Just wanted to come back and give my 2 cents on some of the questions!
"I read that a survivor is infectious for 40 days? men have been told no sex for 40 days after ebola?"
OK, think of it like this, you have the day of infection. This is followed by an incubation period during which the person is NOT infectious. Then you get rapid onset of symptoms, and the person becomes infectious. If they survive, they may remain infectious for as much as 40-50 days, which is why hospitals will be monitoring these people for a while!
"I've read that humans can be asymptomatic for Ebola! Doesn't that mean that they could be carriers?"
OK, so Ebola is zoonotic, which means it is transmitted from animals to humans. It's a really rare virus, and there aren't many cases, so there is still a lot of uncertainty about the details of how this transmission works, and where the reservoirs might be (though there is mounting evidence that bats are the natural reservoir, passing it to apes perhaps via fruit that they've nibbled that apes then eat, then to humans). As someone said upthread, the absence of these natural reservoirs of ebola-carrying animals in the UK makes it very very unlikely the virus could persist here.
Anyway, so a research team published some papers about 10 or so years ago, saying that he'd found signs of asymptomatic Ebola infection in humans who had never been sick. While this finding is interesting, it is not by any means conclusive. A lot more work is needed before we can say that.
To explain why there may be problems, you need to know just a tiny bit about immunity. Basically, your adaptive immune system is this incredibly complex defence mechanism against infection. In a nutshell: when you encounter a new pathogen in the environment, it mounts a defensive response, and then some of the cells that are defending you will store away a chemical marker of that specific infection. This means that your body can react even more quickly should it encounter that pathogen again in future. So in your body, you have an enormous number of biochemical memories of the huge number of pathogens you've encountered. Neat, huh?
OK, so the type of research that we're looking at here looks for those biochemical traces that of Ebola, the idea being that if you can show it is there and the person has not been sick, you can hypothesize that humans may be asymptomatic carriers.
Now here's the problem: Ebola is one of a group of pathogens called filoviruses, and there are a lot of different varieties of these in West Africa. As a couple of people have mentioned, there are even several strains of Ebola. Scientists know from an outbreak of a similar filovirus in the States that not all of them are lethal - some may make animals sick, but not people.
The research in question tested for traces of only one type of Ebola. This means that there is a possibility the scientists may have been picking up evidence of encounters with other very similar filoviruses, or even something that wasn't Ebola at all. This, combined with the fact that the virus doesn't spread in a way that suggests humans are a reservoir (i.e. it is fairly easy to control where you have isolation mechanisms and hygiene mechanisms in place), means there is a big question mark over humans as asymptomatic Ebola carriers.
Interesting paper here, with more detail of this argument. I'm just summarising: jid.oxfordjournals.org/content/190/11/1893.full.pdf