Dengue fever
Sometimes, mosquitoes can also get dengue from humans.  If a female mosquito bites someone with dengue, the mosquito may get the dengue virus from the person's blood.  After about 8 to 10 days, the virus spreads to the mosquito's salivary glands, which make saliva (or "spit").  Now the mosquito will make saliva that is infected with the dengue virus.  When the mosquito bites a human, its infected saliva goes into the human and can give that person dengue.