OAHN Bovine Project: Investigation of Mycoplasma wenyonii and Candidatus Mycoplamsma haemobos in Ontario dairy cattle (in progress)

Project Lead: Dr. Stephen LeBlanc

Collaborators:  Dr. Jessica Retterath, Dr. Cynthia Miltenburg

Project Proposal

Mycoplasma wenyonii, is a cattle-specific member of the hemoplasmas and recognized as a hemotrophic, epicellular bacterial parasite found near the membrane of cattle erthryocytes1. M.wenyonii has been recognized in sick animals exhibiting a range of clinical signs, most commonly presenting with edema of the hind limbs and mammary gland, pyrexia, enlarged prefemoral lymph nodes, and general icterus due to a hemolytic anemia,2.  M.wenyonii has also been detected in apparently healthy animals with asymptomatic infection3. Prolonged infection has been linked to lower milk yield, reduced calf birth weights, and bull infertility3,4. The relevance of subclinical infection is unknown, however researchers have hypothesized that hemotrophic mycoplasmas may enhance expression of other diseases5. M. wenyonii can be transmitted by direct transfer of infected blood such as the re-use of contaminated needles, or by vectors such as lice, flies, ticks and mosquitoes2,6. Vertical transmission in utero has also been reported6. Candidatus Mycoplasma haemobos, another hemotrophic Mycoplasma spp. has been shown to cause anemia and depression with similar risks for transmission as M. wenyonii.5

M.wenyonii has been recognized worldwide and was diagnosed in a clinical outbreak on a dairy farm in Ontario in 2017 and more recently in a dairy cow in 2023. Sporadic case reports and detections in the United States of America prompted a prevalence study in Michigan and Wisconsin in 2018 that found an estimated within-herd apparent prevalence of 71.7% ± 1.0% for M. wenyonii and 77.3% ±1.0% for C.M haemobos, indicating infection is endemic5.

To date, there have been no studies in Ontario or Canadian cattle for the presence of M.wenonyii or C.M haemobos. Given the endemic status of nearby American states, it is possible these hemotrophic Mycoplasmas are also prevalent in Ontario cattle, but information is scarce as testing is not commonly conducted. Pursuit of a full prevalence estimate that would require testing thousands of cattle is not warranted until more preliminary information is known. Vector-borne diseases may become of greater consequence in the future as previously inhospitable regions become more suitable for vectors such as ticks, expanding the range of diseases such as M. wenonyii and C.M haemobos.

Given the emerging, unknown situation, the bovine Ontario Animal Health Network is the right organization to lead a first exploration into the presence of M.wenyonii and C. M haemobos. Coordination with an existing research project (described in the methods below) will leverage costs for transportation to farms and technician time collecting blood samples. Results of the proposed project will be available to epidemiologists and researchers to determine if application for further funding from a broader number of agencies is warranted in the future.


  1. Messick J. Hemotrophic mycoplasmas (hemoplasmas): a review and new insights into pathogenic potential. Vet Clin Path 2004;33:2-13.
  2. Strugnell BW, McAuliffe L. Mycoplasma wenyonii infection in cattle. In Pract 2012:34;146-154.
  3. Tagawa M, Yamakawa K, Aoki T, et al. Effect of chronic hemoplasma infection on cattle productivity. J Vet Med Sci 2013;75:1271-1275.
  4. Montes AJ, Wolfe DF, Welles EG, Tyler JW, Tepe E. Infertility associated with Eperythrozoon wenyonii infection in a bull. J Am Vet Med Assoc. 1994 Jan 15;204(2):261-263.
  5. Schambow RA, Poulsen K, Bolin S, Krahn D, Norby B, Sockett D, Ruegg PL. Apparent prevalence of Mycoplasma wenyonii, Candidatus Mycoplasma haemobos, and bovine leukemia virus in Wisconsin and Michigan dairy cattle herds. JDS Commun. 2021 Jan 22;2(2):61-66.
  6. Niethammer FM, Ade J, Hoelzle LE, et al. Hemotrophic mycoplasma in Simmental cattle in Bavaria: prevalence, blood parameters, and transplacental transmission of ‘Candidatus Mycoplasma haemobos’ and Mycoplasma wenyonii. Acta Vet Scand 2018;60:1-8.