Mycoplasma infections in horses: a fresh look using modern methods may reveal an elusive ‘virus’.

This research article examines Mycoplasma infections in horses, detailing a specific case of pericarditis and pleuritis associated with M. felis infection in a horse, and discussing the role of Mycoplasma infections in respiratory diseases in various species. It calls for further investigation into the relationship between Mycoplasma spp. and equine respiratory diseases, suggesting that these infections might be underdiagnosed due to difficulties in culturing.

Mycoplasma and its Characteristics

• Mycoplasma is a type of bacteria that lacks a cell wall and requires cholesterol for growth. Unlike other bacteria, mycoplasmas are exceptionally small, allowing them to pass through filters that typically retain bacteria. They are found in most animals and plants.
• While these bacteria grow slowly and require inhibition of growth with specific antisera for definitive identification, Mycoplasma infections can cause respiratory diseases in various species such as humans, cattle, and pigs. Their role in equine diseases, however, is less clear.

Investigations into Mycoplasma infections in Horses

• Several different Mycoplasma species have been found in horses, such as M.felis, and M. equirhinis, amongst others. However, these have not been definitively linked to equine respiratory disease as yet, though investigations were conducted into this in the UK around 20 years ago.
• Infections produced by M. felis have been associated with pleuritis in horses, and a disease caused by the same was successfully reproduced experimentally.
• The study suggests that Mycoplasma infections, including those caused by M. felis, may be underdiagnosed due to the relative difficulty of culturing them compared to conventional bacteria.

M. felis Infection and Septic Aetiology

• The research paper also discusses a particular case where the horse showed signs of pericarditis caused by an underlying M. felis infection.
• In this instance, lower than usual glucose levels in the horse’s pleural and pericardial effusions indicated a suspected septic origin, though conventional bacterial investigations initially did not reveal the cause.
• The study proposes that more thorough investigations using glucose measurement within pericardial effusions, followed by Mycoplasma culture, could potentially aid in identifying such infections more accurately. This would result in more focused treatments, thereby improving prognosis.

The Need for Further Investigations

• More recent field studies revealing an association between respiratory disease in foals and the presence of Mycoplasma spp. in the nasopharynx highlights a need for further investigation into these infections.
• Though the role of Mycoplasma infections in causing respiratory diseases in foals is still contested, recent observations of an outbreak of respiratory disease in racehorses associated with M. felis infection strengthens the call for further studies.