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More On Myco
8 years ago
More on Myco, Part 1November 06, 2005 6:17 PM
I found this on the Yahoo group Rat Cites and Sites:

An overview of the disease, Mycoplasmosis in rats.
-Mycoplasma is an unusual class of bacteria, lacking a true cell wall. It is pretty species specific, with M.pulmonis affecting rodents. Humans have their own, Mycoplasma pneumoniae.
-All wild, pet and show rats carry Mycoplasma, and are infected at birth by their mothers, passed on in the saliva and nasal secretions. Very rarely it is transmitted vertically ( transplacentally).
-Lab raised rats are free of it. Their ancestral genetic stock were derived via whole uterus C-section with the uterus passed through a disinfectant bath into the "clean" side of a barrier facility, and hand raised. More recently, the lines can be kept clean via rederivation using transplanted fertilized ovum removed from one strain and implanted into surrogate mothers who are known to be clean.
-Genetics in the pet rat play a part in this. Rats with the genetic heritage to be resistant to the organism carry it, suppressed, for most or all of their lives, until they die from other causes. Rats who are genetically susceptable to Myco will start showing clinical signs earlier on, sometimes even as youngsters. Their immune systems are not strong enough to keep it suppressed. Most pet store rats are culls from breeder stock that have proven to be more susceptable.
-That being said, there is no reason that a rat that is showing clinical signs of upper respiratory infection should go untreated. Myco can be suppressed but not eliminated by the proper antibiotics and other drugs. Sooner or later, however, the rat will succomb to the disease. The hope is that you can battle it while keeping the rat comfortable and healthy, for a normal life span, or as long as possible.
-Wild rats of course are more resistant, even though they carry it, because of natural selection...the susceptable ones die off sooner and produce less offspring...etc...
-The organism resides in the nasal passages. When it starts to multiply and cause disease, it can ( and most often does) spread to the lower respiratory tract causing pneumonia. It can also cause middle ear infections and head tilts...and spread to the reproductive organs, most commonly the uterus in females.
-One by product of Mycoplasma metabolic process is, amazingly enough, hydrogen peroxide, that causes terrific inflammation of the tissues, plasma leakage and deposition of lymphoid tissue in the affected areas. The tissue deposition is not reversible. This is why so many rats, left untreated too long, develop nasal squeaks and rattles, due to actual obstruction of the airways. Lymphoid deposition and also scar tissue in the lungs from untreated Mycoplasmosis causes irreversible lung damage, leaving the rat with less lung capacity and increased, labored respiration.
-Yes, you can test for M. pulmonis with Elisa and other test methods, but it is not really worth the expense or the stress to the rat to obtain a blood sample. Almost without exception, you will get positive test results. To differentiate between Myco and the viral pathogens seen in rats like Sendai or SDA you should use history of the onset, age and breeding status, physical exam and knowledge of the viruses and their disease patterns including incubation time. In any case, if the rat is given appropriate antibiotic therapy to suppress secondary infection by opportunistic bacteria and help keep the Myco under control, fluid therapy and good nursing care, it will likely survive the virus and become immune to it.
-If you manage Mycoplasmosis with periodic antibiotic and anti-inflammatory meds, your rat can live a full life span.
-Myco is transmitted mostly by direct contact with other rats. The bacteria does not live long outside of the animal, due to lack of a proper cell wall. Occasionally it can be spread via sneezed out droplets, over a short distance. It is not transmitted via fomites. It will not last long on hands or clothing.
-Other respiratory bacteria can complicate matters, like CARbacillus ( which a big percentage of pet rats are carrying sub-clinically as well) and others.
- In general, the young rats ( under 4 months) with respiratory signs should be treated with Amoxicillin or a similar antibiotic that is appropriate for less serious, non-Myco related disease, since it is unlikely ( but not impossible) that the cause is Myco at that age. Immune systems generally keep it suppressed. Older rats can and should be treated more agressively, and the sooner you treat, the better.
-The most successful therapy, used by experienced exotics vets, is outlined below, and is posted on the Rat Guide:
Part 2
8 years ago
More on Myco, Part 2 November 06, 2005 6:21 PM

Early or mild illness
The following medications for use in rats with mild respiratory infection suspected to have Mycoplasma as the pathogen, are recommended by Dr. Michael Hutchinson, DVM; Animal General, Cranberry Township, PA., and are based on his experience treating rats and current literature:

enrofloxacin (Baytril) 15 mg/kg BID PO (oral) for 10 to 30 days
or
doxycycline 5 mg/kg BID PO (oral) for 10 to 30

If not responding within a reasonable time frame:
give both enrofloxacin and doxycycline at the above doses for 10 to 30 days

If still not responding within a reasonable time frame, continue the meds as described and add nebulization with the following mixture:

Nebulize 15 minutes, 2 to 3 times a day, for 14 days
8 ml sterile saline
0.5 ml gentocin injectable 100 mg/ml
0.5 ml Albuterol 0.083% Inhalation
*Note: excess mixture for nebulization can be refrigerated for up to 3 days.

Dexamethasone at 0.5 mg/lb can be added to the treatment regimen, weaning down as follows:
0.5 mg/lb BID injectable or PO (oral) for 3 days
0.5 mg/lb SID for 3 days
0.25 mg/lb SID for 3 days
0.25 mg/lb orally every other day, three doses

Advanced or more difficult to treat illness

If no response or poor response to one of the above medications, or if illness or symptoms advance to include middle to inner ear infection, or lower respiratory infections, medications such as azithromycin (zithromax), chloramphenicol, or combination therapy such as enrofloxacin (Baytril) and doxycycline, azithromycin (zithromax) and doxycycline, or the addition of an aminoglycoside (like gentamicin), can be instituted. You will note that enrofloxacin and doxycycline (a bactericidal and a bacteriostatic drug) are listed as one of the combinations to be used simultaneously in mycoplasmosis infection. It is normally not a recommendation to use these drugs together, however, it is important to remember that with Murine Mycoplasmosis one is often treating for the presence of more than one organism. Although the use of these two drugs together in rats is empiric, they seem to be very effective at times in controlling clinical signs of illness.

The following treatment regimen for advanced or more seriousrespiratory illness with Mycoplasma as the suspected agent has been used with great success by Dr. Michael Hutchinson:

enrofloxacin (Baytril) 15 mg/kg
BID, PO (oral) for 10-30 days
doxycycline 5 mg/kg BID PO (oral) for 10-30 days

nebulization for 15 minutes, 2 to 3 times a day, for 14 days, with the following mixture:

8 ml sterile saline
0.5 ml gentocin injectable 100 mg/ml
0.5 ml Albuterol 0.083% Inhalation
*Note: excess mixture for nebulization can be refrigerated for up to 3 days.

dexamethasone 1 mg/kg 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.


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, or a macrolide: tylosin, may be prescribed for rats that have difficulty taking the medications orally. Medications for nebulization are dosed at oral dosage recommendation, and need to be diluted in normal saline.

The following are recommended ratios for dilution of those medications in normal saline:

Enrofloxacin(Baytril) 10mg to 1ml normal saline. 3
Gentamicin (gentocin) 5mg to 1ml 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 sections:
Part 3
8 years ago
More on Myco, Part 3 November 06, 2005 6:22 PM Early or mild illness or Advanced or more difficult to treat illness. 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 either mild or serious Mycoplasma based respiratory illness, see doses suggested above by Dr. Michael Hutchinson. *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. Am. J. Respir. Crit. Care Med., Vol 150, No. 5, Nov 1994, 1391-1401; Dexamethasone and oxytetracycline reverse the potentiation of neurogenic inflammation in airways of rats with Mycoplasma pulmonis infection; J.J. Bowden, TR Schoeb, J. R. Lindsey and D.M. McDonald; Cardiovascular Research Institute and Department of Anatomy, UCSF. Am. J. Respir. Crit. Care Med., Vol 164, No. 10 Nov 2001, S39-S45; Angiogenesis and Remodeling of Airway Vasculature in Chronic Inflammation; Donald M. McDonald; Cardiovascular Research Institute and Department of Anatomy, UCSF. Length of Treatment and aintenanceBecause Mycoplasma is probably never eliminated entirely from the airways, it often becomes necessary to use a daily maintenance schedule of antibiotics 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. It is important to complete the medication treatment or regimen prescribed. However, if the rat shows no improvement within five days of starting treatment, or should the ratís condition worsen at any point during treatment, see a veterinarian to discuss alternative antimicrobial or appropriate combination drug therapy. *Note: It is also important to give the correct dose of the medication, to not skip doses, and to give for the prescribed length of time in order to prevent resistance. Additional treatments: 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. Provide adequate hydration to help liquefy secretions. Provide supplemental nutritional support. Weight is lost when working hard to breathe. I hope this helps your vet to feel more comfortable with her treatment of rats with upper and lower respiratory disease. Please let me know if I can be of further help. If you need a nebulizer, our club can loan you one. We will ship it Priority Overnight, and you can use it for as long as you need to. Good luck, Lindsay Pulman, LVT, LATg