Manual of basic techniques for a health laboratory - libdoc.who.int

4. Parasitology 171Cephalic spaceAnal poreR 1 cellWith a sheathWithout a sheathSheathR 4 cell R 3 cell R 2 cellNerve ring Excretory pore Excretory cellMicrofilariaeIn bloodIn skinWith sheath Without sheath Without sheathTail swollen with2 distinct nuclei,cephalic space twiceas long as broadNuclei extendingto tip of tailTail uniform,cephalic spaceas long as broadNuclei not extendingto tip of tail,cephalic spaceas long as broadNuclei extendingto tip of tail,tail bluntNuclei not extendingto tip of tail,small, thin filariaNuclei extendingto tip of tail,small, thin filaria,hooked tailNuclei not extendingto tip of tail,thick filariaBrugiamalayiLoa loaWuchereriabancroftiMansonellaperstansMansonellaozzardiMansonellastreptocercaOnchocercavolvuluswho 90589Fig. 4.128 Microfilariae found in humansR 1, R 2, R 3, R 4: rectal cells.teristically devoid of nuclei and is called the cephalic or head space; it may be shortor long.As you look from the anterior to the posterior end of the body you will see additionalspaces and cells that serve as anatomical landmarks. These include the nervering, excretory pore, excretory cell and anal pore. In some species an amorphousmass called the inner body and four small cells (known as rectal cells) can be seen.Some of these structures and their positions are useful in identifying the species.Other useful features include the shape of the tail and the presence or absence ofnuclei within it.Table 4.8 summarizes the features of common human filarial parasites that areused in their identification.Note:●●Sometimes the microfilariae of the periodic strain of Brugia malayi lose theirsheath.Identification of species can be difficult and mistakes are frequently made. Theguidelines for the identification of microfilariae given above and those that appearin most textbooks make identification seem deceptively simple. Sometimesit is difficult to see the sheath. At other times, the nuclei do not appear in theircharacteristic position at the tip of the tail. It is good practice to examine severalmicrofilariae carefully, before deciding on their species. If a systematic study ismade of all the characteristics mentioned above, it should be possible to identifywith certainty the species observed. The identification must not be based on asingle characteristic, but on all the features taken together.