Trypanosoma cruzi
(American trypanosomiasis - Chagas’ Disease)
Images: http://www.k-state.edu/parasitology/625tutorials/Kinetoplastids01.html
Life
cycle of American trypanosomiasis:
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NOTE: To view the article with Web enhancements,
go to: Blood Donor
Screening for Chagas Disease --- United States,
2006-2007 MMWR. 2007;56(7):141-143. ©2007 Centers
for Disease Control and Prevention (CDC) Posted 03/09/2007
ContentChagas disease, a zoonotic
disease caused by the bloodborne parasite Trypanosoma cruzi,
affects an estimated 11 million persons throughout much of Chagas disease has an acute stage, typically
asymptomatic or with mild symptoms (e.g., fever, malaise, swelling at the
site of innoculation and lymphadenopathy)
during the first 6-8 weeks after infection. If not treated, infection is lifelong with low-level, intermittent parasitemia.
The majority of infected persons remain asymptomatic in the chronic
indeterminate phase (i.e., a prolonged period of clinically silent infection
that follows acute primary infection). However, an estimated 30% will have
onset of chronic symptomatic disease, usually decades after the initial
infection, with cardiac manifestations (e.g., cardiomyopathy,
arrhythmias, and sudden death) or gastrointestinal involvement (e.g., megaesophagus or megacolon). In
the United States, vector-borne transmission of Chagas
disease is rare.[2]
However, one study revealed an increasing Chagas seroprevalence among blood donors in Los Angeles County,
California, from 1996 (one in 9,850 donors) to 1998 (one in 5,400 donors).[7] In
1991, a questionnaire was introduced to screen blood donors; those reporting
a history of Chagas disease are deferred, but most
persons with Chagas disease likely are unaware of
their infections. Seven cases of transfusion-associated transmission have
been documented in the United States and Canada during the past 20 years; all
occurred in immunosuppressed recipients.[3-6]
Because acute infections often are asymptomatic and the level of awareness of
Chagas disease among clinicians is low, cases of
transfusion-associated transmission can go undetected. In
2005, a new commercial test for blood-donation screening for Chagas disease was developed. The test, manufactured by
Ortho-Clinical Diagnostics (Raritan, New Jersey), is an enzyme-linked immunosorbent assay (ELISA) that uses epimastigote
lysate antigens for detection of antibodies to T.
cruzi in serum and plasma.[8] In
clinical trials evaluating the test, including the American Red Cross study,
blood donor specimens with initially reactive results were retested twice and
considered repeat reactive if one or both of the repeat tests were reactive.
Repeat reactive specimens from the clinical trials underwent further testing
using a radioimmunoprecipitation assay (RIPA);
those with positive RIPA results were considered confirmed positive. However,
FDA has not licensed a supplemental test as a confirmatory assay in blood
donation screening for T. cruzi antibodies. After
a clinical trial in 2005 with approximately 40,000 blood donors resulted in
only one repeat reactive specimen (which tested negative with RIPA),[8] the
American Red Cross conducted a larger study of the new screening assay in
areas where Chagas was expected to be more
prevalent. The study was conducted in three collection facilities of the
American Red Cross, including the Southern California Region ( A
total of 148,969 blood-donation specimens were tested; 63 specimens from 61
donors were repeat reactive for T. cruzi antibodies (approximately one in 2,365
donations). Among the 61 donors with repeat reactive speciments,
40 (66%) were male; the age range was 17-84 years, with a mean age of 47
years and a median of 50 years. Of the 63 repeat reactive specimens, 50 (79%;
one in 1,993 donations) were collected from the On
December 13, 2006, based in part on preliminary results from the American Red
Cross study, FDA licensed the Ortho T. cruzi
ELISA Test System to screen blood donors in the Reported by: SL Stramer,
PhD, American Red Cross, Editorial NoteFindings
from the American Red Cross study described in this report provided evidence
to support FDA approval of the first blood donor screening test for Chagas disease in the The
AABB (formerly known as the American Association of Blood Banks) has issued
recommendations to its member facilities regarding how to use the new test.*
AABB recommends that all components from blood donations that are repeat
reactive by the ELISA test should be quarantined and removed from
distribution, and the donor should be deferred from making donations
indefinitely. Recipient tracing should be conducted to identify and test
recipients of blood components collected previously from donors who are
confirmed positive (i.e., repeat reactive by ELISA and positive by RIPA).
AABB also suggests testing at-risk family members of donors who are confirmed
positive or family members with a similar history of exposure to vectors in
an endemic area (e.g., the children of seropositive
women). Deferred donors, at-risk family members, and potentially infected
recipients should be referred to health-care providers for evaluation and
management. Screening
blood donations for T. cruzi antibodies can
identify persons with previously undiagnosed Chagas
disease and further enhance the safety of the For
clinical purposes, no single laboratory test is adequately sensitive and
specific to diagnose Chagas disease. Diagnosis
generally is made by using at least two different serologic tests (e.g.,
diagnostic ELISA tests, immunofluorescence assay,
or indirect hemagglutination)[1] and by
considering clinical findings and exposure risk. Clinical diagnostic testing
for Chagas disease is available through commercial
laboratories and the Division of Parasitic Diseases (DPD) at CDC. After
diagnosis, health-care providers should conduct a thorough clinical
evaluation to determine the stage of disease, develop an appropriate
treatment plan, and provide information regarding prognosis. CDC is preparing
guidance for the clinical evaluation, staging, management, and treatment of
patients with Chagas disease. Cases
of Chagas disease likely will be increasingly
identified as a result of screening blood donors for infection with T. cruzi. In addition, requests for diagnostic testing
might become more frequent as awareness of Chagas
disease increases among clinicians and the general public. Most identified
cases likely will represent chronic infections that were acquired years
earlier. Chagas treatment options are limited and are most
effective during the acute stage of infection. However, increasing evidence
suggests that treatment of persons with chronic infections can result in seroreversion and prevent progression of cardiac
morbidity.[1]
Treatment of women of childbearing age with Chagas
disease can decrease the risk for congenital transmission. Antitrypanosomal medication in the Questions
regarding laboratory diagnosis, evaluation, and management of Chagas disease can be posed to DPD by telephone,
770-488-7775. Additional information regarding Chagas
disease is available at
http://www.cdc.gov/ncidod/dpd/parasites/chagasdisease/default.htm. * Available at
http://www.aabb.org/content/members_area/association_bulletins/ab06-08.htm. References
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Phylogeny: Order Kinetoplastida
Preferred
definitive hosts: Humans
Reservoir
hosts: Dogs, cast,
opossums, armadillos, wood rat
Intermediate/vector
hosts: Triatoma bugs in
Rhodnius prolixus in
northern South
Geographical
location: Central and
Organs
affected: Lymph node,
nervous tissue, heart muscle
Symptoms
and clinical signs: Swelling of lymph nodes,
progressive
deterioration of
nervous
tissue, resulting in loss
of
strength, nervous disorders,
heart
failure, megaesophagus or
megacolon
Treatment: No effective drug
From the November 18, 2003 issue
of the New York Times:
Rare Infection Threatens to
Spread in Blood Supply By DONALD G. McNEIL Jr.
A
parasitic infection common in Latin America is threatening the
The
infection, Chagas disease, is still rare in this
country. Only nine cases are known to have been transmitted by transfusion or
transplant in the
But
hundreds of blood recipients may be silently infected, experts say, and there
is no effective treatment for them. After a decade or more, 10 to 30 percent of
them will die when their hearts or intestines, weakened by the disease,
explode.
Chagas
is still little known in the
Experts
expect it to become better known as new tests are developed.
"I
wouldn't say that it's as rare as hen's teeth, but it's rare," said Dr.
Ravi V. Durvasula, a Chagas
expert at the Yale School of Public Health. "It's one of the top threats
to the blood supply, but it's an emerging threat."
Because
the disease is most common in rural areas from southern
Across
the
But
in 1998 in
No
more recent study of the blood supply has been done.
The
only routine screening for Chagas now is in the
standard set of questions asked of donors — whether they come from or have
visited a country where Chagas is endemic and whether
they ever slept in a thatched hut.
But
that often isn't reliable, said Dr. Louis V. Kirchhoff, a professor at the
Since
1989, several advisory panels to the United States Food and Drug Administration
have recommended that all donated blood be screened for Chagas.
But no test has been approved yet.
Last
year, the F.D.A. invited diagnostics companies to create one, and the two
largest, Abbott Laboratories and Ortho-Clinical Diagnostics, are trying. But
representatives of the companies said they were under little deadline pressure.
Abbott's test may be ready next year.
Little
sense of urgency exists because "there are always new things that come
up," Dr. Leiby said. Hepatitis and AIDS were
followed by mad cow disease,
Mary
Richardson, a spokeswoman for Ortho, which hopes to have a test by 2005, added:
"Clinical trials take time. There's only so much speeding up you can
do."
Nonetheless,
she added, "the F.D.A. feels it's the next biggest threat."
An
F.D.A. spokeswoman said her agency did not like to rank all the threats to the
blood supply — including hepatitis, AIDS and West Nile virus — but reiterated
that "we would certainly recommend a Chagas test
if one is developed."
Prevalence
rates in Latin America vary widely, from 25 percent in
It
is not found on Caribbean islands like Puerto Rico, the
In
some countries, it is a serious threat to the blood supplies; in one Bolivian
city, half of the blood was infected.
About
30 tests are used in different countries, but none meet F.D.A. accuracy
standards. Some Latin American blood banks disinfect with gentian violet, but
it is unpopular because it gives recipients a purplish tinge.
The
disease is named for Carlos Chagas, the Brazilian
doctor who described it in 1909. It is caused by a protozoan, Trypanosoma cruzi, which infects
humans in a particularly disgusting way. Reduviids,
also called kissing or assassin bugs, drop down from the thatch, follow the
trail of carbon dioxide to the mouths of sleeping humans and suck their blood.
They leave behind a protozoan-laden drop of feces, which the sleeper often
inadvertently rubs into the itching wound.
Charles
Darwin may have been infected on his travels; he suffered with Chagas symptoms for many years in
There
is no vaccine and no effective treatment. The first phase, which starts within
weeks of infection, may include fever and swollen glands, liver or spleen, but
is rarely fatal except in infants and in adults with compromised immune
systems. It is often misdiagnosed.
The
disease can then lie dormant for 10 to 30 years, then
kill suddenly as weakened organs rupture.
The
failure of the blood industry and its regulators to develop a test since it was
endorsed by a Blood Products Advisory Committee in 1989 seems to be a
combination of bureaucratic inertia and divided responsibility for such a
decision. Blood banks cannot use a test that the F.D.A. has not approved. The
agency usually defers to its advisory committees, which have many experts from
blood banks as members.
"It's
a political process that is not always fully engaged," said Dr. Stuart J.
Kahn of the Infectious Disease Research Institute, a
Dr.
Hira Nakhasi, director of
transfusion-transmitted diseases at the F.D.A., agreed that neither the blood
banks nor his agency had been very aggressive. Things tended to move when
"the public and media put pressure on," he said.
Cost
concerns made blood banks hesitant, Dr. Kirchhoff said. It may cost $50 million
to $100 million a year to screen the whole
Although
perhaps 120 Americans a year get infected blood, he said, between 70 and 90
percent will not become seriously ill, and few of those who do will live long
enough to die of Chagas.
Most
transfusion recipients are fairly sick, and half die of other causes within two
years anyway.
But
he pointed out that the risk was growing rapidly. Census figures show that net
immigration from
Meanwhile,
blood banks increased their appeals to Hispanics in the 1990's, under extra
pressure when mad cow disease eliminated donors who had made long visits to
Interest
in Chagas seems to be growing, Dr. Kahn said, because
breakthroughs in biogenetics make it easier to attack diseases and because the
interest of the Bill and Melinda Gates Foundation in third world health
"put a lot of diseases up on the radar screen."