Pneumonia caused by pathogens or cecal impaction
Esther van Praag, Ph.D.
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Rabbits are sensitive to respiratory diseases. The most common have a bacterial or fungal origin, but they may also be secondary to viral diseases such as myxomatosis or rabbit. They can affect the upper respiratory tract (nasal cavity), or the lower respiratory tract (bronchia, lungs).
Numerous pathogens can invade the lungs of rabbits and cause pneumonia:
Bacteria: Pasteurella multocida,
Francisella tularensis (tularemia)
Pseudotuberculosis Yersinia pseudotuberculosis,
The diversity of pathogens is great. The frequently used term of �pasteurellosis� is limited to the Pasteurella bacterium. This term is outdated and not reflecting the current knowledge.
Pneumonia is difficult to diagnose in rabbits. Clinical signs are often absent or limited to sneezing or a deep coughing that sounds similar to the barking of a dog. Some rabbits present a light white nasal discharge, a lack of energy (lethargy) and a decreased appetite. The get easily tired and are out of breath after exercise.
At an advanced stage, a rabbit can start to suffer from respiratory distress, with mouth breathing and fever.�
Bacteria infecting the respiratory tract of the rabbit can spread to other parts of the body or organ and cause conjunctivitis, middle ear infection with torticollis, pleuritis (inflammation of the tissues surrounding the lungs), pericarditis (inflammation of the tissues surrounding the heart), pyometra, or testicular abscess.
If the infectious bacteria infiltrate the bloodstream, septicemia develops, which is usually fatal in the rabbit, even with an aggressive antibiotics treatment.
The autopsy of a rabbit deceased by pneumonia shows a reddish or grayish cranio-ventral congestion of the tissue of the lungs, which is typical of pneumonia in rabbits as well as the presence or absence of emphysema.
The following points should be checked when a respiratory infection is suspected:
1. Complete examination of the rabbit. Control of respiratory rhythm (30 to 60/min). A higher rhythm is normal, a lower rhythm is abnormal. Signs of respiratory distress, or mouth breathing should be observed�
2. Careful examination for the presence of mucus in or around the nostrils. This is not always easy, as rabbits groom themselves meticulously. Sometimes the presence of wet and tangled fur is present on one or both front limbs, a possible sign of the presence of nasal mucus discharge.
3. Complete blood examination (CBC) to discover hematological changes, such as increased neutrophil count (neutrophilia) or decreased white blood cell count (leukopenia). This examination allows also to check the function of the vital organs.
4. Chest X-ray, which detects the presence of bacterial infection (increased opacity), bronchitis, mass (abscess or neoplasia) or edema (abnormal accumulation of fluids around the lungs and of the heart).
5. Examination of the head and facial bones to note irregularities such as the presence of a swelling, abscess as well as the eyes for the presence of conjunctivitis or dacryocystitis (lacrimal gland infections) in the eyes.
6. If necessary, a nasal and / or tracheal sample is taken for a bacterial culture. Ideally a sample is taken in each nostril, as the infection may be unilateral. Nasal sampling is done by means of a swap with a calcium alginate tip mounted on a flexible wire, embedded at a depth of 1 and 4 cm into the nostrils or the nasopharyngeal region. An alternative method is a nasal aspiration.
7. Examination of the ears for possible infections. X-rays of the head may reveal an increased opacity of the middle and inner ear. Ear infections often accompany respiratory infections, as bacteria can migrate to the inner ear through the Eustachian tube.
Differentiating bacterial pneumonia from pneumonia caused by cecal impaction
Pneumonia caused by pathogens should be differentiated from the complex cecal impaction/mucoid enteropathy. Indeed, up to 60% of rabbits, cecal impaction/mucoid enteropathy is accompanied by inflammation of the lungs. Bacteria re absent and there is no pus formation. Inflammation is limited to the blunt superior end of the lung (apex). At the end stage, before death, fluid flows out of the mouth and nose. The cause is unknown.
Upon autopsy, the apex appears red and is sharply delineated by healthy tissue. The trachea is filled with spumous fluids. Elongated cells have been observed in the trachea, bronchia and lungs. Since they may have a plant origin, this is why this condition is sometimes referred to as foreign body pneumonia.
Treatment of pneumonia is difficult. It must be long (at least 4 to 12 weeks) and aggressive and essentially aims to increase the quality of life of the rabbit. If pneumonia is mild, oral administration of enrofloxacin or ciprofloxacin, accompanied by nasal drops of gentamicin, may help in the recovery of the rabbit.
Trimethoprim sulfadiazine is a bactericidal antibiotic often used in the treatment of disorders of the gastrointestinal and urinary system. It is effective against many bacterial infections that affect rabbits, such as Pasteurella sp., Clostridia sp., Staphylococcus sp., Bordetella sp., etc. It can be used for a long period of time, at reduced doses. This antibiotic does, however, have poor result in rabbits and often the disease relapses in an aggravated form after discontinuation of the treatment. This may be due to the fact that the half-life of trimethoprim in rabbits is only 40 minutes.
Azithromycin, a modified erythromycin which does not cause side effects in rabbits, is very effective in the treatment of Bordetella sp. (as well as enrofloxacin). The dosage of azithromycin used in rabbits (50mg/kg PO QD (SID)) is much higher than that used in other small animals, such as dogs or cats (5-8 mg/kg). The treatment usually lasts between 7 and 10 days, after which an evaluation is made and a possible prolongation of the treatment is envisaged.
Cephalosporins are broad-spectrum antibiotics used to treat bone, genitourinary, soft tissue and respiratory tract infections (associated with Pasteurella sp.). There are several generations of cephalosporins, and each is targeted against specific groups of bacteria. Although these antibiotics are mostly safe for the rabbit (injected only), they are potentially nephrotoxic.
Treatment against Pseudomonas sp., one of the most difficult bacterial infections to treat, must be aggressive. A sensitivity test must be performed as this bacterium is resistant to many antibiotics. Treatments include a combination of antibiotics, such as:
- Enrofloxacine + gentamycine nasal drops,
- Enrofloxacin + nebulization with amikacin (if located in the upper respiratory airways enrofloxacine + doxycycline),
- Cephalosporin/tobramycin (both injected only).
Azithromycin does not help in case of a Pseudomonas sp. infection.
Further antibiotics, safe for use in rabbits that have shown good results in the treatment of respiratory tract disease, include:
- Amikacin, injected subcutaneously or nebulization, is used to treat Gram-negative bacteria,
- Enrofloxacin (if injected, it can lead to the development of sterile abscesses. This can be avoided by diluting the solution with a sterile saline solution, 50:50),
- Chloramphenicol (exceptionally leads to a decreased appetite),
- Gentamycin, injected, drops, or nebulization, used to treat Gram-negative bacteria.
For more information, see: Antibiotics *safe* for use in rabbits
Aside a longer systemic antibiotic therapy, additional therapy comprises:
- Nasolacrimal flushes;
- Nebulization with a saline solution, mucolytics and antibiotics help bring the medication deep in the bronchia and lungs in cases of rhinitis, sinusitis or pneumonia;
- Fluid therapy and assisted force-feeding, when the rabbit refuses to drink and eat.
If the respiratory disease is accompanied by conjunctivitis or dacryocystitis, local antibiotic therapy (e.g., enrofloxacin, gentamycin) must accompany the treatment protocol.
A. van Praag
Flora held above a bowl of hot water to allow her to breath humid air.
Videos about nebulization
(A big thank you to Debbie Hanson. Without her help, time and expertise, the making of the nebulizer video would not have been possible. Thanks also very much to Rachel Ihlenfeldt and her rabbit Bunbun for the demonstrations)
Using a nebulizer in a rabbit affected by upper respiratory infection (URI).
Nebulizing "chamber", when the rabbit does not like to have a mask, is panicking or aggressive.
Un grand merci au Dr. Estella B�hmer (Chirurgische u. Gyn�kologische Kleintierklinik, Ludwig-Maximilians-Universit�t M�nchen, Germany), � Michel Gruaz (Suisse), � Kim Chilson (USA) et � Tal Saarony (USA) pour la permission d�utiliser leurs photos. Un grand merci � Debbie Hanson. Sans son aide, temps et expertise, ces vid�os au sujet de la n�bulisation d�un lapin n�auraient pas pu �tre r�alis�es. Un grand merci aussi � Rachel Ihlenfeldt et son lapin Bunbun pour la d�monstration des diff�rentes techniques.
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Bourne D. Bacterial Pneumonia in Rabbits and Ferrets. http://wildpro.twycrosszoo.org/S/00dis/Bacterial/PneumoniaRabbits.htm
Ladefoged O. The absorption half-life, volume of distribution and elimination half-life of trimethoprim after peroral administration to febrile rabbits. Zentralbl Veterinarmed A. 1979; 26(7):580-6.
Ladefoged O. Pharmacokinetics of trimethoprim (TMP) in normal and febrile rabbits. Acta Pharmacol Toxicol (Copenh). 1977; 41(5):507-14.