Parasitology 02 Hookworms, Strongyloides Sterocoralis

Front 1

How do you acquire a hookworm infection?

Back 1

By just coming into contact with the worm. You don’t have to swallow these worms. These are small worms, so we are not aware that we are being infected until it is too late.

Front 2

What are the important species of hookworms?

Back 2

Ancylostoma duodenale
Necator americanus

Front 3

What is the maximum a hookworm can crawl?

Back 3

4 feet

Front 4

Describe the construction of the outhouse and the results of its creation

Back 4

They dug it 6 feet deep because the worms could only crawl 4 feet before dying. When polio, Shigella, E. coli, salmonella are sequestered 6 feet deep they can also no longer cause disease. Children no longer developed these infections and started going to school. This increased productivity.

Front 5

How do countries that use human feces as fertilizer prevent hookworm infections?

Back 5

They just ferment the feces for 6 weeks. This only prevents hookworm, not other diseases such as Shigella or Ascaris.

Front 6

Describe the physical appearance of Ancylostoma duodenale

Back 6

These are big worms that are visible to the naked eye

They have teeth allow the parasite to grab onto tissue and break off a piece and eat it. They have a big esophageal bulb that they also use to suck blood through. They derive the oxygen from the blood.

Front 7

Describe what occurs when hookworms suck blood.

Back 7

Adult Ancylostoma duodenale have teeth allow the parasite to grab onto tissue and break off a piece and eat it. They have a big esophageal bulb that they also use to suck blood through. They derive the oxygen from the blood.

The adult Necator americanus suck less blood than Ancylostoma, 10x less.

With enough worms you can have lots of blood loss. They also secrete anticoagulants at the site of the bite to keep the blood flowing. Once they finish eating the villus and move onto the next one the site keeps bleeding for about 3 days, leading to additional blood loss.

Front 8

Describe the role of the esophageal bulb

Back 8

-It is for pumping the blood that the worm gets out of the single capillary in the submucosa.
-The blood goes in oxygenated and leaves the anus deoxygenated. It is not using digesting the blood at all, just using the oxygen.

Front 9

Back 9

Adult female Ancylostoma duodenale

Front 10

Back 10

Adult Ancylostoma duodenale

These teeth allow the parasite to grab onto tissue and break off a piece and eat it. They have a big esophageal bulb that they also use to suck blood through. They derive the oxygen from the blood.

Front 11

Back 11

Adult Necator americanus

These suck less blood than Ancylostoma, 10x less.

Front 12

Describe the life cycle of Necator americanus

Back 12

-Larvae wait for host
-When host touches them they let go of their attachment
-Crawl down hair follicle
-Penetrate into blood
-End up in lungs
-Penetrate alveolar capillary
-Crawl up epiglottus and are swallowed
-Enter small intestine and bite
-Become anergic while still taking blood
-Adults continuously feed and mate
-After mating the male passes out of the GI tract
-Female makes eggs
-Around 2 weeks later passes embryonated eggs out in stool
-2-3 days later eggs hatch in soil and spread

Front 13

Describe the pathogenesis of the adult hookworm

Back 13

Sucks flood and feeds of villus tissue. The anti-coagulant that this worm has involved inhibits coagulation cascade in two different places. The medical leech only does it in one place.

Front 14

Back 14

Hookworm larvae in dog skin penetrating into blood supply

Front 15

Back 15

Hookworm egg

Front 16

How do you diagnose hookworms?

Back 16

Microscopic examination of feces for eggs

Front 17

What is the drug of choice for treating hookworms? How does it act?

Back 17

Mebendazole

It depolymerizes invertebrate microtubules only

Front 18

How do you prevent and control hookworms?

Back 18

Outhouses

Front 19

Describe the distribution of number of hookworms in people

Back 19

There are very few people harboring lots of worms and a lot of people harboring very few worms. The people with lots of worms are thought to be genetically different with regards to their ability to fight off these infections.

Front 20

What is Ancylostoma caninum?

Back 20

Dog hookworm

Front 21

Back 21

Ancylostoma caninum infectious larva

Front 22

What happens when non-human hookworms come into contact with human skin?

Back 22

They penetrate the skin. At which point they begin to sense us with chemoreceptors. A dog parasite that penetrates the dog's skin will continue the lifecycle and end up in the small intestine. In people this parasite instantly realizes it is in the wrong host, so it crawls around trying to escape. It has about 6 weeks of life and then it dies. Along the way it secretes lytic enzymes, mostly metalloproteases. As a result of that wandering they illicit allergic reactions that eventually come to the clinic.

It causes cutaneous larva migrans

Front 23

Back 23

Cutaneous larva migrans or "Creeping eruption"

Front 24

How do you treat creeping eruption/cutaneous larva migrans?

Back 24

You take a gauze pad and you soak it in thiabendazole. Thiabendazole has some anti-inflammatory properties n its on. In addition it will soak through the skin and kills the worm. You will then stop the worm from migrating any further. In a couple days these lesions will resolve.

Front 25

Back 25

Free-living female Strongyloides stercoralis

Front 26

Where does Strongyloides stercoralis live?

Back 26

It can be free-living in soil or a human parasite

Front 27

Back 27

Parasitic female Strongyloides stercoralis

Front 28

Describe the life cycle of Strongyloides stercoralis

Back 28

-Larvae penetrates unbroken skin
-Crawls down hair follicle shaft and enters blood stream
-Larva reaches lung capillaries
-Enters alveolar spaces
-Crawl up esophagus and are swallowed
-In the small intestine, develops into a male
-It makes male organs, builds sperms, then destroys the male organs, keeps the sperm, rebuilds itself as a female and self-fertilizes.
-The female begins to lay eggs. The eggs hatch in the tissues and the larvae develop in the tissues until they reach the second stage of their lifestyle. The second stage passes out with feces into the environment.
-They undergo another molt and become third stage worms and they can then infect another host
-ALTERNATIVELY, If there is a bowel obstruction or the passage of feces is slowed then these worms have the options of advancing to the third stage within the host. It is the third stage that is infectious. If you produce a third stage worm in your large intestine the worm can then penetrate the unbroken intestinal wall, get into the blood supply, and undergo the ascaris life cycle, enter the small intestine and establish another adult worm.

Front 29

How does Strongyloides stercoralis cause sepsis?

Back 29

-Second stage of this worm eats bacteria
-They get the bacteria from your fecal pellet. They will eat whatever the fecal mass is made out of.
-When it becomes a third stage larva, it regurgitates whatever is left in its gut tract and doesn’t feed anymore until it completes its life cycle, ending up in the small intestine.
-A second stage worm in the blood about to become a third stage is going to release all those stored up bacteria that it has ingested and deposit those bacteria in the tissue.
-These worms can migrate everywhere so they can release bacteria everywhere. In these cases, where there is a third stage worm in the stool, you give massive amounts of IV antibiotics. You begin to treat the infection as well. In many cases this is detected too late and the patient can die from the septicemia. This used to be a big deal in kidney transplants, especially when patients became immunocompromised.

Front 30

Where in the small intestine does Strongyloides stercoralis live?

Back 30

It lived embedded in a row of columnar cells in the small intestine. The adult and the larva live inside the matrix of the columnar cells in the small intestine. It doesn’t create a syncytium. Instead it just kills the cells because you make so many of them. This disease looks like Crohn's disease.

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Back 31

Strongyloides stercoralis in situ

Front 32

Back 32

Larva of Stronguloides stercoralis in skin

Front 33

Describe the pathogenesis of Strongyloides stercoralis

Back 33

Worms invade epithelial cells, induce cell death

That cell death, if there are enough worms present, can induce a diarrheal disease.

Front 34

What are the clinical manifestations of Strongyloides stercoralis infection?

Back 34

1. Diarrhea
2. Malabsorption syndrome
3. Secondary bacteremia/septicemia as larvae migrate throughout body and defecate microbes that they ingested in the large intestine
4. Death due to overwhelming bacterial septicemia

Heavy infection results in diarrhea. Malabsorption follows that. You die from an overwhelming septicemia from a bacteremia from the migrating larvae that never left your body and can now infect you.

Front 35

How do you diagnose Strongyloides stercoralis infection?

Back 35

1. Microscopic examination of feces (x6)
2. String test

The diagnosis is made by looking for the larvae. For people receiving an organ, do multiple stool samples to ensure that they do not harbor this worm to begin with. You have to do it for at least 6 times because during the early stages of this infection there are very few larvae being produced so the likelihood of finding anything is low. You can also do a string test, which involves passing a string into the small intestine, letting it sit there overnight, removing it and examining it microscopically.

Front 36

Back 36

Second stage larva of Strongyloides stercoralis

Front 37

Back 37

Adult male Ancylostoma duodenale

Front 38

What is the drug of choice for Strongyloides stercoralis infection? What is its mode of action?

Back 38

Ivermectin

It blocks Cl- ion channels, inhibits the GABA receptor complex

It is also an alternate drug for all geohelminths

Front 39

How do you prevent and control Strongyloides stercoralis infection?

Back 39

By having sanitary disposal of human feces

The dog is a common reservoir host. Cannot control spread of dog feces which may contain infective larvae