Studies on the causative agent of “Hyuganetsu” disease.

X. Vector

Abstract

Vector of the causative agent of “Hyuganetsu” disease has been investigated by the author et al since 1954, and the following results were obtained
1) Trombiculid mites are not considered as vector of the causative agent because of non-correspondence of their season with the outbreak of the disease.
2) Arthropoda is not considered to be vector, because there is no arthropoda parasitic on rodents that is common to the places of the patients and to the places where the rodents harbouring the causative agent were captured.
3) Of 25 patients suffering from “Hyuganetsu” disease, there were 21 patients who had eaten grey mullet (Mugil cephalus) within 30 days before getting ill, 3 patients, who had eaten grey mullet-like fish, and one patient who had never eaten grey mullet what the last patient said, however, being unreliable.
4) Trials were made to eat grey mullet in 6 groups, each consisting of 8-26, volunteers, with the result that five subjects in 4 groups were affected by the disease.
5) The latent period is 19 days in an average, ranging from 13 to 28 days.
6) It has been hitherto unsuccessful to isolate the causative agent from several species of metacercaria that are parasitic on the flesh of grey mullet.
It is considered from the above findings that vector of the causative agent might be a certain metacercaria that is parasitic on the flesh of grey mullet. Accordingly, the relation of this agent with Neorickettsia helmintoeca must be studied in the future, although the agent was named Rickettsia sennetsu by Misao and Kobayasi and Rickettsia todai by the present authors.