whole blood samples. This applies in ma- 
laria, trypanosomiasis, and filariasis (with 
the exception of onchocerciasis ) . 
( 1 ) Blood films 
Citrated, oxalated, or clotted blood 
should not be used to make blood films 
except in emergencies. In thin films the 
blood is spread over a relatively large 
area in a thin layer; in thick films , it is 
concentrated in a small area. For rou- 
tine diagnosis, the thick film is prefer- 
able since it permits the examination 
of a large amount of blood. However, 
parasite morphology is more distinct 
and typical in a thin film. For this rea- 
son, a thin and thick film combination 
on the same slide is recommended. 
Thin films are prepared by pricking the 
ear or finger after the area has been 
cleansed with gauze, not cotton, soaked 
in 70% alcohol, and allowed to dry 
completely. A single drop of blood is 
deposited near one end of a slide and 
spread as though making a preparation 
for a differential count. Thick films are 
made by either touching the under sur- 
face of the slide to a fresh large drop of 
blood on the finger, without touching 
the skin, and rotating the slide to form 
a film about the size of a dime. Alter- 
natively, several drops of blood may be 
deposited close together near one end 
of the slide and puddled with the corner 
of a slide, applicator stick, or toothpick. 
The films are allowed to air dry in a 
horizontal position protected from dust 
and insects. Thin films dry rapidly but 
thick films require 8 to 12 hours. Prop- 
erly and improperly prepared films are 
shown in Figure 1. 
(2) Whole blood 
If concentration methods are to be used, 
blood is collected by venipuncture, and 
sodium citrate or heparin is added to 
prevent clotting. Aseptic technic is es- 
sential in the collection of the sample. 
Do not use preservatives since they may 
kill the organism and make cultivation 
or animal inoculation impossible. 
(3) Time of collection 
Time of specimen collection in malaria 
is important but less so than in filaria 
infections. Parasites are most numerous 
in malaria about midway between 
chills, but their morphology is some- 
what less characteristic. One specimen 
taken at this time and a second 5 to 6 
hours later is ideal. 
Because of the nocturnal periodicity in 
certain filaria infections, notably by 
Wuchereria bancrofti and Brugia ma- 
layi, the specimen should be taken be- 
tween 10 p.m. and 2 a.m. Infections 
with W. bancrofti or Wuchereria paci- 
fica in the southwest Pacific area exhibit 
no such periodicity. In Loa loa there 
is a diurnal periodicity, and specimens 
should be collected between 10 a.m. 
and 2 p.m. Blood collection should also 
be correlated with the stage of the in- 
fection. For example, Trypanosoma 
cruzi is found in the blood only during 
the acute, febrile stage of Chagas’ 
disease. The same is true for infections 
with Trypanosoma gambiense and Try- 
panosoma rhodesiense. 
b. Body fluid, aspirates, and biopsies 
Certain blood parasites are diagnosed by the 
examination of body fluids and tissues rather 
than by direct examination of blood. Thus, 
biopsies of liver, spleen, bone marrow, and 
lymph glands must be studied to demon- 
strate the parasite. This is true in leishma- 
niasis, filariasis (onchocerciasis), and some- 
times in malaria and trypanosomiasis. In 
some cases of onchocerciasis, tissue biopsies 
may reveal microfilariae when examination 
of skin from the nodule is negative. Localiza- 
tion of the nodules on the upper or lower 
part of the body influences distribution of the 
microfilariae and dictates selection of the 
biopsy site which may be the shoulder, calf, 
thigh, or another part of the leg. 
Aspirates of lymph glands or ulcerative skin 
areas are collected for diagnosis of leish- 
maniasis, trypanosomiasis, or filariasis. Cere- 
brospinal, hydrocele, pericardial, pleural, 
and peritoneal fluids may be used for the 
diagnosis of trypanosomiasis, filariasis, or 
toxoplasmosis. 
Handling of tissues or fluids depends on the 
examination to be made. If cultures or ani- 
mals are to be inoculated, asepsis should be 
practiced, and the media or animals should 
be inoculated as soon as possible after the 
specimen is collected. If inoculation is de- 
layed, the specimen should be stored in the 
refrigerator. 
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