Why don't vectors contract the disease they carry?

Answer 1

To start.. the reason is evolution, based on the selective pressures that favor the vector's survival. This is not a conscious decision or planned strategy of the bacteria/virus/vector, it is what worked the best and spread the most quickly. What works best has the best reproduction rates and is therefore the most abundant and over time dominates the other strains of a disease. ok. here is the reason and the explaination. Well, the vectors do contract the disease, some human diseases seem to not affect the vector and others will affect the vector especially behavorally (look at rabies). But usually the vector is an insect and the the reason it doesn't affect the life of the vector is understadable. In short, if the disease killed or greatly harmed the main source of distribution it would die out quickly, by leaving the vector relatively unharmed the disease itself has a greater chance to be spread and to reproduce in acceptable areas. The selective pressures involved with high reproduction rates will surely favor those diseases that keep their hosts alive to spread, it can reproduce high amounts inside the human but does not need to in the mosquito and it would make the reproduction of the disease and range of the vector significantly lower. more specific.. When the bacteria or virus is in the vector it is at a different time of the bacteria/virus' lifecycle that allows the vector to live a somewhat normal life. Using malaria as an example... The gametes which are haploid are taken into the mosquito and fuse once in a suitable environment (the mosquito gut in this case) to form a diploid zygote (ookinete)this is the next step in the diseases' life cycle. Now the fused structure burrows into the lining of the gut to migrate to the salivary glands and multiply. Once the mosquito bites another host then the disease is injected with other proteins created by the mosquito intended to keep the wound from closing while feeding. The vector stays alive long enough to spread the disease, and now the disease can multiply rapidly in the human and spread to other mosquitos and then other humans. The mosquito is necessary to the survival and spread of the disease, where as humans are not needed to spread the disease amongst themselfs so it is benefical to reproduce rapidly at the expense of killing the host (because the offspring will be spread even if the host dies).