Vertical transmission

Definition

The direct transfer of a symbiont, parasite, or pathogen from parent to offspring, typically via eggs, sperm, transovarial passage, or intimate contact during birth or brood care. Contrasts with horizontal transmission, which occurs between unrelated individuals or generations.

Etymology

From Latin verticalis (overhead, ancestral line) and transmissionem (a sending across); emphasizes passage down the generational axis rather than across a population.

Example

Wolbachia bacteria are vertically transmitted through the cytoplasm of eggs in many insect species, ensuring infection persists across host generations without requiring reinfection from the environment.

Synonyms

• Transovarial transmission
• parent-to-offspring transmission

Related Terms

• Horizontal transmission
• Transovarial transmission
• cytoplasmic inheritance
• Wolbachia
• symbiont acquisition
• vector competence

Usage Notes

In arthropod disease ecology, vertical transmission is distinguished from transovarial transmission (strictly passage within eggs) and transstadial transmission (persistence across life stages). The term is sometimes used loosely for any parent-offspring transfer, but specialists reserve stricter definitions for symbiont and pathogen contexts. Not all vertical transmission is 100% efficient; failure rates affect symbiont prevalence dynamics.