APPENDIX A
Microscopic Procedures for Diagnosing Malaria
To establish the diagnosis of malaria, a blood smear must be
prepared
from fresh finger-prick blood (Figure_A1 and Figure_A2). *
The thin
smear is fixed in methanol before staining; the thick smear is
stained
unfixed. Many hospitals have a Wright-Giemsa stain available, which
is
acceptable; however, Wright stain alone will not reliably stain
Plasmodium
parasites. For best results, the smear should be stained with a 3%
Giemsa
solution (pH of 7.2) for 30-45 minutes. In P. falciparum
infections, the
parasite density should be estimated by counting the percentage of
red blood
cells infected_not the number of parasites_under an oil immersion
on a thin
film.
Thick blood smears are more sensitive in detecting malaria
parasites
because the blood is concentrated, allowing a greater volume of
blood to be
examined. However, thick smears are more difficult to read, and
thin smears
may be preferred by laboratories that have limited experience.
Plasmodium
parasites are always intracellular, and they demonstrate, if
stained
correctly, blue cytoplasm with a red chromatin dot. Common errors
in reading
malaria smears are caused by platelets overlying a red blood cell,
concern
about missing a positive slide, and misreading artifacts as
parasites.
Persons suspected of having malaria but whose blood smears do not
demonstrate
the presence of parasites should have blood smears repeated
approximately
every 12-24 hours for 3 consecutive days. If smears remain
negative, then the
diagnosis of malaria is unlikely. For rapid diagnosis, make the
thick and
thin films on separate slides. Air dry the thin film, fix it with
methyl
alcohol, and immediately stain it. If no parasites are found on the
thin
film, wait until the thick film is dry and examine it for organisms
that may
not have been detected on the thin preparation.
In Figure_A1 and Figure_A2, the hands are shown
ungloved to
better illustrate their placement during the procedures. However,
wearing
gloves while processing blood specimens is recommended to prevent
transmission of bloodborne pathogens (MMWR 1988;37:377-82, 387-8
and
MMWR 1987;36{no. S2}).
Disclaimer
All MMWR HTML versions of articles are electronic conversions from ASCII text into HTML. This conversion may have resulted in character translation or format errors in the HTML version. Users should not rely on this HTML document, but are referred to the electronic PDF version and/or the original MMWR paper copy for the official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.
**Questions or messages regarding errors in formatting should be addressed to mmwrq@cdc.gov.
