A strain of Plasmodium vivax characterized by prolonged incubation: the effect of numbers of sporozoites on the length of the prepatent period

Abstract

The North Korean strain of Plasmodium vivax was characterized by its extraordinarily prolonged incubation period in certain circumstances. It was clearly demonstrated by quantitative observations that the phenomenon may be elicited by the inoculation of small numbers of sporozoites. After the intradermal inoculation of 10 or 100 sporozoites, the incubation period was delayed for periods varying between 262 and 628 days; after 1,000 sporozoites, with one exception, the same delay occurred; after 100,000 sporozoites, the incubation period was always of normal duration (13–16 days).