Ectoparasites and Endoparasites Overview

Ectoparasites

• Organisms that live on the outside of their host (skin, feathers, hairs, gills).
• Types:
  • Visiting: Visit hosts for blood meals (e.g., fleas, mosquitoes)
  • Temporary: Remain attached for short periods (e.g., some leeches)
  • Permanent: Remain attached for their entire life (e.g., ticks, mites)

Endoparasites

• Organisms that live within their host's body (gut, cavities, lungs, body fluids).
• Types:
  • Homoxenous/Monoxenous: Use only one host during their life cycle.
  • Heteroxenous: Require multiple hosts (often different phyla) to complete development.
  • Heterogenetic: Have alternating parasitic and free-living generations. 
  • Heterogenic: Alternation of generations where one reproduces sexually and gives rise to the other generation which reproduces asexually.

Hosts

• Definitive/Primary Host: Hosts that harbor the adult parasite stages and where the parasite may reproduce sexually.
• Intermediate Host: Hosts that harbor the larval or juvenile stage of the parasite.
• Reservoir Host: Hosts that harbor the adult parasite without being harmed.
• Transport Host: Hosts that carry the parasite, but the parasite doesn't develop in this host.
• Vector: Hosts that transmit the parasite to other hosts.

Factors Affecting Host Susceptibility

• Host Factors:
  • Age
  • Physiological status
  • Genetic factors
• Parasite Factors:
  • Dose of infective stage
  • Viability of infective stage
  • Species of parasite
  • Site of parasite development
  • Genetic factors

Modes of Transmission (e.g., Entamoeba histolytica)

• Fecal-oral route (most common): Ingestion of contaminated food or water with mature quadrinucleated cysts.
• Infective form: Mature quadrinucleated cyst

Pathology and Symptomatology (e.g., Intestinal Amebiasis)

• Intestinal Amebiasis: Ulcers, dysentery, fever, colic, frequent motions in acute cases; disappear in chronic cases.
• Extraintestinal Amebiasis: Trophozoites carried to organs, causing abscesses (liver, brain etc).
• Cyst Passers: Individuals with parasites that pass cysts in stool without symptoms.

Intestinal (Non-Pathogenic) Amebae

• Entamoeba dispar, Endolimax nana, Entamoeba coli, Entamoeba hartmanni, Entamoeba polecki, Iodamoeba butschlii.

Species living in the small/large intestine

• (Examples too numerous to list; they are highly specific parasite species to particular hosts, so don't expect a perfect list of examples).

Urogenital Flagellates (e.g., Trichomonas vaginalis)

• Found in the urogenital tract, often affecting vagina in women and urethra in men.

Hemoflagellates (Blood Flagellates; e.g., Leishmania spp. and Trypanosoma spp.)

• Live in the blood and/or tissues of humans, causing several diseases.

Trypanosoma spp. (African Trypanosomiasis)

• Transmitted by tsetse flies (Genus Glossina) through the saliva.
• The tsetse fly carries the parasite, and after infecting the mammal, undergoes multiplication by binary fission.
• Affects the lymphatic and circulatory system.
• Has two sub-species (T. brucei gambiense and T. brucei rhodesiense)
• Control and prevention include minimizing contact with tsetse flies, wearing appropriate clothing, insect repellents. There is no vaccine/drug for prophylaxis.

Leishmania spp.

• Causes cutaneous, mucocutaneous, and visceral forms of leishmaniasis.
• Transmitted by sand flies.

Balantidium coli (Ciliophora)

• Only species of Ciliophora that parasitizes man. 
• Lives in the large intestine of pigs.
• Nonpathogenic to pigs.
• Causes balantidiasis (balantidial dysentery).
• Transmitted by ingestion of cysts.