Parasites which reside within the blood or internal organs of the host have logistical problems in terms of infecting a new host. In contrast to fecal-oral transmission, where infective stages are excreted into the environment, potential new hosts would not normally come into contact with the parasite.
http://www.tulane.edu/~wiser/protozoology/notes/vector.html
The disease is transmitted most commonly by an infected female Anopheles mosquito. The mosquito bite introduces the parasites from the mosquito's saliva into a person's blood. The parasites travel to the liver where they mature and reproduce.
https://en.wikipedia.org/wiki/Malaria
Malaria parasites belong to the genus Plasmodium (phylum Apicomplexa). In humans, malaria is caused by P. falciparum, P. malariae, P. ovale, P. vivax and P. knowlesi. Among those infected, P. falciparum is the most common species identified (~75%) followed by P. vivax (~20%).
https://en.wikipedia.org/wiki/Malaria
Protozoa are one-celled organisms that can cause diseases ranging in severity from mild to deadly. These organisms can be classified as parasitic or free-living. Parasitic protozoa are found in organisms such as ticks, flies and mosquitoes. Free-living protozoa are found in water that is contaminated with fecal matter and other wastes.
http://www.livestrong.com/article/28148-protozoan-diseases-list/
Malaria causes symptoms that typically include fever, fatigue, vomiting, and headaches. In severe cases it can cause yellow skin, seizures, coma or death. The disease is transmitted by the biting of mosquitos, and the symptoms usually begin ten to fifteen days after being bitten. If not appropriately treated, people may have recurrences of the disease months later. In those who have recently survived an infection, re-infection typically causes milder symptoms.
https://en.wikipedia.org/wiki/Malaria
Several human diseases caused by protozoa are transmitted by a variety of arthropod vectors (Table). The vectors are not simply 'flying syringes', but represent a second host for the protozoan parasite. Thus the life cycle of vector transmitted diseases also involves complex interactions protozoan-vector interaction analogous to the complex human-protozoan interactions. Vector transmission probably evolved multiple times.
http://www.tulane.edu/~wiser/protozoology/notes/vector.html
(In evolutionary terms, transmission by blood transfusion would be a very recent event.) Predator-prey transmission is one strategy used by protozoa such as Toxoplasma and Sarcocystis to overcome these transmission barriers. As the name implies, predator-prey transmission involves two distinct hosts.
http://www.tulane.edu/~wiser/protozoology/notes/vector.html
Amoebiasis. Amoebiasis is a protozoan disease caused by Entamoeba histolytica, which secretes enzymes that dissolve the host's tissues. Amoebiasis infection is spread by contact with feces, which can occur if water or food are contaminated, or if someone has oral contact with fecal matter.
http://www.livestrong.com/article/28148-protozoan-diseases-list/
Malaria is a mosquito-borne infectious disease of humans and other animals caused by parasitic protozoans (a group of single-celled microorganism) belonging to the genus Plasmodium.
https://en.wikipedia.org/wiki/Malaria
Leishmaniasis. Leishmaniasis is caused by the Leishmania parasite, which is found in southern Europe, the subtropics and the tropics. This disease is spread by the bites of sand flies that are infected with the parasite.
http://www.livestrong.com/article/28148-protozoan-diseases-list/
what disease transmits protozoans
Malaria is a disease that transmits protozoans. Protozoans transmits malaria disease.