The above findings on childhood leukaemia provide further evidence for horizontal transmission of some underlying infection of which leukaemia is a rare response.

Evolutionary medicine has found that under horizontal transmission, the host population might never develop tolerance to the pathogen.

Because of the peculiar natural history of these hosts, the relative importance of horizontal and vertical transmission differs among parasite species.

All the above modes are examples of horizontal transmission because the infecting organism is transmitted from person to person in the same generation.

AE can be spread by both vertical and horizontal transmission.

Such effects of seed defense can also occur in dense stands of conspecifics through horizontal transmission of beneficial fungi.

However, they are thought to be supported by both horizontal and transovarial transmission in the sand fly.

Although horizontal transmission between people has been proposed, it is not clear if this actually happens and if it does, how frequently it occurs.

Moreover, the effects are most difficult to estimate because both heterospecific and horizontal transmission must be accounted for.

Both vertical and horizontal transmissions are possible.