Mycoplasma Pneumonia in Guinea Pigs

Report from a day in the lab

Dr. Birgit Blazey, Veterinary Specialist in Pathology


An unexpectedly high number of four guinea pigs were brought to us in 2015 and 2016 for autopsies. They had the typical pathomorphological and histological lung lesions associated with mycoplasma-caused pneumonia. The diagnosis for all four cases was confirmed by electron microscopy; for some, however, the mycoplasma-caused pneumonia was the secondary finding. No such cases have been brought to us in previous years, and the digital and print media have generally reported very little on this condition.


Photo of a Guinea Pig.


Preliminary report

All four guinea pigs were reported to have respiratory symptoms, such as sniffles, sneezing, nasal discharge and/or dyspnea (difficulty breathing). Most of the animals had already had the symptoms for several days or weeks. In all of the presented cases, multiple animals in the herds had been ill, and individual animals had died. There were occasional reports of a new animal having been acquired prior to the outbreak of the illness. One of the guinea pigs also had stomach pain, and another only anorexia (lack of appetite). A typical age for the development of the disease could not be confirmed. The ages ranged from seven weeks to four years.


Pathomorphological findings of the lungs

The lungs of the four guinea pigs had completely collapsed, and were mostly the color of antique rose. In addition, one of the lungs was interspersed with dark red, well-defined, hard foci. In one animal the lobes at the apex of the lung were unilaterally compressed with flesh-colored, small lesions, with barrette-shaped adhesions between the apex and diaphragmatic lobes, as well as the pleura and diaphragm. Tissue samples taken from the firmly compressed areas of the lungs sank in fluid, indicating a reduced amount of air. The animal with the chronic lung and pleural lesions also had dull, shaggy fur and was malnourished.


Illustration 2: Lobe apex pneumonia, unretracted lungs, focal tissue compression (arrow).

Illustration 2: Lobe apex pneumonia, unretracted lungs, focal tissue compression (arrow)


Illustration 3: Barrette-shaped adhesions between the apex and diaphragmatic lobes .

Illustration 3: Barrette-shaped adhesions between the apex and diaphragmatic lobes


Pathohistological findings of the lungs

In general, the histological picture of the lungs was characterized by mid to high grade, generalized interstitial pneumonia in combination with a proliferation of lymph follicles. In detail, the proliferated lymph follicles were found especially in the areas around the edges and under the surface of the lungs (sub-pleural). In addition, high grade hyperplasia of the bronchial epithelium in the compressed areas, with neutrophilic granulocytes in the alveoli (purulent pneumonia as a secondary finding), were observed. Lymphocytic perivascular inflammatory infiltration was also detectable in two cases. The findings of chronic fibroblastic pleura described above were also reflected histologically. There was one case each of hemorrhage in the parenchyma, as well as individual syncytial cells and few eosinophilic granulocytes.


Illustration 4: Lung with lymph proliferation, H&E, magnification x 200.

Illustration 4: Lung with lymph proliferation, H&E, magnification x 200


Illustration 5: Lymph follicle proliferation with constriction of the bronchiole lumens (arrow), lung, H&E, magnification x 200.

Illustration 5: Lymph follicle proliferation with constriction of the bronchiole lumens (arrow), lung, H&E, magnification x 200


Illustration 6: Interstitial pneumonia, lung, H&E, magnification x 200.

Illustration 6: Interstitial pneumonia, lung, H&E, magnification x 200


Pleurisy (arrow), interstitial pneumonia, lung, H&E, magnification x 400.

Illustration 7: Pleurisy (arrow), interstitial pneumonia, lung, H&E, magnification x 400


Diagnostic procedure

The suspected diagnosis of "mycoplasma-caused interstitial pneumonia“ for the four guinea pigs was made based on pathological-morphological and histological examinations. This was confirmed by the presence of mycoplasma-suspicious particles seen under the electron microscope in our laboratory.


Illustration 8: "Mycoplasma-suspicious particles", TEM, 100,000 x magnification.

Illustration 8: "Mycoplasma-suspicious particles", TEM, 100,000 x magnification


The detection of species-specific mycoplasma-DNA by means of PCR taken from organ or swab samples (e.g. nasopharynx, vagina) is currently not possible in our lab. However, a general mycoplasma ssp.-PCR can be performed.


General information

Respiratory disorders are relatively common among guinea pigs, and are among the most frequent causes of death. In most cases, the respiratory diseases are related to poor husbandry. In addition to drafts, sudden temperature changes, moisture of the bedding, overheating from dry air caused by heaters, and hypovitaminosis, other primary diseases and stress situations also play a role. Moreover, a particular anatomical characteristic seems to foster respiratory illnesses in guinea pigs. Contraction of the well-developed musculature in the bronchia and lung arteries leads to reduced blood circulation and restricted ventilation of the lungs, thus making guinea pigs more susceptible. The list of possible infectious agents is long. In addition to viral and bacterial pathogens (LCMV, herpesvirus, adenovirus, streptococci, staphylococci, diplococci, klebsiella, bordetella, pasteurella, pseudomonaden and chlamydia), mycoplasma are also very often detected. Sometimes pseudotuberculosis (for rodents) is diagnosed . The emergence of a pathogen in the herd comes seldom from humans, but more often from the addition of animals to the herd. Exposure to an infected wild rodent or contaminated feed also plays a role sometimes. In contrast to outwardly visible signs of illness such as scabs or secretions from the nose with rhinitis (infection of the nose) and around the eyes with conjunctivitis (inflammation of the eye), isolated, non-exudative bronchitis is clinically inconspicuous. The disease mycoplasma usually occurs gradually; in chronic cases it is only after several months that there is a significant worsening of the animal’s general condition. The experienced veterinarian can initiate a treatment that the owner must then conscientiously carry forth.


Info Box


Mycoplasmas are the smallest bacteria from the class of Mollicutes capable of independent, self-reproduction. Due to the absence of a cell wall, they can be round or pear-shaped, but they can also form branched or helical filaments. Because of their small size and pleomorphism (multiple shapes), they are able to pass through bacteria-proof filters. In addition, they can’t be cultivated on normal culture media, which is why they were initially included in the group of viruses.

In veterinary medicine mycoplasmas can also be relevant for farm animals. In addition to notifiable epizootic diseases such as contagious bovine pleuropneumonia (Mycoplasma mycoides spp. mycoides SC (small colony type)), other significant mycoplasma infections also occur in livestock. These include enzootic pneumonia (Mycoplasma hyopneumoniae) as well as mycoplasmaarthritis and -polyserositis among swine (Mycoplasma hyorhinis and Mycoplasma hyosynoviae).

Moreover, Mycoplasma bovis has been identified as a cause for udder infections leading to a reduction in milk production in dairy cattle, as well as lung infections and severe joint inflammation in calves. Mycoplasma gallisepticum causes respiratory diseases in fowl, e.g. chronic respiratory disease (CRD) in hens and infectious sinusitis in turkeys.

There is also a group of so-called haematotrophic (blood-loving) mycoplasma, which were earlier included in the Rickettsia group. They are known to infect many vertebrate species, and cause mainly anemia. In swine mainly the Mycoplasma suis (formerly called Eperythrozoonosis) play a role. But also pets can become infected with haematotrophic Mycoplasma. Cats can get infected with Mycoplasma haemofelis, Mycoplasma haemominutum and Mycoplasma turicensis. These cause the so-called feline infectious anemia (synonym Haemobartonellosis of the cat). Mycoplasma haemocanis is known to affect dogs.

In human medicine, in addition to Neisseria gonorrhoeae (so-called gonococci), the primary infectious causes of human urethritis (inflammation of the urethra) are Mycoplasma pneumoniae (atypical pneumonia) and Mycoplasma genitalium. The most recent studies on Mycoplasma pulmonis indicate a zoonotic potential.


In studies of guinea pigs various mycoplasma species were isolated, including, among others, the M. caviae and M. pulmonis; the M. caviae has adapted to the guinea pigs, however, and is therefore not considered a zoonotic agent. In addition to staphylococci and streptococci, Mycoplasma caviae is among the most common causes of acute arthritis (joint inflammation) in guinea pigs. Furthermore, lymphadenitis (lymph node inflammation) and metritis (inflammation of the uterus) occur in connection with infections from M. caviae. The animals can also be infected without any symptoms.

On the other hand, the natural hosts of Mycoplasma pulmonis (potential zoonotic agent) are primarily mice and rats. M. pulmonis settles onto the surface of the mucous membranes of the genitalia and respiratory tract. Guinea pigs are often carriers, but don’t usually become ill. Mycoplasma can cause symptoms of respiratory disease as well as acute and chronic conjunctivitis (inflammation of the eyelid), either in conjunction with viral and bacterial pathogens, or alone.



Illness caused by mycoplasma seems to be widespread among guinea pigs, mainly in connection with pneumonia, as seen in our autopsies. Unsuitable living conditions as well as contact with newly acquired animals and stress can all lead to the emergence of this illness.


Photo Credits

Guinea Pig , Sandra Wiedmann, CVUA Stuttgart

Lung Macroscopy, Pneumonia with Barrette-shaped Pleura, Denise Martin, CVUA Stuttgart

Lung Histology , Blazey, CVUA Stuttgart

TEM, Mycoplasma, Dr. Valerij Akimkin, Dr. Marc Hoferer CVUA Stuttgart



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Catherine Leiblein


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Report published on 02.11.2017 08:28:14