West Nile Virus antibodies in Colombian horses.

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 C6rdoba 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, Ilheus, 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 Cordoba 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.

Salim Mattar, * Eric Edwards, ([dagger]) Jose Laguado, * Marco Gonzalez, * Jaime Alvarez, * and Nicholas Koma ([dagger])

* University of Cordoba, Monteria, Cordoba, Colombia; and ([dagger]) Centers for Disease Control and Prevention, Fort Collins, Colorado, USA

References

(1.) Komar N. West Nile virus: epidemiology and ecology in North America. Adv Virus Res. 2003;61:185-234.

(2.) 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.

(3.) 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.

(4.) 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.

Address for correspondence: Nicholas Komar, Centers for Disease Control and Prevention, PO Box 2087, Fort Collins, CO 80522, USA; fax: [phone]; email: [e-mail]

The opinions expressed by authors contributing to this journal do not necessarily reflect the opinions of the Centers for Disease Control and Prevention or the institutions with which the authors are affiliated.

Table. PRN[T.sub.90] antibody titers to WNV and other South American
flaviviruses for Colombian equine sera *([dagger])

Equine ID
([double        Depart-   Age
dagger])         ment     (y)    WNV    SLEV    ILHV    ROCV    BSQV

3               Cordoba    4    1:40    <1:10   <1:10   <1:10   <1:10
35              Cordoba    5    1:160   <1:10   <1:10   <1:10   <1:10
39
  ([section])   Cordoba    4    1:40    <1:10   <1:10   <1:10   <1:10
41              Cordoba    6    1:40    <1:10   <1:10   <1:10   <1:10
48              Cordoba    4    1:640   <1:10   <1:10   <1:10   <1:10
76               Sucre     5    1:80    <1:10   <1:10   <1:10   <1:10
85               Sucre     9    1:80    <1:10   <1:10   <1:10   <1:10
94               Sucre     3    1:40    <1:10   <1:10   <1:10   <1:10
101              Sucre     4    1:40    <1:10   <1:10   <1:10   <1:10
109              Sucre     7    1:160    1:40    1:40    1:10   <1:10
  ([section])
123             Cordoba    6    1:40    <1:10   <1:10   <1:10   <1:10
125             Cordoba    4    1:160   <1:10   <1:10   <1:10   <1:10

* These 12 specimens were considered positive for WNV infection; a
4-fold WNV PRN[T.sub.90] titer compared to that of other flaviviruses
was required for a positive determination of previous WNV infection.

([dagger]) PRN[T.sub.90], 90% plaque reduction neutralization test;
WNV, West Nile virus; SLEV, Saint Louis encephalitis virus (South
American strain); ILHV, Ilheus virus; ROCV, Rocio virus; BSQV,
Bussuquara virus.

([double dagger]) All equines were horses except for 76 and 85, which
were donkeys.

([section]) Also positive for anti-WNV immunoglobulin M by
antibody-capture enzyme-linked immunosorbent assay.