Page 2578 - Hematology_ Basic Principles and Practice ( PDFDrive )

Chapter 158 Hematologic Aspects of Parasitic Diseases 2301

seen, linked to form a tetrad or, colloquially, a “Maltese cross.” a conservative approach has been taken, and all donors who have
However, at low parasitemia, Babesia parasites may easily be mistaken visited the northeastern United States between May and October are
for ring-stage forms of P. falciparum. Moreover, false-positive sight- excluded, in addition to the standard criteria of screening out febrile
ings of Babesia spp. may be caused by platelets, nonspecific stain and/or anemic donors.
deposit overlying erythrocytes, or indeed other intraerythrocytic
inclusions.
Parasitemias are variable, and in B. microti infections may be low EOSINOPHILIA
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or transient. In symptomatic infection, parasitemias typically range
from less than 1% to 10% and rarely much higher, more than 70%, Eosinophilia may be caused by a wide variety of systemic diseases and
in severe infections. Low-level parasitemias may be detected by inocu- parasitic infections. The association with parasitic disease is through
lation of the blood into susceptible animals, including the golden part of the Th2 T-cell response stimulated by helminths (worms), filaria,
hamster (Mesocricetus auratus), but this is not routinely available. and cestodes. In general, protozoan infections, such as malaria, amebia-
An IFAT using crude antigen is available in the United States sis, and giardiasis, are not associated with eosinophilia. However, case
through the Division of Parasitic Diseases at the Centers for Disease reports do exist suggesting that isosporosis due to infection with Isospora
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Control and Prevention. Titers greater than 1 : 64 are regarded as belli, toxoplasmosis, and infection with Dientamoeba fragilis can cause
positive and have been reported to be 88% to 96% sensitive and 90% eosinophilia.
to 100% specific. The rise in absolute eosinophil count depends on the degree of
PCR analysis is the most useful method of detecting or confirming tissue invasion and is therefore modest with tapeworms and adult
low levels of parasitemia, and it can also be used to monitor treat- roundworms resident in the bowel but much higher where invasion
ment. Real-time PCR assays target the Babesia 18S rRNA gene and, occurs, for example, with Toxocara canis or filaria. Some parasites,
with use of a fluorescent probe, can distinguish B. microti from B. such as ascariasis (roundworms) and clonorchiasis, have migratory
duncani. 278,279 PCR tests may be positive in the absence of positive larval stages.
serology in immunocompromised patients and/or those patients who The differential diagnosis of eosinophilia in those who have lived
have received rituximab, whereas serology for Babesia spp. may be in tropical areas is therefore wide. Evaluating the patients must begin
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positive in the absence of positive microscopy or positive PCR tests by establishing the degree of eosinophilia (minimal, <1 × 10 /L;
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in asymptomatic individuals who were infected but who have cleared moderate, 1 to 3 × 10 /L; high, >3 × 10 /L), the relation to travel
the infection spontaneously. (where necessary), and the presence of symptoms. A wide range of
systemic diseases are associated with eosinophilia, and the eosinophil
count may be high in drug allergy, pulmonary infiltrate with eosino-
Treatment philia, and vasculitides.
Many B. microti infections are self-limiting, and therapy is used for
moderate or severe disease. 257,280–282 The combination of atovaquone Eosinophilia in Travelers
and azithromycin is the treatment of choice for mild to moderate
illness, whereas clindamycin and quinine and exchange transfusion Evaluating the cause of eosinophilia in travelers to tropical areas
are indicated for severe disease. where many parasitic diseases are endemic requires a systematic
B. divergens infections are often fatal in splenectomized patients, approach to narrow down likely possibilities by considering existing
and therapy is based on somewhat limited experience. Three cases systemic diseases that may cause eosinophilia (particularly allergy,
have been treated successfully with large-volume exchange transfu- drug ingestion and autoimmune disease, vasculitis, or arthritis); the
sions (two to three blood volumes) and intravenous clindamycin and areas visited; duration of stay; and history of exposure to soil-
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oral quinine. This regimen of clindamycin and intravenous and transmitted nematodes, freshwater potentially infected with schisto-
oral quinine gives the best chance of success in the absence of ran- somiasis, and rural areas where loiasis, onchocerciasis, and hydatid
domized controlled trial evidence. disease may be contracted.
Exchange transfusion has been suggested as a useful adjunctive Physical examination may show subcutaneous swellings associated
treatment if the parasitemia rises to greater than 10% and/or in with filaria or hepatosplenomegaly consistent with schistosomiasis,
severely ill patients. B. divergens infections can run a rapidly progres- hydatid disease, or toxocara. Laboratory examination requires a
sive course, and early exchange transfusion should be considered. A stepwise approach, given the breadth of the differential diagnosis
prolonged course of treatment may be required in immuno- (Table 158.4). The details of specific parasitologic tests are beyond
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compromised patients. The parasite and hemoglobin levels should the scope of this chapter, and detailed investigation would certainly
be regularly monitored during treatment. require consultation with colleagues in infectious diseases.
Serologic testing and PCR testing of seropositive cases may be Some parasitic causes of eosinophilia may not be diagnosed during
helpful in making a diagnosis. An indirect IFAT is available for B. the incubation period, because larval stages of nematode worms may
divergens and B. microti. The IFAT titer is usually greater than 1 : 64 cause eosinophilic drug migration, but eggs will not be excreted in
in acute infection. The reported sensitivity of the B. microti IFAT is stools for many months. Moreover, filarial infections do not produce
88% to 96%, and its specificity is 90% to 100%. Antimalarial detectable parasites in blood or skin for many months after
antibodies may cross-react in this test. exposure.
In immunocompromised patients or those about to receive a
diagnosis, eosinophilia may be crucial, given the risks of giving
Babesia and Transfusion-Transmitted Infection immunosuppressive therapy such as chemotherapy or hematopoietic
stem cell or solid organ transplant to a patient with a chronic para-
Babesia infection poses a substantial and increasing threat to the sitologic infection. Patients with undiagnosed eosinophilia and pos-
blood supply. Between 150 and 170 cases of transfusion-transmitted sible exposure to Strongyloides should be given an empirical course of
babesiosis have been reported from 1979 to 2009, with 12 recorded treatment.
fatalities. 285–287 There are no approved serologic screening tests for
donors, and prevention of transfusion-transmitted babesiosis in the
United States requires screening donors about a previous history of OTHER PARASITIC DISEASES
babesiosis and excluding patients with fever and a low hematocrit
level. The scale of infection can be gauged from surveys of blood Many parasitic diseases cause some minor hematologic disturbance.
donors in the northeastern United States, where 1% to 2% of donors A few may present with distinct hematologic features or indeed
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in some panels are seropositive for Babesia. In the United Kingdom, syndromes.