bacterial disease Fancy rat

Rat Pneumonia

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Definition Signs Causes Diagnosis Treatment Prevention Complications When to see a vet Prognosis FAQ Sources Affected species

What is it?

Rat pneumonia is a lung infection very common in domestic rats. It mainly affects the lower respiratory tract and can develop slowly over several months or, sometimes, worsen suddenly. It is one of the leading causes of illness in pet rats, particularly in older animals. It is often linked to a bacterium called Mycoplasma pulmonis, which is widespread in this species, but other microbes can also be involved.

Key point

Rat pneumonia is a common and potentially serious disease, particularly in older or immunocompromised animals; careful monitoring of breathing is recommended for any pet rat.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Related signs — each one links to its page:

Cough Sneezing Runny nose Difficulty breathing Noisy breathing or snoring Rapid breathing Loss of appetite Weight loss Reduction Fatigue Fever

The most common signs are repeated sneezing, noisy or wheezy breathing, and sometimes coughing. The rat may breathe faster or with difficulty, especially after exercise. Discharge may appear around the nose or eyes; in rats, it is often reddish because it contains a natural pigment called porphyrin, which can look like blood. The animal gradually becomes less active, eats less, and loses weight. In advanced cases, the rat may crouch, have a dull coat, and show real respiratory distress.

When to consult without delay

This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.

Causes and risk factors

The most common cause is a bacterium called Mycoplasma pulmonis, present in the vast majority of domestic rats, often without causing symptoms as long as the animal remains healthy. Other opportunistic bacteria, such as certain species of Streptococcus, Pasteurella, or Bordetella, can also be involved and worsen the infection. Respiratory viruses can also play a triggering role by weakening the respiratory tract before bacteria take hold.

Stress, poor cage ventilation, air high in ammonia (dirty bedding), overcrowding, sudden temperature changes, and a weakened immune system promote the onset or worsening of the disease. Older rats and those living in groups are particularly at risk, because latent infection with Mycoplasma pulmonis can reactivate at any time.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

The veterinarian examines the animal's breathing, listens to the lungs with a stethoscope, and assesses its overall condition. Additional tests such as chest X-rays or respiratory tract samples may be recommended to confirm lung involvement and identify the causative organisms.

Treatment

Treatment usually involves antibiotics suited to the rat's respiratory bacteria, sometimes combined with anti-inflammatory medications to relieve discomfort. General supportive care (diet, hydration, calm environment) often accompanies treatment. Management is decided and adjusted only by the veterinarian.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

Good cage hygiene, regular bedding changes, proper ventilation of the living space, and avoiding drafts or sudden temperature fluctuations reduce the risk. Limiting stress, avoiding overcrowding, and isolating any new rat before introducing it to an existing group are also helpful measures. There is no vaccine available for this disease in rats.

Possible complications

Without treatment, the infection can spread and become chronic, leading to irreversible lung damage. Episodes of acute respiratory distress may occur, putting the animal's life at risk. Complications such as lung abscesses or systemic infection are possible in severe cases.

When to see a veterinarian

Wheezing, rapid, or labored breathing

Frequent sneezing or persistent nasal discharge

Decreased activity, dull coat, or loss of appetite

Unexplained weight loss

Any sign of sudden respiratory distress (emergency)

Prognosis

The outcome depends on how quickly treatment is started. Caught early, the disease can be stabilized long-term, though complete recovery is not always possible because the organism often remains present in a dormant state. Left untreated, the disease may progress severely, particularly in elderly or debilitated rats.

Frequently asked questions

Is rat pneumonia contagious between rats?

Yes, the causative pathogen, namely Mycoplasma pulmonis, spreads easily between rats living together, especially through the respiratory route.

My rat has a red discharge around its nose, is this serious?

This reddish liquid is often a natural pigment called porphyrin, secreted in response to stress or illness, and not necessarily blood. However, you should still consult a veterinarian to determine the cause.

Can my rat be completely cured?

A clear improvement is often possible, but the causative microorganism frequently remains present silently, with a risk of relapse in cases of stress or immune decline.

Can the disease be transmitted to humans?

No, this disease is specific to rodents and is not considered transmissible to humans.

References

Cornell Feline Health Center

Content reviewed by the TunisieVet editorial team · Updated 27 August 2026

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AT A GLANCE

AgentBacterium

SpeciesFancy rat

VaccineNo

Transmissible to humansNo

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