Potential New Causes of Pinkeye Uncovered
Van Schothorst is inclined to believe that bacteria must be transmitted in ways other than by flies because several herds in southern Alberta have histories of pinkeye occurring in winter and worsening throughout the summer, and many ranchers say that the period after weaning is a high-risk time for pinkeye.
“I had the idea when I looked at herds dealing with outbreaks that the eye and nose communicate with each other. In most mammals, the naso-lacrimal duct drains tears into the nose, therefore, perhaps aerosolized nasal secretions or even nose-to-nose contact would be the more likely predominant mode of transmission,” she explains.
Another perplexing aspect of pinkeye is that even though M. bovis is the only bacteria confirmed to cause pinkeye in cattle, it cannot be reliably isolated from the eyes of all infected cattle. Moraxella bovoculi, first identified as a distinct species in 2002, is becoming an increasingly common isolate in cultured samples from cattle with pinkeye. The role of M. bovoculi in the disease process isn’t clear because it has not yet been shown to reproduce the classical pinkeye lesions in the eye.
Van Schothorst’s project with Dr. Eugene Janzen, his assistant, Cynddae McGowan, and Dr. Claire Windeyer of the school’s faculty of veterinary medicine, investigated the frequency with which M. bovis and M. bovoculi occurred alone and together in the eyes and noses of calves with pinkeye during naturally occurring outbreaks. Samples were obtained by swabbing the eyes and noses of approximately 60 affected calves during outbreaks on seven ranches in southern Alberta.
M. bovis was found in 38 per cent of the eye samples and 10 per cent of the nose samples. M. bovoculi was found in 25 per cent of the eye samples and two per cent of the nose samples.
“Both species were cultured from samples from four of the seven ranches. The main point is that overall the same organism could be cultured from both the eye and nose of an individual 20 per cent of the time. We believe this supports the view that there is a similar microbiological biome in the eye and nose and, because of the naso-lacrimal duct communication, direct contact or aerosolized nasal secretions could be a potential route of pathogen transfer between cattle.