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Medical Corner:
Sendai Virus: Not Just A Mouse Disease


Jan McArthur, RVT
From the November/December 1999 Rat & Mouse Gazette

The Sendai virus is primarily a disease of young mice; however, it can and does affect several species of small rodents. Mice, rats, hamsters, guinea pigs, and even swine (real pigs) are affected by this devastating disease. Sendai is an RNA paramyxovirus-parainfluenza type 1 virus. To give the reader a familiar idea of what his means, Sendai is very similar to canine parainfluenza virus (CPIV) which is also a paramyxovirus - commonly called distemper.

Because it is a virus, there is no treatment for it. It is highly contagious and presents a high mortality rate for rodents. Supportive care, along with antibiotics for prevention of secondary bacterial infections, is all that can be done for rodents infected with this disease.


OTHER DISEASES DONíT HELP THE SITUATION


In mice, there are only two respiratory diseases recognized as causing serious clinical symptoms. Those are the Sendai virus and Mycoplasma pulmonis, a bacterium. Sendai virus is the most significant disease for mice, causing terrible epidemics with high mortality when in the acute phase.

For rats, there are five respiratory diseases that are considered significant even though there are other respiratory diseases that can affect them. The five are: Mycoplasma pulmonis, Streptococcus pnuemoniae, Corynebacterium kutscheri, cilia-associated respiratory bacillus (CAR), all bacteria. Finally, number five, the Sendai virus. Bacterial diseases are commonly carried subclinically by rats and mice. These bacterial diseases can present a problem by compromising the immune system which, in turn, causes the Sendai virus to be much more severe. Poor environment such as high ammonia levels in an unclean cage combined with poor quality bedding materials can also exacerbate the problems seen with any of these respiratory diseases for both mice and rats.

The rodents not affected by these other bacterial diseases, if you can find any that aren't, stand of better chance of surviving Sendai virus if infected.


HOW DO THEY GET IT?


That is the $64,000 question; the answer is not fully known. It is known that the virus is carried in the respiratory tract. It is thought that passage may be through direct contact with an infected animal, fomites, or by aerosol. The disease is extremely contagious. Recently weaned mice, rats, hamsters, and guinea pigs are the main carriers of this disease. This disease is usually associated only with mice, but that seems to be because it isn't abnormal for mice to carry it with or without symptoms. For the other rodents mentioned, if they are previously not exposed to the disease, then they are at high risk of being infected when exposed to a carrier. Sendai is just as deadly to any of these rodents as it is for mice.


SUBCLINICAL VS ACUTE PHASE


It is common for colonies of mice to carry the disease subclinically. The adults seem to develop an immunity to it; because of that developed immunity, the mother mice passively give that immunity to their offspring through their milk. When the natural immunity from mother is gone for the young mice at four to six weeks of age, the babies will then be infected with the disease and those that do not die will also develop an acquired immunity to it. These surviving mice rarely show any signs of disease.

Previously uninfected, mice or other rodents that are exposed to these subclinical carriers of Sendai virus can be acutely affected. Clinical signs are seen in the acute phase which can be seen within 48 hours after exposure. Those clinical symptoms are: rough hair coat, weight loss, labored breathing, chattering, and a high mortality rate. It can take up to two months for an adult to recover from the symptoms of the disease.

The problem with this Sendai virus for all of these rodents is that, unlike the SDA virus of rats, these infected colonies continue to carry the disease. With SDA, which is a corona virus, rats shed the disease for about seven days and then the disease is gone. Sendai virus doesn't go away, so the carriers are always a danger for the uninfected.


PREVENTION IS THE KEY


Since there is no cure, the only way to fight it is through prevention. All the veterinary textbooks and literature claim that there is a commercially prepared vaccine that should be available to research laboratories. If it does exist, then it should be available to veterinarians, too. As of yet I have been unable to find the manufacturer. Hopefully, your own veterinarian could locate this vaccine.

The only other way to prevent this would be to keep your own rodents isolated from other rodents. Quarantine will help to prevent many diseases, however, there is no guarantee that it will prevent the onset of Sendai virus if a subclinical carrier is exposed to those that are not carriers.

Keeping newly weaned or young animals out of a previously infected colony for one to two months may make it possible for the virus to die out on its own. Be aware that this is not known for certain. The possibility exists that new arrivals may still become infected if never before exposed to this disease.

Blood testing performed by a vet using an ELISA can tell you if your rodents are now infected. Rather than quarantining, it may be worth the time and money to test any new arrivals you purchase.


SENDAI VIRUS DEFINITIONS


Paramyxovirus: Virus having outer envelope. Outer envelopes are sensitive to common household detergents and disinfectants, so it's easily killed on surfaces.
Subclinical: Describes a disease that is suspected but not sufficiently developed to produce definite signs and symptoms in the patient.
Acute: Describes a disease of rapid onset, severe symptoms with brief duration.
Mortality: The incidence of death in a population in a given period of time.
Fomite: An object that is contaminated with a communicable disease.
Carrier: An animal that harbors a contagious disease while showing no signs or symptoms but can spread the disease to others.
ELISA: acronym for enzyme-linked- immunosorbent assay. Blood serum is used to detect antibodies for specific diseases. ELISA tests are an extremely accurate way to detect diseases.

references used:

John E. Harkness, DVM M.S. , M.Ed.
Joseph E. Wagner, DVM, M.P.H., PhD
The Biology and Medicine of Rabbits and Rodents
copyright 1989

Elizabeth V. Hillyer, DVM
Katherine E. Quesenberry, DVM
Ferrets, Rabbits & Rodents Clinical Medicine and Surgery
copyright 1997

The Merck Veterinary Manual
Eighth Edition
copyright 1998