Transstadial

Transstadial transmission is the passage of a pathogen or parasite from one developmental stage of a vector to the next, typically through metamorphosis or molting. In arthropod vectors, this means a microbe acquired during a blood meal in larval or nymphal stages can survive the molt into the next life stage and remain capable of transmission during a subsequent blood meal.

Mechanistically, the pathogen must survive the vector’s physiologic changes during molt and reside in tissues that permit persistence and eventual transmission, such as the gut, hemolymph, or salivary glands. In many cases the pathogen does not replicate to high levels, but it remains viable enough to be transmitted when the vector feeds again.

Examples of transstadial transmission are well documented in tick-borne pathogens. Borrelia burgdorferi, the agent of Lyme disease, can persist from larva to nymph and from nymph to adult in Ixodes ticks. Other examples include Anaplasma phagocytophilum and Babesia species, which have been shown to survive across life stages in certain tick species. Transstadial persistence is also observed for some pathogens in other vectors, such as certain insects, though the best-characterized cases are in ticks.

Significance lies in its role in maintaining pathogen cycles within vector populations, enabling transmission to vertebrate hosts even when only certain life stages feed. This influences disease ecology and control strategies, since interventions may target specific stages of the vector’s life cycle. Transstadial transmission is distinct from transovarial (vertical) transmission, where infection passes from a female to her offspring via eggs. It is also distinguished from horizontal transmission, which occurs between hosts.