Page 2573 - Hematology_ Basic Principles and Practice ( PDFDrive )

2296 Part XIII Consultative Hematology

Patients require prolonged specialist follow-up over 2 years,
including blood and CSF examination for parasites. A rising CSF
leukocyte count is a good guide to CSF relapse even in the absence
of a demonstration of parasites. 211
In treatment for early-stage T. b. rhodesiense, suramin is given as
five intravenous injections (20 mg/kg, up to 1.5 g) on days 1, 3, 6,
14, and 21. Adverse effects include fever, proteinuria, paresthesia,
pruritus, and urticaria. Hemolytic anemia, agranulocytosis, and
thrombocytopenia have been reported as side effects. Combination
therapies of the antitrypanosomal drugs nifurtimox and eflornithine,
and also the combination of melarsoprol and nifurtimox, are under
trial for the treatment of second-stage disease to increase the efficacy
of treatment and to overcome increasing drug resistance. 212

African Trypanosomiasis as a Transfusion-
Transmitted Infection

Trypanosomiasis is a transfusion-transmitted infection. Asymptomatic
or early-stage patients with trypanosomiasis are clearly a threat to the
blood supply. Patients are excluded in the United Kingdom, Europe,
and North America by the general donor queries relating to fever and
constitutional symptoms. In endemic areas, exclusion of infected
donors with early-stage T. b. gambiense is clearly a more complex
problem because patients may be asymptomatic for long periods if the
degree of risk is unknown and no specific screening procedures are in
place. In summary, hematologic involvement in trypanosomiasis is
peripheral to the main two features of the disease, but examination of
lymph node aspirates, blood, and CSF is essential for diagnosis and
management of the disease. Occasionally, patients may become
severely ill and have complex hematologic abnormalities. In endemic
areas, trypanosomiasis may pose a risk to the blood supply. Fig. 158.13 DISTRIBUTION OF CHAGAS DISEASE. Human infection
is endemic in parts of Central and South America from the Andes to the
AMERICAN TRYPANOSOMIASIS Atlantic coast and as far south as the latitude of the River Plate (Río de la
Plata), shown here in green. Two major intergovernmental programs were
started in 1991 to eliminate domestic vectors by a combination of spraying
American trypanosomiasis (or Chagas disease, named after the Brazil- residual insecticides in houses, the use of insecticidal paints, and the deploy-
ian parasitologist Carlos Chagas) is caused by infection with Trypano- ment of fumigant canisters. The countries covered in the two initiatives, the
soma cruzi. This flagellated protozoan is transmitted by the triatomine second of which started in 1997, are shown in the figure. The latter program
insects, the reduviid bugs. The acute phase of infection is character- instituted universal blood screening to avoid transmission from infected
ized by fever and high parasitemia, followed by a chronic phase with blood donors. Remarkable progress has been made. Transmission (by the
positive serologic results and low parasitemia but with end-organ major vector Triatoma infestans) was eliminated in Uruguay by 1997 and in
damage to the heart, peripheral nervous system, and gastrointestinal Chile by 1999. Major reductions in transmission but, to date, not complete
tract, causing a chronic cardiomyopathy, neuropathy, megaesophagus, control have also been reported in other endemic countries. (Southern Cone
and megacolon. Initiative; Andean and American Initiative areas.)

Epidemiology
Parasitology
Chagas disease may occur in the Americas from the southern United
States to Chile, but the highest prevalence is in Bolivia and Brazil T. cruzi parasites are from the order Kinetoplastida and family
(Fig. 158.13). There are approximately 10 million seropositive Trypanosomatidae, existing as infective trypomastigotes in the
people in Latin America, and the number of people infected and bloodstream of vertebrate hosts. These organisms are fusiform cells,
213
the incidence of new infection are falling rapidly. Infections are 10 to 20 µm in length, with a distinctive large posterior kinetoplast
found not only in rural areas but also in recent immigrants to urban containing mitochondrial DNA. They can enter phagocytes, muscle
214
areas in North and South America and to Europe. It is estimated and nerve cells, and a wide variety of other cell types and here
that approximately 100,000 seropositive individuals are living in the transform to oval amastigotes 2 to 5 µm in diameter. They multiply
United States. True, endogenous (autochthonous) infection in the by fission, and amastigotes develop into mature trypomastigotes
United States is vanishingly rare, but human infections have been released on rupture of the cell to begin a new cycle of invasion and
reported in Texas, California, Tennessee, and Louisiana. Visitors to multiplication.
endemic areas are only rarely infected, with only a handful of cases Slender, highly motile and broader, less motile trypomastigotes
being recorded in intrepid travelers spending time in traditional have been distinguished, which may be relatively more infective for
housing in rural areas. The range of reservoir hosts and species of host cells and insects, respectively. The species of triatomine bugs that
triatomine bugs transmitting infection is wide. commonly transmits disease is able to cause extensive infestation of
215
Parasites may also be transmitted by blood transfusion (see later), simple mud-and-wattle thatched houses in rural Latin America,
vertically from mother to child by breastfeeding, organ transplant, where Chagas disease is a disease of poverty associated with poor
and rarely by sexual transmission. Several outbreaks in Brazil have housing. These bugs are infected by circulating trypomastigotes after
been reported after contamination of food by triatomine bugs and taking a blood meal on sleeping victims. In the midgut, trypomasti-
their feces. Laboratory infection by accidental ingestion or inocula- gotes transform into epimastigotes and multiply by fission before
tion of parasites is well recorded. migrating to the hindgut, where they develop into metacyclic