Cambridge O Level Biology · Syllabus 5090 · Disease and Immunity
Vector
What is Vector?
An organism that transmits a pathogen from one host to another. A mosquito is the vector for the malarial parasite: it carries the parasite between people but is not itself the cause of the disease, which is why control of malaria means control of the mosquito and of the parasite in people, not of one alone.
This definition is part of the Disease and Immunity chapter in Cambridge O Level Biology.
Vector in context
Malaria is caused by a parasite. The parasite is transmitted from an infected person to a new person by a mosquito, which acts as a vector. The mosquito takes in the parasite when it feeds on the blood of an infected person, and passes parasites into a new person in its saliva at a later blood meal.
Common mistakes with Vector
- "The mosquito causes malaria." The mosquito is the vector. A parasite is the pathogen. Naming the wrong organism as the cause loses the mark even when the rest of the transmission chain is correct. Write Malaria is caused by a parasite, which is transmitted from person to person by a mosquito acting as a vector.
- "Malaria can spread by touching someone who has it." There is no such route. Natural transmission goes through the mosquito, and an answer that abandons the vector has abandoned the mechanism. Write Malaria is transmitted only when a mosquito that has fed on an infected person later feeds on another person.
Questions students ask about Vector
Why is malaria classed as indirect transmission when the mosquito puts the parasite straight into the blood?
Because the parasite passes through another organism on the way. Direct transmission means nothing in between; the mosquito is an intermediate, and an intermediate organism is called a vector. The injection at the end does not change the classification, because the parasite still had to travel through the mosquito to get there.