Can downloading pictures from my camera into my computer cause a virus?

Not acctualy, however if your camera's memory card is infected by a certain virus, there are posibilities that your computer may be infected too. If in case your computer is infested by viruses you better check your camera's memory if there are viruses. Commonly, they are not noticable, sometimes those viruses hide themselves and portray that they are one of your files. So, better to scan first your camera's memory before connecting to your PC. Use a reliable anti virus software for it and with just a minute or two, those viruses will be eliminated. If you don't want to ruin your precious moment(videos, pictures, movies, etc.) , install an anti-virus on your PC.