Re: Response from Ft Dodge re: Horse Vaccine Efficacy

<x-charset iso-8859-1>Forwarding the message and abstract below from another list, with the
permission of Ft. Dodge.

As a side issue related to their challenge findings, would appreciate
comments from anyone regarding information on serological surveys of horses
and opinions on the morbidity of this infection, apparent vs inapparent
infection rates, minimum infective dose of virus in horses, minimum disease
producing dose.

Eleanor Kellon, V.M.D.

> Fort Dodge Animal Health has just received approval from the USDA to
release
> the follow abstract regarding the WNV vaccine. This paper will be
presented
> at the OIE meeting "Vaccines for OIE list A and emerging diseases" in
Ames,
> IA on the 15th of September 2002. This study was done on normal healthy
> horses, isolated from natural exposure. Hopefully this will help answer
some
> questions.
>
> Equine Vaccine for West Nile Virus T. Ng, D. Hathaway, N. Jennings, Y. -W.
> Chiang, H. -J. Chu. Biological R&D, Fort Dodge Animal Health, Fort Dodge,
> Iowa, 50501
>
> The West Nile virus (WNV) was first isolated and identified from birds,
> mosquitoes, and mammals including horses in three states of the
northeastern
> United States in 1999. Since then, WNV infection has been spread to
> southeastern and Midwestern states. In order to meet the urgent need of
> controlling the WNV infection in equine population, we have developed a
> killed WNV vaccine. A dose titration study in horses was first conducted
to
> evaluate serum neutralization antibody responses against WNV in horses.
> Horses were randomized into three vaccinated and one control groups.
Horses
> were vaccinated with the test vaccine at low, median and high dose
> respectively. All vaccinated horse were administered the test vaccine
> intramuscularly twice, three weeks apart. Serum samples were collected
> periodically and were measured for serum neutralization titers using
plaque
> reduction neutralization test. Twelve months after the second
vaccination,
> horses vaccinated with the median dose of WNV vaccine and non-vaccinated
> control horses were experimentally challenged with WNV. After challenge,
> horses were monitored for rectal temperature and any clinical signs twice
> daily for two weeks and once daily thereafter until 21 days post challenge
> (DPC). Serum samples were collected twice daily for two weeks and once
> weekly thereafter for detection of viremia. Horses were euthanized and
> necropsied on 21 and 22 DPC. Cerebrospinal fluid (CSF), spinal cord
> (cervical, thoracic, and lumbar) and brain (frontal, occipital, medulla
> oblongata, and brain stem) tissue samples were examined for gross
pathology
> and collected for virus isolation. Nine out of 11 (81.8%) controls
developed
> viremia after challenge while only one out of 19 (5.3%) vaccinates had
> transient viremia. No WNV associated clinical signs were observed in any
of
> the challenged animals throughout the observation period. No febrile
> responses were observed in any of the challenged horses. No WNV was
isolated
> from any of the tissue or CSF samples collected from any of the challenged
> horses. Results from this study demonstrate a significant protection (94%
of
> preventable fraction) against viremia in horses vaccinated with the killed
> WNV vaccine and the long duration of the protective immunity.
>
> A conference call to discuss the issues surrounding WNV and vaccination
will
> be conducted on September 12th at 9pm central time. The number to call is
> 1-800-500-0177 passcode is 355287#. If you have any questions, please
feel
> free to contact me-Rob
>
> Rob Keene DVM
> Equine Field Services
> Fort Dodge Animal Health
> cell 801-231-5752
>

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Received on Fri Sep 13 15:14:31 2002