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Orthobunyavirus antibodies in humans, Yucatan Peninsula, Mexico.
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MedLine Citation:
PMID:  23017592     Owner:  NLM     Status:  MEDLINE    
We performed a serologic investigation to determine whether orthobunyaviruses commonly infect humans in the Yucatan Peninsula of Mexico. Orthobunyavirus-specific antibodies were detected by plaque reduction neutralization test in 146 (18%) of 823 persons tested. Further studies are needed to determine health risks for humans from this potentially deadly group of viruses.
Bradley J Blitvich; Rungrat Saiyasombat; Lourdes G Talavera-Aguilar; Julian E Garcia-Rejon; Jose A Farfan-Ale; Carlos Machain-Williams; Maria A Loroño-Pino
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Emerging infectious diseases     Volume:  18     ISSN:  1080-6059     ISO Abbreviation:  Emerging Infect. Dis.     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-09-28     Completed Date:  2013-02-19     Revised Date:  2013-07-11    
Medline Journal Info:
Nlm Unique ID:  9508155     Medline TA:  Emerg Infect Dis     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1629-32     Citation Subset:  IM    
Iowa State University College of Veterinary Medicine, Ames, Iowa 50011, USA.
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MeSH Terms
Antibodies, Viral / blood*
Bunyaviridae Infections / epidemiology*,  immunology,  virology
Mexico / epidemiology
Neutralization Tests
Orthobunyavirus / immunology*
Reg. No./Substance:
0/Antibodies, Viral

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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Journal Information
Journal ID (nlm-ta): Emerg Infect Dis
Journal ID (iso-abbrev): Emerging Infect. Dis
Journal ID (publisher-id): EID
ISSN: 1080-6040
ISSN: 1080-6059
Publisher: Centers for Disease Control and Prevention
Article Information
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Print publication date: Month: 10 Year: 2012
Volume: 18 Issue: 10
First Page: 1629 Last Page: 1632
PubMed Id: 23017592
ID: 3471633
Publisher Id: 12-0492
DOI: 10.3201/eid1810.120492

Orthobunyavirus Antibodies in Humans, Yucatan Peninsula, Mexico Alternate Title:Orthobunyavirus Antibodies in Humans, Mexico
Bradley J. Blitvich
Rungrat Saiyasombat
Lourdes G. Talavera-Aguilar
Julian E. Garcia-Rejon
Jose A. Farfan-Ale
Carlos Machain-Williams
Maria A. Loroño-Pino
Iowa State University College of Veterinary Medicine, Ames, Iowa, USA (B.J. Blitvich, R Saiyasombat);
and Universidad Autónoma de Yucatán Centro de Investigaciones Regionales Dr. Hideyo Noguchi, Mérida, México (L.G. Talavera-Aguilar, J.E. Garcia-Rejon, J.A. Farfan-Ale, C. Machain-Williams, M.A. Loroño-Pino)
Correspondence: Address for correspondence: Bradley J. Blitvich, 2116 Veterinary Medicine, Iowa State University, Ames, IA 50011, USA; email:

We previously reported the isolation of Cache Valley virus (CVV), Kairi virus (KRIV), Cholul virus (CHLV), and South River virus (SOURV) from mosquitoes in the Yucatan Peninsula of Mexico (13). Antibodies to CVV, CHLV, and SOURV were also detected in livestock in this region (4). These viruses belong to the genus Orthobunyavirus (5). All viruses in this genus possess a tripartite, single-stranded, negative-sense RNA genome.

CVV is a recognized human pathogen (5) that has been linked to severe encephalitis and multiorgan failure. KRIV has not been implicated as a cause of human disease, although antibodies to this virus have been detected in humans in Argentina (6). Recent data suggest that CHLV is a reassortant that acquired its small RNA segment from CVV and medium and large RNA segments from Potosi virus (POTV) (1). No clear evidence exists for human susceptibility to infection with CHLV or SOURV. However, diagnostic laboratories rarely test for orthobunyavirus infection; therefore, the true disease incidence and seroprevalence of these viruses remains to be determined. Because orthobunyaviruses comprise a neglected but potentially deadly group of viruses and recent studies have provided evidence of orthobunyavirus activity in the Yucatan Peninsula (14), we investigated whether orthobunyaviruses commonly infect humans in this region.

The Study

Serum samples were obtained from 823 febrile patients at the Secretaria de Salud de Yucatán and other health institutions in Merida during January–October 2007. The patients resided in all 3 states of the Yucatan Peninsula of Mexico: Yucatan (n = 809), Quintana Roo (n = 8) and Campeche (n = 6). The study was approved by the Institutional Biosafety Committees at Iowa State University (Ames, IA, USA) and the Universidad Autónoma de Yucatán (Mérida, Mexico).

All serum samples were examined at a dilution of 1:20 by plaque reduction neutralization test (PRNT) by using CVV (strain CVV-478), and PRNTs were performed as described (7). A subset of serum samples with antibodies that neutralized CVV were titrated and further analyzed by PRNT by using CVV, CHLV (strain CHLV-Mex07), KRIV (strain KRIV-Mex07), SOURV (strain NJO-94f), Maguari virus (strain BeAr7272), and Wyeomyia virus (strain prototype). All of these viruses belong to the Bunyamwera (BUN) serogroup except SOURV, which belongs to the California (CAL) serogroup.

Titers were expressed as the reciprocal of highest serum dilutions yielding >90% reduction in the number of plaques (PRNT90). For etiologic diagnosis, the PRNT90 antibody titer for each virus was required to be >4-fold greater than that to the other viruses tested.

Antibodies that neutralized CVV were detected in 146 (18%) of 823 study participants. The mean ages of patients with and without antibodies that neutralized CVV were 32.0 and 22.3 years, respectively. Logistic regression analysis showed that the risk for infection increased significantly with age (p = 0.0001).

Serum samples from 50 seropositive patients were titrated and analyzed by comparative PRNT to identify the orthobunyaviruses responsible for these infections. Six persons were seropositive for CVV, 5 for CHLV, and 1 for SOURV or a SOURV-like virus; 38 had antibodies to an undetermined orthobunyavirus (Table). Because SOURV was the only CAL serogroup virus used in this study, and another CAL serogroup virus may have been responsible for the infection, the person who had a SOURV PRNT90 titer >4-fold than that to the other viruses tested received a conservative PRNT diagnosis of seropositive for SOURV or a SOURV-like virus. Because interserogroup crossreactivity of neutralizing antibodies to viruses in the BUN and CAL serogroups has not been seen, the 17 persons with antibodies that neutralized SOURV and >1 of the BUN serogroup viruses might have been exposed to >1 viruses from each serogroup.

CHLV and POTV share the same medium RNA segment, so antibodies for these viruses cannot be differentiated by PRNT. Furthermore, antibodies to CHLV and POTV cannot be differentiated by complement fixation test (4). Thus, we cannot dismiss POTV as a possible cause of infection in some or all of the study participants who were seropositive for CHLV. However, it appears more likely that these persons had been infected with CHLV because this virus has been isolated in the Yucatan Peninsula, whereas no direct evidence has been found for POTV in this region.

As already noted, serum samples from 38 (76%) of the study participants analyzed by comparative PRNT had antibodies to an undetermined orthobunyavirus. Most of these persons had low PRNT90 titers; the highest PRNT90 titer for 29 of these persons did not exceed 40. Because neutralizing antibody levels decline over time, these findings may indicate that many of these infections occurred years ago, and the trace amounts of neutralizing antibodies that remained were insufficient to yield a >4-fold difference between the titers of the virus responsible for the infection and the other viruses used in the PRNTs. Another explanation is that some of these persons had been infected with an orthobunyavirus not included in the PRNTs, although all orthobunyaviruses known to occur in the Yucatan Peninsula were represented.


We found 18% of the 823 Yucatan residents participating in our study had evidence of orthobunyavirus exposure. This number is presumably an underestimate; additional seropositive persons might have been identified if the initial PRNTs had not been restricted to CVV. In particular, additional seropositive persons likely would have been detected if SOURV was used in the initial PRNTs, because a screening algorithm that includes only a BUN serogroup virus would likely miss many CAL serogroup virus infections. Nevertheless, we provide evidence that orthobunyaviruses commonly infect humans in the Yucatan Peninsula.

Previous serosurveys have provided information on the seroprevalence of orthobunyaviruses in humans in the United States. For example, antibodies that neutralized CVV were detected in 42/356 (12%) residents in Maryland and Virginia in 1961–1963 (8). Antibodies that neutralized Maguari virus or Tensaw virus were detected in 71/≈300 humans in Florida in the 1980s (9); as observed in our study, the highest PRNT titers for most of the seropositive persons in that study did not exceed 40.

All persons in our study cohort initially sought care for unspecified fever; however, we could not determine whether any of these febrile illnesses were a direct consequence of orthobunyavirus infection. The detection of acute orthobunyavirus infections is limited because no IgM-capture ELISA for orthobunyavirus diagnosis exists. PRNTs can be used to identify recent orthobunyavirus infections when paired acute and convalescent serum samples are available, but for our study, only single serum samples were available from each participant. Orthobunyavirus viremias in humans are transient and of low magnitude, which makes reverse transcription PCR ineffective for the detection of orthobunyavirus RNA in serum samples. However, a duplex reverse transcription PCR was recently developed for the detection of CVV RNA in human cerebrospinal fluid (10).

In conclusion, we provide evidence that orthobunyaviruses commonly infect humans in the Yucatan Peninsula. These viruses are also a common cause of infection of livestock in this region (4). Our findings underscore the need to determine whether orthobunyaviruses represent an unrecognized cause of illness in humans and vertebrate animals in Mexico.


We thank Amanda J. Panella for providing labile serum factor; Robert B. Tesh for providing isolates of SOURV, Maguari virus, and Wyeomyia virus; and Nubia Rivero-Cárdenas for technical assistance with the serum sample collections.

This study was supported by the Iowa State University Plant Sciences Institute Virus–Insect Interactions Initiative.

Dr Blitvich is an associate professor in the College of Veterinary Medicine at Iowa State University, Ames, Iowa. His research interests are the mechanisms of vector and host interactions in arbovirus transmission cycles.

1. . BlitvichBJ, SaiyasombatR, DormanKD, Garcia-RejonJE, Farfan-AleJA, Lorono-PinoMASequence and phylogenetic data indicate that an orthobunyavirus recently detected in the Yucatan Peninsula of Mexico is a novel reassortant of Potosi and Cache Valley viruses.Arch Virol. Year: 2012;157:1199–20410.1007/s00705-012-1279-x22407405
2. . Farfan-AleJA, Lorono-PinoMA, Garcia-RejonJE, HovavE, PowersAM, LinM, et al. Detection of RNA from a novel West Nile–like virus and high prevalence of an insect-specific flavivirus in mosquitoes in the Yucatan Peninsula of Mexico.Am J Trop Med Hyg. Year: 2009;80:85–9519141845
3. . Farfan-AleJA, Lorono-PinoMA, Garcia-RejonJE, SotoV, LinM, StaleyM, et al. Detection of flaviviruses and orthobunyaviruses in mosquitoes in the Yucatan Peninsula of Mexico in 2008.Vector Borne Zoonotic Dis. Year: 2010;10:777–8310.1089/vbz.2009.019620370430
4. . BlitvichBJ, SaiyasombatR, Travassos da RosaA, TeshRB, CalisherCH, Garcia-RejonJE, et al. Orthobunyaviruses are a common cause of infection of livestock in the Yucatan Peninsula of Mexico.Am J Trop Med Hyg. In press.
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7. . RodríguezML, RodriguezDR, BlitvichBJ, LopezMA, Fernandez-SalasI, JimenezJR, et al. Serologic surveillance for West Nile virus and other flaviviruses in febrile patients, encephalitic patients, and asymptomatic blood donors in northern Mexico.Vector Borne Zoonotic Dis. Year: 2010;10:151–710.1089/vbz.2008.020319492946
8. . BuescherEL, ByrneRJ, ClarkeGC, GouldDJ, RussellPK, ScheiderFG, et al. Cache Valley virus in the Del Mar Va Peninsula. I. Virologic and serologic evidence of infection.Am J Trop Med Hyg. Year: 1970;19:493–5024392807
9. . CalisherCH, LazuickJS, LiebS, MonathTP, CastroKGHuman infections with Tensaw virus in south Florida: evidence that Tensaw virus subtypes stimulate the production of antibodies reactive with closely related Bunyamwera serogroup viruses.Am J Trop Med Hyg. Year: 1988;39:117–222899978
10. . WangHS, NattanmaiS, KramerLD, BernardKATavakoli NP. A duplex real-time reverse transcriptase polymerase chain reaction assay for the detection of California serogroup and Cache Valley viruses.Diagn Microbiol Infect Dis. Year: 2009;65:150–710.1016/j.diagmicrobio.2009.07.00119748425

[TableWrap ID: T1] Table  Endpoint titers of serum samples collected from persons in Mexico and analyzed by using comparative PRNT*
ID no. Demographic characteristics
PRNT90 titers
28 Yucatan 18/M 80 20 40 UND
34 Yucatan 39/F 80 20 20 CVV
52 Quintana Roo 39/F 160 40 80 UND
54 Yucatan 32/M 40 20 40 UND
62 Yucatan 44/M 40 20 20 UND
72 Yucatan 23/M 80 40 UND
81 Yucatan 60/F 20 20 20 UND
92 Yucatan 13/M 160 20 20 80 UND
93 Yucatan 42/F 40 20 20 UND
113 Yucatan 24/F 20 UND
114 Yucatan 29/F 40 20 UND
120 Yucatan 60/F 20 320 SOURV or
SOURV-like virus
159 Yucatan 54/M 20 20 UND
161 Yucatan 53/M 20 20 UND
163 Yucatan 27/F 160 80 40 40 UND
167 Yucatan 16/M 160 40 CVV
183 Yucatan 69/F 20 20 UND
184 Yucatan 34/M 160 40 80 UND
185 Yucatan 25/F 20 UND
192 Campeche 54/F 80 40 20 UND
193 Yucatan 16/F 80 20 CVV
194 Yucatan 69/F 20 20 UND
200 Yucatan 3/F 40 40 40 UND
205 Yucatan 53/M 40 20 20 UND
208 Yucatan 57/F 20 160 CHLV
210 Yucatan 42/M 20 20 UND
224 Yucatan 34/M 20 20 20 UND
234 Yucatan 39/F 20 80 20 CHLV
236 Yucatan 74/F 20 20 UND
386 Yucatan 14/F 20 20 UND
388 Yucatan 60/M 160 1,280 160 40 CHLV
389 Yucatan 5/M 20 20 UND
390 Yucatan 33/M 40 20 40 20 40 UND
392 Yucatan 22/M 20 UND
393 Yucatan 29/M 40 20 40 UND
396 Yucatan 34/F 80 20 CVV
397 Yucatan 32/M 80 40 UND
399 Yucatan 27/M 320 1,280 160 320 CHLV
400 Yucatan 37/F 20 UND
401 Yucatan 30/F 160 40 CVV
402 Yucatan 18/M 20 20 UND
403 Yucatan 50/F 20 20 UND
407 Yucatan 27/M 80 20 40 UND
408 Yucatan 40/F 20 UND
412 Yucatan 60/M 20 320 80 40 40 CHLV
415 Yucatan 17/F 20 20 UND
420 Yucatan 16/F 160 20 CVV
429 Yucatan 37/F 20 UND
442 Yucatan 10/F 20 40 20 UND
455 Yucatan 30/F 20 20 20 UND

*PRNT, plaque reduction neutralization test; CVV, Cache Valley virus; CHLV, Cholul virus; KRIV, Kairi virus; SOURV, South River virus; MAGV, Maguari virus, WYOV, Wyeomyia virus; –, titer <20; UND, undetermined orthobunyavirus.

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Keywords: Keywords: orthobunyavirus, Cache Valley virus, Cholul virus, South River virus, serology, surveillance, Mexico, Yucatan Peninsula, viruses.
Keywords: Suggested citation for this article: Blitvich BJ, Saiyasombat R, Talavera-Aguilar LG, Garcia-Rejon JE, Farfan-Ale JA, Machain-Williams C, et al. Orthobunyavirus antibodies in humans, Yucatan Peninsula, Mexico. Emerg Infect Dis [Internet]. 2012 Oct [date cited].

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