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Lecture Details[]

Ross Coppel; Week 11 MED1011; Microbiology

Lecture Content[]

A parasite lives upon or within another living organism from who's expense it obtains some advantage. Commonly from helminths (multicellular eukaryotic organisms with complex life cycle), protozoans (unicellular eukaryotic organisms), ectoparasites (arthropods attached to human host eg mosquitos, ticks).

Helminths are multicellular and have 3 main groups; nematodes, platyhelminths (cestodes, trematodes). Can be cm or meters long. Can attack virtually all organs and have an extracellular habitat. Their life cycle can be direct when reproductive stages are released and directly infect new host (active skin penetration, eating) or indirect where reproduction must go through intermediate host or vector (ingestion in intermediate host, bite).

Filarisis is from nematodes (roundworms), can be lymphatic (Brugia malayi, Wucheria bancrofti) or subcutaneous. Is endemic in 80 countries worldwide. Transmitted by blood feeding vectors. Brugia malayi can be diagnosed by blood tests, PCR, treated with diethylcarbamazine/hygeine, and prevented with mosquito control.

Protozoans are single celled eukaryotes, mostly free living but some are parasites. Transmission occurs through insect, ingestion of infective stages or venereal transmission.

Giardia is a diarrhoeal disease, worldwide distribution and waterborne, has diarrhoea, greasy stools, nausea and stomach ache. Once infected, the parasite lives in the intestines and is passed in the faeces. It is diagnosed by stool analysis, and is treated with fluids, metronidazole or tinidazole. Prevention is with hygeine, avoid contaminated foods.

Kinetoplastids are flagellated parasites, there are two main groups, trypanosomes (American or African), Leishmania. American Trypanosomiasis (Chagas disease) is caused by Trypanosoma cruzi (zoonosis of humans), 16-18m people infected, transmitted by Triatomine bug which pass parasites in their faeces. Infection typically occurs when faeces are on skin and are rubbed into bite, wound, eyes or mouth. There is an acute phase (fever, fatigue, headache, loss of appetite, diarrhoea, vomiting, swelling at sites of entry) and a chronic phase (cardiac complications, intestinal complications). Diagnosed by presence of parasite in samples of blood smear, serology and muscle biopsy. Treatment is with anti-parasitics. African Trypanosomiasis (African sleeping sickness) is caused by Trypanosoma brucei, can be lithal in weeks to months if untreated. Distributed in Sub-Saharan Africa. Transmitted in the tsetse fly. Symptoms are sore, severe headache, fatigue, aching muscles and joints, swollen lymph glands, progressive confusion, ataxia, personality changes, slurred speech and seizures from invasion of CNS. Treatment is difficult. Fly is attracted to dust. T brucei multiplies within the blood of the host (is exposed to immune system). Leishmaniasis is geographically diverse, transmitted by sandly bite, natural hosts include rodents, small mammals and dogs. Invades macrophages in liver and spleen and invades cutaneous and mucosal tissues.

Apicomplexa is characterised by specialised organelles, range of important veterinary and human diseases (toxoplasmosis, malaria). Toxoplasmosis is cat faeces, contaminated meat, drinking water. Normal people have flu like, swollen glands, muscle aches and pains. Pregnant and immunocompromised people have serious health problems, foetal abnormalities and death.

Malaria has plasmodium life cycle, treated with chloroquine, aretmisinin, pyremethamine. P falciparum infected RBCs adhere to vascular endothelium.


Mims Ch 5, 6, 19 (250-1), 22 (304-11), 22 (320-1), 24 (347-8), 26 (373-4).[]