The significance of surveillance and reporting on the prevention and control of equine diseases.

Examples of equine disease surveillance at the local, regional, national and international level are discussed in this article. Reporting systems at each level are also considered, and the increasing importance of laboratory confirmed diagnoses is emphasized. The need to develop national disease reporting systems is addressed, particularly with respect to conforming to international trading standards.

Stress and a glycinergic intervention interact in the modulation of MK-801-elicited mouse popping behavior.

The ability of D-cycloserine, a partial glycine agonist, to modulate mouse popping behavior elicited by MK-801, a noncompetitive NMDA receptor antagonist, was studied in unstressed and stressed mice. In unstressed animals, D-cycloserine (5.6 and 10 mg/kg) attenuated the ability of MK-801 (1.0 mg/kg) to elicit this behavior. However, the ability of D-cycloserine to attenuate MK-801-elicited mouse-popping behavior was not evident in stressed mice, 24 h after they were forced to swim for up to 10 min in cold water. Thus, the therapeutic value of glycinergic interventions may be limited by environmental factors, such as stress.

Inbred mouse strains differ in their sensitivity to an antiseizure effect of MK-801.

The ability of MK-801 to antagonize the electrical precipitation of tonic hindlimb extension was studied in four inbred mouse strains (BALB/c, C57BL/6, AKR, and DBA/2) and the outbred NIH Swiss strain, using an incremental electroconvulsive shock (IECS) procedure. Strains differed in the threshold voltages required for the electrical precipitation of tonic hindlimb extension. They also differed in their sensitivity to antagonism of electrically precipitated tonic hindlimb extension by MK-801. The BALB/c, C57BL, and DBA strains required a significant elevation of the threshold voltage for the elicitation of tonic hindlimb extension in response to 0.18 mg/kg of MK-801, the lowest dose tested; whereas the AKR and NIH Swiss strains did not respond to this dose with an increase of threshold voltage for the elicitation of tonic hindlimb extension. Moreover, a higher percentage of BALB/c mice were maximally protected against seizure elicitation by MK-801 over a dosage range of 0.18 to 0.56 mg/kg, compared to the other strains. The demonstration of strain differences suggests that genetic factors influence the anticonvulsant properties of MK-801.

Field study of the safety, immunogenicity, and efficacy of an inactivated equine rotavirus vaccine.

OBJECTIVE: To determine safety, immunogenicity, and efficacy of an inactivated equine rotavirus vaccine. DESIGN: Prospective randomized controlled trial. ANIMALS: 316 pregnant Thoroughbred mares during the first year of the study and 311 during the second year. PROCEDURE: During the first year, mares received 3 doses of vaccine or placebo, IM, at 8, 9, and 10 months of gestation. Serum neutralizing antibody titers were measured before vaccination and 1 and 35 days after foaling. Antibody titers were measured in foals 1, 7, 35, 60, 90, and 120 days after birth. During the second year, mares that had been vaccinated the previous year received a single booster dose of vaccine approximately 1 month prior to parturition. Mares that had received the placebo the previous year and mares new to the study received 3 doses of vaccine or placebo. Serum neutralizing antibody titers were measured in samples taken from mares approximately 1 day after foaling and from foals approximately 1 and 60 days after birth. RESULTS: Adverse reactions were not observed. Antibody titers were significantly increased at the time of foaling and 35 days after foaling in vaccinated, compared with control, mares and for 90 days after birth in foals born to vaccinated, compared with foals born to control, mares. Incidence of rotaviral diarrhea was lower in foals born to vaccinated, compared with foals born to control, mares, but the difference was not significant. CLINICAL IMPLICATIONS: Results suggest that the equine rotavirus vaccine is safe and immunogenic and that reasonable efficacy under field conditions can be expected.

The impact of a helicopter emergency medical services program on potential morbidity and mortality.

INTRODUCTION: The evaluation of the effectiveness of helicopter emergency medical services is currently a major focus of air transport research, and dispatch judgment likely will play a significant role in any research aimed at measuring outcome or impact. SETTING: Two rotor-wing programs in Alberta, Canada. METHODS: A panel of experts evaluated the effectiveness of a helicopter service in Canada. Four hundred sequential patient records were examined and categorized into four risk levels. Level 1 included patients who required critical intervention. Level 2 included patients in whom a major deterioration of vital signs could be expected. Level 3 patients were those for whom transport by an advanced life support ground unit would have been adequate. Level 4 was strictly for missions in which patient transport by any other means would have been impractical, such as remote locations (these cases were double-rated). RESULTS: Risk level 1 included 98 cases (24.5%); risk level 2, 266 cases (66.5%); risk level 3, 36 cases (9%); and risk level 4, 16 cases, two of which were rated level 1, 11 rated level 2, and three rated level 3. CONCLUSION: The results indicate that in 91% of the reviewed cases, helicopter transport was appropriate, representing a reasonable and judicious use of a helicopter emergency medical service.

Outbreak of equine influenza among horses in Hong Kong during 1992.

Equine-2 influenza virus A (H3N8) infection occurred among vaccinated thoroughbred horses in Hong Kong during November and December 1992. The outbreak was unique in that it occurred among a large population stabled under intensive conditions. It resulted in the postponement of seven race meetings over a period of 32 days. The outbreak originated after the importation of horses 25 to 32 days before any clinical signs were reported. Vaccination did not prevent 75 per cent of the population from becoming infected, and half the infected horses developed clinical signs. Vaccination did, however, contribute to reducing the morbidity and the severity and duration of the clinical signs.

The cutting edge: surgical education for medical students and a patient care system.

This paper describes computer-assisted instruction designed for medical students on their clinical surgery rotation. Patient care systems continue to evolve; incentives for physician participation should include educational benefits and clinical practice guidelines. Sometimes overlooked in the rush to develop expert systems are medical students, who do not have the depth of knowledge inherent in decision support. Foothills Hospital in Calgary, Canada, uses the TDS HC4000 patient care system, where physicians and medical students enter their orders directly on the terminals. The Surgical Patient Care Program was developed to help students learn the basics of peri-operative patient management. The Program runs on the HC4000 and consists of a collection of order sets with appended educational information to guide students in their automated order selection. Unlike other instructional programs, which use fictitious patients, students enter real orders on real patients. Tracking of usage indicates that the Program is popular with students, who each access it an average of 20 times per week. An ongoing study will determine any educational benefit by measuring student performance at Foothills Hospital against a control group at another hospital, which does not have a computerized patient care system.

Genetic and antigenic analysis of the influenza virus responsible for the 1992 Hong Kong equine influenza epizootic.

An outbreak of influenza occurred among thoroughbred racehorses in Hong Kong in November-December 1992, with morbidity of 37%. All horses involved had been vaccinated against equine-1 and equine-2 influenza viruses but not against the virus responsible for the 1989 equine influenza outbreak in northern China (influenza A/equine/Jilin/89, subtype H3N8). Therefore the source and nature of the virus causing the Hong Kong outbreak was investigated. Virus isolated from a horse infected during the outbreak was used for genetic analysis. All the viral gene segments were similar to those of equine-2 (H3N8) influenza viruses and unrelated to those of equine/Jilin/89 virus. The nucleotide sequence of the viral hemagglutinin gene showed high homology (99.4%) to that of influenza A/equine/Suffolk/89 (H3N8) virus which has circulated extensively in Europe. However, these viruses differed in their antigenic reactivity to a panel of monoclonal antibodies. Preliminary epizootiological information plus the concordance of amino acid sequence between hemagglutinins of the Hong Kong isolate and a contemporaneous equine-2 influenza virus isolate from the United Kingdom indicated that the probable source of the Hong Kong outbreak was horses recently imported from England or Ireland.

Rapid diagnosis of equine influenza by the Directigen FLU-A enzyme immunoassay.

The Directigen FLU-A enzyme immunoassay was tested for its ability to detect equine-2 influenza viruses in nasopharyngeal fluids from horses and ponies. A total of 125 swabs from experimental infections and from different sources of natural infection in the USA and Hong Kong were examined. The assay results were compared with the results of standard virus culture in embryonated chicken eggs or Madin-Darby canine kidney cells, and with the serology of the horses sampled. In comparison with virus culture the enzyme immunoassay exhibited 83 per cent sensitivity, 78 per cent specificity, 70 per cent positive predictive value and 88 per cent negative predictive value. The test appeared to be more sensitive than haemagglutination for the detection of low levels of virus in embryonated egg cultures. It also detected equine-1 influenza virus in culture. The test is rapid (15 minutes), simple, and should be a convenient method for the rapid diagnosis and screening of horses for equine influenza infection.

Temporal control in fixed-interval schedules.

The peak procedure was used to study temporal control in pigeons exposed to seven fixed-interval schedules ranging from 7.5 to 480 s. The focus was on behavior in individual intervals. Quantitative properties of temporal control depended on whether the aspect of behavior considered was initial pause duration, the point of maximum acceleration in responding, the point of maximum deceleration, the point at which responding stopped, or several different statistical derivations of a point of maximum responding. Each aspect produced different conclusions about the nature of temporal control, and none conformed to what was known previously about the way ongoing responding was controlled by time under conditions of differential reinforcement. Existing theory does not explain why Weber's law so rarely fit the results or why each type of behavior seemed unique. These data fit with others suggesting that principles of temporal control may depend on the role played by the particular aspect of behavior in particular situations.

Abdominal compressions during CPR: hemodynamic effects of altering timing and force.

To determine the optimal method of applying abdominal compressions during cardiopulmonary resuscitation (CPR), 3 levels of pressure (25, 50, and 100 torr) were applied to the abdomen a) continuously and b) as 500 msec pulses at 10 different phases during the CPR cycle in 8 anesthetized dogs. Thoracic aortic (Ao) and right atrial (RA) pressures were measured and PAo-PRA was calculated as the coronary perfusion gradient. A pneumatic piston device provided external chest compression (60/min, 120 lbs, for 50% of the cycle) and ventilation (80% O2, 12/min, at 20cm, H2O). Another identical device provided abdominal compression (AC) via an air-filled bladder. High-pressure (100 torr) AC applied for 500 msec commencing 200 msec prior to chest compression demonstrated the best overall profile, raising mean aortic pressure 26 torr (P less than 0.001) and peak coronary perfusion gradient pressure 17 torr (P less than 0.02) from control values during standard CPR of 58 and 41 torr, respectively. We conclude that applying high-pressure, 500-msec pulses of AC 200 msec before chest compressions significantly improves CPR hemodynamics.

Arthropod faunal composition on Kentucky equine premises.

Thirty-nine arthropod species representing the families Muscidae, Chloropidae, Tabanidae, Simuliidae, Culicidae, and Ixodidae were collected from Kentucky equine premises using dry ice-baited canopy traps, light traps, water samples, tick drags, and animal inspections during late April to mid-October 1987 and 1988. Thirty-three species were collected from canopy traps, consisting of 74.3% muscid, 16.7% chloropid, 5.0% simuliid, 3.8% tabanid, and 0.2% culicid species. Light traps attracted eight culicid and water samples yielded three culicid species. One ixodid species was collected with drags, and animal inspections yielded two muscid and two ixodid species. Comparison of species assemblages among farms and across years using multivariate principal component analysis (PCA) yielded three distinct principal components, and PCA scores for each farm per year were correlated with biotic and abiotic environmental factors and management practices. The proximity to cattle herds was the best predictor of similarity in species assemblages among farms, reflecting the high percentage of muscid species collected. Poor management practices were partially responsible for proportionally larger populations of culicids, ixodids, and muscids on some farms.

Analysis of serotypes and electropherotypes of equine rotaviruses isolated in the United States.

Equine group A rotaviruses isolated over a 10-year period in New York State, New Jersey, Kentucky, and Texas were compared serotypically and electropherotypically. All isolates were determined to be serotype 3 by reaction with hyperimmune antiserum to the serotype 3 H-2 strain of equine rotavirus. All displayed RNA electrophoretic migration patterns related to that of the H-2 strain but distinct from that of serotype 5 strain H-1. A serologic survey of 184 mares in Kentucky, which was done to determine the incidence of H-1 and H-2 infections, showed geometric mean serum neutralizing titers to the H-2 strain of equine rotavirus to be significantly higher than those to the H-1 strain. These data suggest that the serotype 3 H-2 strain is the dominant equine rotavirus in Kentucky and perhaps elsewhere in the United States. We were unable to produce confirmational evidence that the H-1 strain occurs as a natural infection in the United States.

Viral respiratory disease of the horse.

The diagnosis of any viral respiratory disease relies on laboratory procedures to isolate the virus and demonstrate a significant rise in serum antibody titers. To isolate viruses from the upper respiratory tract, it is imperative that nasopharyngeal swabs are obtained from animals in the early acute stage of illness, i.e., during the pyrexic phase when the virus is replicating. Nasopharyngeal swabs must be placed in a virus transport medium and forwarded immediately to the laboratory at refrigerated temperature. Equine influenza, rhinopneumonitis, and equine viral arteritis are the three viral infections causing outbreaks of respiratory disease in North America. African horse sickness, although foreign to North America, could be introduced despite stringent horse importation regulations. Specific antiviral therapy is not available to treat viral respiratory disease in the horse. A variety of inactivated and modified live vaccines, however, are available to prevent clinical disease and the spread of infection caused by the common viral respiratory pathogens. A considerable amount of research is underway to enhance the potency and duration of immunity of the present vaccines against influenza and rhinopneumonitis. This research is directed at defining and characterizing the importance of specific glycoprotein antigens on the surface of the virus, which trigger the various host immune responses, and determining whether they are stimulatory or suppressive.

Attempted transmission of Ehrlichia risticii (Rickettsiaceae) with Stomoxys calcitrans (Diptera: Muscidae).

Experimental transmission of Ehrlichia risticii, the causal agent of Potomac horse fever, was attempted with adult stable flies, Stomoxys calcitrans, (L.) using two feeding schedules. In schedule A, a set of 140 flies was allowed to feed once on an experimentally infected donor pony and once 24 h later on a recipient pony. A different set of flies was used each day for a 12-d period. In schedule B, 240 flies were allowed to feed once daily for 12 consecutive d on the donor pony followed by five consecutive daily feedings on the recipient pony. E. risticii was isolated from the blood of the experimentally infected pony during the entire fly-feeding schedule. The recipient pony did not develop clinical signs of Potomac horse fever and remained seronegative to E. risticii up to 60 d after the last stable fly feeding. Mice injected intraperitoneally with emulsions of schedule A and B stable flies were seronegative for E. risticii 30 d after inoculation, and ehrlichial organisms were not demonstrated in impression smears from the digestive tracts of the flies. The stable fly did not transmit E. risticii under these experimental conditions.