Health Guide: Pneumonia

Pneumonia

Definition

An infection and inflammatory process of the bronchioles, alveolor spaces, and interstitial tissue of the lung parenchyma.

Clinical Signs

May see any of the following signs:

Porphyrin (rust colored) stains about nose and/or eyes.

Wheezing, small coughs, congestion, sneezing, increase in rapid breathing, labored breathing, use of abdominal muscles to breathe, and gasping.

Hunched posturing with rough coat

Lethargy

Poor or loss of apetite.

May hear Rales (crackling, often sounds like rice krispies in milk) when listening to chest with stethoscope.

May hear Rhonchi (rumbling indicating presence of thick fluid) when listening to chest with stethoscope.

If significant consolidation present in lungs breath sounds may be diminished even when listening with a stethoscope.

Presence of head tilt if otitis media/interna (ear infection) is present.

Presence of secondary illness, eg: tumors.

Panic type movement related to inability to get enough oxygen into lungs.

Changes in behavior due to illness (e.g. nipping, biting, avoidance)

Feet and tail tip cyanosis (as oxygen in blood decreases) may be a late sign.

Etiology

Pneumonia is the result of primary or secondary infections by organisms such as bacteria, viruses, or fungal and parasitic infections. These organisms may reach the lungs through droplet (aerosolization), contact, or hematogenous (in the blood) spread. Pneumonia can also result through the inhalation of chemical irritants, or due to the aspiration of food or of drugs being administered.

The inflammation, swelling, congestion or consolidation of the airways and lungs contributed to by these organisms and irritants decreases the ability to breathe effectively.

There are several classifications or types of pneumonia, such as focal, lobar, or Bronchopneumonia. Determination of the type is based on the area and pattern of distribution found in the lobes of the lungs or bronchi. It can be further described based on the pathophysiology of the various organisms that cause infection and or inflammation.

In bacterial infections, pneumonia is believed to be initiated when there is a change, alteration, or increase in the number of organisms normally residing in the nasopharynx that results in the overwhelming of the host’s immune system, or where normal defenses fail to protect the respiratory tree from filtering the organisms from the lungs.

In rats, where severe respiratory disease or pneumonia is present, more than one organism or infection is involved. The most prevalent and naturally occuring organism in the rat that contributes to the development of pneumonia is the bacterium, Mycoplasma pulmonis.

Other bacteria that contribute to the development of pneumonia in association with Mycoplasma pulmonis are Ciliated-Associated Respiratory (CAR) Bacillus, Corynebacterium kutscheri, Streptococcus pneumoniae, Pasturella pneumotropica, Bordetella bronchiseptica, and Klebsiella (klebsiella is a part of normal gut flora that under certain conditions result in an opportunistic infection) pnuemoniae.

Viruses such as SDA (sialodacryadenitis) and Sendai can also act in conjunction with Mycoplasma overwhelming the immune system and leading to the developement of pneumonia.

In rats that are severely immunosuppressed, pnuemonia may be further complicated by the presence of a fungal or protozoan organism such as Pneumocystis carinii, an opportunistic species specific organism.

In aspiration pneumonia where food or liquids have entered the lungs, atelectasis (an airless lung) or pulmonary edema and hemorrhage can occur, especially if the substance aspirated is very acidic.

Lastly, some of the complications occuring in severe cases of pneumonia can be:

Abscesses and empyema (pus filled fluid), or pus filled lumina in pneumonias with mixed organisms such as Klebsiella, CAR bacillus, and Mycoplasma. Empyema in Pneumocystis carinii.

Bacteremia, where the infection has spread via blood, particularly in those pneumonias caused by gram negative organisms.

Pleural effusion, when the small amount of fluid normally present that lubricates the pleural membranes starts to build up.

Photos showing lung tissue of rat in the following figure. Please note, photos are graphic.

Fig. 1: Photos of fibrotic, abscessed lungs taken on necrospsy from a rat with pneumonia due to Mycoplasmosis.

Diagnostics

Radiography exam of lungs may show the following:
Mycoplasma: films in early stage may appear clear. Later may become patchy in lower lobes and show infiltrates in alveolar walls.

In viral pneumonias: films may show infiltrates in the bronchi leading to consolidation.

In Pneumocystis carinii : diffuse, bilateral interstial pnuemonia.
Fungal pneumonias : consolidation, cavitation, and empyema.

ELISA test. *Note: Bacterial cultures may result in false negative for mycoplasma.*

Complete blood count with low WBC may indicate mycoplasma or viral illness.

Gram stain.

Blood cultures to rule out bacteremia.

Treatment

See the Rat Medication Guide for a listing of the following drugs, dosages, and use.

Giving Antimicrobials

Give broad spectrum antibiotics, or if culture and sensitivity results are known, give specific antibiotic.

Preferred and alternate antimicrobrial therapy in humans as recommended by CURRENT Medical Diagnosis & Treatment 2002, 41st Edition, Edited by: Lawrence M. Tierney,Jr.,MD ; Stephen J. McPhee,MD. ; Maxine A. Papadakis,MD. , for the following listed identified organisms. These antimicrobials are also helpful in rats:

Streptococcus pneumoniae
- Preferred: Amoxicillin
- Alternatives: Macrolides, cephalosporins, doxycycline, fluoroquinolones, or clindamycin.
Klebsiella
- Preferred:Third-generation cephalosporin. For severe infections add aminoglycoside.
- Alternatives: Beta-lactam/beta-lactamase inhibitor, or a fluoroquinolone
Mycoplasma
- Preferred: Doxycycline or erythromycin
- Alternative:Clarithromycin; azithromycin, or a fluoroquinolone.

The choice of treatment in Pneumocystis carinii pneumonia is TMP/SMX (trimethoprim/sulfamethoxazole), along with a corticosteroid such as prednisone.

A treatment regimen for serious and advanced respiratory illness

The following treatment regimen for use in rats with advanced lung infection or more serious respiratory illness with Mycoplasma as the suspected agent , is recommended by Dr. Michael Hutchinson, DVM; Animal General, Cranberry Township, PA., and is based on his experience treating rats and current literature:

dexamethasone 1 mg/lb BID, then weaned down as follows:
1 mg/lb BID injectable or PO (oral) for 3 days
1 mg/lb SID for 3 days
0.5 mg/lb SID for 3 days
0.5 mg/lb orally every other day, three doses

Other veterinary recommended reduction schedules for dexamethasone may also be used.

Additional antimicrobial choices

Besides the above recommended antimicrobial choices, and treatment regimens for pneumonia, the following drug choices may also be used.

Tetracycline

Cefadroxil (for secondary infections - best used in combination with Gentocin)

Chloramphenicol

Enrofloxacin (Baytril) and Doxycycline simultaneously.

An aminoglycoside: (such as amikacin or gentamicin) in combination with Cefadroxil.

*Note: Combination of drugs given simultaneously like enrofloxacin (Baytril) + doxycycline, azithromycin + doxycycline, clarithromycin + doxycycline, have been found to be very effective in rats.

The choice of an antibiotic/antimicrobial or combination can be more effective when selected based on culture and sensitivity of organism.

Bronchodilators and Corticosteroids In Therapy

The use of bronchodilators given orally, such as Aminophylline/Theophylline, or Albuterol, may be added to help relax the smooth muscle and dilate the bronchi in the lungs to aid breathing.
Nebulized treatments with these medications as well as certain antibiotics (e.g., fluoroquinolones: enrofloxacin (Baytril), aminoglycosides: amikacin or gentamicin (gentocin), or a macrolide: tylosin, may be prescribed for rats that have difficulty taking the medications orally. Medications for nebulization need to be diluted in normal saline.
Ratio for dilution of medication per normal saline recommended as follows:
Enrofloxacin(Baytril) 10mg to 1 mL normal saline. ³
Gentamicin 5mg to 1 mL normal saline. ³
All others a 1 to 10 solution. ³

For the nebulization formula using gentocin and Albuterol in a treatment regimen, recommended by Dr. Michael Hutchinson, see above in the section: treatment regimen for serious and advanced respiratory illness. See Nursing Care below for more information on nebulizers.

In addition, a corticosteroid such as prednisone or dexamethasone may be added to the treatment regimen to help reduce inflammation of the bronchi and bronchioles in order to help the rat breath easier.

For dexamethasone therapy , in a treatment regimen, for serious and advanced respiratory illness, see doses suggested above by Dr. Michael Hutchinson, listed under: treatment regimen for serious and advanced respiratory illness.

*Note*
Dexamethasone has been shown, in the controlled studies cited below, to reduce plasma leakage, resolve Mycoplasma induced inflammation, and also reduce the number of Mycoplasma organisms even when used as the only therapy.

Length of Treatment and Maintenance

The prognosis for rats with pneumonia is very grave, and will require long term antibiotic therapy.
Due to the belief that Mycoplasma is probably never eliminated entirely from the airways in rats, and because it is a contributor to the development of pneumonia, it often becomes necessary to use a daily antibiotic maintenance schedule for rats with chronic Mycoplasmosis. Dr. Hutchinson has had some success with the long term maintenance dose of enrofloxacin 4.4 mg/kg daily PO (oral), and based on his experience, no discernable side effects have been noted.

Remember, it is important to give all doses of a prescribed medication even if clinical signs seem to lessen or disappear. If clinical signs seem to worsen or no improvement is seen, do not stop medication. Contact the veterinarian to discuss changes in medication.

Treatment in Pregnant and nursing does, and rats under 4 months:

Recommended antimicrobials are azithromycin (zithromax) or tylosin (tylan).
*Note: The use of enrofloxacin (Baytril) and doxycycline is not recommended for initial treatment in pregnant and nursing does, or rats under 4 months.
However, where symptoms are progressing, these stronger antimicrobials may be necessary. The benefits of using a fluoroquinolone (such as enrofloxacin), doxycycline, or a combination of drugs, may outweigh the risks. Discuss with a veterinarian.

Additional Therapy

Providing adequate hydration will help to liquefy and loosen secretions.

If respiratory distress is present (gasping, or laboring to breathe), and/or gums, ears, feet, or tail appear to be cyanotic (blue-tinge) or are very pale, Oxygen therapy should be initiated.

Nursing Care

Use recommended nebulizers with a particle size of 0.5-5 micrometer when nebulizing medication in rats. Nebulizers with a larger particle size that are used for humans or small animals will not be as effective in delivering the medication to the rat.

Nebulized treatment may take from 10 to 30 minutes depending on the volume to be given, and how well the rat tolerates the treatment. Observe for any signs of increased agitation or intolerance. If noted stop treatment and contact vet.

Sites for purchasing nebulizers:

http://www.petiatric.com/Medicalnebulizer.htm

http://lambriarvet.com/catalog/Medical-Supplies.htm

Examples of nebulizer set up:

http://www.rmca.org/Articles/albuterol.htm

Fig. 3

Provide humidification with a humidifier, or stay with rat in a closed steamed bathroom at 10 to 15 minute intervals, to loosen secretions.
*Note: cool mist humidifiers or vaporizers may be helpful where steam has not benefited. It is important to remember to clean humidifiers or vaporizers following each use to prevent growth of organisms from standing water.

When antibiotics are given remember to include Benebac or yogurt with live active cultures, to prevent normal gut flora from being destroyed by the antibiotics.

Provide additional warmth using a hot water bottle or heating pad on low under one side of cage (ensure rat does not overheat and become dehydrated).

Provide additional nutritional supplement , such as Soy baby formula, Ensure, Boost, NutriCal paste (for dogs and cats found in pet store), mashed avocado, and baby foods. If the rat is not willing to eat on its own, provide feeding in an oral syringe every 2 hours being careful to prevent aspiration. Providing small amounts of food in this fashion will help to promote intestinal motility during illness. Also because so much energy is being expended to breathe in pneumonia, the added dietary supplements will keep up the rat’s strength.
It is also helpful to include an additional multi-vitamin supplement (can be found in pet store) if food intake is poor.

Place food and water close and on same level with the rat to prevent from exerting itself. Over exertion in a rat who already has difficulty breathing will prevent the rat from wanting to eat.

Provide fluids to prevent dehydration. If the rat is willing to drink on its own or by syringe (using needless syringe), the following are suggested: fresh water, or a glucose mixture of 3 teaspoons of honey in 1 pint of warm water (be sure water is warm enough to dissolve honey and then cooled just enough so as not to burn rat’s mouth), or Jello water , or electrolyte replacement drinks such as Pedialyte or Gatorade which can be found in local grocery stores. Please note that Pedialyte is only good refrigerated for 24 hours after opened, but can be frozen as ice cubes and kept longer, and then thawed when needed. Care should be taken to prevent aspiration when giving fluids with an oral syringe. If the rat is not drinking discuss providing warmed SQ fluids with your vet.

If possible let rat remain with cage/litter mate for additonal comfort, unless there is competition for food or undue stress.

Contact vet to discuss changes in treatment options if condition does not seem to be improving. If condition continues to deteriorate and precludes further comfort or quality, discuss euthanasia with veterinarian.

Outcomes

Airway remains clear.

Nutrition level adequate

Comfort and quality of life maintained.

Emotional support for those having to consider euthanasia for their rat.

Prevention

Early treatment of upper respiratory symptoms as appropriate.

Prevent ammonia build up by maintaining clean cage enviroment.

Use dust free litter. Do not use pine or cedar due to phenols present in shavings.

Locate cage or housing in draft free area.

Quarantine all new rats for a minimum of two weeks prior to introducing into existing colony.

Breeders should establish a system to record and track diagnosis and treatment in their lines.

Do not smoke around your rats!

Posted on June 25, 2003, 12:19, Last updated on May 5, 2008, 15:20 | Lower Respiratory