2006, 44(4):1550. DOI:
J. Clin. Microbiol.
Thiam, Lamine Diakhaté and Antoine Gessain
Saliou Diop, Sara Calattini, Julienne Abah-Dakou, Doudou
Donors from Dakar, Senegal
Virus Type 1 (HTLV-1) and HTLV-2 in Blood
Epidemiology of Human T-Cell Leukemia
Seroprevalence and Molecular
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JOURNAL OF CLINICAL MICROBIOLOGY, Apr. 2006, p. 1550–1554
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Vol. 44, No. 4
Seroprevalence and Molecular Epidemiology of Human T-Cell
Leukemia Virus Type 1 (HTLV-1) and HTLV-2 in
Blood Donors from Dakar, Senegal
Saliou Diop,1Sara Calattini,2Julienne Abah-Dakou,1Doudou Thiam,1
Lamine Diakhate ´,1and Antoine Gessain2*
Centre National de Transfusion Sanguine, Ave. Cheikh Anta Diop, Fann, BP 5002 Dakar, Se ´ne ´gal,1and
Unite ´ d’Epide ´miologie et Physiopathologie des Virus Oncoge `nes, De ´partement Ecosyte `mes et
Epide ´miologie des Maladies Infectieuses, Institut Pasteur, 75015 Paris, France2
Received 24 October 2005/Returned for modification 13 January 2006/Accepted 20 January 2006
In 2002, human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 seroprevalence was 0.16% (8/4,900) in
blood donors from Dakar, Senegal. Most of the positive donors originated from the country’s southern region.
Seven donors were infected by HTLV-1 (of cosmopolitan subtype), and one was infected by HTLV-2. These data
highlight the problem of transfusion safety in this area where HTLV-1-associated lymphoproliferative and
neurological diseases are endemic.
Human T-cell leukemia virus type 1 (HTLV-1) is the etio-
logical agent of adult T-cell leukemia/lymphoma (ATL), trop-
ical spastic paraparesis/HTLV-1-associated myelopathy (TSP/
HAM), and other inflammatory disorders, including infective
dermatitis and uveitis (30). HTLV-1 is not a ubiquitous virus,
but its geographical distribution is mainly restricted to some
areas of high endemicity, including sub-Saharan Africa, South-
ern Japan, Central and South America, and some regions of
the Middle East and Melanesia (30). In some of these coun-
tries, as well as in some areas of low endemicity (e.g., the
United States, Canada, and a few European countries), public
health measures aimed at reducing HTLV-1 transmission and
dissemination have been taken in the last few decades. This
includes the screening of blood donors for the presence of
Sub-Saharan Africa is considered to be one of the largest
areas of endemicity for HTLV-1 infection, with an estimated 2
to 4 million HTLV-1-infected individuals. However, most of
the early sero-epidemiological studies performed in Africa ap-
plied Western blot criteria for HTLV-1 seropositivity that were
subsequently shown not to be stringent (3–7). This has led to
some overestimation of the HTLV-1 seroprevalence in several
African areas. Thus, even up to now, there are only a few
studies on HTLV-1 infection in the African continent in which
the authors used stringent serological and/or molecular criteria
for the diagnosis of HTLV-1 infection (18, 20, 21, 23). More-
over, most of the epidemiological studies have been performed
in hospitalized patients or in individuals at risk for acquiring
HTLV-1 (prostitutes, human immunodeficiency virus [HIV]-
infected patients, etc.) or in rural populations (2, 10, 15, 34,
35). Therefore, very few data have been reported thus far for
large populations of blood donors from west or central Africa
(1, 9, 12). Furthermore, no data are available on the molecular
subtyping of the HTLV present in blood donors from western
The objectives of the present study were thus to perform a
seroepidemiological and a molecular study of HTLV-1 in a
large population of blood donors from Senegal, a country of
western Africa where ATL, TSP/HAM, and infective derma-
titis cases have been reported (19, 20, 22, 24, 27).
The National Blood Transfusion Center (CNTS) of Sene-
gal currently selects nonpaid, voluntary blood donors on the
basis of a health check questionnaire and examination per-
formed by a physician (33). All donated samples are then
tested for detection of HBsAg and of antibodies directed
against HIV type 1 (HIV-1), HIV-2, and hepatitis C virus, as
well as of syphilitic serology.
Our prospective HTLV study took place from May to Oc-
tober 2002. A total of 4,900 blood donors (mean age, 29.6
years; range, 18 to 65) from the CNTS were included in this
serological survey. There were 3,585 men (mean age, 31.8
years; range, 18 to 65 years) and 1,315 women (mean age, 26
years; range, 18 to 52 years). All of the blood donors lived in
the Dakar area, and most of them (58%) originated from
Dakar. Other blood donors included in the study originated
from the northern (17%), southern (13%), and eastern (12%)
regions of the country. The majority (53.1%) of them were
students from schools or universities. Fourteen percent were
unemployed, and the others (33%) had very diverse profes-
sions. A total of 61% were born in a town, and 39% were of
rural origin. This survey was approved by the Ethic Committee
of Senegal and was performed after obtaining the informed
consent of the blood donors.
All plasma samples were screened with an enzyme-linked
immunosorbent assay (ELISA; HTLV-I?II; Abbot/Murex,
United Kingdom). The positive and/or borderline samples
were further tested by a confirmatory Western blot assay (WB;
HTLV-I/II Blot 2.4; Diagnostic Biotechnology, Singapore). A
sample was considered HTLV-1 positive if it reacted to the two
* Corresponding author. Mailing address: Unite ´ d’Epide ´miologie et
Physiopathologie des Virus Oncoge `nes, De ´partement Ecosyte `mes et
Epide ´miologie des Maladies Infectieuses, Batiment Lwoff, Institut
Pasteur, 25-28 Rue du Dr. Roux, 75724 Paris, Cedex 15, France.
Phone: 33 (0)1 45 68 89 37. Fax: 33 (0)1 40 61 34 65. E-mail: agessain
on June 13, 2013 by guest
Gag proteins (p19 and p24) and both env-encoded glycopro-
teins: the HTLV-1-specific recombinant gp46-I peptide
(MTA-1) and the specific HTLV-1/HTLV-2 recombinant
GD21 protein. It was considered HTLV-2 positive if it reacted
to the Gag protein p24 and both env-encoded glycoproteins:
the HTLV-2-specific recombinant gp46-II peptide (K55) and
the GD21 protein. Plasma samples were considered negative
when they exhibited no bands and indeterminate when they
were partially reactive. Moreover, determination of the
HTLV-1 and HTLV-2 antibody titers was performed by two-
fold limited dilution using an immunofluorescence assay (IFA)
with either HTLV-1 (MT2)- or HTLV-2 (C19)-producing cell
lines, as previously described (21, 25).
Among the 4,900 tested samples, only 14 were repeatedly
considered to be ELISA positive. Furthermore, only 8 of these
14 samples were considered HTLV seropositive (0.16%) ac-
cording to stringent WB criteria, 7 of them being HTLV-1 and
1 being HTLV-2 (Table 1). The six other samples exhibited
either no reactivity (four cases) or an indeterminate WB pat-
tern (p19 alone and GD21 alone). The HTLV-1 and HTLV-2
seroprevalence increased with age, ranging from 0.1% in blood
donors that were ?30 years old to 0.8% in blood donors that
were ?50 years old (Fig. 1).
The seven HTLV-1-seropositive plasma originated from six
men and one woman with a mean age of 34.5 years, while the
only HTLV-2-seropositive individual was a woman of 53 years
(Table 1). None of these individuals had been previously trans-
fused, and they all denied any intravenous drug use. Three of
the six children of these donors were tested for HTLV and
were found to be ELISA seronegative.
The eight blood donors had given during their life a total of
79 blood gifts (Table 1). Of these eight blood donors, six,
including the HTLV-2-infected woman, originated from the
southern part of the country, the Casamance, an area from
which only 13% of the blood donors originated. Thus, in the
subpopulation of the 637 blood donors from Casamance, the
HTLV-1 and HTLV-2 seroprevalence reached nearly 1%
(0.94%) with an increase with age (Fig. 1).
High-molecular-weight DNA was extracted from the buffy
coats from four of the six HTLV-1-seropositive blood donors,
from the HTLV-2-seropositive blood donors, and from the two
blood donors with HTLV-indeterminate results by means of
the QIAamp DNA Blood Minikit (QIAGEN GmbH, Hilden,
Germany). The seven DNA samples were subjected to PCR
with primers specific for the human ?-globin gene to check that
cellular DNA was amplifiable. The DNA samples were then
subjected to two series of PCR in order to obtain the complete
long terminal repeat (LTR; 755 bp) and a 522-bp region of the
HTLV-1 env gene as previously described (22, 25). For
HTLV-2, only a fragment comprising most of the LTR (622
bp) was amplified by using specific primers as described pre-
viously (28). The PCR products were then cloned and se-
quenced, and phylogenetic studies were performed as previ-
ously described (25).
Analysis of both LTR and env sequences demonstrated that all
TABLE 1. Main
HTLV-1- or HTLV-2-infected blood donors from Dakar, Senegala
epidemiological and virologicalfeatures of
MT2 C19LTR ENV
aNA, DNA not available; ND, not done; Pos, positive.
FIG. 1. Age-dependent seroprevalence rates for HTLV-1 and HTLV-2 in 4,900 blood donors from all Senegal and in 637 blood donors
originating only from the southern region of Senegal (Casamance). An increase with age is observed in both populations.
VOL. 44, 2006NOTES1551
on June 13, 2013 by guest
a nucleotidic interstrain difference ranging from 0 to 0.9% for the
LTR sequences and from 0 to 0.2% for the 522-bp env genomic
fragments. Furthermore, phylogenetic analyses, using several rep-
resentative strains of the different HTLV-1 molecular subtypes,
indicated clearly that the four novel strains belonged to the large
cosmopolitan HTLV-1 subtype (Fig. 2). They constituted more
specifically a highly phylogenetically supported clade (bootstrap
FIG. 2. Phylogenetic tree generated with the neighbor-joining method, performed by using the PAUP program (v4.0b10), on a 750-bp fragment
of the LTR region. The sequence alignment was submitted to the Modeltest program (version 3.6) to select the best model to apply to phylogenetic
analyses. The selected model was the TrN?G one. Bootstrap support (1,000 replicates) is noted on the branches of the tree. The branch lengths
are drawn to scale, with the bar indicating 0.01 nucleotide replacement per site.
1552NOTESJ. CLIN. MICROBIOL.
on June 13, 2013 by guest
of 90% in the neighbor-joining analysis), located between the
northern African and the western African HTLV-1 subgroups
(Fig. 2) and comprising most of the other HTLV-1 strains known
from Senegal (20).
Regarding the sole HTLV-2 strain, LTR sequence analysis
(data not shown) indicated that this strain belonged surpris-
ingly to the HTLV-2 subtype C phylogenetic clade, being
closely related to some strains from Brazilian Amerindians
In conclusion, we demonstrate here the presence of HTLV-1
infection in blood donors from Senegal. These strains belong
to the cosmopolitan subtype. Moreover, our data suggest that
the Southern part of the country (a forest area much more
humid than the other areas of Senegal) is a probable cluster of
HTLV-1 infection, with a level for areas of endemicity reach-
ing 1 to 2% in the adult population. This finding resembles the
situation found in Guinea, a neighboring country of the south-
ern region of Senegal, where the prevalence in the general
population has been found to range from 0.2 to 1.9% (16). In
Guinea, it is also worthwhile to note that a similar level of
HTLV-1 seroprevalence (1%) was found in a series of 1,700
blood donors from the capital city, Conakry (12). Another
north-to-south gradient of HTLV-1 seroprevalence was also
observed in Cameroon, with the highest level of viral infection
being also clearly in the humid rain forest area (23).
Finally, the data presented herein illustrate the current trans-
fusional risk of HTLV-1 in Senegal. This concerns not only the
dissemination of such viral infection by transfusion but also the
and TSP/HAM cases have been diagnosed in neurological de-
partments in Dakar (27). Moreover, transfusion is a major risk
factor for TSP/HAM development in several areas of endemicity,
history of blood transfusion has been demonstrated to be an
important risk factor for HTLV-1 infection in Africa, including
urban population of Guinea Bissau (26) and children from Ga-
bon, Central Africa (31).
We also demonstrated here the presence of HTLV-2 infec-
tion, which has been very rarely reported in western Africa (12)
and whose origin is still a matter of discussion (13, 32).
Nucleotide sequence accession numbers. The nine new LTR
and env sequences determined herein were deposited in the
National Center for Biotechnology Information database. The
GenBank accession numbers are DQ235698 to DQ235706, cor-
responding to LTR HTLV-1, env HTLV-1, and LTR HTLV-2.
We thank the Institut Pasteur and the Virus Cancer Prevention
Association for financial support. S.C. and S.D. were supported finan-
cially by the Virus Cancer Prevention Association.
We thank Sylviane Bassot for excellent assistance during the IFA
and Western blot serological testing of the samples.
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