Apparent prevalence of transplacental transmission of hemotropic mycoplasmas in Holstein dairy calves

Hemotropic mycoplasmas are unculturable bacteria that infect the surface of red blood cells of several mammalian species including cattle. The importance of hemoplasmas in cattle remains unclear and limited information is available about biological routes of transmission. The objective of this cross-sectional study was to determine the prevalence of transplacental transmission of hemoplasmas and to determine if colostrum of infected cows contained DNA from hemoplasma organisms. In March 2023, researchers collected colostrum and peripheral blood samples from 39 dairy cows and their newborn calves (before ingestion of colostrum) at a single dairy farm in Michigan. Detection of Mycoplasma wenyonii and Candidatus Mycoplasma haemobos was performed using real-time PCR. The apparent prevalence of hemoplasma infection in dams was 100%, with 84.6% (33/39) co-infected with both M. wenyonii and C. M. haemobos, whereas the remaining 15.3% (6/39) were infected solely with C. M. haemobos. The prevalence of newborn calves infected with C. M. haemobos was 10.2% (4/39), and none were infected with M. wenyonii. No colostrum samples tested positive for either M. wenyonii or C. M. haemobos. This is the first report of vertical transmission of hemoplasmas in a dairy herd located in the United States. However, the relatively low prevalence of infected newborn calves suggests that transplacental transmission is not the predominant pathway of infection. The absence of positive tests in colostrum may indicate ingestion of colostrum contaminated with hemoplasmas is not common. The clinical importance of fetal infection remains known.