Thursday, May 7, 2009

Spread of bat-variant rabies virus in other species.

I started to hear rumors about rabies virus spreading through the air from clients today. Then I got an e-mail referencing this article from National Geographic today. Apparently the article is the source of the rumors. There are a couple of problems with the article that make it difficult for people unfamiliar with the science involved to interpret.
First, calling this a new rabies virus in the title makes people think that the current outbreak of Rabies in foxes and a few skunks in the Flagstaff area might be something new and different.
The Rabies outbreak in foxes is a bat variant rabies virus that has crossed into other species several times in the last decade in the Flagstaff area. The thing that is different about these outbreaks is that the virus seems to be better at spreading in a new species of animals than bat variants usually are.
Rabies virus has many different genetic variants that are adapted to different species. All of these variants are capable of infecting other species, and basically all mammals are susceptible to infection with rabies. Often, when an animal or human is infected with a variant of rabies from another species, the new host is considered a "dead end" because the disease is fairly rapidly fatal after the virus reaches the central nervous system and the new host may not spread the virus very efficiently. When a host is infected with a variant of rabies that is adapted to that host, it is more likely to spread to another animal. The primary mechanism of spread is by bites or scratches that are exposed to saliva from the infected animal. On rare occasions the virus can spread by oral or nasal inoculation as well. This still requires close contact with the saliva or tissues, especially nervous tissue or salivary glands of an infected animal. There are several different places around the country with different variants of rabies in their respective species.
The CDC publishes annual reports on rabies epidemiology which list the number of animals tested positive for rabies and the human cases along with the variants that caused the disease in humans. This shows that Rabies is a common disease in wild mammals, and it is not unusual for it to be spread from one species to another. It is less usual for the virus to mutate and then spread widely in the new species. Apparently the outbreaks of bat variant rabies in foxes, skunks and bobcats in Northern Arizona over the past decade is the first time that humans have observed the mutation of the virus and its spread in a new species. This has obviously happened many times in the past, hence all the different rabies variants in many different species. It is even possible that bats are the initial reservoir for all rabies viruses and occasional mutations in the virus result in new variants that are better adapted to other species of mammals.
This paper documents the original outbreak of the bat variant rabies in skunks in Flagstaff in 2001. The current outbreak in foxes is also a bat variant, and is probably the same or a similar variant as the previous outbreaks were.
The main problems I have with the National Geographic article are the author's assertion that skunks described in the paper by Leslie, et. al. were spreading the virus "passively" whatever that means. Some people in the Flagstaff area have already interpreted this to mean that rabies is being spread as an airborne virus. It is spreading in a new species, but there is no reason to suspect that the virus is not spreading through bites or very close contact just like Rabies has always spread. The other problem I have is the quote from Barbara Worgess, the head of the Coconino County Health Department that "It shouldn't be able to spread from skunk to skunk."
There is no reason that the virus cannot spread from animal to animal, it is just unusual and does create a concern for the Health Department. Unfortunately Ms Worgess seems to say things like this to the media which make it look like she really does not know what is going on.
Fortunately, this new variant of the Rabies virus can be prevented by the same Rabies vaccinations that have been available for years. The fact that bats are often carriers of Rabies is an excellent reason to keep your pets vaccinations (including cats!) up to date, and the spread of the virus in a new species is a good reason to be cautious in the woods and around any wild animal that is acting sick or agressive. People that have been exposed to Rabid foxes in the Flagstaff area have been effectively treated with standard protocols just like other exposures to other rabies variants. Any time someone has been bitten by a wild animal or exposed to a bat (bat bites can be very hard to identify due to their small size) they should seek medical attention immediately. Rabies antisera and vaccinations do not work once symptoms appear.
The Natonal Geographic article is another example of the media publishing an overly sensational, inaccurate story. No one should panic, but should take sensible precautions.

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