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Subject 4 (Labours, 1st year DDS)


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Trypanosoma brucei gambiense/rhodesiense

Kind of parasite: heteroxenous and polyxenous.

Host(s): humans and animals.

Infective stage: metacyclic trypomastigote.

Transmission vectorborne; the tsetse fly (Glossina sp.) introduces the metacyclic trypomastigotes into the human blood-stream by the injection of its saliva.

Site of infection: blood, lymph nodes, CSF.

Diagnostic method(s):
Demonstration of trypomastigote forms in:
• blood (thick or thin smears);
• aspirates from enlarged lymph nodes (in the early stage of sleeping sickness);
• the CSF.
Inoculation of biological material from man into laboratory animals
Serological tests

Geographical distribution: West-Central or East-Central Africa.

Remarks:
• the trypomastigotes of T. b. gambiense and T. b. rhodesiense are indistinguishable;
T. b. gambiense causes the chronic form of the disease and is found in West-Central and Central Africa;
T. b. rhodesiense occurs in Central and East-Central Africa and causes an acute type of the disease.

Trypanosoma cruzi

Kind of parasite: heteroxenous and polyxenous.

Host: humans and animals.

Infective stage: metacyclic trypomastigote.

Transmission vectorborne; the blood sucking reduviid bugs (Triatoma, Rhodinus, Panstrongylus) - the infective forms of parasites are excreted onto the host’s skin with reduviid bug feces during feeding.

Site of infection: blood, reticuloendothelial system, neuroglia, and cardiac, smooth and skeletal muscles.

Diagnostic method(s):
• demonstration of trypomastigote forms in stained blood films and in aspirates of enlarged lymph nodes;
• detection of amastigotes and trypomastigotes forms from chagomas or tissue;
• blood inoculation into laboratory animals;
• xenodiagnosis;
• serological tests.

Geographical distribution: T. cruzi is distributed in the South and Central America.

Remarks:
• trypomastigotes mainly occur in the blood of patients in the acute phase of Chagas' disease, whereas they are very rare or absent in the blood of patients with the chronic phase of Chagas' disease;
• in the chronic phase of Chagas' disease culture techniques, xenodiagnosis and serological tests are recommended.

Leishmania sp.

Kind of parasite: heteroxenous and polyxenous.

Host: humans and animals.

Infective stage: promastigote.

Transmission vectorborne; the infective forms of parasites are injected into the host by the saliva of sandfly (Phlebotomus and Lutzomyia).
Site of infection: reticuloendothelial system (bone marrow, spleen and liver).

Diagnostic method(s):
• microscopic examination of bone marrow, lymph node and splenic aspirates;
• immunodiagnostic tests;
in vitro culture.

Geographical distribution: Africa, the Mediterranean region, Southwest Asia, Central and South America.

Remarks: There are many species or subspecies of Leishmania which cause different variants of the disease:
• the etiological agent of mucocutaneous leishmaniosis is L. braziliensis;
• the etiological agents of cutaneous leishmaniosis is L. tropica;
• the etiological agent of visceral leishmaniosis is L. donovani.

Plasmodium sp.

Kind of parasite: heteroxenous and monoxenous.

Host(s): humans as the intermediate host and mosquito (Anopheles) as the definitive host.

Infective stage: sporozoite.

Transmission by the injection of sporozoites with female mosquito saliva.

Site of infection: the parenchyma cells of the liver and RBC.

Diagnostic method(s):
• microscopic examination of thin or thick stained smears of peripheral blood;
• molecular methods.
Geographical distribution: in tropical, subtropical and temperate climate zones.

Remarks: the most important species parasitizing human beings are: P. falciparum (malignant tertian malaria), P. malariae (quartan malaria), P. vivax (benign tertian malaria), and P. ovale (tertian malaria).

 Author: Piotr Nowosad date: 2020-04-23  print    back  
 
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