Vertical transmission, also known as mother-to-child transmission, is the transmission of an infection or other disease from mother to child immediately before and after birth during the perinatal period. A pathogen's transmissibility refers to its capacity for vertical transmission. The concept of vertical transmission is also used in population genetics to describe inheritance of an allele or condition from either the father or mother.
Vertical transmission tends to evolve benign symbiosis. It is therefore a critical concept for evolutionary medicine.
Because a pathogen's ability to pass from parent to child depends significantly on the hosts' ability to reproduce, pathogens' transmissibility tends to be inversely related with their virulence. In other words, as pathogens become more harmful to and thus decrease the reproduction rate of their host organism, they are less likely to be passed on to the hosts' offspring, since there will be fewer offspring.[1]
Although AIDS is sometimes transmitted through perinatal transmission, its virulence can be accounted for by the fact that its primary mode of transmission is not vertical. Moreover, medicine has further decreased the frequency of vertical transmission of AIDS. The incidence of perinatal AIDS cases in the United States has declined as a result of the implementation of recommendations on HIV counseling and voluntary testing practices and the use of zido\aidinc therapy by providers to reduce perinatal HIV transmission. [2]
The price paid in the evolution of symbiosis is, however, great: For many generations, almost all cases of vertical transmission will continue to be pathological -- in particular if there are any other routes of transmission. It takes many generations of random mutation and selection to finally evolve symbiosis. During this time, the vast majority of vertical transmission cases will exhibit the initial virulence.
In Dual Inheritance Theory, vertical transmission refers to the passing of cultural traits from parents to children.[3]
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