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[08/25/2004]
 Diagnostic strategy |
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 The normal microscopic diagnostic techniques are the thick
blood films and especially the thin film blood smear test. The
reliability of these examinations is conditioned by their
successful technical performance. The routine use in medical analysis laboratories of the majority
of the new parasitological diagnostic techniques may not be
envisaged for a number of years yet. Only the QBC-Malaria Test® and
the HRP2 based tests, specifically
for Plasmodium falciparum, currently
present any practical interest.
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The QBC-Malaria Test® remains the most sensitive parasitologic
test: it should retain its place in the front line. HRP2 detection
should be associated with it in the event of positive reaction,
systematically for a poorly trained biologist, and when parasitemia
is low.
When the QBC-Malaria Test® is negative, HRP2 detection is only of
interest if a search finds signs of recent antimalarial treatment:
evidence of HRP2, in this case, provides proof of the plasmodium at
the origin of the disease.
In a susceptible population, if the QBC-Malaria Test® is not
available, the thin blood film smear– HRP2 test combination is
necessary.
HRP2 based tests are adapted for use in a precarious or isolated
situations. In this case, it should be considered as a standby test
in the absence of medical and/or biological assistance.
The presence of rare false positives and the existence of other
plasmodium species prohibit, while awaiting multi-species tests,
the isolated and exclusive use of HRP2 based tests for the
biological diagnosis of malaria. | Diagnostic strategy in laboratories equipped with a microscope and QBC-Malaria Test® equipment
Respective interest of the 3 tests: QBC Malaria Test® - parasitological diagnosis of the Plasmodium of
human interest
- parasitological diagnosis of other sanguicolous parasites
(trypanosomes, filariae, etc.)
Search for the HRP2 antigen: - identification argument for Plasmodium falciparum
when a Plasmodium is shown to exist by the QBC
Malaria Test®
- elimination of false positives linked to the reading of the QBC
Malaria Test® by staff not familiar with parasitological
diagnosis
- argument for incriminating Plasmodium
falciparum when a patient is seen "a second time around"
after self-treatment or a presumptive treatment which lowered the
parasitic density below the detection threshold of the
parasitological tests.
- Possibility of remote supervision in time and
space
Smear test - evaluation of the parasitic density of Plasmodium
falciparum
- parasitological diagnosis of
the Plasmodium of human interest and
other sanguicolous parasites
- indirect hematological signs of malaria infection
(hematological syndrome associating relative thrombopenia and the
presence of activated lymphocytes)
- possibility of remote supervision in time and space
| Diagnostic strategy in laboratories equipped with a microscope
Respective interest of the two tests: Smear test - evaluation of parasitic density of Plasmodium
falciparum
- parasitological diagnosis of
the Plasmodium of human interest and
other sanguicolous parasites
- indirect hematologiqal signs of malarial infection
(hematological syndrome associating relative thrombopenia and the
presence of activated lymphocytes)
- possibility of remote supervision in time and
space
Search for the HRP2 antigen: - confirms the identification of Plasmodium
falciparum, in particular when the parasitic density is
too low for a parasitological identification on a thin blood film
smear
- argument to incriminate Plasmodium
falciparum when a patient is seen "a second time around"
after a self-treatment or a presumptive treatment which lowered the
parasitic density below the detection threshold of the
parasitological tests
- possibility of remote supervision in time and
space
| Diagnosis in the field
Interest of the test: Positive test - major argument to confirm the presence of trophozoites
of Plasmodium falciparum, without being able to
differentiate between a malaria infection and a malaria disease
which, in these circumstances, has no repercussions on the conduct
to be taken.
- argument for the adaptation of the presumptive treatment of
malaria in relation to the local level of resistance
of Plasmodium falciparum to
antimalarial drugs.
- argument for judging the urgency of sanitary
evacuation
- possibility of remote supervision in time and
space
Negative test - strong argument against malaria disease or malaria infection
by Plasmodium falciparum.
This strategy should be integrated into a strategy of standby
treatment and imposes a medical consultation as soon as possible.
It does not dispense the performance of a blood smear test which
would be read later. A negative test does not dispense the patient
undergoing systematic treatment. |
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