Parasitism Overview

Study Notes

Parasitism is a symbiotic relationship where one organism benefits at the expense of another (the host).
Parasites gain advantages by living on or in other living organisms.

Ectoparasites:
- Reside outside the host's body.
- Examples include mites, ticks, and lice.
Endoparasites:
- Live inside the host’s body.
- Examples include parasitic protozoa and helminths.
Facultative Parasite:
- Can exist independently or as a parasite.
Obligate Parasite:
- Must live as a parasite to survive.
- Most human-infecting parasites are obligate.

Classified by locomotion:
- Amebas (Amoeba): Use pseudopodia (false feet) for movement.
- Flagellates: Move with whiplike flagella.
- Ciliates: Move using hairlike cilia.
- Sporozoa: Non-motile; do not exhibit movement.

Caused by the genus Leishmania, a flagellated protozoa.
Transmission:
- Bites from infected female sandflies.
- Blood transfusions and person-to-person contact.
Forms of Leishmaniasis:
- Cutaneous: Papule enlarges into crater-like ulcers.
- Mucocutaneous: Severe tissue destruction and disfigurement from individual ulcers.
- Visceral (Kala-azar): Presents with fever, enlarged liver/spleen, anemia, and may result in death if untreated.

Transmission:
- Through soft contact lenses and nonsterile solutions.
- Contaminated spas or hot tubs.
Causes conjunctivitis and keratoconjunctivitis, leading to corneal inflammation.

Caused by Toxoplasma gondii, a sporozoan.
Transmission:
- Ingesting undercooked meat containing cysts.
- Contact with feces from infected cats or transplacentally.
Symptoms may be mild or resemble infectious mononucleosis, with severe outcomes in immunocompromised individuals.

Infection by Entamoeba histolytica.
Transmission:
- Fecally contaminated food/water, usually via flies or food handlers.
Symptoms may vary in severity, often resulting in dysentery, fever, and diarrhea.

Caused by Trichomonas vaginalis, a flagellate.
Transmission:
- Direct sexual contact via infected vaginal and urethral discharges.
Typically causes vaginitis in women, manifesting as profuse, malodorous discharge.

Caused by the genus Plasmodium (e.g., P. vivax, P. falciparum).
Transmission:
- Injection of sporozoites by Anopheles mosquitoes.
Symptoms include malaise, fever, chills, intermittent paroxysms, and can lead to severe complications such as renal failure and death if untreated.