Infectious diseases

EMERGENT AND RESURGENT EQUINE I N F E C T I O U S DISEASES FROM A GLOBAL PERSPECTIVE R J. Timoney, Universityof Kentucky,DepartmentofVeterinaryScience The last 40 to 50 years has seen the recognition of a range of equine infectious disease that previously were etiologically undefined and in many cases, neither pathogenetically nor epidemiologically characterized. In some instances, e.g., contagious equine metritis and equine morbillivirus pneumonia, the diseases in question were considered emergent infections, having never been previously described or identified as specific clinical or clinico-pathological entities in the horse. In other cases, e.g., Venezuelan equine encephalomyelitis caused by/the epidemic variants of the virus, diseases have re-emerged after varying intervals, sometimes many years. Such occurrences clearly illustrate the fact that certain equine infections can remain undetected for long periods of time until precise agent, host and environmental conditions arise that are conducive to the occurrence of an outbreak or epidemic. The escalating increase in the international movement of horses that has taken place, especially within the past 30 years, has heightened the risk of certain infectious diseases being introduced into previously susceptible and unprotected horse populations. There have been numerous confirmed instances where this has occurred, with serious and economically significant consequences for the respective industries involved. Such occurrences serve to underscore the fact that the known geographic distribution of equine infectious diseases is not static and can be subject to change, the latter frequently related to the international movement of horses. While acknowledging the need for facilitation of global trade by minimizing restrictions on international movement, pursuit of this objective should not be at the expense of maximizing protection for at-risk horse populations throughout the world. N E O N A T A L E H V - I : CLINICAL, H E M A T O L O G I C A L AND B I O C H E M I C A L FINDINGS G. Perkins 1, F. Del Piero 2, D. Ainsworth 1, M. Miller 3, J. Palmer3, P. Wilkins 3, M. Frazer 4 l Dept.ClinicalSciences,NYSCVM - Comell University, Ithaca, NY; 2NYS Diagnostic Lab. Cornell University, Ithaca, NY; 3New Bolton Center, University of Pennsylvania, Kennen Square, PA; 4Hagyard Davidson & McGee, Lexington, KY, USA

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The purpose of this study was to document the clinical and laboratory findings of neonatal foals with Equine Herpes Virus-1 (EHV-1) and to determine if these parameters were distinct f r o m foals with neonatal s e p t i c e m i a . A retrospective study was performed involving foals presented to the N Y S C V M - C o r n e l l University, New Bolton Center-University of Pennsylvania and Hagyard Davidson and McGee Associates in Kentucky from 1985 to 1997. The clinical diagnosis of EHV was confirmed with the pathognomic histological lesions and immunoperoxidase histochemistry (6/6). The historical, clinical, biochemical; hematological and pathological findings were summarized. Most foals with EHV- 1 were of gestational age <325 days. All cases presented at <24 hours of age. Most died spontaneously (4/6) or were euthanized (2/ 6) within 48 hours of presentation. Failure of passive transfer had occurred in most cases. Based on tissue cultures 50% of the foals (3/6) were septic. All foals (6/6) were found to be leukopenic and neutropenic, although a left shift (4/6) was not a predominant feature. The foals were also lymphopenic (6/6) and monocytopenic (6/6). Relative to chemistry profiles, most had a slight increase in the total bilirubin but AST and GGT were not elevated. Blood gases performed on four of the foals showed a moderate respiratory acidosis. Establishing a difference between the clinicopathologic findings of septic foals versus those with EHV- 1 could allow the practitioner to make a more accurate assessment of a critically ill foal's prognosis. Based upon our preliminary results, distinguishing between these two conditions, using basic clinical or laboratory findings, could not be achieved. (The authors acknowledge assistance of Dr. E.J. Dubovi of the New York State Diagnostic Laboratory.) PERINATAL EQUINE VIRAL ARTERITIS: P A T H O L O G I C A L I M M U N O H I S T O C H E M I C A L , VIRUS ISOLATION, C L I N I C A L AND S E R O G I C A L FINDINGS E Del PieroI P.A.Wilkins2, J.W. Lo~ez3, E. J. Dubovi3, A. Glaser3, D.H. Schlafer4, D. Lein-~ 1padua College of Veterinary Medicine, Institute of Pathology and Hygiene; 2Cornel 1 University College of Veterinary Medicine Department of Physiology, 3Diagnostic Laboratory and 4Department of Pathology, Ithaca, NY USA Equine Viral Arteritis (EVA) is a disease of horses characterized by panvasculitis leading to edema, hemorrhage and abortion in mares. The EVA etiologic agent is an arterivirus and little is known regarding the pathogenesis and pathophysiology of the disease in the newborn foal. Tissues harvested during necropsy of 10 foals in 2 separate epizootics of EVA were fixed in 10% buffered formalin, paraffin embedded and cut in

serial section. Hematoxyllin and eosin stained sections were evaluated for histopathological findings. Sections mounted on poly-L-lysine coated glass slides were evaluated with an avidin-biotinperoxidase immunohistochemical technique using a monoclonal antibody that recognizes a 30 kDa virion membrane protein from the Bucyrus strain of the EVA virus. For virus isolation tissue extracts were inoculated onto primary equine kidney cells and RK-13 cells. Isolated viruses were identified using the Bucyrus strain of EVA virus. Gross findings were increased lung volume, consistency and weight. Ventral edema was noted in 2 foals. Common histologic findings included interstitial pneumonia with bronchiolar arteritis, renal tubular necrosis (2 foals) and vasculitis in multiple tissues. The greater majority of foals were positive for EAV antigen (Ag). Ag was localized in endothelial cells, arteriolar and venular myocytes, bronchiolar epithelium, macrophages, renal epithelium, enterocytes, thymic stroma, trophoblast and allantoic mesenchyma. Immunoperoxidase histochemistry results correlated well with virus isolation results, demonstrating the reliability and utility of the technique. Clinical signs in these two groups were remarkable, severe and primarily localized to the respiratory tract. Minimal gastrointestinal involvement was noted in these cases, in contrast to previous reports. All foals presented as acute death or with clinical evidence of severe respiratory distress and subsequent death. Edema, fever, depression, leukopenia and thrombocytopenia were noted during the clinical course of all foals not presenting as acute death. Serology supported the potential role of passive humoral immunity in providing resistance to this viral disease. Foals born to EVA seronegative mares may be at increased risk of acquiring severe fatal EVA infection in the i m m e d i a t e p e r i p a r t u r i e n t period. Immunoperoxidase histochemistry, combined with more traditional techniques, should allow for rapid diagnosis of EVA and can be used retrospectively. EQUINE I N F E C T I O U S DISEASES AS AN IMPEDIMENT TO TRADE BETWEEN THE U.S.A. AND E U R O P E P.J. Timoney Universityof Kentucky,DeparlmentofVeterinaryScience Horses have been transported for breeding or competition purposes between Europe and the U.S.A. or vice versa for many years. The volume and economic significance of such movements has increased considerably over the past two decades. Historically, the trade in live animals has been subject to specific import controls drawn up by the individual countries concerned or under a common import policy in the case of France, Ireland and the United Kingdom (the former tripartite group). This situation changed

JOURNAL OF EQUINE VETERINARY SCIENCE

5th WEVA Congress

very significantly in 1990, however, with the implementation of the initial directives on Equidae by the member states of the European Union. Outbreaks of particular infectious diseases, e.g., contagious equine metritis in England, France and Ireland in 1977 and equine viral arteritis in Kentucky, U.S.A. in 1984, led to the imposition of very stringent controls on the movement of horses between these countries. These restrictions have been a considerable impediment to trade and over the years, have resuited in significant economic hardship for those concerned. The stringent restrictions imposed on horses competing at the 1996 Olympic Games in Atlanta, U.S.A. that were serologically positive for piroplasmosis is a more recent example of the adverse effects that infectious diseases can have on the movement of horses between Europe and the U.S.A. It is to be hoped that in accordance with the provisions of the 1995 Sanitary and Plyto-sanitary (SPS) Agreement of the World Trade Organization, there will in time be greater harmonization of the respective import control policies of the USA and the European Union that will help to facilitate movement of horses between the two continents.

V I R O L O G I C A L D I A G N O S T I C RESULTS OF EQUINE ARTERIT1S VIRUS (EAV), FOLLOWING THE I N T R O D U C T I O N OF AN ERADICATION P R O G R A M IN STALLIONS

R.M. Dwyer, DVM, MS Universityof Kentucky,DepartmentofVeterinaryScience Rotavirus outbreaks are a source of significant economic loss to breeding farms worldwide. Ten years of research have let to an understanding of the epidemiology of this disease. Through the serial fecal testing of normal and sick foals over three years, the virus can be shed from foals prior to clinical sign and for an average of three days after the formation of normal feces. Studies in swine indicate that sows are the asymptomatic carriers of the disease, and although rotavirus has not been detected in adult horses' feces, mares have seroconverted during outbreaks on farms, and during controlled experiments. The virus can remain infectious for more than nine months at room temperature. Since one gram of diarrheic feces contains 107 virus particles, the disease is highly contagious, prevention and control revolve around sound management and disinfection practices. Phenolic disinfectant (especially ortho-phenylphenol) are effective against rotavirus in the presence of organic matter, in contrast to hypochlorites (bleach), and quaternary ammonium compounds. The advent of a new equine rotavirus vaccine for use in mares in the United States is an added preventive to this disease, however, no vaccine will replace basic quarantine, management and disinfection practices on horse farms.

E Q U I N E INFLUENZA IN RUSSIA AND

G.L. Autorino; M.T. Scicluma; G. Ferrari; G. Cardeti; G. Vulcano;D. Amaddeo IstitutoZooprofilattico Sperimentaledelle Regioni Lazio e Toscana Results of the diagnostic activity conducted in our Institute deriving from the implantation of the EAV control program are discussed. The prevalence of shedding stallions is analogous to that previously established in other epidemiological studies (P.J. Timoney and W.A. McCollum). Of the seropositive stallion controlled virologically, about 20% can be considered as long-term shedders. Virological positive stallions have been identified in all breeds controlled and the highest percentage of shedding stallions have been found among Trotters and Arabs. Virological controls conducted during two consecutive breeding seasons on 50 seroposirive, non- shedding stallions not only confirmed the validity of virus isolation in cell-culture, but also that no intermittency in virus-shedding occurred: all stallions, confirmed as non-shedders in the first year of control, were reconfirmed in the second year. Jack-asses resulted susceptible to EAV infection and virus-shedding stallions have also been identified; two stallions can be considered as long-term shedders as they had resulted seropositive even the year preceding the virological controls.

ROTAVIRUS E P I D E M I O L O G Y , PREVENTION AND C O N T R O L

Volume 17, Number 9, 1997

E F F I C I E N C Y OF VACCINATION K.E Yurov,E.E Zagebina, E.V.Yarnikh All-Russian Institute of Experimental Veterinary Medicine, Laboratoryof Equine Viral Diseases Equine influenza in Russia (ex-USSR) has been a registered disease since 1969. The first outbreak was determined at the western border of the Ukraine and Hungary in 1969. During 1969, this infection was spread to the entire territory of the Ukraine and the European part of Russia. In the majority of cases equine influenza virus of the 2nd type identical to the strain A/ equine/Miami/63 was isolated. At the same time in separate cases some strains of the 1st type of equine influenza virus were isolated. Later, some epizooties of equine influenza caused by both types of virus were registered at the territory of ex-USSR and Russia. During the outbreak of 1984-1985 in Moscow the strains of equine influenza virus type 2 A/equine 2/Bitsa/84 and A/equine 2/Bista/85 were isolated. These strains were antigenical related to the strain A/equine/Fontainbleu/79. Vaccine against equine influenza virus, which is used in Russia, includes two prototypical strains A/equine 1/Prague/56 and A/equine 2/ Miami/63 and two epizootical strains A/equine 1/Kirghizia/74 and A/equine 2/Bitsa/85. Equine influenza virus which was the cause of the epizooty in 1993-1994 years in China have been brought to the territory of Russia via territories of some Middle Asia republics of ex-USSR. However, the infection didn't spread widely perhaps because of systematical immunization

of horses in the European part of Russia. In our opinion, rather wide application of vaccination helps to support comparative prosperity of equine influenza virus in the European part of Russia.

C O N T R O L OF EQUINE P I R O P L A S M O S I S IN ENDEMIC

COUNTRIES C.E. Kerber,E Ferreira, M.C. Pereira Universidade de Sao Paulo The importance of equine piroplasmosis in endemic countries has increased in recent years and has played an important role in maintaining the international market for the horse industry. The purpose of this study was to demonstrate the occurrence of equine babesiosis (B. equi and B. caballi) in different climatic conditions in Brazil and to evaluate the impact of tick control decreasing the prevalence ofpiroplasmosis. A total of 720 equine blood samples were taken from horses in 28 farms from different regions. We submitted them for the Complement Fixation test. We have found a significant association (p < 0,0001) in the prevalence of infections by both babesia in tropical and subtropical areas and in farms with and without control of tick population. As we could demonstrate, it is possible to achieve a substantial decrease in the number of positive horses just by controlling the population of ticks and treating the chronic carriers. The control can be done by artificial measures as we introduced in some farms but it happens also naturally in lower temperature areas. Tick control is a feasible way to improve the quality of horse population in endemic areas for exportation purposes or athletic performance. We may consider the possibility of new and more sensitive tests (Elisa, PCR, Wblot) being carried out by import countries as a way to control the horse's entrance. In this case, the sanitary barriers will became a serious limitation for the endemic countries.

T H E E F F E C T OF R O A D TRANSPORTATION ON EXTERNAL WATER AND E L E C T R O L Y T E BALANCE OF C O N D I T I O N E D H O R S E S 1 2, J. S. van den Berg, A. J. Guthrie] , R. A. Me'ntjes J. Nurton1, D. Adamson1, C. TraversI & R. Lund1, Department of Medicine, EquineResearch Centre1 DepartmentofPhysiology2, FacultyofVeterinaryScience, University of Pretoria, SouthAfrica

Transportation, strange surroundings and a change in management may all combine to reduce water intake in horses transported by vehicle. Apart from decreased water intake, horses may lose fluids via sweating, urine, evaporative loss from the respiratory system and via the feces. The objectives of this trial were to measure the water and electrolyte intake and loss of

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