respiratory disease in animals vol 5 - سيريا فيت - الطب البيطري

د/عمرو · #1 10-04-2007, 12:48 صباحاً

Control of Respiratory Disease

Sudden dietary changes, weaning, cold, drafts, dampness, dust, high levels of ammonia, poor ventilation in general, and the mixing of widely divergent age groups all play a role in respiratory disease in groups of animals. Stress and mixing of animals from several sources should be avoided or minimized. Establishing individual animal identification, making accurate clinical and postmortem diagnoses, and maintaining a record system of diagnosis and treatment are important to minimize or control outbreaks of pneumonia.

Immunization can help control respiratory infection. However, control may be compromised by improper timing, use of ineffective or inappropriate vaccines, or overwhelmingly negative management practices. In most cases, severe insults to the natural defenses cannot be reversed later by therapeutic agents and biologicals.

The mucosal surfaces of the respiratory tract contain lymphoid follicles that exchange cells with other parts of the body. However, most of the lymphocytes in the respiratory lining produce only IgA, whereas the cells in the lymph nodes of the respiratory tract produce IgM and IgG. Depending on the agent involved, various cell- and antibody-mediated immune responses occur in the respiratory tract and include opsonization, agglutination, immobilization, neutralization of toxins and viruses, blockage of adherence to cells, lysis, and chemotaxis. Variation in the type of immune response occurs because of age, species, and the means to respond to specific virulence mechanisms of the pathogens involved. Species vary in the type of immune response available at different sites in the respiratory tract. Large antigen droplets may immunize the upper tract with IgA, but small replicating particles may be necessary to immunize the lower tract. To develop adequate antibody levels to protect the lungs, repeated doses of antigen plus adjuvant, or a replicating antigen, are often necessary. These results are seldom achieved under field conditions (eg, many field trials using respiratory vaccines in cattle have not demonstrated statistically significant efficacy).

د/عمرو · #2 10-04-2007, 12:48 صباحاً

Principles of Therapy

Respiratory disease is often characterized by abnormal production of secretions and exudates and by a reduced ability to remove them. The primary goal is to reduce the volume and viscosity of the secretions and to facilitate their removal. This can be accomplished by controlling infection, modifying the secretions, and when possible, improving postural drainage and mechanically removing the material. Therapeutic methods include altering the inspired air and administering expectorants, antitussives, bronchodilators, antimicrobials, diuretics, and other drugs.

Hydration should be maintained. Inhalation of humidified air may facilitate removal of airway secretions. Expectorants are sometimes used with the intention of liquefying these secretions. However, they should be used in conjunction with ancillary respiratory therapy such as improved postural drainage, mild exercise, and thoracic percussion, which (in addition to coughing) encourages expectoration and removal of secretions. Expectorants at traditional dosages are of questionable value. Mechanical removal of tenacious and viscid secretions by aspiration may be necessary in severe airway obstruction.

Antitussive agents are indicated to relieve the discomfort associated with nonproductive coughing but are contraindicated when secretion of airway mucus is excessive. Products that contain atropine also are contraindicated, at least in theory, because atropine increases the viscosity of airway secretions.

Increased airway resistance caused by bronchial smooth muscle contraction can be alleviated with bronchodilators, which may be indicated in animals with asthma-like conditions and chronic respiratory disease. Methylxanthines, such as theophylline and aminophylline, are effective bronchodilators in species other than cattle (and possibly dogs). Isoproterenol, clenbuterol, and epinephrine are also generally effective, and sodium cromoglycate is used in horses for treating small airway disease (eg, heaves). Corticosteroid use is justified in allergic conditions. Antihistamines can be used to alleviate the bronchoconstriction caused by histamine release. Bronchospasm also can be reduced significantly by removing irritating factors, using mild sedatives, or reducing periods of excitement.

In bacterial infection, antimicrobial therapy should be instituted. The goal is to select either the most effective agent against a specific organism or the least toxic agent of several alternatives. Culture and sensitivity testing of airway secretions provide a worthwhile, although not infallible, guide to determining the appropriate antibiotic. Knowledge of tissue penetration and pharmacokinetic characteristics of the antimicrobial agents is important as well. The following agents have proved effective in the listed species: cattle—oxytetracycline, erythromycin, penicillins, and sulfonamides; sheep and goats—oxytetracycline, penicillins, and sulfonamides; pigs—lincomycin, spectinomycin, penicillins, and sulfonamides; dogs and cats—cephalosporins, chloramphenicol, amoxicillin-clavulanic acid, aminoglycosides, trimethoprim-sulfamethoxazole, fluoroquinolones, and tetracyclines; horses—penicillins, sulfonamides, and tetracyclines, the latter with caution due to an occasional side effect of severe diarrhea. Aminoglycosides are useful but can be nephrotoxic. Trimethoprim, usually in combination with a sulfonamide, is useful for respiratory therapy in most species but is not licensed for food-producing animals in the USA. Drugs such as enrofloxacin (approved for small but not large animals in the USA) and ceftiofur may prove efficacious. Broad-spectrum antibiotics should be used if specific bacteria cannot be identified, and once begun, a full course of therapy should be completed. Multiple antimicrobial agents should be used only with full knowledge of the potential drug interactions. Because of residues in food-producing animals, veterinarians must use these products appropriately and provide sound advice to producers.

The hypoxemia caused by most lung disorders usually can be corrected by administering oxygen. However, continuous administration of high concentrations increases the tendency for regional resorption atelectasis, thus worsening the hypoxemia, and can cause pneumonitis on its own. Hypoxemia is often accompanied by variable degrees of hypercapnia and acidemia. Endotracheal intubation and mechanical ventilation may be necessary in animals with acute respiratory failure or in animals that are comatose or apneic. Arterial blood gas and pH determinations, when practicable, are extremely valuable in monitoring treatment.

Diuretics are indicated in pulmonary edema. The osmotic diuretics have a minimal action on diuresis. Carbonic anhydrase inhibitors (eg, acetazolamide) have a moderate action on diuresis, and loop diuretics (eg, furosemide) have a profound effect.

د/عمرو · #3 11-09-2007, 01:31 مساء

لا تنسونا من صالح دعائكم

dr.amal · #4 04-10-2007, 09:46 مساء

جزاك الله كل خير يادكتور ونرجو المزيد

tsb · #5 07-10-2007, 11:06 مساء

الموضوع كان رائع جدااااااااا
و انا بصراحة استفدت كتير من هذا الموضوع
مشكووووووورين

د/عمرو · #6 18-05-2008, 06:48 مساء

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