Sendai

This is an article originally written for the Rat & Mouse Gazette. Since the time it was written, questions have arisen on the accuracy of this article. I have researched this further only to find nothing but more evidence to confirm the following statements made in this article. The statements in the article are not my personal opinion, these are the facts as found in many textbooks which are based on scientific research, not personal opinions. More information has been added to this subject at the bottom of this page.

Sendai Virus

Not Just a Mouse Disease

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.

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.

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.

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.

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 it's own. Be aware that this in not known for certain. The possibility still 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.

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.

End of original article.

This virus happens in enzootic and epizootic forms. Enzootic means subclinical infection, and means always present.

Subclinical means that a disease may not appear to be present; that the animal is not ill, but that the animal is infected with a disease and can be a carrier of the disease. This means that YES the carrier who has no symptoms of disease may still spread that disease to others who are susceptible to the disease. The most classic example of this in humans was Typhoid Mary, who was not ill herself but she shed the disease Typhoid fever causing an epidemic.

Epizootic means clinically apparent infection. In other words they are obviously ill. Epizootic infection is a wide spread infection, which affects the entire colony. 

Is it possible if you continue to breed rats that have been infected, and that by doing so they will build up immunity?

No. This is a disease very similar to canine distemper. No dogs have ever been bred with any immunity to distemper. Dogs that live through canine distemper are then latent carriers; at some point in their lives if they don't die by accident this disease will kill still them. If they live to be 10 years old they may suddenly exhibit a fatal swelling of the brain. Distemper will manifest itself one way or another and they will die due to distemper. This is why dog vaccinations are so vital to the health of your dog. There is no escape from canine distemper, if it doesn't kill them when young it will cause death at some point. This is a fact. Since Sendai virus in rats and mice is much like canine distemper there is no reason why this scenario is not also true for them.

This virus changes the respiratory system physiologically forever. They often end up with permanent damage to the lungs, scarring from inflammation may exist for the rest of the animal's life. Is it really wise to breed them anyway just because you can't see the damage with your own eyes?

In research laboratories those infected with this disease are excluded from use when found to be infected with this disease. Most often those infected are simply eliminated. Since it does change them, if you continue to breed those that have been infected you may be lowering the life expectancy of the offspring. 

Rats that carry subclinical diseases cannot spread the disease to others.

Sorry not true. Subclinical means that the animal infected does not exhibit symptoms, this does not mean that they are not infectious. It is possible for the young to become infected without noticeable symptoms. Symptoms might have been there and you may have missed them. It is possible that you can be harboring carriers without knowing it. Since there are no vaccines for rats or mice, it may be wise to not take any to shows or swap meets.

Through research I have found differing opinions on whether or not they remain infectious carriers. Some animal medical professionals believe that they are carriers for life, others claim that if put into strict quarantine for at least two months the virus will naturally clear itself. Personally, I wouldn't take any chances. Research has shown me that the answer is not that simple, too many disagree so that tells me that it's not absolutely known whether they are carriers for life or not.

Whichever you choose to believe, you must take extraordinary measures to quarantine properly. This virus can live in the air ducts of your home. Even if you keep the quarantined rats in another room far away from those that are healthy, this virus may flow through the air of your home. You must also be certain that not even one is still infected before you bring any new rats in either by breeding babies or from another source.

It is a bleak picture I do realize that, but this is one of the most dangerous and most highly infectious diseases of pet rats and mice. If you keep both it would be wise to keep rats and mice separated by barriers such as separate rooms.

If they were not already infected with other respiratory diseases such as Mycoplasma pulmonis, CAR, as well as other latent and subclinical infections, there wouldn't be so many deaths. By itself this disease is not that deadly. The combination of diseases is the reason there has been much death.

What to do about this disease is to be extremely cautious and keep those rat/mouse cages clean. NEVER bring in any animals from another source without strict and long quarantine. Two months should always be the standard for quarantine. Just because your newly acquired pets don't seem to be ill does not mean that they won't spread disease to all your other pets and visa-versa.

Written by Jan McArthur, R.V.T.

References used:

The Biology and Medicine of Rabbits and Rodents by: John E. Harkness and Joseph E. Wagner

Infectious Diseases of Mice and Rats from: The National Research Council

The Merck Veterinary Manual Eight Edition

UC Davis School of Veterinary Medicine: Book of Dogs

Diseases from: Nurse's Reference Library

Microbiology : Tortora, Funke, and Case