Lecture 6 - Metazoa

Question 1

Three types of metazoa/heminths?

Answer 1

1. nematodes
2. trematodes
3. cestodes

Question 2

What are nematodes?

Answer 2

round worms with complete digestive systems (mouth, intestine and anus)

Question 3

two types of nematodes where the eggs are the infective stage?

Answer 3

1. Enterobius vermicularis (pinworms)

2. Ascaris lumbricoides

Question 4

Enterobius vermicularis

Answer 4

“pinworm”

• transmitted by ingestion of eggs in dust or direct contact
• type of nematode (round worm)
• humans are biological vectors of E.vermicularis because it spends its entire life cycle (including reproduction) in the human body
• live in the large intestine –> females migrate to anus and lay eggs on the skin around the anus
• is not serious but is super infectious

Question 5

Ascaris lumbricoides

Answer 5

• type of nematode (round worm)
• lives in small intestine of pigs, cows, and horses
• has eggs in soil and the eggs have a hardy protein coat
• transmitted fecal-orally
• can be very large (up to 30cm)
• dioecious (have distinct sexes)
• humans are infected by the egg
• the eggs hatch in the intestines and then the larvae move to the lungs and trachae –> they come up the nose and mouth of kids but not adults due to the swallow reflex

Question 6

four types of nematodes where the larvae is the infective stage?

Answer 6

1. Hookworms
2. Anisakis
3. Trichinella spiralis
4. Blood nematodes (Filaria) –> lymphatic filariasis and onchoceriasis

Question 7

Hookworms

Answer 7

• type of nematode
• infects humans at the larvae stage
• transmitted by entering intact skin of bare feet (direct skin contact)
• enters the lymph nodes through the feet and then the circulatory system, it gets into the lungs and can be coughed up and then swallowed down into the intestine where they attach onto the intestinal walls with the hooks on their scolex (heads)
• they cause anemia because they suck blood
• eggs are excreted in human feces

Question 8

Anisakis

Answer 8

• type of ‘fish nematode’
• infects humans at the larvae stage
• occurs when fish are not cleaned after they are caught, the eggs of Anisakis live in the intestines of the fish, and then they hatch and move into the flesh which gets eaten by humans
• the worm can borrow into the intestinal lining and lead to ulcers

Question 9

Best ways to prevent Anisakis?

Answer 9

1. heat fish up to 60 degrees celsius for 10 minutes
2. blast freeze to -35 degrees celsius for 15 hours OR freeze at -23 degrees for 3 days
3. clean fish (evisceration) and remove its guts as soon as possible

Question 10

Trichinella spiralis

Answer 10

• type of nematode
• infects humans at larvae stage
• occurs when undercooked pork, boar, bear or walrus is ingested by humans
• causes muscle weakness
• this is because the larvae live in striated muscles including the heart and form “nurse cells” [encysts itself]
• particularly dangerous if it lives in the striated muscle of the heart because it causes mm. weakness
• difficult to treat

Question 11

Two types of Filaria (blood nematodes) and examples?

Answer 11

1. lymphatic filariasis –> adult worms live in the lymph tissue (i.e. elphantiasis)
2. onchoceriasis –> adult worms live in subcutaneous tissue (i.e. river blindness)

Question 12

what are microfilariae? How are they transmitted?

Answer 12

offspring of adult worm (larvae of filariae) that circulate through the blood stream or migrate through subcutaneous tissue

• they are transmitted by mosquitos and are common in africa, asia and latin america (in the tropics)

Question 13

What is an example of a Trematode?

Answer 13

Schistomas

Question 14

Schistoma

Answer 14

• trematode
• infects humans at larvae stage called cercariae
• contracted in fresh water ponds
• penetrates intact skin of humans
• adult schistomas have a coat of protein that they get from their host that hides them from the host’s immune system
• worms live in the venous plexus (veins above and around) the bladder or intestine
• eggs of schistomes cause inflammation

Question 15

Three types of Schistoma infections in humans?

Answer 15

1. S.haematobium
2. S.japonicum
3. S.mansoni

Question 16

Shistoma haematobium

Answer 16

• Type of Schistome (trematode) that infects humans in larvae stage
• causes urinary schistosomiasis or Bilharzia
• results in inflammation of bladder wall, and chronic sequalae- cancer [sequalae means as a result of the infection]
• found in africa and middle east

Question 17

S.japonicum

Answer 17

• type of schistome (trematode) that infects humans in larvae stage
• intestinal parasite
• found in far east

Question 18

S. mansoni

Answer 18

• type of schistome (trematode) that infects humans in larvae stage
• intestinal parasite that can cause liver fibrosis
• found in africa, south america, caribbean and infects 250 million people world wide

Question 19

What is “swimmers itch”?

Answer 19

‘duck schistome’

• type of schistome (trematode)
• Cercariae (larvae form) do not enter human circulation
• causes itch or rash in humans due to immune response

Question 20

C. Cestodes

Answer 20

• tapeworms
• live in the human intestine
• dependent on host for nutrients and have no digestive system
• they have a head called scolex that has suckers/hooks for attachment to gastric mucosa
• infects humans via ingestion of undercooked contaminated beef, pork or fish
• hermaphrodites –> male and female reproductive organs live on each proglottid

Question 21

what are proglottids on C.Cestodes?

Answer 21

they are segments on the body of the tapeworms, each of which contains a male and female reproductive organ

Question 22

What are two types of disease caused by tapeworms?

Answer 22

1. Intestinal infection –> mild; caused by ingestion of pork, beef, fish or rodent tapeworms
2. Deep tissue infection –> serious; pork tapeworm (cysticerocosis) and echinococcosis (dog tapeworm)

Question 23

Taenia saginata

Answer 23

• beef tapeworm (c.cestode)
• life cycle needs both cattle and humans
• humans ingest the tissue larvae (cysticerci) by eating infested cow meat
• T.saginata mature into adult tapeworms in the human intestine
• cows pass the eggs into their feces
• symptoms are mild and can cause weight loss

Question 24

Taenia solium

Answer 24

• pork tapeworm (c.cestode)
• life cycle needs both pig as the intermediate host and humans
• CAN BE CONTAGIOUS
• humans ingest the tissue larvae by eating infested pig meat (pork)
• Ingestion of T. solium eggs are more dangerous than the T.saginata (beef tapeworm) eggs because it causes cerebral cysts; the larvae penetrate the intestinal wall and move to the brain where it calcifies and causes and lives in the calcium cyst (encysts in the brain) and causes fainting and seizures
• Ingestion of T.solium larvae results in adult worm in intestine

Question 25

Echinococcus granulosus

Answer 25

• Dog tapeworm (c.cestode)
• humans are its dead end hosts
• starts life cycle in dogs, coyotes, dingos
• can’t grow into full form in humans and can only grow to adult size in canines
• larvae develops into hydatid cyst with alot of worm parts (contains scolex, and proglottids but does not come together to form a full worm in humans)
• kids are susceptible to this
• can be infected by contact with dog or swallowing the cyst/breathing it in
• causes alot of liver issues

Question 26

What are ectoparasites?

Answer 26

Metazoa/ parasites that live on the skin but do not enter deep tissues

can cause secondary infections

Question 27

Sarcoptes scabei

Answer 27

• scabies (mange in dogs)
• mites
• they live in finger webs, elbows, armpits, breasts, groin and butt –> never on the head
• burrow into the skin, mate, lay eggs in their burrow
• life span is 30 days
• the host’s defense system causes inflammation around the burrows which results in intense itching
• can cause secondary infections because of the constant scratching opening the skin and allowing skin bacteria to get through
• Dog mange does not cause infection in humans

Question 28

example of Sarcoptes scabei

Answer 28

bed bugs

Question 29

Phthirus pubis and Pediculus humanus

Answer 29

Phthirus pubis –> pubic lice or “crabs”
Pediculus humanus –> head lice

• dwell on the surface
• penetrate skin with mouth and suck blood (bite)
• females glue their eggs to the shaft of the hair
• eggs hatch in 5-10 days
• can cause secondary infection when lice feces get into the wounds cause by constant scratching