Identifying the Infectious Cause of Pinkeye in Beef Cattle

Background

Infectious bovine keratoconjunctivitis, commonly known as pinkeye, impacts cattle performance and is a major welfare concern worldwide with reported losses of $0.78 to $9 USD per head each year. For years, it was the common assumption that Moraxella bovis or Moraxella bovoculi were the main bacteria responsible for this disease. However, vaccines targeting these pathogens have not worked, and Moraxella bovis is found in less than 5% of pinkeye lesions. This could mean that Moraxella spp. may not be solely to blame for pinkeye. Therefore, it is important to understand which microorganisms cause pinkeye to ensure current treatments and vaccines are targeted toward them.

Objectives

• Identify and compare the microorganisms (bacterial, viral and fungal) that exist in healthy bovine eyes and those that are infected with pinkeye, using a pathogen identification platform previously described.
• Identify microorganisms that are specific to pinkeye and understand how they work to create lesions on the eye.

What they Did

Fifty-six samples from a 70-head herd undergoing a pinkeye outbreak were collected. Not all animals in the herd were sampled. A veterinary ophthalmologist performed eye exams to identify active pinkeye cases, and other animals were categorized as inactive (i.e., healed eyes, old lesions) or normal (i.e., healthy). Cattle presumed to have pinkeye had samples collected as did cattle with normal eyes for comparison. These samples were then processed in a lab using a “shotgun” metagenomics approach—a technique that detects any genetic material present—not limited to bacteria only, for example. All the microorganisms identified were used to compile a database, and a comparison between pink eyes and healthy eyes was used to identify potential agents linked to pinkeye disease.

What They Learned

Of the 56 eyes evaluated, 22 (39.3%) exhibited active pinkeye, nine (16.1%) were classified as inactive pinkeye, and 25 (44.6%) were normal. Bacteria was the most prevalent microbe detected, followed by eukaryota and fungi. No viruses were detected. Moraxella bovis, the proposed agent of pinkeye, was detected in animals with active lesions as well as normal eyes. Moraxella bovoculli, a potential agent, was detected only in normal eyes. Four bacteria and one parasite were exclusively detected in cattle with active lesions, suggesting they may play a role in disease development. Future research would be required to confirm whether and how these additional microbes may be involved in pinkeye development.

What It Means

Historically, pinkeye has been associated with eye disease and the presence of Moraxella bovis, a bacterium. However, these results showed that M. bovis is also present in normal eyes without disease and that animals with active pinkeye have other microbes present in their eyes that are not present in normal eyes. This isn’t entirely surprising—many pathogens are found in normal tissue and only cause disease when the wrong combination of pathogen numbers, environmental stress and host animal defences are met. These new microbes may play a role in the development of pinkeye, which might help explain the lack of an effective vaccine or other disease control methods.