Page 2572 - Hematology_ Basic Principles and Practice ( PDFDrive )

Chapter 158 Hematologic Aspects of Parasitic Diseases 2295

or thin Giemsa-stained blood films are made as for malaria diagnosis. this variant antigen. Further versions of this assay have been developed
The sensitivity may be increased by microcentrifugation. 196 to use dried blood on filter paper, namely the micro-CATT and
More recent methods used to detect the low levels of parasitemia macro-CATT, but these are less sensitive than the whole-blood assay.
seen in T. b. gambiense include quantitative examination of the buffy In T. b. gambiense, serologic tests are not widely available, and
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coat using acridine orange and small-scale ion-anion exchange direct examination of blood and CSF for parasites is the first line of
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chromatography. Erythrocytes are retained in the column, whereas investigation. The card indirect agglutination trypanosomiasis test
trypanosomes are eluted and are visible after concentration by cen- (TrypTect CIATT) can detect circulating antigens in T. b. gambiense
trifugation. The sensitivity of detection with these methods ranges and T. b. rhodesiense infection by latex agglutination. The sensitivities
4
2
from 10 /mL for wet smears to 10 /mL for ion-exchange columns of the test are 95.8% for T. b. gambiense and 97.7% for T. b. rhodesiense,
and centrifugation. In T. b. rhodesiense, examination of the blood is and therefore significantly higher than that of lymph node puncture,
more likely than aspiration of lymph nodes to yield a positive result. microhematocrit centrifugation, and CSF examination after single-
Inoculation of the aspirate or samples into susceptible animals or and double-centrifugation. 204
in vitro culture has been used to detect low-level parasitemia. Mice A rapid latex agglutination test (LATEX/T. b. gambiense) contains
and rats were used to detect T. b. rhodesiense, whereas the multimam- a mixture of three variable surface antigens of the bloodstream form
mate rat (Mastomys natalensis) and guinea pigs were used for T. b. of trypanosomes and has been used to detect antibodies in patients
gambiense. PCR of the 18S rRNA gene can detect parasites with infected with T. b. gambiense. At 1 : 16 serum dilution, test specificity
sensitivity similar to that of parasitologic and serologic methods. 199 was 99%, whereas sensitivity ranged from 83.8% to 100%, depend-
ing on the geographic origin of the samples. The test sensitivity falls
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to 66% for CSF samples from second-stage patients. A rapid latex
Cerebrospinal Fluid agglutination test, LATEX/IgM, for the semiquantitative detection
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of IgM in CSF is available. Finally, immunofluorescence assays and
Trypanosomes may be found in the CSF as disease progresses, ELISA tests for antibodies using whole parasites are highly sensitive
although a double-centrifugation technique may be required to and specific, although they are less practical for mass screening. A
demonstrate organisms. In this technique, 5 to 10 mL of CSF is series of new approaches is being evaluated for control and elimina-
centrifuged, and the sediment is taken up into a capillary tube and tion of trypanosomiasis, including tiny targets for tsetse fly control,
recentrifuged before the capillary tube is examined under a coverslip use of RDTs, and oral treatment with fexinidazole or oxaboroles. 207
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(Fig. 158.12). Specific molecular markers for this stage of CNS
disease are being sought by proteomic analysis of the CSF.
Treatment
Serology Treatment of trypanosomiasis depends on the subspecies of trypano-
some present. The drugs may be difficult to source and are toxic, so
Serologic tests are used for passive population screening in control treatment requires expert help.
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programs (for review, see Chappuis et al ). A Card Agglutination Early-stage T. b. gambiense may be treated with pentamidine for
Test for Trypanosomiasis (CATT) is robust and can be used without 14 days (intravenously or more usually intramuscularly, 4 mg/kg/
extensive laboratory facilities. 202,203 The test contains freeze-dried day). Hematologic side effects include neutropenia, and more general
trypanosomes with the LiTat 1.3 variant antigens and can be obtained side effects include hypotension, hypercalcemia, hyperkalemia, renal
from the Institute of Tropical Medicine Antwerp (www.itg.be). It is failure, and hyperglycemia. Pentamidine will not cure CNS disease,
quite sensitive (>95%), but it lacks specificity owing to cross- and so examination of the CSF is required after initial treatment of
reactivities with animal Trypanosoma spp. Although useful as a patient the blood-stage disease.
screening test in a hospital for suspected cases of trypanosomiasis, the Eflornithine (α-difluoromethylornithine) for 14 days (IV;
predictive value for positive test results falls when screening popula- 100 mg/kg every 6 hours) is effective for CNS treatment for T. b.
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tions for active cases. It has nevertheless been reported to double the gambiense. It is a toxic drug suppressing DNA replication by inhibi-
number of active cases found. Some patients may have false-negative tion of ornithine decarboxylase and thus polyamine synthesis and
results for this test if they are infected by parasites that do not express DNA replication. It causes dose-dependent bone marrow suppression
with anemia, neutropenia, and thrombocytopenia in the majority of
patients. The effects are reversible and are rarely dose limiting. It is
effective neither in children nor in patients with coinfection with
HIV, where melarsoprol is required.
Melarsoprol is a trivalent organic arsenical compound and is more
toxic but cheaper than eflornithine. It is used in Africa for the treat-
ment of late-stage CNS trypanosomiasis. It is given as three daily
intravenous injections at a dose of 3.6 mg/kg up to 180 mg on two
occasions 1 week apart. If the CNS leukocyte count is greater than
3
20/mm , a further three injections are given 1 week later.
Melarsoprol causes a secondary encephalopathy in 5% to 10% of
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treated cases and is fatal in half of these. The incidence and severity
of encephalopathy may be reduced by concurrent administration of
prednisolone (1 mg/kg/day up to 40 mg) started 1 to 2 days before
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melarsoprol treatment. When steroids are used, it is necessary to
give patients antimalarial and antihelminthic therapy, especially if
Strongyloides stercoralis is present.
Prior treatment of blood-stage disease with pentamidine may
reduce antigen levels and possibly adverse events. Promethazine,
anticonvulsants, and antiemetics are important adjunctive treatments
before commencing CNS therapy.
Polyneuropathy occurs in 10% of cases treated with melarsoprol
Fig. 158.12 TRYPOMASTIGOTE OF TRYPANOSOMA BRUCEI and may be severe, causing quadriplegia. If neuropathy is suspected,
BRUCEI IN CEREBROSPINAL FLUID. A single organism is seen in this melarsoprol should be stopped immediately and thiamine (100 mg,
sample taken from cerebrospinal fluid filtered in a “minicolumn.” three times daily) given until symptoms subside.