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Variation in seroprevalence of antibodies against Mycoplasma gallisepticum and Avipoxvirus in nine species of birds with differential access to feeders

Posted on 9. March, 2018.

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Congregation of individuals at high densities is known to increase disease transmission and bird-feeding activities are specifically aimed at attracting many birds to a single location. Studies have shown that implementing bird feeders increases the likelihood of host infection to Mycoplasma gallisepticum, a causative agent of conjunctivitis in birds.

Alternatively, very few studies have examined the potential role of feeders in spreading viral pathogens, and no study has explicitly examined the role of bird feeders in avian pox disease dynamics.

Disease ecologists have been closely following the spread of MG in wild bird populations for over 20 years. This was initially a pathogen primarily found in poultry until it began to spread in the House Finch Haemorhous mexicanus in 1994 and, eventually, to other wild birds. MG conjunctivitis causes ocular lesions that are the result of past inflammatory effects to infection with MG. In addition, MG is also an important respiratory pathogen.

Avian pox is a well-known disease of captive and wild birds caused by dsDNA viruses in the genus Avipoxvirus, and it affects a wide range of species on a global scale. Avian poxviruses typically cause small, ‘wart-like’ lesions on the featherless regions of the head, legs and feet. Affected birds with mild lesions frequently recover and this is considered to be the most common outcome in wild birds; however, avian pox lesions may compromise vision, the ability to feed, or lead to secondary bacterial or fungal infection leaving wild birds vulnerable to predation.

Wilcoxen et al. completed a three-year study examining the effects of bird feeding on the health of wild birds. Though the primary focus of that work was to assess physiological condition of the birds, they also examined birds for outward signs of disease. In that study, it was found that birds with access to feeders had greater incidence of signs of each conjunctivitis (presumably from MG) and avian pox. That study of the effects of bird feeding on bird health was conducted from April 2011 to June 2014 and it included a ‘pre-feeder’ survey of bird health from April 2011 to mid-June 2011. Feeders were then installed and filled continuously until June 2013. Captured birds were used to assess their health during this entire stretch when feeders were active. Then, from April–June 2014 (after feeders had been removed), Wilcoxen et al. (2015) again captured birds to assess the effects of feeder removal on their health. This study found that birds with access to supplemental food were in better physiological condition, unless they contracted disease.

Though Wilcoxen et al. was an important study in understanding the effects of human-provided food on bird physiology, that study likely underestimated how many birds had important diseases by only using the observation of birds demonstrating outward signs of pathology to determine disease status. Using remaining blood plasma samples from the Wilcoxen et al. study, the objective of this study was to assess what percentage of birds were actually infected with Mycoplasma gallisepticum (MG) and Avipoxvirus at some point in time, rather than simply assessing which birds had severe pathology.

The objective of this study was to examine the differences in pathogen exposure among nine species of birds at sites with bird feeders and sites without bird feeders. We hypothesised that birds at feeder sites would have greater prevalence of antibodies against MG and avian pox than control sites. We also hypothesised that birds would have a greater prevalence of antibodies against MG and avian pox than those that showed signs of infection in the Wilcoxen et al. study.

Read the full article in Avian Biology Research, Volume 11, Number 1, February 2018, pp. 7-11.


Authors: Emily R. Vanaa, Elizabeth R. Wrobela,b and Travis E. Wilcoxena*  
aBiology Department, Millikin University, 1184 West Main Street, Decatur, Illinois 62522, USA
bDepartment of Poultry Science, University of Georgia, Athens, Georgia, USA

Keywords: anthropogenic food, disease, avian, pox, conjunctivitis

Image: Percentage of individual birds from nine species seropositive for antibodies against Mycoplasma gallisepticum
or Avipoxvirus.