed, larvae hatch and invade intestinal mucosa, carried via portal and systemic circulation to lungs —> mature further and penetrate alveolar walls –> ascend bronchial tree –> swallowed again
Usually asymptomatic. Large number of worms may cause ab pain. Adults feed on contents of SI. Dangerous if malnourished.
Penetration of larvae from capillaries to lungs can cause Loefflers pneumonia
Diagnosis = stool examination
Treatment = albendazole and mebendazole
Give an example of a hookworm (type of roundworm)
Ancylostoma duodenale
Can cause iron deficiency anaemia due to bleeding.
Reside in SI. Can also cause GIT/nutritional symptoms. May also cause respiratory symptoms.
Diagnosed by stool examination, treated by albendazole and mebendazole
Give another example of a hookworm, which is transmitted via faecal-oral route
Trichuris trichuria - whipworm.
Eggs hatch in SI –> larvae released and establish as adults in colon. Live in caesium and ascending colon. May be asymptomatic, may get bloody diarrhoea ad anaemia.
Diagnosed by stool exam, treated by albendazole and mebendazole
Filaria are examples of roundworms. What are the 2 main types of filaria
- Brugia Malayi
- Wucheria bancrofti
Filaria can cause lymphatic filariasis (may cause elephantiasis)
Filaria both transmitted by mosquito
Diagnosed by blood smear/ELISA. But at night they become more superficial, during day they go into deeper vein
Treated with albendazole and ivermectin
Give an example of a filaria that lingers in the eye
Loa Loa - causes loaiasis
Migrates through subcutaneous tissue
Give an example of a flatworm
Taenia spp.
Humans are the only definitive hosts Tania sodium/asiatica/saginata
Describe symptoms of Taenia infections
Asymptomatic usually
Taenia solium is hâte commonest acquired cause of epilepsy worldwide
(T. saginata can also present with more symptoms)
Treated with praziquantel
Name a type of fluke (trematode).
Schistosoma - can cause schistosomiasis.
Different types - s mansoni, haematobium, japonicum
Transmission:
Eggs eliminated into water via faeces/urine –> hatch and release miricidia —> penetrates snail –> snails release cercariae that penetrate skin —> migrate into tissues and become adults —> eventually reside in venules
Treated with praziquantel
Give examples of ectoparasites
- Sarcoptes scabiei - scabies - transmitted by skin
Diagnosed by appearance of rash and presence of burrows. Treated with scabicides
- Lice (headlice, body lice, pubic lice).
Lice have 3 stages in development - egg, nymph and adult
Describe leishmania
Flagellate, transmitted via sand fly
2 forms:
- Promastigotes - have flagellum, can be cultured
- Amastigotes - no flagellum, no longer motile - within human or other host
There are 2 major forms of leishmaniasis
- Visceral - affects internal organs (aka Kala azar)
Causes fever, weight loss and spleno/hepatomegaly
FATAL IF UNTREATED
- Cutaneous - skin lesions on body parts (may self heal). Can create serious disability + scars. Can be localised, diffuse, musculocutaneous.
