In very general terms there are two types of viruses with respect to immune response. First, you have viruses like rhinovirus (common cold) or smallpox, where the virus has limited ability to mutate, so once you have gotten it, you are largely immune for the rest of your life. The reason we get so many colds is that there are dozens of different rhinovirus strains, but they don't mutate, so once you get a given strain, you never get it again. That's why kids get more colds than adults (of course there are adenovirus, RSV, and other viruses that cause cold and flu-like symptoms).
With smallpox (called
variola), there were severals strains - from
variola major (near 100% mortality) to
variola minor (<10% mortality), and several in between; however, they were all genetically close enough that catching any strain conveyed immunity to all strains (if you survived). Interestingly, the smallpox vaccine isn't even made with
variola virus. It's made with cowpox virus (
vaccinia - where the term vaccine was derived), which is close enough to convey immunity. If ranavirus is like this, then the chances are that most captive frogs have been exposed, with some being asymptomatic, others getting sick and recovering, and others dying from it. Perhaps this explains why a certain percentage of frogs just die for no apparent reason - like juvenile obligates.
Then there are viruses like influenza, that inject their RNA into a human cell and cause the cell to produce millions of viruses with many reasorted combinations of the virus's eight RNA strands. Those that are recognized by the immune system are killed and those that are not cause symptoms and are passed on. That's why we have different flu strains every year and vaccines are only effective for one season. If ranavirus is like this, then some strains could be mild and others deadly and this could change over time.
The more I read, the more I suspect that we could all test for RA and a large percentage of collections would test positive. If this is the case, and people panic, then it could virtually shut down the frog trade until the implications of the virus are known. Hopefully, the result will be that it is a common pathogen with a low mortality rate that shouldn't affect the hobby. There are certain pathogens that simply cannot be eradicated from a population and their immune systems have evolved to deal with it. We are so used to having medication to treat any illness that we forget that the vast majority of pathogens are dealt with by our immune system. Most meds only make the symptoms more tolerable. Why would frogs (or any other animals be different). We certainly can't expect to keep our frogs in sterile environments.
What I'd like to know is whether ranavirus is like chytrid - introduced into populations with no prior exposure and no immune protection, or is it like cold and flu viruses in humans, where it is ubiquitous, most frogs are exposed at some time in their life and it is only deadly if an animal is weak, stressed, or doesn't have a strong immune system.
RichFrye Wrote:There's also the chance that if the frogs have one strain and their bodies have fought off that strain successfully , the next strain could wipe them out easier since the body may think it's fighting the first strain and not the second.
Think Dengue .
BluePumilio Wrote:...
Of course, there is the aspect, too, that exposure of non-lethal Rana-virus strains could protect against other strains of RV. I don't think there is any research to support this, though. I guess it would depend on how the immune system ID's and attacks it if non-lethal exposure could "vaccinate" against more lethal serotypes.
frogfreak Wrote:I have 20+ infected frogs in my collection. They were from a US import from last November and I'm 99.9% sure of that. They are in isolation two floors from the rest of my frogs. Separate shoes are used to enter the room and disposable gloves are used. Separate feeders are used as well. Nothing comes out of the room that isn't sterilized or double bagged. When I first discovered that I have the virus in my collection I was in total panic mode and was prepared to euthanize all the frogs. After multiple conversations with Ed and people from all across North America and the UK I decided to keep them. I've read so much about this virus it makes my head hurt! Bottom line is in my case. The frogs are doing fine. I see no ill effects from the virus, so far. The strain has not been identified as of yet. I have two pairs breeding and they are not passing the virus onto the offspring. These are all Tincs and Auratus. I'm not where I want to be yet. The goal is do set up and house each frog individually in 10g tanks except for two breeding pairs and study them long term with the help of others.
Best
