Cyclo-developmental transmission

Definition

A mode of biological transmission in which a pathogen undergoes essential developmental changes (growth, multiplication, or metamorphosis) within an arthropod vector but does not reproduce; the vector is required for the parasite to reach an infective stage, though no amplification occurs in the vector. Contrasts with cyclo-propagative transmission (where the pathogen also multiplies) and mechanical transmission (no development or multiplication).

Etymology

From Greek kyklos (circle, cycle) + developmental, referring to the cyclic developmental changes the pathogen undergoes; contrasted with 'propagative' transmission where propagation (multiplication) occurs.

Example

The filarial nematode Wuchereria bancrofti undergoes cyclo-developmental transmission in mosquitoes: ingested microfilariae penetrate the midgut, migrate to thoracic muscles, molt twice to become infective third-stage larvae, then migrate to the proboscis—without increasing in number—before transmission to a new human host.

Synonyms

• developmental transmission

Related Terms

• cyclo-propagative transmission
• biological transmission
• mechanical transmission
• Transstadial transmission
• vector competence
• extrinsic incubation period

Usage Notes

Distinguished from cyclo-propagative transmission by the absence of pathogen multiplication; the number of infective units emerging equals the number ingested (minus mortality). Sometimes loosely grouped with 'biological transmission,' but specialists reserve cyclo-developmental for cases where metamorphosis or essential development is vector-dependent. Common in filarial worms and some cestodes with arthropod intermediate hosts.