Graduate Student Literature Review: Hemotropic mycoplasmas in cattle

The objective of this narrative literature review is to better understand bovine hemoplasmosis, an emerging disease that threatens dairy animal health. Several species of hemotropic mycoplasma are known to infect both animals and humans, and Mycoplasma wenyonii and Candidatus Mycoplasma haemobos are the species that infect red blood cells of cattle. These microorganisms are associated with clinical signs in dairy cattle, but the effects of infection on health and productivity of dairy cows are poorly understood. In this paper, we review information about the epidemiology of bovine hemoplasmosis in different countries, including clinical signs associated with hemoplasmosis in cattle, methods of diagnosis, treatment, possible routes of transmission, risk factors for infection, and disease progression. Although hemoplasmas have been reported to infect cattle in many countries, and methods used to detect these organisms have improved, numerous gaps in knowledge were identified. The pathogenesis of the disease and potential effect on animal health and productivity remain unclear. With this review, we seek to contribute to the understanding of hemoplasmosis in cattle and provide insights for further research to improve disease management strategies and overall animal health in the dairy industry.

Apparent prevalence of hemotropic mycoplasma in dairy calves and replacement heifers on Michigan farms

The bovine hemoplasmas include Mycoplasma wenyonii and Candidatus Mycoplasma hemobos which are increasingly recognized as infecting cattle throughout the world. Infection with hemotropic mycoplasma has been reported to be widespread in mature dairy cows, but little is known about prevalence in calves and heifers. The objective of this study was to investigate the prevalence and dynamics of infection with M. wenyonii and C.M. hemobos infections in calves and replacement heifers on Michigan dairy farms and assess potential associations between infection status and hematological values. The study was designed as a prospective cross-sectional study with a longitudinal component. A convenience sample of 11 farms agreed to participate and were visited twice between March and September 2022. During the first farm visit, researchers collected blood samples from up to 94 animals per farm distributed among newborn and pre-weaned calves (n ≤ 31), weaned calves (n = 21), pre-breeding heifers (n = 21), and pregnant heifers (n = 21). During the first visit, blood samples (n = 174) were also collected from a convenience sample of mature cows to confirm the herd infection status. The same calves and heifers were sampled again about 95 d (±3.0) later. During the first visit, blood samples were collected from 797 calves and replacement heifers, while 675 samples were collected during the second visit due to inability to locate some animals. Detection of M. wenyonii and C. M. hemobos were based on results of real time PCR. The hematocrit was determined using microcentrifugation and the concentration of leukocytes using an automated cell counter. In all herds, most mature cows that were sampled tested positive for infection. The within herd apparent prevalence of hemoplasma in calves and replacement heifers was 100% for both M. wenyonii and C. M. hemobos. The apparent prevalence of hemoplasma in youngstock was associated with age. In calves that were 1 to 6 mo old, the prevalence of infection was 6-8% but sharply increased to 31% by 8 mo of age. In older animals, the prevalence remained high, and was almost 100% in animals greater than 17 mo of age. Based on calves and heifers sampled twice, the cumulative incidence varied widely among herds ranging from 3.7% to 96.0% and increased with age of animals. There was no difference in hematocrit or number of lymphocytes, monocytes, neutrophils, or total leukocytes based on infection status. The number of eosinophils was greater in infected animals. This is the first study to report the prevalence of hemoplasmas in calves and replacement heifers in the US It indicates that young calves can be infected with hemoplasmas, but the rate of infection is low. The likelihood of infection increases as animals age, with a notable rise in the proportion of infected heifers occurring by 8 mo old and the prevalence eventually reaching nearly 100% of infection in older animals. Once infected, heifers appear to remain chronic carriers. Hemoplasma infection alone does not usually lead to the development of clinical signs and most of the animals remain apparently healthy.

Detection of Mycoplasma wenyonii and "Candidatus Mycoplasma haemobos" from Japanese Black breeding cows in Kyushu and Okinawa region, southern part of Japan

This study aimed to elucidate the epidemiological status of hemoplasma infection and investigate the interaction between Theileria orientalis and hemoplasmas in Japanese Black breeding cows raised in the Kyushu and Okinawa regions. Blood samples were collected from 400 cows from 80 different farms in eight prefectures (five samples per farm and 10 farms per prefecture). Mycoplasma wenyonii (Mw), “Candidatus Mycoplasma haemobos” (CMh), and T. orientalis were examined by polymerase chain reaction (PCR) assay using whole blood samples. PCR results showed that 91.5% (366/400) of cows were positive for bovine hemoplasma: 40.3% were infected with Mw only, 9.5% with CMh only, and 41.8% with both species. T. orientalis was detected in 36% (144/400) of cows. The infection rate of T. orientalis was higher in the grazing group (P<0.001) than in the housed group, while the rate of CMh infection was higher (P<0.05) in the housed group than in the grazing group, suggesting that not only the tick but also other arthropod vectors may contribute to hemoplasma transmission. Although the cows with hemoplasma dual infection showed higher (P<0.05) white blood cell counts compared with hemoplasma-negative cows, there was no difference in hematologic parameters related to the anemia between the hemoplasma-positive and -negative animals. This may indicate that Japanese Black cattle could have resistance to the anemia caused by infection with hemoplasma.

Investigation of bovine haemoplasmas and their association with anaemia in New Zealand cattle

CASE HISTORY AND CLINICAL FINDINGS

A dairy cow, from a herd in the Waikato region of New Zealand, was reported with regenerative anaemia on 12 September 2014. Testing of blood from the animal using PCR assays for Theileria orientalis produced a negative result for both Chitose and Ikeda types.

LABORATORY FINDINGS

Using PCR and DNA sequencing, blood from the cow was positive for Candidatus Mycoplasma haemobos. Further testing of another 12 animals from the case herd, 27 days after the affected cow was first reported, showed 11 animals were positive for Candidatus M. haemobos or Mycoplasma wenyonii in the PCR. None of these cattle were clinically anaemic or positive for T. orientalis Ikeda type using PCR. A convenience sample of 47 blood samples from cattle throughout New Zealand, submitted to the Investigation and Diagnostic Centre (Ministry for Primary Industries) for surveillance testing for T. orientalis Ikeda, was selected for further testing for bovine haemoplasmas. Of these samples, 6/47 (13%) and 13/47(28%) were positive for M. wenyonii and Candidatus M. haemobos, respectively. There was no difference in the proportion of samples positive for the bovine haemaplasmas between cattle with anaemia that were negative for T. orientalis (6/20, 33%), or without anaemia or T. orientalis (10/18, 56%), or from cattle herds experiencing anaemia and infection with T. orientalis Ikeda type (3/9, 33%).

DIAGNOSIS

Bovine haemoplasmosis.

CLINICAL RELEVANCE

The presence of bovine haemoplasmas in blood does not establish causality for anaemia in cattle. Diagnosis of anaemia associated with haemoplasmosis would require exclusion of other causes of regenerative anaemia and an association of the agent with anaemia in affected cattle herds. The data collected in this study did not provide evidence that bovine haemoplasmas were associated with a large number of outbreaks of anaemia in cattle in New Zealand.