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Mycoplasma spp





  • Phylum: Firmicutes.
  • Class: Mollicutes.
  • Order: Mycoplasmatales.
  • Family: Mycoplasmataceae.
  • Genus: Mycoplasma.

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Clinical Effects



  • Most Mycoplasmas tend to be host-specific, although there is some evidence that interspecies transmission can occur and may be significant in immunosuppressed hosts.
  • Many mycoplasma species have been isolated from birds and animals without any clear indication of their pathological significance.

Pathological effects

  • Most Mycoplasma that cause pathological conditions have the ability to adhere firmly to mucus membranes of the host.
  • Some species have shown that they can affix to cells by specific attachment structures, including surface proteins (variable surface proteins - VSPs). VSPs may help the organism to evade the host's humoral immune response and, in the longer term, contribute to the persistence of the organism in the host due to failure of antigen determination.
  • Occasionally specific toxins are produced in human species, but they have not been detected in animal species. It is thought that the toxic effect on the hose cells results from the action of toxic metabolic products (hydrogen peroxide Hydrogen peroxide and other reactive oxygen species) which diffuse into tissues of the host following adherence of the organism. Proteases and hemolysins may also be involved.
  • M. equigenitalium has been isolated from the cervical mucus of mares, the semen of stallions (both fertile and infertile), and an aborted fetus:
    • The organism has been detected in Canada, Germany and the Balkans. In Ontario in Canada, isolation of M. equigenitalium and M. subdolum was made from the clitoral fossa of mares and the urethra of a stallion on 6 stud farms.
    • Clinically healthy stallions may act as a reservoir of infection for mares via venereal transmission. The organism was found to be able to attach to the equine uterine tube and oviduct ciliated cells and cause cytopathology and decreased ciliary movement.
    • Its precise role in uterine infections in mares is at present unclear, although it has been stated by some workers that it can cause endometritis Uterus: endometritis - bacterial, vulvitis, abortion Abortion: overview and infertility in mares, and possibly balanoposthitis Penis: balanoposthitis and decreased fertility in stallions.
  • Mycoplasma spp have been isolated at post mortem from horses with rhinitis:
    • M. felis and M. equirhinum have been associated with outbreaks of respiratory disease in Thoroughbred racehorses, and there are occasional reports that it may be a cause of poor performance in athletic horses Poor performance: overview mainly due to mild to moderate equine asthma (MMEA) Lung: mild to moderate equine asthma (MMEA).
    • M. equirhinum has also been isolated from the pharynx, tonsils and upper respiratory tract in normal horses and the significance of this organism is not always clear.
    • For pathological changes to occur, the organism must adhere to the horse's respiratory epithelium, followed by the production of a variety of substances that induce local damage and stimulate the host's inflammatory mediators.
    • The severity of the disease is related to the degree of the host's immune response but these factors are not clearly indentified at present.
    • It can spread between experimental ponies and has caused seroconversion.
  • M. felis has also been reported in a case of pericarditis Heart: pericarditis and pleuritis Lung: pleuropneumonia - bacterial (pleuritis). Serological tests Serology have detected evidence of Mycoplasma spp in cases of endocarditis Heart: endocarditis, although the significance of this has not been confirmed.
  • Mycoplasma spp have been suggested as a cause of primary conjunctivitis Conjunctivitis: overview.
  • Hemotrophic mycoplasmas (HM) are parasites on the surface of red blood cells and known to infect a wide range of animals. In 2010 HM were detected for the first time in the blood of two horses suffering from poor performance, apathy, weight loss and anemia. Using an HM specific PCR assay and subsequent sequencing, the infective agents isolated from the blood of said horses were confirmed as 'closely related to the HM species M. haemofelis and Candidatus Mycoplasma haemobos'.


Control via chemotherapies

  • Culture and sensitivity testing should be consulted, but initial treatment with broad spectrum antibacterials Therapeutics: antimicrobials should be initiated: oxytetracycline Oxytetracycline would be a good first choice.


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Further Reading


Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Dieckmann S M et al (2010) Haemotrophic Mycoplasma infection in horses. Vet Microbiol 145 (3-4), 351-353 PubMed.
  • Wood J L et al (2005) Association between respiratory disease and bacterial and viral infections in British Racehorses. J Clin Microbiol 43 (1), 120-126 PubMed.
  • Newton J R et al  (2003) A case control study of factors and infections associated with clinically apparent respiratory disease in UK Thoroughbred racehorses. Prev Vet Med 60 (1), 107-132 PubMed.
  • Morley P S et al (1996) Pericarditis and pleuritis caused by Mycoplasma spp and their relationship to reproductive performance in selected equine herds in southern Ontario. J Reprod Fertil Suppl 35, 671-673.

Other sources of information

  • Markey B et al (2013) Eds. Clinical Veterinary Microbiology. Elsevier Health Sciences.

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