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Veterinary Forum July 2007 (Vol 24, No 7)

CIV may have started circulating earlier than originally thought

by Marie Rosenthal

    SEATTLE, Wash. - Recent evidence suggests that the transfer of influenza from horses to dogs may have occurred before the first outbreak of canine influenza virus (CIV) was reported among racing greyhounds in Florida in 2004.

    "CIV appears to have been circulating in racing greyhounds as early as 1999. The locations of these seropositive dogs suggests that CIV may have caused respiratory disease outbreaks at tracks in 1999 and 2003," Tara Anderson, DVM, recently said here at the ACVIM Forum. "The interspecies transmission of influenza virus from horse to dog may have occurred before 1999."

    CIV is highly transmissible and virulent. Cynda Crawford, DVM, PhD, reported statistics from pet dogs in Florida from August 2004 to December 2005 earlier this year. In these 195 dogs, the mortality rate was 7%; however, among dogs that developed pneumonia, the fatality rate was 44% (14/32). Crawford is an immunologist at the department of small animal clinical sciences, University of Florida College of Veterinary Medicine. Anderson is a PhD student working under Crawford and Dr. Paul Gibbs.

    CIV is a subtype H3N8 influenza virus that jumped species from horses to dogs. Researchers are trying to determine when that jump occurred.

    Anderson and her colleagues tested archived serum samples that had been collected from 702 racing greyhounds between 1984 and 2004. The samples were tested multiple times for CIV using a hemagglutination inhibition assay, she said. Samples from 153 greyhounds in Florida had been collected in 1984 and 1985, and samples from 549 racing greyhounds throughout the country were collected from 1999 to 2004 (see box). The samples were compared with 288 samples taken from other breeds admitted to a Florida shelter from 1999 to 2004.

    Seropositive results were found among greyhound samples taken in 1999. Among the samples collected from 1999 to 2004, 20% were positive in 1999 (35/174), 18% were positive in 2000 (13/71), 9% in 2001 (4/43), 44% in 2003 (55/126) and 28% in 2004 (17/61), Anderson said.

    They traced the dogs' racing histories through the unique ear tattoos that all racing greyhounds carry and compared the locations of seropositive dogs (locations of 1999, 2000, and 2001 seropositive dogs during the 1999 outbreaks; locations of 2003 and 2004 seropositive dogs during the 2003 and 2004 outbreaks) with the loca­tions of respiratory outbreaks in which the cause was unknown.

    "Most of the dogs that were CIV seropositive were at tracks or farms in Arkansas, Arizona, Colorado, Florida, Iowa, Kansas, Oklahoma, Texas and Wisconsin during respiratory disease outbreaks in 1998, 1999 and 2003," the researchers said in their abstract.

    It is likely, Anderson explained, that CIV caused the outbreaks.

    Only one shelter dog tested positive in the 1999 to 2004 samples, and that dog entered the shelter in 2004.

    More work needs to be done to confirm these findings, she said, and the researchers are seeking more archived blood and tissue samples, especially from greyhounds because the virus was first recognized in this population.  

    The researchers will begin testing additional serum samples from a donor bank. "We have been fortunate to receive samples from a donor bank that contains serum from 1,600 non-greyhound dogs. These dogs have been located in Florida shelters from 1984 to 2004," Anderson said.

    For more information:

    Anderson TC, Grimes L, Pompey J, Osborne C, Dodds WJ, Katz JM, Courtney CH, Crawford PC. Serological evidence for canine influenza virus circulation in racing greyhounds from 1999 to 2004. Abstract #16. Presented at: The ACVIM Forum. Seattle, Wash.; June 6-9, 2007.

    NEXT: Clinical Report: "Rapid diagnosis needed for cytauxzoonosis"

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