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In January 2008, a flock of 400 breeding pairs of pigeons associated with an integrated international pigeon breeding corporation experienced a 10% loss among a group of 200 young pigeons starting at 8 wk of age and spanning a 4-wk period. The losses were restricted to 1 pen of 200 birds on the farm. No losses were noted in the other 3 pens of young pigeons. The farm had experienced similar losses among 8- to 12-week-old pigeons in the summer of 2007. However, no postmortems were conducted and no diagnosis was obtained. Losses were not recorded in breeding pairs during either mortality event.
The farm had started raising pigeons in December 2006 and housed the flock in a former poultry (pullet) barn that had been depopulated, cleaned, and held empty for 2 y. The farm operated on a continuous flow system where 24-week-old pigeons were sold back to the corporation each month for distribution to new breeders. The young pigeons were held in 4 age groups in pens separated by permeable barriers (plastic snow fencing). The groups were not mixed on the farm. At the time of the event, the farm output was 300 birds per month, on average.
Normal flock management included continuous use of feed-based coccidiostats mixed in with a 21% protein chick feed and intermittent use of water based penicillin (Pot Pen, Vétoquinol Canada, Lavaltrie, Quebec) at a rate of 297 000 IU/L water for 3 to 5 consecutive days. Individual pens were cleaned when emptied, but not disinfected. The flock owner was the sole worker in the operation.
The attending veterinarian noted clinical signs of emaciation, depression, conjunctivitis, and respiratory distress in approximately 20% of the affected group. Three dead pigeons were submitted to the Veterinary Diagnostic Services Laboratory in Winnipeg, Manitoba. Necropsy and histopathology results were consistent with a systemic bacterial infection and Chlamydophila psittaci was confirmed by conventional polymerase chain reaction (PCR) of respiratory and ocular exudates. Other significant findings included an intestinal roundworm infestation (Ascaris columbae). Bacteriology of multiple tissues, fecal flotation, conventional PCR for Pigeon Paromyxovirus, and real-time PCR for Influenza A were all negative.
Prior to, and as a result of the diagnosis, the flock owner took the following precautions when working in the barn to prevent zoonotic transmission: use of a N95 half respirator, dedicated coveralls and boots, disposable gloves, and immediate shower after exiting the barn.
Treatment of the entire flock was initiated with water-based oxytetracycline at 200 mg/L for 14 d. The dose was calculated to give 15–20 mg of antibiotic per bird per day. However, consumption of the medicated water was not measured. A treatment for roundworms was initiated at the same time using piperazine dihydrochloride (Vétoquinol) at 75 mg/L water.
Due to the zoonotic nature of the disease and interprovincial movement of birds from the flock, a level of assurance was sought for effectiveness of treatment prior to recommencing trade. Two weeks post-treatment, 60 birds were selected at random from the treated group and conjunctival swabs were taken by the flock veterinarian. Polymerase chain reaction, with an estimated sensitivity and specificity of 85%, was performed on individual swabs. No test positive birds were detected. Analysis of the results (Survey Tool Box Version 1.0, Australian Centre for International Agricultural Research, Canberra, Australia) revealed that there was a 99.9% confidence that the affected group had disease prevalence below 1%. Additionally, no clinical signs consistent with avian chlamydiophilosis were reported by either the owner or the flock veterinarian, in either the treated group or the rest of the flock.
Large-scale commercial pigeon breeding operations were a relatively new phenomenon in Manitoba; they had arisen with farm diversification away from traditional livestock and poultry. The challenge for producers and animal health professionals is to establish the diseases of significance and the methods of disease prevention, control, and treatment necessary for alternative agricultural species. In this particular case, a zoonotic agent was identified in a continuous flow production operation that moved large numbers of birds to many regions within Canada. The probability of disease spread from such a system could be significant, but is currently unknown. In Manitoba, avian chlamydiophilosis is reportable to the chief veterinarian under The Animal Diseases Act (Manitoba). Under the federal Health of Animals Act for the purpose of export certification, chlamydiophilosis is an immediately notifiable disease.
Avian chlamydiophilosis is an avian respiratory disease caused by C. psittaci, an obligate intracellular bacterium. There are several genotypes of which B and E are most commonly associated with pigeons. All genotypes have significant zoonotic potential. While all species of birds can become infected, pigeons are thought to have the highest infection rates (over 30%) (1,2). Avian chlamydiophilosis is common among captive psittacine birds, especially cockatiels and parakeets (3), is considered endemic in feral pigeon populations globally, and in commercial turkey operations in the United States and Europe (4).
Chlamydophila psittaci infection in humans is known as psittacosis and cases typically feature respiratory or conjuntival presentations with varying degrees of severity from inapparent illness to severe respiratory disease (3–6). Approximately 70% of psittacosis where the source of the infection was known resulted from human exposure to caged birds (3). The remainder occurred in individuals who had a high risk of exposure: zoo employees, poultry processing plant employees, farmers, veterinarians, laboratory technicians, and others who work in facilities that handle avian species in closed settings (3). Biosecurity precautions for individuals with high risk of exposure include the use of protective clothing, N95 rating or higher respirator, gloves, and head covering. Isolating new introductions for 30 to 45 d with follow-up testing and/or prophylactic treatment, creating solid separations between groups of birds, daily cleaning of waterers and feeders, and thorough disinfection of all cages or pens between groups of birds are also highly recommended procedures to prevent avian chlamydiophilosis.
Varying degrees of precautions were taken in the case described herein. The farm owner was diligent with personal biosecurity. Use of protective clothing, masks, and gloves was routine and a shower out procedure was implemented once the disease had been diagnosed. Additionally, access to the barn was restricted to only 1 individual. Biocontainment was poor; the continuous flow of birds through the barn and the lack of full separation between age groups created a risk of spread within the whole flock and ultimately required full treatment of the flock. Additionally, there was no specific quarantine protocol in the integrated system for the movement of pigeons between sites, creating considerable risk for disease spread.
This report highlights the need for veterinarians to be aware of potential disease implications, zoonotic and otherwise, of alternative livestock production systems. Additionally, veterinarians should be aware of both the reporting requirements and available investigation support for zoonotic diseases in their areas.
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