With our current knowledge we can only say that there's only one strain, but they are accumulating changes randomly. Usually those changes are deletereous (bad for the virus), some are neutral and a very minor amount increase the fitness of the virus (good for the virus).
It has been proposed that one of those mutations (D614G) increases the fitness of the virus. If that was the case, viruses with D614G would slowly take over the population. The problem here is that if some "founder effect" [1] happens, it will appear exactly like some mutation gives an increased fitness but what happened in reality was that some guy travelled to a meeting and infected 100 people.
This mutation was first reported in january-2020 in Germany (AFAIK), so it's a very posible that it was just one of the very first viruses to arrive in Europe and "founded" a new population when the virus was spreading almost freely. Then some scientist noted that a lot of european sequences included the mutation and hipotesized that the change was behind the quick spreading of march and april.
Right now, about 80% of the sequences reported to Gisaid include that mutation, but that is about the same percentage than in april/may. I'm personally inclined to believe that D614G is close to have neutral effects, as other variants of the virus without the mutation are also being quite successful in spreading and keeping themselves in the population.
It has been proposed that one of those mutations (D614G) increases the fitness of the virus. If that was the case, viruses with D614G would slowly take over the population. The problem here is that if some "founder effect" [1] happens, it will appear exactly like some mutation gives an increased fitness but what happened in reality was that some guy travelled to a meeting and infected 100 people.
This mutation was first reported in january-2020 in Germany (AFAIK), so it's a very posible that it was just one of the very first viruses to arrive in Europe and "founded" a new population when the virus was spreading almost freely. Then some scientist noted that a lot of european sequences included the mutation and hipotesized that the change was behind the quick spreading of march and april.
Right now, about 80% of the sequences reported to Gisaid include that mutation, but that is about the same percentage than in april/may. I'm personally inclined to believe that D614G is close to have neutral effects, as other variants of the virus without the mutation are also being quite successful in spreading and keeping themselves in the population.
[1] https://en.wikipedia.org/wiki/Founder_effect