Influenza H3N8 virus was first isolated from racing greyhounds that died from hemorrhagic pneumonia during multiple respiratory-disease
outbreaks at tracks in 2004 and 2005. In addition to virus isolation, substantial serological evidence indicated that CIV
was associated with these respiratory-disease outbreaks. Limited testing of archived tissue and serum samples from racing
greyhounds has suggested that CIV may have circulated in this population prior to 2004. To further investigate this possibility,
serum samples collected from racing greyhounds during the period from 1984 to 2004 were tested for CIV antibodies.
Archived serum samples collected from 702 racing greyhounds were tested for CIV antibodies using the hemagglutination inhibition
(HI) assay. One set of samples was collected from greyhounds in Florida in 1984 and 1985 (n=153 dogs). Another set of samples
was collected from dogs in multiple states from 1999 to 2004 (n=549 dogs).
In these dogs, prior racing history was traced using unique ear tattoos carried by all racing greyhounds and a corresponding
database housed at
http://www.greyhound-data.com/. For comparison, serum samples from non-greyhound dogs collected upon entry into a Florida animal shelter from 1999 to 2004
(n=288) were tested for CIV antibody.
None of the samples from greyhounds in Florida in 1984 and 1985 were positive for CIV antibody. For samples from greyhounds
collected from 1999 to 2004, 20 percent were seropositive in 1999; 18 percent in 2000; 9 percent in 2001; 44 percent in 2003;
and 28 percent were seropositive in 2004. Most of the CIV- seropositive dogs were at tracks or farms in AR, AZ, CO, FL, IA,
KS, OK, TX and WI during respiratory-disease outbreaks in 1998, 1999 and 2003. None of the shelter dogs was seropositive for
CIV except for one dog that entered the shelter in 2004.
Based on the serological evidence, we conclude that CIV was circulating in the racing-greyhound population as early as 1999.
The seropositive dogs were located at tracks involved in respiratory-disease outbreaks of unknown etiology that involved thousands
of dogs across the United States. This suggests that CIV may have been the causative agent of those outbreaks.