Micro 6 - Parasitic infections

Question 1

What is a parasite

Answer 1

Organism living in or on the host and dependent on it for nutrition - causing damage

Question 2

What are the 2 classes of endoparasites

Answer 2

1. Protozoa - amoeba, coccidiae, ciliate, flagellates

2. Metazoa - roundworms, flatworms, flukes

Question 3

What is a protozoa

Answer 3

Single celled organism - they are eukaryotes (genome within a nucleus, complex organelles in cytoplasm).

NOT ASSOCIATED WITH EOSINOPHILIA

Question 4

What is a metazoan

Answer 4

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

Question 5

What are the 4 groups of protozoa

Answer 5

1. Amoebae - entamoeba histolytica, entamoeba dispar
2. Coccidia - plasmodium species, toxoplasma, cryptosporidium
3. Ciliates - balantidium coli
4. Flagellates - trichomonas, giardia, trypanosoma, leishmania

Question 6

Describe amoebae

Answer 6

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

Question 7

What is the cause of invasive amoebiasis

Answer 7

E. histolytica –> but be differentiated from entamoeba dispar (which is normal GIT commensal)

Question 8

How is invasive amoebiasis (due to E. histolytica) diagnosed?

How is it treated?

Answer 8

By a wet mount

(mature cyst has 4 nuclei, immature = 1-3 nuclei)

Treated via nitroimidazole derivatives - act on trophozoite, but not cysts

Question 9

Coccidial infections in humans are mostly?

Answer 9

Zoonoses.

e.g. coccidial organisms = plasmodium (malaria), toxoplasma (toxoplasmosis), cryptosporidium (diarrhoea)

Question 10

Plasmodium is a type of coccidia. Describe the different types of plasmodium.

Also what are the hosts?

What are the stages in human?

Answer 10

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

Question 11

What are the symptoms/complications of malaria

Answer 11

Fever/headache/vomiting/muscle pain

May also cause severe anaemia (RBC destroyed), cerebral malaria (swelling of brain, seizures, coma)

Question 12

How is malaria diagnosed and treated

Answer 12

Diagnosis = blood film, giemsa stained

(Can also do rapid test - antigen detection tests)

Treatment:

uncomplicated malaria = chloroquine, mefloquine

Severe malaria - ACT

Question 13

Toxoplasma is a type of coccidia. Describe its transmission

Answer 13

Eating undercooked meat

Immunocompromised patients may develop CNS disease, brain lesions, pneumonitis or retinochoroiditis. Can also be transplacentally transmitted

Question 14

Cryptosporidium is a type of coccidia. It is mainly a problem in HIV patients. How is it diagnosed and treated/

Answer 14

Diagnosed via stool examination

Treated with fluid rehydration

Question 15

Give an example of a ciliate (ciliates = type of protozoa)

Answer 15

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

Question 16

Flagellates are a type of protozoa. Give examples of flagellates

Answer 16

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)

2. Trichomonas - STD. Many cases are asymptomatic. Can be odours. Associated with detrimental pregnancy. Infection may enhance HIV transmission. Diagnosed by microscopy, treated by metronidazole

Question 17

Aside from giardia lamblia and trichomonas, name another flagellate

Answer 17

Leishmania

Question 18

Give examples of metazoa (endoparasites)

Answer 18

Roundworms, flatworms, flukes

Question 19

Describe helminths (metazoan)

Answer 19

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

Question 20

Name some roundworms (nematodes)

Answer 20

Ascaris, hookworm, filaria, strongyloides

Question 21

Describe ascariasis

Answer 21

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

Question 22

Give an example of a hookworm (type of roundworm)

Answer 22

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

Question 23

Give another example of a hookworm, which is transmitted via faecal-oral route

Answer 23

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

Question 24

Filaria are examples of roundworms. What are the 2 main types of filaria

Answer 24

1. Brugia Malayi
2. 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

Question 25

Give an example of a filaria that lingers in the eye

Answer 25

Loa Loa - causes loaiasis

Migrates through subcutaneous tissue

Question 26

Give an example of a flatworm

Answer 26

Taenia spp.

Humans are the only definitive hosts Tania sodium/asiatica/saginata

Question 27

Describe symptoms of Taenia infections

Answer 27

Asymptomatic usually

Taenia solium is hâte commonest acquired cause of epilepsy worldwide

(T. saginata can also present with more symptoms)

Treated with praziquantel

Question 28

Name a type of fluke (trematode).

Answer 28

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

Question 29

Give examples of ectoparasites

Answer 29

1. Sarcoptes scabiei - scabies - transmitted by skin

Diagnosed by appearance of rash and presence of burrows. Treated with scabicides

2. Lice (headlice, body lice, pubic lice).

Lice have 3 stages in development - egg, nymph and adult

Question 30

Describe leishmania

Answer 30

Flagellate, transmitted via sand fly

2 forms:

1. Promastigotes - have flagellum, can be cultured
2. Amastigotes - no flagellum, no longer motile - within human or other host

Question 31

There are 2 major forms of leishmaniasis

Answer 31

1. Visceral - affects internal organs (aka Kala azar)
   Causes fever, weight loss and spleno/hepatomegaly

FATAL IF UNTREATED

2. Cutaneous - skin lesions on body parts (may self heal). Can create serious disability + scars. Can be localised, diffuse, musculocutaneous.