Characterization of Experimental Mycoplasma gallisepticum Infection in Captive House Finch Flocks

Abstract

The use of controlled, horizontal-transmission experiments provides detailed information on the spread of disease within fixed social groups, which informs our understanding of disease dynamics both in an empirical and theoretical context. For that reason, we characterized in 2002, horizontal transmission of Mycoplasma gallisepticum (MG) in two flocks of 11 wild-caught house finches housed in outdoor aviaries over a 6-mo period. All birds were initially free of MG by a polymerase chain reaction (PCR)-based test, rapid plate agglutination (RPA), and the scoring of physical signs. We inoculated one flock member bilaterally in the palpebral conjunctiva and reintroduced it into its cage. Index birds developed conjunctivitis within 3 to 5 days but died 13 and 20 days postinfection (PI) possibly because of very severe weather. The proportion of birds with physical signs increased gradually, reached 40% at 6 wk PI, and fluctuated around 40% until 21 wk PI. By the time our experiment ended at 24.5 wk PI, 28% of the birds still exhibited physical signs. Across both flocks, 80% of the birds developed unilateral or bilateral conjunctivitis, and several birds relapsed. The appearance of physical signs in new individuals occurred between 10 and 144 days PI (median 41 days PI). Physical signs lasted 1-172 days (median 42 days). Birds that became infected earlier during the experiment developed more severe conjunctivitis, and there was a tendency for birds that developed bilateral conjunctivitis to develop physical signs earlier. Most birds that developed physical signs of MG were also PCR- and RPA-positive, although we detected a single asymptomatic carrier and a single symptomatic false negative. No birds died as a result of secondary MG infection.

Experimental evidence for transmission of Mycoplasma gallisepticum in house finches by fomites

“…Although a polymerase chain reaction or culture would have provided more direct evidence of transmission in these experiments, we accepted the presence of clinical signs and/or the presence of antibodies measured by agglutination as evidence of transmission. This was based on multiple previous experiments carried out in similar housing conditions (Kollias et al ., 2004;Sydenstricker et al ., 2006). These earlier studies have never provided evidence of false positive reactions even for blood samples that had previously been frozen (Kollias et al ., 2004), although the possibility of false negative agglutination reactions cannot be ruled out.…”

“…Both exposure groups were inspected for physical signs of infection twice a week until day 38 post exposure. Eye scores for these birds were recorded on a scale of 0 to 3 as described in Sydenstricker et al (2006), and blood samples for rapid plate agglutination testing were taken on days 13, 27 and 38 post exposure.…”

Attenuated Phenotype of a Recent House Finch-Associated Mycoplasma gallisepticum Isolate in Domestic Poultry

“…13295-2) at North Carolina State University (NCSU) as described previously (18,19,28,29) and shipped frozen to Virginia Tech and Cornell.…”

Immune-system activation depletes retinal carotenoids in house finches (Carpodacus mexicanus)

“…The time course of the study is justifiable because long-term infections are common among wild house finches. The symptoms of Mycoplasma gallisepticum (MG) infection, which include extreme inflammation of the conjunctiva of the eye, last on average 10weeks and up to 24weeks in captive experimentally infected house finches (Kollias et al, 2004;Sydenstricker et al, 2006). Active infections of avian pox can last as long as 3 months (McClure, 1989).…”