Hello dear, Thank you for your contact to health care magic. I read and understand your concern. I am Dr Arun Tank answering your concern. No, pimple is not caused by the Giardia at all. But mouth ulcer can be caused by it. Giardia stick to the intestine lumen and suck the nutrition particularly fat and vitamins related to it. So ulcer can occur because of nutirtuonal deficiency. You should take the complete treatment for the Giardia. Otherwise it will recurr and cause infection again and again. It is transmitted by feco oral route means either the food or water is contaminated with such parasite is consumed by you causing the infection to you. I advice you should maintain hygiene in the future otherwise contaminated food causes infection again. In order to combat such effect you should take multivitamin particularly the vitamin A and others. This will help treating the ulcer. I will be happy to answer your further concern on bit.ly/DrArun. Thank you, Dr Arun Tank Infectious diseases specialist, HCM.