Difficulty: Introductory | Prerequisites: Basic understanding of eukaryotic cell structure (Week 5) and the concept of infectious agents (Week 6).
Helminths and prions sit at opposite ends of the pathogen size spectrum. Helminths (parasitic worms) are macroscopic, multicellular organisms that can grow to over 50 feet long. Prions are the smallest known pathogens: misfolded proteins with no genetic material at all. Both are covered in Week 7 of CM101, and both are relevant to mortuary science because they present unique challenges for infection control and tissue handling. If you are coming in cold, make sure you understand the basic categories of infectious agents (bacteria, viruses, protozoans, fungi) from earlier weeks before tackling this material.
Helminths are parasitic worms (nematodes, trematodes, cestodes) that infect roughly half the world's population at any given time. They damage hosts by consuming tissue, stealing nutrients, secreting toxins, and causing bowel obstructions. Prions are infectious misfolded proteins that cause fatal, incurable brain diseases called transmissible spongiform encephalopathies (TSEs). They contain no genetic material, resist standard sterilisation methods, and "replicate" by converting normal proteins into misfolded copies.
Helminth
A parasitic worm. Helminths are macroscopic, multicellular organisms that range from barely visible to over 50 feet long. Think of them as the largest category of human parasite.
Nematode
A roundworm. Cylindrical in cross-section. Includes hookworm. In simple terms, these are the round, unsegmented worms.
Trematode
A fluke. Flat worms (platyhelminthes) that are one piece (not segmented). Schistosoma is a key example. Think of them as flat, leaf-shaped parasites.
Cestode
A tapeworm. Flat worms that are segmented. Taenia saginatum (beef tapeworm) is a key example. Think of them as long, ribbon-like, segmented parasites.
Prion
An infectious misfolded protein. The smallest of all pathogens. Contains no DNA or RNA. Prions are definitively non-living.
PrP (Prion Protein)
A normal cellular protein found in healthy tissue. When it misfolds into the abnormal form PrPSc (Scrapie Isoform), it becomes the disease-causing agent.
PrPSc (Scrapie Isoform)
The misfolded, disease-causing form of the prion protein. It converts normal PrP molecules into copies of itself, spreading the misfolding through the brain.
Transmissible spongiform encephalopathy (TSE)
The class of fatal neurodegenerative diseases caused by prions. "Spongiform" refers to the sponge-like holes that develop in brain tissue. Examples include Creutzfeldt-Jakob disease (CJD) and kuru.
Fomite
A non-living surface or object that can carry and transmit infectious agents. Prions may possibly be transmitted on fomites such as surgical instruments.
Debridement
The removal of dead or damaged tissue, sometimes required to treat subcutaneous helminth or fungal infections.
Helminths are macroscopic, multicellular organisms. Individual worms range from barely visible to over 50 feet long. At any given time, roughly 50% of all people carry worms, with children being the most common carriers. They are most often associated with the digestive system but can infect any organ, including the eyes and the brain.
Nematodes (roundworms): cylindrical worms. Includes hookworm.
Trematodes (flukes): flat, unsegmented worms. Includes Schistosoma.
Cestodes (tapeworms): flat, segmented worms. Includes Taenia saginatum.
The flat worms (trematodes and cestodes) are collectively called platyhelminthes. The cylindrical worms are called nemathelminthes.
Helminths cause harm through four main mechanisms:
Consuming tissue as they migrate through the body
Consuming nutrients intended for the host
Secreting toxins into the tissues
Creating bowel obstructions due to sheer numbers
Swelling of organs due to the immune response
Haemorrhage (bleeding) resulting in anaemia (low red blood cell count, leading to reduced oxygen delivery to tissues)
Weight loss
Treatment is typically through drug therapy using medications that paralyse the worm's muscles, allowing the body to expel them.
Prions are infectious misfolded proteins. They are the smallest of all pathogens and are most definitely non-living, since proteins are biological molecules with no capacity for independent life.
Prions are among the hardiest of all pathogens.
They are resistant to chemicals, radiation, and heat.
They lack genetic information (no DNA, no RNA), unlike every other type of pathogen.
They "replicate" by inducing properly folded PrP proteins to misfold into the PrPSc form. Each newly misfolded protein then converts more normal proteins, creating a chain reaction.
Prion diseases are triggered by the misfolding of a normal cellular protein called PrP (Prion Protein) into an abnormal form known as PrPSc (Scrapie Isoform). The misfolded PrPSc is central to the pathogenesis of all prion diseases.
Prions cause a class of fatal neurodegenerative diseases called TSEs. These diseases attack the brain and nervous system, leading to progressive decline in cognitive function and motor abilities. The brain develops a characteristic sponge-like appearance.
Examples of TSEs:
Creutzfeldt-Jakob disease (CJD): the most commonly cited human prion disease.
Kuru: historically associated with ritualistic cannibalism in Papua New Guinea.
Symptoms include spasms, personality changes, dementia, and memory loss. Symptoms get progressively worse over six to eight weeks. There is no cure and all TSEs are 100% fatal.
Prions may be:
An inherited genetic defect (mutations that cause the body to produce abnormal PrP)
Transmitted by consumption of contaminated meat or brain tissue (e.g. mad cow disease, where cattle feed is sometimes fortified with animal byproducts including brains of other livestock)
The result of sporadic misfolding events within the body
Possibly transmitted on fomites (non-living surfaces) such as surgical instruments, because standard sterilisation may not destroy them
Students often think helminths are microscopic. Most are macroscopic (visible to the naked eye), and some grow extremely large.
Students sometimes confuse the three helminth categories. Nematodes = round (think "nema-round"), trematodes = flat and unsegmented (flukes), cestodes = flat and segmented (tapeworms).
Students often assume prions contain DNA or RNA. They do not. Prions are pure protein, which is what makes them so unusual and so difficult to destroy.
Students sometimes think TSEs can be cured or treated. They cannot. All TSEs are 100% fatal with no available treatment.
⚠️ Know the three categories of helminths (nematodes, trematodes, cestodes) with one example of each.
⚠️ Be able to list the four ways helminths damage the host.
⚠️ Know the three pathological effects of helminth infection (organ swelling, haemorrhage/anaemia, weight loss).
⚠️ Understand that prions contain no genetic material and are non-living.
⚠️ Know the difference between PrP (normal) and PrPSc (misfolded/disease-causing).
⚠️ Be able to name two TSEs (Creutzfeldt-Jakob disease and kuru) and list the symptoms.
⚠️ Know that all TSEs are 100% fatal with no cure.
⚠️ Understand the three routes of prion transmission (inherited, contaminated tissue, sporadic misfolding) plus the possibility of fomite transmission.
True or false: Helminths are microscopic organisms. (False. They are macroscopic and can grow very large.)
Fill in the blank: The three categories of helminths are nematodes, trematodes, and ________. (Cestodes.)
True or false: Prions contain RNA. (False. Prions contain no genetic material.)
Fill in the blank: The misfolded form of the prion protein is called ________. (PrPSc / Scrapie Isoform.)
True or false: Some TSEs can be cured with antibiotics. (False. There is no cure for any TSE, and they are 100% fatal.)
Q: Name the three categories of helminths and give one example of each.
A: Nematodes (roundworms, e.g. hookworm), trematodes (flukes, e.g. Schistosoma), and cestodes (tapeworms, e.g. Taenia saginatum).
Q: List four ways helminths damage their host.
A: Consuming tissue during migration, consuming host nutrients, secreting toxins into tissues, and creating bowel obstructions through sheer numbers.
Q: What makes prions unique among all pathogens?
A: Prions contain no genetic material (no DNA or RNA). They are misfolded proteins, making them non-living. They are also uniquely resistant to chemicals, radiation, and heat.
Q: Explain how prions "replicate" without genetic material.
A: Prions replicate by inducing normally folded PrP proteins to misfold into the abnormal PrPSc form. Each newly misfolded protein then converts more normal proteins, creating a chain reaction of misfolding.
Q: A patient presents with progressive dementia, spasms, and personality changes that have worsened over the past six weeks. What class of disease should be considered, and what is the prognosis?
A: Transmissible spongiform encephalopathy (TSE), a prion disease. The prognosis is invariably fatal. There is no cure.
Q: How can prion diseases be acquired? Name three routes.
A: Inherited genetic defect (mutation producing abnormal PrP), consumption of contaminated meat or brain tissue (e.g. mad cow disease), and sporadic misfolding events within the body. Fomite transmission (e.g. contaminated surgical instruments) is also considered possible.
Helminth infections connect to the osmotic principles from Weeks 3–4: worm-induced haemorrhage depletes red blood cells, and understanding how fluid and nutrient balance works at the cellular level helps explain the resulting anaemia and tissue damage.
Prions connect to the organic chemistry material on protein structure. Understanding why a protein's shape matters (and what goes wrong when it misfolds) is fundamental to grasping prion disease.
Both helminths and prions are relevant to mortuary science infection control: helminths because they are so prevalent, and prions because they resist standard sterilisation and require special handling protocols.