November 2019

Bringing attention to a potentially under-recognized pathogen of small ruminants in the United States: Mycoplasma ovis

By Dr. Maggie Highland

Mycoplasma ovis, formerly Eperythrozoon ovis (“Epe”) prior to 2004, is a blood-borne bacterium of worldwide distribution, reported to infect sheep, goats, deer, and reindeer. Although M. ovis is reported to have a worldwide distribution, most of the investigations and publications identifying the importance of M. ovis as a relevant pathogen in domestic sheep and goats have come from Australia, with fewer publications and reports on this bacterium from other countries including, New Zealand, Canada, Hungary, Norway, Brazil, China, and Japan; a few small scale or regional investigations in the United States can also be found in the literature.

Disease in lambs caused by infection with M. ovis can have considerable mortality with postmortem findings that include anemia, enlarged soft spleen, and pericardial effusion. A 1966 publication out of Australia found that the majority of anemias in young sheep and the majority of outbreaks of ill-thrift in lambs were due to infection with M. ovis. Infection can also cause disease in adults, with symptoms that include fever, anemia, abnormal heart rhythm/rate (cardiac palpitation, tachypnea), and hemoglobinuria (“red urine”). Infection can be associated with either yellow mucous membranes (jaundice due to acute red blood cell lysis) or pale mucous membranes (chronic anemia), as well as “bottle jaw” (a sign of hypoproteinemia), neurological signs due to low oxygen (anemic hypoxia), and weight loss or stunted growth (ill-thrift). Some evidence suggests that chronically infected animals, particularly young, may exhibit otherwise unexplained bouts of transient diarrhea immediately preceding episodes of anemia associated with increased circulating M. ovis. Thus, it’s important to recognize that clinical symptoms of M. ovis infection can resemble or mimic those of other disease entities caused by enteric parasitism or vitamin/mineral deficiencies. View an example of a lamb exhibiting signs of weakness and neurologic deficits, which could be mistaken for white muscle disease or thiamine deficiency, at this video. Soon after this video was captured, the lamb was diagnosed with M. ovis infection which caused severe anemia (PCV 16%).

Disease associated with M. ovis infection is usually more severe in young, never before exposed, otherwise compromised (stressed, other infections), and/or pregnant hosts. Often though, infected animals, particularly adults, show no overt signs of clinical disease; such animals may be life-long carriers. Consequence of subclinical infection with this blood-borne bacterium on production in the United States has yet to be thoroughly investigated.

M. ovis is naturally transmitted by blood-feeding arthropods with published research supporting ticks, mosquitoes, lice, and stable flies as potential vectors. Published data does not support the sheep ked as a vector of transmission. Iatrogenic transmission by reusing needles or possibly sharing blood contaminated tools during shearing or tagging may also contribute to the spread of infection within a flock.

Treatment and control of infection, based on reports from Australia, indicate that good nutrition and decreasing stress are the best ways to recover an animal from disease. Those that recover are believed to develop immunity and some level of resistance to re-infection and/or subsequent bouts of clinical illness. Tetracyclines can be used to control disease; however, treatment has not been shown to eliminate the bacteria from infected sheep.

While microscopic examination of blood smears can be diagnostic, infection may be overlooked due to the resemblance of M. ovis organisms to basophilic stippling in erythrocytes, a common finding in ruminants with regenerative anemia. Re-examination of blood smears for the presence of erythrocyte-associated M. ovis is recommended for any susceptible host in which CBC and blood chemistry findings are limited to anemia, basophilic stippling of erythrocytes, and hypoglycemia. While not clearly defined, the cause of hypoglycemia in submitted blood specimens is suspected to be twofold: 1) consumption of circulating glucose by M. ovis within the host (true hypoglycemia); 2) consumption of glucose post-collection by M. ovis that is present within the collected blood sample; therefore longer times between collection and blood analysis may exacerbate the diagnosis of hypoglycemia. Prolonged time between blood collection and analysis can also result in bacteria becoming free within the blood sample, which can present an additional challenge for clinical pathologic diagnosis on blood smears.

This detachment from erythrocytes post collection, and perhaps additionally during centrifugation of blood samples, made it possible to recently perform a large scale investigation on prevalence, distribution, associated risk factors, and associated outcomes of M. ovis infection in the United States using banked serum samples collected from >1000 flocks during the 2001 and 2011 National Animal Health Monitoring System (NAHMS) sheep studies (for more information on the NAHMS studies, please visit: This study identified M. ovis presence in 68.6% and 75.8% tested flocks that were sampled in 2001 and 2011, respectively. The mean within-flock prevalence was determined to be 23.2% with a similar overall prevalence of 24.3% in all sheep tested. Although M. ovis is not currently recognized as a cause of abortion in sheep, the NAHMS sheep samples study identified higher M. ovis within-flock prevalence in flocks reporting abortions. Additional details and results of this recently published study are available in open access form at:

While further investigation is needed to assess the impact(s) of infection on production, the intention of this article is to acknowledge M. ovis for its potentially under-recognized role in morbidity and mortality in small ruminants in the United States.