Vector-borne disease
Diseases passed between people or animals by living carriers, usually blood-feeding insects such as mosquitoes, fleas and ticks.
A vector is a living creature that carries an infection from one host to another. Many are blood-feeding insects and their relatives: mosquitoes, ticks, fleas, sandflies and others. When one feeds on an infected person or animal it picks up the microbe, and when it feeds again it can pass it on. Vector-borne diseases account for more than 17 per cent of all infectious diseases and cause more than 700,000 deaths a year.
Mosquitoes are the most dangerous. Anopheles mosquitoes spread malaria, which kills more than 608,000 people a year, most of them children under five. Aedes mosquitoes spread dengue and can spread yellow fever. Fleas carry plague from rats to people.
The microbe often has to do more than hitch a ride. After a mosquito takes an infected blood meal, a virus or parasite must multiply inside it and reach its salivary glands before the insect can infect anyone. That delay, the extrinsic incubation period, typically lasts from several days to a couple of weeks and is shorter in warm weather. A mosquito that has just bitten a sick person is not yet infectious, a detail that once confused attempts to prove mosquitoes spread disease.
Because the vector is essential, these diseases can be fought by attacking the carrier: draining standing water where mosquitoes breed, using bed nets and screens, and controlling fleas and ticks. Vectors have also been used deliberately, to spread a virus among rabbits to control their numbers.
Coming up in future stories
- The Doctor Who Found a Disease's Whole Life Story 1907–1909 · Lassance, Minas Gerais, Brazil
- The Man Who Killed Europe's Rabbits 1952 · Maillebois, France
- The 'Mosquito Man' Everyone Laughed At 1881–1900 · Havana, Cuba