american college of veterinary internal medicine (acvim) forum

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346 Journal of Equine Veterinary Science August 2006 AMERICAN COLLEGE OF VETERINARY INTERNAL MEDICINE (ACVIM) FORUM Louisville, KY May 31–June 3, 2006 The ACVIM Forum is a meeting that I probably will not forget for a while for at least two reasons. One is that this was my first time attending the ACVIM Forum. I was extremely impressed with the organization and science that was presented at this meeting. Second, the trip to Louisville was one to remember. We arrived in Chicago thinking that we had a one- hour layover before we caught the shuttle to Louisville, but because of thunderstorms our flight was delayed for three hours, then eventually can- celed. We then had to make the deci- sion whether to spend the night in Chicago and arrive at the meeting a day late or rent a car and drive from Chicago to Louisville. After making some new veterinary friends, six of us rented a car and drove the 300 miles to Louisville in time for the meeting. I must say that the scientific ses- sions were more enjoyable than the 300-mile drive. Subjects in the pro- gram sessions included cardiology, neurology, oncology, small animal internal medicine, Forum Focus, equine, food animal, State-of-the- Art speaker, business management, and research abstracts. On Thursday, June 1, there was a half-day session on Rhodococcus equi. The first two lectures were given by Dr. Stephen Hines from Pullman, Washington. The first lecture dis- cussed pathophysiology of rhodo- coccal pneumonia. He reviewed the basic biology of the organism and the pathogenesis. Dr. Hines went on to explain the practical issues that limit or complicate Rhodococcus equi vac- cination studies, which include cost, problem of confounding environ- ment, and selection of a challenge model, whether natural or experi- mental. His second lecture was enti- tled “Immunity and Prospects for Immunological Prevention.” The goal of this presentation was to review what is known about protective im- munity to Rhodococcus equi, discuss the barriers to immunological strate- gies for prevention of rhodococcal pneumonia, and to consider the prospects for an effective vaccine in foals. In the Proceedings, Dr. Hines listed five observations: 1. Other than immunocompro- mised humans, rhodococcal pneumonia is almost strictly a disease of horses. 2. Although horses are likely ex- posed to Rhodococcus equi throughout life, susceptibility is age dependent. Rhodococcal pneumonia is rarely seen in horses older than 6 months of age. 3. Especially on endemic farms, im- munization to prevent rhodo- coccal pneumonia will likely need to be initiated early in life, very possibly during the first week. The inherent limitation in the ability of the neonatal or perina- tal foal to respond may be the sin- gle most significant challenge to development of an immunologic strategy for the prevention of equine rhodococcal pneumonia. 4. Although controversial, it seems probable that anti-rhodococcal equine antibodies have benefi- cial effects even though these effects may be partial. 5. Oral administration to foals with virulent Rhodococcus equi beginning at the second day of age provides complete protec- tion against experimental chal- lenge 3 weeks later. Noah Cohen from Texas A&M University provided a lecture on foal pneumonia, epidemiology con- trol, and prevention. Dr. Cohen mentioned that Rhodococcus equi is an important cause of pneumonia in foals one to three months of age. He discussed why some farms are af- fected and others are not. The three factors discussed were the environ- ment, host, and the agent. Mares may be a source of the infection; thus, the foals may have widespread exposure to Rhodococcus equi. He explained that data conflict as to how important environment is as a source of infection. Dr. Cohen went on to describe three areas that af- fect the control and prevention of Rhodococcus equi: (1) treating af- fected foals, (2) screening for earlier identification and treatment of sub- or pre-clinical affected foals, and (3) preventing pneumonia among exposed foals. He indicated that screening should begin the second or third week and should be done repetitively. This should include not only blood work but also physical examination along with radiographs and ultrasonography. Keith Chaffin from Texas A&M University continued the subject with a discussion of treatment and chemoprophylaxis of Rhodococcus equi pneumonia in foals. He indi- cated that, in the past 25 years, the use of highly lipid-soluble antibi- otics, such as erythromycin and ri- fampin, have markedly improved the survival rates of foals with Rhodococcus equi pneumonia. Unfortunately, erythromycin has been associated with numerous ad- verse side effects. Newer antimi- crobials have been recommended, including azithromycin and clar- ithromycin. These have fewer side effects and longer half-lives. Dr. Chaffin suggested that clar- ithromycin plus rifampin may be a superior combination. He went on Meeting Report 0737-0806/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2006.06.005

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346 Journal of Equine Veterinary Science August 2006

AMERICAN COLLEGE OFVETERINARY INTERNALMEDICINE (ACVIM) FORUM

Louisville, KYMay 31–June 3, 2006

The ACVIM Forum is a meetingthat I probably will not forget for awhile for at least two reasons. One isthat this was my first time attendingthe ACVIM Forum. I was extremelyimpressed with the organization andscience that was presented at thismeeting. Second, the trip to Louisvillewas one to remember. We arrived inChicago thinking that we had a one-hour layover before we caught theshuttle to Louisville, but because ofthunderstorms our flight was delayedfor three hours, then eventually can-celed. We then had to make the deci-sion whether to spend the night inChicago and arrive at the meeting aday late or rent a car and drive fromChicago to Louisville. After makingsome new veterinary friends, six of usrented a car and drove the 300 milesto Louisville in time for the meeting.

I must say that the scientific ses-sions were more enjoyable than the300-mile drive. Subjects in the pro-gram sessions included cardiology,neurology, oncology, small animalinternal medicine, Forum Focus,equine, food animal, State-of-the-Art speaker, business management,and research abstracts.

On Thursday, June 1, there was ahalf-day session on Rhodococcusequi.The first two lectures were givenby Dr. Stephen Hines from Pullman,Washington. The first lecture dis-cussed pathophysiology of rhodo-coccal pneumonia. He reviewed thebasic biology of the organism and the

pathogenesis. Dr. Hines went on toexplain the practical issues that limitor complicate Rhodococcus equi vac-cination studies, which include cost,problem of confounding environ-ment, and selection of a challengemodel, whether natural or experi-mental. His second lecture was enti-tled “Immunity and Prospects forImmunological Prevention.” The goalof this presentation was to reviewwhat is known about protective im-munity to Rhodococcus equi, discussthe barriers to immunological strate-gies for prevention of rhodococcalpneumonia, and to consider theprospects for an effective vaccine infoals. In the Proceedings, Dr. Hineslisted five observations:1. Other than immunocompro-

mised humans, rhodococcalpneumonia is almost strictly adisease of horses.

2. Although horses are likely ex-posed to Rhodococcus equithroughout life, susceptibility isage dependent. Rhodococcalpneumonia is rarely seen inhorses older than 6 months of age.

3. Especially on endemic farms, im-munization to prevent rhodo-coccal pneumonia will likely needto be initiated early in life, verypossibly during the first week.The inherent limitation in theability of the neonatal or perina-tal foal to respond may be the sin-gle most significant challenge todevelopment of an immunologicstrategy for the prevention ofequine rhodococcal pneumonia.

4. Although controversial, it seemsprobable that anti-rhodococcalequine antibodies have benefi-cial effects even though theseeffects may be partial.

5. Oral administration to foalswith virulent Rhodococcus equibeginning at the second day ofage provides complete protec-tion against experimental chal-lenge 3 weeks later.

Noah Cohen from Texas A&MUniversity provided a lecture onfoal pneumonia, epidemiology con-trol, and prevention. Dr. Cohenmentioned that Rhodococcus equi isan important cause of pneumonia infoals one to three months of age. Hediscussed why some farms are af-fected and others are not. The threefactors discussed were the environ-ment, host, and the agent. Maresmay be a source of the infection;thus, the foals may have widespreadexposure to Rhodococcus equi. Heexplained that data conflict as tohow important environment is as asource of infection. Dr. Cohen wenton to describe three areas that af-fect the control and prevention ofRhodococcus equi: (1) treating af-fected foals, (2) screening for earlieridentification and treatment of sub-or pre-clinical affected foals, and (3) preventing pneumonia amongexposed foals. He indicated thatscreening should begin the secondor third week and should be donerepetitively. This should include notonly blood work but also physicalexamination along with radiographsand ultrasonography.

Keith Chaffin from Texas A&MUniversity continued the subjectwith a discussion of treatment andchemoprophylaxis of Rhodococcusequi pneumonia in foals. He indi-cated that, in the past 25 years, theuse of highly lipid-soluble antibi-otics, such as erythromycin and ri-fampin, have markedly improvedthe survival rates of foals withRhodococcus equi pneumonia.Unfortunately, erythromycin hasbeen associated with numerous ad-verse side effects. Newer antimi-crobials have been recommended,including azithromycin and clar-ithromycin. These have fewer sideeffects and longer half-lives. Dr.Chaffin suggested that clar-ithromycin plus rifampin may be asuperior combination. He went on

Meeting Report

0737-0806/$ - see front matter© 2006 Elsevier Inc. All rights reserved.doi:10.1016/j.jevs.2006.06.005

Volume 26, Number 8 347

to give the results of a study performed in 2005 on 10 equinebreeding farms with endemic Rho-dococcus equi infection. The pur-pose of the study was to determinethe effects of azithromycin admin-istered at 10 mg/kg by mouth every48 hours for the first 2 weeks oflife. The study demonstrated a re-duction in the prevalence andseverity of the disease. In the finalpart of his talk, Dr. Chaffin presented a novel approach to pre-vention of Rhodococcus equi pneu-monia using the administration ofgallium maltolate to foals duringthe critical time period when theyare most susceptible to infection.Most pathogenic bacteria are de-pendent on availability of iron forsurvival. Gallium is a semi-metalused to treat hypercholemia inhuman cancer patients. “The antimi-crobial effects of gallium are relatedto its ability to compete with ironfor binding sites of host iron-bind-ing proteins. Bacteria acquire gal-lium and incorporate it into thecrucial iron-dependent enzyme sys-tems, which leads to inactivation ofthose systems and bacterial death.”A recent study in their laboratoryshowed that gallium inhibited invitro growth of Rhodococcus equi.Dr. Chaffin stated that, based onpreliminary findings, gallium malto-late appears to have potential to reduce the prevalence of Rhodococ-cus equi pneumonia among foals atbreeding farms.

Other lectures in the equine ses-sion included one by Tom Diversfrom Cornell on equine Lyme dis-ease and equine leptospirosis. In ad-dition, Nathan Slovis fromHagyard-Davidson-McGee pre-sented an interesting lecture on hy-perbaric oxygen therapy in horses.

On Friday, a half-day session waspresented on equine herpesvirus 1(EHV-1). Julia Kidd from theAnimal Health Trust in Newmarket,England, presented the pathogene-sis of EHV-1. Her second lecturewas titled “Immunology of EHV-1

Infection.” Josh Slater fromLondon, England, also presented alecture on epidemiology and con-trol of EHV-1 infection. Dr. Slatermentioned that environmentaltransmission of EHV-1 is extremelyimportant during outbreaks.Infected horses shed large quanti-ties of virus and are contagious bydirect or indirect contact. However,environmental transmission plays aminor role in the maintenance ofthe virus in horse populations. Thereservoir of latently infected adulthorses is responsible for infection ofnew horses early in life, especially asfoals. The length of time for whichclinical cases of EHV-1 respiratory,abortion, and neurological diseasesare contagious was discussed. Theincubation period appears to be 1 to10 days. Clinical cases are most con-tagious for the first 7 days after in-

fection. Viremia persists up to 21days after infection, but for all prac-tical purposes, virus shedding is un-likely after 21 days and horses are“safe” after 28 days. Most adulthorses carry viruses in a quiescentstate for many years and possiblytheir entire life. These latent virusesperiodically reactivate to become areservoir for infection.

Dr. Paul Lunn from ColoradoState University presented a lecturethat included defining vaccinationgoals and measuring success. He dis-cussed current commercial vaccinesas well as experimental vaccines.Lastly, Dr. Lunn presented some fu-ture vaccine technologies.

The two in-depth sessions onRhodococcus equi and EHV-1 in-fection were extremely useful inproviding the latest information onthese two diseases.