Chapter 5 Kinetoplasta: Trypanosomes and Their Kin

Kinetoplastida: Trypanosomes and Kin

  • Overview: Members of this class have a single large mitochondrion containing a kinetoplast, a disc-shaped DNA-containing organelle (kDNA). The kinetoplast is associated with the kinetosome throughout the parasite’s life cycle.
  • Families: Bodonidae and Trypanosomatidae. Focus here on Trypanosomatidae, which includes several important medical and veterinary pathogens with dramatic pathology.

Genus Trypanosoma

  • Heteroxenous definition: life cycle that involves both vertebrate tissues/blood and the intestine of blood-feeding invertebrate vectors.
  • Insect host development-based division: two major groups – Salivaria and Stercoraria.

Section Salivaria

  • Subspecies in the T. brucei complex:
    • $T.\ brucei$, $T.\ b.\ gambiense$, $T.\ b.\ rhodesiense$
  • Vector: Tse Tse flies (Glossina spp.).
  • Africa belt: Sub-Saharan Africa.
  • Disease caused by $T. b. brucei$: Nagana (domestic cattle wasting disease).
  • Diseases caused by $T. b. gambiense$ and $T. b. rhodesiense$: African sleeping sickness (west and east Africa).
  • Differences between subspecies in humans (as described in the transcript):
    • West African (gambiense): flies in riverine, heavily forested habitats; few animal reservoirs; human disease is common; disease course described as months to years.
    • East African (rhodesiense): flies prefer dry earth; many animal reservoirs; human disease is rare; disease course described as weeks to months.
  • Diagnosis, treatment, and control (as provided):
    • Diagnosis: not detailed in the transcript.
    • Treatment: arsenicals (dangerous; rapid tolerance) and other safer drugs if caught early.
    • Control measures: brush method; elimination of wild game reservoirs; fly catching; night grazing; tolerant cattle stocks; insecticide spraying.
  • Antigenic variation: New variants based on membrane proteins (mechanism for immune evasion).

Section Stercoraria

  • Disease and agent: Trypanosoma cruzi causes Chagas disease.

  • Vector (common name): kissing bug, assassin bug, coned-nosed bug.

  • Reservoir mammals: raccoons, opossums, armadillos, cats, dogs (strays).

  • Geographic distribution: not specified in the transcript.

  • How parasites gain entry into vertebrate host: through bite wound; through broken skin; via mucous membranes; animals may become infected by ingesting the vector.

  • Life cycle in the vertebrate host: parasites multiply in the host (multiply cells).

  • Phases of infection:

    • Acute phase: heart involvement ± other organ involvement.
    • Chronic phase: nerve and muscle damage (heart, esophagus, intestines).

  • Why this disease is emerging in the United States: enough people positive for disease that kissing bugs are affected (transmission potential in the U.S.).

Genus Leishmania

  • Vector (genus and common name): Phlebotomus species (sandflies) feed on blood.

  • Species of interest and diseases:

    • L. tropica → Cutaneous leishmaniasis (skin ulceration—healing; 98% protective)
    • L. braziliensis → Mucocutaneous leishmaniasis (ulceration at site of bite, weeks to months to years; disease spreads along mucocutaneous zones)
    • L. donovani → Visceral leishmaniasis (spreads to organs of the lymphatic system)

  • Reservoir mammals: dogs and rodents.

  • Geographic note: Leishmaniasis is not endemic to North America.

  • Why dog cases have been increasing in the US: not endemic; reported increase in canine cases (question posed in the transcript without a provided answer).

  • Connections to broader themes: vector-borne parasites often show complex life cycles requiring multiple hosts; antigenic variation (Trypanosoma cruzi and Trypanosoma brucei) underlies persistence and treatment challenges; reservoir hosts play key roles in regional epidemiology; public health control relies on vector management and reservoir control alongside treatment strategies.

  • Key terms to remember:

    • kinetoplast, kDNA, kinetosome
    • heteroxenous life cycle
    • Salivaria vs Stercoraria
    • antigenic variation
    • cutaneous, mucocutaneous, visceral leishmaniasis
    • Chagas disease, sleeping sickness, nagana

  • Quick cross-check of subspecies and diseases:

    • T. brucei complex: brucei (nagana in cattle), gambiense and rhodesiense (African sleeping sickness in humans)
    • Chagas disease: Trypanosoma cruzi
    • Leishmania spp.: tropica (cutaneous), braziliensis (mucocutaneous), donovani (visceral)

  • Note on transcript specifics: some wording appeared garbled (e.g., “moths to years” likely intended as “months to years”). The notes above reflect the intended meanings as described in the transcript. Also, where the transcript posed questions without answers (e.g., geographic distribution for Trypanosoma cruzi host entry or Leishmaniasis epidemiology in the U.S.), those prompts are included as items to be revisited with standard references.