Parasitology Lecture 8

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Questions and Answers

What is the main focus of medical parasitology?

Investigating the response of parasites to their hosts

Classifying parasites into different types

Studying the life cycle of parasites

Understanding the diseases caused by parasites in humans and their diagnosis, prevention, and treatment (correct)

What is the defining characteristic of a parasite?

It is a type of virus

It is a type of bacteria

It is entirely dependent on another organism for its life cycle and metabolic requirements (correct)

It is a multi-cellular organism

What type of parasite is Toxoplasma gondii?

Facultative parasite

Accidental parasite

Ectoparasite

Obligate parasite (correct)

What is the term for the infection caused by ectoparasites?

Infestation Signup and view all the answers

Which type of parasite is characterized by being small, unicellular, and multiplying within its vertebrate host?

Microparasite Signup and view all the answers

What is the term for the invasion of the body by endoparasites?

Infection Signup and view all the answers

Which type of parasite is capable of living either a parasitic or free-living existence?

Facultative parasite Signup and view all the answers

What is the term for parasites that live within the body of the host?

Endoparasites Signup and view all the answers

What is the primary method for diagnosing Entamoeba histolytica?

Microscopic identification of cysts and trophozoites in the stool Signup and view all the answers

Which of the following is NOT a characteristic of Entamoeba coli?

Has chromatoidal bodies with rounded ends Signup and view all the answers

What is the drug of choice for asymptomatic Entamoeba histolytica infections?

Paromomycin Signup and view all the answers

Which of the following is used to distinguish Entamoeba histolytica from Entamoeba dispar?

Isoenzymatic analysis Signup and view all the answers

What is the purpose of using Iodine or trichrome in stool samples?

To permanently stain preparations Signup and view all the answers

Which of the following is NOT a treatment option for symptomatic Entamoeba histolytica infections?

Surgical intervention Signup and view all the answers

What is the characteristic feature of Entamoeba hartmanni?

Smaller in size compared to E. histolytica Signup and view all the answers

What is the purpose of molecular methods in diagnosing Entamoeba histolytica?

To differentiate E. histolytica from E. dispar Signup and view all the answers

What is the primary characteristic that distinguishes E.histolytica from E.dispar?

Presence of ingested red blood cells Signup and view all the answers

What is the primary site of infection for Entamoeba histolytica?

Colon Signup and view all the answers

What is the primary enzyme secreted by E.histolytica during growth?

Proteolytic enzyme Signup and view all the answers

What is a common complication of intestinal amoebiasis?

Amoebic appendicitis Signup and view all the answers

What is the primary factor that determines the pathogenicity of E.histolytica?

Virulence of the strain Signup and view all the answers

What is a common symptom of E.histolytica infection?

All of the above Signup and view all the answers

What is the estimated percentage of individuals with intestinal amoebiasis that develop hepatic amoebiasis?

5-10% Signup and view all the answers

What is the incubation period of intestinal amoebiasis?

1-4 weeks Signup and view all the answers

What is the typical outcome of Naegleria fowleri infection if left untreated?

Death within 72 hours of symptom onset Signup and view all the answers

What is the primary method of diagnosing Naegleria fowleri infection?

Microscopy of CSF for motile amoebae Signup and view all the answers

What is the purpose of using a lawn of E. coli or Enterobacter aerogenes in culturing Naegleria fowleri?

To provide a substrate for the amoebae to feed on Signup and view all the answers

What is the most common stage of Naegleria fowleri infection when diagnosis is made?

At autopsy Signup and view all the answers

What is the primary drug used to treat Naegleria fowleri infection?

Amphotericin B Signup and view all the answers

What is the characteristic morphology of Naegleria fowleri amoebae in CSF?

Motile and amoeboid Signup and view all the answers

What is the primary difference between the trophozoite and cyst stages of Giardia lamblia?

Cysts are resistant to desiccation, while trophozoites are not Signup and view all the answers

What is the typical timeframe between exposure to Naegleria fowleri and the onset of symptoms?

7-15 days Signup and view all the answers

What is an example of a commensalism relationship?

Entamoeba coli in the large intestine of humans Signup and view all the answers

How is a species scientifically designated?

Using binomial nomenclature Signup and view all the answers

Which of the following correctly defines a vector?

Any living creature that can pass an infection to another Signup and view all the answers

What primarily differentiates mechanical vectors from biological vectors?

Mechanical vectors assist in transfer but are not essential for the parasite's life cycle Signup and view all the answers

What is the role of a vector in transmitting disease?

Transporting the pathogen between hosts Signup and view all the answers

What kind of organisms do the terms 'parasite' and 'host' refer to in parasitism?

An organism that lives at the expense of another Signup and view all the answers

Which of the following represents a population capable of continuous reproduction but typically cannot interbreed with other populations?

Species Signup and view all the answers

Which kingdom do vectors typically belong to?

Animalia Signup and view all the answers

Study Notes

Laboratory Diagnosis of Entamoeba histolytica

Entamoeba histolytica must be differentiated from other intestinal nonpathogenic amebae, such as Entamoeba dispar, through isoenzymatic or immunologic analysis and molecular methods.
Microscopic identification of cysts and trophozoites in the stool can be done using wet mount and permanently stained preparations with Iodine or trichrome or by Flotation or Sedimentation method for stool samples.
Blood examination shows moderate leukocytosis.
Serological tests, such as ELISA, Indirect Hemagglutination Assay (IHA), and Indirect Immunofluorescence Assay (IFA), can detect antibodies in the later stages of invasive amoebiasis.
Histology can identify trophozoites in aspirates or biopsy samples obtained during colonoscopy or surgery.
Molecular methods, such as DNA probe and polymerase chain reaction (PCR), can also aid in diagnosis.

Treatment of Entamoeba histolytica

For asymptomatic infections, paromomycin or iodoquinol are the drugs of choice.
For symptomatic intestinal or extraintestinal infections, metronidazole or tinidazole are the drugs of choice, followed by treatment with paromomycin or iodoquinol.
Failure of metronidazole therapy may necessitate surgical intervention.

Nonpathogenic Amoebae

Entamoeba dispar is morphologically identical to E. histolytica and must be separated by isoenzymatic, immunologic, or molecular analysis.
Entamoeba hartmanni is smaller in size than E. histolytica and has an eccentric endosome, and mature cysts have 8 nuclei.
Entamoeba coli has 8 nuclei, and chromatoidal bodies have splintered ends.

Parasitology

Parasitology is the study of the phenomenon of dependence of one living organism on another.
Medical parasitology deals with parasites that infect humans, the diseases they produce, the response generated by the host, and various methods of diagnosis, prevention, and treatment.

Parasite Classification

Microparasites are small, unicellular, and multiply within their vertebrate host, often inside cells. Examples include protozoa.
Macroparasites are large, multicellular, and do not directly reproduce within their vertebrate host. Examples include helminths.
Parasites can be classified based on their location:
- Ectoparasites: live on the surface of the body, e.g., human lice.
- Endoparasites: live within the body of the host, e.g., protozoa and helminths.

Pathogenesis of Entamoeba histolytica

Intestinal amoebiasis: E. histolytica invades colonic mucosa, secretes proteolytic enzymes, and produces flask-shaped ulcers and profuse bloody diarrhea.
Extraintestinal amoebiasis: E. histolytica may cause liver abscesses, and may involve other organs such as the lungs, brain, spleen, skin, etc.

Symptoms of Entamoeba histolytica

Fever, chills, and diarrhea, sometimes with bloody or white mucus and abdominal cramps.
Some people may have mild abdominal discomfort or no symptoms at all.
Involvement of the olfactory lobes may lead to disturbances in smell or taste.
Patient may also develop visual disturbances, confusion, irritability, seizures, and coma.

Laboratory Diagnosis of Naegleria fowleri

Microscopy of CSF: motile amoebae with characteristic morphology can be demonstrated in simple wet-mount preparation of fresh CSF specimen.
Culture: N. fowleri can be cultivated by placing CSF on non-nutrient agar with Escherichia coli or Enterobacter aerogenes and incubated at 37°C.

Treatment of Naegleria fowleri

There is no satisfactory treatment for PAM.
Amphotericin B is the antinaeglerial agent with evidence of clinical effectiveness, but it has considerable toxicity.
Antibacterial antibiotics and antiamoebic drugs are ineffective.

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Description

This lecture covers the basics of parasitology, including the concept of parasitism, medical parasitology, and the diagnosis, prevention, and treatment of parasitic diseases.