Birds have a highly developed. and specialized respiratory system. Nature has, over millions of years, modified these descendents of reptiles for flight. There have been changes and modifications in every organ system as well as physiological adaptations enabling birds to perform their aeronautical feats. To the casual observer feathers are the most obvious of the birds specialized adaptations. If one considers these creatures in their total functional and structural context the respiratory system in many ways may be an even more remarkable work of nature.
To the veterinary practitioner interested in the clinical care of avian patients as well as the aviculturalist, respiratory diseases and/or conditions affecting the respiratory tract represent one of the most commonly encountered abnormalities. To effectively observe, identify, evaluate, diagnose, treat and prognosticate respiratory problems one must understand and appreciate the normal anatomy and physiology of the system.
Following are some of the primary aspects of the structure and function of the respiratory system: As is the case in all terrestrial species, gas exchange is the primary function of the respiratory system. It is remarkable that birds can obtain enough oxygen to function at altitudes in which mammals show severe stress and require supplementation to prevent anoxia and blacking out. The respiratory system also represents an important method of body heat control. The insulating feather coat limits heat loss by radiation and a lack of sweat glands prevents heat loss by evaporation.
Structurally .the system has a number of unique features. There is no diaphragm dividing the upper (thoracic) and lower (abdominal) cavities. Therefore birds rely on movement of the intercostal muscles and excursions (outward movement) of the abdominal muscles to move air. There are thin walled sacs, some nine in number, which are extensions of the lungs that hold and warm air, fill considerable portions of the bird's anatomy thereby decreasing weight for flight and greatly increasing the internal air capacity.
Air moves on inspiration through the lungs to the air sacs and then back through the lungs on expiration. This is a one way system. There is no gas exchange in the air sacs which have poorly vascularized walls and respiration (exchange of gases) primarily occurs on expiration. Although birds have a larynx they lack vocal cords. Their vocalizations are produced in the syrinx, a modification of the trachea and bronchi where the bronchi arise deep in the chest just anterior to the heart. All these are dramatic departures from a typical mammalian respiratory system.
A variety of pathogens can invade and affect the respiratory system. Bacteria, viruses, fungi, toxins, parasites and neoplastic processes, as well as trauma can produce inflammation and. loss of functional capacity. In addition, abnormalities outside the respiratory tract can compromise the respiratory tract itself.
Signs of respiratory associated illness, regardless of cause, are often similar. Malaise, ruffled feathers, depression, anorexia (loss of appetite), decreased vocalization or change in vocalization, gaping (open mouth breathing), tail- bobbing, sneezing, nasal discharge, coughing, dyspnea (difficulty breathing), decreased activity and weakness are some of these signs. One must remember that birds mask symptoms of illness, a very sophisticated survival strategy, and when noted any of the above stated signs may represent chronic rather than acute disease.
To differentiate cases of respiratory disease a thorough examination needs to be performed starting with cage observation and. including laboratory evaluations, radiographs (X-rays), and if indicated laparoscopic procedures. To the severely compromised patient this does represent some risk, but without a proper work-up treatment protocols are at best guesses at therapeutic agents. One may as well flip a coin, roll dice or cut cards to choose treatments. Contemporary knowledge is such that we now have the capabilities, with reasonable safety and accuracy, to diagnose and treat conditions in avian patients.
A careful history needs to be taken. Respirations should be observed with the bird in its cage. Oxygen should be available particularly for birds exhibiting severe respiratory distress. Nostrils and plumage can be observed for discharge, and the clinician should listen for sneezing, coughing, and abnormal respiratory sounds (wheezing, clicking). The face should be viewed for distortions about the nostrils, cere and orbital areas. Weighing the bird is most Important both to determine absence of or degree of emaciation and if necessary calculate doses of therapeutic agents selected for treatment. The physical exam includes palpations of the body for emaciation, surface masses, and subcutaneous emphysema as well as evaluation of the oral cavity including the choana. Samples can be collected at this time for further evaluation and the bird then returned to its cage and observed for stress.
Useful clinical tests to aid in diagnosis of respiratory disease include: gram stains of choanal swabbing, bacterial and fungal cultures, blood counts, and x-rays. Tracheal washes and sampling of air sac contents, when indicated, are also useful procedures. "When sampling the respiratory tract for pathogens, the choana is a much more suitable source of material than the nostrils because the choanal sampling does not represent a source of environmental contaminants.
Of the conditions affecting the upper respiratory tract, sinusitis is the most common. The sinuses of birds are extensive, extending into the beak and large portions of the skull, Sinusitis may manifest itself as nasal discharge (pasted, feathers above the nostrils or plugged, nostrils), swelling of the face around, the eyes, or choanal discharge (post-nasal drip). Remember that "birds do not liquefy pus which may remain as cheesy plugs within the sinuses. Bacteria are usually associated, with sinusitis, "but Mycoplasma and cryptococcosis may "be involved. Treatment involves selected antibiotics administered, at suitable levels for adequate periods of time, at proper intervals and, by effective methods. Flushing the sinuses may aid in the process by removing debris and surgically removing foci of infected, material is indicated.
As with any illness, good nursing care is essential and ambient temperatures should, be kept "between 80° and. 85°F. Anorexic birds should, be tube fed until self-feeding at adequate levels and. vitamins supplied. Vitamin A is essential for normal tissue health and is the most common vitamin deficiency encountered. Seeds are notoriously deficient in vitamin A, and. when lacking in adequate amounts for periods of time the membranes lining the respiratory tract are weakened, thus making the tissues more susceptible to invasion by opportunistic pathogens as well as producing proliferative lesions in the mouth and. nasal cavity. Proliferation of tissue also occurs in birds from avian pox (eg. Amazons, canaries) which is often transmitted, mechanically by mosquitoes, Trichomoniasis (often called "Frounce") which is common in colombiforms and raptors, neoplasia (ie. tumours), and candidiasis (yeast) often associated with poor sanitation of young and long term use of antibiotics. "Scaly face" mite can also produce proliferation of tissue on the surface of the face. Treatment for these include: supportive care for pox, injection of vitamin A for deficiency, Dimetridazole or Ipronidazole for trichomoniasis, surgery for tumours, Mycostatin, ketoconazole, and Ancobon for Candida and Ivermectin for mites.
The middle respiratory tract, glottis-larynx, trachea, syrinx, bronchi, is on occasion affiliated with infections (bacteria and fungi such as aspergillus), but is more often obstructed by foreign bodies such as seeds and food, plugs of caseous pus, plugs of aspergillus or external pressure from tumours and other space occupying lesions as well as mites (finches) and parasites (gape worms).
The lower tract comprising lungs and air sacs is subject to a wide variety of insults both from within and without. Because of their extensive distribution with poor circulation, the air sacs are more commonly involved than the lungs. Bacteria are most common as infectious agents. Coliform, gram negatives are the primary pathogens (disease producers) in birds. They unfortunately are often resistant strains created by inappropriate use of commonly available antibiotics.
The classic example of this is E, coli, its resistance to tetracycline and its ability to teach this resistance to other bacteria in relatively short periods of time by the exchange of plasmids. Aspergillus is a frustrating problem in birds. This fungus is found worldwide and all air-breathing creatures inhale it's spores on every breath. Normal bacterial flora help hold this organism in check. Compromised immune systems, dampness, long-term use of antibiotics and/or any event that disturbs a creature's state of homeostasis may result in the growth of Aspergillus sp. This fungus produces toxins which are damaging to the patient as well as the growth of the organism compromising the tract. Raptors, ansiforms (ducks, geese) and. Psittacines are highly susceptible to this disease. Treatment is difficult and. drugs used. Are toxic (amphotericin and ancobon).
Psittacosis, a primary gastrointestinal disease, can also affect the respiratory tract and diagnosis can be made by identifying the organism from smears of air sac material using special stains. This disease is also diagnosed "by serum titres and culturing. Although tuberculosis in birds is primarily a digestive tract disease it can "be found in the respiratory tract. It is most common in amazons, grey-cheek: parakeets and older gallinaceous birds (chickens, quail, pheasants). Although the avian strain has a low pathogenicity for man, it can be a problem in immune compromised populations (AIDS, organ recipient patients, diabetes) and is always fatal. Older amazons have been known to contact human or bovine T.B. from their stewards as a respiratory disease producing gradual wasting.
Newcastle virus may present as a respiratory disease. It usually has neurological signs. There is no treatment. The disease is not present in Australia at this time. Gapeworms can "be diagnosed from adult worms or ova in the faeces. Levamisole is used to treat. Air sac (lung) mites, as mentioned before, are common in canary’s and Lady Gouldian finches. Until recent times various insecticides were tried with poor results. Depopulation and restocking with clean birds was effective. Now ivermectin is "being used.
There are a variety of external causes of respiratory symptoms: Goitre (iodine deficiency) in the Midwest produces enlargement of the thyroid with pressure on the trachea resulting. On the west coast (once under the ocean) goitre is rare, but thyroid, tumours are described. Other tumours occur in birds. The "budgie is often called a tumour factory, has a life expectancy of five to seven years, and 90% of fatalities are from tumours, large masses often involving 30% of the bird's weight, forming in the kidneys, genitals or liver mechanically press or/and collapse portions of the respiratory tract. Hepatomegaly, especially common in mynahs and ovarian cysts can have a similar effect.
It is hopefully obvious that numerous diseases affect the respiratory tract. Antibiotics are not necessarily appropriate treatments for what may appear at first observation to he an infection. Seeking competent veterinary evaluation and therapeutic advice is a wise and prudent choice for anyone stewarding an avian species that exhibits signs of illness or disease.
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