Rat Respiratory Disease
When I examine a rat for Mycoplasma disease, I begin by looking in its nasal cavity and the "cleft" in its palate (the naso-palatine ducts). I look for snotty material, mucous, and little ulcers or red dots- all signs of inflammation. Then I look in the rat's sinuses for the same sort of problems. In older rats I look for mineralization of the trachea (wind pipe) - although this is common in all old rats. Normal lungs are a uniform light rosy pink color and float high in water. Rats with advanced mycoplasmosis have grayer, heavier, wetter lungs.
Husbandry Delaying the Onset of Mycoplasmal Pneumonia in Your Rat
If your rat came from a source like a pet store, you can safely assume it came with some Mycoplasma. How this will affect the life of your ratty depends on some things that you can control and some things that you can't.
First, the Things you Can't Change
1) Some strains of Mycoplasma are stronger (more virulent) than others - you don't know which strain(s) are present.
2) Some strains of rats are genetically hardier than others. Fisher 344 strain seems the most resistant to Mycoplasma disease while Lewis rats seem the most susceptible.
3) The Mycoplasma probably didn't come alone. Other freeloaders came with it: most likely bacteria, and virus - maybe parasites as well.
4) It had a rough life in the pet store and where ever it was bred. The momma rat was probably worn out from producing litter after litter and may not have passed much immunity on to the ratling.
5) A rat-year is about equal to 25 human years, so each rat month equals about 2 of our years. So the older the rat is when you get it, the more advanced the disease is likely to be.
Now the Good News!
1) Early in the ratling's life, it should be checked for intestinal and superficial parasites that can be eliminated. This will improve its general health and immune system.
2) You need to put the rat on the highest-quality low calorie, low protein diet you can find. One that meets or exceed the nutritional requirements of rats as determined by the U.S. National Research Council (N.R.C.). Some good ones are Mazuri 5663 or ZuPreem Rodent Maintenance diet. Most quality brands meet N.R.C. guidelines on rat nutrition. However, their protein content, 23.5%, and caloric content is a bit too high for maximum longevity and their fiber content (3.8%) is too low. You can get around this by mixing it 50-50 with an equine range pellet, like Mazuri 5661 with 13% protein and 2.9% fat and 13.2% fiber. This will give you an 18% protein diet. With this mixture, the rats will attain their top body weight later in life, become reproductively active later in life, and, on the whole, live longer lives.* They are also less likely to suffer from kidney disease later in life. To this diet, I would add an additional 10 to 12 units (iu) of vitamin E as well as a portion of the contents of a mixed anti-oxidant, anti-aging microcapsule, such as those produced by Landco Corp and omega 3 and 6 fatty acids, which stimulate the immune system that Mycoplasma suppresses. Vitamin A deficiencies are known to speed the progress of mycoplasmosis in rats. However, too much vitamin A is also toxic and the diet I suggested has plenty of vitamin A.
3) The temperatures of your rat's home should be kept between 65°F and 80°F. Temperatures should be kept as constant as possible - rats don't do well when their temperature varies up and down a lot. Humidity should be between 30% to 70%. Twelve hours of light and 12 of darkness is a good ratio but some rats breed better with 14 hours of light and 10 of darkness.
4) Good air quality is the most important thing you can provide for your rat to minimize the lung damage Mycoplasma
5) Frequent cleaning of the rat's cage and as much space per individual rat as possible is also very important. Rat urine breaks down into ammonia. Over time, this causes lung damage. Aromatic (pungent) cleaning compounds such as strong bleach, Pine Sol, and perfumed products are also a bad idea. Bleach is an excellent cleaning product - but it should be diluted to 1 part standard bleach in 20 parts water. The cages and utensils must be pre-cleaned in soapy water before being soaked in this mixture. Cage construction is very important. Cages should be made of durable smooth, non-porous and easily cleaned materials such as plastic or non-toxic metals.
6) Mycoplasma are more complex than virus. They never cause sudden (acute) disease. Because they utilize primarily RNA instead of DNA to reproduce, they are only killed by the protein-synthesis inhibiting, nucleophilic, antibiotics -the macrolides. These include DIRITHROMYCIN (Dynabac®), BIAXIN: Clarithromycin (kla-RITH-roe-mye-sin) and Azithromycin (Zithromax).
Biaxin can be given to rats at 3.5 mg/kg three times a day for 20 days in combination with ranitidine and corticosteroids. Zithromax can be given at 3.5mg/kg three times a day for 20 days. Dynabac can be given at 2.5mg/kg three times a day for a 20 to 30 day period. After 30 days, the daily total dose must be lowered. All can cause loose stools and other digestive problems in rodents and must be given, supplemented with a good horse and ruminant bacterial jelly and brewer's yeast. They are all best when given four times a day after food is consumed. They should be used at the lowest possible dose since double the pediatric dose can cause liver and kidney problems in rats. Most indigestion remedies interfere with macrolide absorption. I compound most in berry syrups, which must be shaken and kept refrigerated.
**Older remedies relied on destroying the freeloading bacteria that accompany the Mycoplasma, such as Streptococci, Pasteurella, Klebsiella, and Pseudomonas bacteria. We have nothing that will affect Sendai virus, another freeloader. Traditionally, chlortetracycline was given in the rat's drinking water at 0.25mg/ml for 14 to 20 days or tetracycline, mixed fresh daily, in the drinking water at 2 to 5mg/ml and sweetened with Karo syrup. Some used Tylosin (a sulfa) at 25mg/378 ml of water.
Obtaining Mycoplasmal-free Rats
University origin rats are not necessarily clean. Rats from the conventional colonies at Emory University, have enzootic Rat Parvovirus (RPV), Kilham's Rat Virus (KRV, RV) and Toolan's H-1 and have cultured positive for Helicobacter spp, Pasteurella pneumotropica, Proteus spp, staphylococci, fecal coliforms and enterococci. I can arrange to have your rat's serum or pooled colony rat serum tested for antibody to: Mycoplasma Pulmonis, Pneumonia virus of mice (PVM); Kilhams rat virus (KRV); Toolans H-1 virus; Rat coronavirus (RCV); Sendai virus; CAR bacillus; Reovirus (Reo); Lymphocytic choriomeningitis virus (LCM); Mouse Adenovirus (Ms.Ad.); Tracheal cultures can be examined by any competent local lab for Pasteurella, Bordetella, Corynebacterium, Salmonella, and pathogenic streptococci. Sophisticated labs can culture for Mycoplasma pulmonis.
New Research Discoveries That May Soon Help Us
Currently, work is going on in Europe and the United States to decode the approximate 677 proteins that make up rat Mycoplasma. The hope is that soon a vaccine will be developed against the disease. The reason this work is going on is that if a vaccine could be produced against rat respiratory Mycoplasma, it could probably also be produced against the serious Mycoplasma diseases of people. It is the surface proteins that most intrigue researchers. These are the ones that give the Mycoplasma stealth, suppress the rat's immune system and prevent it from killing the bug. They also produce oxidative stress through the production of superoxide radicals, which is why antioxidants are so important to give your rats.
Sources of Mycoplasma-Free Rats
The three largest commercial vendors of Mycoplasma-free rats in the United States presently are:
Charles Rivers Laboratories
Harlan Sprague Dawley Inc.
Taconic Farms
Some strains may be available from the Roscoe B. Jackson Laboratories. These institutions accept orders only from universities and research establishments throughout the world. I could attempt to make contact with these breeders if enough rat enthusiasts were willing to pool their resources.
* In 1935,Clyde McCay published a groundbreaking paper that showed that rats on calorically restricted (CR), nutritionally sound diets lived longer than rats that were allowed to eat as much as they wanted. Animals fed about 30 percent less than controls allowed to eat as much as they want, achieved an increase of about 40 percent in maximum life span. It has also been shown that CR retards or eliminates various chronic disorders, such as cancer, diabetes, and renal disease, and improves immune system function in lab animals (E. Masaro, American Journal of Clinical Nutrition, 55:1250S-52S, 1992).
**Newer drugs are never approved for use in pocket pets. But in 1988, Drs. Sedgwick and Pokras published a method of determining theoretical drug dosages for all warm-blooded animals using a process they called "Allometric scaling". I have mislaid my copy of this article, but essentially it relies on the body weight of the animal and its core body temperature - both of which are easy to determine. Dr. Pokras can be reached at [email protected]. I used this and FDA studies of the drugs in rats to determine the dosages.
causes. It is this lung damage that ultimately causes the rat's decline. First, they need to be kept in a dust and mold-free room, preferably with central heat and air-conditioning and at least four air changes an hour. We used 14 air changes per hour at N.I.H. The bedding material you use is extremely important. I like hard wood chips. The worst are pine, corncobs, cedar shavings and bentonite clays (cat litter products). Shredded ordinary newspaper with black soya ink is probably also OK - I have never used it. What you want to avoid is dust, mold, bacterial spores, airborne mineral products and atmospheric pollutants. These are all known to produce lung lesions in all animals. Of course, no wild rodents should have access to your rat's room, food or utensils.
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