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Parasitology

Parasitology tests

The laboratory diagnosis of parasitic diseases relies either on the detection of the parasite at different stages in its development, or on the detection of antibodies proving an immune response by the body to its presence. These two methods cannot be used interchangeably; the choice depends on the parasite being investigated.

Certain commonly encountered situations are described.

Thin-film showing the presence of Plasmodium falciparum in the red blood cells
Thin-film showing the presence of Plasmodium falciparum
in the red blood cells (RBCs)

Credit : Parasitology – Faculty of Medicine Necker Paris
JF Pays - http://www.cdanofel.fr

Malaria

The biggest global parasite endemic: Half of the world population lives in countries where there is a risk malaria transmission, i.e. 109 countries. 200 to 300 million people are infected and 700,000 to 1 million deaths have been recorded, 90% of these in Africa. The disease is transmitted by a mosquito (Anopheles). There is an effective chemoprophylaxis for travellers, but no vaccination.

Any fever and/or indicative clinical signs after returning from an area at risk should be treated as a potential manifestation of malaria.

The diagnosis must be performed urgently since the life of the patient could be at risk (Plasmodium falciparum cerebral malaria).

In the laboratory, we use a combination of 3 standard techniques (thick-film test, thin-film test and rapid HRP2 test). The first results can be forwarded to the doctor within less than 30 minutes.

 
Eggs of Schistosoma haematobium, the causative agent of urinary Bilharzia
Eggs of Schistosoma haematobium, the causative agent of
urinary Bilharzia

Credit : Parasitology – Dijon University Hospital
JF Pays - http://www.cdanofel.fr

Schistosomiasis (bilharzia)

Second biggest global parasite endemic, after malaria. More than 200 million individuals are infected. It is a disease transmitted via bare feet and as a result of swimming in fresh water contaminated by the lavae of a flatworm of the genus Schistosoma.

This parasite causes potentially serious visceral complications (bladder, digestive tract, etc.).

The occurrence of blood eosinophilia and microscopic hematuria associated with a stay in a country at risk (even if this occurred a long time ago) will automatically lead to testing for eggs in the urine and/or the stools.

 
Loa loa microfilariae
Loa loa microfilariae
Credit : Parasitology – Faculty of Medicine Necker Paris
JF Pays - http://www.cdanofel.fr

The filariases

Third biggest global parasite endemic. It occurs in all the tropical and subtropical regions of the globe. Roughly 150 million people are infected with the various forms of filariasis and this parasite produces a broad variety of clinical manifestations.

The common feature of these various forms is that they all result from an infestation by nematodes (roundworms) and their larvae, called microfilariae, which can be found in the peripheral blood circulatory system.

Any occurrence of eosinophilia in a patient returning from a country at risk will automatically trigger the careful examination of a concentrated drop of blood by a technician, searching for microfilariae.

 
Vegetative forms of Entamoeba histolytica/dispar
Vegetative forms of Entamoeba histolytica/dispar
Credit : Parasitology – Faculty of Medicine Necker Paris
JF Pays - http://www.cdanofel.fr

Amoebiasis

This is an endemic, common and sometimes fatal disease found in the hot and humid regions of the globe, linked to faecal contamination and to poor hygiene conditions.

The parasite: Entamoeba histolytica is responsible in the conventional "amoebic dysentery” form; other forms with reduced symptomatology can occur and the carrier is often asymptomatic - often the case in temperate countries.

The diagnosis is performed by the direct examination of freshly produced stools in the laboratory, for the detection of the vegetative pathogenic forms and of the cysts, after applying concentration techniques. It is a difficult microscopic examination requiring staff who have been trained to make the distinction between Entamoeba histolytica and other non-pathogenic commensal amoeba, living in the digestive tract of humans.

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