The original Wuhan one mutated. In one of his pressers, Andrew Cuomo pointed out that the strain in California was different to the one on the east coast.
The west coast one may well have come directly from China (shorter flying time, immigrant Chinese population...) and Cuomo said the one on the east coast came from Europe. Seems likely it mutated at some point over there.
There's a third strain, but I can't find the article for the mo.
Re dengue fever, Dr Fauci said the Covid-19 couldn't be transmitted by mosquitoes. It doesn't appear to be related to the coronaviruses, either.
When they are talking about different strains the difference is relatively minor, a couple of base differences.
Has the virus got 29904 bases? So Covid 19 virus differs by around 5980 bases compared to the original bat virus it may be related to.
Why is Dengue only transmitted by certain types of mosquitoes? Covid 19 virus can infect the eyes and I've noticed some houseflies have a habit of landing on one's eye. So I wouldn't reject the idea that Covid 19 isn't transmitted by flies.
"How does an Aedes aegypti mosquito become a dengue vector? After a mosquito feeds on the blood of someone infected with the dengue virus, that mosquito becomes a dengue vector. The mosquito must take its blood meal during the period of viremia, when the infected person has high levels of the dengue virus in the blood. Once the virus enters the mosquito's system in the blood meal, the virus spreads through the mosquito's body over a period of eight to twelve days. After this period, the infected mosquito can transmit the dengue virus to another person while feeding. Does a mosquito infected with the dengue virus only transmit the virus to the next person it feeds on? No, once infected with dengue, the mosquito will remain infected with the virus for its entire life. Infected mosquitoes can continue transmitting the dengue virus to healthy people for the rest of their life spans, generally a three- to four-week period."
https://www.nature.com/scitable/topicpage/dengue-transmission-22399758/So the virus infects humans and some species of mosquitoes.