Lecture 4: Approach to Understanding Parasites

Question 1

What are parasitic organisms

Answer 1

• Organisms that live on or in another organism (host) and derives a benefit and/or nutrients at the expense of the host
• Acquired as a result of a bite (tick, mosquitoes); contaminated water, contaminated environment (bed bugs etc…) or contaminated food

Question 2

2 types of parasites

Answer 2

1. Exoparasite: lives on the host and causes an infestation
2. Lives in the host and causes an infection

Question 3

Examples of exo(ecto) parasites

Answer 3

• Scabies
• Body Louse
• Head Lice
• Pubic Lice (head lice)

Question 4

2 Parasitic life cycles

Answer 4

1. Direct Life Cycle
2. Complex/indirect life cycle

Question 5

What is the Direct Life Cycle

Answer 5

The entire lifecycle is completed in one host.
Control is easier.
Eggs often only viable for a short time in the environment.

Question 6

What is the complex/indirect life cycle

Answer 6

The life cycle is completed in more than one host.
Control of the parasite is often much more difficult.
Examples include: Malaria, Lyme Disease

Question 7

Classifying single celled parasites

Answer 7

Parasites -> Single celled -> Protozoa -> Intestinal or Blood and Tissue

Question 8

Classifying multicellular parasites

Answer 8

Parasites -> Multicellular -> Helminths -> Cestodes (flatworms) or Trematodes (flukes) or Nematodes (roundworms)

Question 9

Name all 5 Types of Protozoa: Intestinal Protozoa

Answer 9

1. Entamoeba histolytica
2. Giardia lamblia
3. Cyclospora cayetanensis
4. Dientamoeba fragilis
5. Cryptosporidium parvum

Question 10

Intestinal Protozoa: Entamoeba histolytica

Answer 10

Major pathogen associated with poor sanitation

Question 11

Intestinal Protozoa: Giardia lamblia

Answer 11

“Beaver Fever” associated with contaminated H20

Question 12

Intestinal Protozoa: Cyclospora cayetanensis

Answer 12

Contaminated water and produce exposed to contaminated water including raspberries, lettuce, fresh fruit, and vegetables.

Question 13

Intestinal Protozoa: Dientamoeba fragilis

Answer 13

Ubiquitous and found in children worldwide. Transmitted person to person.

Question 14

Intestinal Protozoa: Cryptosporidium parvum

Answer 14

Major outbreaks. Carried in cattle and other zoonosis. Can transmit human to human or from cattle.

Question 15

Characteristics of Intestinal Protozoa

Answer 15

• 500 million cases/yr worldwide
• All of them have a direct lifecycle
• Route of transmission is typically via contaminated H20, food, or soil (indirect contact) and zoonosis (direct contact)
• Virulence factors include either production of toxins (watery diarrhea) or the ability to invade the GI epithelia (bloody diarrhea)

Question 16

3 types of Protozoa: Blood/Tissue Protozoa

Answer 16

1. Trichomonas vaginalis
2. Plasmodium spp.
3. Toxoplasma gondii

Question 17

Blood/Tissue Protozoa: Trichomonas vaginalis

Answer 17

2-3 million infections/yr. Common sexually transmitted infection. Diagnosis is via a wet-prep and antigen detection.

Question 18

Blood/Tissue Protozoa: Plasmodium spp.

Answer 18

Malaria ~ 3 million infections/yr. Transmission via anopheles mosquitoes.

Question 19

Blood/Tissue Protozoa: Toxoplasma gondii

Answer 19

~ 60% of cats are infected and can infect other invertebrates. Human infection as a result of exposure to cat feces or uncooked meat.

Question 20

What is Trichomonas vaginalis

Answer 20

• One of the most common sexually transmitted infection
• Most common complaint is vaginal discharge
• May be associated with urinary frequency and dysuria - cystitis observed in a small proportion of women

Question 21

Malaria (Plasmodium spp.)

Answer 21

• Has 5 species; P. faliciparum, P. malariae, P. knowlesi, P vivax, P. ovale
• Over 3 million infections each yr, with almost a million deaths
• Transmitted by mosquitos (indirect life cycle) - sexually mature in the mosquito and asexual states in human red blood cells
• The mosquitos that transmit Malaria bite dusk to dawn so mosquito nets are other control measures work quite well
  Look on lecture slides for image about the lifecycle

Question 22

Lab diagnosis of Malaria Mechanisms

Answer 22

• Microscopy
• Molecular Detection
• Protein Detection

Question 23

What is Protozoa: Toxoplasma gondii

Answer 23

• Complex life cycle with multiple hosts and environmental maturation
• Humans and other mammals are dead end hosts (doesn’t get transmitted onwards)
• Asymptomatic infections in immunocompetent hosts
• Serious clinical manifestations if acute infection during pregnancy - infects the baby in utero and lead to significant morbidity to the baby including deafness, microcephaly, meningitis, encephalitis, hydrocephalus, retinitis and even death

Question 24

3 Types of Helminths: Cestodes (Tapeworms)

Answer 24

1. Diphyllobothrium latum (fish)
2. Tinea solium (pork)
3. Tinea saginata (beef)

Question 25

Cestodes: Taenea solium (Pork tapeworm)

Answer 25

- Multiple hosts - Human gets teniasis is contaminated meat is ingested - In the case of tinea solium - if the eggs in feces are ingested by humans they can migrate to different tissues including the eye, brain (neurocysticercosis), muscle and bone (reason why some cultures won't eat pork)

Question 26

Cestodes: Taenea saginata (Beef tapeworm)

Answer 26

- Multiple hosts***** BIG DIFF. - Human get Tenaisis if they ingest contaminated meat or are exposed to cattle faecal matter - Does not develop tissue phase disease

Question 27

Cestodes: Diphyllobothrium latum (Fish tapeworm)

Answer 27

- This is why you don't fish out of Lake Ontario - Complex life cycles with multiple hosts - Crustaceans, fish, and humans - Humans can transmit - Can live outside a host in water - But always looking for a host

Question 28

3 types Helminths: Nematodes (Round worms)

Answer 28

1. Ascaris lumbricoides 2. Enterobius vermacularis 3. Strongyloides stercoralaris

Question 29

Helminths Nematodes (Round worms): Ascaris lumbricoides

Answer 29

- Contaminated food/water ingestion of eggs - Largest worm, very rare - Almost 1 billion people infected worldwide - Eggs have to mature in the environment or several days - Life of the worm is between 10 months and 2 years - Sometimes they get lost - You can have multiple worms - It cannot reinfect you or transmit - You swallow them, reach gut, they hatch, they migrate into the lungs, keeps coming up because it wants to be reswallowed

Question 30

Helminths Nematodes (Round worms): Enterobius vermacularis

Answer 30

- Females come out at night lay their eggs outside the anus - very itchy - Very common - Transmission is from person to person via contaminated surfaces - Often in day care centres - Most common worm infection in North America - Leads to intense anal itching and often is passed on person via faecal matter (after they itch their bum)

Question 31

Helminths Nematodes (Roundworms): Strongyloides stercoralaris

Answer 31

- Very serious/most severe - Contact with the environment - Free larval forms found in contaminated soil - Single cycle with only ONE host - Can be free living - Found in warm climates with beaches - Symptoms of infections include dermatitis, swelling, itching, larva currens - Immunocompromised individuals - can develop a hyper-infective syndrome - associated with 90% mortality - The worm can cause autoinfection so can continue a cycle of infection for over 30 yrs

Question 32

Name 2 types of Helminths: Trematodes

Answer 32

1. Shistosoma species (blood flukes) 2. Clonorchis sinensis (chinese liver fluke)

Question 33

Trematodes: Shistosoma spp.

Answer 33

- Complex life cycle with > 1 host - Includes an environmental stage with an intermediate host - Found in tropical to semi tropical waters - Burrow into the skin of humans when in contact with contaminated water - Can be ingested - One to bladder - Other goes to gut

Question 34

Trematodes: Clonorchis spp.

Answer 34

- Complex life cycle > 1 host - Includes an environmental stage with an intermediate host - Found in tropical to semi tropical waters - Result of ingestion of contaminated or infected fish - Easily treated