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Biomedical subjects

H G Townsend

Publications and source records attributed to H G Townsend.

At least 19 recordsLinked to original sources
PubMed2001

Effect of vaccination on experimental infection with Bordetella bronchiseptica in dogs.

OBJECTIVE: To determine comparative efficacy of vaccines administered IM and intranasally, used alone or sequentially, to protect puppies from infection with Bordetella bronchiseptica and determine whether systemic or mucosal antibody response correlated with protection. DESIGN: Randomized controlled trial. ANIMALS: 50 specific-pathogen-free Beagle puppies. PROCEDURE: In 2 replicates of 25 dogs each, 14-week-old puppies that were vaccinated against canine distemper virus and parvovirus were vaccinated against B bronchiseptica via intranasal, IM, intranasal-IM, or IM-intranasal administration or were unvaccinated controls. Puppies were challenge exposed via aerosol administration of B bronchiseptica 2 weeks after final vaccination. Clinical variables and systemic and mucosal antibody responses were monitored for 10 days after challenge exposure. Puppies in replicate 1 were necropsied for histologic and immunohistochemical studies. RESULTS: Control puppies that were seronegative before challenge exposure developed paroxysmal coughing, signs of depression, anorexia, and fever. Vaccinated puppies (either vaccine) that were seronegative before challenge exposure had fewer clinical signs. Puppies that received both vaccines had the least severe clinical signs and fewest lesions in the respiratory tract. Vaccinated dogs had significantly higher concentrations of B bronchiseptica-reactive antibodies in serum saliva before and after challenge. Antibody concentrations were negatively correlated with bacterial growth in nasal cavity and pharyngeal samples after challenge exposure. CONCLUSIONS AND CLINICAL RELEVANCE: Parenterally and intranasally administered vaccines containing B bronchiseptica may provide substantial protection from clinical signs of respiratory tract disease associated with infection by this bacterium. Administration of both types of vaccines in sequence afforded the greatest degree of protection against disease.

Administration, Intranasal↗
PubMed2001

Diverged evolution of recent equine-2 influenza (H3N8) viruses in the Western Hemisphere.

We reported previously that equine-2 influenza A virus (H3N8) had evolved into two genetically and antigenically distinct "Eurasian" and "American" lineages. Phylogenetic analysis, using the HA1 gene of more recent American isolates, indicated a further divergence of these viruses into three evolution lineages: A South American lineage, a Kentucky lineage, and a Florida lineage. These multiple evolution pathways were not due to geographic barriers, as viruses from different lineages co-circulated. For the Kentucky lineage, the evolution rate was estimated to be 0.89 amino acid substitutions per year, which agreed with the previously estimated rate of 0.8. For the South American lineage, the evolution rate was estimated to be only 0.27 amino acid substitutions per year. This low evolution rate was probably due to a unique alternating Ser138 to Ala138 substitutions at antigenic site A. For the Kentucky lineage, there was a preference for sequential nonsynonymous substitutions at antigenic site B, which was also a "hot spot" for amino acid substitutions. Convalescent sera had minimal cross-reactivity to viruses of different lineages, indicating antigenic distinctions among these viruses. In contrast to human H3N2 viruses, our results suggested that the evolution of equine-2 influenza virus resembled the multiple evolution pathways of influenza B virus.

Amino Acid Sequence↗
PubMed2001

A new modified live equine influenza virus vaccine: phenotypic stability, restricted spread and efficacy against heterologous virus challenge.

Flu Avert IN vaccine is a new, live attenuated virus vaccine for equine influenza. We tested this vaccine in vivo to ascertain 1) its safety and stability when subjected to serial horse to horse passage, 2) whether it spread spontaneously from horse to horse and 3) its ability to protect against heterologous equine influenza challenge viruses of epidemiological relevance. For the stability study, the vaccine was administered to 5 ponies. Nasal swabs were collected and pooled fluids administered directly to 4 successive groups of naïve ponies by intranasal inoculation. Viruses isolated from the last group retained the vaccine's full attenuation phenotype, with no reversion to the wild-type virus phenotype or production of clinical influenza disease. The vaccine virus spread spontaneously to only 1 of 13 nonvaccinated horses/ponies when these were comingled with 39 vaccinates in the same field. For the heterologous protection study, a challenge model system was utilised in which vaccinated or naïve control horses and ponies were exposed to the challenge virus by inhalation of virus-containing aerosols. Challenge viruses included influenza A/equine-2/Kentucky/98, a recent representative of the 'American' lineage of equine-2 influenza viruses; and A/equine-2/Saskatoon/90, representative of the 'Eurasian' lineage. Clinical signs among challenged animals were recorded daily using a standardised scoring protocol. With both challenge viruses, control animals reliably contracted clinical signs of influenza, whereas vaccinated animals were reliably protected from clinical disease. These results demonstrate that Flu Avert IN vaccine is safe and phenotypically stable, has low spontaneous transmissibility and is effective in protecting horses against challenge viruses representative of those in circulation worldwide.

Administration, Intranasal↗
PubMed2001

Efficacy of a cold-adapted, intranasal, equine influenza vaccine: challenge trials.

A randomised, controlled, double-blind, influenza virus, aerosol challenge of horses was undertaken to determine the efficacy of a cold-adapted, temperature sensitive, modified-live virus, intranasal, equine influenza vaccine. Ninety 11-month-old influenza-naïve foals were assigned randomly to 3 groups (20 vaccinates and 10 controls per group) and challenged 5 weeks, 6 and 12 months after a single vaccination. Challenges were performed on Day 0 in a plastic-lined chamber. Between Days 1 and 10, animals were examined daily for evidence of clinical signs of influenza. Nasal swabs for virus isolation were obtained on Day 1 and Days 1 to 8 and blood samples for serology were collected on Days 1, 7 and 14. There was no adverse response to vaccination in any animal. Following challenge at 5 weeks and 6 months, vaccinates had significantly lower clinical scores (P = 0.0001 and 0.005, respectively), experienced smaller increases in rectal temperature (P = 0.0008 and 0.0007, respectively) and shed less virus (P<0.0001 and P = 0.03, respectively) over fewer days (P<0.0001 and P = 0.002, respectively) than did the controls. After the 12 month challenge, rectal temperatures (P = 0.006) as well as the duration (P = 0.03) and concentration of virus shed (P = 0.04) were significantly reduced among vaccinated animals. The results of this study showed that 6 months after a single dose of vaccine the duration and severity of clinical signs were markedly reduced amongst vaccinated animals exposed to a severe live-virus challenge. Appropriate use of this vaccine should lead to a marked reduction in the frequency, severity and duration of outbreaks of equine influenza in North America.

Administration, Intranasal↗
PubMed2000

Clinical and pathologic findings in donkeys with hypothermia: 10 cases (1988-1998).

OBJECTIVE: To describe clinical signs and clinicopathologic findings in donkeys with hypothermia. DESIGN: Retrospective study. ANIMALS: 10 hypothermic donkeys. PROCEDURE: Information on signalment, history, physical examination findings, results of diagnostic tests, treatments, and necropsy findings was extracted from medical records of all donkeys with hypothermia between 1988 and 1998 and compared with information from medical records of all normothermic donkeys and hypothermic horses admitted to the hospital during the same period. RESULTS: Donkeys were more likely to be hypothermic than horses. The mean age of hypothermic donkeys was 6 years (range, 7 months to 11 years), compared with 4.2 years (range, < 1 month to 15 years) for normothermic donkeys; this difference was not significant. Ten of 12 horses with hypothermia were neonates; there were no hypothermic neonatal donkeys. At admission, 7 of 8 hypothermic donkeys were in good body condition and all hypothermic donkeys were weak. Six hypothermic donkeys were able to maintain sternal recumbency, 1 remained in lateral recumbency, and 3 were able to stand. Of the 10 hypothermic donkeys, 2 survived, 1 died, and 7 were euthanatized. Histologically, the thyroid glands from 4 of 5 hypothermic donkeys appeared abnormal and were similar to those of foals with hypothyroidism. During the months that hypothermic donkeys were admitted, there was not a significant difference in environmental temperatures on days of admission between hypothermic and normothermic donkeys. CONCLUSIONS AND CLINICAL RELEVANCE: Hypothermia is a problem in donkeys during cold winter months, and may not be secondary to other disease or related to diet or management.

Animals↗
PubMed2000

Descriptive epidemiologic study of disease associated with influenza virus infections during three epidemics in horses.

OBJECTIVE: To describe 3 epidemics of respiratory tract disease caused by influenza virus infections in a large population of horses. DESIGN: Cross-sectional and prospective longitudinal observational studies. ANIMALS: All horses stabled at a Thoroughbred racetrack. PROCEDURES: During a 3-year period, descriptive information was collected as horses arrived at the racetrack and throughout race meetings. Routine observations and physical examinations were used to classify horses' disease status. Cause of epidemics was established by use of serologic testing and identification of influenza virus in nasal secretions. RESULTS: An epidemic of respiratory tract disease caused by influenza virus infections was identified during each year of the study. Attack rates of infectious upper respiratory tract disease (IURD) ranged from 16 to 28%. Incidence of disease caused by influenza virus infections during racing seasons in the second and third years was 27 and 37 cases/1,000 horses/mo, respectively. Physical distributions of stall locations revealed that affected horses were stabled throughout the population; horses affected later in epidemics were often clustered around horses affected earlier. Mucopurulent nasal discharge and coughing were observed in 83 and 62% of horses with IURD, respectively. Median duration of clinical disease was 11 days. Serologic testing was the most sensitive method used to detect influenza virus infections; 76% of affected horses seroconverted to influenza virus. CONCLUSIONS AND CLINICAL RELEVANCE: Epidemics of IURD were observed annually in association with influenza virus infections. Few precautions were taken to limit spread of infection. Preventing or decreasing the likelihood of exposure and improving immunity in the population could substantially decrease risk of disease in similar populations.

Animals↗
PubMed2000

Risk factors for disease associated with influenza virus infections during three epidemics in horses.

OBJECTIVE: To identify risk factors associated with respiratory tract disease in horses during 3 epidemics caused by influenza virus infections. DESIGN: Cross-sectional and prospective longitudinal observational studies. ANIMALS: 1,163 horses stabled at a Thoroughbred racetrack. PROCEDURES: Investigations were conducted during a 3-year period. An epidemic of respiratory tract disease caused by influenza virus infections was identified in each year. Routine observations and physical examinations were used to classify horses' disease status. Data were analyzed to identify factors associated with development of disease. RESULTS: Results were quite similar among the epidemics. Concentrations of serum antibodies against influenza virus and age were strongly associated with risk of disease; young horses and those with low antibody concentrations had the highest risk of disease. Calculation of population attributable fractions suggested that respiratory tract disease would have been prevented in 25% of affected horses of all horses had high serum antibody concentrations prior to exposure. However, recent history of vaccination was not associated with reduction in disease risk. Exercise ponies had greater risk of disease than racehorses, which was likely attributable to frequent horse-to-horse contact. CONCLUSIONS AND CLINICAL RELEVANCE: Particular attention should be paid to young horses, those with low serum antibody concentrations, and horses that have frequent contact with other horses when designing and implementing control programs for respiratory tract disease caused by influenza virus infections. It appears that control programs should not rely on the efficacy of commercial vaccines to substantially reduce the risk of disease caused by influenza virus infections.

Age Factors↗
PubMed2000

Equine vaccination.

Equine infectious disease remains a constant and important threat to the health of domesticated horses. Vaccination plays a critical role in protecting against such disease, but at the present time the efficacy of some equine vaccination strategies is in doubt. The best strategy for resolving these concerns is an improved knowledge of the immunologic basis of successful vaccination, combined with the appropriate integration of effective vaccines into well-designed disease control policies.

Animals↗
PubMed2000

Immunity to equine influenza: relationship of vaccine-induced antibody in young Thoroughbred racehorses to protection against field infection with influenza A/equine-2 viruses (H3N8).

Field outbreaks of influenza that occurred in vaccinated Thoroughbred racehorses in Newmarket in 1995 and 1996 were investigated by nucleoprotein ELISA and serology. Investigations showed that serum levels of vaccine-induced single radial haemolysis (SRH) antibody correlated closely with protective immunity against equine influenza and were consistent with observations made in previous experimental studies using nebulised aerosol challenge. In the second part of this study, antibody levels stimulated by vaccination were investigated to examine probable protection in high risk groups, such as yearlings and horses in training. Results for yearlings correlated closely with experimentally derived antibody profiles described for several equine influenza vaccines. The horses in training had levels of antibody immediately prior to revaccination, which were higher than those measured in the yearlings. In conclusion, SRH antibody, used in the investigation of outbreaks and surveillance of post vaccination responses, was shown to correlate with and validate experimental vaccination and challenge models currently used in ponies in the licensing of modern vaccines. There may be benefit from serological monitoring of horses following vaccination through identification of susceptible periods to infection and demonstration of poor vaccine responders. This would allow appropriate and timely amendment of vaccination strategies to maximise protective immunity against influenza.

Animals↗
PubMed1999

Efficacy of a commercial vaccine for preventing disease caused by influenza virus infection in horses.

OBJECTIVE: To evaluate efficacy of a commercial vaccine for prevention of infectious upper respiratory tract disease (IURD) caused by equine influenza virus. DESIGN: Double-masked, randomized, controlled field trial. ANIMALS: 462 horses stabled at a Thoroughbred racetrack. PROCEDURE: Vaccine or saline solution placebo was administered 4 times in the population at 6-week intervals. The vaccine contained 3 strains of inactivated influenza virus, and inactivated equine herpesvirus type 4. Horses received 1 or 2 doses of vaccine or placebo prior to onset of a natural influenza epidemic, and were examined 5 d/wk to identify and monitor horses with IURD. Serum antibody concentrations were determined, and virus isolation was performed. RESULTS: Vaccination of horses prior to the influenza epidemic did not result in significant decrease in risk of developing respiratory tract disease. Severity of clinical disease was not different between affected vaccinated horses with IURD and controls with IURD, but median duration of clinical disease was 3 days shorter in vaccinated horses. Serum concentrations of antibodies to H3N8 influenza viruses were lower prior to initial vaccination in horses that were sick during the epidemic, and did not increase in these horses in response to vaccination. On arrival at the racetrack, young horses had lower antibody concentrations than older horses, and did not respond to vaccination as well. CONCLUSIONS AND CLINICAL RELEVANCE: Vaccination was of questionable benefit. A greater degree of protection must be obtained for influenza vaccines to be effective in protecting horses from IURD. Objective field evaluations of commercial vaccines are needed to adequately document their efficacy.

Animals↗
PubMed1999

Validity of saddle pressure measurements using force-sensing array technology--preliminary studies.

Back pain is a common and poorly understood clinical problem. An important factor in this regard is the induction or exacerbation of back pain from badly designed or poorly fitting saddles. This study used a pressure-sensing mat to investigate saddle fit. The aims of the study were to confirm the accuracy and reliability of the force-sensing array technology when used to measure pressure beneath the saddles of horses, and to collect some initial data from normal healthy horses with well-fitting saddles. Experiments were undertaken to establish that a linear relationship existed between the total force (weight) exerted and the pressure measured beneath the saddle, using both a wooden horse and a live horse in the standing position. Further studies were performed to demonstrate that characteristic changes of the centre of pressure occur while horses move at the walk, sitting trot, rising trot, and canter.

Animals↗
PubMed1999

Investigations on the ability of clenbuterol hydrochloride to reduce clinical signs and inflammation associated with equine influenza A infection.

Twenty-four Quarter Horse and Quarter Horse-cross yearlings were experimentally infected with influenza A virus (Influenza A/equine/Saskatoon/90 [H3N8]) by nebulisation. In a double blind controlled trial the horses were randomly assigned to 3 groups of 8 animals. Group 1 received a placebo, (carrier syrup), Group 2 the labelled dose and Group 3 twice the labelled dose of clenbuterol hydrochloride. All treatments were given per os b.i.d. for 10 days and started on the day of infection. The horses were monitored for clinical signs of influenza infection for 14 days. Bronchoalveolar lavages were performed 4 days prior to, and 5 and 13 days after infection. Cell counts and concentrations of prostaglandin E2 and prostaglandin F2alpha in the lavage fluid were determined. Blood samples for haematology and serology were taken 4 days before, on the day of infection, 5, 9 and 13 days after infection. All horses experienced a typical influenza infection with fever, coughing and secondary bacterial infections with mainly Actinobacillus spp. and Streptococcus spp. There was no statistically or clinically significant effect of treatment with clenbuterol hydrochloride on measured clinical or laboratory parameters within 14 days of infection.

Adrenergic beta-Agonists↗
PubMed1999

Urethrorectal fistula in a horse.

Anomalies of the urethra are uncommon. Urethrorectal fistula in horses has only been reported in foals and only in conjunction with other congenital anomalies. This report describes the diagnosis, surgical management, and possible etiologies of a unique case of urethrorectal fistula in a mature gelding.

Animals↗
PubMed1999

Effect of feed rate and drill speed on temperatures in equine cortical bone.

OBJECTIVE: To examine the amount of heat generated in equine cortical bone by a 6.2-mm drill, using low- and high-speed and controlled feed rate drilling. SAMPLE POPULATION: 10 metacarpal bones harvested from five 2-year-old draft-type horses. PROCEDURE: Drilling on metacarpal bones was done using a machine shop mill with which the feed rate and drill speed could be precisely controlled. Bones were drilled, using 6 combinations of feed rate (1, 2, and 3 mm advance/s) and drill speed (317 and 1,242 revolutions/min [rpm], with maximal temperatures recorded by thermocouples placed 1, 1.5, and 2 mm from the drill. Maximal temperatures were evaluated for the effect of feed rate, drill speed, cortical thickness, and distance from the drill, using linear regression analysis. RESULTS: Increasing feed rate from 1 to 2 and from 2 to 3 mm/s significantly decreased mean maximal temperature. Increasing drill speed from 317 to 1242 rpm significantly increased mean maximal temperature. Increasing cortical thickness significantly increased mean maximal temperature, and increasing the distance from the drill hole significantly decreased mean maximal temperatures. CONCLUSIONS: On the basis of our results, we recommend using low drill speeds while applying sufficient axial force to advance the drill as rapidly as possible through the bone. CLINICAL RELEVANCE: Results of using this in vitro model suggest that temperatures at the drill-bone interface may be sufficiently high to result in significant thermal necrosis when drilling equine cortical bone.

Animals↗
PubMed1999

The effect of opioid and acepromazine premedication on the anesthetic induction dose of propofol in cats.

The median effective dosage (ED50) for induction of anesthesia with propofol was determined by using the up-and-down method in 31 unpremedicated cats, in 30 cats premedicated with butorphanol, 0.4 mg/kg body weight (BW), and acepromazine, 0.1 mg/kg BW, intramuscularly, and in 30 cats premedicated with morphine, 0.2 mg/kg BW, and acepromazine, 0.1 mg/kg BW, intramuscularly. The dose required for a satisfactory anesthetic induction in 50% of unpremedicated cats (ED50) was 7.22 mg/kg BW and of premedicated cats was 5.00 mg/kg BW. The reduction in dose was statistically significant in both premedicated groups compared with no premedication. There was no significant difference in ED50 between premedication regimes. Cyanosis was the most common adverse effect observed in all groups following anesthetic induction with propofol.

Acepromazine↗
PubMed1997

An outbreak of respiratory disease in horses associated with Mycoplasma felis infection.

Lower respiratory tract disease developed in a group of racehorses in training between two and six years of age. Disease was observed in 22 of 25 horses for which full records were available. Seroconversion to Mycoplasma felis was demonstrated by indirect haemagglutination assay in 19 of 22 paired sera and high titres (> or = 64) were found in convalescent sera from the three remaining horses. Evidence of respiratory viral infection was confined to seroconversions to equine herpesvirus-4 in two of the horses. Tracheal wash samples, taken from four horses with visibly increased tracheal mucopus, contained more than 10(4) colony forming units/ml M felis and high proportions of neutrophils. This is the first description of an outbreak of lower respiratory tract disease in horses in training associated with M felis infection.

Animals↗