Homologous and heterologous strains of Plasmodium vivax; a cross-inoculation study of malaria strain immunity.

Abstract

Abstract The problem of partially immune responses to vivax inoculation in white patients with neurosyphilis who have no previous history of attacks of natural malaria has been a provoking one. These patients, part of an ever-increasing group occasioned by the prolonged residence of soldiers in hyperendemic overseas areas, cannot readily be screened out for inoculation with other species of malaria because of their negative histories. They may, therefore, require reinoculation for the completion of therapeutic courses. The present custom of reinoculating these patients with quartan malaria raises two objections: (1) Quartan reinoculation materially prolongs hospitalization and morbidity because of the prolonged incubation period and the longer duration and cycle of paroxysms and (2) quartan infections, differing from the other species of malaria, often become latent for many years and may recur or act as the source of accidental transfusion malaria. Homologous immunity is characterized by the production of minimal clinical activity in patients reinfected with the same or similar substrain of vivax malaria. The duration of the homologous reinfection in this series of patients averaged 10.5 per cent (reinfection index) of the duration of the original infection with that same strain. Heterologous immunity exists when reinfection of a patient with a strain of P. vivax differing in geographic origin from the original strain results in definite clinical activity sufficient for the completion of a course of malaria therapy. In this cross-inoculation study, the duration of the heterologous reinfection averaged 74.3 per cent (reinfection index) of the duration of the original infection. In a control series of seventy-eight susceptible patients, intravenous inoculation with various parasite dosages of P. vivax revealed that the subsequent prepatent and incubation periods varied inversely with the total quantitative dosage. This correlation, however, does not apply to any series of patients with immunity to malaria. It seems desirable, as a result of malaria immunity studies, to reinoculate with heterologous strains ∗2 ∗2Heterologous Southwest Pacific strains of P. vivax are currently available at the Florida State Hospital, Chattahoochee, Fla. of P. vivax those white patients with neurosyphilis experiencing partially immune types of original infection (from five to eight paroxysms). Adequate completion of therapeutic courses and avoidance of unnecessary quartan infections thus can be accomplished.