1. Mechanical: infectious agent is mechanically transported through soiling of vector’s feet or proboscis or by passage through its gastrointestinal tract. for example spread of e coli by housefly
2. Biological:
a. Propogative: infectious agent merely multiplies inside the vector e.g. plague in rat flea
b. Cyclo-propogative: agent changes in number and also in form e.g. malaria parasites in mosquito
c. Cyclo-developmental : the disease agent undergoes only development but no multiplication e.g. microfilaria in mosquito
Reference:
K. Park, 2019. Environment and Health, In: Park’s Textbook of Preventive and Social Medicine, 25th ed. Jabalpur, 2019