Mosquitoes are carriers of the malaria parasite, which is transmitted to humans through their bites. Malaria is a disease caused by the Plasmodium parasite, and it is primarily spread by female Anopheles mosquitoes. These mosquitoes become infected by feeding on the blood of an infected person and then transmit the parasite to other individuals when they bite them. Malaria can cause symptoms such as fever, chills, headache, and fatigue, and if left untreated, it can be life-threatening. Therefore, the correct answer is malaria.