Experimental Transmission of Corynebacterium pseudotuberculosis Biovar equi in Horses by House Flies

Background

The route of Corynebacterium pseudotuberculosis infection in horses remains undetermined, but transmission by insects is suspected.

Objectives

To investigate house flies (Musca domestica L.) as vectors of C. pseudotuberculosis transmission in horses.

Animals

Eight healthy, adult ponies.

Methods

Randomized, controlled, blinded prospective study. Ten wounds were created in the pectoral region where cages for flies were attached. Three ponies were directly inoculated with C. pseudotuberculosis. Four ponies were exposed for 24 hours to 20 hours C. pseudotuberculosis‐inoculated flies. One negative control pony was exposed to noninoculated flies. Ponies were examined daily for swelling, heat, pain, and drainage at the inoculation site. Blood was collected weekly for CBC and biochemical analysis, and twice weekly for synergistic hemolysis inhibition titers.

Results

Clinical signs of local infection and positive cultures were observed in 7/7 exposed ponies and were absent in the negative control. In exposed ponies, peak serologic titers (1 : 512 to 1 : 2,048) were obtained between days 17 and 21. Seroconversion was not observed in the negative control. Neutrophil counts were higher in the positive and fly‐exposed groups than in the negative control (P = .002 and P = .005) on day 3 postinoculation. Serum amyloid A concentrations were higher in the positive control than in the negative control and fly‐exposed ponies on days 3 (P < .0001) and 7 (P = .0004 and P = .0001). No differences were detected for other biochemical variables.

Conclusions and Clinical Importance

House flies can serve as mechanical vectors of C. pseudotuberculosis and can transmit the bacterium to ponies.     

Laryngeal Hemiplegia in Draft Horses A Review of 27 Cases

Case records of 27 draft horses with laryngeal hemiplegia were reviewed. Twenty-one horses were treated by ventriculectomy with or without prosthetic laryngoplasty, and 17 owners were contacted to determine the results. Fifteen horses improved after surgery and were able to perform to the owners' expectations. Performance improved significantly and hospitalization was shorter after ventriculectomy alone. Results of this study indicate that the clinical signs of exercise intolerance and excessive inspiratory noise associated with left laryngeal hemiplegia in draft horses can be treated successfully by ventriculectomy without prosthetic laryngoplasty.     

Streptococcus equi Infections in Horses: Guidelines for Treatment,Control, and Prevention of Strangles—Revised Consensus Statement

This consensus statement update reflects our current published knowledge and opinion about clinical signs, pathogenesis, epidemiology, treatment, complications, and control of strangles. This updated statement emphasizes varying presentations in the context of existing underlying immunity and carrier states of strangles in the transmission of disease. The statement redefines the “gold standard” for detection of possible infection and reviews the new technologies available in polymerase chain reaction diagnosis and serology and their use in outbreak control and prevention. We reiterate the importance of judicious use of antibiotics in horses with strangles. This updated consensus statement reviews current vaccine technology and the importance of linking vaccination with currently advocated disease control and prevention programs to facilitate the eradication of endemic infections while safely maintaining herd immunity. Differentiation between immune responses to primary and repeated exposure of subclinically infected animals and responses induced by vaccination is also addressed.     

Review of Corynebacterium (Rhodococcus) equi lung abscesses in foals: pathogenesis, diagnosis and treatment

Corynebacterium (Rhodococcus) equi is becoming increasingly significant as a cause of bronchopneumonia and lung abscessation in foals. The organism can survive within macrophages and may thus escape normal pulmonary defence mechanisms, particularly in immunocompromised animals. The disease has hitherto been associated with mortality rates as high as 80 per cent, partly as a result of inappropriate therapy. The selection of lipid-soluble antibiotics capable of intracellular penetration is critical for the successful treatment of C equi lung abscesses. A combination of two such antibiotics, erythromycin (25 mg/kg three times daily) and rifampicin (5 mg/kg twice daily) has been used on foals since 1981. Most of these animals had radiographic evidence of extensive lung abscessation, and in all cases the presence of C equi was confirmed on culture of tracheal aspirates. The duration of therapy ranged from four to nine weeks. Mild gastritis and diarrhoea were occasionally noted, but never such as to require termination of the therapy. No other adverse side effects were encountered. The success rate, as judged by a return to normal of chest radiographs and plasma fibrinogen concentrations, has exceeded 80 per cent.     

Palmar Digital Neurectomy in Horses 57 Cases (1984–1990)

The medical records of 57 horses that had palmar digital neurectomy performed between 1984 and 1990 were reviewed. Neurectomies were performed either by transection and elec-trocoagulation (47 horses) or by the guillotine technique (10 horses). Middle-aged geldings, Quarter Horses, and Thoroughbreds were significantly over-represented when compared with the hospital population. Horses used as hunter/jumpers also appeared to be over-represented. Complications occurred in 17 (34%) of the 50 horses for which follow-up information was obtained. Recurrence of heel pain was the most common complication (14 horses). Palpable painful neuromas were detected in three horses. One year after neurectomy, 74% of the horses were sound; this decreased to 63% after 2 years.     

Epidemiological Aspects of Babesia equi in Horses in Minas Gerais,Brazil

The prevalence of Babesia equi in two climatic regions of Minas Gerais state was determined using the indirect fluorescent antibody test (IFAT) with blood samples obtained from horses in two slaughterhouses. Of 399 samples, 241 (60.4%) showed a positive reaction. Anti-B. equi antibody was detected in every county studied, the prevalence being 59.7% for horses in the area where the temperature rises above 18°C in winter and 61.4% in the area where it remains below 18°C, indicating that climatic variation has no substantial effect on the prevalence of the infection in Brazil. Blood samples collected from all 95 horses on a ranch in the state of Minas Gerais, Brazil, on which clinical babesiosis had never been reported, were subjected to the IFAT. Anti-B. equi antibodies were detected in horses of all ages, but with a significantly lower prevalence in animals less than 6 months old.     

Corynebacterium equi in the gastrointestinal tract of ruminants

Corynebacterium equi has been recovered from the gastrointestinal tract of sheep and cattle. It can be found in all parts of the gut, and around 80% of animals have the organism in one or more intestinal sites.C. equi could be detected in the faeces of sheep which were kept caged and free from recontamination by the organism.     

Treatment of Corynebacterium equi pneumonia of foals: a review

Combined antimicrobial drug treatment was recommended for foals with Corynebacterium equi pneumonia. The preferred combination is orally administered erythromycin estolate (25 mg/kg of body weight, QID) plus rifampin (10 mg/kg, BID). Erythromycin estolate also can be combined for synergistic effect with sodium benzyl penicillin given IV (100,000 IU/kg, QID) or with ampicillin given IV (11 to 15 mg/kg, QID). A third choice is sodium benzyl penicillin IV with gentamicin IM (2.2 mg/kg, TID) or with kanamycin IM (10 mg/kg, QID). Gentamicin should be combined with penicillin G or ampicillin and not used for longer than one week without monitoring for nephrotoxicosis. Rifampin should be used only in combination with erythromycin or penicillin. Erythromycin or rifampin and gentamicin give antagonistic interactions in vitro. Chloramphenicol or trimethoprim-sulfamethoxazole may be effective if given in high doses but are not preferred drugs. Treatment response should be monitored clinically and radiographically and treatment should be continued for 2 weeks after the foal is clinically and radiographically normal.     

Clinical and radiographic findings in Corynebacterium equi pneumonia of foals

Thirty-nine foals with pneumonia were admitted to the Veterinary Medical Teaching Hospital at the University of California, Davis. Corynebacterium equi was recovered from each of them on bacteriologic culture of transtracheal aspiration specimens or lung specimens at necropsy. The foals were divided into 2 groups. Group I consisted of 20 foals that died because of C equi pneumonia and were subsequently necropsied. Group II consisted of 19 foals that were treated and discharged from the hospital. Radiography was performed on all foals. Clinical signs included increased respiratory rate, fever, cough, nasal discharge, increased bronchovesicular sounds over large airways, and wheezing over small airways. Highly significant differences were found in the mean respiratory rate (P less than 0.005) and temperature (P less than 0.001), recorded at admission, between the 2 groups; both factors were higher for group I. Hematology revealed leukocytosis with neutrophilia, monocytosis, and high plasma fibrinogen content in all foals. Significant differences were recorded in the mean total leukocyte count (P less than 0.05), mean neutrophil count (P less than 0.05), mean monocyte count (P less than 0.005), and mean fibrinogen value (P less than 0.05) between the 2 groups; values from group I were higher than those from group II. Although C equi was isolated alone from 25 of the tracheal aspirates and lung specimens, 14 cultures yielded multiple pathogens. At the time of initial examination, all foals had radiographic evidence of pneumonia. Pulmonary consolidation indicative of bronchopneumonia was identified in 31 of the 39 foals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antibody to equi factor(s) in the diagnosis of Corynebacterium equi pneumonia of foals.

Antibody to equi factor(s) in cases of Corynebacterium equi pneumonia in foals was detected using C. pseudotuberculosis exotoxin sensitized calf red blood cells. The test was standardized using antitoxin produced in rabbits by injection of equi factor(s). All sera from ten foals with culture-diagnosed C. equi pneumonia had antibodies to equi factor(s) (titre range 8-256, mean 74.0) and nine sera from 11 foals with suspected C. equi pneumonia also showed antibodies (titre range 4-512, mean 136.4). Two of five pneumonia foals with transtracheal aspirate cultures not yielding C. equi had such antibodies. Fifty-eight of 59 control horse sera had no antibodies; the one positive serum came from a foal on a farm where C. equi pneumonia was endemic. By contrast only five of 15 foals with experimentally-induced C. equi pneumonia had antibodies to equi factor(s), probably because the acute nature of the disease produced did not mimic the chronic course of the natural disease. Antibody to equi factor(s) can be used in the diagnosis of naturally-occurring corynebacterial pneumonia in foals.     

Bronchointerstitial Pneumonia and Respiratory Distress in Young Horses: Clinical, Clinicopathologic, Radiographic, and Pathological Findings in 23 Cases (1984–1989)

Twenty-three foals, between 1 and 7 months old, with signs of acute respiratory distress, were examined at the Veterinary Medical Teaching Hospital (VMTH), University of California, Davis, between 1984 and 1989. Characteristic features included sudden onset of severe respiratory distress and tachypnea, cyanosis unresponsive to nasal oxygen, pyrexia, hypoxemia, hypercapneic respiratory acidosis, poor response to treatment, and histopathologic lesions of bronchiolitis and bronchointerstitial pneumonia. Seven of the 23 foals were normal before the onset of respiratory distress, 3 foals were found dead, aqd 13 foals were being treated for respiratory tract infections at the time of presentation. Laboratory data obtained for 13 horses showed increased plasma fibrinogen concentration (630.7 ±193 mg/dL), leukocy-tosis (18,607 ± 7,784/μL), and neutrophilia (13,737 ± 8,211/μL). Thoracic radiographs showed a diffuse increase in interstitial and bronchointerstitial pulmonary opacity and, in 5 foals, an alveolar pulmonary pattern of increased density was also seen. In 3 foals heavy interstitial infiltration proceeded to a coalescing nodular radiographic appearance. Microbiological culture of tracheobronchial aspirates (TBA) from 9 foals yielded bacterial growth, but no one bacterial species was consistently isolated. Microbiological culture of postmortem specimens of the lung from 6 foals yielded growth of bacteria that included Escherichia coli, Enterobacter spp., Proteus mirabilis, Klebsiella pneumonias, Rhodococcus equi, or β-hemolytic Streptococcus spp. Tracheobronchial aspirates from 4 foals and lung samples collected from a further 4 foals at necropsy yielded no bacterial growth. Cultures were not taken from two foals premortem or postmortem. Virologic examination of TBA, lung tissue, or pooled organ tissue from 12 foals was negative. Viral culture of TBA from 1 foal showed cytopathic effects and positive immunoflu-orescence for equine herpes virus type II (EHV-II). In addition to the 3 foals that were found dead, 11 foals died or were euthanatized. Pathologic lesions were limited to the lungs in 50% of the foals; the remainder also had bowel lesions suggestive of hypoxic injury. The predominant histopathologic pulmonary lesions included bronchiolitis, bronchiolar and alveolar epithelial hyperplasia, and necrosis. Many bronchioles were filled with mucoid and fibrinocellular exudate. The peribronchiolar interstitium and adjacent alveolar spaces were also infiltrated with inflammatory cells and contained proteinaceous edema fluid. Type II cell hyperplasia and hyaline membrane formation were observed in the majority of foals and in 2 foals alveolar multinucleate giant cells were also present. Nine of 13 foals (69%) on which treatment was attempted at the VMTH survived after aggressive medical care that included external thermoregulatory control, oxygen by nasal insufflation, antimicrobial drugs, bronchodilating agents, nonsteroidal anti-inflammatory drugs, and corticosteroids. Persistent radiographic evidence of increased interstitial density was noted up to 24 months after initial presentation, and one horse remained exercise intolerant for at least 15 months after discharge. The exact etiopathogenesis of this disorder and long-term sequalae in the survivors have yet to be fully determined. However, it is likely that a number of different insults rather than a single agent may initiate the pulmonary damage that leads to severe interstitial pneumonia and subsequent acute respiratory distress or apparent sudden death in foals. (Journal of Veterinary Internal Medicine 1993; 7:277–288. Copyright © 1993 by the American College of Veterinary Internal Medicine.)     

Experimental Studies on the Pathogenesis of Corynebacterium equi Infection in Foals

Four month-old foals were infected orally with 75 mL of a suspension of 5.0 × 10⁸ Corynebacterium equi per mL. Two foals were killed after ten days and had scanty number of C. equi in the caeco-colic lymph nodes. No C. equi were recovered from the other two foals, killed 20 days after infection. No gross pathological change was detected in these four foals, although mild microscopic lesions were seen in the ileum of one foal. Results of lymphocyte blastogenesis using peripheral blood lymphocytes and C. equi antigens showed, however, that lymphocytes became sensitized to C. equi following this challenge.

In a second experiment four month-old foals were given orally the same dose of organisms but on five consecutive days. Two foals were killed ten days after infection and showed mild histological changes in the large bowel mucosa and C. equi could be recovered from all intestinal lymph nodes cultured. In one of these foals moderate numbers of C. equi were present in the bronchial lymph node. Of the other two foals, one died after 22 days with severe ulcerative enterocolitis and intestinal lymphadenitis. Only one small pulmonary abscess was detected despite large numbers of C. equi in the lungs. The other foal developed similar intestinal changes and was euthanized 25 days after infection. No C. equi were detected in the lungs or bronchial lymph node. Lymphocyte blastogenesis in these animals showed a rapid rise in response to C. equi antigens.

These studies suggest that C. equi pneumonia in foals does not always arise from an intestinal infection, that minor intestinal infection causes a cellular immune response and that massive exposure of the bowel over a sustained period is necessary to induce intestinal lesions.

     

Heparin: A Review of its Pharmacology and Therapeutic Use in Horses

Heparin is used clinically in horses to treat hemostatic abnormalities associated with severe gastrointestinal disease, septicemia, and endotoxemia. The primary anticoagulant effect of heparin is through the suppression of thrombin-dependent amplification of the coagulation cascade, and inhibition of thrombin-mediated conversion of fibrinogen to fibrin. Heparin may be of benefit in preventing the complications associated with hypercoagulable states such as jugular vein thrombosis, laminitis, and organ failure. Heparin may also be beneficial in the prevention of intraabdominal adhesions after gastrointestinal surgery, and in amelioration of hemodynamic abnormalities associated with endotoxic shock. Because a sequential rise in serumheparin concentration occurs during a uniform dosage regimen, a decreasing dosage regimen is recommended. The initial dose recommended is 150 U heparin/kg body weight subcutaneously, followed by 125 U heparin/kg body weight subcutaneously, every 12 hours for six doses. The dose should be decreased to 100 U heparin/kg body weight subcutaneously, every 12 hours, after the seventh dose. Anemia, hemorrhage, thrombocytopenia, and painful swelling at injection sites are complications of heparin administration in horses.     

禽源冠状病毒感染情况概述

以国内外对冠状病毒在禽类中的流行病学调查、监测和基因分析等研究报道为基础,从病毒分类学角度,对各“种”冠状病毒在禽类中的感染情况和引起的相关疾病进行简要概述。全球在禽类中发现的冠状病毒种类较多,至少涉及丙型和丁型冠状病毒属。其中,鸡传染性支气管炎病毒几乎在全球所有养鸡国家中存在,并呈地方性流行;火鸡冠状病毒、鸭冠状病毒、鹅冠状病毒、鸽冠状病毒也在禽类中被发现,部分病毒已在禽群中流行;其他丁型冠状病毒属病毒仅在少数野鸟中被发现。