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Ascaris Lumbricoides

by Vincent Racaniello, PhD
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    00:01 Alright, back to roundworms. Again helminths, nematodes are roundworms, the example is ascaris lumbricoides. These worms are the largest of human parasites, up to 30 cm long, and this lives in your intestinal tract. Up to 25% of the world’s population has these worms in your intestine. Do you have one? It's a good chance that you might, depending on where you live, you could look at this map and see the parts of the world that are heavily infested, ascaris lumbricoides. Now if you have one or a few worms, you'll probably be okay, you won’t have symptoms perhaps and you wouldn't even know it. You might live many years with such worm in you, maybe one day it will pass out of you and you'll be surprised. On the other hand, you may have many worms, by repeated infections, in which case you will have serious illness and we will talk about this. Now here is a photograph I love, which a colleague of mine gave to me, this is a jar of ascaris adults. So look closely at this jar. It is a big jar, you can see the size by the stack of books next to it, alright, it looks like a foot or two high, couple of gallons of liquid in it and it is full of these ascaris roundworms. You can see the individual worms, looks like there's a thousand or more worms in that jar, so where did these come from? They're preserved in formalin so they don't rot. They came from people in a small village in Bangladesh. What happened is a few doctors and scientists went to this village, they gave the inhabitants of the village a drug to kill the worm and when the worm is dead, it passes out of the intestine and they collected all the worms that the people in this village shed in this day of treatment and they put them in this jar. So many, many villages have this high burden of infection and here in more developed countries perhaps, you won’t have this, but in other parts of the world it's quite common.

    02:24 So let's take a look at the lifecycle of an ascaris infection. It typically begins when we ingest the egg form of the worm and we acquire this by fecal contamination of our food and water. So we eat the eggs, they are very small, we can't see them, they go into our stomach, they pass through the stomach into the small intestine where they hatch.

    02:50 The eggs hatch, they become larvae and these penetrate the intestinal wall and enter the bloodstream. And then they go to the liver, as all good things do when they pass through the blood. They migrate to the heart and eventually are pumped through the lung capillaries.

    03:10 In the capillaries they make their way to those capillaries that wrap around the alveolar spaces, the terminal sacs of the lung, that's where gas exchange takes place, so the capillaries are in close proximity to the alveoli and what do these tiny worms do? They pierce their way out of capillary into the airspace, so now they're out of the blood, they're in your lung, and what do they do? They wiggle their way up into the bronchi and the trachea, all the way up to the back of your throat. So these little worms are crawling up there and then what happens, you swallow and they go down to your intestine. They've been there before, that's right, the first time they were just hatching, this time they're going to colonize your intestine and grow into some of those large adults that we saw in the photograph, and the adults mature in your small intestine and as I said if you have one, it's not much of a problem, but the small intestine is not very big in diameter and if you have many worms, this can be a problem. It can obstruct your small intestine and you will have disease.

    04:21 These worms can also make their way to the bile duct, where the bile duct comes from the gallbladder through the small intestine, they can penetrate that and clog it up and cause pathology, as well as a consequence of the obstruction. So that is the lifecycle of ascaris and it starts all over again, you have worms in your intestine, they are producing eggs, which you shed in your feces and those eggs then contaminate someone else's water or food to start the cycle all over again. Fruits and vegetables commonly can be contaminated.

    05:01 In many countries where ascaris is prevalent, human feces are used as fertilizer because it's nutrient rich, it's taken and spread over the fields, it gets on the leaves and the fruits and in it are eggs of ascaris, they are very stable and then you go to eat them without cleaning them very well, bingo you have another ascaris infection. So you can see how you could get many, many worms in you, if you keep eating eggs over and over again, each one gives you a new worm and you get multiple worms in you.

    05:38 So light infections are typically asymptomatic, but the worms themselves as you get more and more can cause biliary obstruction or inflammation of peritoneum peritonitis. So the more worms the more problems you have. Heavy infections, malnutrition, you can't absorb the food, the worms are blocking the intestine, bowel obstruction, you can't defecate, aberrant migration. So many worms are really problematic and you need to get rid of them. Now here is a very unfortunate little girl whose belly is full of worms. Look at the poor thing, so sad whenever I see this picture, she has been contaminated over and over again; she's obviously living in unsanitary conditions where her food and water is contaminated with ascaris eggs, so she has many, many eggs in her belly. You can see how swollen and distended it is. Now fortunately we can take care of this. This child was given an anti-ascaris drug that kills the worms, makes them leave her intestines and here is the result. They were all collected and now she's better. Look at all that worms, all those worms that came out of her. Unfortunately she will get infected again and again, because her lifestyle isn't changing. She continues to eat contaminated food. If the worms happen to leave your intestinal tract and penetrate other tissues, which can happen from time to time, this can be fatal, here's an example of someone's liver filled with ascaris worms. This is someone who died as a consequence of having so many worms in the liver, which disrupts the tissue and its function.

    07:24 It's fatal.

    07:25 Alright so how do you diagnose and treat this infection? Diagnosis is very simple, you get some stool from a person who has a swollen abdomen, who you suspect has ascaris and you look and you will see the eggs of the ascaris in the stool. Each adult female releases 200,000 eggs a day in your intestine. One female, so if you have 10, well 2 million eggs a day, you can certainly see that in someone’s stool without being very skilled. You can treat these infections with a variety of drugs that will cause the worms to leave, mebendazole, albendazole, ivermectin, nitazoxanide and other drugs. The thing is, you usually don't treat unless you have lots of worms and you have a swollen belly or other symptoms. I should point out that ivermectin was discovered by William Campbell. He was awarded the Nobel Prize for that discovery. Mebendazole selectively depolymerizes invertebrate microtubules, so worms are invertebrates; they have no vertebral column, so this is a rather specific drug.

    08:39 How do we prevent infection? Very simple, but not so easily achieved. Sanitary disposal of feces, keep human feces away from your food and your water and don't use it to fertilize your crops. Unfortunately in many parts of the world, this simply isn't possible.


    About the Lecture

    The lecture Ascaris Lumbricoides by Vincent Racaniello, PhD is from the course Parasites.


    Included Quiz Questions

    1. Fecal oral route
    2. Transplacental
    3. Blood transfusion
    4. Sexual contact
    5. Respirator droplets
    1. Small intestine
    2. Stomach
    3. Large intestine
    4. Appendix
    5. Sigmoid colon
    1. Small intestine -> blood -> liver
    2. Small intestine -> liver -> blood
    3. Stomach -> liver -> lungs
    4. Lungs-> heart -> small intestine
    5. Heart -> blood -> liver
    1. Bowel obstruction
    2. Jaundice
    3. Rhinitis
    4. Conjunctivitis
    5. High fever with chills
    1. Ivermectin
    2. Aspirin
    3. Itraconazole
    4. Methotrexate
    5. Propranolol

    Author of lecture Ascaris Lumbricoides

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD


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