Parasitology Lecture: Nematode Infections

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18 Questions

What is the significance of the filiform larva stage in roundworms?

It is the third stage where larvae are most often infective

How can infection with roundworms occur?

By larval penetration of skin

What proportion of nematodes parasitic for humans are found in various tissues?

One-half

What may contribute to the pathogenicity of intestinal nematodes?

Piercing of the intestinal wall

Which stage of roundworm larvae is most often infective?

Third stage

How can eggs or larvae of roundworms be transmitted to a new host?

By insect bite

What are the three possible factors that may contribute to the ultimate severity of a nematode infection?

The number of worms present, the duration of infection, and the overall health of the host

What are some common signs and symptoms of nematode infections mentioned in the text?

Abdominal pain, diarrhea, and skin irritation

How long can nematode infections last according to the text?

Up to 12 months or longer

To which Phylum do nematodes belong?

Phylum Nematoda

What are the two groups into which nematode species may be divided according to the text?

Intestinal species and intestinal tissue species

Which of the following is NOT mentioned as a possible factor contributing to the severity of nematode infections?

The weather conditions where the host lives

What is the characteristic feature of nematode eggs after fertilization?

Constant in size and shape within a genus

Which nematode shows an exception where filariform larvae penetrate the skin to gain entry?

Strongyloides stercoralis

In which location do Strongyloides stercoralis eggs hatch?

Intestine

How is the diagnosis of nematodes typically accomplished in a laboratory setting?

Specimens of choice vary by species

What is a common method for laboratory diagnosis of nematodes involving the anal opening?

Cellophane tape preparations

Which nematode initiates a heart-lung cycle enroute to the intestinal tract to mature to adults?

Ascaris lumbricoides

Study Notes

Male and Female Reproductive Systems

  • Male reproductive system consists of testes, vas deferens, seminal vesicle, and an ejaculatory duct
  • Female reproductive system consists of ovaries, oviduct, seminal receptacle, uterus, and vagina

Roundworm Life Cycle

  • Adult female produces fertilized eggs or larvae that can infect new hosts in three ways
  • Eggs are immediately infective after ingestion by humans
  • Eggs or larvae require a period of development in the environment to become infective
  • Eggs or larvae are transmitted to a new host by an insect

Nematode Life Cycle Stages

  • Eggs: female sex cells after fertilization, relatively consistent in size and shape
  • Larvae: juvenile worms that undergo several molts, with the third stage being the infective one
  • Adult: varies in size from genus to genus, ranging from less than 1 mm to over one meter

Nematode Life Cycle

  • Human ingests infective eggs, with Hookworm and Strongyloides stercoralis being exceptions that penetrate the skin
  • Larvae hatch in the intestine, and male and female adults develop in the intestine
  • Fertilized eggs are produced, and diagnostic stage is characterized by eggs or larvae in feces

Laboratory Diagnosis

  • Diagnosis is accomplished by recovery of eggs, larvae, and occasional adult worms
  • Specimens of choice vary by species and include cellophane tape preparations, stool samples, tissue biopsies, and serologic tests

Pathogenesis and Clinical Symptoms

  • Three factors contribute to the severity of a nematode infection: number of worms present, length of infection, and overall health of the host
  • Infections can last up to 12 months or longer, and may cause minimal discomfort or severe symptoms
  • Signs and symptoms include abdominal pain, diarrhea, nausea, vomiting, fever, eosinophilia, skin irritation, and muscle involvement

Explore concepts related to nematode infections in parasitology, including diagnosis methods, pathogenesis, and clinical symptoms. Learn about analyzing stool samples, tissue biopsies, infected skin ulcers, and serologic test methods for diagnosing nematode infections.

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