Ecological studies on reovirus pollution of rivers in Toyama Prefecture

Reoviruses (reos) were isolated from river water in various areas of Toyama Prefecture. The frequency of reo isolation was higher in the river water, the basin of which has a larger human population. The degree of river contamination with reo paralleled that with the Escherichia coli group of organisms, and reos were frequently isolated from sewage, too. The high antibody-positive (greater than or equal to 1:8 or greater than or equal to 1:10) rates against reos in humans and other animals tested (swine, cattle, and field rodents) indicated their wide-spread infection with reos. These results suggested that the major source of reos present in the river water may be the excretion by humans and other animals, especially the former. Survival experiments in which reos were added into the filtered or centrifuged river water and kept at various temperatures, revealed that reos survived for more than 3 years at 5 C. In the field experiment where reos suspended in cellophane tubes were kept in an agricultural water stream in winter (water temperatures below 10 C), they survived for 6 months until the water temperature rose above 20 C in summer.