Important diagnostic test methods for avian patients (Proceedings)

Article

For a veterinary technician overseeing an avian or exotic animal patient, diagnostic testing is an essential tool in formulating a definitive diagnosis, prognosis and treatment plan. Diagnostic testing is simply not a luxury for veterinary teaching hospitals, but a necessity for every clinical practice that sees these patients.

For a veterinary technician overseeing an avian or exotic animal patient, diagnostic testing is an essential tool in formulating a definitive diagnosis, prognosis and treatment plan.  Diagnostic testing is simply not a luxury for veterinary teaching hospitals, but a necessity for every clinical practice that sees these patients.  Avian patients do not allow any guesswork for the attending clinician and will quickly succumb to a disease process if not properly treated.  The diagnostic test results will give the veterinarian a snapshot window to “look” inside the patient at that particular point in time.  By developing a baseline of values the veterinary technician can follow the progress of a disease process through a treatment period.  If the patient responds to the treatment it is continued or if the patient does not respond a treatment alternative is considered.  One must always remember to collect the samples that will be affected by stress at the beginning of an examination and follow with those that are least affected by the physical and emotional stress.  In most cases, blood is collected for a complete blood count (CBC) and plasma chemistry panel first because a stressed patient is likely to adversely affect the white blood cell count.

Blood collection

The amount of blood that can be safely collected from relatively healthy avian patients is 1cc/100 grams body weight.  With this amount of blood, the basic diagnostic tests, CBC and plasma chemistry panel can be ordered, even on small patients.  Always discuss submission requirements for a blood sample with your diagnostic laboratory to reduce errors that may occur due to improper shipment.  If enough blood cannot be drawn from a small patient to run both tests, a practitioner has to decide which test will give the most useful information.

Common sites for blood collection include the right jugular v., basilic v. And median tarsometatarsal v.

The right jugular vein is the vein of choice for blood collection in most companion bird species.  The jugular vein can be found in a featherless tract on the ventrolateral aspect of the cervical region.  When collecting blood from birds, the procedure should be performed when the vein is visual.  The advantage of collecting blood from birds is that the skin is thin making the veins easy to see.  The disadvantages to collecting blood are that birds have mobile under the skin and the vessel walls are extremely elastic making needle punctures difficult.  When visualizing the vein, it should be held off with the thumb allowing the syringe barrel to rest on the finger for stability while drawing the sample.  For most avian species a 3cc syringe with a 26 gauge needle is adequate for collection.

The basilic v. located on the ventral surface of the wing coursing over the proximal radius and ulna is another choice for avian blood collection.  The disadvantages for the basilic v. are the vein is superficial with little support tissue to disperse a hematoma and in most species it is small precipitating collapse.  Often if the basilic v. is used the person collecting the sample must “milk” the syringe to reduce pressure on the vessel.  The location of this vein is optimum for intravenous injections because you can see the needle in the vessel lumen and the therapeutic agent being injected into the vein.   

In some avian species the medial tarsometatarsal v. can be used for blood collection or the placement of an indwelling intravenous catheter.  This vein can be located in a groove that extends down the medial surface of the tarsometarsal bone.  The larger the bird the more developed and usable this vein is for blood collection or catheter placement. 

Although 3 veins have been described for blood collection in avian patients, these locations should not limit the veterinary technician in the selection process for a suitable site.  If one sees a large vessel that is readily available for blood collection then it should be used (e.g., humeral v., lateral tarsometarsal v.)

Fecal gram's stains

Fecal gram's staining as part of a companion avian physical examination is a controversial subject.  Often birds are able to mask illness or it is difficult for the veterinary technician to determine underlying conditions that may lead to illness during the stress of the bird adapting to a new environment.  Overtly the animal may appear normal but there could be pathogenic organisms within the gastrointestinal tract that are waiting for an opportunity to cause disease when the bird's immunologic system is compromised. 

 

In a bird that is exhibiting no external clinical disease signs, Gram negative organisms (e.g., Pseudomonas spp., Klebsiella spp.) are considered potential pathogens. Gram positive organisms that may be problematic include the α and β  hemolytic Streptococcus spp and more than 3 candida organisms per oil immersion field.  The normal flora of most parrot species is primarily gram positive rods.

Microbiologic cultures

When obtaining culture samples from avian patients the veterinary technician must again contact the diagnostic laboratory to make sure that proper protocol is followed for transport and maintenance of the sample to optimize organism recovery.  If one is seeking an aerobic or anaerobic organism this must also be discussed with the laboratory to ensure the proper collection and transport media is used for survival of the bacteria or fungal organism.  When collecting microbiologic cultures, veterinarians and technicians have a tendency to use the smallest culturette possible, commonly called the Mini-tip culturette (Becton Dickinson Microbiology Systems, Cockeysville, MD), most likely due to a fear of injuring the small patient.  It is a known fact that the larger the surface area on the culturette the better chances a laboratory has of isolating the organism.  Use a regular size culturette when possible to increase your chances of isolating an organism. 

Common sites for culture include the choana, crop, cloaca and skin.  When determining if an area needs to be cultured a specific protocol needs to be followed.  This protocol should start with evidence of clinical disease.  If the choanal papilla, small epithelial projections that protrude toward the center of the opening in the dorsal respiratory/oral interface opening, are blunted or missing this may indicate a condition of upper respiratory inflammation or irritation.  Swelling and hyperemia along the choanal slit may be a sign of a more chronic disease condition.  Often clinical signs that have been described above are found in conjunction with other disease problems (e.g., sneezing, nasal and/or ocular discharge, dyspnea).  A culture of the choana is recommended if disease signs are observed during the physical exam or the owner mentions abnormalities during the course of taking the medical history.  To reduce the chance of culturing transitory organisms, the choana should be cultured in a specific manner.  In most companion bird species the choana is a triangular opening on the dorsal surface of the oral cavity.  The base of the triangular structure is missing as the skin of the choanal opening transitions into the oral cavity.  The apex of the triangle points in the direction of the beak.  The culturette should be directed toward the apex of the triangle and the cotton tip of the culturette buried into the underlying choana into the nasal septum.  One can flush fluid into the nares to “push” nasal material possibly containing the organisms desired onto the culturette once it is in position within the choana.  Other options that may be used to obtain culture samples of the upper respiratory system is an infraorbital sinus lavage of the area between the medial canthus and nares (lores).  This site can be identified as a depression approximately half-way between the lores.  If the area described for infraorbital sinus lavage is swollen and contains fluid, a sample of this material can be aspirated and submitted for culture.

Culturing the crop is indicated when birds are exhibiting signs of crop stasis or regurgitation.  When working with hand fed birds, in most cases, it is easy to culture the crop because they readily accept material being placed in their mouth.  The baby bird should be positioned as if being hand fed and shown the culturette, most baby birds will open their mouth and quickly swallow the cotton tipped swab.  Once in the crop, located at the thoracic inlet, the culturette can be palpated and should be vigorously rubbed against the crop mucosa.  As with all cultures, it should be emphasized to owners how important identification of the potential disease causing organism is and the determination of the correct antimicrobials to treat the infection(s).  It is not unusual to find that many complex, highly regarded new antimicrobial agents are ineffective in treating avian isolates.  What is surprising is that these same organisms are sensitive to simple commonly used antibiotics.  This again emphasizes the need for culture and sensitivity for avian cases that are showing clinical disease signs. 

Culturing the cloaca will often provide information on possible infections affecting the reproductive, urinary or intestinal tract.  The confluence of the three body systems at the cloaca, in particular the intestinal tract, makes it clear that organisms will be identified.  The important factor for veterinarians treating avian species is to recognize what the normal intestinal flora is for that particular bird.  For most parrots, gram positive organisms are uniformly the organisms most commonly found within the gastrointestinal tract.  There may be nonpathogenic gram negative bacteria (e.g., E. coli or Enterobacter spp.) in small numbers in many cases.  Large numbers of gram negative bacteria is not normal flora for many parrot species and gram positive bacteria, in particular Streptococcus spp., can cause disease.  When culturing the cloaca, the cotton tipped swab should be “buried” into the cloaca and rubbed against the cloacal lining.  Upon slow removal of the swab, the cloacal mucocutaneous interface with the vent can be everted to examine for papilloma lesions.  An important clinical result of the cloacal culture that should be shared with the owner is that for a short time after the examination the bird may have a blood tinged stool due to the irritation of the cloacal lining.

Fine needle aspirates

The first line of diagnostic testing for an avian patient that presents with a tissue mass is a fine needle aspirate (FNA).  Advantages of collecting and submitting a fine needle aspirate include minimal trauma to the site being sampled and the ability to obtain the sample without putting the bird under general anesthesia.  Unfortunately the results of fine needle aspirate samples are often nondiagnostic.  Although most FNA samples will not be helpful in determining a diagnosis, the advantages of no general anesthesia and the atraumatic nature of the sample collection make this a recommended primary diagnostic technique.

 

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