Pneumonia in mice and rats

Pneumonia is defined as an ‘infection and inflammatory process of the bronchioles, alveolar spaces and interstitial tissue of the lung parenchyma.’ In severe cases of pneumonia, the lungs will fill with fluid and pus. Additionally, pneumonia can be one sided and only affect one lung (unilateral), or it can affect both lungs (bilateral).

The major problem with pneumonia patients is that once your mouse’s or rat’s lungs are filled with infection, their ability to exchange oxygen becomes severely reduced which leads to breathing difficulty.

There can be multiple causes of pneumonia in mice and rats and it is commonly referred to as a ‘multifactorial disease,’ meaning that it involves a number of factors. Pneumonia is a result of primary of secondary infection by organisms such as viruses and bacteria, or (more rarely) parasites or fungi. Infectious causes are the most common on the differentials list and this is why outbreaks of respiratory diseases in rodents (particularly in large colonies) can be extremely difficult to control.

The following points will discuss some potential causes (this list is not exhaustive)

Rats

Respiratory disease and pneumonia is often caused by either one or a mixture of the following: Mycoplasma pulmonis, streptococcus pneumoniae, bacillus or sendai virus.

Mice

Respiratory diseases and pneumonia causes are very similar to rats, they are often more affected by mycoplasma or sendai virus. When mice contract the sendai virus, they often develop serious acute respiratory disease and this has a high mortality rate in neonates.

Respiratory disease and pneumonia is sadly one of the most common diseases of mice and rats. Individuals that live in smaller groups are at much lower risk of contracting pneumonia, compared to rodents that live in large colonies e.g. in pet shops. This is often the case with most infectious diseases, if you have a larger susceptible population of individuals they are all more likely to be infected and spread the disease.

Typical signs of pneumonia in rats and mice include difficulty breathing, termed ‘dyspnoea,’ fast or rapid breathing rates, sneezing, nasal and/or ocular discharge and you may be able to hear ‘rattling’ breathing noises. In more chronic pneumonia cases, they may be also experiencing weight loss, reduced appetite and poorer body condition, loss or reduction in appetite and tiredness.

If you see your rat or mouse open-mouth breathing/panting, this is very concerning as it suggests severe respiratory difficulty.

In very unwell patients, often a diagnosis is quickly made based on the clinical history and physical examination without the aid of diagnostic tools, as you do not want to delay treatment. Sometimes x-rays are performed to investigate further to assess their lungs in more detail.

It can sometimes be difficult to generalise a treatment plan in pneumonia cases as the management will understandably vary between individuals. Given that, in most pneumonia cases initial treatment involves an antibiotic course, anti-inflammatories and supportive therapy. In severe cases, supportive therapy may include oxygen delivery, nutritional feeding support and fluid therapy. Often these medications are delivered orally because surprisingly, rodents often tolerate oral medications really well.

Antibiotics do not target viruses and are used solely to treat bacterial infections. The antibiotic choice will be selected carefully by your Vet. Bronchodilators and mucolytics are also frequently prescribed to try to open up their airways to help them to breathe easier and break down the mucus.

Depending on the severity of the pneumonia the prognosis may be varied. A complete cure, although desirable, is not always achieved but it is important to start treatment as early as possible.

Prevention is always better than cure! As a major cause of pneumonia in rats and mice is infectious diseases, it is extremely important to ensure a strict isolation period is carried out for new pets before allowing an individual to mix amongst a larger group. As some rats and mice can be affected by the respiratory disease lifelong, long-term management strategies can help to optimise their health. Environmental control is essential and it is recommended to ensure that their environment is regularly cleaned, well ventilated and that substrate e.g. bedding is frequently replaced to reduce the ammonia build up, which can exaggerate respiratory conditions in rodents.