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816 Part VI: The Erythrocyte Chapter 53: Hemolytic Anemia Resulting from Infections with Microorganisms 817

Decrease in Erythropoiesis hemolysis, hemoglobinemia, hemoglobinuria, and the passage of dark,
P. falciparum also decreases the erythropoietin response, resulting in almost black, urine. This disorder, also called blackwater fever, is no lon-
less erythropoiesis than expected for the degree of anemia, reticulocy- ger common. At one time it was seen frequently among Europeans in
topenia, and coincidentally striking dyserythropoiesis with stippling, Africa and in India, usually after quinine was given to treat malaria. The
cytoplasmic vacuolization, nuclear fragmentation and multinuclearity. event seems to be related to the intermittent use of antimalarials. 81
66
The inhibition of the erythroid response (anemia of chronic disease) is
secondary to release of the cytokines interferon-γ and tumor necrosis DIAGNOSTIC METHODS
factor-α, and the interleukin-10–to–tumor-necrosis-factor ratio, which
when low correlates with severe malarial anemia in children (Chap. 37). 66 Diagnosis of malaria depends upon demonstration of the parasites on
the blood film, or the presence of antigenic parasite proteins using rapid
detection tests (RDTs). Alternative techniques involve polymerase
82
BLACKWATER FEVER chain reaction (PCR) to demonstrate the appropriate DNA sequences
The fever associated with malaria, accompanied by rigors, headache, in the blood 83,84 or the use of automated hematology analyzers to iden-
abdominal pain, nausea and vomiting, and extreme fatigue, is charac- tify parasites as part of a routine complete blood count (CBC) investi-
teristically cyclic, varying in frequency according to the malaria type. gation. The morphologic differentiation of P. falciparum from other
85
Although classic periodicity is often absent, febrile paroxysms of P. forms of malaria, principally P. vivax, is clinically important as P. fal-
vivax malaria tend to occur every 48 hours; those of P. malariae infec- ciparum infection may constitute a clinical emergency. If more than
tion occur each 72 hours; and those of P. falciparum malaria, daily. 5 percent of the red cells infected contain parasites, the infection is
In the latter cases, the periodicity is the result the synchronization of almost certainly with P. falciparum. In an infection with this organism,
schizogony with schizont rupture occurring at regular intervals. It is rings are practically the only form of parasite evident on the blood film.
schizont rupture that accounts for the fever and associated symptoms. The finding of two or more rings within the same red cells is regarded
Falciparum malaria is occasionally associated with particularly severe as pathognomonic of P. falciparum (Fig. 53–1A and B). In nonimmune

A B

C D
Figure 53–1. A. Blood film from a patient with malaria caused by Plasmodium falciparum. Several red cells contain ring forms. Note red cell with
double ring form in center of the field, characteristic of P. falciparum infection. Note the ring form with double dots at the left edge of figure, sug-
gestive of P. falciparum infection. Note also high rate of parasitemia (~10 percent of red cells in this field) characteristic of P. falciparum infection.
B. Blood film from a patient with malaria caused by Plasmodium vivax. Note mature schizont. C. Blood film from a patient with Babesia microti infec-
tion. The heavy parasitemia is characteristic of babesiosis (approximately two-thirds of red cells infected). D. Blood film from a patient with Clostridium
perfringens septicemia. Few red cells evident as a result of intense erythrolysis. Neutrophil with two bacilli (C. perfringens). (Reproduced with permission
from Lichtman’s Atlas of Hematology, www.accessmedicine.com.)

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