Volume 15, Number 4—April 2009
Lethal Bluetongue Virus Serotype 1 Infection in Llamas
To the Editor: Since 1999, of the 24 known bluetongue virus (BTV) serotypes (1, 2, 4, 9, and 16), 5 have spread extensively throughout portions of the Mediterranean basin. Since 2006, the range of serotype 8 (BTV-8) has extended northward into areas of Europe never before affected, causing the greatest epizootic of the disease on record. In 2008, a severe epizootic of serotype 1 (BTV-1) occurred in southwestern France; >3,340 outbreaks occurred in <4 months. We report 2 of these outbreaks, which indicate that BTV-1 can infect llamas and induce a lethal disease.
The first outbreak occurred in September 2008 on a sheep breeding farm in Crampagna, France. After bluetongue disease was suspected on the basis of clinical signs, all sheep and all 9 healthy llamas on the farm were tested for BTV by quantitative real-time reverse transcription–PCR (qRT-PCR) (Taqvet BTV “All genotypes,” LSI, Lissieu, France). Of the 9 llamas, 7 had positive results; cycle threshold (Ct) values ranged from 28.1 to 36.2, indicating that these animals were sensitive to BTV infection. Serotype 1 was confirmed by a specific qRT-PCR. After 6 weeks, all infected llamas showed serologic response to BTV (ELISA ID Screen, Bluetongue, ID-Vet, Montpellier, France), and 1 llama remained positive by qRT-PCR, which suggests that viremia lasted at least 42 days in this animal. None of the 9 llamas showed clinical signs during the outbreak.
The second outbreak, also during September 2008, was identified on a llama breeding farm in Auzat, France. Two days before the onset of the disease, 1 female had aborted a 10-month-old fetus; she had no additional clinical signs. Of the 20 llamas on the farm, clinical signs were observed for 1 female and 1 male. The signs were anorexia and lethargy followed by acute respiratory distress with polypnea, dyspnea, hiccup-like breathing, and edema. The legs of the male became rigid with moderate paresis. Both animals died <24 hours after the onset of respiratory signs.
Postmortem examination of each of the 2 dead llamas 6–16 hours after death showed similar results: acute and severe hydrothorax, severe congestion and edema of the lungs, and fibrinous pericarditis. Histopathologic examination showed diffuse and severe congestion of the lungs, heart, and kidneys. Virus detection by qRT-PCR was positive for all postmortem tissue samples (spleen, lungs, kidneys, heart); Ct values ranged from 23.5 to 33.7. A 7-cm-long fetus that had been in utero in the female was also positive by qRT-PCR (Ct 38.6). From the aborted fetus, viral RNA was detected in the heart (Ct 39.4) and spleen (Ct 38.3); the blood of the female that had aborted was also positive. Infectious BTV was isolated (in a BioSafety Level 3 laboratory) from the lungs and the spleen of the 2 dead llamas and from both fetuses after 4–6 passages on baby hamster kidney–21 cells (ATCC-CCL10). The specificity of the cytopathic effect was confirmed by BTV-1 qRT-PCR and immunoperoxidase detection using a rabbit polyclonal serum directed against the VP7 viral protein.
The natural host range of BTV is limited to domestic and wild ruminants (1,2), although seroconversion with no disease in carnivores (3) and BTV-8 lethal disease in Eurasian lynx (4) have been reported. To date, serologic prevalence of BTV has been demonstrated in alpacas (5) but not in llamas or in guanacos (6,7). South American camelids have been considered to be resistant to the disease, although lethal bluetongue infection in 1 alpaca was suggested in a recent report (8).
Our isolation of the virus and detection of large amounts of viral genomes in blood and postmortem samples suggest lethal BTV-1 infection in llamas. In contrast to the clinical signs of paresis, acute respiratory distress syndrome was not frequently reported in domestic ruminants during the BTV-1 epizootic. Nevertheless, pulmonary edema is considered to be a feature of severe bluetongue disease because the lungs of ruminants are most susceptible to permeability disorders of the vasculature after BTV infection (9,10). Finally, bacterial isolation attempts from the lungs of the 2 llamas that died and PCR tests for bovine viral diarrhea virus and ovine herpesvirus type 2 were all negative. Thus, results of gross examination, histopathologic examination, and virus detection and isolation from postmortem samples strongly indicate that BTV-1 infection was responsible for the death of the 2 llamas.
During the first outbreak, high prevalence of subclinical BTV-1 infection in llamas was detected. BTV-1 was also detected by qRT-PCR in 50% of the healthy llamas tested in the second outbreak and in 60% of those tested in a recent third outbreak (Escalquens, France, November 2008). Healthy llamas in northern France were also found to be positive for BTV-8 (B. Giudicelli, pers. comm.). BTV-1 isolation from 2 fetuses indicates that the strain currently circulating in southwestern France is competent to cross the placental barrier. These findings clearly indicate that llamas are currently infected with BTV-1 and that, although infrequently, the disease can be fatal.
We thank Benoit Severac for helpful comments on the manuscript.
This study was conducted with financial support from the National Institute for Agronomic Research and from the General Council of Ariège.
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Table of Contents – Volume 15, Number 4—April 2009
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Please use the form below to submit correspondence to the authors or contact them at the following address:
Gilles Meyer, UMR1225, Ecole Nationale Vétérinaire de Toulouse, 23 chemin des Capelles BP87614, Toulouse CEDEX 3, France