Mosquitoes can transmit disease causing agents (pathogens) through their bite. Female mosquitoes require nutrients found in blood to support the development of their eggs. Therefore, only female mosquitoes bite humans or other animals to obtain that blood, while male mosquitoes feed exclusively on plants. If the human or animal the female mosquito bites is infected with a suitable level of a pathogen capable of being transmitted by mosquitoes, the female mosquito can pick the pathogen up when she takes a blood meal. She may then be able to pass that pathogen to the next human or animal she bites.
Some pathogens cannot be transmitted by mosquitoes in this way. To be transmitted to the next person, the pathogen must survive the mosquitoes’ digestive system, ideally to multiply and make its way back into the mosquitoes’ mouthparts. Many blood-borne pathogens, like HIV and hepatitis viruses, have not been found to survive in mosquitoes. Moreover, the pathogen and the mosquito must be compatible – only certain pathogens can survive and multiply in certain mosquito species. For example, malaria parasites only can be transmitted by Anopheles mosquitoes. Finally, the pathogen also must be compatible with the human or animal host. Some animal pathogens cannot live in humans, and vice versa. For example, certain malaria parasites that cause disease in birds cannot infect humans.