The Importance of Lab Tests
for Caged and Aviary Birds

   Introduction

   Diagnostic Laboratories

Subclinical illness in caged birds makes diagnosis of disease difficult. Consequently, the avian veterinarian must rely heavily on diagnostic laboratories to provide tests that can aid in the diagnosis and treatment of disease, as well as help monitor the clinical course of the avian patient.

Bacterial and fungal diseases can be diagnosed in the microbiology laboratory, and the proper and most effective antimicrobial drugs (antibiotics, etc.) to use in treating these diseases can be determined.

   Collection and Analysis of Blood

Blood samples may be obtained from the avian patient in a number of ways. The lease stressful and easiest method involves clipping one or more toenails and allowing the blood to flow freely into tiny capillary tubes that contain an anti-coagulant. Blood smears are made from a single drop of blood placed on a microscope slide or cover slip. Blood can also be withdrawn from the jugular or a peripheral vein using a syringe equipped with a very small needle. This latter method is often less stressful than nail clipping when dealing with the smaller caged birds (budgies, canaries, finches, etc) and may be necessary if a relatively large blood sample is required. Only very small volumes of blood are required by the laboratory. Therefore, there is no caged bird that cannot be examined in this manner. Chemical cautery agents are used to stop the nail from bleeding, and finger pressure is used to prevent excessive bleeding when blood is withdrawn from a vein using a needle and syringe.

The blood sample can be examined in 2 different ways. Analysis of the cellular portion of the blood yields red and white blood cell counts. These are useful in diagnosing anemia and determining whether a patient is experiencing enough of an insult to its system to cause changes in the circulating white blood cells. These changes either influence the total number of white blood cells circulating in the peripheral blood or the proportions of the 5 different types of avian white blood cells, or both. Blood smears can be stained and examined for the presence of blood parasites and to obtain information about all the blood's cellular components.

The fluid portion of the blood (plasma) is also examined (blood chemistry evaluation) and yields information about the biochemical status of the patient and the integrity of the patient's vital organs (liver, kidneys, etc). This information provides the clinician with specific diagnoses, such as diabetes and gout. In other cases, biochemical profiling of the blood indicates the organ systems involved and the severity of the disease.

Blood work ups provide information that enables the avian veterinarian to understand the severity of the patient's condition, to know the extent of the disease, and to follow the patient's clinical course with successive blood samples. Serial laboratory testing enables the clinician to follow the patient's progress and make changes in treatment much more rapidly than would otherwise be possible by simply monitoring the patients visible response (or lack of) to treatment.

   Urinalysis

Examination of urine from the avian patient presents some obvious problems (collection of a large enough volume to analyze, separation of it from the fecal portion of the droppings, etc.) but urine samples are of significant diagnostic value. The urine's physical (color, clarity, specific gravity, pH, etc.) and biochemical (presence of protein, glucose, blood, etc) properties are analyzed. The urine sample is centrifuged and the sediment is examined for its cellular debris (white and red blood cells, lining cells of the urinary system, etc) crystals, and microorganisms (bacteria, parasites, etc).

   Examination of Body Fluids and Tissues

The clinical pathology laboratory also enables the veterinarian to examine and analyze various body fluids and cells that may be present in a particular sample. Fluids may be aspirated by syringe from body cavities and cysts, and studied in the same manner as a urine sample. Microscopically examining the cellular portion of the sample is called cytologic analysis. Pressing a microscope slide against a particular tissue results in the deposition of some of its cells on the slide's surface. Such impression smears can be made from tissue masses (lumps, etc), abscesses, discharges, wounds, etc. Various stains can be used to prepare these impression smears before their microscopic examination. Cytologic and fluid analyses are valuable diagnostic tools in avian medicine.

   Bacterial Culture and Antimicrobial Sensitivity Testing

Since infectious diseases are the most common causes of illness in caged and aviary birds, the microbiology laboratory plays a vital diagnostic role for the avian veterinarian. Samples collected from the patient may yield pathogenic (disease-causing) bacteria or fungi. The major function of the microbiology laboratory is to identify these microorganisms so that the appropriate treatment can be initiated.

Once one or more bacterial isolates from a specimen have been identified, the next step is to conduct antimicrobial sensitivity testing. Drug-impregnated discs are placed in contact with colonies of each previously identified microbial isolate. The effectiveness of each antimicrobial is determined by measuring the zone around each disc in which the growth of the organisms have been completely inhibited. Generally speaking, the larger the zone, the more effective the antimicrobial. It is from these "effective" antimicrobials, then, that the veterinarian selects a drug with which to treat the patient. This type of antimicrobial testing is not used with fungal isolates.

   The Gram Stain

Another effective tool available to the avian veterinarian is the Gram stain. Various specimens (feces, discharges, pus, etc.) from the patient can be Gram stained and examined microscopically. Such a preparation yields a surprisingly large amount of information; whether or not bacteria and yeasts are present in the sample; the relative numbers of organisms present; their shape and relative size; and their Gram stain reaction (Gram-negative bacteria appear light red or pink and are generally considered the major disease-causing bacteria among caged birds; Gram-positive bacteria appear dark blue or violet and make up most of the normal gastrointestinal and respiratory tract microflora of caged birds). Just knowing this information aids in the tentative identification of the bacteria present. An actual culture would be necessary to make a positive identification. The advantage of the Gram stain is that it represents a relatively inexpensive method of determining the microbiologic status of a patient. More important, it provides a convenient method for monitoring a patient's progress during and after antibiotic therapy.

   Parasite Identification

The methods employed to diagnose parasitic problems in birds are simpler than the laboratory methods described previously. As previously stated, blood parasites may be noted upon examination of stained blood smears. External parasites (biting lice are the most common) either have a superficial location (on or within the feathers) or they may be buried within the top layers of the skin (scaly-face mange in parakeets). Careful visual inspection (with or without magnification) is required to diagnose blood parasites and biting lice. Visual inspection and skin scrapings (microscopic examination of scraped debris) are required to diagnose scaly-face mange. Intestinal parasites are rarely detected by bird owners. Occasionally, a caged bird will pass entire worms or parts of worms (roundworms, tapeworms, etc) in the droppings. Sometimes these parasites are seen hanging from the bird's vent. Most often, however, microscopic examination of droppings is necessary to diagnose intestinal parasites. Fecal flotations (to detect parasite eggs) and direct smears (fresh feces mixed with saline and examined immediately) are the 2 most common methods.

   Miscellaneous Laboratory Tests

Samples for certain special tests must be submitted to other laboratories for analyses. Diagnosis of lead poisoning (a common intoxication of caged birds) requires a specific analysis of the patients blood. Diagnosis of chlamydiosis ("parrot fever") requires submission of feces (or cloacal swabs) or tissue samples to the State laboratory for very specific testing procedures. Blood samples can be submitted to other laboratories for serologic analyses (detection of antibodies to certain disease agents, such as chlamydiosis).

Viral diseases are difficult to diagnose in caged birds. Virus isolation and identification require submission of specific tissues or body fluids, secretions or excretions, and must be performed by State laboratories, or laboratories located within veterinary colleges. These tests are time-consuming and costly.

   The Necropsy

Ideally, the avian veterinarian would cure every bird presented for treatment. Unfortunately, some avian patients die in spite of the vet's best efforts. In these cases, an autopsy (vets call it a necropsy) can be extremely useful. The results may confirm the diagnosis suspected before death, or will at least help the vet to better understand why the bird died. This can have a tremendous importance to surviving birds (cage mates. etc.) and to other similarly ill birds that my be presented to the vet in the future.

The necropsy is an excellent diagnostic tool in an avicultural situation. It is often advisable to sacrifice one or more living individual of a group to more rapidly arrive at a diagnosis for the disease affecting, or at least threatening, all members of the group. Unfortunately, necropsies do not always provide conclusive results.

Bird owners should submit their deceased bird for necropsy as soon as possible after death. It is a good idea, soon after death, to immerse the body in icy water for about 30 minutes to rapidly cool the body and delay decomposition. This is especially important with small caged birds. If any delay in necropsy is anticipated, the body should be refrigerated immediately but not frozen Freezing produces significant changes in the tissues and interferes with the microscopic interpretation of the tissue samples. Freezing of the cadaver may be necessary in certain circumstances, but it should be avoided whenever possible.

It is always an unhappy situation when a bird dies. The death is painful for the bird's owner because it often represents the loss of a wonderful and joyful companion or a valuable breeder, or it represents some other loss. The death is distressing, too, for the vet, because it represents treatment failure. A necropsy and the results it provides, however, can be of great value to both parties. The owner of the deceased bird benefits from gaining a better understanding of why the bird died and from determining whether or not other birds in the household or aviary are at any risk. The veterinarian is given the opportunity to further his or her own education. Both parties benefit because they are contributing to the advancement of avian medicine and aviculture.