Medical Corner - SDA Virus - Sialodacryoadentitis Virus in Pet Rats

Mary Ann Isaksen
From the January/February 1998 Rat & Mouse Gazette

Sialodacryoadenitis, pronounced si-al-o-dac-re-o-ad-e-ni-tis, (SDA Virus) is a naturally occurring pathogen in rats. It is a coronavirus antigenically related to the mouse hepatitis virus (MHV), rat coronavirus (RCV), and the human coronavirus OC38.

Clinical disease caused by this agent alone is self-limiting and is highly infectious, causing most or all of the colony to show signs of disease with very few deaths resulting. But, if it is exacerbated by any other virus or bacterial infection, which, unfortunately in our pet population, most often is, the mortality rate changes significantly. Although most veterinary books say it is primarily seen in young rats, older rats, with or without previous mycoplasmal infections, seem to be the hardest hit and can die within a very short period of time. You cannot treat for this disease, but immediate treatment for any secondary bacterial infection is the only hope for some affected animals.


SDA is passed very quickly through the air, or by direct contact, when one rat comes in contact with anotherís respiratory secretions. It can also be passed via fomites, meaning that you can handle an infected animal and then handle another, thereby passing it to the uninfected rat. These animals may not always be showing symptoms of SDA while able to transmit the disease, so it is very important that you do not handle rats in pet shops, at friendsí houses, or at shows without washing your hands with a disinfectant, and even changing your clothes before handling your own rats again.

It is always recommended to quarantine any new rats, or rats you have taken to a show for at least two weeks prior to introducing them back into your colony. Although this may be successful, it is still possible for your quarantined colony to be infected unless you can quarantine the new animals in another building. Rooms sharing the same air in the house are not adequate for quarantining when disease is spread through the air.

Infected animals carry and secrete the virus for about a week. The disease can occur frequently in a particular population, but the organism does not exist in a latent, carrier state.


I have purposely called this section "Possible Symptoms" because many people think they couldnít possibly have had SDA run through their rats because they didnít see all the so-called ďsignsĒ of SDA. I strongly recommend that, no matter what virus or bacterial infection you have run through your colony, you make it a point NOT to breed for a specified period of time and NOT to bring in any new blood. Unless you can afford to have your animals tested and know exactly what has infected them, donít take any chances. Make sure you protect your rats and those of friends and aquaintances around you. Donít sell any of your rats until all symptoms are gone and be sure to let the buyer know that you have just had an illness run though your colony. Be honest and up front about everything. Be responsible. Remember, lives of innocent animals are at stake and only you can prevent the spread of disease from your rattery.

Having said all of that, the following are symptoms that are possible signs of SDA. All symptoms need not be present for SDA to be the cause of illness in your rattery. Remember, the clinical signs (symptoms) vary widely in severity from colony to colony, and from one infection to another at different times.

  • Sneezing.
  • Porphyrin-pigmented nasal and ocular (eye) discharge.
  • Swelling under the neck (caused by cervical edema, enlarged cervical lymph nodes, and necrotic inflamed salivary glands).
  • Squinting, blinking, and eye rubbing.
  • Swelling or infection of the eyes or surrounding eye tissues.
  • Ulcers of the cornea.
  • Bleeding into the chamber of the eye that lies in front of the lens.

These are symptoms of SDA and may be seen for several weeks in your colony, but each individual rat will only show them for a week. (You are likely to see many other symptoms during an outbreak which are caused by secondary infection.) Self-mutilation may occur as a result of scratching affected eyes, and damage can be permanent. Some young rats may even remove the eyeball altogether. Most other eye lesions usually resolve, but occasionally may progress to chronic inflammation of the cornea, and abnormal enlargement of the eyeball itself.

During the infection rats usually remain active and eating, although acutely infected rats will lose their appetite and some females may not go into season. During the pneumonic phase of the disease, rats may be at a much higher risk of dying while under general anesthesia.


Because SDA weakens the ratís immune system, secondary infections can get a strong hold extremely fast, so it is very important to treat your entire colony at the first sign of infection. Pregnant and nursing females, for the most part, seem to be relatively unaffected by SDA and should not be treated as antibiotics could cause problems with the babies. However, in rare cases, where a pregnant or nursing female is affected and pneumonia follows, treatment will likely be necessary to save her life. In any event, it is recommended that a maternity/pediatrics area be set up away from the rest of your colony. It is also imperative that you stop breeding for at least two months from the birthdate of your last litter, or from the end of all symptoms, whichever is longer. It is also crucial that you do not bring any new rats into your colony, or even your home during this period. Any new blood will just keep it going.

Mycoplasma pulmonis, being the most common pathogen to cause respiratory disease in pet rats, is also the most common secondary infection to accompany SDA, but CAR bacillus (cilia associated respiratory bacillus) is also common. Other pathogens can also accompany SDA, but unless youíre able to have your rats tested, you wonít know which pathogens are present, and even if you do test, you need to start treatment immediately, so treat as if you are treating mycoplasma related pneumonia. Refer to the following articles for information regarding specific treatment of respiratory disease and critical/intensive care procedures for pet rats. 1) Nursing Care (May/June 1996 Gazette, Volume 2 Issue 3, pages 6 through 8), 2) Mycoplasmosis In The Pet Rat (September/October 1997 Gazette, Volume 3 Issue 5, page 8), and 3) Respiratory Infections In Pet Rats (November/December 1997 Gazette, Volume 3 Issue 6, pages 8 and 9). These articles are available on the RMCA web page in the contents section of the Gazette.


Diagnosis of SDA is based on clinical signs, histologic lesions (testing tissue samples), and the detection of serum antibodies to the virus. The latter can be accomplished by sending a blood sample to a pathology lab to be tested, but obtaining a sample large enough is sometimes difficult. The procedures used to draw blood from a live rat should not be done without general anesthesia. If your vet is very good, he/she may be able to obtain a blood sample large enough via the tail vein. If not, the blood must be extracted from behind the eyeball or directly from the heart.

Unless you are in a laboratory situation, I donít consider this is to be necessary. Since we are dealing with pet rats, I believe diagnosing on the basis of symptoms should be good enough and wonít involve painful procedures for your pet, who has already gone through enough with the virus, and wonít hurt your wallet, either. The bottom line is to be responsible and not let any rats in or out of your rattery before you are sure everything is fine.


The only way to ensure that your rats do not become infected with SDA is to keep them isolated from all other rats. Any newly acquired rat must be considered suspect until it has gone through the quarantine period without incident. Simply going to a show where there is an infected rat can start an epidemic and has done so in recent years too many times.

As much as we would like to think that everyone has high moral standards and would not risk our pets, it is simply not true. People have knowingly taken infected rats to shows, to other ratteries to be bred, and sold or given them to friends and customers. Of course, there are also cases where people unknowingly pass it around, so itís best just to keep your rats as isolated from other rats as possible. Iíve learned this the hard way. In two outbreaks in my rattery within the same year, 19 of my beloved pets were lost. I donít necessarily want to make you all paranoid, but maybe being paranoid is better for our precious pets, who count on us to keep them healthy.