Can a transvaginal ultrasound detect pregnancy 5 days after implantation occurs? How long before it can be detected?

NO not 5 days. In order to see gestational sac ( evidence of pregnancy need just over 30 days , blood HCG level of 1500 , how ever pregnancy test will be positive 10 days after fertilization.
No! Way too early. A blood test is positive , and a missed/late menstrual period will be a couple of weeks before ultrasound can detect a pregnancy. Ultrasound is not dependable until HCG levels are around 2000 (some say 1500.).