Parasitology lecture 9 Protozoans parasitic intestinal

Direct transmission of protozoans

Occurs through intimate body contact, such as kissing or sexual intercourse. The organism typically remains within the host, undergoing changes or expanding it’s presence

Fecal/oral transmission of protozoans

Involves ingesting environmentally resistant cysts via contaminated food or water. These cysts are shed in feces and contaminate the environment

Vector-borne transmission of protozoans

Transmitted by blood-sucking arthropods. The arthropod becomes infected during a blood meal from an infected host and transmits the parasite during the subsequent blood meals. Vectors often serve as intermediate hosts, meaning life cycle stages occur within them

Predator-prey transmission

The parasite resides in the tissues of prey. Intermediate host predators ingest the infected prey, and then shed spore or infective stages into the environment, which are then picked up by new prey

Trophozoite form of protozoans

This is the active, vegetative stage responsible for multiplication, typically through binary fission. It involves nuclear and cytoplasmic division

Cyst form of protozoans

A protective stage where the parasite secretes a resistant covering. Cyst formation is triggered by environmental factors

Factors that trigger cyst formation

Excess or reduced food availability

Excess waste products

Desiccation

Changes in oxygen levels

Temp. fluctuations

Protective cyst

The cyst wall protects the organism and no significant morphological changes occur within this stage

Reproductive cyst

The cyst protects the parasite and nuclear division occurs, leading to an increased number or trophozoites that exit the cyst upon excystation

Entamoeba histolytica

A protozoan parasite that causes amebiasis, a disease with intestinal and potentially extra-intestinal manifestations

The trophozoite morphology of Entamoeba histolytica is characterized by what?

The formation of “explosive” pseudopodia for movement

What may be observed of the trophozoites or Entamoeba histolytica that indicates active feeding?

Erythrocytes (RBCs) that may be observed withing cytoplasmic vacuoles

Size of trophozoites of Entamoeba histolytica

20-30 microns in diameter (range 8-60 microns)

The cysts of Entamoeba histolytica contain how many nuclei

1-4 nuclei, this is the reproductive and resistant stage that is 10-20 microns in diameter

In the intestinal phase of Entamoeba histolytica, mature cysts are ingested by a host to which ________

Excystation occurs in the small intestine, releasing multinucleated trophozoites

In the intestinal phase of Entamoeba histolytica, Trophozoites multiply by _______ in the large intestine, becoming __________

Binary fission; mononucleated and multinucleated

After trophozoites of Entamoeba histolytica multiply in the intestine, what happens next?

Encystation occurs, forming immature cysts which mature into infective cysts. Mature cysts are then passed in the feces

Extra-intestinal phase of Entamoeba histolytica

Invasion of tissues beyond the intestine, commonly affecting the liver, brain or lungs

Amebiasis is the __________

Second leading cause of parasitic disease death globally

only 10-20% of individuals infected with Entamoeba histolytica are

symptomatic cases often present with dysentery (blood in stool)

80-90% of individuals infected with Entamoeba histolytica are

Asymptomatic carriers with no symptoms

Acute intestinal stage of Entamoeba histolytica

Characterized by flask-shaped ulcers that penetrate the submucosa

Multiple ulcers can form on the surface of the large intestine, with most pathology occurring below the mucosal surface

Chronic intestinal stage of Entamoeba histolytica

Occurs when the immune response balances tissue damage and repair

Symptoms include diarrhea, constipation, lower back pain, fatigue

Liver abscesses of Extra intestinal phase of Entamoeba histolytica

Develops via mesenteric blood vessels or direct erosion through the gut wall. Pulmonary involvement, cutaneous manifestations, and cerebral involvement can also occur

intestinal diagnosis of Entamoeba histolytica

Examination of loose stools or dysenteric stools for cysts or trophozoites. Protoscopic exams may be performed

Extra-intestinal diagnosis of Entamoeba histolytica

Imaging studies, aspirates, and assessment of clinical signs and symptoms