W. D. Wilson

Passive transfer of maternal immunoglobulin isotype antibodies against tetanus and influenza and their effect on the response of foals to vaccination

Influenza and tetanus-specific antibodies of the IgG sub-isotypes are posively transferred to foals via colostrum and inhibit their response to inactivated influenza vaccines and tetanus toxoid. High titres of influenza antibodies of IgGa and IgGb subisotypes and tetanus antibodies of the IgGa, IgGb and IgG(T) subisotypes were detected in postsucking serum samples collected from foals born to mares that had received booster doses of multicomponent vaccines during the last 2 months of gestation. Thereafter, titres declined in an exponential manner but were still detectable in all foals at age 26 weeks, regardless of whether they had been vaccinated prior to age 26 weeks. Mean +/- s.e. half-life of decline of influenza IgGa antibodies (27.0 +/- 2.3 days) was significantly shorter than that of influenza IgGb antibodies (39.1 +/- 2.7 days; P<0.005). Tetanus IgGa and IgGb antibodies declined with half-lives of 28.8 +/- 3.0 and 34.8 +/- 5.1 days, respectively. Titres of tetanus IgG(T) antibodies were substantially higher than those of influenza IgG(T) antibodies in postsucking samples and remained so through age 26 weeks, declining with a half-life of approximately 35 days. Postsucking titres of tetanus and influenza antibodies of the IgA isotype were low and declined rapidly to undetectable levels. Yearlings showed significant increases in titre of influenza IgGa, IgGb and IgG(T) subisotype antibodies but no increase in influenza IgA antibodies in response to 2 doses of multicomponent vaccines containing tetanus toxoid and inactivated influenza A-1 and A-2 antigens. Yearlings also showed strong tetanus IgGa, IgGb and IgG(T) subisotype responses to one dose of vaccine and a substantial further rise in titre in response to administration of a second dose 3 weeks later, but failed to show an increase in titre of tetanus IgA antibodies. The influenza and tetanus IgGa, IgGb and IgG(T) subisotype responses of 6-month-old foals to vaccination followed the same pattern as those shown by yearlings but titres were generally lower. In contrast, 3-month-old foals failed to show increases in titre of either influenza or tetanus IgG subisotypes in response to 2 doses of vaccine and generally needed 1-3 additional booster doses of vaccine to achieve titres similar to those achieved by yearlings after 2 doses. Based on the finding that maternal antibodies exert a significant inhibitory effect on the response of foals to tetanus toxoid and inactivated influenza antigens, it is recommended that primary immunisation of foals born to vaccinated mares should not commence before age 6 months.

Intestinal neoplasia in horses

BACKGROUND Intestinal neoplasia of horses is inadequately described. HYPOTHESIS Intestinal neoplasia of horses has characteristic clinicopathologic features. ANIMALS Thirty-four horses with intestinal neoplasia. METHODS Retrospective study. RESULTS Anamnesis, clinical signs, clinicopathologic and pathologic findings in 34 adult horses diagnosed histologically with intestinal neoplasia were reviewed. The horses ranged in age from 2 to 30 years (mean 16.6 years at presentation). The Arabian breed was most represented and there was no sex predisposition. The most common presenting complaints were weight loss, colic, anorexia, and fever. The most consistent clinical signs were poor body condition, tachycardia, tachypnea, fever, and diarrhea. Useful diagnostic tools included rectal examination, routine blood analyses, abdominocentesis, ultrasonographic examination, rectal biopsy, and exploratory laparotomy. Alimentary lymphoma was the most common intestinal neoplasia identified, followed by adenocarcinoma and smooth muscle tumors. The small intestine was the most common segment of intestine affected for all neoplasms. Intestinal neoplasia was diagnosed antemortem in 13 of 34 (38%) horses. The median time from onset of clinical signs to death or euthanasia was 1.9 months. The discharge rate was 15%. Although the longest survival was observed in horses with jejunal adenocarcinoma, all horses were eventually euthanized because of intestinal neoplasia. CONCLUSIONS Arabian horses were 4.5 times more likely to have intestinal neoplasia diagnosed than were other breeds.

Purpura haemorrhagica in 53 horses.

The medical records of 53 horses with purpura haemorrhagica were reviewed. Seventeen of them had been exposed to or infected with Streptococcus equi, nine had been infected with Corynebacterium pseudotuberculosis, five had been vaccinated with S equi M protein, five had had a respiratory infection of unknown aetiology, and two had open wounds; the other 15 cases had no history of recent viral or bacterial infection. The horses were between six months and 19 years of age (mean 8-4 years). The predominant clinical signs were well demarcated subcutaneous oedema of all four limbs and haemorrhages on the visible mucous membranes; other signs included depression, anorexia, fever, tachycardia, tachypnoea, reluctance to move, drainage from lymph nodes, exudation of serum from the skin, colic, epistaxis and weight loss. Haematological and biochemical abnormalities commonly detected were anaemia, neutrophilia, hyperproteinaemia, hyperfibrinogenaemia, hyperglobulinaemia and high activities of muscle enzymes. All of the horses were treated with corticosteroids; 42 also received non-steroidal anti-inflammatory drugs and 26 received antimicrobial drugs. Selected cases received special nursing care, including hydrotherapy and bandaging of the limbs. Most of the horses were treated for more than seven days and none of them relapsed. Forty-nine of the horses survived, one died and three were euthanased, either because their severe clinical disease failed to respond to treatment or because they developed secondary complications. Two of the four non-survivors had been vaccinated against S equi with a product containing the M protein, one had a S equi infection and the other had a respiratory infection of undetermined aetiology.

Bacteraemia in neonatal foals: clinicopathological differences between Gram-positive and Gram-negative infections, and single organism and mixed infections

REASONS FOR PERFORMING STUDY Treatment for bacteraemia in foals must be started before the identity of the causative organism is known. Information aiding selection of effective antimicrobials should improve outcome. OBJECTIVES To describe differences in clinical and clinicopathological data and outcome in foals with bacteraemia due to different classes of bacteria. METHODS Records of foals with a positive blood culture, age < 10 days and presenting to a university hospital 1995-2004, were reviewed. Bacterial culture results, subject details, historical information, physical examination findings at admission and clinicopathological data generated during the first 48 h of hospitalisation were analysed. Results from foals with Gram-positive or Gram-negative organisms, single or mixed organism bacteraemias, and with bacteraemia due to 3 commonly isolated organisms were compared. RESULTS Eighty-five foals met the inclusion criteria. Gram-negative organisms (n = 59) Gram-positive organisms (n = 13) or multiple organisms (n = 19) were cultured from individual foals. Foals with Gram-negative bacteraemia had lower total white blood cell and lymphocyte counts at admission than did those from which only Gram-positive bacteria were cultured. Mixed organism bacteraemia was associated with tachycardia, increased serum concentrations of sodium, chloride and urea nitrogen, acidosis, respiratory distress, recumbency on admission and nonsurvival. Actinobacillus spp. infections were associated with leucopenia, neutropenia, lymphopenia and depression on hospital admission. CONCLUSIONS AND POTENTIAL RELEVANCE Recognising particular patterns of clinical and clinicopathological findings associated with infection with specific groups of bacteria may, in the future, aid antimicrobial selection and influence prognosis in bacteraemic foals.

Cytokine gene signatures in neural tissue of horses with equine protozoal myeloencephalitis or equine herpes type 1 myeloencephalopathy

This study was designed to determine the relative levels of gene transcription of selected pathogens and cytokines in the brain and spinal cord of 12 horses with equine protozoal myeloencephalitis (epm), 11 with equine herpesvirus type 1 (ehv-1) myeloencephalopathy, and 12 healthy control horses by applying a real time pcr to the formalin-fixed and paraffin-embedded tissues. Total rna was extracted from each tissue, transcribed to complementary dna (cdna) and assayed for Sarcocystis neurona, Neospora hughesi, ehv-1, equine gapdh (housekeeping gene), tumour necrosis factor (tnf)-α, interferon (ifn)-γ, interleukin (il)-1β, il-2, il-4, il-6, il-8, il-10 and il-12 p40. S neurona cdna was detected in the neural tissue from all 12 horses with epm, and two of them also had amplifiable cdna of N hughesi. The relative levels of transcription of protozoal cdna ranged from 1 to 461 times baseline (mean 123). All the horses with ehv-1 myeloencephalopathy had positive viral signals by pcr with relative levels of transcription ranging from 1 to 1618 times baseline (mean 275). All the control horses tested negative for S neurona, N hughesi and ehv-1 cdna. The cytokine profiles of each disease indicated a balance between pro- and anti-inflammatory markers. In the horses with epm the pro-inflammatory Th1 cytokines (il-8, tnf-α and ifn-γ) were commonly expressed but the anti-inflammatory Th2 cytokines (il-4, il-6 and il-10) were absent or rare. In the horses with ehv-1 the proinflammatory cytokine il-8 was commonly expressed, but il-10 and ifn-γ were not, and tnf-α was rare. Tissue from the control horses expressed only the gene gapdh.

Temporal trends in in vitro antimicrobial susceptibility patterns of bacteria isolated from foals with sepsis: 1979-2010

REASONS FOR PERFORMING THE STUDY Monitoring the development of antimicrobial resistance is important for the rational selection of appropriate antimicrobial drugs to initiate treatment of foals with sepsis. OBJECTIVES To identify temporal trends in antimicrobial susceptibility patterns of bacteria isolated from foals with sepsis. STUDY DESIGN Retrospective review of medical records. METHODS Foals aged <30 days with a diagnosis of sepsis, confirmed by culture of bacteria, were included. Susceptibility data, expressed as minimum inhibitory concentrations (MICs) (MIC50 , MIC90 , MIC range) and percent of isolates that were susceptible to a particular antimicrobial drug, were compared for bacteria isolated from foals during 3 different time periods: 1979-1990, 1991-1997 and 1998-2010. The Cochran-Armitage trend test and the Jonckheere-Terpstra test were used for statistical analysis. RESULTS A total of 1091 bacterial isolates were cultured from 588 foals. Enterobacteriaceae, Actinobacillus spp. and β-haemolytic Streptococcus spp. showed a decrease in percent of isolates susceptible to gentamicin over time. Enterobacteriaceae, Actinobacillus spp. and β-haemolytic Streptococcus spp. showed an increase in MIC values for amikacin. Enterobacteriaceae showed a decrease in percent of isolates susceptible to ceftiofur. Enterococcus spp. and Pseudomonas spp. showed increased MIC values to ceftiofur. Enterobacteriaceae showed increased MIC values to ceftizoxime. Enterococcus spp. became more resistant to imipenem and showed increased MIC values to ticarcillin/clavulanic acid. In contrast, several trends in increased susceptibility were also seen. CONCLUSIONS Based on these in vitro results, the combination of amikacin and ampicillin remains an appropriate choice for initiating treatment of sepsis in foals while awaiting culture and susceptibility test results, although increasing development of resistance to amikacin was demonstrated. The decrease in in vitro activity of ceftiofur against Enterobacteriaceae is of concern. Similarly, the development of resistance of Enterococcus spp. to imipenem is an important finding that warrants monitoring in the future. Judicious use of antimicrobials is therefore crucial.

Diagnostic evaluation of real-time pcr in the detection of Rhodococcus equi in faeces and nasopharyngeal swabs from foals with pneumonia

Rhodococcus equi is a Gram-positive, facultative, intracellular bacterial pathogen and the most common cause of severe infectious pneumonia in foals of less than six months of age (Prescott 1991). The pathogen is ubiquitous in the environment, but becomes concentrated in breeding farm situations due to its ability to reproduce in the gastrointestinal tract of herbivores. A foal is suspected of having R equi pneumonia if it originates from an endemic farm, has signs of pneumonia, a severe inflammatory leukogram and a prominent alveolar and/or interstitial pattern on thoracic radiographs (Ainsworth 1999). Bacterial culture combined with cytological examination of a tracheobronchial aspirate is the only acceptable way of making a definitive diagnosis of R equi pneumonia. Although culture is the only means of identifying concurrent bacterial pathogens and testing in vitro antimicrobial susceptibility, it can yield false-negative results, possibly because of previous antimicrobial administration or overgrowth by multiple bacterial species (Sweeney and others 1987). Furthermore, culture does not allow differentiation between virulent and avirulent strains of R equi. In recent years the use of PCR amplification based on the VapA gene sequence has been shown to be a more sensitive means of identifying R equi in tracheal wash (TW) fluid samples than bacterial culture, especially if the foal sampled is being treated with antimicrobials at that time (Sellon and others 2001, Halbert and others 2005). Occasionally, the severity of clinical signs in foals suspected of having R equi pneumonia precludes the sampling of the lower airways. This short communication describes a study in which, during the search for alternative diagnostic specimens, it was hypothesised that PCR analysis of nasopharyngeal swabs (NS) and faeces collected from foals diagnosed with R equi pneumonia would be a sensitive alternative to standard culture techniques. Clinical samples were collected from 31 foals that had been referred to the Veterinary Medical Teaching Hospital, University of California, Davis, due to pneumonia. The foals ranged from four weeks to seven months of age (mean [sd] 3·3 [1·6] months). There were 17 female and 14 male foals, which included 15 thoroughbred, five quarter horse, five Arabian, two paint horse and one of each of Friesian, warmblood, standardbred and Percheron breeds. Before presentation, 19 of the 31 foals had been treated with a variety of antimicrobials (rifampin, azithromycin, erythromycin, doxycycline, penicillin procaine G, ampicillin, gentamycin, ceftiofur and trimethoprim-sulfamethoxazole) for one to 30 days (8·9 [7·7] days). All foals displayed clinical signs (cough, nasal discharge, tachyponea, fever and adventitial lung sounds) consistent Veterinary Record (2007) 161, 272-275

Internal abdominal abscesses caused by Streptococcus equi subspecies equi in 10 horses in California between 1989 and 2004

Streptococcus equi subspecies equi has been recognised for many years as the causative organism of strangles, an infectious and highly contagious respiratory disease of young horses. Due to the highly contagious nature of the pathogen, morbidity rates range from 30 to 100 per cent, depending on the immune status of the exposed horse population (Sweeney and others 1987a). Strangles is characterised by the sudden onset of fever and upper respiratory tract catarrh, as evidenced by mucopurulent nasal discharge. These signs are commonly followed by the formation of abscesses in the submandibular and retropharyngeal lymph nodes. After the affected lymph nodes rupture and drain spontaneously or are surgically lanced and flushed, the disease runs its course and affected horses usually recover uneventfully, leaving 75 per cent of exposed horses with a solid, enduring immunity (Hamlen and others 1994). However, a number of complications, including metastatic spread of infection or immunemediated processes, have been reported to occur in approximately 20 per cent of S equi infections and are associated with a significant increase in fatality rate (Ford and Lokai 1980, Sweeney and others 1987b, Spoormakers and others 2003). Metastatic spread of the organism to locations such as the thorax, lungs, brain, mesentery, liver, spleen and kidneys has been reported and may occur haematogenously, through lymphatic migration or via extension from a closely associated septic focus (Ford and Lokai 1980, Sweeney and others 1987b). Although internal abdominal abscesses due to S equi are mentioned in the veterinary literature, there is little reference to the clinical diagnosis and management of this condition. This short communication describes the history, clinical signs, laboratory data, results of diagnostic imaging techniques, treatment and outcome in 10 horses with internal abdominal abscesses caused by S equi. A computer search of the medical record database of horses examined at the Veterinary Medical Teaching Hospital (VMTH), University of California, between 1989 and 2004 was undertaken to identify potential candidates. Ten horses with one or more internal abdominal abscesses due to S equi were included in the study, based on clinical signs (presence of an internal abdominal mass on rectal examination), ultrasonographic findings, inflammatory peritoneal fluid, positive culture of S equi from an abdominal abscess or a high to very high titre against S equi. The data derived from the medical records included signalment, presenting complaint, duration of clinical signs, physical examination findings, laboratory results (haematology, biochemistry, peritoneal fluid cytology, culture and S equi serology), abdominal ultrasound, treatment and outcome, as well as postmortem examination findings when available. The horses ranged in age from one to 12 years (mean four years) and included four mares, four geldings and two stallions (Table 1). The mean duration of illness before admission to the VMTH was 25 days, with a range of one day to three months. Nine horses had been boarded at facilities on which an outbreak of S equi infection had occurred between three weeks and four months before presentation to the VMTH. During the reported outbreaks, these nine horses had experienced signs compatible with strangles. One horse originated from a facility with an unknown S equi status and had no previous history of respiratory disease. Historical problems reported by owners were weight loss, fever, colic, partial or complete anorexia, depression and tachypnoea. While seven horses presented with chronic signs, three horses were referred to the VMTH for acute colic. Eight horses had been treated with antimicrobials and/or anti-inflammatory drugs by a referring veterinarian or the owner before presentation. Seven horses were bright and alert at presentation, two horses were mildly depressed and one horse showed signs of severe colic (Table 1). Other commonly reported clinical findings included tachycardia (heart rate >44 bpm), tachypnoea (respiratory rate >20 breaths/minute), fever (rectal temperature >38·5°C) and low body condition score (BCS) (<5/9). Rectal examination revealed a mass caudal to the left kidney in four horses or in the caudoventral abdomen in four horses. Rectal examination was unremarkable in two horses. Results of a complete blood count and serum biochemical panel were available for all horses. The most common laboratory abnormalities detected were anaemia (packed-cell volume <30 per cent), leucocytosis (>11,600 white blood cells/μl), neutrophilia (>6800 neutrophils/μl), thrombocytosis (>225,000 platelets/μl), hyperproteinaemia (>7·7 g/dl), hyperglobulinaemia (>4·7 g/dl) and hyperfibrinogenaemia (>400 mg/dl) (Table 2). The only biochemical abnormalities were elevated creatinine concentration (>2 mg/dl) and blood urea nitrogen (>27 mg/dl) in two horses, elevated aspartate

Prevalence of equine herpesvirus type 1 in trigeminal ganglia and submandibular lymph nodes of equids examined postmortem.

The objective of this study was to detect and characterise the biovar of equine herpesvirus type 1 (EHV-1) from submandibular lymph nodes (SMLNs) and trigeminal ganglia from 153 equids undergoing routine postmortem examination for various medical and surgical reasons. A combination of nucleic acid precipitation and preamplification steps was used to increase the analytical sensitivity of the analysis. The presence of latent EHV-1 was determined when tissue samples were PCR-positive for the glycoprotein B (gB) gene and the DNA polymerase (ORF 30) gene of EHV-1 in the absence of detectable late structural protein gene (gB gene) mRNA. The SMLNs of five of the study animals (3.3 per cent) were PCRpositive for the gB gene of EHV-1. Two SMLNs carried a latent neurotropic strain of the virus, whereas three SMLNs were PCR-positive for both neurotropic and non-neurotropic EHV-1. A total of 30 trigeminal ganglia collected from 19 horses were PCR-positive for the gB gene of EHV-1. Nine trigeminal ganglia harboured either latent non-neurotropic or neurotropic EHV-1 strains. Twelve trigeminal ganglia contained both latent neurotropic and non-neurotropic EHV-1. The prevalence and distribution of EHV-1 biovars among the study horses appeared to be influenced by their breed and the type of tissue tested.

Temporal trends in prevalence of bacteria isolated from foals with sepsis: 1979–2010

REASONS FOR PERFORMING STUDY Sepsis is an important cause of death in foals. Knowledge of which pathogens are likely to be involved is important for selection of antimicrobial drugs for initial treatment. OBJECTIVES To identify temporal trends in prevalence of bacteria isolated from foals with sepsis between 1979 and 2010. STUDY DESIGN Retrospective review of medical records. METHODS All foals ≤30 days of age presented to the Veterinary Medical Teaching Hospital (VMTH) at the University of California, Davis between 1979 and 2010, with a diagnosis of sepsis confirmed by culture of bacteria from blood or internal organs (antemortem or at necropsy), were included in the study. Conventional microbiological methods were used to identify isolated organisms. The Cochran-Armitage trend test was used for statistical analysis. RESULTS The percentage of Gram-positive isolates increased significantly over the years. The percentage Enterobacteriacea, and Klebsiella spp. in particular, decreased over time. Enterococcus spp. isolates were cultured more often in recent years. CONCLUSIONS Whereas Gram-negative bacteria, particularly Enterobacteriaceae, remain the most common isolates from neonatal foals with sepsis, the prevalence of Gram-positive bacteria is increasing. This trend underlines the importance of including antimicrobial drugs active against both Gram-positive and Gram-negative bacteria in treatment protocols while awaiting the results of bacteriological culture and susceptibility tests. The increased prevalence of Enterococcus spp. is of concern because antimicrobial susceptibility patterns for enterococci are unpredictable and enterococci can also act as donors of antimicrobial resistance genes to other bacteria.