Which of the following shows "cyclodevelopmental" type of biological transmission: September 2011

Ans. A: Filarial parasite Cyclodevelopmental biological transmission is shown by filarial parasite in culex mosquito and guineaworm embryo in Cyclops (when the disease agent undergoes cyclical changes but do not multiply in the body of the ahropod) Propagative transmission In the case of viruses, rickettsiae, bacteria and parasites, the parasites reproduce (i.e. propagate) in the vector, but do not pass through developmental stages. Transmission cannot occur until the parasite population has increased many fold and been disseminated, e.g. to the salivary glands. Cyclopropagative transmission In this case, protozoan parasites undergo both development and reproduction within the vector. These parasites both increase in number and transform to a different life stage before transmission can occurs. However, the veebrate stages of these parasites can invoke a new infection if they are directly transferred to another veebrate host blood transfusion or across the placenta (e.g. malaria parasites) or through sexual intercourse. (e.g. trypanosomes). Cyclodevelopmental transmission Microfilarial parasites ingested by the vector with the blood meal undergo development to 3rd stage larvae (L3) before being transferred back to another veebrate host. There is no replication and not all ingested microfilaria survive to L3. Thus, the number of parasites leaving the vector is always less than the number entering.