A recently recognized infectious agent is killing companion, aviary, and free ranging birds throughout the world. At present, no birds are known to be resistant. This dreaded affliction is called Proventricular Dilatation Disease (PDD).
What species are susceptible to PDD? In the order Psittaciformes, PDD has been reported in more than 50 species, including the families Cacatuidae (Cockatoos and Cockatiels) and Psittacidae (Lovebirds, Macaws, Parakeets, Amazons, Conures). Pacific, South American, and Afro Asian species have been described with characteristic lesions. Suggestive lesions have been reported in free ranging Canada Geese and Spoonbills, Toucans, and Weavers. Other nonpsittacine birds may also prove to be susceptible to this disease as improved tests are developed to accurately diagnosis affected individuals. Clinical reports suggest that adults are more commonly affected than neonates.
When was PDD first recognized and what synonyms have been used? Proventricular Dilatation Disease has been recognized since the late 1970s. Initially, the disease seemed limited to Macaws. This fact, in conjunction with an unknown cause, gave rise to the terms Macaw Wasting or Fading Syndrome, Macaw Wasting Syndrome, and Gastric Distention of Macaws. As it became apparent that the disease occurred in psittacines other than Macaws, a more general terminology was used to describe the disease, including Psittacine Wasting Syndrome, Proventricular Hyper trophy, or Proven- tricular Dilatation Syndrome. Various terminology has also been used to describe the pathological features of this disease.
What are the signs of PDD? The most common clinical signs of PDD include depression, weight loss, constant or intermittent regurgitation, and/or passage of undigested food in the feces indicating a malabsorptive or maldigestive disorder. Proventricular impaction, muscle atrophy, abdominal enlargement, lethargy, weakness, polyuria, diarrhea, scant feces or hypotension have also been reported in some birds. When the central nervous system is involved, signs may include ataxia (bird may fall from the perch), abnormal head movements or seizures. Some affected birds may develop central nervous system signs in the absence of gastrointestinal abnormalities.
How is PDD diagnosed? A presumptive diagnosis of PDD is based on historical information, clinical signs, and radiographic evidence of proventricular dilatation or dysfunction. Confirming that a living bird has PDD is difficult. Biopsy of the ventricular or proventriculus can be used to diagnosis the disease. However, obtaining a tissue sample from these organs is invasive and dangerous. In some birds, biopsy of the crop can be used to diagnosis the disease. At necropsy, emaciation, pectoral muscle atrophy, and dilatation of the esophagus, proventriculus, ventriculus, or small intestine are observed commonly. The proventiculus may appear thin walled and friable. Microbial infections, parasitism, gastrointestinal obstructions, neoplasms, trauma, malassimilation disorders, toxin ingestion may cause similar changes and also must be considered. A definitive diagnosis is often made after death when microscopic examination of the tissue reveals the characteristic lymphoplasmacytic inflammatory infiltrates in central and peripheral nervous tissues.
What causes PDD? The etiologic agent of PDD remains unconfirmed, although recent research by the Psittacine Research Group, University of Georgia implicates an infectious agent. The disease apparently has subacute, acute, and chronic stages, however, the majority of diseased birds die within several months to a year after developing clinical signs. Interestingly, disease did not develop in all exposed birds, which suggests that some birds have an innate resistance, develop a protective immune response, lack factors that are required for inducing the disease, possess factors which prevent development of the disease, or develop a carrier state. The fact that some exposed birds remain normal is good news for the avicultural community. This suggests that continued research efforts could provide effective control measures to prevent disease.
What can be done? Unfortunately, all birds with confirmed PDD have died. Until further information is available about the virus that is causing this disease, preventative measures such as quarantine of new birds, avoidance of direct or indirect contact between isolated groups of birds and appropriate hygiene are the only available methods to reduce exposure.
Overview of the PDD Research Plan: Currently, the Psittacine Disease Research Group has recovered a virus they suspect is causing PDD. This virus must be identified and characterized. Development of a management technique: After the causative agent I characterized, an accurate testing procedure must be developed to identify infected birds. A vaccine to prevent infections will need to be developed if the virus cannot be managed by testing alone. The International Aviculturists Society estimates the required avicultural contribution to insure PDD is quickly resolved will be $300,000 over a three year period. To raise these funds, the International Aviculturists Society appeals to the entire avicultural community, as well as individual companion bird owners,
(3) IAS is a non profit 501 corporation with NO SALARIED POSITIONS. All donations to the PDD project are directed donations for PDD research, and IAS will absorb any overhead expense in administering this project. Please make your contribution to avian research. PDD Fund International Aviculturists Society, PO Box 280383, Memphis, TN 38168
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