Parasitology 01 Introduction To Parasitic Diseases & Nematodes

Front 1

What is a parasite?

Back 1

Any organism that takes metabolic advantage of another organism

Front 2

What are the three different kinds of helminths?

Back 2

Nematodes - round worms

Cestodes - segmented flat worms

Trematodes - non-segmented flat worms

Front 3

Compare the genetic make up of parasites and their non-parasitic counterparts

Back 3

-Parasites tend to have more genes.
-Parasitism requires more metabolic machinery to maintain itself inside the host
-Our immune systems want parasites to leave, so they must fight againt that

Front 4

Describe nematodes (3)

Back 4

-Round worms
-All are eukaryotic
-Most are non-parasitic

Front 5

Describe the prevalence of nematode parasitic infections

Back 5

Almost 4 billion people harbor at least one species, many more than one

Front 6

What are the important species of parasitic geohelminths (7)?

Back 6

-Enterobius vermicularis (pinworm)
-Trichuris trichura (Whipworm)
-Ascaris lumbricoides (Giant intestinal worm)
-Toxocara canis and T. cati (Visceral larva migrans)
Hookworms:
-Ancylostoma duodenale
-Necator americanus
Strongloides stercoralis

Front 7

Describe the immune response to parasites

Back 7

-Worm infections elicit TH2 protective immune responses. Eosinophils are the reason we can expel a lot of these worm parasites after a while.
-Protozoan infections elicit TH1 protective immune responses

Front 8

What cytokines are more important to the expulsion of protozoa and worms?

Back 8

TH1 cytokines: IFN-gamma
TH2 cytokines: IL-4, IL-5

Front 9

Describe the structure of enterobius vermicularis

Back 9

The tail of the worm is pin shaped. It is about 8-10mm in length. It is visible.

Front 10

Back 10

Adult Female Enterobius vermicularis

Front 11

Explain the life cycle of the enterobius vermicularis (pinworm)

Back 11

-Encounter the egg
-Eat the egg
-Worms hatch in the small intestine
-Worms migrate to the large intestine through peristalsis
-The worms grow for 6-8 weeks in large intestine to become an adult worm
-The adult worms migrate out of the anus and lay eggs on the perianum and secrete chemicals
-The eggs embryonate on the perianum
-Child contaminates fingers with eggs and ingests them

Front 12

What is the aberrant mode of entry for enterobius vermicularis (pinworm)

Back 12

The eggs can hatch on the perinanum. Instead of needing to be swallowed, it can crawl back into the rectum and establish the infection through retro infection.

Front 13

Describe pinworm infections outside for the intestines

Back 13

-If it is a female child the parasite can crawl up the vaginal tract, up the fallopian tubes and die. They become cysts and a granulomatous response occurs. Many years later they can find these odd nodules during hysterectomies. Inside the nodules are the reminants of the parasites that the patient encountered as a child. T

-There have been instances where the worms reach the peritoneum and infect the peritoneum with bacteria that they traveled in with. This can lead to peritonitis. This is a very very rare occurance in adults

Front 14

Back 14

Adult enterobius vermicularis on the perianum

Front 15

Back 15

Unembryonated egg of Enterobius vermicularis

Front 16

How do you diagnose enterobius vermicularis?

Back 16

Sticky tape test.

This parasite's eggs are not found in the fecal matter that you can express almost readily. Doing a stool examination is not going to do any good. To diagnose you have to take clear sticky tape and press it on the perianal region and then look at it under a microscope. Once you have made the diagnosis then you can treat.

Front 17

Back 17

Aberrant infection of Enterobius vermicularis in the appendix

Front 18

What clinical disease is associated with Enterobius vermicularis?

Back 18

None

Front 19

What is the drug of choice for Enterobius vermicularis? What is its mode of action? How do you treat?

Back 19

-Mebendazole
-It depolymerizes invertebrate tubulins, only
-It is well tolerated. You get rid of the adult worms, but you don’t get rid of the eggs and larva. If you are going to treat patient with heavy pinworm infection then you must treat again 3 weeks after the initial treatment. By then the parasites that they have just acquired should be grown enough to be susceptible to the mebendazole.

Front 20

Describe prevention and control of enterobius vermicularis (pinworm)

Back 20

Prevention is impossible among school-aged children, especially those attending day care facilities and lower grades. We "out grow" our pinworm infections once we reach puberty

Front 21

What is the other name for Trichuris trichiura?

Back 21

Whipworm

Front 22

Back 22

Enterobius vermicularis eggs found on sticky tape test

Front 23

Back 23

Female adult Trichuris trichiura

Front 24

Back 24

Adult male Trichuris trichiura

Front 25

Describe the livecycle of Trichuris trichiura

Back 25

-Egg swallows
-Parasite hatches in small intestine
-Worm embedes in the mucosa into the cells themselves
-Becomes intramulticellular parasite
-Grows until it reaches the 4th stage
-Leaves small intestine and goes down to the large intestine and re-embeds itself
-Thin end of worm is embedded in a row of cells.
-his worm forces the columnar cells to form a syncytium. That syncytium supplies the nutrients for this parasites. The tail of the worm hangs out in the lumen of the intestine.
-Female worms shed eggs

Front 26

Describe the resilence of Trichuris trichiura eggs

Back 26

Eggs can last for long periods of time in soil (20-30 years)

Front 27

How many eggs do Trichuris trichiura produce?

Back 27

3000-5000 eggs per day for 3-5 years

Front 28

How long does it take Trichuris trichiura to fully develop

Back 28

~3 months

Front 29

Describe the pathogenesis of Trichuris trichiura

Back 29

-Trichuris adults secrete a pore-forming protein that may play a role in diarrhea. Adult worms do not feed directly on blood or other host tissues. Mechanism of anemia still unknown.

Diarrhea and weight loss are common.

Front 30

What is the relationship between Crohn's disease and Trichuris trichiura?

Back 30

Crohn's disease is ameliorated, not eliminated, by the trichuris parasite.

Front 31

Describe the GI effects of Trichuris trichiura and the results

Back 31

When kids get Trichuris trichiura infection they get tenesmus. This can result in a prolapse of the rectum through a relaxing of smooth muscles that control the muscle tone of the rectum. Here you can make a direct observation of the surface of the mucosa of the last part of the large intestine.

If the prolapsed rectum is due to heavy trichuris infection then you can see the adult worms. You must put the prolapsed rectum back and then begin treatment.

Front 32

What clinical disease is associated with Trichuris trichiura?

Back 32

Light infections cause nothing. A heavy infection depends on your age, your body weight, and the worm count

1. Diarrhea
2. Anemia
3. Malnutrition (protein calorie deficiency?)
4. Cognitive defect (regained with proper nutrition)

Front 33

Describe the eggs of Trichuris trichiura

Back 33

The egg is football shaped. It has a pore at either end. When the embryo develops it can exit through either of these pores.

Front 34

How do you diagnose Trichuris trichiura infection?

Back 34

Microscopic examination of feces for eggs

Front 35

Back 35

Egg of Trichuris trichiura

Front 36

What is the drug of choice for Trichuris trichiura? What is its mode of action?

Back 36

Mebendazole

Depolymerizes invertebrates microtubules, only

Front 37

Describe how to prevent and control Trichuris trichiura

Back 37

Have sanitary disposal of feces

Front 38

What is the other name for Ascaris lumbricoides?

Back 38

Giant intestinal worm

Front 39

Describe the physical characteristics of Ascaris lumbricoides

Back 39

This worm is about as big as a pen

Front 40

How many people are infected with Ascaris lumbricoides?

Back 40

1.5-2 billion

Front 41

Back 41

Adult Ascaris lumbricoides

Front 42

Describe the resilience of Ascaris lumbricoides eggs

Back 42

They can live up to 20 years in soil

Front 43

Describe the life cycle of Ascaris lumbricoides

Back 43

-Ingest egg
-Egg hatches in small intestine
-Larva penetrates small intestine and enters blood supply
-Spreaads to liver and hosts on parenchymal cells
-Reaches third stage and migrates to blood stream
-Gets stuck in capillaries of lungs
-Breaks out into the alveolus
-Crawls up the bronchial tree to epiglottus
-Swallowed and enters small intestine
-Continues developing into an adult
-Female mates with male and you pass eggs

Front 44

How long does it take for Ascaris lumbricoides to become an adult?

Back 44

~3 months

Front 45

How does Ascaris lumbricoides feed?

Back 45

The parasite eats the meal by secreting an anti-trypsin factor. This inhibits your ability to digest proteins before it gets to your protein. If you have many worms this can be a major problem

Front 46

How many eggs does the adult Ascaris lumbricoides produce?

Back 46

Over 200,000 eggs daily for up to 5 years

Front 47

Back 47

Cross section of the adult Ascaris lumbricoides

Front 48

Back 48

Larvae of Ascaris lumbricoides in
liver

Front 49

Back 49

Larva of Ascaris lumbricoides in
lung

Front 50

Describe the pathogenesis of Ascaris lumbricoides

Back 50

1. "Verminous" pneumonia, lung tissue damage due to migratory larvae

2. Bowel obstruction - too many adult worms

3. Parasite secretes trypsin inhibitor, prevents host from digesting proteins; cause of malnutrition

4. Aberrant migration of adult worms to
a) Ampula of Vater
b) Common duct
c) Liver
d) Pharynx
e) Peritoneum

Front 51

Describe how Ascaris lumbricoides causes stasis

Back 51

Lots of worms can block the small intestine. You can develop stasis. Stasis can lead to anaerobes, such as C. difficile. These will secrete lots of toxins that will erode away the lining to the small intestine and can create a lesion that will connect to the peritoneal cavity. This can result in peritonitis, which can lead to death.

Front 52

Describe the clinical disease caused by Ascaris lumbricoides

Back 52

1. Light infections are asymptomatic as long as the adult worms do not migrate

2. Heavy infection leads to:
a. Protein calorie malnutrition - "failure to thrive" syndrome
b. Bowel obstruction
c. Aberrant migratory events

Front 53

How do you diagnose Ascaris lumbricoides?

Back 53

Microscopic examination of feces for eggs

Front 54

Back 54

Ascaris lumbricoides egg

Front 55

What is the drug of choice for Ascaris lumbricoides infections? How does it act?

Back 55

Mebendazole

It depolymerizes invertebrate microtubules

Front 56

Describe the distribution of ascaris in people?

Back 56

Very few people harbor lots of worms. Very large numbers of people harbor very few worms. The people with lots of worms are supplying lots of eggs for the rest of the community. They are likely genetically different people. The individuals with many worms may be missing a component of their immune response.

Front 57

How do you prevent and control Ascaris lumbricoides?

Back 57

By having sanitary disposal of feces

Front 58

Back 58

Adult Toxocara canis

Front 59

Describe the life cycle of Toxocara canis and cati

Back 59

-If you swallow the egg and you are a dog then you get the equivalent of the Ascaris infection
-This worm can cross the placenta in a pregnant female dog
-If a human swallows the egg, the worm senses it is in the wrong host
-The egg hatches in the small intestine
-The worm begins to circulate in the blood supply
-The worm begins to wander aimlessly through tissue
-It can wander to the eye or the brain

Front 60

What occurs when the Toxocara canis wanders throughout the tissue?

Back 60

They can cause significant damage leading to visceral larva migrans and ocular larva migrans

Front 61

Back 61

Embryonated egg of Toxocara canis

Front 62

Describe the pathogenesis of the Toxocara canis parasite

Back 62

There is tissue damage (systemic) due to migratory 3rd stage larva

Front 63

Describe the clinical disease associated with Toxocara canis

Back 63

The clinical symptoms depend on the organ system being invaded
1. Fever
2. Loss of visual acuity
3. Blindness
4. Learning disabilities

Front 64

How do you diagnose Toxocara canis?

Back 64

Serological test (ELISA-based)

Front 65

What is the drug of choice for Toxocara canis?

Back 65

Mebendazole

You have to give steroids as well in this case to keep down the inflammatory responses that are generated by the migratory worms that migrate to places like the eye or the brain and die.

Front 66

How do you prevent and control Toxocara canis infections?

Back 66

-Sanitary disposal of dog and cat feces
-Cover sand boxes at night
-Regular treatment of pets