Mycoplasma bovis Infections in Free-Ranging Pronghorn, Wyoming, USA

Abstract

T he bacterium Mycoplasma bovis is an economically important pathogen of cattle that contributes to the multifactorial bovine respiratory disease complex. In addition to causing respiratory disease, this bacterium can cause polyarthritis, mastitis, otitis media, and a chronic pneumonia-polyarthritis syndrome, impacting beef and dairy cattle worldwide (1). Despite increased recognition of its role in economic loss in the cattle industry, M. bovis remains a clinical challenge because of a common carrier state in clinically healthy animals, variable disease expression, intermittent shedding, and the lack of rapid accurate diagnostic assays (1,2). Clinical disease is not considered necessary to maintain M. bovis in populations, and M. bovis is commonly detected in asymptomatic adult feedlot cattle (2). Although the upper respiratory tract mucosa is a primary site for M. bovis colonization, presence of the bacterium in the lung is variable in occurrence and clinical manifestation. In 1 study, M. bovis was detected in 46% of cattle with normal lungs, 82% of cattle with acute fibrinous pneumonia, and 98% of cattle with chronic pneumonia (3). Manifestation of M. bovis-associated respiratory disease is particularly common in the wake of stress (e.g., from transportation, comingling, feedlot entry, and harsh temperatures or conditions). In the early 2000s, M. bovis caused several highmortality (case-fatality rate 45%) epizootics in bison (Bison bison) in North America (4). These events raised concern about emergent virulent strains, and research began to characterize isolates from different host species (5). An important difference between outbreaks of mycoplasmosis in bison and cattle is that, in the former, few or no co-infecting bacterial or viral pathogens are consistently detected (4,6-8). Although M. bovis virulence factors are poorly defined, evasion of immune response is implicated in maintaining chronic infection (9). One study found that that up to 79% of bison herds in western Canada have >1 M. bovis-seropositive animal and that 8 of 11 herds with no history of M. bovis disease had seropositive animals (10). These findings suggest that host response to M. bovis varies; some exposed bison become subclinical carriers and might also

Source and Seasonality of Epizootic Mycoplasmosis in Free-Ranging Pronghorn (Antilocapra Americana)

“…When compared globally, the pronghorn sequence type is identical to a single isolate recovered from a bovine with mastitis in Japan (ST 111) (Hata et al 2019). These findings build on previous characterization of pronghorn isolates from 2019 (Malmberg et al 2020), which was limited due to a gene deletion in one of seven target loci employed in a previous MLST scheme (Register et al 2015). The 2020 assemblies from pronghorn contained the same deletion of the adh-1 gene that was documented in isolates from 2019.…”

“…Other species are rarely infected, but cases have been documented in captive and free-ranging white-tailed deer (Odocoileus virginianus) (Dyer et al 2004, Register et al 2019 as well as in free-ranging mule deer (O. hemionus) (Register et al 2019). We previously identified M. bovis as the cause of epizootic pneumonia in pronghorn in northeastern Wyoming during early 2019 (Malmberg et al 2020) and herein document additional mortalities occurring in early 2020. Documented cases have been limited in geographic distribution; however, population impacts remain unclear.…”

“…Diagnostic evaluation included histopathology, bacteriology (aerobic and anaerobic culture, Mycoplasma culture, and M. bovis PCR (all respectively described below); parasitology (Baermann technique for lungworm); and virology (PCR for bovine herpesvirus-1, parainfluenza virus-3, bovine viral diarrhea virus, bovine respiratory syncytial virus, epizootic hemorrhagic disease virus, bluetongue virus, and cervid adenovirus) as described in Malmberg et al 2020 (Supplemental Table 1). When only minimal tissues or nasal swabs were available, we performed PCR for M. bovis detection, followed by culture on a subset (n=13) of positive samples.…”

“…(Brown et al 1994). The most recent example of mycoplasma emergence in wildlife is M. bovis in pronghorn (Antilocapra americana) (Malmberg et al 2020).…”

Contrasting management paradigms for pronghorn in the arid Southwest and their northern range: a review

“…Transmission was hypothesized to occur through shared water sources and were prominent between February and April. The bacteria persists for <2–6 hours in shaded, humid and cool temperatures, and is therefore less likely in the arid Southwest, although still a possibility wherever cattle are present (Malmberg et al 2020). A novel pestivirus (genus Pestivirus , family Flaviviridae) was isolated from a wild pronghorn (Vilcek et al 2005).…”