Avian Chlamydiosis

Avian chlamydiosis is a zoonotic disease occurring among birds especially turkey and pigeons, characterized by respiratory, digestive, or systemic infection. It was earlier known as ‘Psittacosis’ or ‘Parrot fever’ since the disease originally recognized in psittacine birds and humans in contact with these birds. The term ‘Ornithosis’ was introduced in 1941, to refer to chlamydial disease in, or contracted from, domestic poultry and wild birds other than psittacine birds (Meyer, 1941). Psittacosis was first described in 1879 when Ritter (1880) described an epidemic of unusual pneumonia associated with exposure to tropical pet birds in seven individuals in Switzerland. 

Avian chlamydiosis is caused by a gram-negative coccoid organism, Chlamydia psittaci, Currently, 8 serotypes of Chlamydia psittaci are recognized. Out them 6 serotypes (A-F) infect avian species and are distinct from mammalian chlamydia serotypes. Each avian serotype tends to be associated with certain type of birds. Serotype D is highly virulent for turkeys and can cause mortality of 30% or higher. Serotypes B and E are most frequently recovered from wild birds. Avian serotypes are capable of infecting people and other mammals. 

The disease has a worldwide prevalence and infections have been identified in at least 150 avian species, particularly colonial nesting birds, ratites, caged birds, raptors, and poultry. Among domestic poultry, turkeys are most susceptible and then ducks and pigeons. Although chickens appear to be more resistant, natural infections have been reported in breeder flocks, broilers and layers (Hafez and Sting, 1997 and Vanrompay et al., 1997). The prevalence in psittacine birds ranges between 16 and 81%, and a mortality rate of 50% or even higher is not unusual (Dovc et al., 2007).This may increase to 100% when the birds are subjected to the stress of shipping, crowding, and breeding.

Being zoonotic in nature, the disease also occurs in humans but as a febrile pulmonary infection. Ornithosis in humans, contracted from turkeys is usually more severe than that from psittacine birds. Psittacosis outbreaks have identified occupational exposure  to turkeys and ducks (Newman et al.,1992) and domiciliary exposure to psittacine birds (Schlossberg et al.,1993) as sources of infection. The largest epidemic occurred in 1930 and affected 750-800 individuals. This epidemic led to the isolation of C. psittaci in several laboratories in Europe and the United States. 

Infection occurs directly when birds are in close contact with each other and indirectly through fomites and ingestion of infectious material. Further, transmission may also occur through blood-sucking ectoparasites such as lice, mites and flies or, less commonly, through bites or  wounds (Longbottom and Coulter, 2003). Some birds may act as subclinical carriers of the disease and intermittently shed the bacterium, especially when immunosuppressed. Vertical transmission has been demonstrated in turkeys, chickens, ducks, parakeets, seagulls and snow geese, although the frequency appears to be fairly low (Wittenbrink et al., 1993). Transmission from parent to young may occur in many species, such as Columbiformes, cormorants, egrets, and herons, through feeding, by regurgitation, while contamination of the nesting site with infective exudates or faeces may be important in other species, such as snow geese, gulls and shorebirds.

People become infected through inhalation of aerosolized bacteria when exposed to infected birds or by the handling of contaminated feather, fecal material, or body tissue. Other means of exposure can include beak-to-mouth contact. People most at risk for infection are those exposed to birds through their daily activity in aviaries, poultry farms, pet shops, veterinary clinics, and as pet bird owners. 

The organism enters the body mainly through inhalation and multiplies in the lungs, airsacs and pericardium. Then the organism reaches the liver, kidney and spleen, by hematogenous route to replicate with the production of reticulate and elementary bodies. 

Depending on the species and age of the bird and on the strain of chlamydia, clinical signs in birds vary greatly in severity. Hence, clinical signs may be absent, mild or severe. In turkey, duck and pigeon, signs include depression with ruffled feathers, purulent nasal discharge, anorexia and conjunctivitis. Sometimes tracheitis with rales and grey-green diarrhoea containing blood may also occur.  Incubation period is reported to be 3 days to several weeks (NASPHV, 2010) in birds. In humans, incubation period is 5 to 14 days and common symptoms include abrupt onset of fever, chills, headache, malaise, myalgia, nonproductive coughing, and dyspnea (NASPHV, 2010). 

Clinical signs and gross lesions are usually insufficient for definitive diagnosis. Diagnosis of the disease can be hence made by detection of antigens, immunohistochemical staining, polymerase chain reaction assays and serology. One of the more common and reliable method is the isolation and demonstration of the organism. It involves isolation of organism in cell culture or embryonated hen’s eggs. Inoculation of the susceptible material in mice can also be used. Serological methods of detecting and measuring antibodies include complement fixation test (CFT), ELISA, immunofluorescence and gel diffusion tests. 

Birds infected with avian chlamydiosis should be treated with doxycycline for 45 days. A variety of treatment methods can be used, including doxycycline-medicated feeds, medicated water, oral medication, or injectable doxycycline. Antibiotic treatment is however discouraged in birds because of the fear of development of resistance against the drug. Although antibiotic resistant C. psittaci has not yet been reported in birds yet, tetracycline-resistant C.suis have been isolated from pigs in several countries (Di Francesco et al., 2008). When treating infected birds, it is recommended to limit stress, monitor body weight daily, isolate affected animals, and keep the cage environment clean. It is also important that the bird’s caretaker follow appropriate standard hygiene. practices to minimize the zoonotic potential associated with the disease. No commercial vaccine is available for avian chlamydiosis. 

Any newly purchased bird should be tested for C.psittaci and quarantined for at least 30 days. Any birds that travel to exhibitions or shows should also be isolated from other birds. Sale and purchase of the suspected birds should be avoided. Create awareness among the persons in contact with birds or bird-contaminated materials about potential health risks. Due to zoonotic nature of the organism, great care should be taken in handling the infected birds or suspected carcass. When cleaning cages or handling potentially infected birds, caretakers should wear protective clothing. Necropsies of potentially infected birds should be performed in a biological safety cabinet and the carcass should be moistened with detergent and water to prevent aerosolization of infectious particles during the procedure. Proper managemental and disinfection measures should be undertaken as a regular practice. 

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Dovc, A., Slavec, D., Lindtner-Knific, R., Zorman-Rojs, O., Racnik, J., Golja, J., Vlahovic, K., 2007. The study of a Chlamydophila psittaci outbreak in budgerigars. In: Proceedings of the 5th Annual Workshop of COST Action 855 Animal Chlamydioses and Zoonotic Implications 24.

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Meyer, K.F., 1941. Phagocytosis and immunity in psittacosis. Schweizerische Medizinische Wochenschrift 71: 436-438.

National Association of State Public Health Veterinarians (NASPHV), 2010. Compendium of measures to control Chlamydophila psittaci infection among humans (Psittacosis) and pet birds (Avian Chlamydiosis). Available at: http://www.nasphv.org/Documents/Psittacosis.pdf, (accessed on 2 October 2012)

Newman, C.P., Palmer, S.R., Kirby, F.D. and Caul, E.O, 1992. A prolonged outbreak of ornithosis in duck processors. Epidemiol Infect, 108:203–10.

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Schlossberg, D., Delgado, J., Moore, M.M., Wishner, A. and Mohn, J. 1993. An epidemic of avian and human psittacosis. Arch Intern Med,153:2594–6.

Vanrompay, D., Butaye, P., Nerom A. V., Ducatelle, R. and Haesebrouck, F., 1997. The prevalence of Chlamydia psittaci infections in Belgian commercial turkey poults. Vet Microbiol,54(1): 85-93.

Wittenbrink, M.M., Mrozek, M. and Bisping, W., 1993. Isolation of Chlamydia psittaci from a chicken egg: evidence of egg transmission. Zentralbl. Veterinarmed. B 40:451–452.