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Letter
West Nile Virus Antibodies
in Colombian Horses
Salim Mattar,* Eric Edwards,† Jose Laguado,* Marco González,* Jaime
Alvarez,* and Nicholas Komar†
*University of Córdoba, Montería, Córdoba, Colombia; and †Centers for
Disease Control and Prevention, Fort Collins, Colorado, USA
Suggested
citation for this article
To the Editor: West Nile Virus (WNV) is rapidly spreading in the
Western Hemisphere (1). We report the first evidence
for WNV transmission in South America.
WNV is serologically related to the Japanese encephalitis complex of
flaviviruses (Flaviviridae), which includes Saint Louis encephalitis virus
(SLEV) (in North and South America), Japanese encephalitis virus (Asia),
and Murray Valley encephalitis virus (Australia) (2).
Because of antigenic cross-reactivity within this complex, WNV serologic
diagnosis requires highly specific assays, such as the plaque-reduction
neutralization test (PRNT) (3). We used PRNT to evaluate
serum collected from 130 healthy equines (horses and donkeys) in Colombia,
where WNV had not been previously reported. These equines were sampled
between September 15 and October 29, 2004, in the northern departments
of Córdoba and Sucre in the Caribbean region of Colombia. Samples were
heat-inactivated and titrated by PRNT for antibodies to WNV, SLEV, and
3 other South American flaviviruses: Rocio, Ilhéus, and Bussuquara. Twelve
specimens (9%) from 10 different premises tested positive for WNV (Table).
None of these animals had been vaccinated against WNV or had traveled
outside of the region. An equine immunoglobulin (Ig) M-capture enzyme-linked
immunosorbent assay (ELISA) that used WNV antigen detected anti-WNV IgM
in 2 of the 12 specimens, which indicated that some of these infections
were relatively recent (probably within 3 months of sampling). The positive
findings in both Córdoba and Sucre were corroborated by a WNV-specific
blocking ELISA (4). Numerous other samples exhibited
flavivirus reactivity in the neutralization and blocking ELISA assays,
mostly because of SLEV. Complete test results from these horses, as well
as from Colombian cattle and chickens, will be presented elsewhere.
These serologic data should be considered indirect evidence of WNV activity
in Colombia. We encourage Colombian human and animal health authorities
to enhance surveillance for human, equine, and avian disease attributable
to WNV. Efforts are needed to isolate the virus or detect specific viral
RNA to confirm this finding and to identify vectors and vertebrate hosts
involved in WNV transmission in Colombia.
Acknowledgments
We thank Robert
Lanciotti, Janeen Laven, Jason Velez, and Vanesa Otero for technical
assistance.
References
- Komar N. West
Nile virus: epidemiology and ecology in North America. Adv Virus
Res. 2003;61:185–234.
- Calisher CH, Karabatsos N, Dalrymple JM, Shope RE, Porterfield JS,
Westaway EG, et al. Antigenic
relationships between flaviviruses as determined by cross-neutralization
tests with polyclonal antisera. J Gen Virol. 1989;70:37–43.
- Beaty BJ, Calisher CH, Shope RE. Arboviruses. In: Lennette EH, Lennette
DA, Lennette ET, editors. Diagnostic procedures for viral, rickettsial,
and chlamydial infections. 7th ed. Washington: American Public Health
Association; 1995. p. 189–212.
- Blitvich BJ, Marlenee NL, Hall RA, Calisher CH, Bowen RA, Roehrig
JT, et al. Epitope-blocking
enzyme-linked immunosorbent assays for the detection of serum antibodies
to West Nile virus in multiple avian species. J Clin Microbiol.
2003;41:1041–7.
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Table. PRNT90
antibody titers to WNV and other South American flaviviruses for
Colombian equine sera*†
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Equine ID‡
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Department
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Age (y)
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WNV
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SLEV
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ILHV
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ROCV
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BSQV
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3
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Córdoba
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4
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1:40
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<1:10
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<1:10
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<1:10
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<1:10
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35
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Córdoba
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5
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1:160
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<1:10
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<1:10
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<1:10
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<1:10
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39§
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Córdoba
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4
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1:40
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<1:10
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<1:10
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<1:10
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<1:10
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41
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Córdoba
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6
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1:40
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<1:10
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<1:10
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<1:10
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<1:10
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48
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Córdoba
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4
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1:640
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<1:10
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<1:10
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<1:10
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<1:10
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76
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Sucre
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5
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1:80
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<1:10
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<1:10
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<1:10
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<1:10
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85
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Sucre
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9
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1:80
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<1:10
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<1:10
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<1:10
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<1:10
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94
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Sucre
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3
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1:40
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<1:10
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<1:10
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<1:10
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<1:10
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101
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Sucre
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4
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1:40
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<1:10
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<1:10
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<1:10
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<1:10
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109§
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Sucre
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7
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1:160
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1:40
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1:40
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1:10
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<1:10
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123
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Córdoba
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6
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1:40
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<1:10
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<1:10
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<1:10
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<1:10
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125
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Córdoba
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4
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1:160
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<1:10
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<1:10
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<1:10
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<1:10
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*These 12 specimens were considered positive for
WNV infection; a 4-fold WNV PRNT90 titer compared to
that of other flaviviruses was required for a positive determination
of previous WNV infection.
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†PRNT90, 90% plaque reduction neutralization
test; WNV, West Nile virus; SLEV, Saint Louis encephalitis virus
(South American strain); ILHV, Ilhéus virus; ROCV, Rocio virus;
BSQV, Bussuquara virus.
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‡All equines were horses except for 76 and 85, which
were donkeys.
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§Also positive for anti-WNV immunoglobulin M by
antibody-capture enzyme-linked immunosorbent assay.
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Suggested citation
for this article:
Mattar S, Edwards E,
Laguado J, González M, Alvarez J, Komar N. West Nile virus antibodies
in Colombian horses [letter]. Emerg Infect Dis [serial on the Internet].
2005 Sep [date cited]. Available from http://www.cdc.gov/ncidod/EID/vol11no09/05-0426.htm
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