Bacterial diseases often occur in companion and aviary birds. Birds often mask signs of illness and are usually presented to a veterinarian in a debilitated, advanced state of disease. In order for treatment to be successful, the correct diagnosis and appropriate medical management are necessary.
Antibiotics are used in the treatment of bacterial infections. Whenever possible, cultures should be taken from the site of infection to identify the organism present and the most effective antibiotic against that organism.
Treatment is often instituted before results of cultures are obtained since identification of the most appropriate antibiotic based on sensitivity may take three to four days. Antibiotics may be changed if a more effective antibiotic against the inciting organism is demonstrated. Several factors must be understood once the most appropriate antibiotic is chosen. Proper dose is essential. The bird must be weighed accurately and given the calculated amount of medicine. Underdosing may lead to treatment failure and drug resistance, while excessive amounts may be toxic and damage the kidneys or liver.
The route of administration of the drug is very important. A bird in an advanced state of illness must be given medication that will be absorbed rapidly and reach therapeutic levels in the bird's body. If a bird is too sick to eat or drink, putting medication in the food or water will not be effective. Birds may be given medication by intravenous injection, intramuscular injection, or by direct administration into the mouth. Medicated food may be used under certain circumstances, but the patient must be eating in order to obtain therapeutic levels in his body.
The frequency of administration and the duration of treatment must be closely adhered to. Certain drugs require twice a day or three times a day administration in order to obtain optimal levels in the patient. Dosing less than the recommended number of times can lead to treatment failure and antibiotic resistance. Treatment must be continued for the prescribed period of time. Stopping medication too soon can lead to the failure of eliminating the infection.
The goal of antibacterial therapy is to aid in the elimination of the infecting agent from the patient. Antibiotics play only a partial role, the host's immune system is required to clear the infection. Supportive care and good nutrition are essential for a successful outcome.
CANDIDIASIS
ASPERGILLOSIS
Aspergillosis is the most frequently occurring fungal infection in birds. It occurs in acute and chronic forms. The acute form primarily occurs in young birds and newly imported birds and is the result of exposure to a large number of spores. The chronic form is more likely to occur in older birds that have been in captivity. Aspergillosis spores are widespread in the environment and many birds may carry them in their lungs and air sacks until immunosuppression or stress triggers clinical disease. Aspergillosis has been diagnosed in a variety of captive and free-living species of birds. It is characteristically a disease of captivity and close confinement, particularly when birds are kept in an unclean environment. Aspergillosis is most commonly caused by A. fumigatus, although A. flavus, A. niger, A. nidulans, and A. terreus may cause the disease as well. The fungus is ubiquitous in the environment and flourishes in rotting vegetation and decaying organic material.
The disease is contracted as the result of inhalation of spores. It may also be contracted by oral ingestion, especially if birds are fed moldy seed. The fungus is also capable of penetrating broken skin and egg shells, and so is able to infect a developing embryo.
Susceptibility to aspergillosis is greatly increased in the immunocompromised and malnourished avian patient. Stress pre-existing disease, and the prolonged use of antibiotics and steroids, may further increase a bird's susceptibility.
Contaminated food, water, and nesting material are sources of exposure to spores. In birds, aspergillosis is primarily a disease of the lower respiratory tract. Although the lungs and air sacs are usually involved, the trachea, syrinx, and bronchi may be affected as well. Infection can spread from the respiratory tract to pneumatized bone or enter the peritoneal cavity. Any organ can become infected by the fungus.
In the acute form, anorexia, dyspnea, or sudden death may occur. White, mucoid exudation, marked congestion of the lungs and air sacs, and pneumonic nodules may be present.
In the chronic form, dyspnea, voice change, lethargy, depression, emaciation, polydipsia, and polyuria may occur. Extensive involvement of the respiratory tract can be present before clinical signs are apparent. Ataxia and paralysis occur of the central nervous system is affected.
Diagnosis of aspergillosis can be difficult. A tentative diagnosis may be made of the basis of physical findings, a history of environmental conditions suitable for fungal growth, and recent stress. A hemogram may show a significant leukocytosis (elevated white blood cell count) with a heterophilia early in the disease. As the disease becomes more chronic, a monocytosis, lymphopenia, and non-regenerative anemia develop. An increase in total blood protein with a hyperglobulinemia may develop. Deep tracheal cytology and culture may be performed under anesthesia. A positive culture will usually be present in 18 hours. A single colony growth is considered significant.
Endoscopic examination of the respiratory tract and abdominal cavity will allow cultures to be taken and granulomas (large walled-off areas) visualized.
An indirect ELISA blood test will permit the detection of antibodies, which will be present within a week of exposure to a large number of spores. This test permits detection of a patient early in the course of the disease, before clinical signs become apparent. Antibody titers decline during remission, and thus this test is useful in monitoring a patient's response to treatment. Unfortunately, an infected bird may fail to show a positive titer due to a poor immune state.
Radiographs may be helpful in supporting a diagnosis of aspergillosis. Hyperinflation of air sacs in the lateral and ventraldorsal views is the classic presentation. This occurs as a result of stenosis near the syrinx or mainstem bronchi which results in the trapping of air in the caudal air sacs. Nodular densities may be present in the air sacs and lungs. Loss of definition of air sac lining may occur early in the disease. Asymmetry of the air sacs as a result of air sac collapse, hyperinflation, or filling with necrotic material may be present.
Treatment of aspergillosis involves several objectives:
1. removal of lesions restricting the flow of air through major airways
2. killing and eliminating fungal organisms, and
3. supportive care
