It was like yesterday when all I hear around me is Ebola, needless to say that at first it was taken for a joke, but later we all realise that God who gave man science doesn't kid. Man is surrounded by thousands of potentially dangerous microscopic organism which has the ability to invade a living host and cause a disruption in the normal living process, so notorious among these are the viruses, which fall in between a living and nonliving organism in classification.
Living because it has to ability to replicate (reproduce) inside a living host, meaning that in the presence of a living host, viruses are able to function in the natural live process termed "living".
Viruses are termed nonliving because they do not and cannot reproduce outside the living host, meaning that outside the host viruses are inactive, and they remain like that until they can find a living host.
Most at times viruses attaches itself to bacteria and other living cells, and using the resources provided by these cells they are able to reproduce and replicate to becomes numerous, the process of utilization of the hosts resource does not go unnoticed by the host because the host itself eg. man, has a defence mechanism which is set in place to attack all foreign materials in the body, and it is funny that they either get rid of the foreign material or die trying..... with the host defence mechanism set in place, there is a negative feedback which in continuous occurrence lead to symptoms and signs shown by the host, if the host defence mechanism like antibodies cannot deal with the invasion, the host eventually dies.
Now in the case of virus, naturally some viruses are not harmful to the host, such is the case of Ebola residing in Bats, Lassa fever in rats. These animals are carriers of these viruses and they are not affected by it, but they can shed it out of their body through body fluids, like saliva, urea, faeces etc. fluids which already has a virus in it (don't forget in nonliving or dormant form), they are exposed to it and if by chance the virus get in vivo through a broken skin like wound or scratches, nose picking, ingestion or some cases transfer through sexual inter course (with human already infected or animals ), the virus began it multiplication at this stage the host has no knowledge of this infection because he or she is still asymptomatic, this period is called incubation period.
Incubation period may last for days, weeks months or year depending on the virus type and the host immunity strength(anti bodies). During this incubation period the host shows no symptom and cannot shed it.
After the incubation period the host begins to show symptoms of sickness which varies depending of the virus type. Also at this stage the host is now a loaded gun, any contact with the body fluid can lead to transfer of the virus to a new host because the virus are shed in the body fluid.

to be continued.