Southeastern Cooperative Wildlife Disease Study, College of Veterinary Medicine, The University of Georgia, Athens, GA, USA
Abstract
Conjunctivitis in house finches (Carpodacus mexicanus) due to infection with Mycoplasma gallisepticum was first reported in suburban Washington, DC in 1994.1 Since the initial observations of affected house finches in the mid-Atlantic region, the disease has become widespread and currently has been reported throughout the eastern range of the house finch in the United States and Canada, and by late 1995, mycoplasmal conjunctivitis was confirmed in American goldfinches (Carduelis tristis).1 House finches and American goldfinches remain the only species in which mycoplasmal conjunctivitis has been confirmed.
In natural and experimental infections, mycoplasmal conjunctivitis is characterized by chronic inflammatory changes in the eye and adnexae as well as the upper respiratory system.4,5 Grossly, there may be unilateral or bilateral eyelid swelling with feather loss and serous exudate. Mucoid nasal exudate may accumulate on the bill and face and plug the nares. Microscopically, lymphoplasmacytic inflammation with epithelial and lymphoid hyperplasia is present in the conjunctivae, cornea, nasal turbinates, and rarely the trachea. Ultrastructurally, large numbers of mycoplasmas adhere to mucosal surfaces.
The MG strain associated with finch conjunctivitis grows very slowly in culture and has been difficult to isolate.3 Molecular characterization of the house finch MG isolates collected from 1994–1996 throughout the range of the disease as well as two MG isolates from goldfinches suggested that a single strain of MG appears responsible for the widespread epornitic in wild birds.2 Furthermore, the isolates appeared genetically dissimilar to MG strains commonly associated with vaccination or clinical disease of domestic poultry. The original source of the MG strain responsible for conjunctivitis in wild finches remains undetermined.
The effect of mycoplasmal conjunctivitis on house finch populations has not been determined. Natural MG infection in captive house finches was highly transmissible and nearly all finches caged with infected birds developed lesions and antibodies.5 The severity of disease was evident as 25% of the naturally infected birds died or were euthanatized because of debilitation. Field surveys for MG in house finches and other wild passerines in northeastern Georgia in winter 1997–1998 revealed that house finch populations appeared low when compared to 1994–1996. Similar anecdotal information has been received from other areas of the eastern United States. Based on U.S. Fish and Wildlife Service Breeding Bird Surveys from 1966–1996, a declining trend in house finch populations in several mid-Atlantic states has been detected since mycoplasmal conjunctivitis was first documented in 1994.
In addition to fewer house finches in northeastern Georgia in winter 1997-1998, there was a marked reduction in the prevalence of clinical disease and antibodies in house finches in the region. Gross conjunctivitis was observed in only one of 54 captured birds and only five of 54 were seropositive. Isolates of MG were obtained from the house finch with conjunctivitis and one clinically normal house finch. This is in stark contrast to the previous two winters when the vast majority of house finches captured in northern Georgia were infected with MG.
Literature Cited
1. Fischer, J.R., D.E. Stallknecht, M.P. Luttrell, A.A. Dhondt, and K.A. Converse. 1997. Mycoplasmal conjunctivitis of wild songbirds: The spread of a new contagious disease in a mobile host population. Emerging Infectious Diseases 3:69–72.
2. Ley, D.H., J.E. Berkhoff, K. Joyner, L. Powers, and L. Levinsohn. 1997. Molecular epidemiologic investigations of Mycoplasma gallisepticum conjunctivitis in songbirds by random amplified polymorphic DNA analysis. Emerging Infectious Diseases 3:375–380.
3. Ley, D.H., J.E. Berkhoff, and J.M. McLaren. 1996. Mycoplasma gallisepticum isolated from house finches (Carpodacus mexicanus) with conjunctivitis. Avian Diseases 40:480–483.
4. Luttrell, M.P., J.R. Fischer, D.E. Stallknecht, and S.H. Kleven. 1996. Field investigation of Mycoplasma gallisepticum infections in house finches (Carpodacus mexicanus) from Maryland and Georgia. Avian Diseases 40:335–341.
5. Luttrell, M.P., D.E. Stallknecht, J.R. Fischer, C.T. Sewell, and S.H. Kleven. 1998. Natural Mycoplasma gallisepticum infection in a captive flock of house finches. Journal of Wildlife Diseases 34:289–296.