Worms

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Overview & Worms Objectives

List the various groups of macroparasites and microparasites (pathogens) that can cause disease in humans.
Describe different types of intestinal worms, including how they enter the human body and their impact on human hosts.
Examine the potential coevolution occurring between humans and intestinal worms.

We are starting with an overview of the agents (organisms and otherwise) that cause infectious diseases.

Agents that cause infectious diseases range in size from many feet long (intestinal tapeworms) to smller than a virus (viroids).

A parasite lives off the body of another organism for food (like a fungus) or as a means of reproducing (like a virus). The ones we can see without magnification are the macroparasites and include worms, arthropods (including insects), and some fungi. The microscopic microparasites are often called pathogens and include yeast fungi, protists, bacteria, and organisms that are too small to live independently without another organism’s cells (viruses, prions, viroids).

Intestinal Worms

Approximately two billion people on Earth are infected with worms. The number is staggering. Clearly these worms are not typically lethal, or we would have heard of these numbers before. However, worms often reside in the intestines, stealing nutrients away from their human hosts. This can lead to malnutrition and an individual becomes more vulnerable to other diseases.

First, an introduction to the various worm groups, including two that include worm species that parasitize humans.

Just to reiterate: most worm species are not harmful to humans, some species are beneficial like earthworms. These Planaria flatworms are commonly found in freshwater where they are omnivores and are eaten by larger carnivores. Those big eyespots detect light and are one of their most recognizable features. We keep them as pets.

Back to the parasites.

This video shows how humans become infected, how large the worms get, and their impact on the human population.

It’s time to see real worm specimens, including tapeworms and Ascaris roundworms

Note: some of these worms can be disturbing. If you have had a cat or dog with worms, you know what we are talking about.

This microscopic view looks like blood vessels, but it is something else entirely.

Organisms can parasitize other parts of the human body, but it is the intestinal worms that impact the largest number of humans. Drug treatments that damage the worms are also often hard on the human hosts.

The larvae of Ascaris roundworm can leave the intestines, travel though blood vessels in the lungs, move up the trachea (windpipe) and get swallowed, re-entering the intestines to grow into adults. All grotesqueness of this aside, the lung migratory stage is particularly dangerous for people who may already have lung damage from Tuberculosis (TB) and other diseases. Researchers have noted that there are fewer “lung migrators” in some populations of Ascaris.

A hypothesis is that intestinal worms are co-evolving with our species to become less deadly. The last thing intestinal worms need to do is kill their host where they feed, grow, and breed, releasing eggs with fecal material. Fewer lung migrating worms may improve worm fitness, and be less dangerous to humans.

The next section introduces the arthropods that can directly cause disease or transmit pathogens directly into the human body.

Check your knowledge. Can you:

list the various groups of macroparasites and microparasites (pathogens) that can cause disease in humans?
describe different types of intestinal worms, including how they enter the human body and their impact on human hosts?
examine the potential coevolution occurring between humans and intestinal worms?