Mycoplasma Infections in Small Mammals

Pathogen	Disease	Species
Mycoplasma pulmonis	murine respiratory mycoplasmosis (MRM), genital tract infections, arthritis	Mouse, Rat, Rabbit (Guinea Pig, Syrian Hamster, Human)
Mycoplasma arthritidis	mostly subclinical, rarely arthritis	Mouse, Rat
Mycoplasma neurolyticum	“rolling mouse syndrome,” only experimental, no known natural infections	Mouse, Rat
Mycoplasma collis	conjunctivitis (one report from 1980)	Mouse, Rat
Mycoplasma muris	none known	Mouse
Mycoplasma coccoides	mostly subclinical, rarely hemolytic anemia	Mouse
Candidatus Mycoplasma haemomurismusculi	mostly subclinical, rarely hemolytic anemia	Mouse (Wild rodents)
Candidatus Mycoplasma haemomuris ssp. ratti	mostly subclinical, rarely hemolytic anemia	Rat (Wild rodents)
Candidatus Mycoplasma ravipulmonis	grey lung disease	Laboratory Mice
Mycoplasma caviae	respiratory diseases	Guinea Pig
Mycoplasma cavipharyngis	none known	Guinea Pig
Mycoplasma cricetulli	none known	Chinese Hamster
Mycoplasma oxeniensis	none known	Chinese Hamster

Table 1: Classified Mycoplasma species in small mammals – M. pulmonis and M. cavie are of particular clinical relevance; (Image source: Klas, E-M., Liebscher)

Mycoplasma pulmonis

Mycoplasma (M.) pulmonis is the causative agent of murine respiratory mycoplasmosis and is considered the most important pathogen in respiratory diseases of rats and mice. The signs of disease range from non-specific symptoms, such as reduced general well-being and weight loss, to rhinitis, otitis, dyspnoea, and severe pneumonia. In addition, arthritis and fertility disorders such as endometritis and salpingitis occur in connection with M. pulmonis infections (especially in rats).

M. pulmonis has also been detected in guinea pigs, rabbits, and hamsters. However, a connection with respiratory symptoms has only been established in rabbits; so far, this has been more common in food-supplying animals than in pets. At the moment, it is assumed that M. pulmonis does not cause disease in humans, although it has been detected (serologically and directly by PCR) in humans.
In the differential diagnosis of disease in rats, Streptococcus pneumoniae, Corynebacterium kutscheri, and Filobacterium rodentium (CAR bacillus) are of particular importance.

 

Important: All illnesses caused by mycoplasmas are factor illnesses. Stress, vitamin deficiency, poor husbandry conditions, or other infections favour an illness and worsen the clinical course.

 

We evaluated 496 M. pulmonis PCR tests from submissions between 2021 and 2023. Of these 496 tests, 221 were positive, which corresponds to 44.6%. Looking at the individual years, 43.4% (85/196) were positive in 2021, while M. pulmonis was detected in 48.2% (94/195) in 2022 and 40% (42/105) in 2023 (Fig. 1). PCR tests were carried out on many different small mammals, including rats, mice, guinea pigs, rabbits, gerbils, hamsters, and other species. Since the pathogen mainly plays a role in mice and rats, we looked at these species separately (Fig. 2). Here, a total of 77.6% (218/281) of the submissions were positive. This is consistent with the literature, which reports a prevalence of 70% in pet rats (PCR detection). M. pulmonis should always be considered in the differential diagnosis of rats and mice with respiratory symptoms.

Mycoplasma caviae

This pathogen has only recently been the subject of increased attention, although it was first described in the 1900s. M. caviae is responsible for symptoms in guinea pigs that are similar to those of M. pulmonis in mice and rats: anorexia, lethargy, rhinitis, dyspnoea, and severe interstitial pneumonia. Here, too, arthritis and fertility disorders (metritis) are possible. In addition, conjunctivitis and lymphadenitis have been described. Differential diagnoses are mainly infections with Streptococcus pneumoniae and Bordetella bronchiseptica.

We retrospectively examined a total of 171 samples (nasal and/or throat swabs, rinses) from guinea pigs from 2021 to 2023. M. caviae was detected in 9.3% (5/54) of the samples in 2021, in 6.8% (3/44) in 2022, and in 5.5% (4/73) of the samples in 2023 (Fig. 3). Overall, 7% (12/171) of the guinea pigs examined were M. caviae positive. Since these investigations were carried out without any specific mandate and without any prior knowledge of the respective guinea pigs, the actual prevalence is presumably higher. The only data available from the literature dates from 1971, when the prevalence was 10%.

 

Note: It has only recently become possible to detect Mycoplasma caviae using PCR.

 

Mycoplasma spp.

To date, no mycoplasma species has been described in rabbits, but Mycoplasma spp. have been detected in rabbits with respiratory symptoms. They may be involved in the so-called “rabbit rhinitis complex.” Here, too, the symptoms range from weight loss, apathy, nasal discharge, and dyspnoea to pneumonia. Furthermore, mycoplasmas have been detected in conjunction with conjunctivitis, so the detection of Mycoplasma spp. is particularly useful in rabbits with respiratory or eye problems. Differential diagnoses would include, in particular, pathogens from the Pasteurellaceae or Enterobacteriaceae family and Pseudomonas spp..

 

Tip: The main differential diagnoses for mycoplasma are other bacteria. In addition to the specific mycoplasma PCR, a culture examination is particularly useful in animals with respiratory symptoms. For this, an additional swab with transport medium is needed.

 

Conclusion:

In particular, in small mammals with respiratory symptoms, a mycoplasma infection is a possible differential diagnosis; this applies especially to rats and mice. Mycoplasma infections are factor diseases, and mycoplasma detection is only necessary in conjunction with clinical symptoms. PCR is the detection method of choice (from smears without transport medium or rinsing samples).

Dr Eva-Maria Klas

 

Range of services:

8189 Mycoplasma pulmonis PCR
8885 Mycoplasma caviae PCR
NEW!! 8897 Mycoplasma spp. PCR (rabbit)
8801 Respiratory tract profile, rat/mouse (M. pulmonis, Bordetella bronchseptica)
8278 Respiratory tract profile
(Bacteriology + PCR: Bordetella bronchiseptica, Pasteurella multocida Toxinbildner, Mycoplasma spp).