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ORIGINAL ARTICLE
Serological Evidence of Dengue and West Nile
Virus Human Infection in Juarez City, Mexico
Pedro M. Palermo,
1
Antonio De la Mora-Covarrubias,
2
Florinda Jimenez-Vega,
2
and Douglas M. Watts
1
Abstract
Arboviruses are significant causes of human and animal diseases, globally. In the Rio Grande Valley of the
United States–Mexico border region, endemic transmission of Dengue (DENV), Zika (ZIKV), and West Nile
(WNV) viruses have been documented as a cause of human disease. Otherwise, very little is known about the
distribution of arboviruses and their possible cause of human disease in other areas of the United States–Mexico
border region. Therefore, a pilot serosurvey was conducted to determine if there was evidence of DENV and
WNV infection among a human cohort in Anapra, Ciudad Juarez, Mexico. Baseline blood samples were
obtained from 78 participants during May–June, 2015 and from 60 of the same participants again during
November–December, 2015, and all the samples were tested for DENV and WNV indirect immunoglobulin G
antibodies by an enzyme-linked immunosorbent assay and plaque reduction neutralization test (PRNT). The
results showed that 14.1% (n=11) of the 78 participants had neutralizing antibody to DENV and 5.13% (n=4)
had WNV-neutralizing antibody. Among 48 of 60 participants who were negative for DENV and WNV
antibody during the baseline survey, 10.4% (n=5) had acquired antibody to DENV (n=4) and WNV (n=1) by
the second survey during November–December, 2015. These data support the local transmission of DENV and
WNV in the Anapra, Ciudad Juarez community and therefore warrant further epidemiological studies to better
understand the dynamics of transmission of these viruses in this United States–Mexico border city.
Keywords: Dengue, West Nile, antibodies, Ciudad Juarez
Introduction
Dengue fever is caused by the mosquito-borne dengue
virus (DENV), serotypes 1, 2, 3, and 4 of the Flaviviridae
family, genus Flavivirus (Westaway et al. 1985). Among the
mosquito-borne viruses, DENV is the most significant cause
of human disease (Bhatt et al. 2013, Murray et al. 2013). An
estimated 390 million DENV infections occur annually, of
which about 96 million are symptomatic infection, with
approximately 20,000 deaths. Most DENV infections are
asymptomatic; however, the spectrum of illness may range
from nonsevere to severe dengue that can progress to fatal
dengue hemorrhagic fever and/or dengue shock syndrome
and can be caused by any of the four DENV serotypes. (Burke
et al. 1988, Rodriguez-Figueroa et al. 1995, Endy et al. 2002,
Gubler 2011, Guzman et al. 2013). The primary vector of
DENV is Aedes aegypti, whereas Ae. albopictus is the most
important secondary vector, with both species being common
throughout the tropics and subtropics regions (Gubler 1998a,
1998b, Hotta 1998, Gratz 2004).
All four DENV serotypes cause an estimated 40 million
infections annually throughout most of Latin America, with
about half of these in Brazil and Mexico (MX) alone (Bhatt
et al. 2013, Burke et al. 1988, Rodriguez-Figueroa et al. 1995,
Gubler 1998a, 1998b, 2011, Hotta 1998, Endy et al. 2002,
Gratz 2004, Guzman et al. 2013). Since the recognition of the
four serotypes in MX in 1995, the annual incidence of non-
severe dengue in MX has increased from 1.72/100,000 in
2000 to 14.12/100,000 in 2011, with a marked increase in the
incidence at locations close to the border with the United
States (U.S.) (CDC 1987, Dı
´az et al. 2006, Brunkard et al.
2007, Ramos et al. 2008, Carrillo-Valenzo et al. 2010). The
reason for the increase is not fully understood, but most likely
reflects the circulation of multiple dengue serotypes, an in-
crease in clinical recognition, and the establishment of the
national dengue surveillance program (Dante
´s et al. 2014).
All four serotypes of DENV are endemic in urban com-
munities of the Rio Grande Valley (RGV) of Texas that
borders Mexico. One or more serotypes have circulated on
the Texas side of the border periodically since 1980, but
1
Department of Biological Sciences and Border Biomedical Research Center, University of Texas at El Paso, El Paso, Texas.
2
Instituto de Ciencias Biome
´dicas, Universidad Auto
´noma de Ciudad Juarez, Juarez City, Mexico.
VECTOR-BORNE AND ZOONOTIC DISEASES
Volume XX, Number XX, 2018
ªMary Ann Liebert, Inc.
DOI: 10.1089/vbz.2018.2302
1
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fewer cases of dengue have been reported on the U.S. side
than on the MX side (Hafkin et al. 1982, Malison and Wa-
terman 1983, CDC 2007). Most of the cases have been re-
ported during sporadic outbreaks of dengue primarily in the
urban communities of Matamoros, MX and in the Browns-
ville, Texas (Brunkard et al. 2007, CDC 1996, Ramos et al.
2008, Thomas et al. 2016). The outbreaks on the Texas side
were associated with concurrent dengue epidemics in Ta-
maulipas, MX, and the presence of Ae. aegypti and Ae. al-
bopictus (Champion and Vitek 2014, Vitek et al. 2014).
Outbreaks of dengue were also reported from 2007 to 2014
along the United States–Mexico border in Sonora, MX, with
93 travel-documented cases reported during 2014 in Yuma,
Arizona with all infections apparently acquired in MX ( Jones
et al. 2016). Although Ae. aegypti inhabits the entire border
region, with a sporadic distribution pattern for Ae. albopictus,
DENV has not been reported from other communities in the
border region (Hahn et al. 2016).
West Nile virus (WNV) is a zoonotic mosquito-borne virus
of the family Flaviviridae genus Flavivirus (Simmonds et al.
2017). The virus is transmitted primarily by Culex species
mosquitoes to a variety of wild avian species that serve as the
virus amplifying host and to man and equine as dead-end
hosts. Since the 1990 s, outbreaks of West Nile (WN) fever
and encephalitis have occurred globally, and the virus is now
enzootic in Africa, Asia, Australia, the Middle East, Europe,
United States, Canada, and Central and South America.
WNV was first recognized as a cause of human disease during
2002 in Texas and has since been the cause of annual epi-
demics with a total of 5254 cases from 2002 to 2016 (Arb-
oNET 2016, Texas Department of State Health Services
2016). The first human cases of WN were reported during
2003 in El Paso, Texas, where WNV has repeatedly been
isolated from Cx. quinquefasciatus and Cx. tarsalis, the pri-
mary vectors of this virus in the El Paso community (Car-
denas et al. 2011, Mann et al. 2013). Estimates of cases based
on passive surveillance indicated that 271 cases of WN oc-
curred in El Paso from 2003 through 2016, with cases oc-
curring each year during late June to early November, and
peaking in August (Cardenas et al. 2011, ArboNET 2016,
Gonzales, F, 2017, unpublished data).
The El Paso/Ciudad Juarez region is considered one of the
largest binational metropolitan areas in the United States–
Mexico border, where humans (12,258,192 pedestrians and
19, 982, 407 personal vehicle passengers) cross the border,
annually (annual border crossing in 2015; available from
URL: www.bts.gov/content/border-crossingentry-data). Ae.
aegypti and Cx. quinquefasciatus mosquitoes were first re-
ported during 2005 to be abundant in Ciudad Juarez (de la
Mora-Covarrubias et al. 2008, de la Mora-Covarrubias et al.
2010). WNV has been isolated from Cx. quinquefasciatus,
but evidence of WNV human infection and/or disease has not
been reported from Ciudad Juarez, but eight cases of human
WN disease have been reported from other areas of MX
(CDC 2001, Blitvich et al. 2003, Estrada-Franco et al. 2003,
Ferna
´ndez-Salas et al. 2003, Elizondo-Quiroga et al. 2005,
Rios-Ibarra et al. 2010, Rodrı
´guez et al. 2010). The absence
of WN cases in Ciudad Juarez and the low number of cases in
other areas of MX may reflect underreporting because of
limited surveillance and resources for testing human samples.
Anapra is one of the most impoverished communities in
Ciudad Juarez with insufficient water supply, sanitation, and
waste collection (Ruiz-Hernandez 2015). Therefore, water is
stored in artificial containers that provide suitable mosquito
breeding habitat close to human dwellings that pose a risk for
DENV infection as reported previously in other United
States–Mexico border communities in Brownsville and Ma-
tamoros (Brunkard et al. 2007). Previous studies in Anapra
reported that a high population density of Cx. quinque-
fasciatus was correlated with the low quality of housing,
income, and population density (de la Mora-Covarrubias and
Granados 2007) and that dengue viral ribonucleic acid (RNA)
was detected in Ae. aegypti mosquitoes in this community
(de la Mora-Covarrubias et al. 2010). However, since there
has not been any reported association of WNV and DENV
with humans, this study was conducted to determine if
DENV and WNV were causing human infection and/or
disease in Anapra, Ciudad Juarez, a United States–Mexico
border community.
Materials and Methods
Study site
Ciudad Juarez has an area of 188 km
2
and is located in the
state of Chihuahua, MX. The estimated population size is 1.32
million inhabitants (INEGI 2014). The climate is arid with
annual mean temperature of 18.3C reaching extreme tem-
peratures (41C) during the summer season. The rainy season
extends from July to September, with an annual precipitation
of 264.5mm (INEGI 2015). Anapra is a neighborhood in
Ciudad Juarez with an estimated population of 16,990 inhab-
itants, most of whom lack sanitary services (water and sewer).
Also, most residents work in manufacturing plants, the main
economic activity of the community.
A serosurvey was performed for DENV and WNV anti-
bodies among a convenience subsample of humans in Anapra
between May and June 2015 and between November and
December 2015, or during the peak activity of Ae. aegypti
and Culex mosquitoes. One member of each family among 87
households was selected to participate in the survey. The first
family was chosen from the geographic center (centroid) of
the Anapra neighborhood. Subsequent households of sepa-
rate families located between 100 and 200 meter radius were
selected according to accessibility, security, and presence of
inhabitants (de la Mora-Covarrubias and Corral-Dı
´az 2011).
The survey was explained to all the household members and
one member per house was invited to participate in the study.
The inclusion criteria included household participants >18
years of age. One member of each of the 87 houses agreed to
participate in the study. When possible, two blood samples
were collected from each of the participants. The first blood
sample was used as a baseline to determine the DENV and
WNV antibody prevalence rate and the second sample was
used to measure the incidence of seroconversion to these
viruses as evidence of infection. All the participants signed a
consent form approved for this survey by the Ethics Com-
mittee at the Institute of Biomedical Sciences of the Auton-
omous University of Ciudad Juarez, and all except nine
participants completed a questionnaire to provide demo-
graphic information and any history of travel outside of
Ciudad Juarez. These nine participants were excluded, and
therefore a total of 78 participants were included in the study.
Blood samples were obtained by venipuncture using
standard aseptic techniques with a vacutainer collection tube
2 PALERMO ET AL.
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containing an anticoagulant. All samples were collected from
each of the participants in their homes, and then placed in an
Igloo container on ice packs and transported to the laboratory.
Samples were centrifuged at 1200 Gs at 4C for 10 min. The
plasma samples obtained were transferred to sterile vials and
stored at -20C until tested for immunoglobulin G (IgG) and
neutralizing antibodies.
Indirect IgG enzyme-linked immunosorbent assay
Plasma samples were tested by an indirect enzyme-linked
immunosorbent assay (ELISA) for IgG antibodies to DENV
and WNV using lysate of infected Vero cells as an antigen
coated to the bottom of the wells of 96 microtiter plates as
previously described (Ansari et al. 1993). Each plasma
sample was diluted 1:100 in blocking buffer (5% skim milk,
1%Tween, in phosphate-buffered saline [PBS] 1X pH 7.4)
and tested in duplicate against a pool of DENV antigens
(DENV1–DENV4) or WNV antigen and uninfected lysate
cells were used as control antigen. Then, 96-well microplates
coated with the cell lysates (100 lL) were incubated over-
night at 4C. The next day, microplates were washed with
PBS 1·Tween 0.1% and the diluted plasma samples (100 lL/
well) were added. Then, 100 lL of a secondary antibody
(Horseradish peroxidase [HRP]-conjugated mouse anti-
Human IgG) was added to each well of the 96-well micro-
plates, followed by the addition of a colorimetric substrate
ABTS (2,2’-Azinobis [3-ethylbenzothiazoline-6-sulfonic
acid]-diammonium salt). After incubation for 30 min, the
optical density (OD) values at 410 nm were recorded. The
cutoff OD value was calculated as the mean of six antibody-
negative controls plus three times the standard deviation of
the negative plasma samples (Ansari et al. 1993). Plasma
samples diluted at 1:100 with an OD higher than the cutoff
value were considered antibody positive and then were re-
tested at dilutions ranging from 1:100 to 1:6400 to determine
the IgG antibody titers. Negative and positive control anti-
bodies had a titer lesser than 1:100 and higher than 1:6400,
respectively.
IgM-capture ELISA to DENV
Dengue-specific IgM antibody was determined by an IgM-
capture ELISA, as previously described (Innis et al. 1989),
for samples that were positive for DENV IgG antibodies.
Briefly, 96-well microplates were coated with anti-human
IgM antibody and incubated at 4C overnight. Plasma test
samples were diluted 1:100 in blocking buffer as described
above for testing for IgG antibody. The next day, microplates
were washed, and the plasma samples were added into the
microplate. Attempts to detect IgM antibody was performed
by the addition of dengue viral antigen, followed by virus-
specific hyperimmune ascitic fluid and HRP-conjugated
rabbit anti-mouse IgG. After adding the colorimetric sub-
strate, OD values were read at 410 nm for each sample. The
procedures for the calculation of the OD cutoff value and
antibody-positive samples and titers were performed as de-
scribed above for WNV and DENV IgG antibody.
Plaque reduction neutralization test
Plasma samples that were reactive in the indirect IgG
ELISA to DENV or/and WNV were tested by plaque re-
duction neutralization test (PRNT) to each of the DENV
serotypes: DENV 1 (16007), DENV 2 (16681), DENV 3
(H87), DENV 4 (1036); and WNV (NY-99) as previously
described (Morens et al. 1985). Briefly, four-fold dilutions of
heat-inactivated plasma samples were incubated at 4C
overnight with 30–60 plaque-forming units (PFU) of either
DENV or WNV suspensions. The next day, mixtures of
plasma/virus were inoculated on baby hamster kidney cells,
clone 15, or Vero cells for DENV and WNV neutralization
assays, respectively. After 3–7 days of incubation, cells were
fixed and stained with Naphthol Blue–Black solution. Virus
dose was determined as the mean number of PFU recorded on
12-well cells infected with 30–60 PFU based on testing of an
equal volume of a dilution of the virus stock and antibody-
negative control human plasma. Plaques were counted, and
the dilution of plasma that reduced 70% of the virus dose was
considered as the antibody titer. Samples with titers 1:40 or
higher were considered antibody positive.
Seroconversion was defined as the first plasma sample
being antibody negative for either DENV or WNV and the
second plasma sample from the same individual having a
four-fold or higher rise in the antibody titer and confirmed by
PRNT to DENV or WNV.
Results
A total of 78 study participants provided a blood sample
during the May and June 2015 survey period and 60 of the 78
participants provided samples during the November and
December 2015 survey. Eighteen participants (23.1%) were
not available to participate in the study after the first survey
period. Most of the participants were females (66.7%), with
primary education (79.5%) and 48.7% were working as
housekeepers (Table 1). The results of interviewing partici-
pants during the baseline survey revealed that 30.8% (n=24)
had a history of travel outside Ciudad Juarez. All of the
plasma samples positive for DENV and/or WNV IgG anti-
bodies during the first (n=14) and second survey (n=17)
were confirmed by PRNT. DENV IgM antibody with titers of
1:400 was detected in 2 of the 17 IgG antibody-positive
samples during the second survey.
In the first survey period, the prevalence of DENV- and
WNV-neutralizing antibody was 14.1% (11/78) and 5.13%
(4/78), respectively; with one of those being positive for both
DENV and WNV (Table 2). Four of the 11 DENV antibody-
positive samples had neutralizing antibodies to DENV 1, 2,
and 3. Only four participants had monotypic antibodies (one
for DENV 2 and three for WNV). The remaining participants
(n=6) had polytypic responses to DENV and/or WNV.
A total of 60 participants of the 78 included in the first
survey period were enrolled in the second survey period
(Table 2). Among these 60 participants, 17 had neutralizing
antibodies; 12 participants had the same distribution of
DENV and/or WNV antibodies as during the baseline survey.
Of those 12 participants, 8 had neutralizing antibody to
DENV only. Among 48 participants who were negative for
antibody during the first survey, 10.4% (n=5) acquired an-
tibody to WNV or DENV. Of these five participants, four
seroconverted to DENV (one individual seroconverted to
DENV 1 (PRNT
70
titer: 1:320), one seroconverted to DENV
2 (PRNT
70
titer: 1:1280) and the other two seroconverted to
DENV 1/DENV 2, with DENV 1 neutralizing antibody titers
DENGUE AND WEST NILE ANTIBODIES IN MEXICO 3
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four-fold higher than the DENV 2 antibody titers), and 1
individual seroconverted to WNV (PRNT
70
titer: 1:1280)
(Table 2). Also, as stated in the comparison of DENV and
WNV antibody prevalence and incidence among the human
cohort in Ciudad Juarez (Table 3), the five participants who
seroconverted did not have any travel history outside Ciudad
Juarez during the study. Finally, two of the four individuals
who seroconverted to DENV 1 and/or DENV 2 were positive
for DENV IgM antibody (Table 2).
Discussion and Conclusions
Our findings are the first evidence of DENV infections in
humans in Ciudad Juarez, MX, where dengue RNA was de-
tected during 2005 in field-collected Ae. aegypti mosquitoes
(de la Mora-Covarrubias et al. 2010). In addition, even
though the sample size of this study was small (n=78), the
serological data supported the local circulation of DENV in
Ciudad Juarez because of the detection of neutralizing anti-
bodies to DENV 1 and DENV 2 serotypes and DENV IgM
antibody in two of four study participants who seroconverted
to DENV infection. Also, the individuals with DENV sero-
conversion did not report any travel history outside Ciudad
Juarez, and three of the four individuals stated that most of
their time was spent at home during the survey, suggesting
that DENV infection occurred at home (Table 3). However,
further studies are needed to confirm this possibility. An
understanding of our observations for two of the partici-
pants, who were negative during the first survey for DENV
antibody, but were positive for DENV IgG antibody and
negative for DENV IgM antibody during the second survey,
is unknown. However, it is possible that the IgM antibody
waned to undetectable levels for these two individuals
during the 5–6-month interval between the initial and
follow-up survey period.
Our results represent the first evidence of endemic DENV
transmission along the United States–Mexico border west of
the DENV endemic areas in Brownsville, Texas and Ma-
tamoros, MX and surrounding urban communities in the
RGV. Seroconversions in our study as evidence of a recent
DENV infection was detected in 8.3% (4/48), and DENV
IgG antibody as evidence of past infections was detected in
14.1% of the study participants. Although the sample size
was much lower in our study, the rate of recent infections
was higher than the 2% and 7.3% rates reported during 2004
for residents of Brownsville and Matamoros, respectively
(Brunkard et al. 2007). However, the 14.1% DENV ser-
oprevalence rate for past infection in Ciudad Juarez during
this study was lower than the 40% rates reported during
Table 1. Description of the 78 Participants
Enrolled in the 1st Survey Period,
(May–June 2015) in Ciudad Juarez, Mexico
Sociodemographic characteristics N(%)
Sex
Male 26 (33.3%)
Female 52 (66.7%)
Occupation
Housekeeper 38 (48.7%)
Manufacturing worker 16 (20.5%)
Merchant 12 (15.4%)
Unemployed 2 (2.6%)
Retired 2 (2.6%)
Professional 1 (1.3%)
Others 7 (9.0%)
Education
None 4 (5.1%)
Elementary school 32 (41.0%)
Middle School 30 (38.5%)
High school 10 (12.8%)
Professional/Technician 2 (2.6%)
House construction
Wood 9 (11.5%)
Concrete 11 (14.1%)
Mixture 58 (74.4%)
Years living in house
0–5 22 (28.2%)
6–10 15 (19.2%)
11–15 11 (14.10%)
16–20 15 (19.2%)
>21 15 (19.2%)
Sewage
Sewer 61 (78.2%)
Septic tank 17 (21.8%)
Travel history outside Ciudad Juarez
Yes 24 (30.8%)
No 54 (69.2%)
Table 2. Neutralizing Antibody to Dengue and West Nile Virus Infection Among
a Human Cohort in Ciudad Juarez, Mexico, 2015
Serotype 1st period (n=78) 2nd period (n=60) Seroconversion
a
(PRNT
70
titer)
b
DENV 1 0 1 (1.66%)
c
1 (DENV 1, 1:320)
DENV 2 1 (1.28%) 2 (3.33%) 1 (DENV 2, 1:1280)
DENV 1, DENV 2 2 (2.57%) 4 (6.66%)
c
1 (DENV 1, 1:640; DENV 2, 1:80)
1 (DENV 1, 1:1920; DENV 2, 1:320)
DENV 1, DENV 3 2 (2.56%) 2 (3.33%) 0
DENV 1, DENV 2, DENV 3 4 (5.13%) 2 (3.33%) 0
DENV 1, DENV 2, DENV 3, DENV 4 1 (1.28%) 1 (1.66%) 0
DENV 1, DENV2, DENV 3, WNV 1 (1.28%) 1 (1.66%) 0
WNV 3 (3.84%) 4 (6.66%) 1 (WNV, 1:1280)
No antibody 64 (82.05%) 43 (71.66%) —
a
Seroconversion, four-fold or greater rise in antibody titer in paired sera.
b
PRNT
70
titer, 70% plaque reduction neutralization test titer.
c
Number of individuals DENV IgM positive.
4 PALERMO ET AL.
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2004 in the residents of Brownsville and 78% rate reported
in Matamoros (Brunkard et al. 2007). In Nuevo Laredo, MX,
the rate of recent DENV infection during an outbreak, in
1999 was 16%, but in Laredo, Texas, the rate of 1.3% was
substantiallylowerthanourfindingof8.3%rateinCiudad
Juarez (Reiter et al. 2003). Also, the seroprevalence rate for
past infection in the Ciudad Juarez community (14.1%) was
lower than the 23% rate reported for Laredo, Texas, and
48% in Nuevo Laredo (Reiter et al. 2003). Overall, the
seroprevalence rates as evidence of DENV infections have
been reported to vary in the border communities. Hotez
(2008) estimated that more than 100,000 dengue infections
occur annually among the entire border population of 10
million people (Pew Hispanic Center 2015), based on the
observation that 2% of humans in Brownsville had a recent
DENV infection (Brunkard et al. 2007).
As an example of the possible underestimation of dengue
cases, the RGV is the better-known region of endemic DENV
transmission on both sides of the border. Still, the under-
standing of the ecology and epidemiology is insufficient
because of the lack of any systematic and poorly designed
studies that have failed to provide an accurate estimate of the
incidence and the public health impact of the DENV infec-
tions. As an example, during 1980–1999, there were 65,514
cases of dengue reported from the MX side of the border in
the RGV as compared with only 64 cases on the U.S. side of
the border (Gubler 2001, Reiter 2001, Brunkard et al. 2007).
One study suggested that this disparity could be attributed to
the human behavior and the air conditioning system on the
U.S. side of the border (Reiter et al. 2003). However, a
subsequent study revealed that dengue cases were being
underreported in the United States near the Mexican border
(Brunkard et al. 2007). Efforts to understand possible reasons
for the underestimation of cases indicated that this could be
attributed to passive surveillance (Hafkin et al. 1982). For
example, during the 1980 outbreak in Texas, passive sur-
veillance failed to detect any dengue cases, but 63 cases
were detected by active surveillance at outpatient clinics,
Table 3. Comparison of Dengue and West Nile Virus Antibody Prevalence and Incidence
of Seroconversion Among Human Cohort During May to December, 2015 in Ciudad Juarez, Mexico
Variable % of Prevalence
a
(No. positive
b
/No. tested
c
) % of Incidence
d
(No. positive
b
/No. tested
c
)
Sex DENV WNV DENV WNV
Male 15.38 (4/26) 3.85 (1/26) 11.11(2/18) 5.55 (1/18)
Female 11.54 (6/52) 5.76 (3/52) 6.66 (2/30) 0/30
Occupation
Housekeeper 10.53 (4/38) 7.89 (3/38) 9.52 (2/21) 0
Manufacturing worker 12.5 (2/16) 0/16 8.33 (1/12) 8.33 (1/12)
Merchant 25 (3/12) 0/12 0/6 0/6
Unemployed 50 (1/2) 50 (1/2) 100 (1/1) 0
Professional 100 (1/1) 0/1
Retired 0/2 0/2 0/1 0/1
Others 0/7 0/7 0/7 0/7
Education
None 25 (1/4) 25 (1/4) 0/1 0/1
Elementary school 15.62 (5/32) 3.13 (1/32) 5.56 (1/18) 0/18
Middle school 6.66 (2/30) 6.66 (2/30) 9.09 (2/22) 4.55 (1/22)
High school 20 (2/10) 0/10 16.6 (1/6) 0/6
Professional/Technician 50 (1/2) 0/2 0/1 0/1
House construction
Wood 22.22 (2/9) 22.22 (2/9) 20 (1/5) 0/5
Concrete 18.18 (2/11) 0/11 0/6 0/6
Mixture 12.08 (7/58) 3.45 (2/58) 8.11 (3/37) 2.7 (1/37)
Years living in house
0–5 18.18 (4/22) 9.09 (2/22) 16.67 (2/12) 0
6–10 6.67 (1/15) 0/15 8.33 (1/12) 8.33 (1/12)
11–15 18.18 (2/11) 0/11 0 0
16–20 20 (3/15) 0/15 12.5 (1/8) 0/8
>21 7.14 (1/14) 14.29(2/14) 0/10 0/10
Sewage
Sewer 8.2 (5/61) 4.92 (3/61) 5.13 (2/39) 2.56 (1/39)
Septic tank 35.29 (6/17) 5.88 (1/17) 22.22 (2/9) 0/6
Travel history
e
Yes 20.83 (5/24) 0 0/16 0/16
No 11.11 (6/54) 7.4 (4/54) 12.5 (4/32) 3.13 (1/32)
a
Prevalence, individuals with evidence of past WNV or DENV infection.
b
No. Positive, number of seroconversion to DENV or WNV.
c
No. Tested, the total number of samples available.
d
Incidence, individuals who contract WNV or DENV infection during May–December, 2015.
e
Travel history outside Ciudad Juarez.
DENGUE AND WEST NILE ANTIBODIES IN MEXICO 5
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including 52 (83%) in counties adjacent to the Texas–Mexico
border. Another example related to misdiagnosis of cases was
during a dengue outbreak in 2013 in Brownsville when less
than half of the cases were reported to the Texas Department
of State Health Services because commercial laboratory di-
agnostic testing results were false negative for about one in
five of the cases (Thomas et al. 2016). Other possible reasons
were that dengue cases might go unrecognized because
DENV strains caused mostly silent or subclinical infections
and mild diseases. Also, 59% of Brownsville residents cross
the border into MX for medical care, which is likely to limit
disease reporting on the U.S. side of the border (CDC 2001,
Brunkard et al. 2007)
In this study, serological evidence of past (n=4) and re-
cent (n=1 seroconversion) WNV infections were detected
in humans in Ciudad Juarez, where WNV-positive Cx.
quinquefasciatus mosquitoes were reported in a previous
study (Mann et al. 2013). These results support endemic
WNV transmission in Ciudad Juarez similar to observations
in the neighboring El Paso border community (Cardenas
et al. 2011) and northern MX (Nuevo Leon) (Rodrı
´guez
et al. 2010).
Since our testing was for only performed DENV and WNV
antibodies, we cannot exclude the possibility that other Fla-
viviruses were circulating in Ciudad Juarez, such as St Louis
encephalitis virus or ZIKV because of the possibility of Cross-
reactivity that has been reported among Flaviviruses, espe-
cially among humans who had secondary infections (Lanciotti
et al. 2008). However, ZIKV has not been reported from the
Ciudad Juarez community but has been documented in
other areas, especially in Chiapas, MX (Guerbois et al. 2016).
In addition, the distribution of neutralizing antibodies to
DENV and WNV in the 12 individuals with paired samples in
this survey were similar for the baseline (May–June 2015)
and the second survey (November–December 2015), sug-
gesting that ZIKV and/or other Flavivirus infection were not
involved in the neutralizing antibody response in those 12
individuals.
Our results suggested that further studies are warranted to
determine the incidence and clinical outcome of DENV in-
fections in the Ciudad Juarez community. This observation is
further supported by a recent report of 1 and 9 dengue cases in
this community during 2016 and 2017, respectively. (DGE
2016, DGE 2017), and therefore, is likely to reflect an in-
creasing trend in dengue cases. In case of WNV, the lack of
WN cases reported in Ciudad Juarez and other Mexican areas
could be related to the limited resources for testing human
samples, or else the endemic level of WNV is low. However,
further studies are needed to determine the clinical outcome
of WN in the Ciudad Juarez community. Also, longitudinal
cohort studies and mosquito surveillance could lead to a
better understanding of the transmission dynamics and public
health importance of DENV and WNV in this border com-
munity and provide critically needed data to develop more
effective mosquito control programs.
Acknowledgments
This work was funded by the Office of Research and
Sponsored Project at the University of Texas at El Paso. The
study protocol was approved by the University Autonomous
of Ciudad Juarez Institutional Review Board in compliance
with all applicable Federal regulations governing the pro-
tection of human subjects.
Author Disclosure Statement
No competing financial interests exist.
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Address correspondence to:
Pedro M. Palermo
Department of Biological Science
and Border Biomedical Research Center
University of Texas at El Paso
500 West University Avenue c/o Veterinary Services
El Paso, TX 79968
E-mail: ppalermo@utep.edu
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