PATB 4110 Diseases of Food Animals and Horses Respiratory System Overview and Diseases of Horses Don Montgomery Veterinary Sciences Rm 119 742-6638 ACROSS SPECIES, DISEASES OF THE RESPIRATORY SYSTEM ARE ONE OF THE MOST, IF NOT THE MOST SIGNIFICANT ! In horses, respiratory diseases are second only to digestive tract disease (colic) as the major health problem Major anatomic components of the Respiratory System Nasal cavity Paranasal sinuses Naso/oropharynx Larynx Trachea Lung Muscles Disorders affecting any or all of these components can affect function Functions of the Respiratory System The sole major function of the respiratory system is to deliver oxygen-rich air to the lung where gas exchange occurs and to eliminate waste gases Miscellaneous functions Control of acid-base balance via exchange of O2 for CO2 Sensory organ - smell Immunologic sentinel Microanatomy: correlation of structure and function Respiratory Epithelium Up to four different types of epithelium Simple or stratified columnar epithelium Nasal passages Nasopharynx Caudal larynx and trachea Bronchi and bronchioles Ciliated Goblet cells How would damage to this epithelium affect defense mechanisms? 1 The Lung Bronchi Epithelium simple columnar with cilia Smooth muscle allow bronchi to constrict or relax Cartilage The Lung Alveoli (where gas exchange occurs) Two types of epithelial cells Type 1 squamous (90+%) Type 2 cuboidal cells that secrete surfactant Alveolar space Bronchioles Simple columnar epithelium Less smooth muscle No cartilage Alveoli the place where gas exchange occurs Simple capillary lined by endothelial cells Fibroblastic cells Minimal tissue between the air in alveoli and erythrocytes in capillaries Any disease process that alters the tissue thickness between the capillary and alveolar space interferes with gas exchange Alveolar septae Defense Mechanisms of the Respiratory System Mucous secretion and mucociliary escalator Mucous secretions help moisten the tissues and entrap bacteria and particulate matter that can then be eliminated Clinical Signs of Respiratory Disease Upper <a href="/keyword/respiratory-tract/" >respiratory tract</a> Nasal discharge Sneezing Open mouth breathing (species variations) Dry hacking, nonproductive cough Unusual respiratory sounds such as wheezing, whistling, etc. Obviously, based on the nature of the disease process both upper and lower respiratory signs can occur together. Lower <a href="/keyword/respiratory-tract/" >respiratory tract</a> Deep cough, may or may not be productive Tachypnea rapid respiration Dyspnea labored respiration Cyanosis blue coloration to mucous membranes indicating poor oxygenation of blood and tissues Abnormal (or absent) lung sounds Resident microflora The normal microflora includes some bacteria that are potential pathogens but these are kept in check by a balance with nonpathogens Lymphoid tissues Lymphoid tissues are scattered throughout the <a href="/keyword/respiratory-tract/" >respiratory tract</a> , either as diffuse or follicular accumulations of lymphocytes. These are a part of mucosal immunity and secrete IgA Neurogenic reflex mechanisms Some of these reflex mechanisms can Coughing be harmful! Sneezing At least 8 other reflexes including laryngeal chemoreflex Respiratory Diseases of the Horse The Upper Respiratory System The Lower Respiratory System Diseases of the nasal passages Horses are obligate nasal breathers and about 50% of the total airway resistance to the passage of air occurs in the nasal passages. Disease of the nasal passages can further increase this airway resistence. This lecture will cover only some of the major respiratory diseases in the horse. Special emphasis will be given diseases likely to be encountered. Dr. John King 2 Diseases of the nasal passages Rhinitis Inflammation of the nasal cavity / nasal passages. Can also involve sinuses and other components of the upper airways and even lungs Causes Viruses: Equine rhinopneumonitis (herpesvirus) &amp; influenza (orthomyxovirus) Allergy, irritants Rhinitis Clinical Signs Nasal discharge: is initially clear and colorless but later can become opaque (due to mucous or purulent inflammation that accompanies secondary bacterial infection) Treatment Antihistamines, decongestants, anti-inflammatory If allergic try to identify and alleviate cause Antibiotics for secondary bacterial infection usually not indicated unless severe Outcome Ethmoid hematoma Viral infections are usually self-limiting with no permanent sequela Scarring, polyp formation, if chronic inflammation persists Ethmoid Hematoma Also called progressive hematoma or hemorrhagic nasal polyp Usually affects horses &gt; 8 yrs Cause is unknown but lesions are due to chronic unilateral hemorrhage Forms a hemorrhagic mass that can extend as far forward as the nares or caudally through the choanae Diseases of the Pharynx Chronic pharyngitis The horse has diffuse lymphoid tissue in mainly the dorsal pharynx Enlargement of the lymphoid tissue due to chronic antigenic stimulation may cause narrowing of the pharyngeal opening and respiratory difficulty Causes may include chronic irritation +/viruses and bacteria but a specific role for microorganisms is unproven Epidemiology more bacteria can be cultured from pharyngeal secretions than in normal horses and affected animals more likely to have pulmonary viral infections Treatment: Usually palliative, anti Foals, horses less than 5 years inflammatories, analgesics, antibiotics Treatment: Surgical excision or chemical ablation. Intraoperative hemorrhage may be a problem. Can recur. Diseases of the Pharynx Strangles, Distemper Cause: Streptococcus equi subspecies equi Some analogies can be made with 'strep throat in humans Highly contagious, passed from animal to animal from secretions, fomites, etc. Usually affects horses 1 5 years of age Foals &lt; 4 months usually protected by colostral immunity Horses &gt; 5 years typically have acquired immunity Strangles Clinical Signs Dr. John King Incubation period is 3-4 days Disease begins as a pharyngitis Bacteria spread to regional lymph nodes and lymph node abscessation lymphadenitis Sudden onset of fever and catarrhal inflammation of the upper <a href="/keyword/respiratory-tract/" >respiratory tract</a> Enlargement of lymph nodes in neck. The lymph nodes are initially firm but then become soft and fluctuant 7 14 days later, heralding abscessation. Typical outcome is rupture of node abscesses through skin with drainage of puss Morbidity 30% to 100% Mortality 9% - 10%, usually from complications 3 Strangles treatment Isolate clinically affected and exposed animals Treatment based on four stages 1. Horses exposed to infected animal but no clinical signs: Antibiotic therapy (variety will work penicillin, tetracycline, etc.) will not stop pharyngitis but may prevent seeding of lymph nodes Antibiotics may help prevent spread of infection to lymph nodes Enhance maturation and drainage of abscesses Studies have shown antibiotic treatment at this stage may prolong the disease Disseminated ( bastard ) strangles Appropriate antibiotics Purpura hemorrhagica antibiotics and corticosteroids Strangles Management &amp; Control Separate sick horses Separate recovered horses for 6 weeks Rest contaminated pastures 6 weeks Isolate new / returning horses 1 month Sanitation clean water troughs, feed buckets, brushes, bridles, etc. Vaccination (may only reduce clinical incidence 50%) Strepguard Intervet (killed product) Pinnacle IN Fort Dodge (live, attenuated) 2. Horses with early clinical signs: 3. Horses with lymph node abscessation: 4. Complications: Identify carriers by culture or PCR Diseases of the Pharynx Guttural pouches Guttural pouches are saccular dilations of the auditory (eustachian tube) connecting the middle ear and pharynx Major nerves and large arteries course thru the wall of the pouches Functions unknown Equalizing pressure on ear drums? Resonant chamber for vocalization? Temperature control? Tympany of the Guttural pouches Definition = uni- (most common) or bilateral distension with air Cause undetermined may be a congenital redundancy in a fold of the pharyngeal mucosal that acts as a valve allowing air into but not out of the pouches Diagnosis Uni- or bilateral swelling in retropharyngeal space. Can be confirmed by endoscopy or radiography Clinical signs Nonpainful swelling, dysphagia, respiratory distress, extension of the head in horses less than 1 year old Treatment Aspiration of air results in only temporary improvement. More effective treatment requires surgery Complications of guttural pouch disease may include nerve paralyses and hemorrhage Guttural pouch empyema Empyema = distension of a body cavity with pus Causes Ascending infection from bacterial pharyngitis or rupture of retropharyngeal lymph node abscess into the guttural pouch Streptococcus equi (the cause of strangles) is commonly involved Guttural pouch empyema With chronicity, the disease is more difficult to treat successfully. Chondroids accumulations of hard inspissated exudate Clinical signs Uni- or bilateral opaque white to tan nonodorous nasal discharge, pain, dysphagia, respiratory distress Chondroids Diagnosis Clinical signs, culture of aspirates, radiography, endoscopy Treatment Lavage (irrigation of the pouch with antibiotic-saline combination), parenteral antibiotics, surgical drainage Prognosis Favorable if diagnosed and treated early Early accurate diagnosis and appropriate treatment are the clues to successful management of many diseases. 4 Guttural pouch Mycotic infection Commonly Aspergillus spp. Usually single animal Chronic infection Clinical signs: Epistaxis (definition ?) Cranial nerve deficits such as dysphagia (CN 10 &amp; 12) Nasal discharge (uni- or bilateral?) Swelling Guttural pouch Mycotic infection Fungi such as Aspergillus commonly cause invasive type lesions with extension into blood vessels. Severe and sometimes fatal hemorrhage can occur from rupture of the internal carotid artery that courses through the wall of the pouch. Prognosis and treatment: Guarded to poor prognosis. Common treatments reflect a combination of medical and surgical management Dr. John King Equine Upper Airway Disease Larynx: Laryngeal hemiplegia Also called roarers Due to damage to the left recurrent laryngeal nerve Cause unknown, probably multifactoral Unilateral atrophy of most laryngeal muscles, mainly cricoarytenoid Result: failure to abduct laryngeal cartilage (and vocal fold) Respiratory difficulty, mainly during inspiration and at excercise Lower <a href="/keyword/respiratory-tract/" >respiratory tract</a> disease THE LUNG Anatomic differences Horse has much larger lung capacity than other animals Lobes not distinctly separated Each ruminant lung lobe is divided into lobular divisions supplied by one large bronchus Equine Bovine Lower <a href="/keyword/respiratory-tract/" >respiratory tract</a> disease THE LUNG - Inflammation Terminology Definitions Pneumo(pertaining to the lung); ia(state of disease) = pneumonia; Used to denote inflammatory disease of the lung Bronchopneumonia implies infection arising via the airways and beginning initially at the level of the terminal bronchioles Lobar pneumonia A fulminant, rapidly progressing form of bronchopneumonia Pleuropneumonia Inflammation of the lung and pleural surfaces Embolic pneumonia Infection of the lung via the blood vessels Aspiration (inhalation) pneumonia Inhalation of foreign material Lower <a href="/keyword/respiratory-tract/" >respiratory tract</a> disease THE LUNG - Inflammation Various etiologies Viral Equine influenza ( flu ) Equine rhinopneumonitis ( rhino ) Equine adenovirus Bacterial Rhodococcus equi Others Pneumo(pertaining to the lung); itis(inflammation) = pneumonitis Inflammation of the lung As commonly used, is synonymous with interstitial pneumonia inflammation of the lung tissue (alveolar septae), per se Fungal not common except one covered with adenovirus Parasitic not common (see Merck Manual if interested) Miscellaneous Chronic obstructive pulmonary disease 5 Lower <a href="/keyword/respiratory-tract/" >respiratory tract</a> disease Influenza Orthomyxovirus Two subtypes H3N8 common since 1963 H7N7 rare since 1979 H = hemaglutinin N = neuraminidase Lower <a href="/keyword/respiratory-tract/" >respiratory tract</a> disease Influenza Treatment Rest, cough may persist up to 3 weeks Antipyretics, analgesics Antibiotics if needed to control secondary bacterial infections: Prolonged fever Change from serous to purulent nasal secretion or if cough becomes productive Clinical signs High morbidity in susceptible horses, low mortality Initial high fever Serous nasal discharge (may become purulent signaling secondary bacterial infection Cough, dry hacking, if productive may signal 2 bacterial infection Pain (myalgia?), depression Lipid envelope renders the virus susceptible to disinfectants simple chlorine bleaches are effective and inexpensive Prevention: Vaccines (most contain both subtypes) Multiple manufacturers Killed (formalin inactivated): initial followed by booster in 3-6 weeks, annual or semi-annual boosters Colostral antibodies persist for up to 5 6 weeks Lower <a href="/keyword/respiratory-tract/" >respiratory tract</a> disease Rhinopneumonitis Alphaherpesvirus types 1 (EHV-1) and 4 (EHV-4) EHV-1 mainly abortion, neonatal infection, myeloencephalitis EHV-4 the main respiratory pathogen Lower <a href="/keyword/respiratory-tract/" >respiratory tract</a> disease Rhinopneumonitis Treatment Usually supportive care and rest Analgesics, antipyretics if needed Antibiotics, only if necessary to control 2 bacteria Highly contagious transmitted by aerosols Incubation period 3 to 7 days May be high morbidity in susceptible; mortality low High fever Depression Serous nasal discharge becoming mucopurulent or purulent Cough +/Clinical signs may be indistinguishable from influenza rhino often less severe and protracted Vaccines Both inactivated and modified live Multiple products and manufacturers Several are multivalent contain both EHV-1&amp;2 Vaccination schedules differ depending on needs (breeding mares, etc) Lower <a href="/keyword/respiratory-tract/" >respiratory tract</a> disease Rhinopneumonitis Equine Herpesvirus EHV-1: Pneumabort-K (inactivated); 5th, 7th, 9th month gestation EHV-1: Prodigy (inactivated); same vaccination schedule EHV-1: Rhinommune (MLV)* EHV-1&amp;4: Prestige (inactivated)* *Approved for use in pregnant mares but no label claim for prevention of abortion. No label claims for preventing neurological disease Lower <a href="/keyword/respiratory-tract/" >respiratory tract</a> disease Immunodeficie...